Northeastern Bering Sea Research Articles

Spatiotemporal Distribution of Nitrous Oxide on the Northeastern Bering Sea Shelf

Rapid warming and loss of sea ice in the Arctic Ocean could play an important role in the dissolution and emission of greenhouse gas nitrous oxide (N2O). We investigated dissolved N2O in spatiotemporal distribution on the northeastern Bering Sea shelf (NEBS) in the summer of 2012. The results showed that N2O concentrations were higher in the Chirikov Basin (mean ± SD, 14.8 ± 2.4 nmol/L) than in the south of St. Lawrence Island (mean ± SD, 17.7 ± 2.3 nmol/L). In the Chirikov Basin, N2O displayed a decreasing distribution pattern from west (~20.4 nmol/L) to east (~12.9 nmol/L). In the area south of St. Lawrence Island, N2O almost presented a two-layer structure, although it showed a vertically homogeneous distribution in the inner shelf. In the cold bottom water, the N2O was affected mainly by in situ production or sediment emission. Longer resident time may cause N2O accumulation in the cold bottom water. The calculated sea–air flux (−1.6~36.2 μmol/(m2·d)) indicates that the NEBS is an important potential source of atmospheric N2O and could play an important role in global oceanic N2O emission with intensifying global issues.

The zonal North Pacific Oscillation: a high-impact atmospheric teleconnection pattern influencing the North Pacific and North America

Based on unfiltered daily Japanese 55 year reanalysis covering the 60 winters in 1958–2018, a new teleconnection pattern called the zonal North Pacific Oscillation (ZNPO) pattern has been detected. The ZNPO pattern describes a mass oscillation in the troposphere between the eastern and western North Pacific, persisting for a week or so. It is shown that the ZNPO pattern is a high-impact teleconnection pattern that brings the wintertime North Pacific and North America severe weather and hydroclimate events. It may cause rapid surface air temperature drop or rise over the northern North Pacific and North America, remarkable sea ice concentration anomalies over the northeastern Bering Sea, and strong convective anomalies in the lower troposphere over the eastern and western midlatitude North Pacific. The ZNPO pattern arises from two westward-moving geopotential height disturbances over the North Pacific and North America and is driven mainly by baroclinic energy conversion and feedback forcing by transient eddies. The baroclinic energy conversion acts to overcome the available potential energy (APE) loss caused by the heat flux of transient eddies and at the same time acts as a major kinetic energy (KE) source to maintain the ZNPO pattern. The barotropic feedback forcing by transient eddies acts as a major KE source to drive the ZNPO pattern during the growing stage of the ZNPO pattern and as a major KE sink to heavily damp the ZNPO pattern during the decaying stage.

Differential north–south response of juvenile Chinook salmon (Oncorhynchus tshawytscha) marine growth to ecosystem change in the eastern Bering Sea, 1974–2010

Abstract Chinook salmon (Oncorhynchus tshawytscha, Salmonidae) returns to western Alaska were historically high and variable but recently reached record lows. Understanding the differential influence of climatic and oceanic conditions on the growth of juvenile Chinook salmon in the north and south eastern Bering Sea is key to understanding mechanisms and factors affecting the production dynamics of Chinook salmon from western Alaska and the Arctic. Summer growth was lower and more variable among years for Chinook salmon in the south than the north eastern Bering Sea. Summer growth decreased with a rise in sea temperatures in the north and south and increased with more sea ice coverage and a later time of ice retreat in the south but not in the north. Capelin (Mallotus villosus), an important prey for juvenile Chinook salmon in the north and during cold years may link increased growth to cooler sea temperatures. Reduced and more variable summer growth of juvenile Chinook salmon from the eastern Bering Sea with warming may have implications on overwintering survival.

