Spatio-temporal distribution of dissolved inorganic carbon and net community production in the Chukchi and Beaufort Seas

Transcription

1 Deep-Sea Research II 52 (2005) Spatio-temporal distribution of dissolved inorganic carbon and net community production in the Chukchi and Beaufort Seas Nicholas R. Bates a,, Margaret H.P. Best a, Dennis A. Hansell b a Bermuda Biological Station For Research, Inc., 17 Biological Station Lane, Ferry Reach, Bermuda b Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA Received 10 March 2004; accepted 10 September 2005 Abstract As part of the 2002 Western Arctic Shelf Basin Interactions (SBI) project, spatio-temporal variability of dissolved inorganic carbon (DIC) was employed to determine rates of net community production (NCP) for the Chukchi and western Beaufort Sea shelf and slope, and Canada Basin of the Arctic Ocean. Seasonal and spatial distributions of DIC were characterized for all water masses (e.g., mixed layer, halocline waters, Atlantic layer, and deep Arctic Ocean) of the Chukchi Sea region during field investigations in spring (5 May 15 June 2002) and summer (15 July 25 August 2002). Between these periods, high rates of phytoplankton production resulted in large drawdown of inorganic nutrients and DIC in the Polar Mixed Layer (PML) and in the shallow depths of the Upper Halocline Layer (UHL). The highest rates of NCP ( mg C m 2 d 1 ) occurred on the shelf in the Barrow Canyon region of the Chukchi Sea and east of Barrow in the western Beaufort Sea. A total NCP rate of g for the growing season was estimated for the eastern Chukchi Sea shelf and slope region. Very low inorganic nutrient concentrations and low rates of NCP (o15 25 mg C m 2 d 1 ) estimated for the mixed layer of the adjacent Arctic Ocean basin indicate that this area is perennially oligotrophic. r 2005 Elsevier Ltd. All rights reserved. Keywords: Ocean carbon cycle; Productivity; Remineralization; Chukchi Sea; Arctic Ocean 1. Introduction Arctic Ocean shelf seas are sites of major biological productivity. Northward flow of nutrient-rich Pacific Ocean waters through Bering Strait supports a brief but intense photosynthetic season in the Chukchi Sea, with rates of primary production at X300 g C m 2 y 1 (e.g., Sambrotto et al., 1984; Springer and McRoy, 1993; Hansell Corresponding author. Tel.: ; fax: address: nick@bbsr.edu (N.R. Bates). et al., 1993; Springer et al., 1996; Hill and Cota, 2005). This production supports substantial benthic (e.g., Grebmeier et al., 2004) and pelagic biomass (e.g., Bates et al., 2005a, b; Ashjian et al., 2005) that, in turn, supports higher trophic levels (e.g., fish, marine mammals, seabirds) and important human socio-cultural activities. The Arctic Ocean, however, is particularly sensitive to global climate change and potentially to ecosystem changes associated with warming and sea-ice loss (e.g., Walsh et al., 1990; Moritz and Perovich, 1996; Grebmeier and Whitledge, 1996; Manabe and Stouffer, 2000) /$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi: /j.dsr

2 3304 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005) Primary production in the Chukchi Sea and adjacent Arctic shelf seas are influenced by a dynamic interplay of light, ice conditions, and coastal inputs, although there are limited data on the timing, extent and mechanistic controls of production. It remains unclear how warming, enhanced stratification and thinning sea-ice in the Arctic Ocean basin might affect productivity and ecosystem dynamics of this region. For example, could productivity be enhanced in the Arctic Ocean basin in response to the continued contraction of polar sea-ice extent and exposure of nutrient-laden surface water to light? To date, only limited measurements of in vitro primary productivity in the Chukchi Sea have been collected. Furthermore, it is difficult to extrapolate these rate measurements, typically determined using dawn-to-dusk 14 C incubations (Williams, 1993), both spatially and temporally. An alternative approach involves observing changes in the in situ water column inventories of the reactants and products (e.g., dissolved oxygen, DO; inorganic nutrients; CO 2, dissolved organic carbon, DOC; particulate organic carbon, POC) of photosynthesis. Estimates of net community production (NCP; sensu Williams, 1993) can be determined from changes in dissolved inorganic carbon (DIC), thereby offering spatially and temporally integrative measures of productivity (e.g., Weiss et al., 1979; Codispoti et al., 1982, 1986; Karl et al., 1991; Chipman et al., 1993; Yager et al., 1995; Bates et al., 1998, 2005a; Lee, 2001; Lee et al., 2002). As part of the Western Arctic Shelf Basin Interactions (SBI) project, the timing, extent and dynamics of production were evaluated during two cruises to the Chukchi Sea region in In this study, the spatio-temporal patterns of primary production over the Chukchi and Beaufort Sea shelves, the adjacent shelf slope and Canada Basin of the Arctic Ocean were determined from changes in the water-column distributions of DIC. Previous studies measured only surface DIC (Murata and Takizawa, 2003) or calculated DIC from measurements of ph and alkalinity (Pipko et al., 2002). In this study, we estimate rates of NCP from DIC inventory changes (corrected for ice-melt and air sea CO 2 gas exchange) and compare these with 14 C data collected during the 2002 field activities (Hill and Cota, 2005) and earlier (Cota et al., 1996). Ice algae and phytoplankton are both significant contributors to primary production, with ice algae being quantitatively important early in the growing season (Hill and Cota, 2005). Here, we determine if there was significant NCP early in the growing season, since direct measurements suggest that ice algae contribute to 10% of total primary productivity (Gradinger and Eicken, 2004). We also evaluate whether there were significant rates of NCP in the surface layer of the Arctic Ocean basin, since Gosselin et al. (1997) observed relatively high rates of primary productivity and organic carbon production during the 1994 Arctic Ocean Study (AOS). 2. Materials and methods Physical, biogeochemical and biological measurements were made from the USCGC Healy during two cruises to the Chukchi and Beaufort Seas as part of the 2002 field phase of the Western Arctic SBI project. During the spring cruise (5 May 15 June 2002), 40 CTD/rosette stations were occupied at the Bering Strait, over the Chukchi and Beaufort Sea shelves, the shelf-slope region and into the Arctic basin (Fig. 1). During the summer cruise (17 July 26 August 2002), 45 stations were occupied in the region. Three sections across the Chukchi and Beaufort Sea shelf, shelf-slope and Arctic Ocean basin were repeated each cruise, including: (1) West Hanna Shoal (WHS); (2) East Hanna Shoal (EHS) transect, and; (3) Barrow Canyon (BC) transect. In addition, during summer field activities, a fourth section East of Barrow (EB), and a section extending from the Alaskan side of the Bering Strait to the Diomede Islands also were taken. At each CTD/rosette station, a suite of biological and chemical measurements was collected, including salinity, inorganic nutrients (ammonium, nitrate, nitrite, phosphate, reactive silicon, and urea) DIC, dissolved oxygen and particulate organic matter (further details are given in Bates et al., 2005b). CTD, bottle and rate data are available at the SBI web site, and archived at the National Snow and Ice Data Center (NSIDC; Seawater samples for DIC were drawn from the Niskin samplers into pre-cleaned 300-ml borosilicate bottles. DIC samples were subsequently poisoned with HgCl 2 to halt biological activity, sealed, and returned to BBSR for analysis. DIC samples were analyzed using a highly precise and accurate (0.025%; o0.5 mmol kg 1 ), gas-extraction/coulometric-detection system (Bates et al., 1996, 1998; Bates, 2001). The analytical system consists of a Single-Operator Multi-parameter

