ENVIRONMENTAL FACTORS AFFECTING PLANKTONIC FORAMINIFERA ABUNDANCE AND DISTRIBUTION IN THE NORTHEAST GULF OF MEXICO. A Thesis SHARATH REDDY RAVULA

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1 ENVIRONMENTAL FACTORS AFFECTING PLANKTONIC FORAMINIFERA ABUNDANCE AND DISTRIBUTION IN THE NORTHEAST GULF OF MEXICO A Thesis by SHARATH REDDY RAVULA Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 4 Major Subject: Oceanography

2 ENVIRONMENTAL FACTORS AFFECTING PLANKTONIC FORAMINIFERA ABUNDANCE AND DISTRIBUTION IN THE NORTHEAST GULF OF MEXICO A Thesis by SHARATH REDDY RAVULA Submitted to Texas A&M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Approved as to style and content by: Niall Slowey (Chair of Committee) John Wormuth (Member) Mitch Malone (Member) Wilford Gardner (Head of Department) May 4 Major Subject: Oceanography

3 iii ABSTRACT Environmental Factors Affecting Planktonic Foraminifera Abundance and Distribution in the Northeast Gulf of Mexico. (May 4) Sharath Reddy Ravula, B.S.M.E., Columbia University Chair of Advisory Committee: Dr. Niall Slowey The shell composition of planktonic foraminifera used in many paleoreconstructions assumes they are accurately representing conditions at the surface/mixed layer. However, planktonic foraminifera are known to inhabit a depth range that extends below the mixed layer. In the present study, foraminifera were collected at discrete depth intervals using a Multiple Opening and Closing Net Environmental Sensing System (MOCNESS) in either cyclonic or anticyclonic eddies that had contrasting environmental conditions. The foraminifera abundances and distributions were compared to the water depth, temperature, density, and chlorophyll profiles. Nine species were found consistently among all the tows and composed at least 96% of the species found, though a shift in the species abundances and depths occurred between eddies. Species occurred where physical factors were compatible with conditions and feeding opportunities they were adapted to. Three species pink and white Globigerinoides ruber and Globigerinoides sacculifer thrived best when a steep density gradient resulted in a shallower mixed-layer that restricted them under more intense light and allowed them to better exploit their algae symbionts. Globigerina bulloides was found outside its sub-polar habitat because the waters of the cyclones were cool enough (less than 26 C) at the same depths that sufficient chlorophyll was available. Two

4 iv species Orbulina universa, and Globorotalia menardii were consistently absent in the mixed layer, but tracked deeper chlorophyll concentrations. Three other species were found inconsistently among the tows: Hastigerina pelagica, Globigerinella siphonifera, and Globigerinella calida. H. pelagica probably follows chlorophyll concentrations. G. siphonifera, and G. calida have a preference for deeper waters within the photic zone. The drastic doubling to tripling of the foraminifera abundances in cyclones biases downcore reconstructions of sea surface temperature towards cooler conditions. Also, the shift in species composition between the two eddies indicates that in environments where eddies, upwellings, or rings exist may bias the downcore composition of each species towards cooler conditions. G. sacculifer was found to live primarily in the mixed layer and at least 75% of its downcore individuals are expected to represent conditions there. Researchers should consider the described species distributions to better understand the water column conditions they are reconstructing.

5 v DEDICATION I am blessed in that I can do what I enjoy the most with the support of my loving family and friends without whom this work would not have been possible. Even those of you who have left me here have continued to send me your love and support. After you read this dedication, call and remind me that I owe you dinner, a cool beverage, and a few stories.

6 vi ACKNOWLEDGMENTS I would like to thank my friends, family, and everyone I worked with while I conducted my research. I would like to especially thank the people below for their specific contributions to my thesis. Dr. Niall Slowey, Dr. John Wormuth, Dr. Mitch Malone provided me intellectual guidance, office, laboratory space, equipment, comments, suggestions, and patience. Dr. Doug Biggs provided me with the complete GulfCet II hydrographic data and the appropriate calibration data. Dr. George Jackson helped me with the gradient plots (Figures 13-21). Sandy Drews provided me with a foil for my pranks and wit, and helped me navigate through university paperwork. Commander Ed Shaar (retired) supported me when my previous advisor left and provided me with three semesters of support. I would also like to thank the other graduate students in the department. Dan Bean helped me with the myriad hardware, software, and other gripes. Debora Berti helped me get started in Illustrator and in Java programming. Darin Case got me through the Departmental inventory, safely. Amy and John Bratcher let me live with them and let me occasionally win. Brian Brookshire helped me with statistics, and the SPSS plots (Figure 9&1). Rob Cady helped me survive my microscope work and taught me how to get myself in shape. Susie Escoria helped me survive my first advisor. Simone Francis checked that my mathematical explanations made sense. I need to thank Dr. Patrick Ressler for the template of the GulfCet map with the hydrodynamic data (Figure 1) and of course, for all the social engineering ideas: root-beer floats, potlucks, the beard. Rebecca Ross (a.k.a Rebecca Scott) humored me. Jennifer Smith for making sure my shirt tag wasn t sticking out and showing me that Niall does graduate students. Cristina Urizar and Eli Williams for also helping me survive Aggieland. Numerous other friends for making graduate a pleasant experience if you are reading this you need to call. I would also like to thank the following professors in the Departments of Geography, Geology and Oceanography for their assistantships: Dr. Wormuth, Dr. Matheson, Dr. Popp, Dr. Cairns, Dr. Lafon, Dr. Smith, Commander Ed Shaar, Finally, I must thank my family for supporting me through nine years of graduate school: Srinivas Reddy, Seshe, Vijay, and Ramana Ravula.