Improved Chlorophyll-a Algorithm for the Satellite Ocean Color Data in the Northern Bering Sea and Southern Chukchi Sea

The Bering and Chukchi seas are an important conduit to the Arctic Ocean and are reported to be one of the most productive regions in the world’s oceans in terms of high primary productivity that sustains large numbers of fishes, marine mammals, and sea birds as well as benthic animals. Climate-induced changes in primary production and production at higher trophic levels also have been observed in the northern Bering and Chukchi seas. Satellite ocean color observations could enable the monitoring of relatively long term patterns in chlorophyll-a (Chl-a) concentrations that would serve as an indicator of phytoplankton biomass. The performance of existing global and regional Chl-a algorithms for satellite ocean color data was investigated in the northeastern Bering Sea and southern Chukchi Sea using in situ optical measurements from the Healy 2007 cruise. The model-derived Chl-a data using the previous Chl-a algorithms present striking uncertainties regarding Chl-a concentrations – for example, overestimation in lower Chl-a concentrations or systematic overestimation in the northeastern Bering Sea and southern Chukchi Sea. Accordingly, a simple two band ratio (Rrs(443)/Rrs(555)) algorithm of Chl-a for the satellite ocean color data was devised for the northeastern Bering Sea and southern Chukchi Sea. The MODIS-derived Chl-a data from July 2002 to December 2014 were produced using the new Chl-a algorithm to investigate the seasonal and interannual variations of Chl-a in the northern Bering Sea and the southern Chukchi Sea. The seasonal distribution of Chl-a shows that the highest (spring bloom) Chl-a concentrations are in May and the lowest are in July in the overall area. Chl-a concentrations relatively decreased in June, particularly in the open ocean waters of the Bering Sea. The Chl-a concentrations start to increase again in August and become quite high in September. In October, Chl-a concentrations decreased in the western area of the Study area and the Alaskan coastal waters. Strong interannual variations are shown in Chl-a concentrations in all areas. There is a slightly increasing trend in Chl-a concentrations in the northern Bering Strait (SECS). This increasing trend may be related to recent increases in the extent and duration of open waters due to the early break up of sea ice and the late formation of sea ice in the Chukchi Sea.

Relations between salinity in the northwestern Bering Sea, the Bering Strait throughflow and sea surface height in the Arctic Ocean

The correlation between transport via the Bering Strait throughflow (BTF) and sea surface salinity (SSS) in the Bering Sea has been examined mainly using an atmosphere–ocean–ice coupled climate model that has an eddy-permitting ocean component. The SSS anomaly in the northwestern Bering Sea is high from winter to spring when the BTF transport anomaly is large in the cold season. Similar features can be seen in an observation dataset and two kinds of ocean data assimilation product. BTF transport is strongly correlated with sea surface height (SSH) in the northeastern Bering Sea, the southwestern Chukchi Sea and the East Siberian Sea. The SSH along the Russian coast in the Arctic Ocean is uncorrelated with the SSH in the Bering Sea, the meaning being that the Arctic SSH affects the BTF and the SSS independently of the SSH in the Bering Sea. The low SSH along the Siberian coast is correlated with easterly wind anomalies over the Laptev Sea and north of the New Siberian Islands. The relationship between the low Siberian-coast SSH and the high SSS in the Bering Sea, however, is not confirmed in 10 years of satellite-derived SSH. Mixed-layer salt budget analysis has revealed that the high SSS anomalies are mainly caused by the increases of horizontal advective salt convergence north of 62.5°N, and by the decreases of sea-ice melting south of 62.5°N, through the strengthening of the near-surface northeastward currents. In the warm season, these two factors fade and the salinization disappears.

The response of the Bering Sea Gateway during the Mid-Pleistocene Transition

The Mid-Pleistocene transition and the response of sea ice in the subarctic North Pacific are examined using a diatom record from the north eastern Bering Sea slope (IODP core U1344A). High percentages of diatom sea ice species in the assemblage foster the development of groupings specific to differing ice conditions. Thalassiosira antarctica var. borealis emerges as a key diatom species that delineates the development of thick multiannual sea ice and marks a series of advancements from 0.9 to1.2Ma after which it dominates the assemblage until 0.6Ma. The decline of Neodenticula seminae, indicative of Alaskan Stream water inflow, is in agreement with neighbouring core U1343E confirming the reduction of Bering Sea circulation after 0.9Ma. We propose that during the MPT a stepped advancement of sea ice occurs in the Bering Sea as a response to increased moisture delivery to the high latitudes. An extended period of diatom productivity between 0.75 and 0.65Ma, marks major deglacial conditions towards the end of the MPT by 0.6–0.55Ma. The work highlights the important role played by sea ice and supports the contention of a colder MPT in the subarctic Pacific.

