Sediment Phosphorus Reservoirs in Tropical Bays: Implications for Phosphorus Availability and Bioluminescent Dinoflagellate Populations

Transcription

1 Wesleyan University The Honors College Sediment Phosphorus Reservoirs in Tropical Bays: Implications for Phosphorus Availability and Bioluminescent Dinoflagellate Populations by Andrea Pain Class of 2008 A thesis submitted to the faculty of Wesleyan University in partial fulfillment of the requirements for the Degree of Bachelor of Arts with Departmental Honors in Earth & Environmental Sciences Middletown, Connecticut April, 2008

2 Table of Contents Acknowledgements Abstract List of tables and figures i ii iv 1. Introduction 1 2. Background and relevance to Vieques, Puerto Rico Nutrient controls on Pyrodinium Bahamense var. Bahamense populations Sediment phosphorous reservoirs 5 3. STUDY LOCATION Geologic Setting The Bioluminesent Bays of Vieques Physical Setting of Puerto Mosquito, Puerto Ferro, and Bahia Tapon Watersheds Methods Field sampling Laboratory methods Results Sedimentary Facies Surface sediments C data and 210-Pb mass accumulation rates Sediment total phosphorus concentrations 27

3 5.5 Sediment Phosphorus Reservoirs Phosphorus Reservoirs with depth Discussion Sedimentary Phosphorus Reservoirs Sedimentation and Phosphorus Availability Between Study Environments Implications for Phosphorus Availability and Future Studies Conclusions 56 References 58 Tables 65 Figures 74

4 Acknowledgements I would foremost like to thank Tim Ku for the great research experiences I ve had at Wesleyan, both in the field and in the lab. I would also like to thank Suzanne O Connell for her guidance, as well as Anna Martini for her assistance with this project; Joel Labella for all his help with the laboratory work; The Keck Consortium for funding this research, and the 2006 and 2007 Keck Fellows and Vieques researchers; and Vera Pospelova for her consultation in the cyst-counting procedure. i

5 ABSTRACT Sediment phosphorus reservoirs were analyzed from two adjacent bay ecosystems, Puerto Mosquito and Puerto Ferro, in Vieques, Puerto Rico. Puerto Mosquito contains high concentrations of the bioluminescent dinoflagellate Pyrodinium bahamense var. bahamense (10,000 cells/liter), while neighboring Puerto Ferro has much lower concentrations (>700 cells/liter). In both bays, the modern depositional facies is a mixed carbonate-siliciclastic or carbonate mud that is distinguished from older, shallow marine sedimentary facies by higher terrigenous sediment concentrations, higher Fe/Al ratios, and greater phosphorus abundances. In Puerto Mosquito, the accumulation of the mixed carbonate-siliciclastic mud began within the past 200 years. This change was marked by a change in terrigenous source material, an increase in terrigenous sedimentation rates, and elevated sediment phosphorus concentrations. Sediment phosphorus speciation indicates that organic P and detrital/authigenic calcium-bound (Ca-bound) P are the major forms of P in both bays, with P adsorbed to Fe- and Mn- oxides (Fe-bound P) a relatively minor reservoir. Cabound P and organic P average 91.3±12% (1σ) of the total phosphorous (TP) with Cabound P concentrations greater than organic P concentrations in deep depositional environments in Puerto Mosquito and Puerto Ferro. Overall, total phosphorus (TP) sediment concentrations are higher in Puerto Mosquito than in Puerto Ferro and the highest TP concentrations in both bays are found in locations of the greatest water depth. Sediments from these deep depositional environments show Ca-bound P increasing with depth at the expense of organic P, indicating precipitation of ii

6 authigenic carbonate fluorapatite (CFA, Ca 10 (PO 4, CO 3 ) 6 F 2 ). The rate of phosphorus burial due to CFA formation in the deep Puerto Mosquito site is μmol P/ cm 2 /yr, accounting for 49% of the organic P deficit. The rate of CFA burial in the Puerto Ferro site is 0.33 μmol P/cm 2 /yr, accounting for over 100% of the organic P deficit. Carbonate dissolution in the deep Puerto Ferro sediments suggests carbonate substitution and increased Ca 2+ concentrations in pore waters as a mechanism for CFA formation. In contrast, CFA formation in the deep Puerto Mosquito sediments may be caused by high organic phosphorus accumulation rates accompanied by relatively low terrigenous and carbonate accumulation rates resulting in organic-rich sediments enabling apatite formation. Mirroring of organic P loss and Ca-bound P gain is not observed in cores from shallow water environments, suggesting that CFA formation may be restricted to deep environments or that rates of CFA formation may be too low to quantify using sediment chemistries. Puerto Mosquito may have more bioavailable phosphorus than Puerto Ferro due to higher TP sediment concentrations and lower rates of CFA formation in deep depositional environments. To further quantify possible phytoplankton phosphorous limitation in Vieques, future studies should assess the sediment production and benthic fluxes of phosphorous. iii

7 List of tables and figures Table 1: Depositional Environments and associated cores Table 2: Sediment chemistry for sedimentary facies Table 3: Sediment chemistry for surface sediments Table 4: Mass accumulation rates from 210-Pb dating Table 5: Radiocarbon results Table 6: Phosphorus reservoir abundances across study location Table 7: Comparative phosphorus reservoir abundances in other studies Table 8: Authigenic apatite rate calculations for PMD1 and PFD1 Table 9: Saturation ratios for carbonate fluorapatite in PMD1 and PFD1 Figure 1: Geologic map of Vieques Figure 2: Satellite view of Puerto Mosquito, Puerto Ferro, and Bahia Tapon Figure 3:Watersheds of Puerto Mosquito, Puerto Ferro, and Bahia Tapon Figure 4: Map of sediment core locations and benthic communities Figure 5: Phosphorus extraction methods flow chart Figure 6: Total phosphorus concentrations between depositional environments Figure 7: Total phosphorus concentrations between sedimentary facies Figure 8: C/P Ratios in Puerto Mosquito and Puerto Ferro Figure 9: Correlations between Fe-bound P and Fe concentrations and terrigenous sediment concentrations Figure 10: Correlations between Ca-bound P and CaCO3 and terrigenous sediment concentrations Figure 11: Correlations between organic P and organic carbon concentrations and terrigenous sediment concentrations iv

8 Figure 12: Percent abundance of phosphorus reservoirs among depositional environments Figure 13: Percent abundances of phosphorus reservoirs among sedimentary facies Figure 14: Total P concentrations vs depth per core Figure 15: Fe-bound P concentrations vs depth per core Figure 16: Ca-bound P concentrations vs depth per core Figure 17: Organic P concentrations vs depth per core Figure 18: Puerto Mosquito Shallow (PM12): Phosphorus and sediment chemistry depth profile Figure 19: Puerto Mosquito Shallow (PM4): Phosphorus and sediment chemistry depth profile Figure 20: Puerto Mosquito Shallow (PM14): Phosphorus and sediment chemistry depth profile Figure 21: Puerto Mosquito Deep (PMD1): Phosphorus and sediment chemistry depth profile Figure 22: Puerto Ferro Shallow (PF12): Phosphorus and sediment chemistry depth profile Figure 23: Puerto Ferro Shallow (PF7): Phosphorus and sediment chemistry depth profile Figure 24: Puerto Ferro Deep (PFD1): Phosphorus and sediment chemistry depth profile Figure 25: Puerto Mosquito Hypersaline lagoon (PM24): Phosphorus and sediment chemistry depth profile Figure 26: Mirroring of Ca-bound and organic P reservoirs in cores PMD1 and PFD1 Figure 27: Calculation of authigenic apatite formation in PMD1 Figure 28: Calculation of authigenic apatite formation in PFD1 Figure 29: Calculation of total phosphorus decrease in PMD1 and PFD1 Figure 30: Carbonate saturation indices for PMD1 and PFD1 v

9 1. Introduction Phosphorus is commonly the limiting nutrient for primary productivity in coastal marine environments, and has been cited as the ultimate limiting nutrient for primary productivity in marine ecosystems over geologic timescales (Toggweiler, 1999; Tyrell, 1999). This is largely a function of the fact that, unlike nitrogen, it cannot be fixed from the atmosphere. With over 95% of the phosphorus contained in the earth s crust, inorganic apatite minerals are the largest reservoir of phosphorus. In the ocean, the largest source of phosphorus is riverine input of weathered particulate matter and dissolved phosphorus species. Up to 99% of particulate phosphorous and 25% of dissolved phosphate delivered by rivers are buried in deltas and continental shelves (Paytan, 2007). As the main repository of oceanic phosphorus, sediment phosphorous cycling commonly plays a large role in controlling the concentration of phosphorus in overlying waters. Dominant forms of phosphorus in sediment include organic phosphorus, phosphate adsorbed to Fe-oxide minerals or carbonate particles, and phosphorus stored in minerals such as carbonate fluorapatite (CFA). Diagenetic interactions between these reservoirs affect the rate and extent by which phosphorus can be remobilized and returned to the water column (Ruttenberg, 1992; Sundby, 1992; Koch, 2001). These interactions can lead sediment to be a net source as well as a net sink of phosphorus (Short, 1997; Jensen, 1998). The factors controlling the net flux of phosphorus transport into or out of sediment depend on many factors including sediment composition, nutrient sources, 1

10 and geographic area. While nitrogen is generally considered to be the limiting nutrient for primary productivity in the open ocean and in many temperate coastal environments that are associated with dominantly terrigenous aluminosilicate sediments with low CaCO 3 concentrations, phosphorous limitation has been noted in many subtropical/tropical marine environments that contain high concentrations of CaCO 3 and very little terrigenous aluminosilicate phases (Short, 1985; Short, 1990; Jensen, 1998; Nielsen, 2007). Phosphorous limitation is derived, in part, from pore water evidence in low CaCO 3 sediments along temperate coasts, which have higher PO 4 concentrations than shallow marine CaCO 3 -dominated sediments in the tropics (Rosenfeld, 1979; Short, 1985). The low concentration of PO 4 in CaCO 3 -rich sediments is largely influenced by the chemisorption of P onto CaCO 3 surfaces and the conversion into more stable apatite phases (DeKanel and Morse; 1978; Millero, 2001). Thus, tropical CaCO 3 dominated sediments have an additional sink of bioavailable phosphorous, which may cause P-limited primary productivity in Florida Bay and Bermuda where seagrasses or other macroalgae is P-limited (Short, 1985; Short, 1990; Fourqurean and Zieman, 1992; Jensen, 1998; Fourqurean and Zieman, 2002). In this study, sedimentary phosphorus reservoirs are compared between two different bay ecosystems, Puerto Mosquito and Puerto Ferro, on the island of Vieques, Puerto Rico. The bays contain vastly different concentrations of the bioluminescent dinoflagellate, Pyrodinium bahamense var. bahamense with Puerto Mosquito containing persistent blooms of this bioluminescent dinoflagellate and Puerto Ferro containing so few that bioluminescence is not noticeable by the human eye (Selliger, 2

11 2001). Though less than 2 km apart, the environmental differences that support Pyrodinium bahamense var. bahamense must be significantly different between the two bays. Identifying these differences could help pinpoint the parameter(s) that allows dinoflagellates to proliferate in Puerto Mosquito compared to Puerto Ferro. While only a few studies have examined the Atlantic dinoflagellate species Pyrodinium bahamense var. bahamense, the ideal growing conditions for the related Pacific, toxic species, Pyrodinium bahamense var. compressum, has been fairly well studied (Azanza, 2001; Azanza, 2004; Villanoy, 2006). In general, Pyrodinium bahamense var. compressum reaches bloom concentrations in environments characterize by low tidal exchange and high nutrient input (Monbet, 1992; Phlips et al., 2002; Badylak et al., 2004). 2. Background 2.1 Nutrient controls on Pyrodinium Bahamense var. Bahamense populations Globally, high dinoflagellate populations commonly coincide with limited phosphorus availability, which is characterized by decreases of seawater N: P ratios (elevated phosphorus concentrations relative to nitrogen), toward values lower than the Redfield N:P Ratio of 16:1 (Hodgkiss, 1997). Nutrient limitation for this particular species of dinoflagellate has been observed in blooms of P. bahamense in Indian River Lagoon, Florida, where large rainfall events increased runoff and stimulated dinoflagellate blooms by significantly increasing concentrations of 3

12 bioavailable phosphorus and nitrogen, though largest blooms were more associated with large increases in dissolved phosphorus (Phlips, 2004). In theory, short term bio-assays that measure increases in chlorophyll with various additions of N, P, or light can determine the limiting nutrient of aquatic life, however, these experiments provide only a snapshot in time and results can be inconclusive (Brylinsky, 1973; Havens, 1996; Phlips, 1997). Seagrass C:N:P concentrations and ratios can serve as nutrient limitation proxies because overall productivity is correlated with C, N, and/or P concentrations, or related to C:P or N:P ratios (Fourqurean and Zieman, 1992; Fourqurean, 2002; Fourqurean, 2005). In addition, seagrasses integrate the average nutrient availability for the lifespan of the stalk and provide a more spatially and temporally constrained measure of nutrient concentrations compared to nearly instantaneous measurements from bioassays or from seawater nutrient concentrations at a single point in time (Fourqurean, 1992; Fourqurean 2002; Fourqurean, 2005). Thalassia testudinum is the dominant seagrass species of Vieques and compared to Thalassia testudinum in Florida Bay and other worldwide locations, Thalassia testudinum from Puerto Mosquito has high nitrogen concentrations and N:P ratios near or above the seagrass Redfield ratio (Fourqurean and Zieman, 2002; Algeo, 2008). These results imply an abundance of biologically available nitrogen and possible phosphorus limitation. If seagrass primary productivity in Puerto Mosquito is indeed phosphorus limited, then phosphorus sources and availability are likely a determining factor controlling the population dynamics of Pyrodinium bahamense var. bahamense in Puerto Mosquito and Puerto Ferro. 4

