Some characteristics of Yakutat Eddies propagating along the continental slope of the northern Gulf of Alaska

Data from array for real-time geostrophic oceanography (ARGO) profiling floats, oil tanker thermosalinographs, shipboard ADCP and towed-CTD surveys, and satellite altimetry are used to examine properties of two ∼200 km diameter, anticyclonic Yakutat Eddies that propagated westward at ∼1.5 km day⁻¹ along the continental slope of the northern Gulf of Alaska (GOA) in 2001 and 2003. The eddies had lifetimes of up to 5 years, remained close to the shelfbreak, and had relatively constant size and strength until they encountered the Alaskan Stream where they appeared to spawn smaller, shorter-lived anticyclones. The azimuthal velocity field was vigorous (25–40 cm s⁻¹) and in gradient wind balance with Rossby numbers of ∼0.05. Conservation of salt and azimuthal mass transports (between 20 m and the depth of the 32.2 isohaline) from shipboard surveys in May and August 2003 suggest little mass exchange occurred between the surface layers of the eddy and ambient waters. Chlorophyll concentrations were greater in the eddy than in ambient waters in both May and August. In May, the chlorophyll was patchily distributed, while in August dense chlorophyll concentrations occurred in and beneath the seasonal thermocline within 50 km of the eddy center. The high August chlorophyll concentrations might have been fostered by a broad and shallow (<∼150 m) upwelling of the eddy center between May and August.It appears likely that as Yakutat Eddies approach the shelfbreak non-linear processes will modify the slope flow field (and the stability and structure of the shelfbreak front), leading to cross-slope flows and flow reversals. This interaction may induce ∼30 km-wide streamers of shelf water to flow around the trailing edge of the anticyclone. The role of streamers in the freshwater and nutrient budgets of the GOA shelf and basin is unknown, but their contribution to these budgets will depend on the trajectory of a Yakutat Eddy, especially its proximity to the shelfbreak as the eddy propagates along the GOA continental slope.     

Mesozooplankton prey preference and grazing impact in the western Arctic Ocean

The role of mesozooplankton as consumers and transformers of primary and secondary production in the Beaufort and Chukchi Seas was examined during four cruises in spring and summer of both 2002 and 2004 as part of the western Arctic Shelf–Basin Interactions (SBI) program. Forty-seven grazing experiments using dominant mesozooplankton species and life stages were conducted at locations across the shelf, slope, and basin of the Chukchi and Beaufort Seas to measure feeding rates on both chlorophyll and microzooplankton and to determine mesozooplankton prey preferences.Mesozooplankton biomass was at all times dominated by life stages of four copepod taxa: Calanus glacialis, Calanus hyperboreus, Metridia longa, and Pseudocalanus spp. Significant interannual, seasonal, regional, between species and within species differences in grazing rates were observed. Overall, the dominant zooplankton exhibited typical feeding behavior in response to chlorophyll concentration that could be modeled using species and life-stage specific Ivlev functions. Microzooplankton were preferred prey at almost all times, with the strength of the preference positively related to the proportion of microzooplankton prey availability. Average mesozooplankton grazing impacts on both chlorophyll standing stock (0.6±0.5% d⁻¹ in spring, 5.1±6.3% d⁻¹ in summer) and primary production (12.8±11.8% d⁻¹ in spring, 27.6±24.5% d⁻¹ in summer) were quite low and varied between shelf, slope, and basin. Coincident microzooplankton grazing experiments [Sherr, E.B., Sherr, B.F., Hartz, A.J., 2009. Microzooplankton grazing impact in the Western Arctic Ocean. Deep-Sea Research II] were conducted at most stations. Together, microzooplankton–mesozooplankton grazing consumed only 44% of the total water-column primary production, leaving more than half directly available for local export to the benthos or for offshore transport into the adjacent basin.     