Growth and condition of juvenile chum and pink salmon in the northeastern Bering Sea

As the Arctic continues to warm, abundances of juvenile Pacific salmon (Oncorhynchus spp.) in the northern Bering Sea are expected to increase. However, information regarding the growth and condition of juvenile salmon in these waters is limited. The first objective of this study was to describe relationships between size, growth, and condition of juvenile chum (O. keta) and pink (O. gorbuscha) salmon and environmental conditions using data collected in the northeastern Bering Sea (NEBS) from 2003–2007 and 2009–2012. Salmon collected at stations with greater bottom depths and cooler sea-surface temperature (SST) were longer, reflecting their movement further offshore out of the warmer Alaska Coastal Water mass, as the season progressed. Energy density, after accounting for fish length, followed similar relationships with SST and bottom depth while greater condition (weight-length residuals) was associated with warm SST and shallower stations. We used insulin-like growth factor-1 (IGF-1) concentrations as an indicator of relative growth rate for fishes sampled in 2009–2012 and that found fish exhibited higher IGF-1 concentrations in 2010–2012 than in 2009, although these differences were not clearly attributable to environmental conditions. Our second objective was to compare size and condition of juvenile chum and pink salmon in the NEBS between warm and cool spring thermal regimes of the southeastern Bering Sea (SEBS). This comparison was based on a hypothesis informed by the strong role of sea-ice retreat in the spring for production dynamics in the SEBS and prevailing northward currents, suggesting that feeding conditions in the NEBS may be influenced by production in the SEBS. We found greater length (both species) and condition (pink salmon) in years with warm thermal regimes; however, both of these responses changed more rapidly with day of year in years with cool springs. Finally, we compared indicators of energy allocation between even and odd brood-year stocks of juvenile pink salmon, finding support for the idea that the even-year stock allocates more energy to storage, as opposed to growth, than does the odd-year stock. Over all, our results support the idea that sea-ice dynamics influence energy allocation and growth of juvenile salmon in the northern Bering Sea and provide a foundation for further understanding of how environmental conditions influence juvenile salmon at the northern edge of their range.

Shifts in the distribution of molting Spectacled Eiders (Somateria fischeri) indicate ecosystem change in the Arctic

ABSTRACT Shifts in the distribution of benthivorous predators provide an indication of underlying environmental changes in benthic-mediated ecosystems. Spectacled Eiders (Somateria fischeri) are benthivorous sea ducks that spend the nonbreeding portion of their annual cycle in the Bering, Chukchi, Beaufort, and East Siberian seas. Sea ducks generally molt in biologically productive areas with abundant prey. If the distribution of eiders at molting areas matches prey abundance, spatial shifts may indicate changes in environmental conditions in the Arctic. We used a randomization procedure to test for shifts in the distribution of satellite telemetry locations received from Spectacled Eiders in the 1990s and 2008–2011 within 4 late-summer, ice-free molting areas: Indigirka–Kolyma, northern Russia; Ledyard Bay, eastern Chukchi Sea; Norton Sound, northeastern Bering Sea; and Mechigmenskiy Gulf, northwestern Bering Sea. We also tested for interannual and interdecadal changes in dive depth required to reach pre...

Effects of warm and cold climate conditions on capelin (Mallotus villosus) and Pacific herring (Clupea pallasii) in the eastern Bering Sea

Climate warming has impacted the southern extent of sea ice in the eastern Bering Sea (EBS) ecosystem, leading to many changes in ocean conditions and food webs there. We explore how these changes have affected two key forage fish species, capelin (Mallotus villosus) and Pacific herring (Clupea pallasii), examining the effects of climate change on this commercially important ecosystem in the EBS. Catch per unit effort (CPUE) data from surface trawls, size, and diet of capelin and Pacific herring were collected during a series of warm and cold years by fisheries oceanographic surveys conducted from mid-August to early October 2003 through 2011. Overall, mean CPUE for both species was higher in the northeastern Bering Sea [NEBS; capelin=1.2kg/km2 (warm) and 40.0kg/km2 (cold); herring=141.1kg/km2 (warm) and 132.4kg/km2 (cold)] relative to the southeastern Bering Sea [SEBS; capelin=0.2kg/km2 (warm) and 5.8kg/km2 (cold); herring=15.8kg/km2 (warm) and 24.5kg/km2 (cold)], irrespective of temperature conditions. Capelin mean CPUE was significantly lower during warm years than during cold years [p<0.001; 0.6kg/km2 (warm), 19.0kg/km2 (cold)]. Pacific herring mean CPUE was less variable between warm and cold years [p<0.001; 63.8kg/km2 (warm), 66.2kg/km2 (cold)], but was still significantly less during warm years than cold. Capelin and herring lengths remained relatively constant between climate periods. Capelin lengths were similar among oceanographic domains [104mm (South Inner domain), 112mm (South Middle domain), 107mm (North Inner domain), and 104mm (North Middle domain)], while herring were larger in domains further offshore [123mm (South Inner domain), 232mm (South Middle domain), 260mm (South Outer domain), 129mm (North Inner domain), and 198mm (North Middle domain)]. Diets for both species were significantly different between climate periods. Large crustacean prey comprised a higher proportion of the diets in most regions during cold years. Age-0 walleye pollock (Gadus chalcogrammus) contributed >60% to the diets of Pacific herring in southern Middle Domain and >30% in the northern Middle domain during warm years. A switch to less energetic prey for these forage fishes during warm years may have implications for fitness and future recruitment. The shifts in the distribution and lower biomass of capelin in the EBS during warm years could lead to disruptions in energy pathways in this complex marine ecosystem.

