Northern Chukchi Sea Research Articles

The diatom distribution in the surface sediments of the Eastern Arctic seas of Russia

The distribution features of diatoms in the surface sediments of the Laptev, East Siberian, and Chukchi seas were studied. The sediment diatom content varied widely, being lowest in the East Siberian Sea and highest in the Chukchi Sea. Cluster analysis revealed several diatom assemblages in the surface sediments of the studied region; their distribution depended on the hydrological conditions. A benthic Amphora libyca assemblage, a freshwater Aulacoseira subarctica one, and a brackish-water Thalassiosira hyperborea assemblage were identified in the Laptev Sea. A cold-water Th. antarctica assemblage was distinguished in the eastern part of the East Siberian Sea and in the northern Chukchi Sea; a highly productive Chaetoceros assemblage was noted in the Herald Canyon area; a sublittoral Odontella aurita assemblage occurred in sandy sediments of the Herald Shoal; a Paralia sulcata assemblage, which is an indicator of low salinity waters, was found in the eastern Chukchi Sea near Alaska; and ”sea-ice” Th. nordenskioeldii and Fragillariopsis oceanica assemblages occurred in the southern Chukchi Sea.

Comparison of phytoplankton macromolecular compositions and zooplankton proximate compositions in the northern Chukchi Sea

The macromolecular (proteins, lipids, and carbohydrates) composition of phytoplankton and the proximate (water, proteins, lipids, and ash) and elemental (carbon and nitrogen) compositions of mesozooplankton were determined in the northern Chukchi Sea to establish the relationship between zooplankton and their phytoplankton food source. Among the phytoplankton macromolecules examined in this study, lipids had the highest contents (58.4±8.2%) and proteins had the lowest (16.1±7.3%), which may be a consequence of a nitrogen deficiency in phytoplankton growth during the study period. In contrast, proteins (59.7±10.6% DW) were the major proximate components in the mesozooplankton community, which was dominated by copepods up to 71% of total abundance. The low lipid contents (13.8±12.4% DW) in the mesozooplankton community in this study might be due to the dominance of small species such as Calanus glacialis, which generally have relatively lower lipid contents than large copepods. Moreover, the spawning period of C. glacialis from April to June might be an additional reason for the low lipid contents, because copepods have normally very low lipid contents after spawning. The low lipid contents resulted in a low energy content in this mesozooplankton community in the northern Chukchi Sea. The different biochemical compositions of phytoplankton and zooplankton should be considered in order to understand the impacts of climate change on the quality of prey provided by lower trophic levels and subsequently on Arctic marine ecosystems.

High lipid composition of particulate organic matter in the northern Chukchi Sea, 2011

We investigated the biochemical compositions (lipids, proteins, and carbohydrates) of particulate organic matter (POM) as a potential food source in the northern Chukchi Sea. We aimed to understand physiological status of phytoplankton, determine important controlling factors, and estimate the energetic contents of POM. The major inorganic nutrients were generally depleted at upper mixed-layer depth (>20m). The average chlorophyll a (chl-a) concentration was 31.9mgm−2 (S.D.=±31.3mgm−2) in this study, significantly higher than that reported previously in the northern Chukchi Sea. Small phytoplankton (0.7–5µm) accounted for 65.9% of total chl-a concentration. The overall average compositions of lipids, carbohydrates, and proteins were 50% (S.D.=±10.7%), 35% (S.D.=±11.0%), and 15% (S.D.=±11.2%) for POM, respectively. Along with other evidence (e.g., low N:P and protein–carbohydrate ratios), the high lipid and low protein compositions of POM in this study suggests that phytoplankton might have had a nitrogen limitation and/or stationary growth phase in the northern Chukchi Sea during the cruise period, 2011. The overall average calorific content of food material (FM) was 149.2μgL−1 (S.D.=±36.5μgL−1) or 1.0Kcalm−3 (S.D.=±0.2Kcalm−3). The relatively higher calorific contents in the northern Chukchi Sea were due to high lipid contributions and the considerably high calorific content of FM per POC.