Net community production in the northeastern Chukchi Sea

To assess the magnitude, distribution and fate of net community production (NCP) in the Chukchi Sea, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), and particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured during the spring and summer of 2004 and compared to similar observations taken in 2002. Distinctive differences in hydrographic conditions were observed between these two years, allowing us to consider several factors that could impact NCP and carbon cycling in both the Chukchi Shelf and the adjacent Canada Basin. Between the spring and summer cruises high rates of phytoplankton production over the Chukchi shelf resulted in a significant drawdown of DIC in the mixed layer and the associated production of DOC/N and POC/N. As in 2002, the highest rates of NCP occurred over the northeastern part of the Chukchi shelf near the head of Barrow Canyon, which has historically been a hotspot for biological activity in the region. However, in 2004, rates of NCP over most of the northeastern shelf were similar and in some cases higher than rates observed in 2002. This was unexpected due to a greater influence of low-nutrient waters from the Alaskan Coastal Current in 2004, which should have suppressed rates of NCP compared to 2002. Between spring and summer of 2004, normalized concentrations of DIC in the mixed layer decreased by as much as 280 μmol kg⁻¹, while DOC and DON increased by ∼16 and 9 μmol kg⁻¹, respectively. Given the decreased availability of inorganic nutrients in 2004, rates of NCP could be attributed to increased light penetration, which may have allowed phytoplankton to increase utilization of nutrients deeper in the water column. In addition, there was a rapid and extensive retreat of the ice cover in summer 2004 with warmer temperatures in the mixed layer that could have enhanced NCP. Estimates of NCP near the head of Barrow Canyon in 2004 were ∼1500 mg carbon (C) m⁻² d⁻¹ which was ∼400 mg C m⁻² d⁻¹ higher than the same location in 2002. Estimates of NCP over the shelf-break and deep Canada Basin were low in both years, confirming that there is little primary production in the interior of the western Arctic Ocean due to near-zero concentrations of inorganic nitrate in the mixed layer.     

Arctic ocean shelf–basin interaction: An active continental shelf CO2 pump and its impact on the degree of calcium carbonate solubility

The Arctic Ocean has wide shelf areas with extensive biological activity including a high primary productivity and an active microbial loop within the surface sediment. This in combination with brine production during sea ice formation result in the decay products exiting from the shelf into the deep basin typically at a depth of about 150 m and over a wide salinity range centered around S ～33. We present data from the Beringia cruise in 2005 along a section in the Canada Basin from the continental margin north of Alaska towards the north and from the International Siberian Shelf Study in 2008 (ISSS-08) to illustrate the impact of these processes. The water rich in decay products, nutrients and dissolved inorganic carbon (DIC), exits the shelf not only from the Chukchi Sea, as has been shown earlier, but also from the East Siberian Sea. The excess of DIC found in the Canada Basin in a depth range of about 50–250 m amounts to 90±40 g C m^?2. If this excess is integrated over the whole Canadian Basin the excess equals 320±140×10¹² g C. The high DIC concentration layer also has low pH and consequently a low degree of calcium carbonate saturation, with minimum aragonite values of 60% saturation and calcite values just below saturation. The mean age of the waters in the top 300 m was calculated using the transit time distribution method. By applying a future exponential increase of atmospheric CO₂ the invasion of anthropogenic carbon into these waters will result in an under-saturated surface water with respect to aragonite by the year 2050, even without any freshening caused by melting sea ice or increased river discharge.     

Observations on the Rim Current structure,CIW formation and transport in the western Black Sea

CTD and ADCP measurements together with a sequence of satellite images indicate pronounced current meandering and eddy activity in the western Black Sea during April 1993. The Rim Current is identified as a well-defined meandering jet stream confined over the steepest topographic slope and associated cyclonic–anticyclonic eddy pairs located on both its sides. It has a form of highly energetic and unstable flow system, which, as it propagates cyclonically along the periphery of the basin, is modified in character. It possesses a two-layer vertical structure with uniform upper layer speed in excess of 50 cm/s (maximum value ∼100 cm/s), followed by a relatively sharp change across the pycnocline (between 100 and 200 m) and the uniform sub-pycnocline currents of 20 cm/s (maximum value ∼40 cm/s) observed up to the depth of ∼350 dbar, being the approximate limit of ADCP measurements. The cross-stream velocity structure exhibits a narrow core region (∼30 km), flanked by a narrow zone of anticyclonic shear on its coastal side and a broader region of cyclonic shear on its offshore side. The northwestern shelf circulation is generally decoupled from the influence of the basinwide circulation and is characterized by much weaker currents, less than 10 cm/s. The southward coastal flow associated with the Danube and Dinepr Rivers is weak during the measurement period and is restricted to a very narrow coastal zone.The data suggest the presence of temperature-induced overturning prior to the measurements, and subsequent formation of the Cold Intermediate Water mass (CIW) within the Northwestern Shelf (NWS) and interior of the western basin. The newly formed shelf CIW is transported in part along the shelf by the coastal current system, and in part it flows downslope across the shelf and intrudes into the Rim Current convergence zone. A major part of the cold water mass, however, seems to be trapped within the northwestern shelf. The CIW mass, injected into the Rim Current zone from the shelf and the interior region, is then circulated around the basin.     