3 N.R. Bates et al. / Deep-Sea Research II 52 (2005) Metabolic Analyzer (SOMMA) coupled to a CO 2 coulometer (model 5011; UIC Coulometrics) and personal computer (Johnson et al., 1993). Routine analyses of Certified Reference Materials (provided by A.G. Dickson, Scripps Institution of Oceanography) ensured that the accuracy of the DIC measurements was within 0.05% (0.5 mmol kg 1 ). The SOMMA-coulometer system has been used at BBSR for 14 years to analyze DIC samples from the Bermuda Atlantic Time-series Study (BATS) site and to determine long-term trends in oceanic CO 2 and air sea CO 2 exchange in the subtropical gyre of the North Atlantic Ocean (Bates et al., 2002). The salinity of each DIC sample also was directly measured during analysis using a SeaBird SBE-911 conductivity sensor. The salinity data generated from the DIC analyses were compared with discrete salinity measurements made onboard the USCGC Healy as part of the quality control and assurance protocols. However, discrete salinity data from the USCGC Healy (Codispoti et al., 2005) were used here in data analysis and interpretation. Dissolved oxygen was determined by Winkler titration, while inorganic nutrients were determined using a nutrient auto-analyzer onboard the USCGC Healy (Codispoti et al., 2005). The general circulation of the region is primarily driven by northward flow of Pacific Ocean water through Bering Strait into the Chukchi Sea shelf and exiting through outflows into the Arctic Ocean basin (Fig. 1). At the Bering Strait, waters defined as Alaskan Coastal Current Water (eastern Bering Strait), Anadyr Current (central Bering Strait) and Bering Shelf Water (western Bering Strait; Coachman et al., 1975) were sampled during the summer cruise (Codispoti et al., 2005). Several recent studies characterize the flow fields of the Chukchi Sea shelf (Pickart et al., 2005; Aagaard et al., 2005), including transport at Bering Strait (Woodgate and Aagaard, 2005; Woodgate et al., 2005b), and outflows through the Herald Valley (Woodgate et al., 2005a) and Barrow Canyon (Weingartner et al., 2005). The upper several hundred meters of the Arctic Ocean and adjacent seas such as the Chukchi and Beaufort Seas are strongly stratified (e.g., Kinney Fig. 1. Location map: (A) CTD/rosette stations from the HLY spring cruise to the Chukchi Sea (5 May 15 June 2002). Three sections were sampled from Chukchi outer shelf into the Arctic basin, included: (1) West Hanna Shoal (WHS); (2) East Hanna Shoal (EHS) transect, and (3) Barrow Canyon (BC) transect. (B) CTD/rosette stations from the HLY summer cruise to the Chukchi Sea (17 July 26 August 2002). Four sections were sampled from Chukchi outer shelf into the Arctic basin, included: (1) West Hanna Shoal (WHS); (2) East Hanna Shoal (EHS) transect; (3) Barrow Canyon (BC) transect, and (4) East of Barrow (EB). Northward transport of Pacific Ocean water occurs through Bering Strait into the Chukchi Sea shelf. The major offshore outflow occurring through Long Strait (to the west onto the East Siberian shelf), Herald Valley and Barrow Canyon into the Arctic Ocean Canada basin.

4 3306 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005) et al., 1970; Aagaard et al., 1985; Jones and Anderson, 1986; Anderson et al., 1988; Aagaard and Carmack, 1994; Anderson et al., 1994a, b; Schlosser et al., 1995). Identifiable signatures in temperature and salinity (Aagaard et al., 1981), and nutrient/oxygen distributions and stoichiometry (Wallace et al., 1987; Salmon and McRoy, 1994; Jones et al., 1991) were used to identify principal water masses in the study region (Codispoti et al., 2005). Water masses over the Chukchi and Beaufort Sea shelves and Arctic Ocean included: (1) the Polar Mixed Layer (PML; upper 0 50 m, salinity typically o31); (2) the Upper Halocline Layer (UHL; m deep; core layer has salinity of 33.1, nitrate concentration of 1472 mmol kg 1, and phosphate concentration of mmol kg 1 ); (3) Lower Halocline Layer (LHL; m deep; core layer has salinity of 34.3, nitrate concentration of 1271 mmol kg 1, and phosphate concentration of mmol kg 1 ); (4) Atlantic Water Layer water (AWL; m deep, core layer has salinity of , nitrate concentration of 1471 mmol kg 1, and phosphate concentration of mmol kg 1 ), and; (5) Arctic Ocean Deep Water (AODW; 4800 m deep, core layer has salinity of 34.95, nitrate concentration of 1571 mmol kg 1 ). 3. Results and discussion 3.1. Spatio-temporal distributions of DIC PML and UHL waters were present on the Chukchi and Beaufort Sea shelves during both cruises (see Bates et al., 2005b; Codispoti et al., 2005 for details). Water masses of the PML, halocline, Atlantic Water and AODW were sampled at the shelf-slope and Arctic Ocean basin stations (i.e., WHS, EHS, BC, EB). Each water mass had distinctive hydrographic (i.e., salinity, temperature), biogeochemical (e.g., nitrate, phosphate, dissolved oxygen) and DIC properties Springtime observations Most of the Chukchi Sea shelf and slope-basin region was heavily ice covered during the spring cruise. In the PML (depths of 0 to m), temperatures ranged from 1.5 to 1.8 1C (see Bates et al., 2005b; their Fig. 3) and salinities ranged from 29 to 32 (Fig. 2A). Nitrate contents were variable (0 8 mmol kg 1 ; Fig. 2C) as were dissolved oxygen ( mmol kg 1 ; Fig. 2E) and DIC contents (o mmol kg 1 ; Fig. 2A,C,E). At the surface (0 5 m depth), DIC concentrations increased northward by 100 mmol kg 1 from the Bering Strait (2127 mmol kg 1 at station 0; 55 km S of Bering Strait; Fig. 3A) to the central Chukchi Sea shelf (2236 mmol kg 1 at station 3). Over the slope-basin region, DIC contents decreased to o2000 mmol kg 1 in the Arctic Ocean basin surface layer (low nitrate of o0.2 mmol kg 1 ) observed at the northernmost stations (Fig. 3A). Over the shelf-slope regions, DIC contents were higher in the vicinity of BC and East of Barrow (EB). Below the surface layer, DIC contents increased vertically, with maxima ( mmol kg 1 ) in the saline (33; Fig. 2A), high nitrate (10 15 mmol kg 1 ; Fig. 2C) core of the UHL (Fig. 4A). At greater depths, DIC contents decreased gradually from the LHL to the Atlantic Water Layer and AODW ( mmol kg 1 ) Summertime observations Approximately 6 weeks later, most of the Chukchi Sea shelf was ice-free. However significant sea-ice (430 80%) remained in the shelf-slope and basin regions of the Chukchi and Beaufort Sea shelves. Surface layer temperatures were warmer ( 1.5 to +7 1C; see Bates et al., 2005a, b; their Fig. 3) and ice melt had contributed to a freshening of the mixed layer (Fig. 2B). Nitrate contents were low (generally o0.2 mmol kg 1 in the mixed layer across the region; Fig. 2D), and dissolved oxygen had increased ( mmol kg 1 ; Fig. 2F) compared to springtime. Fig. 2. Hydrographic and dissolved inorganic carbon (DIC) properties observed in the Chukchi and Beaufort Seas. Units for DIC, nitrate and dissolved oxygen (DO) are mmol kg 1. (A) DIC versus salinity on the spring cruise. (B) DIC versus salinity on the summer cruise. (C) DIC versus nitrate on the spring cruise. (D) DIC versus nitrate on the summer cruise. (E) DIC versus dissolved oxygen on the spring cruise. (F) DIC versus dissolved oxygen on the summer cruise. Closed circle (green) symbols denote all Polar Mixed Layer (PML) water data. Cross (red) symbols denote all Upper Halocline Layer (UHL) data. Closed diamond (blue) symbols denote waters of the Lower Halocline Layer (LHL). Closed diamond (yellow) symbols denote waters of the Atlantic Layer (AWL). Closed diamond (orange) symbols denote waters of the Arctic Ocean Deep Water (AODW). Magenta square symbols denote data observed at Bering Strait. In Figs. 2B, D and F, several low DIC values ranging from 4500 to 1700 mmol kg 1 observed in the upper 3 m are not shown.