Timing of sea ice retreat can alter phytoplankton community structure in the western Arctic Ocean

Abstract. This study assesses the response of phytoplankton assemblages to recent climate change, especially with regard to the shrinking of sea ice in the northern Chukchi Sea of the western Arctic Ocean. Distribution patterns of phytoplankton groups in the late summers of 2008–2010 were analysed based on HPLC pigment signatures and, the following four major algal groups were inferred via multiple regression and cluster analyses: prasinophytes, diatoms, haptophytes and dinoflagellates. A remarkable interannual difference in the distribution pattern of the groups was found in the northern basin area. Haptophytes dominated and dispersed widely in warm surface waters in 2008, whereas prasinophytes dominated in cold water in 2009 and 2010. A difference in the onset date of sea ice retreat was evident among years–the sea ice retreat in 2008 was 1–2 months earlier than in 2009 and 2010. The spatial distribution of early sea ice retreat matched the areas in which a shift in algal community composition was observed. Steel-Dwass's multiple comparison tests were used to assess the physical, chemical and biological parameters of the four clusters. We found a statistically significant difference in temperature between the haptophyte-dominated cluster and the other clusters, suggesting that the change in the phytoplankton communities was related to the earlier sea ice retreat in 2008 and the corollary increase in sea surface temperatures. Longer periods of open water during the summer, which are expected in the future, may affect food webs and biogeochemical cycles in the western Arctic due to shifts in phytoplankton community structure.

Connecting subsistence harvest and marine ecology: A cluster analysis of communities by fishing and hunting patterns

Alaska Native subsistence hunters and fishers are engaged in environmental sampling, influenced by harvest technology and cultural preferences as well as biogeographical factors. We compared subsistence harvest patterns in 35 communities along the Bering, Chukchi, and Beaufort coasts of Alaska to identify affinities and groupings, and to compare those results with previous ecological analyses done for the same region. We used hierarchical cluster analysis to reveal spatial patterns in subsistence harvest records of coastal Alaska Native villages from the southern Bering Sea to the Beaufort Sea. Three main clusters were identified, correlating strongly with geography. The main division separates coastal villages of western Alaska from arctic villages along the northern Chukchi and Beaufort Seas and on islands of the Bering Sea. K-means groupings corroborate this result, with some differences. The second node splits the arctic villages, along the Chukchi, Beaufort and northern Bering Seas, where marine mammals dominate the harvest, from those on islands of the Bering Sea, characterized by seabird and seal harvests. These patterns closely resemble eco-regions proposed on biological grounds. Biogeography thus appears to be a significant factor in groupings by harvest characteristics, suggesting that subsistence harvests are a viable form of ecosystem sampling.

Rates of nitrification and ammonium dynamics in northeastern Chukchi Sea shelf waters

Nutrient concentrations are often depleted in surface waters during the late summer open-water period in the northern Chukchi Sea. Yet the rate of re-supply of nutrients to the pelagic environment controls phytoplankton community abundance and productivity, which in turn influences the benthic components of this relatively shallow ecosystem. We measured nitrogen cycling rates at four experimental stations on the northeastern Chukchi Sea shelf in the western arctic. At each station, rates for net NH4+ regeneration, actual NH4+ uptake, and nitrification were measured using 15N isotope enrichment methods with 24-h bottle incubations under both light and dark conditions. Net NH4+ regeneration rates throughout the water column ranged between −0.25 and 0.23μmolNL−1h−1, with highest net positive regeneration occurring under light exposure in surface waters. Actual uptake rates ranged between −0.41 and −0.01μmolNL−1h−1. Nitrification rates (measured at two stations) were generally highest in the sediment overlying waters, ranging between 0.14 and 0.67μmolNL−1h−1, and appear to account for most NH4+ uptake. Calculations of turnover time indicate that N is recycled within one day throughout the water column under natural conditions in the northern Chukchi Sea. Our findings confirm the results of previous studies that suggest a significant portion of surface nutrients on the Chukchi Shelf are products of horizontal advection through the Anadyr Current but also highlight the role of sediment regenerated N in supporting water-column primary production.