210Pb as a tracer of shelf–basin transport and sediment focusing in the Chukchi Sea

Activities of dissolved, particulate, and sedimentary ²¹⁰Pb were measured in the shelf-slope region of the Chukchi Sea. Samples were collected as part of the Shelf–Basin Interactions (SBI) Phase II process study (6 May–15 June, 2002) along three shelf–basin transects identified as West Hanna Shoal, East Hanna Shoal, and Barrow Canyon. Distributions of ²¹⁰Pb and suspended particulate matter indicate efficient removal of ²¹⁰Pb over the shelf by particle scavenging. Low ²¹⁰Pb activities measured throughout the halocline of the Canada Basin are attributed to shelf scavenging and subsequent advective transport into the interior basin. Additionally, ²¹⁰Pb inventories were used to construct a water-column-sediment budget of ²¹⁰Pb and determine regions of particle export and deposition on the continental shelf and slope. Sediment focusing calculated with this ²¹⁰Pb budget was observed throughout the shelf-slope region, particularly in shallow (∼100 m) shelf waters at Barrow Canyon. Despite elevated concentrations of suspended particulate matter in Barrow Canyon, the ²¹⁰Pb budget does not indicate that sediment transport occurred from the West and East Hanna Shoals into Barrow Canyon.     

Zooplankton distribution across Fram Strait in autumn: Are small copepods and protozooplankton important?

We investigated zooplankton distribution in September 2006/2007 at eight stations across Fram Strait in contrasting water masses ranging from cold Polar water to warm Atlantic water. Our main objectives were: (1) to describe the plankton community in the upper 200 m during autumn, and (2) to investigate the importance of small-sized copepods and protozooplankton in an arctic ecosystem when the majority of the large Calanus species had entered diapause. We sampled both with a WP-2 net and Go-Flo bottle and show that small copepods <1 mm are significantly undersampled using a WP-2 net with 90 μm mesh.Small copepods and protozooplankton made a significant contribution both in terms of abundance and total zooplankton biomass at all stations in September, when the large calanoid copepods had left the upper 200 m. The dominating group in the upper 60 m at all stations was Oithona spp. nauplii and their daily estimated grazing potential on the <10 μm phytoplankton ranged from 0.1% to 82% of the standing stock. Both Oithona copepodites and nauplii biomass showed a significantly positive relation with temperature, but not with potential food. Heterotrophic protozooplankton, on the other hand, were most likely bottom-up regulated by the availability of phytoplankton <10 μm. We hypothesise that Oithona nauplii and protozooplankton compete for food and conclude that there was a strong link between the zooplankton community and the microbial food web in Fram Strait.     

Phytoplankton of the western Arctic in the spring and summer of 2002: Structure and seasonal changes

We analyzed the taxonomic structure and spatial variability of phytoplankton abundance and biomass in the Chukchi and Beaufort Seas during spring and summer seasons of the SBI program. Phytoplankton samples were collected during two surveys from May 10 to June 13 and from July 19 to August 21 of 2002. In May and June, ice cover exceeded 80% over most of the study area and there was no vertical stratification, indicating that the successional state of the phytoplankton corresponded to the end of the winter biological season. The phytoplankton abundance ranged from a few tens to a few thousands of cells per liter, while biomass varied from 0.1 to 3.0 mg C m⁻³. Small areas of high phytoplankton abundance (0.13–1.3×10⁶ cells L⁻¹) and biomass (22–536 mg C m⁻³), dominated by early spring diatoms Pauliella taeniata and Fragilariopsis oceanica in the surface waters, which indicated the beginning of the spring bloom, were observed only in the southeastern part of the Chukchi shelf and off Point Barrow. In July and August summer period, more than a half of the study area had <50% ice cover and the water column was stratified by temperature and salinity. Over the Chukchi shelf and continental slope of the Beaufort Sea, the phytoplankton abundance and biomass were an order of magnitude higher in July–August than in May–June. The taxonomic diversity of algae also increased due to the appearance of late-spring and summer diatoms, dinoflagellates, and coccolithophorids (Emiliania huxleyi). Interestingly, the seasonal differences between phytoplankton abundance and taxonomic composition in the spring and summer periods varied the least over the Chukchi Sea slope and in the deep-water area of the Arctic Ocean. High algae concentrations in summer were located in the lower layers of the euphotic zone, suggesting that the spring bloom on both the Chukchi shelf and in the western part of the Beaufort Sea occurred in late June/early July. In the spring and summer, the microalgal community was characterized by a high abundance of 4–10 μm flagellates, which exceeded the abundance of all other taxonomic groups. In both seasons studied, phytoplankton reached its maximum abundance within restricted areas in the southern part of the Chukchi Sea southwest of Point Hope, in the northern part of the Chukchi shelf between the 50- and 100-m isobaths, on the shelf northwest of Point Barrow, and over the continental slope in the Beaufort Sea. The pronounced spatial difference in the seasonal state was a characteristic feature of the phytoplankton community in the western Arctic.     