Projected future biophysical states of the Bering Sea

Three global climate simulations from the Intergovernmental Panel on Climate Change Fourth Assessment (AR4) were used as physical forcing to drive a regional model that includes both physical and biological elements of the Bering Sea. Although each downscaled projection indicates a warming of 1–2°C between 2010 and 2040 on the Bering Sea shelf, the interannual and interdecadal details of this trend vary considerably among the three realizations. In each case, the magnitude of presently observed interannual variability of bottom temperatures and ice cover is found in the models to be maintained out to at least 2040, but with a steadily increasing probability of warm years with less ice on the southern shelf. The overall trends indicate warmer temperatures and the retreat of ice in the southeastern Bering Sea, but continued ice cover in the northeastern Bering Sea. Sensitivity analyses suggest both increasing air temperature and northward wind stress as primary drivers of higher water-column temperatures. Based on currently available models, changes in shortwave radiation are not likely to have a significant role in this warming. Warming trends on the outer shelf may lead to decreased production of large crustacean zooplankton at that location, but could increase such production on the inner shelf.

Abrupt changes of intermediate water properties on the northeastern slope of the Bering Sea during the last glacial and deglacial period

Millennial‐scale variability in the behavior of North Pacific Intermediate Water during the last glacial and deglacial period, and its association with Dansgaard‐Oeschger (D‐O) cycles and Heinrich events, are examined based on benthic foraminiferal oxygen and carbon isotopes (δ18Obf and δ13Cbf) and %CaCO3 using a sediment core recovered from the northeastern slope of the Bering Sea. A suite of positive δ18Obf excursions at intermediate depths of the Bering Sea, which seem at least in part associated with increases in the δ18Obf gradients between the Bering and Okhotsk Seas, suggest the Bering Sea as a proximate source of intermediate water during several severe stadial episodes in the last glacial and deglacial period. Absence of such δ18Obf gradients during periods of high surface productivity in the Bering and Okhotsk Seas, which we correlate to D‐O interstadials, suggests a reduction in intermediate water production in the Bering Sea and subsequent introduction of nutrient‐rich deep waters from the North Pacific into intermediate depths of the Bering Sea. We argue that a reorganization of atmospheric circulation in the high‐latitude North Pacific during severe cold episodes in the last glacial and deglacial period created favorable conditions for brine rejection in the northeastern Bering Sea. The resulting salinity increase in the cold surface waters could have initiated intermediate (and deep) water formation that spread out to the North Pacific.

Provenance of terrigenous detritus of the surface sediments in the Bering and Chukchi Seas as derived from Sr and Nd isotopes: Implications for recent climate change in the Arctic regions