13 Analysis of sediment phosphorus reservoirs can provide information about the sources, sinks, and bioavailability of phosphorus in marine settings (Sundby, 1992; Ruttenberg and Berner, 1993; Koch, 2001). Sediment phosphorus solid phases are typically dispersed in very fine-grained minerals, thus conventional chemical or mineralogical methods such as XRD, XRF, or bulk sediment digests cannot distinguish between the main sedimentary phosphorus reservoirs. Thus, operationallydefined phosphorus extraction methods have been developed and calibrated to quantify the different phosphorus reservoirs. Evaluation of these P reservoirs can distinguish between different depositional and diagenetic processes affecting phosphorus cycling, which, in turn could help explain the occurrences of vastly different dinoflagellate populations in Puerto Mosquito and Puerto Ferro. 2.2 Sediment phosphorous reservoirs The dominant forms of sedimentary phosphorus are organic phosphorus, phosphate adsorbed to Fe-oxide minerals or carbonate particles, and phosphorus stored in apatite minerals (Burdige, 2006). The relative contribution of each reservoir is largely dependent on sediment composition, and sediments with large terrigenous (aluminosilicate) fractions typically have high fractions of phosphorus adsorbed to Fe-oxide minerals. In contrast, sediments with high carbonate concentrations usually have the highest phosphorus concentrations in the carbonate-adsorbed phosphorus reservoir (Koch, 2001; Cha, 2005). The composition of Vieques sediments ranges from nearly 100% terrigenous material to mostly calcium carbonate (~85%). Sediments in Puerto Mosquito are 5

14 generally higher in terrigenous matter while those in Puerto Ferro generally have more calcium carbonate (D Aluisio-Guerreri, 1988). The cycling of biologically available phosphorus is dependent upon the magnitude and lability of each sedimentary phosphorous reservoir, which, in turn, could influence the population dynamics of Pyrodinium bahamense var. bahamense Loosely sorbed/labile and Fe-bound P Iron-oxide minerals have a strong affinity for adsorption of phosphate. This is controlled by several factors, including mineralogy, crystallinity, and surface area of the oxide mineral (Burdige, 2006). In coastal marine environments, the principal source of iron oxide minerals is fluvial input. Phosphorus cycling in regions with high concentrations of iron-oxide minerals is strongly linked to iron redox reactions (Sundby, 1992). As iron-oxide minerals are buried in sediment, reducing conditions resulting from organic matter decomposition lead to the reduction of iron-oxides and results in the release of the adsorbed phosphate. Thus, the profile of the Fe-bound P reservoir is expected to decrease with depth. The phosphorus released from Fe-oxide minerals enters the sediment pore water where it can be transported by diffusion, advection, or bioturbation back into the water column to be used by marine biota. Phosphorus transport to the water column can also be attenuated if there are high enough concentrations of iron-oxide minerals at the sediment-water interface (Klump and Martens, 1981; Klump and Martens, 1987). Alternatively, liberated phosphate can interact with other phosphate reservoirs through adsorption onto calcium carbonate particles or through the formation of authigenic apatite. Due to the 6

15 tendency of iron-oxide to be reduced phosphate de-adsorbed, iron-bound phosphorus is not thought to be an important reservoir in terms of permanent phosphorus burial (Burdige, 2006) Carbonate-adsorption Adsorption of phosphate onto calcium carbonate particles is an important mechanism for phosphate burial due to the high adsorption capacity of carbonates, and has been cited as the principal cause of phosphorus limitation for primary productivity in some carbonate-rich sediments (Stumm and Leckie, 1970; de Kanel and Morse, 1978; Fourqurean, 1982; Short, 1985; Short, 1990; Millero, 2000). While carbonate-adsorbed phosphorus has been identified as an important and potentially dominant phase of phosphorus in carbonate-rich sediments, the overall importance of this reservoir in oceanic phosphorus cycling has been the subject of debate. While clearly an important phase of phosphorus in shallow-water tropical carbonate sediments, carbonate-adsorption is not thought to be an important mechanism in global phosphorus burial due to its confinement to carbonate sediments and the ability for diagenetic release of adsorbed phosphate (Burdige, 2006). Diagenetic transformations of carbonate-adsorbed phosphate depend largely on calcite or aragonite mineral saturation indexes (Slomp, 2007). Pore waters that are undersaturated with respect to calcite or aragonite promote net carbonate dissolution and the subsequent release of associated phosphate. Pore waters that are supersaturated with respect to these minerals support net carbonate precipitation and subsequent adsorption of dissolved phosphate. 7

16 2.2.3 Authigenic/detrital apatite Sedimentary apatite minerals are either detrital or authigenic. Detrital apatite delivered via continental weathering of aluminosilicate materials is usually fluorapatite [Ca 5 (PO 4 ) 3 F]. Apatite can also be biogenic in origin, as hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ], in the form of fish scales, teeth, and bones, though the undersaturation of seawater with respect to hydroxyapatite commonly leads to its dissolution in the water column or in the sediment (Burdige, 2006). Authigenic apatite forms in the sediment column and is dominantly in the form of carbonate fluorapatite (CFA) [Ca 10 (PO 4, CO 3 ) 6 F 2 ]. The formation of CFA in sediment has been cited as one of the most important mechanisms by which phosphorus is permanently buried and as one of the least accessible forms of phosphorus for marine biota (Ruttenberg and Berner, 1993). In general, diagenetic processes liberate adsorbed phosphate and organic phosphorus, so the only phosphate that may ultimately be retained in the sedimentary record is authigenic apatite (Faul, 2005). The conditions under which CFA precipitates in sediment are not fully understood. Large sediment deposits of CFA, called phosphorites, are typically found in shallow waters associated with upwelling zones where there is high enough organic matter deposition to concentrate phosphorous to 1 to 2 million times that of normal seawater (Knudsen and Gunter, 2002). At these locations, the sedimentation rate of other components is usually low, so organic matter becomes concentrated in the sediment (Van Cappellen and Berner, 1988; Knudsen and Gunter, 2002). Globally, phosphorite deposits are found exclusively in low latitude waters. All deposits, including those currently forming, are found at below 60 paleoaltitude, and nearly all of these are 8

17 below 40 paleoaltitude (Knudsen and Gunter, 2002). While most of these sites are found at coastal upwelling zones, there have been more recent discoveries of authigenic apatite formation in non-upwelling areas, relying on continental sources of nutrients for biological concentration of phosphorus in sediment (Baturin, 1988; Ruttenberg and Berner, 1993; Lucotte et al, 1994; Knudsen and Gunter, 2002). Experimental evidence suggests that the rate of apatite precipitation is a function of the saturation state of a precursor compound, octacalcium phosphate (OCP) [Ca 4 H(PO 4 ) 3 ], rather than the saturation state of apatite itself (Gunnars, 2004). In laboratory experiments, solutions of 500 µm PO4 and 16 µm F and varying Ca/Mg ratios were monitored. Concentrations of phosphate and fluoride concentrations decreased over time, indicating the precipitation of fluorapatite. Fluorapatite precipitation was found to be dependent on the supersaturation of OCP, which was sensitive to Ca/Mg concentrations, and did not precipitate even when solutions were supersaturated with respect to fluorapatite itself (Gunnars, 2004). High Ca/Mg ratios led to more rapid precipitation of fluorapatite, whereas solutions with molar Ca/Mg ratios less than 0.2 (high concentrations of Mg) did not precipitate any fluorapatite over the 700-day course of the study (Gunnars, 2004). The inhibition of apatite formation by high magnesium concentrations has been confirmed by other studies (Stumm and Leckie, 1970; Gunnars, 2004). Authigenic apatite in the form of CFA has been shown to form at the expense of other reservoirs, serving as a net sink of phosphorus in sediment (Ruttenberg and Berner, 1993; Monbet, 1997). As diagenetic processes lead to the liberation of phosphate adsorbed to Fe-oxide minerals and calcium carbonate particles, and that 9

18 contained in organic matter, pore water concentrations of phosphate increase. Pore water phosphorus is then available for authigenic apatite formation and is effectively removed from biological cycling (Krom, 1980; Sundby, 1992) Organic P The concentration of organic phosphorus in marine sediment is initially determined by the rate of primary productivity in the water column, though detrital materials can also deliver organic phosphorous from terrestrial sources. The source of organic phosphorus can be evaluated by using stoichiometric ratios (C:N:P) of end member organic matter sources (Ingall and van Cappellen, 1990; Monbet, 1997). Organic matter sources in coastal marine sediments can be a mix between three organic sources: phytoplankton, seagrasses, and terrigenous organic matter/mangroves. Marine phytoplankton molar C:P ratios are close to the Redfield Ratio of 106: 1 (Redfield, 1958). Seagrasses typically have higher C: P ratios of 550:1 and mangrove C:P is estimated at 425:1 (Atkinson and Smith, 1983; Fourqurean, 1992; Monbet, 2007). Organic matter from terrestrial sources typically has very high C:P ratios, ranging from (Ingall & van Cappellen, 1990). While C:P nutrient ratios of organic matter can be indicative of differing organic matter sources over time, these ratios can be influenced by diagenetic processes (Fillipelli, 2001; Cotner, 2004; Gonneea, 2004; Monbet, 2007). Organic matter C:P ratios that decrease with depth have been interpreted as selective phosphorus preservation, while high C:P ratios that increase with depth have been interpreted as selective remineralization of phosphorus in organic matter, as well as 10

19 transformation of remineralized organic phosphorus to authigenic apatite (Fillipelli, 2001; Cotner, 2004). 3. STUDY LOCATION 3.1 Geologic Setting The island of Vieques is situated 14 km off the southeastern coast of Puerto Rico at 18 7 N and W. It is approximately 23 km in length and 5 km in width (Fig. 1). Vieques lies along the Greater Antilles Ridge on the edge of the Caribbean Plate, formed when the Caribbean Plate subducted under the North American Plate in the early Jurassic-Eocene (Lewis and Draper, 1990). Vieques is underlain by highly weathered plutonic rocks, composed of mainly quartz and granodiorite as well as Cretaceous marine volcaniclastic rocks (Learned et al, 1973). These rocks are overlain by late-tertiary limestones in several locations on the island, including the southern coast between Esperanza and Ensenada Honda, along which Puerto Mosquito, Puerto Ferro, and Bahia Tapon are situated (Fig. 1). The Esperanza alluvial valley contains sand, silt and clay deposits stretching km wide by 5-6 km long along the southern coast (Fig. 1) 3.2 The Bioluminesent Bays of Vieques Puerto Mosquito fosters a very high concentration of the bioluminescent dinoflagellate Pyrodinium bahamense var. bahamense. Also known as the Biobay, Puerto Mosquito has become one of the biggest tourist draws to Vieques for those 11

20 hoping to witness this nighttime display. Bioluminescence is a characteristic that has evolved in many types of marine organisms, with uses ranging from protection to predation. The specific function of bioluminescence for this species of planktonic dinoflagellate, however, has not been determined. When ambient water is agitated, pressure on the cell walls due to this agitation initiates a chemical reaction between luciferin and oxygen, catalyzed by an enzyme called luciferase, producing oxyluciferase and light. The bioluminescence displayed in Puerto Mosquito is among the most brilliant in the world, with concentrations of Pyrodinium bahamense var. bahamense in Puerto Mosquito from 20, ,000 dinoflagellates/liter (Seliger, 2001). The net effect of this high concentration of bioluminescent dinoflagellate is a brilliant glow exhibited by any kind of movement in the water. Interest in Puerto Mosquito is high not only because of its bioluminescence, but also as a possible environmental health concern. Until recently, Pyrodinium bahamense var. bahamense was thought to be nontoxic, though a closely related species found in areas of the Pacific Ocean, Pyrodinium bahamense var. compressum, has been known to produce neurotoxins linking it to incidences of fatal paralytic shellfish poisoning (Landsberg, 2006). However, cases of saxitoxin pufferfish poisoning associated with the Indian River Lagoon in Florida suggest that Pyrodinium bahamense var. bahamense is also capable of producing dangerous toxins. Though no cases of shellfish or puffer fish poisoning have been reported on Vieques, the potential for this species to be toxic raises concern about the health of the local community and prompts further investigation into the cause for their extraordinary population in Puerto Mosquito. 12