Effects of mesoscale phytoplankton variability on the copepods Neocalanus flemingeri and N. plumchrus in the coastal Gulf of Alaska

The copepods Neocalanus flemingeri and N. plumchrus are major components of the mesozooplankton on the shelf of the Gulf of Alaska, where they feed, grow and develop during April–June, the period encompassing the spring phytoplankton bloom. Satellite imagery indicates high mesoscale variability in phytoplankton concentration during this time. Because copepod ingestion is related to food concentration, we hypothesized that phytoplankton ingestion by N. flemingeri and N. plumchrus would vary in response to mesoscale variability of phytoplankton. We proposed that copepods on the inner shelf, where the phytoplankton bloom is most pronounced, would be larger and have more lipid stores than animals collected from the outer shelf, where phytoplankton concentrations are typically low. Shipboard feeding experiments with both copepods were done in spring of 2001 and 2003 using natural water as food medium. Chlorophyll concentration ranged widely, between 0.32 and 11.44 μg l⁻¹ and ingestion rates varied accordingly, between 6.0 and 627.0 ng chl cop⁻¹ d⁻¹. At chlorophyll concentrations<0.50 μg l⁻¹, ingestion is always low, <40 ng cop⁻¹ d⁻¹. Intermediate ingestion rates were observed at chlorophyll concentrations between 0.5 and 1.5 μg l⁻¹, and maximum rates at chlorophyll concentrations>1.5 μg l⁻¹. Application of these feeding rates to the phytoplankton distribution on the shelf allowed locations and time periods of low, intermediate and high daily feeding to be calculated for 2001 and 2003. A detailed cross-shelf survey of body size and lipid store in these copepods, however, indicated they were indistinguishable regardless of collection site. Although the daily ingestion of phytoplankton by N. flemingeri and N. plumchrus varied widely because of mesoscale variability in phytoplankton, these daily differences did not result in differences in final body size or lipid storage of these copepods. These copepods efficiently dealt with small and mesoscale variations in their food environment such that mesoscale structure in phytoplankton did not affect their final body size.     

Transport of plankton and particles between the Chukchi and Beaufort Seas during summer 2002, described using a Video Plankton Recorder

A key goal of the Western Arctic Shelf Basin Interactions program is to understand how physical and biological processes together impact shelf–basin exchange of biological, chemical, and physical properties. High-resolution vertical distributions of plankton and particles were obtained using an Auto Video Plankton Recorder from 29 locations on the Chukchi Shelf, in the deep Beaufort Sea, and across the Beaufort–Chukchi Shelf-break during a cruise on the USCGC Healy in July–August, 2002. Coincident velocity estimates were collected using hull-mounted acoustic Doppler current profilers. Images of plankton and particles were extracted automatically and identified manually to taxa and type. Copepods, diatom chains, decaying diatoms, marine snow, and radiolarians were the most abundant categories observed. Distinct regional differences in abundance were observed that were associated with different oceanographic regimes and with the prevailing circulation in the region. Vertical distributions were closely associated with the physical structure of the water column. A sharp horizontal discontinuity in abundance of all categories between shelf and basin was observed, located over the shelf break and potentially established and maintained by transport of plankton and particles along-shelf to the east rather than northwards towards the basin. Barrow Canyon and the shelf and shelf-break east of Barrow Canyon had very high concentrations of plankton and particles, especially marine snow, that may have resulted from elevated production on the eastern Chukchi Shelf that subsequently was advected out of Barrow Canyon and to the east. Comparisons of downward flux, estimated from particle sinking rates based on individual marine snow particle size, and horizontal velocities suggested that much of the marine snow carbon was sinking to the benthos of the Chukchi Sea prior to being advected off-shelf. Velocities and plankton concentrations together indicated that little off-shelf flux of plankton or particles to the basin was occurring except in an eddy located off of the Beaufort Shelf.     