Strontium and Nd isotope analysis of the detrital fractions extracted from the marginal sea sediments in the Arctic was applied to examine regional and temporal changes in the inflow and transportation of terrigenous material in the Chukchi and Bering Seas over the past 100 years. Regional distributions of the Sr and Nd isotopes of the surface sediments show higher Sr isotope ratios and lower Nd isotope ratios in the Chukchi Sea (87Sr/86Sr=0.7106–0.7150; εNd=–10.1 to –8.3), and lower Sr isotope ratios and higher Nd isotope ratios in the eastern Bering Sea (0.7045–0.7109; –8.6 to +3.0). In addition, the Rb and Sr contents and REE patterns (e.g., Eu/Eu⁎) changed noticeably across the Bering Strait. These variations mean that the sediments in the Bering and Chukchi Seas have clearly distinct sources. The terrigenous detritus in the Chukchi Sea is mainly derived from northeastern Siberia (87Sr/86Sr=0.711; εNd=–9) and Bering Strait inflow (essentially from the Yukon River), and additionally from the Mackenzie River basin including the Canadian Shield (0.732–0.734; –14). The detritus in the eastern Bering Sea mainly consists of two components: the continental material from the Yukon River basin mainly underlain by Mesozoic and Paleozoic rocks in the Alaskan mainland (0.708–0.709; –9 to –8), and the Aleutian-arc volcanics (0.703; +6 to +10) transported northward by the Alaska Coastal and Bering Shelf Waters. The eastern Bering sediments over the past 100 years show slight variations of the Sr isotope ratio and relatively wide variations of the Nd isotope ratio, and the variations and trends of the time-series of the northeastern Bering Sea in the Sr–Nd isotope diagram are probably controlled by changes in the grain size of the detritus from the Yukon River basin. Some of the εNd time-series show periodic fluctuations correlating with the annual mean surface air temperature (SAT) for the Arctic: the εNd value is low in the high SAT period, and high in the low SAT period. In the warm period, the Yukon River was likely to supply a higher amount of the fine-grain material with a relatively low εNd value such as surficial overburden, probably because partial melting of continental glaciers and permafrosts in the Alaskan mainland increased. More detailed analysis with high time resolution is needed to clearly understand the effects the SAT have on the Arctic continental and marine environments.

Coupled organic and inorganic carbon cycling in the deep subseafloor sediment of the northeastern Bering Sea Slope (IODP Exp. 323)

We studied microbially mediated diagenetic processes driven by carbon mineralization in subseafloor sediment of the northeastern Bering Sea Slope to a depth of 745 meters below seafloor (mbsf). Sites U1343, U1344 and U1345 were drilled during Integrated Ocean Drilling Program (IODP) Expedition 323 at water depths of 1008 to 3172 m. They are situated in the high productivity “Green Belt” region, with organic carbon burial rates typical of the high-productivity upwelling domains on western continental margins. The three sites show strong geochemical similarities. The downward sequence of microbially mediated processes in the sediment encompasses (1) organoclastic sulfate reduction, (2) anaerobic oxidation of methane (AOM) coupled to sulfate reduction, and (3) methanogenesis. The sediment contains two distinct zones of diagenetic carbonate formation, located at the sulfate–methane transition zone (SMTZ) and between 300 and 400 mbsf. The SMTZ at the three sites is located between 6 and 9 mbsf. The upward methane fluxes into the SMTZ are similar to fluxes in SMTZs underlying high-productivity surface waters off Chile and Namibia. Our Bering Sea results show that intense organic carbon mineralization drives high ammonium and dissolved inorganic carbon (DIC) production rates (> 4.2 mmol m − 3 y − 1 ) in the uppermost 10 mbsf and strongly imprints on the stable carbon isotope composition of DIC, driving it to a minimum value of − 27‰ (VPDB) at the SMTZ. Pore-water calcium and magnesium profiles demonstrate formation of diagenetic Mg-rich calcite in the SMTZ. Below the SMTZ, methanogenesis results in 13C-enrichment of pore-water DIC, with a maximum value of + 11.9‰. The imprint of methanogenesis on the DIC carbon isotope composition is evident down to a depth of 150 mbsf. Below this depth, slow or absent microbially mediated carbon mineralization leaves DIC isotope composition unaffected. Ongoing carbonate formation between 300 and 400 mbsf strongly influences pore-water DIC and magnesium concentration profiles. The linked succession of organic carbon mineralization and carbonate dissolution and precipitation patterns that we observe in the Bering Sea Slope sediment may be representative of passive continental margin settings in high-productivity areas of the world's ocean.