21 3.3 Physical Setting of Puerto Mosquito, Puerto Ferro, and Bahia Tapon Puerto Mosquito, Puerto Ferro, and Bahia Tapon are located on the southern coast of Vieques along a 6-km stretch (Fig. 2). All bays are formed from openings in the carbonate cliffs that form the southern coast of the island (Fig. 1). The terrestrial environment along the coastline is arid tropical, with extensive mangrove forests lining the coast (D Aluisio- Guerrieri, 1988). Puerto Mosquito lies to the west of Puerto Ferro and Bahia Tapon, and displays the brightest bioluminescence. In June, 2006, the highest dinoflagellate concentration in Puerto Mosquito was 27,500 cells per liter, with an average of 10,000 cells per liter (Gasparich, 2007). Puerto Mosquito has an average depth of 1.26 meters, with a maximum depth of 4 meters in the center of the bay. It has the largest surface area of the three study bays, totaling 912,370 square meters (Tainer, 2007). Puerto Mosquito is connected to the ocean by a narrow channel approximately 200 meters long and less than 2 meters deep. This morphology could restrict tidal exchange between the bay and the open ocean, however, Rhodamine WT dye tracing experiments have determined the water residence time of Puerto Mosquito is only slightly longer than that of Puerto Ferro, at 5-6 days in Puerto Mosquito versus 4 days in Puerto Ferro (Greeney, 2007). Puerto Ferro lies directly to the east of Puerto Mosquito. It has a much lower concentration of dinoflagellates than Puerto Mosquito, with a maximum measured concentration of 700 cells per liter (Gasparich, 2007). It is a deeper bay than Puerto Mosquito, with an average depth of 2.21 meters. Its surface area is close to that of Puerto Mosquito s at 856,000 square meters. The mouth of the bay is wider and 13

22 deeper than that of Puerto Mosquito, at 240 meters in width and 7 meters in depth (Tainer, 2007). Only one core was analyzed from the third study bay for comparative purposes. With an average depth of 0.65 meters and surface area of 248,000 square meters, Bahia Tapon is the smallest and shallowest of the three study bays, lying directly east of Puerto Ferro. Dinoflagellate concentrations are considerably lower than that of Puerto Mosquito, with measurements in June 2006 ranging from a minimum of cells per liter in most samples to a maximum of 18,000 cells per liter (Gasparich, 2007). A 1972 study measured much higher concentrations of dinoflagellates, reporting concentrations of up to 80,000 cells per liter (Cintron and Maddux, 1972). The discrepancy between the 1972 and 2006 measured concentrations has not been thoroughly investigated, but may be due to changes in environmental conditions. 3.4 Watersheds Analysis of watersheds in the study region have identified that there are significant differences in the watershed draining Puerto Mosquito versus those draining Puerto Ferro and Bahia Tapon. The watersheds of Puerto Ferro and Bahia Tapon are of similar size at 6,790,000 and 6,137,000 square meters, respectively, and are largely undeveloped, due to the fact that they lie within the Vieques National Wildlife Refuge (VNWR) and are protected from development (Fig. 3). This contrasts with the much larger watershed of Puerto Mosquito, which covers an area of approximately 16,740,000 square meters, and contains a much higher proportion of 14

23 developed and agricultural land (Tainer, 2007). Differences in flux and source of terrestrial matter could be important to the nutrient dynamics in the coastal bays. This may be especially important for phosphorus, as terrigenous material is one of the main sources of phosphorous to the bays. 4. Methods 4.1 Field sampling Sediment cores were taken by a percussion corer, vibracorer, or a soil auger during the summers of 2006 and Percussion cores were taken by driving a clear polycarbonate tube into the sediment with the use of a hammer or slide hammer device. Vibracores were collected in aluminum pipes with the use of a gas-powered vibration system. Percussion cores ranged in length from cm while vibracores reached lengths of up to 232 cm. During 2006 and 2007 sediments from a total of 48 coring locations were collected from Puerto Mosquito (26 sites), Puerto Ferro (12 sites), and Bahia Tapon (10 sites). A subset of 10 sites was chosen for further sediment phosphorous analyses. These sites are laterally representative of the bays and include all major depositional sediment facies. Core locations, bay bathymetries, and modern depositional environments are presented in Figure 4 and Table 1. In Puerto Mosquito, three cores represent modern shallow water, taken in regions with water depths of approximately 1 m (PM4, PM12, PM14). One core was taken to represent the deeper water 15

24 environment in the center of the bay, at water depth of 2.6 m. In addition, one core was taken in the hypersaline lagoon bordering Puerto Mosquito on its northwest side (PM24) and the soil auger was collected ~15m inland from the western edge (Fig. 4). In Puerto Ferro, two cores (PF7, PF12) characterize the modern shallow depositional environment (water depth of 1-2 m) and one core (PFD1) represents the deeper water environment, at a water depth of 4.5 m. One core was examined in Bahia Tapon (BT9) for comparison. Upon collection, sediment cores were transported vertically to the field laboratory. Cores were extruded and cut open, described sedimentologically, photographed, and sampled in 1-5 cm intervals depending on nature of the sediment facies. 4.2 Laboratory methods At Wesleyan University, sediments were oven-dried at ~60ºC and homogenized with a mortar and pestle. Sediments were analyzed for inorganic carbon concentration using a UIC coulometer. All inorganic carbon released upon acidification was assumed to be calcium carbonate carbon. Total carbon and nitrogen concentrations were determined on a Thermo Flash 1112 Elemental Analyzer. Organic carbon was calculated as the difference between total carbon and inorganic carbon. Selected sediments were analyzed for solid phase chemistry by multi-acid (HCl/HNO 3 /HF/HClO 4 ) digests followed by ICP analysis at SGS Mineral Services (Toronto, Canada) or by XRF analyses at Colorado College (see Nelson, 2007 for XRF details). 16

25 4.2.1 Phosphate extraction (phosphate = PO4; Phosphorous = P) Sequential chemical extractions of phosphorous were used to quantify the main sediment phosphorous reservoirs. Phosphorous extractions were modified from those outlined by Koch (2001) (Fig. 5). The Koch (2001) method was modified for sediment with high calcium carbonate content from methods developed by Ruttenberg (1992) and Jensen and Thamdrup (1993). The only diversion from the Koch (2001) method was the combination of the first two extractions: (1) loosely sorbed or exchangeable labile P and (2) crystalline/amorphous Fe- and Mn- bound P. This combination was made under the assumption that loosely sorbed P would most likely be associated with Fe- and Mn- oxide minerals (Anderson, 2000). Sediments in Puerto Mosquito contain a much higher amount of Fe- and Mn- oxide minerals than the site studied by Koch (2001). The ionic strength of seawater leading to few positive sites available for adsorption combined with the typically much higher thermodynamic gains for phosphorus adsorption on oxide minerals than on clays would cause oxide minerals to adsorb the majority of phosphorus (Anderson, 2000). Extractions began with approximately 1 g of sediment (Fig. 5). Loosely sorbed, exchangeable phosphate and Fe- and Mn-bound phosphate were extracted first with 40 ml of 0.11 M dithionite solution (0.11 M Na 2 S 2 O NaHCO 3 ) and 10 ml of 1 M MgCl 2. Sediment and solution was agitated for three hours and centrifuged for 5 minutes at 4000 rpm. The supernatant was decanted and the sediment was rinsed with 25-ml of 1 N MgCl 2. This solution was agitated for 30 seconds, centrifuged for 5 minutes at 4000 rpm, and the supernatant was decanted. 17

26 Supernatant solutions were then bubbled with N 2 -gas for 20 minutes to remove excess hydrogen sulfide and to precipitate elemental sulfur. Four ml of 1 N H 2 SO 4 was added to each sample for preservation before refrigerated storage until analysis. Authigenic and detrital calcium-bound phosphate was extracted with 30 ml of 1 N HCl solution. Samples were agitated for 16 hours, centrifuged for 5 minutes at 4000 rpm, and decanted into 30 ml polypropylene bottles. Samples were refrigerated until analysis. Residual sediment was then transferred to 20 ml borosilicate bottles and ashed in a muffle furnace for 5 hours at 550ºC. After ashing, 15 ml of 1 N HCl was added to each sample before autoclaving for 50 minutes at 21 psi and 121ºC. Sediment and solution were then transferred to 50-ml centrifuge tubes, brought to a volume of 50 ml with deionized water, centrifuged for 5 minutes at 4000 rpm, and refrigerated until analysis. All extractions were analyzed for soluble reactive phosphorus (SRP). For phosphorus liberated by the dithionite solution and the hydrochloric acid extraction, this measured only inorganic phosphorus. For the residual organic extraction, this measured both organic and inorganic forms, since organic P was converted into phosphate during the ashing and autoclaving steps. Samples were analyzed for SRP on a Beckman-Coulter DU 530 spectrophotometer using the ascorbic acid reduction method (EPA, 1983). Briefly, 500 µl of sample was diluted with 5.5 ml of ultrapure water and 960 µl of a mixed reagent composed of ammonium molybdate, sulfuric acid, L-ascorbic acid, and potassium antimony tartrate. Phosphate concentrations were determined by quantifying the 885 nm peak relative to standard solutions. 18

27 To calculate the abundance of phosphorus in the organic phase for loosely sorbed, exchangeable phosphate and Fe- and Mn-bound phosphate and authigenic and detrital calcium-bound phosphate, total phosphorus (TP) was analyzed for both of these extractions. To break down dissolved organic molecules liberated by the dithionite or HCl extractions, 15 ml of each sample was transferred to a borosilicate bottle. Then, 0.3 ml of 11 N sulfuric acid and 0.12 grams of ammonium persulfate were added before samples were then autoclaved for 35 minutes at 21 psi and 121ºC. Reaction with ammonium persulfate and autoclaving oxidizes organic molecules, thus releasing P that is then converted into orthophosphate. Samples were analyzed on a spectrophotometer using the methods described above. The organic component in each extraction was calculated as the difference between SRP and TP Pb and 14 C Sediment bulk densities (g dry sed/ ml wet sed) were determined by measuring the weight and volume of wet sediment, then reweighing the sediment after drying. Homogenized sediments from seven cores (PM4, PMD1, PM12, PM14, PFD1, PF12, BT9) were analyzed for 210 Pb and 226 Ra at OceanChem Laboratories (Narragansett, Rhode Island) via gamma counting techniques using a well-type pure Ge detector or by alpha spectrometry at Virginia Institute of Marine Science (Cutshall et al., 1983; Moore, 1984; Robertson, 2007). Sediment mass accumulation rates and 210 Pb chronologies were determined by graphing the cumulative dry sediment mass (no salt correction) versus excess 210 Pb activities and applying the constant flux constant rate model (e.g. Appleby and Oldfield, 1992). 19

28 To better constrain the sedimentary history, a subset of marine mollusks and plant remains from four cores (PM12, PM13, PM14, PF12) were analyzed for radiocarbon at the National Ocean Sciences AMS facility (Woods Hole, MA). Samples were photographed, cleaned of adhering sediment with distilled water, dried, and homogenized with a mortar and pestle. Most plant remains were identified as mangrove roots. Conventional radiocarbon ages (present = 1950 A.D.) and Fm concentrations follow the conventions outlined by Stuiver and Polach (1977). Conventional radiocarbon ages were converted in calendar-calibrated ages using the CALIB program. For mollusk samples, the average marine reservoir correction (ΔR=-31; stdev = 24) of the six nearest Caribbean locations from the Marine Correction Database was used with the Marine04 calibration curve. All plant remains had typical C 3 terrestrial δ 13 C values (-25 to -27 VPDB), thus the Northern Hemisphere IntCal04 curve was applied for calibration purposes (Stuiver and Reimer, 1993; 5. Results 5.1 Sedimentary Facies Sedimentary facies were determined both from field notes core descriptions and from chemical data and build upon the previous facies descriptions of D Aluisio- Guerrieri et al. (1988), and Nelson (2007) regarding the same study location. Facies descriptions and chemical data for the subset of ten cores analyzed in this study are 20

29 given in Table 2. (Chemical data is reported as dry weight %, standard deviations are 1σ). Bulk sediment compositions average 38±32% CaCO 3 but range from dominantly calcium carbonate (84%) to nearly 100% terrigenous material (~ 0% CaCO3). Organic carbon content ranges from % with an average of 1.6 ± 1.0%. Terrigenous material ranges from %, averaging 58±33%. Iron concentrations range from %, with an average of 2.4± 2.1%, and scale linearly with terrigenous material concentrations. Molar Fe/Al ratios range from (omitting points where Fe or Al content is 0), with an average of 0.19± Terrigenous mud This facies was described by D Aluisio-Guerrieri (1988) as muddy sand derived from terrigenous material from surrounding hills. It is characterized by a very low CaCO 3 content (0.7 ± 1.6%) and a very high terrigenous component, approaching 100% in some areas. Organic carbon concentrations are lower than all other facies described (0.6±1.4%). Molar Fe/Al ratios are also the lowest among facies, with an average of 0.12±0.04 (Table 2). Terrigenous mud is found in the deepest sections of Puerto Mosquito cores, starting at depths of cm and persisting throughout the length of the core. 21