Rapid removal of terrigenous dissolved organic carbon over the Eurasian shelves of the Arctic Ocean

The fate of terrigenous dissolved organic carbon (tDOC) delivered to the Arctic Ocean by rivers remains poorly constrained on both spatial and temporal scales. Early reports suggested Arctic tDOC was refractory to degradation, while recent studies have shown tDOC removal to be an active but slow process. Here we present observations of DOC, salinity, δ¹⁸O, and ²²⁸Ra/²²⁶Ra in the Polar Surface Layer (PSL) over the outer East Siberian/Chukchi shelf and the adjacent Makarov and Eurasian basins of the eastern Arctic Ocean. This off-shelf system receives meteoric water, introduced by rivers, after a few years residence on the shelf. Elevated concentrations of DOC (> 120 μM C) were observed in low salinity (~ 27) water over the Makarov Basin, suggesting inputs of tDOC-enriched river water to the source waters of the Transpolar Drift. The regression of DOC against salinity indicated an apparent tDOC concentration of 315 ± 7 μM C in the river water fraction, which is significantly lower than the estimated DOC concentration in the riverine sources to the region (724 ± 55 μM C). To obtain the timescale of removal, estimates of shelf residence were coupled with measurements of dissolved ²²⁸Ra/²²⁶Ra, an isotopic tracer of time since shelf residence. Shelf residence time coupled with DOC distributions indicates a first order tDOC removal rate constant, λ = 0.24 ± 0.07 yr^-1, for the eastern Arctic, 2.5–4 times higher than rates previously observed in the western Arctic. The observed removal of tDOC in the eastern Arctic occurs over the expansive shelf area, highlighting the initial lability of tDOC upon delivery to the Arctic Ocean, and suggests that tDOC is composed of multiple compartments defined by reactivity. The relatively rapid remineralization of tDOC on the shelves may mitigate the strength of the Arctic Ocean atmospheric CO₂ sink if a projected increase in labile tDOC flux occurs.     

Mesoscale distribution and advection of overwintering Calanus finmarchicus off the shelf of northern Norway

Data collected on a cruise in January 2008, using a laser optical plankton counter, conductivity–temperature–depth sensors, and a lowered acoustic Doppler current profiler, was used to study the mesoscale distribution and advection of overwintering Calanus finmarchicus in its deep water winter habitat off the shelf of northern Norway. The overwintering animals were generally located immediately below the Atlantic Water (AW) in Arctic Intermediate Water (AIW), in the 600–1200 m depth range. The depth of the interface between AW and AIW varied considerably in the area and this was clearly reflected in the C. finmarchicus distribution. Maximum abundance varied from about 80 ind m^?3 to more than 200 ind m^?3 at the different stations. Current measurements showed the richness of mesoscazle eddies, with speeds exceeding 70 cm s^?1 at the surface and rapidly decreasing with depth. In the main overwintering layer the eddy features were also clearly seen, but with speeds generally below 20 cm s^?1. C. finmarchicus were found in the whole survey area, but they were not homogeneously distributed. Advection of the copepods resulted in relatively high local rates of change in overwintering C. finmarchicus abundance with mean value of 8% per day in the area. It is clear that mesoscale physical processes greatly contribute to the variability in the abundance of overwintering C. finmarchicus off the shelf of northern Norway. The collected data are also a valuable addition to the generally sparse datasets on the C. finmarchicus winter distribution and the role of the Lofoten basin in the large scale system is also discussed.     