7 vii TABLE OF CONTENTS Page ABSTRACT... iii DEDICATION... v ACKNOWLEDGMENTS... vi TABLE OF CONTENTS... vii LIST OF TABLES... viii LIST OF FIGURES... ix INTRODUCTION... 1 OCEANOGRAPHIC SETTING AND FIELD SAMPLING... 4 RESULTS AND DISCUSSION SUMMARY AND CONCLUSIONS REFERENCES APPENDIX A VITA... 74

8 viii LIST OF TABLES TABLE Page 1. Sampling locations, times, total biomass, and circulation regime Equations for calculating species concentrations, abundances, and percentages Planktonic foraminifera species found in MOCNESS tows Common species tow integrated abundances (#/m 2, and %) Rare species tow integrated abundances (#/m 2, and %) Tow factor values Tow foraminifera percentage at each depth interval Species median depth (m) per tow Species factor values Summary of high species concentrations occurring at specific properties

9 ix LIST OF FIGURES FIGURE Page 1. Dynamic height anomaly map with station locations (a) Temperature profiles of MOCNESS tows and the respective CTD casts used to reconstruct MOCNESS salinity profiles. (b) The CTD temperature salinity relationships (a) Isothermals ( C) along transect from CTD1 to MOCNESS 217. (b) Isohalines (psu) (a) Isopycnals (kg/m 3 ). (b) Chlorophyll a concentrations (mg/m 3 ) between tow locations CTD chlorophyll a profiles Percentage of incident radiation at depth (%) Tow factor analysis results Tow species compositions (%) Anticyclonic tow abundances (%) Cyclonic tow abundances (%) Tow factor analysis results Scatter plot of each species versus chlorophyll concentrations O. universa property profiles G. menardii property profiles H. pelagica property profiles G. ruber (pink) property profiles G. ruber (white) property profiles G. sacculifer property profiles G. bulloides property profiles G. siphonifera property profiles G. calida property profiles Comparison of sample collection and lunar cycle dates Temperatures corresponding to percentage of G. sacculifer abundance

10 1 I. INTRODUCTION Planktonic foraminifera shells are used to deduce paleoclimates, but these reconstructions depend on an understanding of how the environment influences foraminiferal abundance, distribution, and ultimately their shells (e.g. Emiliani, 1966; CLIMAP Project Members, 1976; Andreasen and Ravelo, 1997; Lea et al., ). New laboratory methods that allow for smaller samples, and that generate finer analytic resolutions hold promise for new discoveries (e.g., electron microprobe Nürnberg et al., 1996a&b), but may outpace our current understanding of foraminfera biology. Early biogeographic studies revealed that the distribution of each planktonic foraminifera species is limited to the climate they have adapted to, so a species can indicate a climate types: sinistral Globigerina pachyderma for polar temperatures, or Globigerinoides sacculifer for tropical temperatures (Bé and Tolderlund, 1971). Typically, however, a whole assemblage is used to determine one of five general climate types: polar, subpolar, transition (temperate), subtropical, and tropical (Hemleben et al., 1989; Bé and Tolderlund, 1971). The occurrence of a unique species can signify climatic, seasonal or hydrographic changes such as upwelling or stratification (e.g. Peterson et al., 1991). Because they subsist on either plankton and/or their algae symbionts, most planktonic foraminifera are found in the euphotic zone, and reflect the sea surface environment (Bé, 1982). Many migrate throughout the water column through osmotic regulation of their protoplasm controlling their density and thus depth (Savin and Douglas, 1973). Living species can migrate up to 5 m per day compared to dead This thesis follows the style of Geochimica et Cosmochimica Acta.