30 5.1.2 Gravelly shell hash and sand This facies is characterized by very poor sorting and large clast size and has been interpreted as a storm deposit. It has a very low CaCO 3 concentration (7± 8%) and has the second highest terrigenous fraction after the terrigenous mud facies (88±9%), as well as the highest average organic carbon concentration (2.5±0.6%). Fe/Al molar ratios are higher than that of terrigenous mud (0.15±0.01), but low in comparison to other facies. It is found in north and central locations in Puerto Mosquito and Puerto Ferro (cores PM4, PMD1; see Fig. 4 for core locations). Its position relative to other facies is variable, occurring directly above terrigenous mud in some cases, or between layers of marine facies in other locations (Nelson, 2007) Neritina mud This facies is characterized by abundant coarse gastropod shells and, to a lesser extent, bivalve shells. 90% of the gravel fraction is composed of fragments of Neritina Virginia and Neritina punctulata, and was interpreted to be indicative of brackish to hypersaline mud flats (D Aluisio-Guerrieri, 1988). Sediment composition of Neritina mud is highly variable, and chemical composition averages likely include facies transitions. CaCO 3 concentrations are higher than terrigenous mud and gravelly shell hash and sand (53±21%). Terrigenous material content is third highest of all facies (45±21%). Organic carbon concentrations are lower than all other facies except terrigenous mud, with an average concentration of 1.2±0.31%. Fe/Al ratios are considerably higher than that of terrigenous mud (0.20±0.02). This facies is found overlying terrigenous mud in the northwest region of Puerto Mosquito (PM4, PMD1). 22

31 5.1.4 Molluscan gravel This facies is characterized by an abundance of well-preserved, sometimes articulated mollusk shells in a matrix of mud and sand (Nelson, 2007). It was interpreted by D Aluisio- Guerrieri (1988) to indicate moderate turbidity in regions experiencing carbonate mud deposition. It has a higher CaCO 3 content than Neritina mud (62± 19%) accompanied by less terrigenous material (33± 18%) (Table 2). Organic carbon content is also slightly higher than that of Neritina mud (1.82±1.3%). Fe/Al ratios are considerably higher than that of terrigenous mud and slightly higher than Neritina mud, averaging 0.23±0.05. This facies overlies Neritina mud in northwest regions of Puerto Mosquito Halimeda sand This facies is characterized by a high incidence of Halimeda flakes with a matrix ranging from carbonate mud to fine sand. It has been interpreted as indicative of lowturbidity water conditions (Nelson, 2007). Average CaCO 3 content is higher than all other facies (76±4%), with a corresponding terrigenous fraction lower than all other facies (19±3%) (Table 2). The organic carbon fraction is higher than molluscan gravel (2.1±0.5%). Fe/Al molar ratios are similar to Neritina mud (0.2 ±0.08). Halimeda sand is found in Puerto Ferro and Bahia Tapon directly underlying surface sediments. 23

32 5.1.6 Mixed carbonate-siliclastic mud This facies represents the modern depositional environment of most of Puerto Mosquito and Bahia Tapon. It is also found in some surface sediments of Puerto Ferro. It is characterized by the highest average organic carbon fraction in the study area (2.2±0.92%) and is composed of roughly half CaCO 3 (52±18%). Terrigenous fractions are high compared to molluscan gravel and Halimeda sand, averaging 43± 18%. Fe/Al ratios are the highest among all facies (0.26±0.06) (Table 2) Carbonate mud and sand This facies represents the modern depositional environment of much of Puerto Ferro. It is similar to mixed carbonate-siliclastic mud but contains a larger amount of calcium carbonate (74±5%) and considerably less terrigenous material (22±5%). The organic carbon fraction is lower than mixed carbonate-siliclastic mud, (1.69±0.4%) as is average Fe/Al molar ratio (0.19±0.1). 5.2 Surface sediments While most surface sediments in Puerto Mosquito and Bahia Tapon, as well as some in Puerto Ferro, are mixed carbonate-siliclastic mud, there is a large degree of variability within this facies category. Subdividing these facies into surface sediments of Puerto Mosquito, Puerto Ferro, and Bahia Tapon highlights some of the major chemical differences in current deposition between study bays (Table 3). Considering only the top facies (mixed carbonate-siliclastic mud/carbonate mud and sand), Puerto Mosquito has the lowest calcium carbonate concentration (48±17%) 24

33 and highest terrigenous fraction (47±16%) of all surface sediments. Puerto Mosquito also has an intermediate concentration of organic carbon (2.1±0.8 %). Top facies sediments in Bahia Tapon have slightly higher concentrations of organic carbon (2.2±0.2 %) and CaCO 3 (58±1 %) They also have the highest Fe/Al molar ratios of all surface sediments (0.30±0.01). The highest amounts of calcium carbonate are found in carbonate mud and sand in Puerto Ferro (74±5%) Mixed carbonate-siliclastic mud in Puerto Ferro has higher calcium carbonate (67±4 %) than surface sediments in Puerto Mosquito and Bahia Tapon. Carbonate mud and sand in Puerto Ferro has the lowest amounts of organic carbon (1.7±0.4 %), terrigenous material (22±5 %), and the lowest Fe/Al molar ratio (0.20±0.02) among surface sediments C data and 210-Pb mass accumulation rates Mass accumulation rates of sediment as determined by 210-Pb are presented in Table 4. Cores from shallow Puerto Mosquito have the highest sediment mass accumulation rates: core PM4 has a mass accumulation rate of mg/cm 2 /yr for the top 20 cm of sediment, while PM12 has a mass accumulation rate of mg/cm 2 /yr for the top 28 cm of sediment. Deep Puerto Mosquito has the slowest mass accumulation rate, at 48.3 mg/cm 2 /yr for the top 15 cm of sediment. Cores in Puerto Ferro have slower sediment mass accumulation rates: the mass accumulation rate of PFD1 is mg/cm 2 /yr for the top 50 cm of sediment, while that of PF12 is slower, at mg/cm 2 /yr for the top 20 cm of sediment. 25

34 Shallow Puerto Mosquito has much higher terrigenous sedimentation rates than shallow Puerto Ferro, at 152 and mg/cm 2 /yr for PM4 and PM12, respectively, versus 37 mg/cm 2 /yr for PF12 (Table 4). Calcium carbonate accumulation rates between the bays, however, are within the same range, at 114 and 83 mg/cm 2 /yr for PM4 and PM12 versus 98.4 for PF12 (Table 4). These sites also have similar total phosphorus accumulation rates, at 30.1 and 35.5 mg/cm 2 /yr in PM4 and PM12 versus 28.1 mg/cm 2 /yr in PF12, with similar accumulation rates of both Ca-bound and organic phosphorus. Ca-bound P accumulation rates are 11.0 and 11.3 mg/cm 2 /yr for PM4 and PM12 versus 8.3 for PF12 in Ca-bound P, with organic P accumulation rates of 15.8 and 22.6 mg/cm 2 /yr for PM4 and PM12 versus 15.6 mg/cm 2 /yr for PF12 (Table 4). In deep depositional environments in Puerto Mosquito and Puerto Ferro, however, mass accumulation rates of terrigenous material are similar (21.0 and 35.7 mg/cm 2 /yr in PMD1 and PFD1, respectively) with the main difference between the two being much higher rate of calcium carbonate accumulation in PFD1 (22.0 mg/cm 2 /yr in PMD1 versus mg/cm 2 /yr in PFD1; Table 4). Total phosphorus accumulation rates are also considerably different between PFD1 and PMD1, at 38.9 mg/cm 2 /yr in PFD1 and 17.2 mg/cm 2 /yr in PMD1. However, while PMD1 has the lowest overall phosphorus accumulation rate by a wide margin (11 mg/cm 2 /yr slower than the next slowest P accumulation rate, in PF12), the Ca-bound P accumulation rate is within the range of other cores at 9.3 mg/cm 2 /yr, and is higher than that of PF12 (8.3 mg/cm 2 /yr). Proportional to its overall phosphorus accumulation rate, PMD1 has a much higher accumulation rate of Ca-bound P than other sites (Table 4). 26

35 Cores PM14, PM12, PF12 and PM13 (PM13 was not processed for phosphorus or discussed here) were dated using radiocarbon techniques (Table 5). Intervals in the terrigenous mud facies in PM14 range from 3843 years of age in deepest intervals to 2000 years in shallowest intervals. The only interval in the gravelly shell hash and sand and molluscan gravel facies was dated at 459 years of age. Samples from the terrigenous mud facies in PM12 were dated from 2465 years old in deeper intervals and 1428 in a shallower terrigenous mud interval. Attempts to date a mollusk sample from the molluscan gravel facies were inconclusive, as the sample was younger than 1950 AD (Table 5). Mollusk samples from PF12 taken in the mixed carbonatesiliclastic mud facies were dated at 145 years of age, with progressively deeper intervals in the carbonate mud and sand facies dated at 1179 and 2039 years. 5.4 Sediment total phosphorus concentrations Total phosphorus - modern depositional environment relationships Total sediment phosphorus concentrations (calculated in μmol /g sediment) vary considerably between the three study bays (Fig. 6). Terrigenous mud from cores deep enough to reach the terrigenous mud facies (PM12, PM14) are not included in core averages for these cores, but analyzed separately as terrigenous mud. Across all bays and sediment cores, the range of total phosphorus is from 0 to 12.8 μmol/g. For marine sediments, both the highest and lowest core averaged phosphorus concentrations are found in Puerto Mosquito sediments. The highest concentrations are found in the deep depositional environment of Puerto Mosquito (PMD1), with an average concentration of 10.7±1.5 (Fig. 6), while lowest concentrations are found in 27

36 shallow depositional environments (PM4, PM12, PM14), with an average of 3.3±1.0 μmol/g. The lowest overall phosphorus concentrations are found in terrigenous mud (1.6±0.6 μmol/g), with concentrations slightly lower than that measured in the soil auger (2.1±1.7 μmol/g) Total Phosphorus - Sedimentary Facies Relationships Total phosphorus (TP) concentrations also vary considerably between sedimentary facies (Fig. 7). With the exception of the Neritina mud facies, which has a phosphorus concentration of 6.92±3.87 μmol/g, mixed carbonate-siliclastic mud (the dominant surface sediment) has the highest concentrations of phosphorus (6.4± 2.9 μmol/g). Carbonate sand, the surface sediment found in regions of Puerto Ferro and Bahia Tapon, has high overall P concentrations, averaging 4.6±1.9 μmol. Halimeda sand also has high total phosphorus concentrations, averaging 6.06±0.49 μmol/g. Gravelly shell hash and sand (the marine facies most similar to the composition of terrigenous mud) and terrigenous mud have the two lowest total phosphorus concentrations, averaging 2.53±0.89 and 2.85±2.11 μmol/g, respectively. 5.5 Sediment Phosphorus Reservoirs Phosphorus extracted from sediment is classified into three reservoirs: 1) Febound P includes loosely sorbed/labile P and P adsorbed to Fe- or Mn- oxide minerals, liberated by dithionite solution. 2) Ca-bound P is composed of the authigenic/detrital apatite and calcium-bound P liberated by HCl solution. 3) Organic P includes phosphorus extracted from the residual sediment after ashing and autoclaving as well 28

37 as the organic fractions extracted from the Fe-bound P and Ca-bound P extractions in total phosphorus analysis (calculated as the difference between total phosphorus and soluble reactive phosphorus). These organic components are typically very small and represent a minor proportion of the total organic P reservoir (Appendix A). The dominant pools of phosphorus in Vieques sediments are organic and Cabound P. Across all sediment types, phosphorus in organic forms comprises 22-93% of the total phosphorus pool and ranges from μmol/g (Table 6). Ca-bound P comprises 0-76% of total phosphorus and ranges from μmol/g. The Fe-bound P reservoir is generally minor, comprising 0-33% of total phosphorus, with concentrations ranging from μmol/g (Table 6). The correlations between sedimentary P reservoirs and sediment characteristics are presented in Figures Fe-bound P does not correlate strongly with total iron concentrations (R 2 = 0.22) or terrigenous sediment concentrations (R 2 = 0.19) (Fig. 9). Similarly, Ca-bound P does not correlate with calcium carbonate concentrations (R 2 = 0.18) or terrigenous sediment concentrations (R 2 = 0.17) (Fig. 10). Organic P has a moderate positive correlation with organic carbon concentrations (R 2 = 0.38) and weak correlation with terrigenous sediment concentrations (R 2 = 0.20) (Fig. 11) P reservoirs between depositional environments Among all depositional environments, the smallest P reservoir is Fe-bound P (Fig. 12). Averaged per core, this reservoir composes less than 10% of the total phosphorus across all cores. The relative sizes of the Ca-bound P and organic P reservoirs vary over depositional environments. For the shallow Puerto Mosquito, 29