5 N.R. Bates et al. / Deep-Sea Research II 52 (2005)

6 3308 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005) Fig. 3. Surface layer DIC (mmol kg 1 ) distributions in the Chukchi Sea. (A) Spring cruise, and (B) summer cruise. At Bering Strait, surface and halocline DIC values ranged from 1900 to 2050 mmol kg 1 (Fig. 5). In the westernmost stations (closest to Little Diomede Island; i.e., stations 2 5) low DIC values were observed in waters hydrographically characterized as Anadyr Water and Bering Shelf Water. At the easternmost station (station 1), DIC values were much higher in relatively warm, fresh waters hydrographically characterized as Alaskan Coastal Current Water (Codispoti et al., 2005; Woodgate et al., 2005b; Woodgate and Aagaard, 2005). Elsewhere on the Chukchi and Beaufort Sea shelves, surface DIC distributions were highly variable (o mmol kg 1 ; Fig. 2B,D,F), with typically lower values compared to springtime. In the upper 5 m, ice-melt significantly diluted DIC content in the eastern Chukchi Sea shelf (stations 7 12) and in the shelf-slope regions at the BC (BC;

7 N.R. Bates et al. / Deep-Sea Research II 52 (2005) Fig. 4. Sections of DIC (mmol kg 1 ) data from the Chukchi Sea shelf to the Arctic Ocean basin sampled during the spring cruise. (A) West Hanna Shoals (WHS) section. (B) East Hanna Shoals (EHS) section. (C) Barrow Canyon (BC) section. stations 13 15, with DIC as low as 526 mmol kg 1 at station 13) and EB (EB; stations 19 24) (Fig. 3B). At the WHS and EHS sections, surface layer DIC decreased offshore from 1880 mmol kg 1 over the shelf to o1840 mmol kg 1 at the basin stations (e.g., stations 31 and 32). Immediately below the surface layer, DIC rapidly increased with depth (Fig. 6), with the DIC maxima located in the UHL (depth of m). Similar to the spring observations, DIC contents gradually decreased from the UHL into the LHL, Atlantic Water Layer and AODW at all sections. The strong influence of ice melt on DIC distributions was evident at BC (71.91N in Fig. 7C; section of DIC normalized (ndic) to a constant salinity of 35 (see Section 3.7 for further comments on salinity normalization). In this region, relatively low ndic mixed layer water appears to subduct beneath higher ndic surface waters (0 20 m) of the Arctic Ocean basin (Figs. 7C, 8)) DIC distributions in the halocline, Atlantic Water Layer and Arctic Ocean Deep Water On the Chukchi and Beaufort Sea shelves only mixed-layer and upper halocline waters were present during the SBI field sampling. But, at the offshore stations, LHL, Atlantic Water Layer, and AODW water masses were typically observed at depths of m, m, and m, respectively. Both in spring and summer, DIC contents were highest ( mmol kg 1 ) in the core of the UHL (Fig. 4 and 6), gradually decreasing vertically in deeper waters (Fig. 2). These waters could be differentiated with distinct DIC, oxygen, and nutrient properties. For example, high nitrate (14 mmol kg 1 ), low oxygen ( mmol kg 1 ), and DIC contents ( mmol kg 1 ) were observed in the AODW (Fig. 9) compared to the lower nitrate (14 mmol kg 1 ), higher oxygen ( mmol kg 1 ), and DIC content ( mmol kg 1 ) of the Atlantic