11 2 specimens that descend through the mixed layer in less than a day (Hemleben et al., 1989; Takahashi and Bé, 1984). These diel migrations imply that foraminifera have adapted to adjust their depth distributions to seek a preferred water property such as temperature, density, the deep chlorophyll maximum (prey location), or another depth dependent property (Savin and Douglas 1973; Bé, 1977; Fairbanks and Wiebe, 198). Ultimately, depth zonation facilitates algae-symbionts, prey availability, or predator avoidance. Generally, the depth habitats are characterized as shallow, intermediate, or deep (-5, 5-1, and >1 m respectively; Bé, 1977), although most planktonic foraminifera thought to precipitate their shells in a smaller, species-specific depth range above the thermocline (Emiliani, 1954; Fairbanks et al., 1982). At these depths, foraminifera precipitate a calcite shell whose make-up is a function of the seawater composition and temperature (Emiliani, 1955). Some species, however, can precipitate significant amounts of calcite after descending out of the mixed-layer and so their shell geochemistry poorly represents water properties at the sea surface (Rosenthal et al., ). Previous investigators have used these distinctions to calculate seasonal sea surface temperatures (Deuser, 1978; Williams et al., 1979; Deuser et al., 1981). Classically, δ 18 O data is used to estimate sea surface temperature, but more recently, δ 18 O data is interpreted to estimate past sea surface densities and salinities (Epstein et al 1951; Emiliani, 1955; Shackelton and Opdyke, 1973; Billups and Schrag ; Hillaire- Marcel et al., 1). Researchers have also tried to correlate the δ 13 C of tests to surface water structure and nutrient concentration (Williams et al., 1977; Kohfeld et al., ; Mortyn et al., 2). Other researchers have correlated test major or minor element composition such as Mg, Sr, or Nd to temperature, salinity, or nutrient concentrations (Boyle, 1981; Cronblad and Malmgren, 1981; Nürnberg et al., 1996a&b; Lea et al., 1999; Vance and Burton, 1999). Depending on the species, these correlations can characterize a small depth interval across the thermocline, or may span hundreds of meters (Savin and Douglas, 1973; Fairbanks et al 198). Because this data extracted

12 3 from a foraminifera shell reflects its habitat, knowledge of what controls this habitat is important (e.g. Spero, 1998). Ideally, an investigator would want to take a water mass, change its properties, and see how the foraminiferal distribution and abundance are affected. In the Gulf of Mexico, circulation associated with cyclonic/anticyclonic eddies respectively raises or lowers the thermocline, changing the hydrographic properties such as temperature, nutrient concentrations, chlorophyll concentrations, etc.. By examining the surface waters in these eddies, a researcher could determine what the changes in the hydrography had on the foraminiferal abundances and distribution (e.g., Schmuker, ). To this end, I studied foraminifera collected from the upper m at discrete depth intervals to examine their depth and species distribution through the two different environmental regimes (anticyclonic and cyclonic) to find what environmental or genetic factors control their distribution. This characterization of foraminifera distributions through the water column is relevant in ecologic studies to understand how zooplankton is distributed through the water column (Ortiz et al., 1995; Watkins et al 1996). This study also will benefit paleo-temperature reconstructions because it will answer how well a particular species characterizes sea surface temperature and climatic regimes (e.g., Fairbanks and Wiebe, 198; Ottens, 1991; Chen and Prell, 1998).

13 4 II. OCEANOGRAPHIC SETTING AND FIELD SAMPLING Foraminifera samples for this study were collected in the northeastern Gulf of Mexico where the circulation pattern is strongly influenced by the Loop Current. A sharp bend in this current intermittently closes upon itself forming anticyclonic eddies (Leipper, 197; Wiseman et al., 1999). Due to their clockwise rotation and resulting convergence of waters towards their centers, the isopycnals (and so isothermals) within these eddies are depressed (Leipper, 197). At the perimeter of the anticyclonic eddies and loop current, cyclonic eddies can also form but with elevated isopycnals due to divergence of waters from their centers (Hamilton, 1992). These cyclonic eddies tend to be oases of production because divergence draws deeper, nutrient-enriched waters up to the euphotic zone; whereas anicyclonic eddies are depleted in nutrients and less productive (Biggs, 1992). I examined planktonic foraminifera from two stations in each eddy type that were collected during a GulfCet II cruise, a Cetean census study (e.g. Wormuth et al., a&b; Table 1 and Figure 1). Previous authors have found four stations sufficient to describe foraminifera distributions (Fairbanks et al., 1982; Ortiz et al., 1995). At each station, a Multiple Opening/Closing Net and Environmental Sensing System (MOCNESS) was used to collect the samples and hydrographic data from discrete depth intervals (Wiebe et al., 1976). The MOCNESS was towed at 1-2 knots using metersquared, 333 µm mesh nets. Five nets were used to sample m intervals from the surface to 1 m and then four nets in 25 m intervals to m. The tows were collected in August at night when zooplankton are generally more abundant in surface waters. The collected plankton was rinsed out of the nets and preserved in 1% formaldehyde, 8.2 ph borate buffered solution. Depth (pressure), temperature, net angle, and the flow rate of water through the open nets were continuously recorded.