38 shallow Puerto Ferro and Puerto Mosquito soils environments, most P is in the organic P reservoir (Fig. 12). The deep depositional environments of Puerto Mosquito and Puerto Ferro, the hypersaline lagoon flat adjacent to Puerto Mosquito, and one core from Bahia Tapon, display a reversal between the calcium-bound P and organic P reservoirs. In these environments the Ca-bound P pool exceeds the organic P pool, comprising 50-60% of total P (Fig. 12). The deep depositional environments of Puerto Mosquito and Puerto Ferro also have slightly elevated abundances of Fe-bound P (12-15% of total P) compared to corresponding shallow water environments (Fig. 12). The Fe-bound P reservoir is smaller in the hypersaline lagoon and in Bahia Tapon, making up less than 10% of total P. The relative proportion of sediment P pools correlates with total phosphorus (TP) concentrations in sediment. Environments with lower TP concentrations (PM Shallow, PF Shallow, PM soil auger,) have Ca-bound P reservoirs that are smaller than the organic P pool (Fig. 12). In contrast, environments that have higher TP pools (PM deep, PF deep, hypersaline lagoon, BT) have Ca-bound P pools that are larger than the organic P pool Organic C/P Ratios Organic carbon to organic phosphorus ratios (C:P) of surface sediments are notably different between Puerto Mosquito and Puerto Ferro. C:P ratios in Puerto Ferro range from , while those in Puerto Mosquito range from (Fig. 8). With increased depth, C:P ratios in Puerto Ferro increase in a relatively linear 30

39 fashion. The inverse of the linear regression slope is the rate of change of C:P per cm depth. In PFD1, this change is an increase in C:P ratios at a rate of 8.1 C:P ratios per cm, with an R 2 value of 0.64 (Fig. 8). In PF12, the rate of increase of C:P ratios is 1.8 per cm, with an R 2 value of 0.52 (Fig. 8). C:P ratios in Puerto Mosquito do not display the same linear trend with depth. Core PMD1 has a C:P ratio of 380 in the top interval (0-1 cm), increases to values of nearly 600 by 10 cm depth, decreases to about 350 by 18 cm, and then returns to values close to surface values (Fig. 8) Cores PM4, PM12, and PM14 share similar profiles, of high C:P ratios in surface intervals ( in the top 10 cm), decreases to lower values ( ) in the cm range, increases to very high values ( ) in the cm depth range, and then decreases with increased depth ( ), in the cm range (Fig. 8) P Reservoirs between Facies The correlation between high total P concentrations and proportionally higher Cabound P reservoirs is also evident in sedimentary facies data (Fig. 13) In Neritina mud, the facies with the highest total amount of phosphorus per gram of sediment of all the facies analyzed, Ca-bound P comprises 62% of total P. Other sediments with high concentrations of total phosphorus (mixed carbonate-siliclastic mud, carbonate mud and sand, and Halimeda sand) also have elevated Ca-bound P over organic P, though this difference is slight and may not be significant. Organic phosphorus is a greater percentage of total phosphorus in gravelly shell hash and sand, terrigenous mud and molluscan gravel. Terrigenous mud and 31

40 gravelly shell hash and sand share similar profiles, with has over 60-70% of total phosphorus in the organic fraction, 20-30% of TP as Ca-bound P, and a very small Fe-bound P reservoir (Fig. 13). The disparity between organic and Ca-bound P is much lower in molluscan gravel. Organic phosphorus is proportionally higher than Ca-bound P, but only by a few percent. 5.6 Phosphorus Reservoirs with depth Phosphorus reservoir concentrations change considerably over the length of a sediment core. General trends include high concentrations of organic and Ca-bound in uppermost sediments, with a relatively higher concentration of Fe-bound P (Figs ). Thus, TP concentrations are typically highest in the surface sediments (Fig. 14). With increasing sediment depth, organic P and Fe-bound P concentrations usually decrease while Ca-bound P concentrations often show an initial increase followed by a decrease at greater depth. Sediment profiles of TP and P-pools (Fe-bound P, Cabound P, organic P) are shown together with CaCO 3, organic C, and terrigenous material concentrations from representative cores from each depositional environment (Figs ). Bulk sediment Fe/Al molar ratios and 210 Pb- or 14 C-sediment ages are also shown Puerto Mosquito Shallow PM12 Core PM12 represents shallow depositional environments in Puerto Mosquito (Fig. 18). Organic P is the most abundant reservoir throughout the length of the core. Fe-bound P is uniformly very low. The total amount of phosphorus increases 32

41 throughout the top facies (mixed carbonate-siliclastic mud), coming to a maximum between 10 and 15 cm depth. Organic P and Ca-bound P reservoirs also come to a maximum at this point. All P reservoirs decrease throughout the molluscan gravel facies, reaching lowest concentrations at the onset of terrigenous mud. The depthfacies trends of sediment P reservoirs in core PM12 is similar to other shallow water Puerto Mosquito (PM4, PM14) sites, though Ca-bound P becomes the dominant P reservoir in a few isolated intervals in PM14 (Figs. 19, 20). The calcium carbonate, organic carbon, terrigenous component, and Fe/Al values correlate with the sediment facies transitions. The uppermost mixed carbonatesiliciclastic facies (0-20 cm) has CaCO 3 concentrations of about 40%, organic C concentrations of 2.75%, terrigenous components of 50%, and a relatively high Fe/Al ratio of CaCO 3 concentrations, organic C concentrations, and Fe/Al ratios decrease throughout the molluscan gravel facies, coming to their lowest values in terrigenous mud. The terrigenous sediment fraction increases over this interval, reaching highest concentrations in terrigenous mud. The terrigenous mud facies has very low CaCO 3, organic C and is dominantly composed of siliclastic material with a relatively low Fe/Al ratio near Puerto Mosquito Deep PMD1 Sediment phosphorus reservoir profiles are much different in the deep depositional environment of Puerto Mosquito than in shallower regions. In superficial sediment, organic and Ca-bound P concentrations are nearly equivalent. With 33

42 increasing depth through the mixed siliclastic-carbonate mud facies, organic P concentrations decrease almost linearly as Ca-bound P concentrations increase (Fig. 21). This trend of decreasing organic P and increasing Ca-bound P essentially ends at a depth of 12 cm and the remaining concentrations are nearly constant further down core. Beginning at the initial increase of Ca-bound P, the Ca-bound P pool is much larger than the organic P pool. Fe-bound P is the smallest reservoir throughout the core, though it is a significant fraction of total phosphorus, with its highest concentrations in surface sediment at 1.9 μmol/g. Sediment TP decreases consistently down core from μmol/g (Fig. 21). The upper 7 cm of sediments has relatively high concentrations of organic carbon, terrigenous material, and a high Fe/Al ratio. In this same interval, calcium carbonate is relatively low. Organic carbon, terrigenous material, and Fe/Al ratio decrease synchronously below 7 cm and reach nearly invariant concentrations below 20cm at the onset of the Neritina mud facies (Fig. 21). Calcium carbonate concentrations mirror the terrigenous and organic C trends by increasing below 7 cm until a near constant concentration of 70% PF Shallow PF12 PF12 is representative of shallow depositional environments in Puerto Ferro (Figs. 22, 23; PF12 shown in Fig. 22). The most abundant phosphorus reservoir is organic P throughout the length of the core. The uppermost sediment contains nearly 34

43 equivalent amounts of Fe-bound and Ca-bound P, with organic P higher than both of these reservoirs. With progression through the top facies (mixed carbonate-siliclastic mud), total phosphorus concentrations decrease, reaching invariant concentrations by depths of 25 cm, at the onset of the carbonate mud and sand facies. Phosphorus reservoirs also decrease throughout mixed carbonate-siliclastic mud, but do so sequentially. Fe-bound P concentrations decrease to invariant concentrations by 12 cm, while Ca-bound phosphorus remains constant until 12 cm and decreases to invariant levels by 18 cm. Organic phosphorus remains stable throughout the mixed carbonate-siliclastic mud facies and decreases throughout the carbonate mud and sand facies. CaCO 3 and terrigenous sediment concentrations do not vary considerably throughout the core: CaCO3 content is consistently high (64-74 %), and terrigenous sediment is consistently low (21-31%). The facies transition between mixed carbonate-siliclastic mud and carbonate mud and sand correlates with organic carbon and Fe/Al ratios. Organic C concentrations and Fe/Al ratios are high in mixed carbonate-siliclastic mud and decrease through the facies transition reaching lows in carbonate mud and sand PF Deep PFD1 In deep Puerto Ferro, total phosphorus concentrations are elevated in the top facies (carbonate mud and sand) relative to its relatively stable concentrations throughout the rest of the core (Fig. 24). Fe-bound P is also highest in the carbonate mud and sand facies, with a maximum concentration of 1.6 μmol/g. Fe-bound P 35

44 decreases with depth, reaching invariant concentrations by 10 cm depth. Concentrations of organic P and Ca-bound P are nearly equivalent in the top carbonate mud and sand facies, remaining stable through the progression into Halimeda sand. At 30 cm depth, these two reservoirs begin to diverge. Ca-bound P increases, reaching a maximum at around 48 cm depth. The organic fraction also decreases gradually throughout the core, reaching concentrations about half of its surface concentration by the bottom of the sediment core. Calcium carbonate content and terrigenous sediment concentrations do not vary with facies changes. CaCO 3 is consistently high (70%) and terrigenous material is consistently low (18%) throughout the core. Organic carbon concentrations and Fe/Al ratios show slight decreases with depth. These changes are gradual, and do not correlate with facies changes PM hypersaline lagoon PM24 Ca-bound P is the dominant reservoir of phosphorus throughout PM24 (Fig. 25) Surface concentrations of this Ca-bound P are about twice as high as organic phosphorus. All reservoirs remain stable until a peak at 80 cm, at which point all P reservoirs increase. The increase in organic P equilibrates it with Ca-bound P at this peak. With depth, all reservoirs decrease to levels slightly lower than those before the peak. The peak in phosphorus concentrations correlates with a peak in Fe/Al ratios. CaCO 3 concentrations and terrigenous sediment remain constant throughout the core, with CaCO 3 concentrations approaching 0% and terrigenous sediment concentrations 36

45 approaching 100%. At depths of 140 cm, CaCO 3 experiences a slight peak to a maximum of 26%, shared by a decrease in terrigenous material to a minimum of 73%. Organic carbon concentrations are highest from 0-50 cm at around 0.8%. A large peak in concentrations is evident at 20 cm to 3.5%. Concentrations decease with depth to concentrations of 0.2%. Fe/Al ratios increase gradually throughout the core from 0.10 to 0.20 (Fig. 25). 6. Discussion Relative sea-level has been rising in the Caribbean since the mid-holocene. Evidence of drowned eolianites on Puerto Rican coastlines has been used to estimate this rise at approximately 4000 B.P. (Kaye, 1959; D Aluisio- Guerrieri, 1988). Evidence from other locations in the Caribbean, including south Florida Bay and the northeast coast of the Gulf of Mexico, suggests that sea-level rise, while decreasing in magnitude over the last years, continues to rise to this day (Shepard, 1960; Scholl, 1964a; Scholl, 1964b; Scholl and Stuiver, 1967; Bloom, 1970; D Aluisio- Guerrieri, 1988;). The sedimentary history of Puerto Mosquito, Puerto Ferro, and Bahia Tapon reflects the infilling of these bays as sea level rose (D Aluisio-Guerrieri, 1988; Nelson, 2007). The terrigenous mud facies found at the greatest depths in the Puerto Mosquito, Puerto Ferro, and Bahia Tapon cores represents deposition of weathered igneous alluvium from nearby uplands or possibly a highly weathered paleosol atop 37

46 Upper Cretaceous-Eocene diorite (Renken, 2002). In Puerto Mosquito, radiocarbon dating of plant remains from the terrigenous mud facies indicates deposition at sites PM12 and PM14 from at least years ago though the 1428 age is at or near the end of terrigenous mud deposition (Table 5). Rising sea-level led to the deposition of near intertidal or storm facies, gravelly shell hash and sand or Neritina mud, over the terrigenous mud. The Neritina mud facies has been interpreted to represent an intertidal to slightly subtidal environment associated with fluctuating brackish to hypersaline waters (D Aluisio- Guerrieri, 1988). At sites PM12 and PM14, 14 C results place the transition from terrigenous mud to gravelly shell hash and sand transition between 1428 to 2000 years ago (Table 5). The younger 14 C-age of 1830 years ago found further down core of the 2000 year age in core PM14 likely represents younger mangrove roots penetrating into older sediments (Table 5). Continued sea-level rise led to the colonization of the shoreline by mangroves as well as the deposition of molluscan gravel and Halimeda sand facies at intermediate water depths (Nelson, 2007). Lead-210 and radiocarbon ages from sites PM4, PM12, PM13, PM14, and PMD1 indicate that intermediate-water depth facies, molluscan gravel and Halimeda sand facies, were deposited from years ago up until as recently as 50 years ago (Tables 4, 5). The transition from intertidal/slightly subtidal facies to intermediate water depth facies over the last ~2000 years signifies that the rate of sea level rise exceeded the rate of sedimentation over this time interval. Modern sedimentation in Puerto Mosquito, Puerto Ferro, and Bahia Tapon includes deposition of carbonate mud and sand (Puerto Ferro) as well as mixed carbonate-siliclastic mud (Puerto Mosquito, Bahia Tapon). The modern sedimentary 38