8 3310 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005) Fig. 5. Sections of DIC and ndic (mmol kg 1 ) at Bering Strait sampled during the summer cruise. (A) DIC section. From west to east, the stations were 2 5, and 1. (B) ndic section (see Section 3.7 for further comments on salinity normalization). Water Layer. Although, no significant differences in ndic or nitrate were observed between spring and summer, dissolved oxygen contents of the Atlantic Water Layer and AODW were 10 mmol kg 1 lower. In halocline waters, ndic contents had a generally smaller range in the UHL ( mmol kg 1 ) compared to the LHL ( mmol kg 1 )(Fig. 10) Estimates of NCP from spatio-temporal changes in DIC distributions During the 2002 SBI field program, high rates of primary productivity were measured on the Chukchi Sea shelf in summer (Hill and Cota, 2005), particularly in the vicinity of the shelf-slope regions of the BC and EB. This production manifested itself as drawdown in inorganic nutrients and DIC, as well as production of dissolved oxygen and suspended POM. Portions of the POM produced on the shelf were exported vertically to the sea floor (Moran et al., 2005) or offshore to the UHL (Bates et al., 2005b). DIC concentrations are influenced by a variety of physical and biogeochemical factors. The factors of most importance in the Chukchi Sea shelf region were: (1) NCP and ice-melt (both decreasing DIC), and; (2) air sea CO 2 gas exchange and remineralization of organic matter (both increasing DIC). Between the spring and summer occupations, large decreases ( mmol kg 1 ) of DIC were observed in the entire water column (0 50 m, both PML and UHL) at the shelf stations and in the upper m of the PML and UHL at the slope and basin stations. A large component of this decrease was due to dilution by ice melt (and minor contributions from local precipitation and evaporation), although largely restricted to the surface (e.g., 0 5 m) layer. The contribution of ice-melt to DIC changes can be estimated by normalizing DIC to a constant salinity of 35. This correction assumes that: (1) ice-melt contributed negligible amounts of DIC (i.e., 0 mmol kg 1 ) to the mixed layer, and; (2) an absence of mixing with new water mass sources. Therefore, changes in the spatio-temporal distributions of ndic reflect the influence of other factors such as NCP and air sea CO 2 gas exchange rather than ice-melt and other potential contributors (discussed later in caveat and qualifiers section). The map (Fig. 8A) of springtime ndic shows relatively high ndic in the PML of the Chukchi shelf and slope regions (2340 mmol kg 1 ) with slightly lower values southward at Bering Strait (2260 mmol kg 1 ). Six weeks later, large decreases in ndic were observed over much of the NE Chukchi Sea shelf near BC and eastward on the Beaufort Sea shelf at the EB section (Fig. 8B). In the water column, summertime drawdown of DIC (and

9 N.R. Bates et al. / Deep-Sea Research II 52 (2005) Fig. 6. Sections of DIC (mmol kg 1 ) data from the Chukchi and Beaufort Sea shelves to the Arctic basin sampled during the summer cruise. (A) West Hanna Shoals (WHS) section. (B) East Hanna Shoals (EHS) section. (C) Barrow Canyon (BC) section. (D) East of Barrow (EB) section. nitrate depletion and oxygen production) was evident in the PML and UHL (Fig. 9). Previous studies have shown similar seasonal drawdown of surface DIC and seawater pco 2 in the vicinity of BC (Pipko et al., 2002; Murata and Takizawa, 2003). The drawdown of DIC can be clearly identified in property property plots of ndic versus salinity, nitrate, and dissolved oxygen (Fig. 10). In the PML, the largest depletion of ndic (up to 200 mmol kg 1 ), relative to spring conditions, occurred in the salinity range of (Fig. 10B) and was accompanied by nitrate drawdown (Fig. 10D) and dissolved oxygen production (Fig. 10F). The largest drawdown of ndic (and DIC) occurred in the BC and EB region (Figs. 8 and 10). A more complicated pattern was observed in the UHL (Fig. 11). In the shallower depths of the UHL ( m deep), a modest depletion of DIC (up to 50 mmol kg 1 ; Fig. 11B) was observed (accompanied by a dissolved oxygen increase of similar magnitude; Fig. 11F). However, this feature was geographically restricted to the BC and EB region,

10 3312 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005) Fig. 7. Sections of ndic (mmol kg 1 ) data from the Chukchi and Beaufort Sea shelves to the Arctic basin sampled during the summer cruise. (A) West Hanna Shoals (WHS) section. (B) East Hanna Shoals (EHS) section. (C) Barrow Canyon (BC) section. (D) East of Point Barrow (EB) section. and not observed to the west at the WHS and EHS sections. The core of UHL (at deeper depths of m) remained relatively unchanged (except for a remineralization signal in DIC at a few depths observed during summer) Chukchi Sea shelf and slope productivity estimates The drawdown of DIC in the PML and shallower depths of the UHL can be attributed to primary production (caveats and qualifiers are discussed below). Estimates of NCP were determined from changes in the inventory of DIC over time (i.e., between spring and summer). At each station, the rate of NCP over time (t) was determined as follows: NCP ¼ð spring ndic ð0 30 mþ summer ndic ð0 30 mþ Þ=t. (1) The rate of NCP was expressed as mg C m 2 d 1,with an error of mg C m 2 d 1 due to imprecision

11 N.R. Bates et al. / Deep-Sea Research II 52 (2005) Fig. 8. Surface layer ndic (mmol kg 1 ) distributions and rates of net community production (NCP) in the Chukchi Sea (italicized bold values). (A) Spring cruise and (B) summer cruise. NCP rates were determined at each station. Total NCP was estimated for the region of the Chukchi and Beaufort Sea shelves enclosed within the dashed area. and inaccuracy of 1 mmol kg 1 associated with DIC analyses. ndic data were used rather than DIC data in order to eliminate changes imparted by ice melt (and local precipitation and evaporation). At each station, rates of NCP were computed from ndic data integrated over 0 30 m depth. During the 2002 SBI field season, the 1% light level was typically shallower than 30 m, and productivity was typically confined to the 0 30 m layer (Hill and Cota, 2005). In the springtime condition, mixed-layer DIC concentrations were uniform across much of the Chukchi Sea shelf. Over most of the Chukchi Sea shelf, slope and adjacent basin, the average ndic in the 0 30 m layer was mmol kg 1 during the spring (stations 24, 27, 29 34). The spring ndic value was then used to determine the subsequent ndic changes and rates of NCP observed for the spring to summer period (44 74 d; Table 1). The

12 3314 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005) Fig. 9. Hydrographic and dissolved inorganic carbon (DIC) properties of the surface mixed layer (PML) and the UHL observed in the Chukchi and Beaufort Seas. UHL data are shown for context. Units for DIC, nitrate and DO are mmol kg 1. (A) DIC versus salinity on the spring cruise. (B) DIC versus salinity on the summer cruise. (C) DIC versus nitrate on the spring cruise. (D) DIC versus nitrate the summer cruise. (E) DIC versus dissolved oxygen on the spring cruise (F) DIC versus dissolved oxygen on the summer cruise. Open circle (green) symbols denote West Hanna Shoals (WHS) section data. Closed circle (green) symbols denote East Hanna Shoals (EHS) section data. Magenta circle symbols denote Barrow Canyon (BC) section data. Purple circle symbols denote East of Barrow(EB) section data. Cross (red) symbols denote Upper Halocline Layer data.