14 5 Table 1. Sampling locations, times, total biomass, and circulation regime (after Wormuth et al, a). Tow Initial Position Final Position Collection Time Integrated Biomass (cc m -2 ) Circulation Regime MOC 'N 'N 21:8-22:5 5.6 Anticyclonic 'W 'W August 6, 1997 MOC 'N 'N 23:45 : Anticyclonic 'W 'W August 7, 1997 CTD 'N 13:22-14:22 Anticyclonic 'W August 7, 1997 MOC 'N 'N 23:6 - : Cyclonic Margin 'W 'W August 1, 1997 MOC 'N 'N 1:58-3: Cyclonic Margin 'W 'W August 11, 1997 CTD 'N :4-:54 Cyclonic Margin 'W August 15, 1997

15 m m 1 m CTD2 CTD7 CTD3 M217 M218 XBT7 Latitude 26 m 3 m M8 M9 CTD Longitude Fig. 1. Dynamic height anomaly map with station locations. Negative height (cyclone) is designated by blue dash lines; positive height (confluence and anticyclone) by red solid lines. Ciculation direction shown by arrows. (Modified figure courtesy of Joelle Ortega-Ortiz and P. Ressler).

16 7 There was no functioning conductivity sensor on the MOCNESS, thus salinity values are derived from nearby CTD casts (e.g. Zimmerman and Biggs, 1999). Comparison of the temperature profiles obtained during the MOCNESS tows and neighboring CTD casts demonstrates that the water masses are indeed the same between these stations (Figure2). The temperature of a MOCNESS or XBT point corresponding to the appropriate temperature interval on the CTD T-S curve was used to interpolate the salinity. Salinities calculated outside the appropriate T-S interval, using the T-S relationship of intervals 5 m above or below yielded salinities within ±.15 psu of the values used. Figure 3a shows the isothermals between the location of the first CTD cast to the last MOCNESS tow. After the salinity was interpolated for the casts between the CTDs, Matlab was used to estimate the isohaline depths. The Matlab function interp1 was used to find the depths nearest to the desired contour interval (Figure 3b). The error in calculated depth is estimated to be a meter or less. Isopleths of density and chlorophyll concentrations were determined in a similar fashion (Figure 4). Density was calculated using the UNESCO formula. Chlorophyll data was generated by an in situ fluorometer calibrated to CTD bottle data (Figure 5). The chlorophyll contours through cyclonic MOCNESS 217 and 218 were conservatively extrapolated from the values found at their neighboring CTD cast (#7) that was in close proximity and in the same environment as the tow locations, so chlorophyll profiles were likely similar (Table 1). To estimate the light profile, the exponential decay equation was used with typical values for August in the Gulf (Figure 6). In the lab, portions of the sample were rinsed and transferred into a sorting tray filled with distilled water or alcohol. All foraminfera appeared to be in pristine condition and collected alive. Given the fast sinking times of dead species and the distinct appearance of live species, this assumption is justified (Takahashi and Bé, 1984; Watkins et al., 1996; Boltovskoy et al., ). When a subsample of foraminifera was tested by immersion in a rose bengal solution for the existence of test cytoplasm, all stained red, indicating protoplasm-filled specimens were collected. Every discernable foraminifera was removed from the plankton sample with a small brush and sorted by

17 8 CTD1 Depth (m) MOC8 MOC9 CTD7 MOC217 MOC Salinity (psu) CTD1 CTD2 CTD3 CTD Temperature ( C) Fig. 2. (a) Temperature profiles of MOCNESS tows and the respective CTD casts used to reconstruct the MOCNESS salinity profiles. (b) The CTD temperature-salinity relationships.

18 9 South 5 CTD1 M8 M9 CTD2 CTD3 CTD M218 M217 North Depth (m) CTD data XBT data MOCNESS data Depth (m) Distance from CTD1 (km) Fig. 3. (a) Isothermals ( C) along transect from CTD1 to MOCNESS 217. (b) Isohalines (psu). Dashed-dot lines represent the extent of MOCNESS data. Polygons indicate station location and source data type.

19 1 South 5 CTD1 M8 M9 CTD2 CTD3 CTD M218 M217 North Depth (m) CTD data XBT data MOCNESS data Depth (m) Distance from CTD1 (km) Fig. 4. (a) Isopycnals (kg/m 3 ). (b) Chlorophyll a concentrations (mg/m 3 ) between tow locations. Polygons indicate station location and source data type.

20 11 Anticyclonic CTD Fluorometer Estimated Net Average Upcast Bottle Data µg/l or mg/m Depth (m) Cyclonic CTD Fluorometer Estimated Net Average Upcast Bottle Data µg/l or mg/m Depth (m) Fig. 5. CTD chlorophyll a profiles. Values are estimated to correspond to nearby MOICESS tows.