Pollen Evidence for Late Pleistocene Bering Land Bridge Environments from Norton Sound, Northeastern Bering Sea, Alaska

ABSTRACTAfter more than half a century of paleoenvironmental investigations, disagreements persist as to the nature of vegetation type and climate of the Bering land bridge (BLB) during the late Wisconsin (Sartan) glacial interval. Few data exist from sites on the former land bridge, now submerged under the Bering and Chukchi Seas. Two hypotheses have emerged during the past decade. The first, based on pollen data from Bering Sea islands and adjacent mainlands of western Alaska and Northeast Siberia, represents the likely predominant vegetation on the Bering land bridge during full-glacial conditions: graminoid-herb-willow tundra vegetation associated with cold, dry winters and cool, dry summer climate. The second hypothesis suggests that dwarf birch-shrub-herb tundra formed a broad belt across the BLB, and that mesic vegetation was associated with cold, snowier winters and moist, cool summers. As a step towards resolving this controversy, a sediment core from Norton Sound, northeastern Bering Sea was radiocarbon dated and analyzed for pollen content. Two pollen zones were identified. The older, bracketed by radiocarbon ages of 29,500 and 11,515 14C yr BP, contains pollen assemblages composed of grass, sedge, wormwood, willow, and a variety of herb (forb) taxa. These assemblages are interpreted to represent graminoid-herb-willow tundra vegetation that developed under an arid, cool climate regime. The younger pollen zone sediments were deposited about 11,515 14C yr BP, when rising sea level had begun to flood the BLB. This younger pollen zone contains pollen of birch, willow, heaths, aquatic plants, and spores of sphagnum moss. This is interpreted to represent a Lateglacial dwarf birch-heath-willow-herb tundra vegetation, likely associated with a wetter climate with deeper winter snows, and moist, cool summers. This record supports the first hypothesis, that graminoid-herb-willow tundra vegetation extended into the lowlands of the BLB during full glacial conditions of the late Wisconsin.

Pacific Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean

The spatial pattern of recent ice reduction in the Arctic Ocean is similar to the distribution of warm Pacific Summer Water (PSW) that interflows the upper portion of halocline in the southern Canada Basin. Increases in PSW temperature in the basin are also well‐correlated with the onset of sea‐ice reduction that began in the late 1990s. However, increases in PSW temperature in the basin do not correlate with the temperature of upstream source water in the northeastern Bering Sea, suggesting that there is another mechanism which controls these concurrent changes in ice cover and upper ocean temperature. We propose a feedback mechanism whereby the delayed sea‐ice formation in early winter, which began in 1997/1998, reduced internal ice stresses and thus allowed a more efficient coupling of anticyclonic wind forcing to the upper ocean. This, in turn, increased the flux of warm PSW into the basin and caused the catastrophic changes.

Southeastern Chukchi Sea (Alaska) epibenthos

Epibenthos of the southeastern Chukchi Sea, inclusive of Kotzebue Sound, was sampled in 1976. Crustaceans dominated abundance while echinoderms, mainly sea stars, dominated biomass. Spatial distribution of fauna was determined by cluster analysis. Scavenger-predators were dominant trophic groups, although suspension feeders dominated some regions. Unexpected high abundance and biomass under Alaska Coastal Water and factors related to presence and distribution of fauna are discussed. Dissimilarities between the benthic systems of the southeastern and northeastern Chukchi Seas are attributed to more complex water mass and flow patterns in the southern system. Entrained particulate organic carbon disperses through the area to support an abundant and apparently highly productive benthic fauna, which sustains resident and transient populations of demersal fishes and marine mammals. Epibenthos was sampled again in 1998 and, although little change was apparent in community composition, many taxa had higher abundance and biomass than 22 years earlier, a trend similar to findings observed in the northeastern Bering Sea.

Assessment of Heavy Metals in Red King Crabs Following Offshore Placer Gold Mining

Red king crabs, Paralithodes camtschaticus, with commercial and subsistence importance, seasonally occur nearshore in Norton Sound, north-eastern Bering Sea, Arctic Alaska. Since the end of the nineteenth century, the coastal area in the northern Sound has been intensively mined for placer gold. Mining was extended offshore in 1986–1990. Heavy metal concentrations in the crabs were monitored during 1987–1990 to assess the impact of offshore mining. Crabs were only present in the study area during ice-covered months when mining was seasonally suspended. Arsenic, Cd, Cr, Cu, Pb, Ni, Zn and Hg concentrations in muscle and hepatopancreas tissues were generally not different between mined and unmined reference (control) areas. Furthermore, concentrations of these metals were not different in similar surficial sediments upcurrent and downcurrent of mining. The concentrations of most metals in both tissues fluctuated over the study period, with no temporal trend. Exceptions were for Hg in muscle tissue and As in hepatopancreas tissue which showed progressive significant increases each year. Also, there was a fractionation of selected metals between the two tissues; Cr, Pb and Zn were greater in muscles, whereas Cd, Cu and Ni were greater in hepatopancreas. Arsenic and Hg had similar concentrations in both tissues. All elemental concentrations in the crab muscles from Norton Sound were below or within the range of concentrations observed in red king crabs from five other locations in the North Pacific, including a mined area. In Norton Sound, all metals, except Cd, were at least an order of magnitude below the US Food and Drug Administration guidance levels for contamination or human consumption. This investigation demonstrated that mining activities did not affect the concentrations of the heavy metals measured in red king crabs.