13 N.R. Bates et al. / Deep-Sea Research II 52 (2005) NCP rate calculated for each station (Table 1) estimates the total spring to summer productivity signature imparted on the water mass advected to and present at each station by summertime. Rates of NCP integrated over the top 30 m determined for the spring summer period were highly variable, ranging from low values of 2 mg Cm 2 d 1 over the basin to mg C m 2 d 1 over the shelf (Fig. 8). The highest NCP rates ( mg C m 2 d 1 ) were estimated for the shelf region of BC and EB; with slightly lower values ( mg C m 2 d 1 ) in the slope regions. Lower values ( mg C m 2 d 1 ) of NCP were observed at shelf and slope station in the vicinity of WHS and EHS. The highest NCP rates were geographically located in the BC/EB region of large nitrate depletion, and POM production and export (Bates et al., 2005b; Moran et al., 2005). Previous measurements of 14 C based productivity on the Chukchi Sea shelf and slope were also highly variable, ranging from 340 to 2570 mg C m 2 d 1 (Hameedi, 1978; Cota et al., 1996; Wheeler et al., 1996; Gosselin et al., 1997; Chen et al., 2002; Table 2). During the SBI field program, relatively low rates of primary productivity were measured during the summer field sampling in shelf (340 mg C m 2 d 1 ) and slope locations (404 mg C m 2 d 1 ; Hill and Cota, 2005). At that time, phytoplankton productivity was probably nutrient-limited, since nitrate and phosphate concentrations across the entire Chukchi shelf and slope regions were at or below detection (e.g., NO 3 concentrations o0.2 mmol kg 1 ). Assuming that the growing season of the Chukchi Sea shelf is approximately 120 d, 14 C-based productivity measurements (Hill and Cota, 2005) can be extrapolated to give an annual productivity of g C m 2 yr 1. However, the 14 C-based productivity measurements probably missed the bulk of the productivity occurring between the spring (June) and summer (July August) cruise. NCP rates, estimated from inventory changes of ndic, yielded considerably higher annual productivity estimates of g C m 2 d 1 (Table 3) Areal rate of NCP observed on the Northeast Chukchi Sea shelf In determining an areal estimate of productivity, annual rates of NCP were determined for the northeast sector of the Chukchi Sea shelf (Fig. 8). Within the area shown in Fig. 8 (assuming that all the mixed-layer water masses present in this area were located within the Chukchi Sea shelf during the spring cruise), the average NCP is 1064 mg C m 2 d 1 (Table 1). In this area of km 2, the total rate of NCP for the spring to summer period (60 d) was estimated at gc (Table 4). If a growing season of 120 d is assumed, the total rate of NCP for this region was estimated at gc (Table 4). NCP rates were not determined outside the northeast sector of the Chukchi Sea shelf due to the potential for lateral transport of surface waters with different springtime DIC properties. The dominant pathway of circulation transports shelf water northward from Bering Strait across the Chukchi Sea shelf, with the major offshore outflow occurring through Long Strait (to the west onto the East Siberian shelf), Herald Valley and Barrow Canyon (Woodgate et al., 2005a,b). Flow rates at Bering Strait were highly variable with the strongest northward flow in the Alaskan Coastal Current (up to 100 cm s 1 ). However, across the Chukchi Sea shelf region, typical flow rates vary from 2 to 10 cm s 1, with a mean of 5 cm s 1 in the central Chukchi (Woodgate et al., 2005a). Annual mean velocities suggest a transit time of 4 months from Bering Strait to the heads of Herald Valley and BC (Woodgate et al., 2005a), with a shorter transit time of 3 months during the summer (Weingartner et al., 2005). Other studies suggest it takes 6 months for water at Bering Strait to transit to the shelf break outflow at BC (Aagaard et al., 2005). Since the change in DIC used to estimate NCP occurs over a period of d, the influence of water masses flowing through Bering Strait would likely have influenced the southern part of the Chukchi Sea shelf up to the central Channel (Fig. 1). Given the residence time of waters on the Chukchi Sea shelf ( d), during the time-frame of the 2002 SBI cruises, we assume that lateral transport of waters at Bering Strait had minimal impact on the northeastern sector of the Chukchi Sea shelf during the time-frame of the 2002 SBI cruises. As shown by the DIC properties observed at Bering Strait, the flow of Anadyr/Bering Shelf Water from Bering Strait would have contributed low-ndic waters to the Chukchi Sea shelf. In contrast, flow of the Alaskan Coastal Current would have contributed high-ndic water to the Chukchi Sea shelf (Fig. 5). Most of the stations in the southern sector of the Chukchi Sea shelf appear to be located in regions where the influence of the Alaskan Coastal Current

14 3316 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005)

15 N.R. Bates et al. / Deep-Sea Research II 52 (2005) dominates. The inflow of high ndic water makes estimates of NCP difficult in the southern sector of the Chukchi Sea shelf. The lack of sufficient stations sampled in spring and summer in the western parts of the Chukchi Sea shelf makes NCP estimates not possible in that region Adjacent Canada Basin productivity estimates Early studies suggested that the Arctic Ocean basin is perennially oligotrophic with very low levels of productivity (i.e., 5mgCm 2 d 1 ; English, 1961). More recent studies have reported higher levels of productivity ( mg C m 2 d 1 ; Cota et al., 1996; Wheeler et al., 1996; Gosselin et al., 1997; Chen et al., 2002). Estimates of annual productivity in the central Arctic Ocean basin range from low values ( g C m 2 yr 1, Anderson et al., 2003; 1.8 g C m 2 yr 1, English, 1961; 3.6 g C m 2 yr 1, Moran et al., 1997) to relatively high values (15 g C m 2 yr 1 ; Gosselin et al., 1997). At the Arctic Ocean basin stations adjacent to the Chukchi Sea shelf, very low nitrate and phosphate concentrations were observed during spring and summer of Estimates of NCP from ndic inventory changes between the spring and summer cruises ( mg C m 2 d 1 ; Table 1) were at the lower range of previous productivity estimates, and much lower compared to the slope and shelf regions of the adjacent Chukchi and Beaufort Sea shelves. If a growing season of 120 d is assumed, the total rate of NCP estimated at the Arctic Ocean basin stations was estimated at g C m 2 yr 1. The rates of productivity determined in this study indicates that the Arctic Ocean basin adjacent to the Chukchi Sea has an active carbon and nitrogen cycle, but the region appears perennially oligotrophic with rates of productivity two orders of magnitude lower than the North Pacific (mean of 172 g C m 2 yr 1 ; Karl et al., 2001) and North Atlantic subtropical gyres (mean of 154 g C m 2 yr 1 ; Steinberg et al., 2001). Our estimates of NCP calculated from ndic inventory changes at the periphery of the Canada basin suggest rates of productivity closer to the low values of English (1961), Moran et al. (1997) and Anderson et al. (2003), rather than the higher estimates of Gosselin et al. (1997) and Pomeroy (1997) Early growing season productivity estimates It is difficult to quantify rates of NCP on the Chukchi and Beaufort Sea shelves prior to the spring cruise due to the lack of winter DIC data. In the spring, DIC (ndic) concentrations in the PML were fairly uniform across much of the shelf, slope and basin (Fig. 8). However, ndic concentrations were somewhat lower at the Bering Strait and inner Chukchi Sea shelf (where ice conditions were less than 70 80% ice cover), perhaps indicative of early season productivity. However, these waters were nitrate-rich (10 15 mmol kg 1 ), and the relatively low ndic values may simply represent the DICsalinity properties of Anadyr Current and Alaskan Coastal Current waters (perhaps modified by early season productivity in the Bering Sea) flowing northward from the Bering Sea into the Chukchi Sea. Elsewhere in the Chukchi and Beaufort Sea shelf, slope and adjacent basin, there was no geochemical evidence for significant early season productivity (either as DIC drawdown or elevated DO concentrations). Walsh et al. (2005), using a coupled biophysical model analysis of the Chukchi Sea, also have suggested that productivity was low (5mgCm 2 d 1 ) in the early season (April May) prior to the spring cruise. It was not possible to determine the potential contribution of ice algae productivity to net productivity during the spring (June) to summer (August) period. Gradinger and Eicken (2004) found significant ice algae productivity at a couple of first year ice stations during the heavy sea-ice conditions of the spring cruise. However, this productivity did not appear to Fig. 10. Hydrographic and salinity normalized dissolved inorganic carbon (ndic) properties of the Polar Mixed Layer and the Upper Halocline Layer observed in the Chukchi and Beaufort Seas. UHL data are shown for context. Units for ndic, nitrate and DO are mmol kg 1. (A) ndic versus salinity on the spring cruise. (B) ndic versus salinity on the summer cruise. (C) ndic versus nitrate on the spring cruise. (D) ndic versus nitrate on the summer cruise. (E) ndic versus dissolved oxygen on the spring cruise. (F) ndic versus dissolved oxygen on the summer cruise. Open circle (green) symbols denote West Hanna Shoals (WHS) section data. Closed circle (green) symbols denote East Hanna Shoals (EHS) section data. Magenta circle symbols denote Barrow Canyon (BC) section data. Purple circle symbols denote East of Point Barrow (EB) section data. Cross (red) symbols denote Upper Halocline Layer (UHL) water data. The dashed regions indicate the approximate range of springtime property property distributions. In the summer plots, deviations from the spring range are shown and attributed to net community production (P). ndic is DIC normalized to a salinity of 35.