2003年夏季西北冰洋浮游动物群落结构和地理分布研究

根据西北冰洋43个调查站位的浮游动物种类组成和数量资料,分析了浮游动物的群落结构和地理分布特征,探讨了浮游动物群落与环境因子的关系.结果表明,在调查区域存在三种不同的浮游动物群落类型:楚科奇海台和加拿大海盆地区的高纬度深海群落;楚科奇海中部的陆架群落;阿拉斯加沿岸和楚科奇海北部的沿岸过渡群落.深海群落浮游动物数量较少,...     

Sea-ice algae: Major contributors to primary production and algal biomass in the Chukchi and Beaufort Seas during May/June 2002

Sea-ice and water samples were collected at 14 stations on the shelves and slope regions of the Chukchi and Beaufort Seas during the spring 2002 expedition as part of the Shelf–Basin Interaction Studies. Algal pigment content, particulate organic carbon and nitrogen, and primary productivity were estimated for both habitats based on ice cores, brine collection and water samples from 5-m depth. The pigment content (0.2–304.3 mg pigments m⁻²) and primary productivity (0.1–23.0 mg C m⁻³ h⁻¹) of the sea-ice algae significantly exceeded water-column parameters (0.2 and 1.0 mg pigments m⁻³; <0.1–0.4 mg C m⁻³ h⁻¹), making sea ice the habitat with the highest food availability for herbivores in early spring in the Chukchi and Beaufort Seas. Stable isotope signatures for ice and water samples did not differ significantly for δ¹⁵N, but for δ¹³C (ice: −25.1‰ to −14.2‰; water: −26.1‰ to −22.4‰). The analysis of nutrient concentrations and the pulse-amplitude-modulated fluorescence signal of ice algae and phytoplankton indicate that nutrients were the prime limiting factor for sea-ice algal productivity. The estimated spring primary production of about 1–2 g C m⁻² of sea-ice algae on the shelves requires the use of substantial nutrient reservoirs from the water column.     

Mesoscale physical variability affects zooplankton production in the Labrador Sea

Surface distribution (0–100 m) of zooplankton biomass and specific aminoacyl-tRNA synthetases (AARS) activity, as a proxy of structural growth, were assessed during winter 2002 and spring 2004 in the Labrador Sea. Two fronts formed by strong boundary currents, several anticyclonic eddies and a cyclonic eddy were studied. The spatial contrasts observed in seawater temperature, salinity and fluorescence, associated with those mesoscale structures, affected the distributions of both zooplankton biomass and specific AARS activity, particularly those of the smaller individuals. Production rates of large organisms (200–1000 μm) were significantly related to microzooplankton biomass (63–200 μm), suggesting a cascade effect from hydrography through microzooplankton to large zooplankton. Water masses defined the biomass distribution of the three dominant species: Calanus glacialis was restricted to cold waters on the shelves while Calanus hyperboreus and Calanus finmarchicus were widespread from Canada to Greenland. Zooplankton production was up to ten-fold higher inside anticyclonic eddies than in the surrounding waters. The recent warming tendency observed in the Labrador Sea will likely generate weaker convection and less energetic mesoscale eddies. This may lead to a decrease in zooplankton growth and production in the Labrador basin.     

Microzooplankton grazing impact in the Western Arctic Ocean

Microzooplankton grazing impact on phytoplankton was assessed using the Landry–Hassett dilution technique in the Western Arctic Ocean during spring and summer 2002 and 2004. Forty experiments were completed in a region encompassing productive shelf regions of the Chukchi Sea, mesotrophic slope regions of the Beaufort Sea off the North Slope of Alaska, and oligotrophic deep-water sites in the Canada Basin. A variety of conditions were encountered, from heavy sea-ice cover during both spring cruises, moderate sea-ice cover during summer of 2002, and light to no sea ice during summer of 2004, with a concomitant range of trophic conditions, from low chlorophyll-a (Chl-a; <0.5 μg L⁻¹) during heavy ice cover in spring and in the open basin, to late spring and summer shelf and slope open-water diatom blooms with Chl-a >5 μg L⁻¹. The microzooplankton community was dominated by large naked ciliates and heterotrophic gymnodinoid dinoflagellates. Significant, but low, rates of microzooplankton herbivory were found in half of the experiments. The maximum grazing rate was 0.16 d⁻¹ and average grazing rate, including experiments with no significant grazing, was 0.04±0.06 d⁻¹. Phytoplankton intrinsic growth rates varied from the highest values of about 0.4 d⁻¹ to the lowest values of zero to slightly negative growth, on average 0.16±0.15 d⁻¹. Light limitation in spring and post-bloom senescence during summer were likely explanations of observed low phytoplankton growth rates. Microzooplankton grazing consumed 0–120% (average 22±26%) of phytoplankton daily growth. Grazing and growth rates found in this study were low compared to rates reported in another Arctic system, the Barents Sea, and in major geographic regions of the world ocean.     