21 Percentage of Incident radiation (%) Fig. 6. Percentage of incident radiation at depth (%). Data assumes exponential decay with typical oceanic attenuation coefficient of.4 m -1. Depth (m)

22 13 species onto a dry paper slide. All foraminifera were later examined with an eyepiecemounted micrometer and individuals less than 15 µm were not considered. Species identification follows the nomenclature of Parker (1962). All plankton samples were completely examined and sorted except for the largest, the first net of MOC A one-quarter split of this sample was obtained using a Folsom plankton splitter to expedite sample analysis. Wormuth et al (a) determined the bulk displacement volume of zooplankton (cc m -2 ) in all MOCNESS tows (Table 1). Each net s foraminifera concentration (individuals m -3 ) was determined by dividing the number of a particular species found in that net by the amount of seawater filtered by that net (Table 2, Equation 1). A tow s species abundance (individuals m -2 ) was calculated by multiplying each net s species concentration by the corresponding depth interval (Table 2, Equation 2a) and then summing all the net values for the tow (Table 2, Equation 2b). This depth integrated value represents the number of foraminifera found through the entire sampled, depth interval ( to m). Percentages were calculated using the abundance values. This method normalizes each net according to the volume filtered and the depth interval towed and allows for comparison among nets (Table 2, Equation 3&4).

23 14 Table. 2. Equations for calculating species concentrations, abundances, and percentages Species concentration = Number of species net Seawater volume filtered net (Equation 1) Species abundance = Species net concentration Depth Interval (Equation 2a) net net Species abundance = tow Species (Equation 2b) nets abundance net Net foraminifera population % = Species abundancenet (Equation 3) Species abundance tow Tow species population % = Species abundancetow (Equation 4) Species abundance species tow Net foraminifera property gradient = Foraminife ra concentrationnet (Equation 5) Property range net

24 15 III. RESULTS AND DISCUSSION The hydrologic character of each circulation type is distinct from the other in the upper m of the MOCNESS tows with the anticyclones showing a smaller range in temperature, salinity, density, chlorophyll and nutrient concentrations. For instance, the surface temperatures for both regimes start at 3 C, but the anticyclones extend to 23 C, whereas the cyclones continue through to 14 C (Figure 2; Figure 3a). The warmer anticyclones also have a deeper mixed layer: about 35 m compared to 15 m, respectively. The salinity ranges and profiles between the two eddy types are also different. The anticyclonic salinities start at the surface values of psu and increase to highs of 36.9 psu at the bottom of the tows. The cyclonic salinities do not steadily increase to the tow bottom, but start at a surface value of 33.5 and end at 35.8 psu with a shallower, smaller maximum at 11 m of psu (Figure 3b). Not surprisingly like temperature and salinity, the resulting density anomalies in the anticyclones extend through a smaller range 22. to 25.3 in comparison to.1 to 26.8 kg m -3 in the cyclones. The greater range of temperature and salinity in the cyclones and their shallower salinity peak results in a steep isohaline gradient in the upper 5 m (Figure 4a). With chlorophyll concentrations, both the anticyclonic and cyclonic concentrations peak at. mg/m 3, but the peak concentrations shoal from 11 m in the anticyclones to 79 m in the cyclones (Figure 4b&5). Corresponding nutrient data were not collected, but historically in the Gulf of Mexico nitrate concentrations become measurable at temperatures colder than 22.5 C (Biggs, 1992). The anticyclone MOCNESS tows should have no measurable nitrate beacuse this temperature occurs below the sampled interval at about 21 m. The cyclones, however, could have measurable nitrate starting at about 65 m (see Figure 3a). All the above differences among the MOCNESS tows result in the anticyclonic tows pairing together with nearly

25 16 identical physical properties. Likewise, the cyclonic tows pair together, however, these properties are quite distinct between the two eddy types. Still with this marked difference between the two circulation patterns, at least 96% of the tow abundances (individuals m -2 ) are composed of the same nine species defined in this study as common species (Table 3&4). Another six species found intermittently among the tows at less than 1% of the abundance are defined as rare species (Table 3&5). Although the surface net is missing for MOC1-8 and the last net for MOC1-218, the trends found between the circulation regimes are unaffected by these missing nets. The lowest abundances are found in the counterpart anticyclonic net of MOC1-9 and the last sampled net of MOC1-218, so estimates of the missing portions from a comparison to their counterpart nets results in at most 4% or 7% lost. 1 Among all tows, the common species abundances (individuals m -2 ) range considerably (Table 4). G. bulloides is either the least or most abundant ranging from. to 34.9 individuals m -2. Four species have similar abundances throughout, but have higher absolute concentrations in the anticyclones and relatively more of the anticyclones: O. universa, G. menardii, G. siphonifera, and G. calida (Table 4). In the cyclones, three species are at least four times more abundant and result in a tripling of the total abundance: pink G. ruber, G. sacculifer, and G. bulloides (Table 4). These three species compose 65-8% of the cyclonic abundance. The same species contribute only 5-15% of the abundance in the anticyclonic tows. Of the remaining 15-25% of the 1 If we assume the missing MOC1-8 net has the same composition of individuals as its counterpart, then.7% or.16 #m -2 were not sampled. At most, the missing portion equals the previous portion plus the greatest difference found among any of the nets (.7%+3.7%) or 1.3 #m -2. Likewise for the missing net of MOCNESS 218, assuming the same portion of individuals as its counterpart, then 7.1% or 7.93 #m -2 were lost. This value is probably the upper limit of the missed individuals since the previously sampled net in this tow is at a minimum. For the missing anticyclone net, the missing portion is at worst about 4.4% and for the cyclonic net less than 7.1%. 1