Carbon contribution of sea ice floes in the Arctic Ocean

To estimate detailed contributions of particulate organic carbon (POC) as a potential food source in various environments of the Arctic sea ice floes, intensive investigations were executed at two different types of sea ice stations (ST 1 and ST 2) in the northern Chukchi Sea during the summer period in 2011. The average uptake rates of carbon and nitrogen in melt ponds from this study were within the range measured previously. The surface ice of melt ponds at ST 1 had the highest POC concentration with a mean of 148.0mgCm−3 (S.D.=±86.0mgCm−3), followed by sea ice cores at ST 2 (mean±S.D.=125.7±128.2mgCm−3). The POC concentrations in melt ponds ranged between 90.0mgCm−3 (S.D.=±12.7mgCm−3) and 103.9mgCm−3 (S.D.=±47.7mgCm−3) at ST 1 and ST 2, respectively. Major POC contributors to melt ponds were diatoms with a mean biovolume contribution of 48.7% (S.D.=±39.1%) which was strongly related to in situ salinity. Although the total POC concentration of entire sea ice floes ranged from 2.8% to 5.3% of the POC concentration within the euphotic water column at the study locations, the carbon contribution of sea ice floes could be important to higher trophic levels because of the concentrated POC within sea ice floes.

Severe winter weather as a response to the lowest Arctic sea-ice anomalies

Possible impact of reduced Arctic sea-ice on winter severe weather in China is investigated regarding the snowstorm over southern China in January 2008. The sea-ice conditions in the summer (July–September) and fall (September–November) of 2007 show that the sea-ice is the lowest that year. During the summer and fall of 2007, sea ice displayed a significant decrease in the East Siberian, the northern Chukchi Sea, the western Beaufort Sea, the Barents Sea, and the Kara Sea. A ECHAM5.4 atmospheric general circulation model is forced with realistic sea-ice conditions and strong thermal responses with warmer surface air temperature and higher-than-normal heat flux associated with the sea-ice anomalies are found. The model shows remote atmospheric responses over East Asia in January 2008, which result in severe snow storm over southern China. Strong water-vapor transported from the Bay of Bengal and from the Pacific Ocean related to Arctic sea-ice anomalies in the fall (instead of summer) of 2007 is considered as one of the main causes of the snowstorm formation.

Melt Pond Mapping With High-Resolution SAR: The First View

Melt pond statistics (size and shape) have previously been retrieved from aerial photography and high-resolution visible satellite data. These submeter- or meter-resolution visible data can provide reasonably accurate information on melt ponds, but are greatly constrained by the limited solar illumination and frequent cloud cover in the Arctic region. In this study, we venture into exploring high-resolution synthetic aperture radar (SAR) or imaging radar method for melt pond mapping, which is not severely disrupted by cloud or low solar zenith angle. We analyzed high-resolution airborne SAR images (0.3-m resolution) of midsummer sea ice, acquired from a helicopter-borne SAR system in the northern Chukchi Sea. The pond area and shape (circularity) derived from the airborne SAR images showed that the statistics were comparable to those previously observed from aerial photographs. We argue that high-resolution SAR, together with one-to-one comparison with coincident aerial photographs, can be used to map melt ponds at a level of detail comparable to aerial photography or high-resolution optical satellite remote sensing. Our encouraging results suggest the possibility of using high-resolution SAR (current or future systems) to map melt ponds in the Arctic region.