Diel variations of the bathymetric distribution of zooplankton groups and biomass in Cap-Ferret Canyon,France

The bathymetric distribution, abundance and diel vertical migrations (DVM) of zooplankton were investigated along the axis of the Cap-Ferret Canyon (Bay of Biscay, French Atlantic coast) by a consecutive series of synchronous net hauls that sampled the whole water column (0–2000 m in depth) during a diel cycle. The distribution of appendicularians (maximum 189 individuals m⁻³), cladocerans (maximum 287 individuals m⁻³), copepods (copepods<4 mm, maximum 773 individuals m⁻³, copepods>4 mm, maximum 13 individuals m⁻³), ostracods (maximum 8 individuals m⁻³), siphonophores (maximum >2 individuals m⁻³) and peracarids (maximum >600 individuals 1000 m⁻³) were analysed and represented by isoline diagrams. The biomass of total zooplankton (maximum 18419 μg C m⁻³, 3780 μg N m⁻³) and large copepods (>4 mm maximum 2256 μg C m⁻³, 425 μg N m⁻³) also were determined. Vertical migration was absent or affected only the epipelagic zone for appendicularians, cladocerans, small copepods and siphonophores. Average amplitude of vertical migration was about 400–500 m for ostracods, some hyperiids and mysids, and large copepods, which were often present in the epipelagic, mesopelagic, and bathypelagic zones. Large copepods can constitute more than 80% of the biomass corresponding to total zooplankton. They may play an important role in the active vertical transfer of carbon and nitrogen.     

The western Arctic boundary current at 152°W: Structure,variability, and transport

From August 2002 to September 2004 a high-resolution mooring array was maintained across the western Arctic boundary current in the Beaufort Sea north of Alaska. The array consisted of profiling instrumentation, providing a timeseries of vertical sections of the current. Here we present the first-year velocity measurements, with emphasis on the Pacific water component of the current. The mean flow is characterized as a bottom-intensified jet of O (15 cm s⁻¹) directed to the east, trapped to the shelfbreak near 100 m depth. Its width scale is only 10–15 km. Seasonally the flow has distinct configurations. During summer it becomes surface-intensified as it advects buoyant Alaskan Coastal water. In fall and winter the current often reverses (flows westward) under upwelling-favorable winds. Between the storms, as the eastward flow re-establishes, the current develops a deep extension to depths exceeding 700 m. In spring the bottom-trapped flow advects winter-transformed Pacific water emanating from the Chukchi Sea. The year-long mean volume transport of Pacific water is 0.13±0.08 Sv to the east, which is less than 20% of the long-term mean Bering Strait inflow. This implies that most of the Pacific water entering the Arctic goes elsewhere, contrary to expected dynamics and previous modeling results. Possible reasons for this are discussed. The mean Atlantic water transport (to 800 m depth) is 0.047±0.026 Sv, also smaller than anticipated.     

Metazoan meiofauna within the oxygen-minimum zone off Chile: Results of the 2001-PUCK expedition

A quantitative study of metazoan meiofauna was carried out at continental shelf and slope stations affected by the oxygen-minimum zone in the eastern South Pacific off Chile. Densities of meiobenthos at the investigated stations off Antofagasta (22°S), Concepción (36°S), and Chiloé (42°S) ranged from 1282.1 to 8847.8 ind 10 cm⁻². Oxygen deficiency led only to average abundances, despite higher food availability and freshness at the corresponding sites. Sediment organic carbon, chlorophyll-a, and phaeopigment contents were used as measures of the input from water-column primary production, which accumulated at the oxygen-minimum zone stations. The highest abundances were found at a station with an oxygen content of 0.79 mL L⁻¹, which was slightly elevated from what is defined as oxygen minimum (0.5 mL L⁻¹). The most oxygenated site yielded the lowest densities. Meiofauna assemblages became more diverse with increasing bottom-water oxygenation, whereas nematodes were the most abundant taxon at every station, followed by annelids, copepods, and nauplii.