16 3318 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005)

17 N.R. Bates et al. / Deep-Sea Research II 52 (2005) modify the PML present over much of the shelf, slope and basin during the spring cruise (Fig. 8) Caveats and qualifiers for productivity estimates The carbon mass balance approach employed here to estimate the rate of NCP does not account for contributions from air sea CO 2 gas exchange and vertical diffusion. Although both processes added CO 2 to the mixed layer, the contributions to mixed layer ndic inventory changes were minor. For example, previous studies have indicated that the Chukchi Sea shelf is undersaturated with respect to CO 2 and that the region is a small sink of atmospheric CO 2 during ice-free periods (Pipko et al., 2002; Walsh et al., 2005). Typical air to sea CO 2 flux rates of 5 10 mmol CO 2 m 2 d 1 have been observed during the spring to summer period (Walsh and Dieterle, 1994; Pipko et al., 2002; Wang et al., 2003; Murata and Takizawa, 2003). In the Chukchi Sea shelf region, these CO 2 flux rates add 5 10 mmol kg 1 to the DIC inventory of the 0 30 m layer for the spring to summer period. Accounting for CO 2 gas exchange would add mg C m 2 d 1 to the NCP rates reported in Table 2. However, this contribution is likely to be smaller since the shelf was not 100% ice-free for all of the spring to summer period (see Bates et al., 2005b; their Fig. 2). Surface waters at the slope and Arctic Ocean basin stations were undersaturated with respect to CO 2 (i.e., a potential ocean sink for atmospheric CO 2 ) and air-to-sea CO 2 flux also might significantly affect the NCP rate estimates (Table 2). Even though significant ice cover remained in the slope stations by summer (430 70%), accounting for gas exchange would add mg C m 2 d 1 to the NCP estimates. At the Arctic Ocean basin stations, determining the contribution of gas exchange is difficult since the region is almost perennially ice covered. If a 90% ice cover is assumed, gas exchange might contribute 5 10 mg C m 2 d 1 to the low NCP rate estimates (15730 mg C m 2 d 1 ). Vertical diffusion of CO 2 across the base of the mixed layer would have contributed minor amounts (o1 2 mmol kg 1 )ofco 2 to the DIC pool in the upper 30 m between the spring and summer cruises at the shelf and slope stations. Vertical diffusivity flux of CO 2 was computed as the product of the vertical diffusion coefficient, K v, the vertical gradient of inorganic carbon (ddic=dz) below the mixed layer (i.e., vertical gradient in DIC from m), and the seawater density (Denman and Gargett, 1983). Although K v is highly variable ( cm 2 s 1 ; Denman and Gargett, 1983), an average K v of 30 cm 2 s 1 increased mixed layer (0 30 m) DIC by 2.2 mmol kg 1 over a 45-d period. Thus, accounting for vertical diffusion of CO 2 into the mixed layer would add mg C m 2 d 1 to the NCP rates reported in Table 1. At the Arctic Ocean basin stations, vertical diffusion of CO 2 across the base of the mixed layer would have contributed much less CO 2 to the mixed layer compared to the shelf and slope stations. Vertical diffusivity estimates for the Arctic Ocean basin are very low ( cm 2 s 1 ; Wallace et al., 1987; D Asaro and Morison, 1992; Rudels et al., 1996). Accounting for vertical diffusion of CO 2 into the mixed layer would add mg C m 2 d 1 to the NCP rates reported in Table 1. Here, DIC data normalized to a salinity of 35 (i.e., ndic) was used in the NCP calculation. If, for example, DIC data had been normalized to a salinity of 33.1 (i.e., salinity of the core UHL), similar rates of NCP are calculated with a mean difference of 19 mg C m 2 d 1, within the error of the calculation. These estimates of NCP also do not include DIC depletion due to productivity in the shallow depths of the UHL. By summer, a depletion of DIC in the shallow layer of the UHL was observed at the BC and EB sections (Fig. 11B), although it occurred at depths deeper than the 1% light level. The DIC feature most likely results from transfer of the productivity signal from mixed layer to upper halocline through vertical mixing and Fig. 11. Hydrographic and ndic properties of the Upper Halocline Layer and other water masses observed in the Chukchi and Beaufort Seas. The other water masses, PML and LHL, are shown for context. Units for ndic, nitrate and DO are mmol kg 1. (A) ndic versus salinity on the spring cruise. (B) ndic versus salinity on the summer cruise. (C) ndic versus nitrate on the spring cruise. (D) ndic versus nitrate on the summer cruise. (E) ndic versus dissolved oxygen on the spring cruise. (F) ndic versus dissolved oxygen on the summer cruise. Open pluses (red) symbols denote West Hanna Shoals (WHS) section data. Closed plus (red) symbols denote East Hanna Shoals (EHS) section data. Magenta plus symbols denote Barrow Canyon (BC) section data. Purple plus symbols denote East of Point Barrow (EB) section data. Open circle (green) symbols denote all mixed layer water (PML) data. Open diamond (blue) symbols denote waters of the Lower Halocline Layer (LHL), Atlantic Layer (AWL) and Arctic Ocean Deep Water (AODW). The dashed regions indicate the approximate range of springtime property property distributions. In the summer plots, deviations from the spring range are shown and attributed to net community production (P) and remineralization (R). ndic is DIC normalized to a salinity of 35.