East–west asymmetry in surface mixed layer and ocean heat content in the Pacific sector of the Arctic Ocean derived from AMSR-E sea surface temperature

Deep (greater than 25m) and anomalously warm surface mixed layer (SML) has been evident in the Pacific sector of the Arctic Ocean since 2007. This warm SML contributes to the formation of maximum near surface temperature, which act as the sea-ice formation “inhibitor”, after freeze-up season. In this study, we attempt to estimate the ocean heat content (OHC) in the SML of the Pacific sector of the Arctic Ocean. The surface mixed layer depth (SMLD) and OHC from 2007 to 2010 were estimated from SST measured by the microwave radiometer AMSR-E and NCEP-derived net heat budget, based on the assumption that changes of heat content within SML can be explained by the air–sea heat exchange only.Estimated SMLD and OHC were well comparable with the in-situ CTD measurements, especially, in the western Canada Basin. SMLD greater than 25m (up to 40m) and OHC greater than 300MJ were estimated at southern Northwind Ridge area (73–75°N, 168–150°W), where the catastrophic reduction of sea ice has been reported, while less OHC was estimated at the eastern side of the Canada Basin. Although anomalous high SST has uniformly been captured over the northern Chukchi Sea and the Northwind Ridge area since 2007, our results indicate the nonuniformity of surface OHC distribution in the Canada Basin with relatively large amount in the Northwind Ridge area. Conversely, we can assume that the Northwind Ridge area is the plausible candidate for the Near Surface Temperature Maximum formation area. Recent thin ice condition is probably responsible for deepening SMLD, efficient ocean heat uptake, and delayed onset of sea ice formation in the Pacific sector of the Arctic Ocean. Our results also indicate oceanic horizontal or vertical heat flux along the sea ice edge, which will promote the suppression of sea ice growth during freeze-up season.

Organic sources and carbon sequestration in Holocene shelf sediments from the western Arctic Ocean

To quantify changes in organic carbon inputs and preservation, sediments from the Northern Chukchi Sea spanning the last 9000 years of the Holocene period were collected during the HOTRAX expedition and analyzed. The multi-proxy approach included molecular organic markers, bulk carbon and isotope measurements plus more recent approaches to terrestrial carbon estimation (the BIT index of Branched and Isoprenoid Tetraethers). The upper 1100 cm of the core, corresponding to the last 7.4 ka, showed a relatively stable total organic carbon content of 1.13–1.38% which decreased below 1100 cm to 0.6%. C:N ratios ranged from 8.4 to 10.83 over the Holocene time period examined. The distribution of n-alcohols and n-alkanes revealed major contributions from long-chain n-alcohols and n-alkanes while minimal contributions were seen from short-chain n-alkanes. The majority of the total fatty acids was comprised of saturated and monounsaturated fatty acids with short-chain and long-chain saturated fatty acids present in similar concentrations throughout most of the core and monounsaturated fatty acids decreasing down-core. Total sterol concentrations showed considerable inputs from marine sterols, C 28Δ 5,22, C 28Δ 5,24(28) and dinosterol, as well as C 29Δ 5, typically considered a terrestrial marker. The BIT indices for core sediments ranged from 0.021 to 0.216 with minor changes seen in older sequences. Overall, organic biomarkers indicate marine sources as the more dominant input of organic matter with lower but continual contributions from terrestrial sources at this location during the Holocene. The remarkable consistency among multiple molecular organic markers of both marine and terrestrial origin over the Holocene period encompassed by the core suggests that sinking material or surface sediments were heavily influenced by bottom currents or other mixing processes prior to their deposition.

Upwelling in the Alaskan Beaufort Sea: Atmospheric forcing and local versus non-local response