26 17 Table 3. Planktonic foraminifera species found in MOCNESS tows. Common Species Orbulina universa Globorotalia menardii Globigerinoides ruber (pink) Globigerinoides ruber (white) Globigerinoides sacculifer Hastigerina pelagica Globigerina bulloides Globigerinella siphonifera Globigerinella calida Rare Species Globigerinoides tenellus Globorotalia crassiformis Globorotalia truncatulinoides Globorotalia ungulata Globorotalia tumida Globigerinoides conglobatus Pulleniatina obliquiloculata.

27 18 Table 4. Common species tow integrated abundances (#/m 2, and %). Species MOC1-8 % MOC9 % MOC1-217 % MOC1-218 % O. universa G. menardii G. ruber (pink) G. ruber (white) G. sacculifer H. pelagica G. bulloides G. siphonifera G. calida Total (#/m 2 ) Total all found (common & rare) Total all corrected N/A N/A Table 5. Rare species tow integrated abundances (#/m 2, and %). Species MOC1-8 % MOC9 % MOC1-217 % MOC1-218 % G. tenellus G. conglobatus G. crassiformis G. truncatulinoides G. obliquiloculata G. ungulata G. tumida.3.1 Unknown Total (#/m 2 )

28 19 cyclonic tows are four species that comprise 9% of the anticyclonic tows: O. universa, G. siphonifera, G. calida and G. menardii (Table 4). The distinction between anticyclonic and cyclonic regimes with respect to species abundances is statistically confirmed through principal component analysis (Figure 7). Using the species abundances of each tow, Statview yields two factors, 1 and 2 (Table 6). Factor 2 corresponds with the anticyclones (46% of variance) and Factor 1 with the cyclones (49% of the variance). Consequently, a change in the species composition is evident between the two environmental regimes (Figure 8). Plots of each species percentage versus depth show this shift of dominant species and also a shift in the most abundant depth (Figures 9 & 1; Table 7). The peak abundances for the anticyclonic tows occur comparatively deeper between 1-15 m with over a quarter of the tow s population found in this depth interval (Figure 9). Cyclonic abundances occur shallower between -4 m with over a third of the tow s population (Figure 1). The change in the dominant foraminiferal species and in the depth of peak abundances between the two environmental regimes indicates that some depth dependent properties control their distribution in either eddy type. Also qualitatively, foraminifera without a preference for any depth dependent variable or without any depth control should appear to shoal to the surface in the upwelled cyclones. Three species do not consistently shoal to the surface as shown by their cyclonic median depths indicating that some foraminifera can control their depth and may have a preference as to where they situate in the water column (Table 8) 2. Where foraminifera concentrate generally indicates the location of a water property that the species have adapted to exploit (e.g. Ortiz et al., 1995). If these peaks coincide with a depth, temperature, density, and/or chlorophyll value, a relationship with this variable is implied. 2 The species abundances were found across depth intervals, so the reported median depths imply a greater accuracy than the collection data, but represent an estimate of where the populations reside in the water column.

29 Factor Anticyclones Cyclones Factor 1 Fig. 7. Tow factor analysis results. Table 6. Tow factor values. Variance Tow Factor 1 Factor 2 MOCNESS MOCNESS MOCNESS MOCNESS

30 a G. calida MOC1-8 G. menardii G. truncatulinoides Unknown O. Universa c MOC1-217 G. menardii G. calida Unknown G. siphonifera O. Universa G. ruber, pink G. siphonifera G. bulloides H. pelagica G. ruber, pink G. ruber, white G. sacculifer G. bulloides H. pelagica G. ruber, white G. sacculifer b MOC1-9 O. Universa d MOC1-218 G. menardii G. calida G. tenellus G. siphonifera O. Universa G. menardii G. ruber, pink G. sacculifer G. bulloides G. ruber, pink H. pelagica G. calida G. siphonifera H. pelagica G. sacculifer G. ruber, white Fig. 8. Tow species compositions (%). Left a & b: anticyclones. Right c & d: cyclones. 21

31 22 Depth (m) Depth (m) No Data Species G. bulloides G. calida G. menardii G. ruber, pink G. ruber, white a G. sacculifer G. siphonifera H. pelagica O. universa b Species % of Total Abundance Fig. 9. Anticyclonic tow abundances (%). (a) Species Composition of MOC1-8. (b) Species Composition of MOC1-9. Data points are at each net center and are the species abundances (#m -2 ) divided by tow total (#m -2 ). Points at the tow boundaries are extapolated to the nearest net center's values.