Assessment of the benthic environment following offshore placer gold mining in the northeastern Bering Sea

The effects of offshore placer gold mining on benthic invertebrates were assessed on ‘sand’ and ‘cobble’ substrates in Norton Sound, northeastern Bering Sea. Mining with a bucket-line dredge occurred nearshore in 9–20 m during June to November 1986–90. Sampling nearly a year subsequent to mining demonstrated minor alteration of substrate granulometry with no clear trends. However, benthic macrofaunal community parameters (total abundance, biomass, diversity) and abundance of dominant families were significantly reduced at mined stations. Many of the dominant taxa are known prey of the locally important red king crab ( Paralithodes camtschaticus). Dominance of opportunistic species and small sizes at unmined and mined sites represents faunal responses to the natural dynamics of the region where establishment of populations of large, sexually-mature individuals is typically precluded. Multi-year bathymetric surveys of an area only mined in 1986 showed a continued smoothing of ocean bottom relief, decreasing size of tailing footprint, and shoaling of depressions left by mining. An ordination (multidimensional scaling) of taxon abundance data from mined (1 year after mining), recolonizing (2–7 years after mining) and unmined stations shows configurations that reflect disturbance. Recovery of the biota was underway in both substrates after 4 years, but this process was interrupted in the fall of the fourth year (1990) by several severe storms. Mining effects are contrasted with local natural disturbances.

Clastic components in Quaternary sediments of the northwest Pacific and their paleo-oceanic significance

Ninety-seven mineral analyses (for the total 0.05-0.1 mm fraction and its heavy subfraction) are given of Late Pleistocene to Holocene sediments from the northwestern (subarctic) Pacific, including the Kuril and Aleutian Trenches and Bering Sea. Heavy mineral assemblages indicating ice-rafted debris and its main provenance were defined. The assemblages are derived mainly from the northeastern Bering Sea shelf where large-scale generation of sea-ice is presumed. Temporal and spatial changes of the mineral suites also suggest intermediate to deep water flow along the eastern flank of the Emperor chain during glaciation. The flow might penetrate the Northwest Pacific Basin to the south of 45°N. It was traced by the fine- and medium-grained terrigenous debris in a core from 38°N and 165°E.

High Annual Variability in Reproductive Success of Kittiwakes (Rissa tridactyla L.) at a Colony in Western Alaska

(1) All aspects of reproductive performance of kittiwakes (Rissa tridactyla L.) fluctuated markedly in 1975-89 at a colony of about 10000 nesting pairs in the north-eastern Bering Sea, Alaska. (2) In breeding seasons following cold springs, breeding was delayed, fewer nests were built, fewer nests contained eggs, and clutch size, hatching success and the number of chicks fledging per nest were reduced. Complete reproductive failures followed the three coldest springs in the 15-year period. (3) Reproductive success (chicks fledged per nest) was highest following moderately warm springs; however, growth rates of chicks and fledging success were extremely low following the warmest spring on record. (4) Spring air temperatures were highly correlated with break-up of sea ice and these factors probably influenced seasonal warming trends in the sea water and the consequent availability of prey such as sandeels (Ammodytes hexapterus Pallas) near the colony. (5) During this 15-year period, interannual variability in spring air temperature was pronounced in comparison to that during the previous 68-year period; however, simulations using May temperature as a predictor of reproductive success suggested that high annual variability in reproduction has occurred throughout this century. (6) Numbers of adult-plumaged birds on the cliffs in mid-season were markedly lower and more variable in years when few nests were built, suggesting that relatively few experienced adults breed and consistently are present at the colony in years when overall reproductive performance is poor.