The spin up and relaxation of an autumn upwelling event on the Beaufort slope is investigated using a combination of oceanic and atmospheric data and numerical models. The event occurred in November 2002 and was driven by an Aleutian low storm. The wind field was strongly influenced by the pack-ice distribution, resulting in enhanced winds over the open water of the Chukchi Sea. Flow distortion due to the Brooks mountain range was also evident. Mooring observations east of Barrow Canyon show that the Beaufort shelfbreak jet reversed to the west under strong easterly winds, followed by upwelling of Atlantic Water onto the shelf. After the winds subsided a deep eastward jet of Atlantic Water developed, centered at 250 m depth. An idealized numerical model reproduces these results and suggests that the oceanic response to the local winds is modulated by a propagating signal from the western edge of the storm. The disparity in wave speeds between the sea surface height signal—traveling at the fast barotropic shelf wave speed—versus the interior density signal—traveling at the slow baroclinic wave speed—leads to the deep eastward jet. The broad-scale response to the storm over the Chukchi Sea is investigated using a regional numerical model. The strong gradient in windspeed at the ice edge results in convergence of the offshore Ekman transport, leading to the establishment of an anti-cyclonic gyre in the northern Chukchi Sea. Accordingly, the Chukchi shelfbreak jet accelerates to the east into the wind during the storm, and no upwelling occurs west of Barrow Canyon. Hence the storm response is fundamentally different on the Beaufort slope (upwelling) versus the Chukchi slope (no upwelling). The regional numerical model results are supported by additional mooring data in the Chukchi Sea.

Observations of internal wave generation in the seasonally ice‐free Arctic

The Arctic is generally considered a low energy ocean. Using mooring data from the northern Chukchi Sea, we confirm that this is mainly because of sea‐ice impeding input of wind energy into the ocean. When sea‐ice is present, even strong storms do not induce significant oceanic response. However, during ice‐free seasons, local storms drive strong inertial currents (>20 cm/s) that propagate throughout the water column and significantly deepen the surface mixed layer. The large vertical shear associated with summer inertial motions suggests a dominant role for localized and seasonal vertical mixing in Arctic Ocean dynamics. Our results imply that recent extensive summer sea‐ice retreat will lead to significantly increased internal wave generation especially over the shelves and also possibly over deep waters. This internal wave activity will likely dramatically increase upper‐layer mixing in large areas of the previously quiescent Arctic, with important ramifications for ecosystems and ocean dynamics.

Ocean acidification and biologically induced seasonality of carbonate mineral saturation states in the western Arctic Ocean

Calcium carbonate (CaCO3) mineral saturation states for aragonite (Ωaragonite) and calcite (Ωcalcite) are calculated for waters of the Chukchi Sea shelf and Canada Basin of the western Arctic Ocean during the Shelf‐Basin Interactions project from 2002 to 2004. On the Chukchi Sea shelf, a strong seasonality and vertical differentiation of aragonite and calcite saturation states was observed. During the summertime sea ice retreat period, high rates of phytoplankton primary production and net community production act to increase the Ωaragonite and Ωcalcite of surface waters, while subsurface waters become undersaturated with respect to aragonite due primarily to remineralization of organic matter to CO2. This seasonal “phytoplankton‐carbonate saturation state” interaction induces strong undersaturation of aragonite (Ωaragonite = <0.7–1) at ∼40–150 m depth in the northern Chukchi Sea and in the Canada Basin within upper halocline waters at ∼100–200 m depth. Patches of aragonite undersaturated surface water were also found in the Canada Basin resulting from significant sea ice melt contributions (>10%). The seasonal aragonite undersaturation of waters observed on the Chukchi Sea shelf is likely a recent phenomenon that results from the uptake of anthropogenic CO2 and subsequent ocean acidification, with seasonality of saturation states superimposed by biological processes. These undersaturated waters are potentially highly corrosive to calcifying benthic fauna (e.g., bivalves and echinoderms) found on the shelf, with implications for the food sources of large benthic feeding mammals (e.g., walrus, gray whales, and bearded seals). The benthic ecosystem of the Chukchi Sea (and other Arctic Ocean shelves) is thus potentially vulnerable to future ocean acidification and suppression of CaCO3 saturation states.