18 3320 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005) Table 1 Mean ndic contents for 0 30 m surface layer during the summer HLY cruise (17 July 26 August 2002) Station Location Date Mean ndic (mmol kg 1 ) DnDIC Days NCP (mg C m 2 d 1 ) Barrow Canyon 8 Shelf 20 July Shelf 21 July Shelf 21 July Shelf 21 July Slope 22 July Slope 23 July Slope 24 July Slope/Basin 26 July Basin 28 July East of Barrow 18 Slope/Basin 29 July Slope 31 July Slope 01 Aug Slope 02 Aug Slope 03 Aug Shelf 04 Aug Shelf 04 Aug East Hanna Shoals 25 Shelf 06 Aug Shelf 06 Aug Slope 07 Aug Slope 08 Aug Slope 09 Aug Slope/Basin 10 Aug Basin 11 Aug West Hanna Shoals 32 Basin 13 Aug Slope 14 Aug Slope 15 Aug Slope 16 Aug Slope 17 Aug Shelf 17 Aug Shelf 18 Aug Herald Valley 43 Shelf 19 Aug Average (Stations 8 24; region of Barrow Canyon and East of Barrow Canyon) 1065 NCP rates (mg C m 2 d 1 ) integrated over the upper 30 m were estimated for each station using the DIC change (compared to the average spring ndic of ) observed since springtime. The error estimates for NCP were calculated with the standard deviation of the spring ndic contents. Station 17 is the station furthest offshore. For stations along the East of Barrow (EB) section (stations 18 24), it is assumed that these waters originated west of Point Barrow either from the Chukchi Sea shelf or in the basin. Geostrophic flow along the shelf and shelf break was from west to east (Pickart et al., 2005). The salinity to which the DIC data was normalized did not significantly alter the NCP estimates. If a salinity of 33 was used to normalize DIC data, estimated rates of NCP had a mean difference of 19 mg Cm 2 d 1, within the error estimated below. diffusion processes, and the subsequent lateral transport of UHL from the shelf offshore into the basin. 4. Conclusions As part of the 2002 SBI project, spatio-temporal variability of DIC and rates of net community production (NCP) were determined for the Chukchi and western Beaufort Sea shelf and slope region, and adjacent Arctic Ocean basin. Between spring (5 May 15 June 2002) and summer (15 July 2 5 August 2002), high rates of phytoplankton production resulted in large drawdown of inorganic nutrients and DIC in the PML and in the shallow depths of the Upper Halocline Layer. The highest

19 N.R. Bates et al. / Deep-Sea Research II 52 (2005) Table 2 Comparison of previous primary productivity (PP z ) measurements (average values) and rates of NCP y determined for the 2002 SBI program in the Chukchi Sea shelf, slope and basin Location PP z or NCP y (mg C m 2 d 1 ) Reference Shelf 990 z Hameedi (1978) Shelf 748 z Cota et al. (1996) Shelf 2365 z Wheeler et al. (1996) Shelf 510 z Chen et al. (2002) Shelf 340 z Hill and Cota (2005) Shelf y This study Slope 406 z Hill and Cota (2005) Slope y This study Basin 5 z English (1961) Basin 123 z Cota et al. (1996) Basin 46 z Wheeler et al. (1996) Basin 45 z Chen et al. (2002) Basin 15 y This study Basin o20 25 y This study; adjusted for air sea CO 2 exchange Table 3 Annual rate of primary productivity (PP) or net community production (NCP) for 2002 in the Chukchi Sea assuming a growing season of 120 d Location PP z or NCP y (g C m 2 yr 1 ) Reference Shelf z Hill and Cota (2005) Shelf y This study Shelf 364 z Walsh et al., (2005) and 120 d, respectively. Much of the productivity occurring in this region of the Chukchi Sea shelf was vertically exported laterally, with plumes of suspended POM in the upper halocline observed offshelf extending into the Arctic Ocean basin (Bates et al., 2005a, b), or vertically exported to the sea floor (Moran et al., 2005). In the Arctic Ocean basin, very low inorganic nutrient concentrations and low rates of NCP (15 25 mg C m 2 d 1 ) confirm that this area is perennially oligotrophic, with rates of productivity closer to the low values of English (1961), Moran et al., (1997) and Anderson et al. (2003), rather than the higher estimates of Gosselin et al. (1997) and Pomeroy (1997). Acknowledgements Jackie Grebmeier and Lee Cooper are thanked for their dedicated contributions to the SBI program. We are also grateful to the captain, crew and all scientific participants on the two 2002 Healy cruises. Our thanks to Charlie Farmer (RSMAS), Cindy Miller (RSMAS), Christine Pequignet (BBSR) and Paul Lethaby (BBSR) for their participation in the field activities of SBI. Christine Pequignet and Julian Mitchell (BBSR) are thanked for their organization of pre-cruise and post-cruise logistics. Leif Anderson and an anonymous reviewer are thanked for their detailed and helpful comments. NSF Office of Polar Programs is thanked for the support of this research through Grant OPP Table 4 Total annual net community production (NCP) in the northeast region of the Chukchi Sea shelf. The area, delineated by dashed lines in Fig. 8 is km 2 Location NCP (g C yr 1 ) Growing season (d) Shelf Shelf rates of NCP ( mg C m 2 d 1 ) occurred on the shelf and slope regions in the Barrow Canyon region of the Chukchi Sea and East of Barrow in the western Beaufort Sea. In the northeast sector of the Chukchi Sea shelf, an annual rate of NCP of 9 and g was estimated for a growing season of 60 References Aagaard, K., Carmack, E.C., The Arctic Ocean and climate: a perspective. In: Johannessen, O.M., Muench, R.D., Overland, J.E. (Eds.), The Polar Oceans and Their Role in Shaping the Global Environment, American Geophysical Union, Geophysical Monograph 85, Aagaard, K., Coachman, L.K., Carmack, E.C., On the halocline of the Arctic Ocean. Deep-Sea Research 28, Aagaard, K., Swift, J.H., Carmack, E.C., Thermohaline circulation in the Arctic Mediterranean Sea. Journal of Geophysical Research 95, Aagaard, K., Woodgate, R.A., Weingartner, T., From Bering Strait to the Chukchi Shelf Break: chronology of the Pacific Throughflow, SBI Phase II Meeting, US Naval Postgraduate School, Monterey, California, March Anderson, L.G., Jones, E.P., Lindegren, R., Rudels, B., Sehlstedt, P.I., Nutrient regeneration in cold, high