32 23 a Depth (m) 5 1 Species G. bulloides G. calida G. menardii G. ruber, pink G. ruber, white G. sacculifer G. siphonifera H. pelagica O. universa 15 b 5 Depth (m) 1 15 No Data Species % of Total Abundance Fig. 1. Cyclonic tow abundances (%). (a) Species Composition of MOC (b) Species Composition of MOC Data points are at each net center and are the species abundances (#m -2 ) divided by tow total (#m -2 ). Points at the tow boundaries are extapolated to the nearest net center's values.

33 24 Table 7. Tow foraminifera percentage at each depth interval. (Bold numbers represent peak concentrations.) Anticyclonic Cyclonic Depth range (m) MOC8 MOC9 MOC217 MOC218 - N/A N/A Table 8. Species median depth (m) per tow. *Denotes bimodal species distribution. Species MOC1-8 MOC9 MOC1-217 MOC1-218 O. universa G. menardii G. ruber (pink) 84* G. ruber (white) 77* N/A G. sacculifer 65* H. pelagica G. bulloides 142* N/A G. siphonifera G. calida

34 25 Statistical analysis of the foraminifera species and their tow abundances yields two factors (discussed in further detail below). Factor 1 accounts for 62%, factor 2 28% of the variance among species abundance (Table 9). Six species have a factor 1 value greater than.9: pink and white G. ruber, G. sacculifer, G. bulloides, G. conglobatus, and G. crassiformis. Three other species have a factor 2 value greater than.9: H. pelagica, G. tenellus, and G. truncatulinoides (Table 9). Five species have a factor 1 value that was around -.75: O. universa, G. siphonifera, G. menardii, P. obliquiloculata, G. ungulata, and G. tumida. Two species G. menardii and O. universa share nearly identical factor 1 values, but their factor 2 values are of opposing signs, isolating G. menardii in its own region. Likewise, G. siphonifera and G. calida share similar Factor 2 values, but their factor 1 values are also inverted (Figure 11). To see what these factors correspond to, a comparison was made among several water properties and the corresponding species abundances. Because chlorophyll maximum shoals like the species concentrations in the cyclones, it seems a likely candidate to correspond to factor 1 or 2 (Figure 5). For the anticyclonic tows, the maximum percentage of foraminifera coincides with the chlorophyll peak at 11 m (Table 7; Figure 9). This correlation is primarily due to the largest component of the anticyclonic abundance, O. universa and G. menardii, peaking with the chlorophyll maximum. For the cyclonic tows, the peak foraminifera abundances occur at a depth of -4 m which does not correspond to the chlorophyll maximum at ~8 m (Table 7; Figure 1). In the cyclones, the lowest foraminifera concentrations coincide with the highest chlorophyll concentrations. The foraminifera abundances peak at a low chlorophyll concentration of.8 mg/m 3. Scatter plots of the each species concentration versus the chlorophyll concentration yield poor correlation coefficients (Figure 12). Only O. universa and G. menardii hint at a correlation in the anticyclonic tows with the highest correlation coefficients of.86 and.79. In the anticyclones, a better correlation is expected beacuse the peak abundances and chlorophyll maximum seem to coincide. Even more surprising, an inverse relationship between foraminifera concentrations and chlorophyll is found in the cyclones. In both

35 26 Factor ,16, , Factor 1 Fig. 11. Species factor analysis results. Numbers correspond to species indicated in Table 9. Table 9. Species factor values. Variance.6.28 Species Factor 1 Factor 2 1 Orbulina universa Globigerinoides ruber (pink) Globigerinoides ruber (white) Globigerinoides sacculifer Hastigerina pelagica Globigerina bulloides Globigerinella siphonifera Globigerinella calida Globorotalia menardii Globigerinoides tenellus Globigerinoides conglobatus Globorotalia crassiformis Globorotalia truncatulinoides Pulleniatina obliquiloculata Unknown Globorotalia ungulata Globorotalia tumida

36 27 Individuals m -3 Individuals m -3 Individuals m -3 O. universa R = R = R = G. saculifer 8 R =.5474 R = R = G. siphonifera 15 1 R = R = R =.1728 G. ruber, var. pink 8 R = R = R = H. pelagica R = R = R = G. calida R = R =.5535 R = G. ruber, var. white R = R = R = G. bulloides 8 R = R = R = G. menardii 15 1 R =.79 R =.4439 R = Chlorophyll a mg m -3 Chlorophyll a mg m -3 Chlorophyll a mg m -3 Fig. 12. Scatter plot of each species versus chlorophyll concentrations. The least squares regression coefficient for all regimes is given in black, in red for only the anticyclonic data, and in blue for only the cyclonic data. Red square and diamonds represent MOC1-8 and MOC1-9. Blue plus sign and x marks represent MOC1-217 and MOC218, respectively.