New insights into the spatial variability of the surface water carbon dioxide in varying sea ice conditions in the Arctic Ocean

In the summer of 2005, continuous surface water measurements of fugacity of CO 2 ( fCO 2 sw), salinity and temperature were performed onboard the IB Oden along the Northwest Passage from Cape Farwell (South Greenland) to the Chukchi Sea. The aim was to investigate the importance of sea ice and river runoff on the spatial variability of fCO 2 and the sea–air CO 2 fluxes in the Arctic Ocean. Additional data was obtained from measurements of total alkalinity ( A T) by discrete surface water and water column sampling in the Canadian Arctic Archipelago (CAA), on the Mackenzie shelf, and in the Bering Strait. The linear relationship between A T and salinity was used to evaluate and calculate the relative fractions of sea ice melt water and river runoff along the cruise track. High-frequency fCO 2 sw data showed rapid changes, due to variable sea ice conditions, freshwater addition, physical upwelling and biological processes. The fCO 2 sw varied between 102 and 678 μatm. Under the sea ice in the CAA and the northern Chukchi Sea, fCO 2 sw were largely CO 2 undersaturated of approximately 100 μatm lower than the atmospheric level. This suggested CO 2 uptake by biological production and limited sea–air CO 2 gas exchange due to the ice cover. In open areas, such as the relatively fresh water of the Mackenzie shelf and the Bering Strait, the fCO 2 sw values were close to the atmospheric CO 2 level. Upwelling of saline and relatively warm water at the Cape Bathurst caused a dramatic fCO 2 sw increase of about 100 μatm relative to the values in the CAA. At the southern part of the Chukchi Peninsula we found the highest fCO 2 sw values and the water was CO 2 supersaturated, likely due to upwelling. In the study area, the calculated sea–air CO 2 flux varied between an oceanic CO 2 sink of 140 mmol m −2 d −1 and an oceanic source of 18 mmol m −2 d −1. However, in the CAA and the northern Chukchi Sea, the sea ice cover prevented gas exchange, and the CO 2 fluxes were probably negligible at this time of the year. Assuming that the water was exposed to the atmosphere by total melting and gas exchange would be the only process, the CO 2 undersaturated water in the ice-covered areas will not have the time to reach the atmospheric CO 2 value, before the formation of new sea ice. This study highlights the value of using high-frequency measurements to gain increased insight into the variable and complex conditions, encountered on the shelves in the Arctic Ocean.

Chlorophyll Response to Shelf-Break Upwelling and Winds in the Chukchi Sea, Alaska, in Autumn

In the Chukchi Sea, autumn 1996 was windier than most of the previous 35 years. Conditions in the Bering Strait were anomalous, with fresh coastal water absent from the Strait and a partial flow reversal apparently occurring. In the central Chukchi Sea, the northeastward flow of the Alaskan Coastal Current was reversed. In the northern Chukchi Sea, upwelling of offshore, high-nutrient upper halocline waters inundated much of the shelf near Barrow Canyon. The resulting chlorophyll blooms indicate dramatically enhanced ecosystem productivity along this northern shelf region. With increasing climatic change occurring in this region, shelf break productivity would likely increase in the future.

Sea-ice-thickness variability in the Chukchi Sea, spring and summer 2002–2004

Abstract Measurements of sea-ice thickness were obtained from drill holes, an ice-based electromagnetic induction instrument (IEM), and a ship-borne electromagnetic induction instrument (SEM) during the early-melt season in the southern Chukchi Sea in 2002 and 2004, and in late summer 2003 at the time of minimum ice extent in the northern Chukchi Sea. An ice roughness criterion was applied to distinguish between level and rough or ridged ice. Ice-thickness modes in the probability density functions (PDFs) derived from drill-hole and IEM measurements agreed well, with modes at 1.5–1.6 and 1.8–1.9 m for all data from level ice. The PDFs derived from SEM measurements show that the primary modes are at 0.1 and 1.1 m in 2003 and 0.7 m in 2004. In 2002 and 2004, significant fractions (between one-third and one-half) of level ice were found to consist of rafted ice segments. Snow depth varied significantly between years, with 2004 data showing more than half the snow cover on level ice to be at or below 0.05 m depth in late spring. Ice growth simulations and examination of ice drift and deformation history indicate that impacts of atmospheric and oceanic warming on level-ice thickness in the region over the past few decades are masked to a large extent by variability in snow depth and the contribution of deformation processes. In comparison with submarine sonar ice-thickness data from previous decades, a reduction in ice thickness by about 0.5–1 m is in part explained by the replacement of multi-year with first-year ice over the Chukchi and Beaufort shelves.