20 3322 ARTICLE IN PRESS N.R. Bates et al. / Deep-Sea Research II 52 (2005) salinity bottom water of the Arctic shelves. Continental Shelf Research 8, Anderson, L.G., Olsson, K., Skoog, A., 1994a. Distribution of dissolved inorganic and organic carbon in the Eurasian basin of the Arctic Ocean. In: Polar Oceans and Their Role in Shaping the Global Environment, American Geophysical Unions, Geophysical Monograph 85, Anderson, L.G., Bjo rk, G., Holby, O., Jones, E.P., Kattner, G., Koltermann, K.P., Liljeblad, B., Lindegren, R., Rudels, B., Swift, J.H., 1994b. Water masses and circulation in the Eurasian basin: results from the Oden 91 Expedition. Journal of Geophysical Research 99 (C2), Anderson, L.G., Jones, E.P., Swift, J.H., Export production in the central Arctic Ocean evaluated by phosphate deficits. Journal of Geophysical Research 108, 3199 doi: /2001JC Ashjian, C.J., Gallager, S.M., Plourde, S., Transport of plankton and particles between the Chukchi and Beaufort Seas during Summer 2002, described using a video plankton recorder. Deep-Sea Research II, this issue [doi: / j.dsr ]. Bates, N.R., Interannual changes of oceanic CO 2 and biogeochemical properties in the Western North Atlantic subtropical gyre. Deep-Sea Research II 48 (8 9), Bates, N.R., Michaels, A.F., Knap, A.H., Seasonal and interannual variability of the oceanic carbon dioxide system at the US JGOFS Bermuda Atlantic Time-series Site. Deep- Sea Research II 43 (2 3), Bates, N.R., Hansell, D.A., Carlson, C.A., Gordon, L.I., Distribution of CO 2 species, estimates of net community production and air sea CO 2 exchange in the Ross Sea polynya. Journal of Geophysical Research 103 (C2), Bates, N.R., Pequignet, A.C., Johnson, R.J., Gruber, N., A short-term sink for atmospheric CO 2 in Subtropical Mode Water of the North Atlantic Ocean. Nature 420, Bates, N.R., Pequignet, A.C., Sabine, C.L., 2005a. Ocean carbon cycling in the Indian Ocean II. Estimates of net community production. Global Biogeochemical Cycles, in review. Bates, N.R., Hansell, D.A., Moran, S.B., Codispoti, L.A., 2005b. Seasonal and spatial distribution of particulate organic matter (POM) in the Chukchi and Beaufort Seas. Deep-Sea Research II, this issue [doi: /j.dsr ]. Chen, M., Huang, Y.P., Guo, L.D., Cai, P.H., Yang, W.F., Liu, G.S., Qiu, Y.S., Biological productivity and carbon cycling in the Arctic Ocean. Chinese Science Bulletin 47 (12), Chipman, D.W., Marra, J., Takahashi, T., Primary production at 471N and 201W in the North Atlantic Ocean: a comparison between the 14 C incubation method and the mixed layer carbon budget. Deep-Sea Research 40, Coachman, L.K., Aagaard, K., Tripp, R.B., Bering Strait: The Regional Physical Oceanography. University of Washington Press, Seattle, WA, 172pp. Codispoti, L.A., Friederich, G.E., Iverson, R.L., Hood, D.W., Temporal changes in the inorganic carbon system of the southeastern Bering Sea during spring Nature 296, Codispoti, L.A., Friederich, G.E., Hood, D.W., Variability in the inorganic carbon system over the southeastern Bering Sea shelf during spring 1980 and spring-summer Continental Shelf Research 5, Codispoti, L. Flagg, C., Kelly, V., Hydrographic conditions during the 2002 SBI process experiments. Deep-Sea Research II, this issue [doi: /j.dsr ]. Cota, G.F., Pomeroy, L.R., Harrison, W.G., Jones, E.P., Peters, F., Sheldon, W.M., Weingartner, T.R., Nutrients, primary production and microbial heterotrophy in the southeastern Chukchi Sea: Arctic summer nutrient depletion and heterotrophy. Marine Ecology Progress Series 135 (1 3), D Asaro, E.A., Morison, J.H., Internal waves and mixing in the Arctic Ocean. Deep Sea Research A39, S459 S484. Denman, K.L., Gargett, A.E., Time and space scales of vertical mixing and advection of phytoplankton in the upper ocean. Limnology and Oceanography 28, English, T.S., Some biological oceanographic observations in the central north Polar Sea, Drift Station Alpha, Arctic Institute of North America Scientific Report 15. Gosselin, M., Levasseur, M., Wheeler, P.A., Horner, R.A., Booth, B.C., New measurements of phytoplankton and ice algal production in the Arctic Ocean. Deep-Sea Research II 44, Gradinger, R., Eicken, H., Magnitude and control of sea ice algae in the Chukchi and Beaufort Seas in spring Session SS1.01. Abstract ID 882. ALSO/TOS SBI Special Session, Honolulu Hawaii, February Grebmeier, J.M., Whitledge, T.E., Arctic System Science: Ocean Atmosphere Ice Interactions Biological Initiative in the Arctic: Shelf Basin Interactions Workshop, ARCSS/ OAII Report Number 4, University of Washington, Seattle, 39pp. Grebmeier, J. M., Cooper, L. W., Codispoti, L. A., Benner, R., Benthic carbon cycling and nutrient exchange in the western Arctic Shelf Basin Interactions (SBI) study area. Session SS1.01. Abstract ID 774. ALSO/TOS SBI Special Session, Honolulu, Hawaii, February Hameedi, M.J., Aspects of water column primary productivity in Chukchi Sea during summer. Marine Biology 48 (1), Hansell, D.A., Whitledge, T.E., Goering, J.J., Patterns of nitrate utilization and new production over the Bering Chukchi shelf. Continental Shelf Research 13, Hill, V.J., Cota, G.F., Spatial patterns of primary production on the shelf, slope and basin of the Western Arctic in Deep-Sea Research II, this issue [doi: / j.dsr ]. Johnson, K.M., Wills, K.D., Butler, D.B., Johnson, W.K., Wong, C.S., Coulometric total carbon dioxide analysis for marine studies: maximizing the performance of an automated gas extraction system and coulometric detector. Marine Chemistry 44, Jones, E.P., Anderson, L.G., On the origin of chemical properties of the Arctic Ocean halocline. Journal of Geophysical Research 91, 10,759 10,767. Jones, E.P., Anderson, L.G., Wallace, D.W.R., Tracers of near-surface, halocline and deep waters in the Arctic Ocean: Implications for circulation. Journal of Marine Systems 2, Karl, D.M., Tilbrook, B.D., Tien, G., Seasonal coupling of organic matter production and particle flux in the western Bransfield Strait, Antarctica. Deep-Sea Research 38,