37 28 eddy types, the presence of nitrate also does not correlate with the abundance peaks. The anticyclonic abundance peaks at least 6 m shallower than when nitrate concentrations first appear at 21 m. For the cyclones, the nitrate maximum at 65 m is next to the abundance minimum (Table 7). Neither factor 1 nor 2 corresponds directly to chlorophyll or nitrate. The weak correlation of chlorophyll suggests that although it may not directly correspond to factor 1 or 2, it may correspond to one of these factors in combination with another property. For each tow, the concentration of each species against depth, temperature, and density was examined to see how these hydrographic factors controlled the foraminifera distribution. The depth profiles are shown by species in Figures 13a-21a. The area of each bar is the integrated number of individuals found at the sampled interval (#m -2 /net). Six species shoal at shallower depths in cyclonic conditions: O. universa, G. menardii, pink G. ruber, white G. ruber, G. sacculifer, and G. bulloides (Table 8). Two other species show similar distributions in the first three tows: G. siphonifera, and G. calida. One species shows no recognizable pattern among the tows: H. pelagica. To show the effect of temperature and density on the abundances, the shape of the depth profiles were transformed to show the vertical concentration gradients for each species versus temperature and density (Figures 13b,c - 21b,c). The width of the bars is the temperature or the density range found in the net (e.g., 28.5 to 24.5 C). The horizontal axis of each bar is thus the average value found in the net (e.g., 26.5 C). The height of the bars is the abundance per the temperature or density range found across the net (#m -2 C -1 net -1 or #m -2 σ -1 net -1 ). The resultant area of each bar represents the abundance (#m -2 ) found in a respective net. The shape indicates how concentrated the species are in the net. Species with tall and narrow peaks represent high concentrations in narrow property ranges, whereas short, wide bars represent abundances dispersed across a larger temperature or density range. The same peak, if found among all the tows, would represent a definite species preference for that the particular property value. A comparison among these profiles suggests three patterns that seven of the nine common species follow: O. universa, and G. menardii; white G. ruber, pink G. ruber,

38 29 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ = 7.52 #m , Σ = 4.96 #m -2 Σ = 4.57 #m -2 Σ = 5.42 #m Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 11, Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Fig. 13. O. universa property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data.

39 3 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ = 8. #m Σ = 9.91 #m Σ = 5.35 #m -2 Σ = 7.16 #m Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) , Fig. 14. G. menardii property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data. Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 11,569 13, Individuals m -2 C -1 *1 Individuals m -2 σ -1 *

40 31 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ = 4.47 #m Σ = 1. #m -2 Σ = 2.39 #m -2 Σ = 4.26 #m Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 17, Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Fig. 15. H. pelagica property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data.

41 32 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ = 3.15 #m Σ =.53 #m scale as above Σ = 13.6#m -2 scale as below Σ = #m Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) , Fig. 16. G. ruber (pink) property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data. Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 7,636 7,858 12,756 9, Individuals m -2 C -1 *1 Individuals m -2 σ -1 *

42 33 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ =.17 #m Σ =. #m -2 Σ =.85 #m -2 Σ = 1.44 #m Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 4 6 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Fig. 17. G. ruber (white) property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data.

43 34 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ = 1.75 #m Σ =.8 #m -2 Σ = 7.34 #m -2 scale as below Σ = #m -2 Temperature ( C) Temperature ( C) Temperature ( C) scale as above Temperature ( C) Temperature ( C) , Fig. 18. G. sacculifer property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data. Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 6,518 7, Individuals m -2 C -1 *1 Individuals m -2 σ -1 *

44 35 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ =.33 #m Σ =. #m -2 Σ = #m -2 scale as below Σ = #m Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) scale as above Temperature ( C) , Fig. 19. G. bulloides property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data. Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 12,679 12,888 19,85 29, Individuals m -2 C -1 *1 Individuals m -2 σ -1 *

45 36 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ = 6.9 #m , Σ = 2.8 #m -2 Σ = 1.81 #m -2 Σ = 2.84 #m Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 4 6 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Fig.. G. siphonifera property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data.

46 37 Anticyclones MOCNESS 9 MOCNESS 8 Cyclones MOCNESS 217 MOCNESS 218 Depth (m) Depth (m) Depth (m) Depth (m) a b c Individuals 1 m -3 Individuals m -2 C -1 *1 Individuals m -2 σ -1 * Σ = 3.88 #m Σ = 3.68 #m -2 Σ = 4.53 #m -2 Σ = 1.45 #m Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Temperature ( C) Fig. 21. G. calida property profiles. Column a: concentration (# 1 m -3 ) with temperature profile in red. Column b: temperature (# 1 m -2 C -1 ). Each bar's width represents the temperature range found in the particular net. The height is the net's foraminifera abundance divided by the temperature range through the net, likewise, column c: density (# 1 m -2 σ -1 ). The resulting net areas integrate the same abundance shown in the corresponding net area of column a. Integrated tow abundances given in red. Gray shaded areas represent areas without data. Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) Sigma-t (σ t ) 18,128 11, Individuals m -2 C -1 *1 Individuals m -2 σ -1 *