47 facies is distinguished by a marked increase in terrestrial matter and Fe/Al ratios. In the shallow western portion of Puerto Mosquito (PM4, PM12), the mixed carbonatesiliciclastic facies does not occur until years ago, while this facies and the carbonate mud and sand extend to at least years ago in the deepest parts of Puerto Mosquito and Puerto Ferro (PMD1, PFD1; Table 4). Dinoflagellate blooms are associated with modern sedimentary facies, though this facies extends only to years in shallow parts of Puerto Mosquito, and longer in deep Puerto Mosquito and Puerto Ferro. Thus, it is possible that environmental conditions or nutrient cycling that supports the modern populations of Pyrodinium bahamense have only existed for a relatively short time. 6.1 Sedimentary Phosphorus Reservoirs Total phosphorus concentrations Total phosphorus concentrations in Vieques sediments ( μmol/g) fit within the range of marine carbonate sediments of northeastern Florida Bay ( μmol/g) and Bermuda Bay ( μmol/g), as well as elsewhere in the world ( μmol/g near Majorca, Meditteranean Sea) (Table 7; Jensen, 1998; Koch, 2001; Lopez, 2004). Subtropical and tropical carbonate shelf sediments typically have lower phosphorous concentrations than temperate, shelf sediments containing low carbonate concentrations. Total phosphorous in temperate continental margin sediments are often higher than the ranges reported for carbonate sediments, such as μmol/g in the Long Island Sound FOAM site, in the Mississippi Delta, and μmol/g in the East Sea of Japan (Ruttenberg and 39

48 Berner, 1993; Cha, 2004). Temperate siliclastic lagoonal sediments can be high in total phosphorus concentrations, with those near Minorca measured at μmol/g (Table 7; Lopez, 2004) Iron-bound phosphorus Though it is often a dominant reservoir in temperate sediments with high terrigenous sediment fractions, at up to 63% of total phosphorus, phosphorus adsorbed to iron-oxide minerals is a uniformly minor phosphorus reservoir in the Vieques bays (Cha, 2005). A weak correlation between Fe-bound P and terrigenous sediment concentrations (R 2 = 0.19) indicate that this reservoir is not controlled by terrigenous material concentrations (Fig. 9). The weak correlation between total sedimentary iron concentrations and Fe-bound P concentrations (R 2 = 0.22) also reveals that sedimentary total iron is not controlling the amount of P in this reservoir (Fig. 9). This lack of correlation could be a function of low reactivity of iron phases through complexation with organic phases or by the formation of iron-sulfide minerals that dramatically reduce surface adsorption sites available for phosphate adsorption (Koch, 2001). Diagenetic release of phosphorus due to iron reduction can be observed in all cores where there is enough Fe-bound P to be measured (Fig. 15). Concentrations of Fe-bound phosphate are highest in surface sediments in every core analyzed. Furthermore, the concentrations of Fe-bound phosphorus almost never increase after this initial decrease, indicating that this phosphorus is lost from this reservoir and not readsorbed by other iron oxide minerals (Fig. 15). Thus, much of the phosphate 40

49 originally associated with iron is released to the pore waters and this pool becomes less important with continued sediment burial Organic phosphorus Organic matter in sediment in tropical coastal marine ecosystems is generally derived from one of three types of organic matter: marine phytoplankton, seagrasses, or terrigenous organic matter. Evidence from δ 13 C isotopic compositions and C:N ratios of organic matter indicate that organic matter in PMD1 is almost entirely composed of phytoplankton (Algeo, 2008). However, the organic C/P ratio in surface sediment (0-1 cm) in PMD1, at approximately 380, is much higher than the Redfield C:P ratio for phytoplankton, at 106 mol C: 1 mol P (Redfield, 1958). Similarly, δ 13 C values of organic matter and C:N ratios in Puerto Ferro indicate that the source of organic matter should be dominated by seagrasses, though organic C:P ratios in surface sediments of Puerto Ferro ( in the top 10 cm of sediment) are also much higher than that predicted by the Redfield ratio analogue for seagrasses (550 mol C: 1 mol P; Fourqurean, 1992). These high ratios indicate that phosphorus in organic matter in sediment is being selectively remineralized, so that the remaining organic matter is low in phosphorus relative to carbon. Remineralization of this organic matter, depleted in P, would return to the water column with proportionally less P than was initially deposited. This could cause P limitation, as other nutrients are remineralized into the water column at greater proportions than are needed for growth relative to P. Organic matter cycled through sediment would have 41

50 proportionally less and less P than it was deposited with, leading to a net loss of phosphorus to sediment Authigenic/detrital calcium bound phosphorus Authigenic calcium-bound phosphorus is a key sedimentary phosphorus reservoir because the formation and burial of authigenic P phases represents the removal of biologically available phosphorus (Ruttenberg and Berner, 1993). Ca-bound phosphorus consists of both detrital and authigenic apatite phases as well as phosphate adsorbed to carbonate particles. Surface concentrations of Ca-bound P are uniformly high in all study cores (Fig. 16). This surface Ca-bound P is likely detrital apatite or phosphate adsorbed to carbonate particles, since the formation of authigenic apatite is a diagenetic process usually occurring deeper within the water column. Since sediments from PM24, the hypersaline lagoon, have very little calcium carbonate content and intermediate (2.4 μmol/g) concentrations of Ca-bound P in surface sediment, a significant portion of this pool may be detrital apatite. Ca-bound P often increases with depth, reaching concentrations higher than those in surface sediments (Fig 16). These increases could be due to either increased deposition of detrital apatite, increased adsorption of phosphate on carbonate particles, or formation of authigenic apatite. Increased deposition of detrital apatite should correlate with increased deposition of terrigenous material. Thus, if detrital apatite is a major source of Ca-bound P, Ca-bound P should correlate with terrigenous material. Similarly, if phosphate adsorbed to carbonate particles is a major portion of Ca-bound P, there should be a strong positive correlation between Ca-bound P and calcium 42

51 carbonate concentrations. However, the Ca-bound P reservoir does not correlate well with either terrigenous or calcium carbonate sediment concentrations (Fig. 10). The size of the Ca-bound P reservoir does not appear to be the result of increased deposition of detrital apatite, nor does it appear to be the result of carbonate adsorption. While detrital apatite and Ca-bound P may be important sedimentary components of the Ca-bound P reservoir, they do not appear to be controlling the size of the reservoir. The lack of correlation between calcium carbonate and Ca-bound P has been noted in other mixed carbonate-siliclastic sediments, indicating that carbonate adsorption is often not the dominant form of Ca-bound phosphorus in these sediments (Monbet, 2007) Authigenic apatite formation Carbonate fluorapatite (CFA) is considered to be the most important diagenetic sink for phosphorus in coastal marine sediments (Ruttenberg and Berner, 1993; -3 Jensen et al., 1998). Since PO 4 concentrations in coastal waters are usually extremely low, the major source for CFA formation is derived from within the sediment column (Knudsen and Gunter, 2002). The formation of authigenic apatite is a likely mechanism by which Ca-bound P shows increases with depth in almost all cores studied. Several diagenetic studies have observed mirroring or an increase in Cabound P concentrations associated with a decrease in organic P concentrations with increasing sediment depth (Ruttenberg and Berner, 1993; Monbet, 1997). The pairing of increasing Ca-bound P with decreasing organic P is most evident in cores PMD1 43

52 and PFD1 (Fig. 26). These cores have high TP concentrations and the major phosphorous reservoir is Ca-bound P throughout the length of the core (Figs. 14, 21, 24). Quantitative analysis of sink-switching, or the transfer of one P reservoir to another, reveals the rate of apatite formation as well as its efficiency, which is the fraction of phosphorus formed in CFA relative to phosphorus liberated from adsorption or remineralization of organic matter (Ruttenberg and Berner, 1993). For analysis of authigenic apatite formation, only the intervals over which Ca-bound P increases coincident with organic P decreases will be regarded (Ruttenberg and Berner, 1993). In PMD1, this includes the top 20 cm of sediment. In PFD1, this includes the full length of the core (65 cm). Both of these intervals represent roughly the same duration of time, about 160 years for the top 20 cm in PMD1, and 200 years for the top 65 cm in PFD1. Sediment P reservoir concentrations are plotted against cumulative dry weight of sediment per cm 2 to account for compaction in sediment (Figs. 27, 28). The conversion of organic phosphorous to authigenic apatite can be calculated by integrating the Ca-bound P reservoir increase above background levels over a depth interval (Table 8, Figs. 27, 28). The best example of this sink-switching is shown in core PMD1, where the rate of authigenic apatite formation is approximately μmol P/ cm 2 /year (Table 8). Compared to the rate of organic matter remineralization, which occurs at a rate of 0.15 μmol P/ cm 2 /year, there may be a significant amount of P released by organic matter remineralization that is not consumed by authigenic apatite formation since authigenic apatite formation could 44

53 account for 49% of the decrease in the organic P reservoir (Table 8). A similar integration for the total phosphorus concentrations in PMD1 shows that, over this depth interval, total phosphorus decreases by approximately 0.07 μmol P/ cm 2 /year. This is roughly equivalent to the deficit in the organic reservoir that is not compensated for by authigenic apatite formation, and verifies that the organic matter not taken up by apatite formation is not stored in any other reservoir, but most likely diffused out of sediment. The rate of formation of authigenic apatite in PFD1 is considerably higher than in PMD1. While the rate of P loss from the organic P reservoir is approximately 0.27 μmol P/cm 2 /year, the rate of increase in the authigenic/detrital P reservoir is 0.33 μmol P/cm 2 /year. This translates to over 100% of remineralized organic phosphorus being converted to authigenic apatite. This over-compensation effect can be attributed to complexity involving other diagenetic redistribution of phosphorus or differences in rates between organic matter remineralization and authigenic apatite formation (Ruttenberg and Berner, 1993). Total phosphorus in PFD1 remains relatively constant with depth past the uppermost 10 cm, with the concentration in the uppermost interval higher than throughout the rest of the core (Fig. 28). Integration of changes in surface concentrations of total phosphorus yields an estimate of 0.04 μmol/cm 2 /yr decreases in total phosphorus for the last 32 years. This would not significantly affect overall rates of apatite formation, since this loss of total phosphorus is an order of magnitude smaller than diagenetic processes. The consistency in phosphorus concentrations throughout the rest of the core supports the notion that authigenic apatite formation is 45

54 a sink of remineralized organic matter, and that this liberated P is not being diffused out of the sediment. The difference between the organic P lost and authigenic P formed can be regarded as the P that may have been recycled back to the water column. In PMD1, this estimated benthic flux is 0.08 μmol/cm 2 /yr, while in PFD1, the increase in authigenic Ca-bound P is greater than the deficit in the organic P reservoir. Rates of authigenic apatite formation at the expense of organic phosphorus in PMD1 and PFD1 could lead to a significant difference in P availability between these two depositional environments. Calculations of authigenic apatite burial fit within the range for non-upwelling study locations for both PMD1 and PFD1. Sediments at the Long Island Sound FOAM site were found to have an authigenic apatite burial rate of 0.85 μmol/cm 3, and sediments from Mississippi Delta were found to have an authigenic apatite burial rate of 1.95 μmol/cm 3 (Ruttenberg and Berner, 1993). Other nonupwelling authigenic apatite burial rates have been measured at: μmol/cm 2 /yr in the Long Island Sound (Ruttenberg, 1992), μmol/cm 2 /yr in the California Margin (Kim, 1999), and μmol/cm 2 /yr on the continental platform of the North Atlantic (Slomp, 1996) Mechanisms for apatite formation in PMD1 and PFD1 The potential causes for apatite formation in cores PMD1 and PFD1 are numerous. High concentrations of calcium, phosphate, and fluoride, and low concentrations of magnesium have been determined to be the conditions under which apatite is most 46

55 likely to precipitate (Gunnars, 2004). To determine the thermodynamic conditions necessary for CFA precipitation in PFD1 and PMD1, ion activity products (IAP) were calculated using representative pore water concentrations from Vieques sediments and F concentrations in standard seawater (0.079 mm; Palevksy, 2007). Saturation states were determined by comparing IAPs calculated from WEB-PHREEQ ( and CFA and OCP equilibrium constants given in Elliott (1994), Perrone et al. (2002), and Gunnars (2004). IAP was calculated for top intervals of sediment pore water in PMD1 (0-1 cm) and PFD1 (0-5 cm) and deep intervals of PMD1 (15-20 cm) and PFD1 (30-35 cm), as well as for overlying seawater in Puerto Mosquito. Typical phosphate concentrations in standard seawater are μm at depths of 1 m and dissolved phosphate concentrations range from 0 at the sediment water interface to more than 6.3 µm with depth (Chester, 1999; Sundby, 1992). Phosphate concentrations of 0.1, 1.0 and 6.3 µm were used to calculate the solubility product of CFA and OCP (Table 9). Saturation indices (IAP/ K s ) of ion activity product (IAP) to solubility product (K s ) are shown in Table 9. For phosphate concentrations of 1 µm, only standard seawater and the deep interval of PFD1 are supersaturated with respect to CFA (Table 9). This value of 1 µm is unrealistically high for standard seawater. Using the more typical phosphate concentration in seawater of 0.1 µm, seawater is shown to be undersaturated with respect to CFA. At phosphate concentrations of 6.3 µm, all sediment porewaters are supersaturated with respect to CFA. The deep interval of PFD1 is the most supersaturated, followed by shallow PFD1. Deep PMD1 is more supersaturated than shallow PMD1 (Table 9). OCP is undersaturated at all concentrations of phosphate 47