Circulation and water mass transformation in a model of the Chukchi Sea

The circulation and water mass transformation in a regional ocean‐ice model of the Chukchi Sea are discussed. The model has horizontal resolution of O(4 km), is forced by fluxes derived from daily NCEP reanalysis fields, and has seasonally varying transport, temperature, and salinity imposed at Bering Strait. Many of the observed characteristics of the mean circulation and seasonal cycle in the Chukchi Sea are reproduced. The discussion focuses on: the branching of the inflow transport into pathways following Herald Canyon, Central Channel, and the Alaskan coast; the pattern of ice melt; and the water mass transformation and formation of winter water and hypersaline water. The ice melt pattern and timing is strongly influenced by advection through Bering Strait. High frequency forcing results in a larger region of ice melt, particularly over the shoals and in the northern Chukchi Sea, compared to monthly mean forcing. In the model, the seasonal cycle of salinity in the southern and central Chukchi Sea is dominated by advection through Bering Strait, while local atmospheric forcing and brine rejection are more important north of Herald and Hanna Shoals and in Barrow Canyon. However, since the residence time in the Chukchi Sea is generally less than 1 year, interannual variability in the Bering Strait salinity will be reflected in the salinity across the Chukchi Sea and at Barrow Canyon.

Nineteenth century commercial shipping losses in the northern Bering Sea, Chukchi Sea, and Beaufort Sea

Nineteenth century commercial shipping losses in the northern Bering Sea, Chukchi Sea, and Beaufort Sea

Seasonal and regional patterns in egg production of Calanus glacialis/marshallae in the Chukchi and Beaufort Seas during spring and summer, 2002

Understanding the physical and biogeochemical processes that control the exchange of biogenic carbon within and between the arctic shelves, slopes, and deep basins is a key objective of the Western Arctic Shelf-Basin Interaction program (SBI). Here, egg production (EP) of the dominant copepod Calanus glacialis/marshallae was used as an indicator of food limitation for the mesozooplankton community in the Chukchi and Beaufort Seas in spring and summer, 2002. Both C. glacialis and C. marshallae may occur in this region but the two cannot easily be differentiated visually. Four oceanographic regions were objectively identified that roughly corresponded to the different pathways in circulation of nutrient-rich Pacific water. A ‘transition’ region characterized by ‘older’ Pacific water was located at the shelfbreak and separated the nutrient-rich shelf water and the low-nutrient waters of the deep basin. The observed spatial pattern in EP in C. glacialis/marshallae in spring and summer resulted both from the different water mass environments and from the reproductive cycle of the species. EP was greater on the shelf than in the basin, corresponding to differences in body size and nitrogen condition factor (NCF) in females, while the egg viability was generally high throughout the study area. EP showed no relationship with low-chlorophyll a biomass under heavy ice-cover in spring, while a significant relationship was observed in the more open water in summer. Adult female carbon condition factor (CCF) was much higher in summer, reflecting the accumulation of lipids during the growth season. Small animals with a markedly greater NCF dominated on the shelf. The shelfbreak region contained a mixture of females from the shelf and the basin with intermediate sizes, conditions, and EP rates. The occurrence of water typical of the ‘transition’ shelfbreak region and elevated EP in C. glacialis/marshallae offshore on the Barrow Canyon and East Barrow sections indicated offshore transport of productive shelf water and the associated plankton community. The input of nutrient-rich Pacific water and accompanying elevated production to the northern Chukchi Sea and the Chukchi-Beaufort shelfbreak region may contribute to the reproductive success of C. glacialis/marshallae in this region.