56 used in calculation. However, these calculations are based on theoretical values of phosphate concentrations in seawater, and actual concentrations may be significantly higher. Using standard phosphate concentrations, however, demonstrates that CFA precipitation is likely in these sediments. Compared to other Vieques sites, IAP of CFA and OCP should be higher in PMD1 and PFD1 because of higher sediment TP and calcium concentrations in the pore water. Overall, sediment TP concentrations in PFD1 and PMD1 are higher than all other study cores. These sites also have the highest concentrations of Fe-bound P (1.3±0.4 umol/g in PMD1 and 0.9±0.4 umol/g in PFD1). Increased overall phosphorus concentrations, particularly in the organic reservoir (5.4 μmol/g in PMD1 and 2.9 μmol/g in PFD1, compared to study average of 2.03 μmol/g; Appendix C) and Fe-bound P reservoirs, indicate a larger amount of phosphorus that could be liberated and precipitated as authigenic apatite. Calcium carbonate is an important mineral in apatite formation since carbonates serve both as a surface area of crystallization and as a source of calcium (Gunnars, 2004). The carbonate saturation indices for PFD1, calculated by Palevsky (2007), show that for much of the top 20 cm of sediment, calcite and aragonite are near equilibrium or slightly undersaturated (Fig. 30). Ca/Cl ratios can reflect the net degree of carbonate dissolution because Cl is essentially a nonreactive element in normal seawater. Thus, element/cl ratios are indicative of relative increases or decreases in a particular element due to diagenetic processes. Ca/Cl ratios in PFD1 increase with increasing sediment depth indicating substantial net carbonate dissolution (Fig. 30; Palevsky, 2007). Increased Ca/Mg ratios have been shown to slow the formation of 48

57 apatite so increased availability of Ca 2+ in pore waters relative to Mg would increase the Ca/Mg ratio and lead to more rapid precipitation of apatite (Fig. 30; Gunnars, 2004). Replacement of Ca with Mg within the crystal structure of apatite leads to significant structural deformation due to the much larger atomic radius of Mg than Ca. This can halt apatite formation (Rakovan, 2002). The carbonate saturation indices for PMD1, however, indicates that pore waters are supersaturated with respect to calcite and aragonite for the top 20 cm of sediment, indicating that precipitation of these minerals is likely, which would lead to lower Ca 2+ concentrations in pore waters (Palevsky, 2007). While increased Ca/Mg ratios due to carbonate dissolution leads to higher rates of apatite precipitation in PFD1, this is not a likely mechanism for apatite formation in PMD1 (Fig. 30). The role of the Fe-bound phosphorus reservoir has also been suggested to play a role in authigenic apatite formation. Besides phosphate and calcium, formation of authigenic apatite also requires fluoride. Fluoride can be supplied directly from seawater diffusion into the sediment, or through adsorption to iron-oxide minerals. In the same way that phosphorus is released with depth due to the reduction of the ironoxide mineral, fluoride can be also released into pore waters where it can be subsequently used for authigenic apatite formation (Ruttenberg and Berner, 1993). PMD1 and PFD1 have the highest concentrations of Fe-bound phosphorus of all study locations (1.34 μmol in PMD1 and 0.88 μmol in PFD1, compared to average of 0.4±0.4 μmol for all sediment samples). In both of these cores, this reservoir decreases with depth, indicating possible reduction and liberation of adsorbed phosphate or fluoride (Fig. 15). 49

58 The implications of this organic-to-apatite transformation are profound. Given that sediment can be an important source of phosphate for marine biota (Short, 1987), wholesale attenuation of phosphate that could have diffused back into the water column by authigenic apatite formation could lead to a significantly smaller pool of bioavailable phosphorus in the water column (Ruttenberg and Berner, 1993). 6.2 Sedimentation and Phosphorus Availability Between Study Environments Mass accumulation rates Mass accumulation rates of sediment components reveal differences in modern deposition between Puerto Mosquito and Puerto Ferro. Cores from shallow (<~1.5m water depth) Puerto Mosquito and Puerto Ferro sites have similar calcium carbonate deposition (138 and 83 mg/cm 2 /yr for PM4 and PM12, 97 mg/cm 2 /yr for PF12), but dramatically different terrigenous accumulation rates, with the higher terrigenous accumulation rate in shallow Puerto Mosquito (110 and 173 mg/cm 2 /yr in PM4 and PM12) compared to Puerto Ferro (38 mg/cm 2 /yr in PF12) (Table 4). Overall, the low sedimentation rate of the deeper Puerto Mosquito site, PMD1, results in much lower accumulation rates of terrigenous material, calcium carbonate, and total phosphorus relatively to all other cores. The PMD1 accumulation rate of Cabound P (9.3 mg/cm 2 /yr), however, is higher than shallow Puerto Ferro sites (8.3 mg/cm 2 /yr) and approaches that in Puerto Mosquito shallow cores ( mg/cm 2 /yr) despite bulk sedimentation rates 3 times lower than the next slowest core, PF12. It is the only accumulation rate in PMD1 within the range of other environments. Since the mass accumulation rates of terrigenous and calcium 50

59 carbonate, the main sources of detrital apatite and carbonate-adsorbed P, are so much lower than in PMD1 than in all other environments, the anomalously high Ca-bound P accumulation rate in PMD1 supports a diagenetic origin of Ca-bound P in the form of authigenic apatite (Table 4) Mass accumulation rates and apatite formation Mass accumulation rates between shallow and deep Puerto Mosquito sites also indicate that authigenic apatite formation is more significant in deep Puerto Mosquito. As described in section 2.2.3, apatite formation is more pervasive in regions with high organic matter sedimentation rates relative to bulk sediment deposition rates. Though sedimentation rate of organic P is higher in shallow Puerto Mosquito than deep (15.8 and 22.6 mg/cm 2 /yr in PM4 and PM12 versus 5.6 mg/cm 2 /yr in PMD1; Table 4), this organic P is diluted in sediment by the extremely high terrigenous sedimentation rates in shallow Puerto Mosquito (110.2 and mg/cm 2 /yr in PM4 and PM12 versus 21.1 mg/cm 2 /yr in PMD1; Table 4). The low bulk sedimentation rate in deep compared to shallow Puerto Mosquito (0.05 mg/cm 2 /yr in PMD1 versus 0.26 and 0.27 mg/cm 2 /yr in PM4 and PM12; Table 4) leads to greater organic matter concentration in sediment in deep Puerto Mosquito: organic P concentrations in deep Puerto Mosquito (3.2±1.3 µmol/g) are much higher than in shallow Puerto Mosquito (1.9±0.6 µmol/g; Appendix B). This could explain why mirroring between the organic and Ca-bound P reservoirs is not observed in cores from shallow Puerto Mosquito: the conversion of organic P to authigenic apatite formation is inhibited by the dilution of organic P in sediment by high terrigenous 51

60 sedimentation rates. Ongoing sediment analysis, pore water flux experiments, and geochemical modeling will investigate this possibility and quantify the conditions necessary to precipitate authigenic apatite in Puerto Mosquito and Puerto Ferro Potential terrigenous sources of P While terrigenous deposition rates do not control CFA formation, terrigenous sediments may still be the ultimate source of P to Puerto Mosquito and Puerto Ferro. Fe/Al ratios have been used to infer differences in sources of terrigenous material since both elements are relatively immobile in oxic waters, thus Fe/Al ratios can identify various source materials (Sageman and Lyons, 2004). Molar Fe/Al values for mixed carbonate-siliclastic mud are similar in Puerto Mosquito and Puerto Ferro (averaging 0.26±0.6 in Puerto Mosquito and 0.26±0.3 in Puerto Ferro; Table 3), though the sedimentation rate of terrigenous sediment is over four times higher in shallow Puerto Mosquito than in Puerto Ferro (Table 4). Thus, terrigenous material deposited in Puerto Mosquito and Puerto Ferro is likely derived from similar sources though at greatly different rates. The rate of terrigenous sediment deposition may be a function of the relative sizes of the watersheds. The watershed of Puerto Mosquito covers nearly twice the surface area as that of Puerto Ferro (Fig. 3). GIS analyses of watershed erosion potentials have identified the key factors determining sediment yield to be rainfall, topography, and cultivation/agricultural practices (Pandey, 2007; Vezina, 2006). GIS analysis of the watersheds of Puerto Mosquito, Puerto Ferro, and Bahia Tapon have identified that the watershed of Puerto Mosquito has a higher incidence of developed and agricultural land than that of Puerto Ferro and Bahia 52

61 Tapon (Tainer, 2006). Though a quantitative analysis of land use and erosion potential of Vieques has not yet been done, increased agricultural land combined with a larger watershed in general could explain the relative abundance of terrigenous matter in Puerto Mosquito. Furthermore, the difference in terrigenous sedimentation between shallow and deep depositional environments in Puerto Mosquito (terrigenous sedimentation in shallow Puerto Mosquito is over 5 times more rapid than in deep Puerto Mosquito) suggests that much of this terrigenous material is being deposited rapidly in regions closest to the shore with little of this material being carried to the deeper environments (Table 4) Evidence for recent changes in sedimentation Relative to older facies, surface sediments deposited over the last 50 years have distinctly higher Fe/Al ratios (Fe/Al ratios of 0.26, versus averages from 0.12 to 0.23 in older facies), generally higher terrigenous sediment fractions (particularly Halimeda sand and molluscan gravel) and elevated phosphorus concentrations relative to deeper facies (Table 2; Fig. 14). This suggests that the modern depositional environment is characterized by more rapid terrestrial material input with a net source that is different from that of past depositional conditions. The elevated sediment phosphorus concentrations are likely related to this change in sedimentation and are associated with the persistent blooms of bioluminescent dinoflagellates. 53

62 6.3 Implications for Phosphorus Availability and Future Studies Sedimentary phosphorus dynamics are not only a function of total phosphorous concentration but also the phase of phosphorous present in the sediment (Ruttenberg and Berner, 1993; Monbet, 2007; Cha, 2005). Diagenetic processes can lead to the remobilization of adsorbed and organic phosphorus, while phosphorus stored in phosphate minerals usually results in permanent burial. Detrital apatite, while generally inaccessible for biological purposes, is not considered a phosphorus sink, because it is transferred directly from terrestrial to marine sediments without entering the aqueous phase. The conversion of reactive phosphorus (such as organic phosphorus and that adsorbed to Fe-oxide minerals and carbonate particles) to authigenic apatite is one of the most efficient ways that phosphorus can be buried, and a net loss of phosphorus is found in many locations (Cha, 2005; Faul, 2005; Kim, 1999; Ruttenberg and Berner, 1993). The rate of formation and efficiency of sink-switching are what control the extent to which apatite can form. In this study, both PFD1 and PMD1 site demonstrate authigenic apatite formation. If these cores are representative of all deep depositional environments in Puerto Mosquito and Puerto Ferro, there could be a significant loss of phosphorus in both bays. Authigenic apatite formation consuming >100% of remineralized organic P, sediment in Puerto Ferro could represent an enhanced net sink relative to the water column. In Puerto Mosquito, sediment could replenish up to 50% of buried organic phosphorus back into the water column, which would then be available for uptake by plankton. 54

63 Verification of this hypothesis would require measurements of pore water concentrations of phosphate, calcium and fluoride. Authigenic apatite formation would result in decreases of pore water concentrations of PO 4, Ca, and F according to molar ratios of CFA (Ruttenberg and Berner, 1993). Similar methods could be applied to other cores, which do not show the mirroring that is associated with conversion of organic phosphorus to authigenic apatite, to assess whether authigenic apatite is forming in other locations in Puerto Mosquito, Puerto Ferro, and Bahia Tapon. Benthic phosphorus fluxes could also be integral in describing sedimentary phosphorus dynamics. If, for example, PMD1 had a significantly higher benthic phosphorus flux than PFD1, the argument for higher phosphorus retention in PFD1 due to apatite formation would be strengthened. Benthic phosphorus fluxes could also provide a better picture of overall phosphorus availability across Puerto Mosquito and Puerto Ferro, since availability based on sedimentary phosphorus reservoirs is largely inferred. The effect of phosphorus dynamics on the population of dinoflagellates in this environment could also benefit from further investigation. Methods of tracking dinoflagellate populations using geochemical biomarkers could potentially determine if dinoflagellate populations are responsive to changes in phosphorus availability. Cyst-counting procedures have also been used to quantify dinoflagellate populations through time (Zonneveld, 1997; Pospelova, 2004). 55

64 7. Conclusions Sedimentological and geochemical analyses from Puerto Mosquito and Puerto Ferro indicate a history of rising sea level that deposited normal marine sediments atop terrestrial sediments from years ago until no more than 200 years ago in Puerto Ferro and as recently as 50 years ago in Puerto Mosquito. Presently, Puerto Mosquito has very high concentrations of dinoflagellates at10,000 cells/l, while Puerto Ferro has much lower concentrations of less than 700 cells/l. Depositional conditions over the past years are considerably different from those in the past and modern sedimentation is marked by higher concentrations of terrigenous matter, elevated Fe/Al ratios, and elevated overall phosphorus availability. Vieques sediments have high concentrations of phosphorus compared to global ranges of marine carbonate sediments but low in comparison with that of siliclastic sediments (Table 7). Sedimentary phosphorus reservoirs differ based on depositional environment and as a result of diagenetic processes. While deep depositional environments have higher total phosphorus concentrations than shallow environments in both Puerto Ferro and Puerto Mosquito (10.7±1.5 µmol/g in deep versus 3.3±1.0 in shallow Puerto Mosquito; 6.1±0.7 µmol /g in deep versus 5.3±1.6 µmol /g in shallow Puerto Ferro), diagenetic processes have a strong affect on the dominant phosphorus reservoir in deep environments, with the formation of authigenic apatite consuming >100% of remineralized organic phosphorus in Puerto Ferro and 49% in Puerto Mosquito. The mechanisms for this apatite formation are likely different between Puerto Mosquito and Puerto Ferro, with that in Puerto Mosquito strongly influenced by high organic matter concentrations due to low 56

65 terrigenous sedimentation, and that in Puerto Ferro influenced by carbonate dissolution. Differences in apatite formation rates could result in different overall phosphorus availability between Puerto Mosquito and Puerto Ferro. Puerto Mosquito has higher total phosphorus concentrations compared to Puerto Ferro in both shallow and deep environments. Combined with higher authigenic apatite formation in deep Puerto Ferro versus Puerto Mosquito, the total pool of bioavailable phosphorus in Puerto Ferro may be considerably lower than in Puerto Mosquito. While it is yet unknown whether the high dinoflagellate populations have persisted in Puerto Mosquito since before the onset of modern depositional conditions, phosphorus is a likely key contributor to their proliferation in Puerto Mosquito compared to Puerto Ferro. The formation of authigenic apatite in non-upwelling environments, though a relatively recent discovery, has been shown to be significant phosphorous sink in a variety of marine locations and should be considered in models of oceanic phosphorus cycling (Ruttenberg and Berner, 1993; Lucotte et al, 1994; Benitez-Nelson, 2000; Cha, 2005; Slomp, 2007). If authigenic apatite formation is the key difference in nutrient cycling between Puerto Mosquito and Puerto Ferro, the bioavailable phosphorus reservoir for both of these bays could be among the first tropical coastal systems shown to be significantly affected by this process. 57

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73 Table 1: Depositional Environments and associated cores Depositional environment Puerto Mosquito - Shallow Puerto Mosquito - Deep Puerto Ferro - Shallow Puerto Ferro Deep Puerto Mosquito Hypersaline lagoon Soil Auger Bahia Tapon Cores PM4, PM12, PM14 PMD1 PF7, PF12 PFD1 PM24 Soil Auger BT9 65

74 Table 2: Sediment chemistry for sedimentary facies; Standard deviations are 1σ Sedimentary Facies Average Organic C (wt%) Range of Organic C (wt.%) Average CaCO3 (wt%) Range of CaCO3 (wt %) Average terrigenous (wt%) Range of Terrigenous wt. % Average Fe (wt. %) Range of Fe (wt. %) Average Fe/Al (molar) Range of Fe/Al (molar) n Terrigeneous Mud 0.6%± % 1%±2 0-6% 98%± % 1.5%± % 0.12± Gravelly Shell Hash and Sand 2.5%± % 7 %± % 88%± % 1.9%± % 0.15± Neritina Mud 1.2%± % 53%± % 45%± % 4.5%± % 0.20± Molluscan Gravel 1.8%± % 62%± % 33%± % 1.8%± % 0.23± Halimeda Sand 2.1%± % 76%± % 19%± % 1.8%± % 0.20± Mixed Carbonate - siliciclastic mud 2.2%± % 52%± % 43%± % 3.8%± %. 0.26± Carbonate mud and sand 1.7%± % 74%± % 22%± % 1.5%± % 0.19±

75 Table 3: Sediment chemistry for surface sediments; Standard deviations are 1σ Sedimentary Facies Average Organic C (wt%) Range of Organic C (wt.%) Average CaCO3 (wt%) Range of CaCO3 (wt %) Average terrigen ous (wt%) Range of Terrigeno us wt. % Average Fe (wt. %) Range of Fe (wt. %) Average Fe/Al (molar) Range of Fe/Al (molar) n Mixed Carb- siliciclastic mud- Puerto Mosquito 2.1± % 48± % 47± ± % 0.26± Mixed Carb- siliciclastic mud- Puerto Ferro 3.0± % 67± % 26± % 0.9± % 0.26± Mixed Carb- siliciclastic mud- Bahia Tapon 2.3± % 58± % 37± % 5.5± % 0.30± Carbonate mud and sand - Puerto Ferro 1.7± % 74± % 22± % 1.5± % 0.20±

76 Table 4: Sediment Mass Accumulation Rates (MAR) from Lead-210 Site ID *Depth Interval [cm] *Sediment Age within 210 Pb Range (yrs before 2007) #LSR (cm/yr) #Bulk Sediment MAR (mg/cm 2 - yr) #Organic C MAR (mg/cm 2 -yr) #CaCO 3 MAR (mg/cm 2 -yr) #Terrigenous Sediment MAR (mg/cm 2 -yr) P MAR (ug/ cm2/yr) authigenic P MAR (ug/ cm2/yr) organic P MAR (ug/ cm2/yr) PM4 [0-20] PM12a [0-28] PM14 [0-44] no excess lead-210 below 5 cm PMD1 [0-15] PF12 [0-20] PFD1 [0-50] BT9 [0-35] no consistent excess lead-210 profile (mixing or bioturbation) *only sediment intervals containing excess lead-210 **Age representative of the deepest interval containing excess lead-210 #averaged over sediment intervals containing excess lead-210pb 68

77 TABLE 5 : Radiocarbon results Site (depth interval, cm) Sample type 14 C Fm (Fraction Modern) 14C Fm error *Conventio nal Radiocarbo n Age (yr B.P.) *Conventiona l Radiocarbon Age error (yr) δ 13 C ( VPDB) * # Calendar Age (yr B.P.) # Calendar Age Range (1σ, yr B.P.) PM12A (20-22) mollusc (CaCO 3 ) younger than 1950 A.D. **Calendar Age (yrs before 2007) PM12A (46-48) mollusc (CaCO 3 ) [ ] 1428 PM12A (64-66) plant remains [ ] 2465 PM13 (30-32) mollusc (CaCO 3 ) younger than 1950 A.D. PM13 (88-90) mollusc (CaCO 3 ) younger than 1950 A.D. PM13 ( ) mollusc (CaCO 3 ) [ ] 623 PM14 (28-30) mollusc [ ] 459 PM14 (54-56) plant remains [ ] 2000 PM14 (68-70) plant remains [ ] 3361 PM14 (72-74) plant remains [ ] 3329 PM14 (88-90) plant remains [ ] 1830 PM14 (96-98) plant remains [ ] 2292 PM14 ( ) plant remains [ ] 3843 PF12 (15-20) mollusc (CaCO 3 ) [-1-177] 145 PF12 (45-50) mollusc (CaCO 3 ) [ ] 1179 PF12 (75-80) mollusc (CaCO 3 ) [ ] 2039 *Present = 1950 A.D. # Calendar ages calculated using CALIB (Stuiver and Reimer, 1993), present = 1950 A.D. # Marine mollusc ages were calculated using a marine reservoir correction of DR=31, stdev= ±24 and the Marine04 calibration curve (see text for details) # Plant remains were calibrated using the IntCal04 curve. **Calculated to match 210 Pb ages 69

78 Table 6: Phosphorus reservoir abundances across study location Reservoir Average (umol P / g sediment) Standard Deviation (1 σ) Range (umol P/ g sediment) Fe-bound P 0.40 (7.5%) 0.43 (6.0%) (0-33%) Ca-bound P 2.14 (42.4%) 1.68 (15.7%) (0-76%) Total organic P 2.03 (50.5%) 1.02 (16.8%) (22-93%) Total P

79 Table 7: Comparative phosphorus reservoir abundances in other studies Vieques Northeastern Florida Bay Site description Carbonate marine/ siliclastic Total P (umol P/ g sed) Organic P (% of total P) Ca-bound P (% of total P) Fe-bound P (% of total P) References % 0-76% 0-33% This study Carbonate Marine % 41-94% % Koch, 2001 Bermuda Bay Carbonate Marine Jensen, 1998 Andratx Bay, Majorca Carbonate Marine % 30.9% 16.0% Lopez, 2004 Long Island Sound Mississippi Delta Non upwelling continental margin Non upwelling continental margin % 70-84% 4-8% % 33-53% 28-38% Ruttenberg and Berner, 1993 Ruttenberg and Berner, 1993 SW East Sea, Japan Contintental margin >40% 9-44% (+/- 10 wt% for detrital apatite) 7-63% Cha, 2005 Es Grau, Minorca Lagoonal % 19.8% 19.7% Lopez,

80 Table 8: Authigenic apatite rate calculations for PMD1 and PFD1 Core PMD1 (Cabound P) PMD1 (organic P) PFD1 (Cabound P) PFD1 (organic P) Equation y = x x y = x x y = x x y = x x Interval (cumulat ive g/cm 2 ) Depth interval (cm) R 2 Total chang e (umol P) Rate of change (umol P/cm 2 / year) Sinkswitching efficiency* % % *Sink-switching efficiency = (Total change in Ca-bound P) (Total change in organic P) 72

81 Table 9: Saturation ratios for CFA and OCP in PMD1 and PFD1 P (µm) IAP/K* (CFA) IAP/K** OCP Log(IAP/K) (CFA) Log(IAP/K) (OCP) Puerto Mosquito seawater E E E E PMD1 surface (0-1 cm) E E E E PFD1 shallow (0-5 cm) E E E E PMD1 deep (15-20 cm) E E E E PFD1 deep (30-35 cm) E E E E Positive Log(IAP/K) values indicate supersaturation, negative values indicate undersaturatio * Solubility product (K) for CFA = (Perrone et al., 2002) ** Solubility product (K) for OCP = (Elliott, 1994) 73

82 Figure 1: Geologic map of Vieques (from Renken, 2002) 74

83 Bahia Tapon Puerto Ferro Puerto Mosquito Figure 2: Satellite image of Vieques (from Google Earth) 75

84 Figure 3: Watersheds of Puerto Mosquito, Puerto Ferro, and Bahia Tapon (from Tainer, 2007) 76

85 Figure 4: Map of core locations and benthic environments PM12!!! PM14 SoilAuger! PM4! PMD1! PM24! PF7! PFD1! PF12! BT Kilometers! Core locations Benthic Environment Artificial Hardbottom Land Macroalgae/Patchy Mangrove Mud Reef Sand Seagrass/Continuous Seagrass/Patchy Unknown 77

86 Figure 5: Phosphorus extraction methods flow chart (SRP= Soluble Reactive Phosphorus, TP = Total Phosphorus) 78

87 Figure 6: Phosphorus concentrations between depositional environments (error bars represent 1σ) (PM Hypersaline Lagoon noted as PM Salt Flat) 79

88 Figure 7: Phosphorus concentrations between sedimentary facies (error bars represent 1σ) 80

89 Figure 8: Organic molar C:P ratios for Puerto Mosquito and Puerto Ferro 81

90 Figure 9: Correlations between Fe-bound P concentrations and sediment components with 95% confidence belt for regression line 82

91 Figure 10: Correlations between Ca-bound P concentrations and sediment components with 95% confidence belt for regression line 83

92 Figure 11: Correlations between Organic P concentrations and sediment components with 95% confidence belt for regression line 84

93 Figure 12. Relative phosphorus reservoir abundances between depositional environments (error bars represent 1σ) (PM Hypersaline lagoon notated as PM Salt Flat) 85

94 Figure 13. Relative phosphorus reservoir abundances between sedimentary facies (error bars represent 1σ) 86

95 PMD1 Figure 14: Total P concentrations vs. depth 87

96 Figure 15: Fe-bound P concentrations vs. depth 88

97 Figure 16: Ca-bound P concentrations vs. depth 89

98 Figure 17: Organic P concentrations vs. depth 90

99 Figure 18: Puerto Mosquito Shallow (PM12): Phosphorus and sediment chemistry depth profile 91

100 Figure 19: Puerto Mosquito Shallow (PM4): Phosphorus and sediment chemistry depth profile 92

101 Figure 20: Puerto Mosquito Shallow (PM14): Phosphorus and sediment chemistry depth profile 93

102 Figure 21: Puerto Mosquito Deep (PMD1): Phosphorus and sediment chemistry depth profile 94

103 Figure 22: Puerto Ferro Shallow (PF12): Phosphorus and sediment chemistry depth profile 95

104 Figure 23: Puerto Ferro Shallow (PF7): Phosphorus and sediment chemistry depth profile 96

105 Figure 24: Puerto Ferro Deep (PFD1): Phosphorus and sediment chemistry depth profile 97

106 Figure 25: Hypersaline lagoon (PM24): Phosphorus and sediment chemistry depth profile 98

107 Figure 26: Mirroring of Ca-bound and organic P reservoirs in cores PMD1 and PFD1 99

108 Figure 27: Calculation of authigenic apatite formation for PMD1 100

109 Figure 28: Calculation of authigenic apatite formation for PFD1 101

110 Figure 29: Calculation of total phosphorus decrease vs. cumulative g/cm2 for PMD1 and PFD1 102