Sea Ice Breakup Research Articles

ECOLOGY AND WILDLIFE: Climate Change and the Arctic Diet

Each spring, female polar bears and their cubs emerge from hibernation after months without food, and their survival depends on having good sea ice for hunting seals, their almost exclusive food. Also in spring, the Arctic sea ice begins to melt and break apart. Over the past 25 years, the timing of this melting has become less predictable as a consequence of warming in the Arctic, varying by more than a month. Researchers in Canada now report the first evidence that changes in the timing of the annual sea ice breakup have contributed to a dietary shift for polar bears from western Hudson Bay in the Canadian sub-Arctic. This shift may be accelerating the bears’ bioaccumulation of some classes of persistent contaminants, and people who consume these animals as part of a traditional subsistence diet could face greater exposure to contaminants that are passed up the food chain.

Sea Ice-associated Diet Change Increases the Levels of Chlorinated and Brominated Contaminants in Polar Bears

Two global environmental issues, climate change and contamination by persistent organic pollutants, represent major concerns for arctic ecosystems. Yet, it is unclear how these two stressors interact in the Arctic. For instance, the influence of climate-associated changes in food web structure on exposure to pollutants within arctic ecosystems is presently unknown. Here, we report on recent changes in feeding ecology (1991-2007) in polar bears (Ursus maritimus) from the western Hudson Bay subpopulation that have resulted in increases in the tissue concentrations of several chlorinated and brominated contaminants. Differences in timing of the annual sea ice breakup explained a significant proportion of the diet variation among years. As expected from climate change predictions, this diet change was consistent with an increase in the consumed proportions of open water-associated seal species compared to ice-associated seal species in years of earlier sea ice breakup. Our results demonstrate that climate change is a modulating influence on contaminants in this polar bear subpopulation and may pose an additional and previously unidentified threat to northern ecosystems through altered exposures to contaminants.

Changes in the climate of the Alaskan North Slope and the ice concentration of the adjacent Beaufort Sea

A reliable data set of Arctic sea ice concentration based on satellite observations exists since 1972. Over this time period of 36 years western arctic temperatures have increased; the temperature rise varies significantly from one season to another and over multi-year time scales. In contrast to most of Alaska, however, on the North Slope the warming continued after 1976, when a circulation change occurred, as expressed in the PDO index. The mean temperature increase for Barrow over the 36-year period was 2.9°C, a very substantial change. Wind speeds increased by 18% over this time period, however, the increase were non-linear and showed a peak in the early 1990s. The sea ice extent of the Arctic Ocean has decreased strongly in recent years, and in September 2007 a new record in the amount of open water was recorded in the Western Arctic. We observed for the Southern Beaufort Sea a fairly steady increase in the mean annual amount of open water from 14% in 1972 to 39% in 2007, as deduced from the best linear fit. In late summer the decrease is much larger, and September has, on average, the least ice concentration (22%), followed by August (35%) and October (54%). The correlation coefficient between mean annual values of temperature and sea ice concentration was 0.84. On a monthly basis, the best correlation coefficient was found in October with 0.88. However, the relationship between winter temperatures and the sea ice break-up in summer was weak. While the temperature correlated well with the CO2 concentration (r = 0.86), the correlation coefficient between CO2 and sea ice was lower (r = −0.68). After comparing the ice concentration with 17 circulation indices, the best relation was found with the Pacific Circulation Index (r = −0.59).

EXPOSURE TO SUDDEN LIGHT BURST AFTER PROLONGED DARKNESS—A CASE STUDY ON BENTHIC DIATOMS IN ANTARCTICA

In polar areas, benthic diatoms are regarded to play a major role in supplying energy to the benthic fauna, particularly prior to the release of microalgae from sea ice and the phytoplankton bloom. As phototrophs, benthic polar diatoms have to contend not only with dark polar nights but also with darkness due to sea-ice and snow cover that can prevail in the littoral zone for additional months. Upon sea ice break-up the autotrophs are suddenly exposed to high light intensities including ultraviolet radiation. The aim of our study was to mimic a sudden spring-time sea ice break-up, focusing on the ultraviolet part of the solar spectrum. We therefore exposed a semi-natural community of benthic diatoms to light burst after a period of total darkness. We studied the effects of different spectral qualities: photosynthetically active radiation (PAR, 400–700 nm; P treatment), PAR+ UV-A (UV-A 320–400 nm; PA treatment), and PAR+UV-A+UV-B (UV-B 280–320 nm; PAB treatment) on cell number (growth), species composition and optimum quantum yield (Fv/Fm) in 2 separate experiments where diatoms were kept in darkness for 15 and 64 days, respectively. In both experiments, the most frequently (>50%) observed species were Gyrosigma fasciola and G. obscururn. No growth was observed and no resting spores were found. In both experiments, the initial optimum quantum yield of the PSII prior to dark treatment was comparable (Fv/Fm = 0.70). The Fv/Fm was not affected after 15 days dark incubation but a significant decrease in photosynthetic efficiency was observed after 64 days in the dark (Fv/Fm = 0.39). Exposure to different light treatments (P, PA, PAB) immediately after different dark incubation periods showed higher reduction in Fv/Fm (PAB > PA > P) after the longer dark period. Estimated P-E curve parameters showed an efficient light harvesting and photosynthetic conversion capacity (α= 0.20; rETRmax=14) that was significantly reduced after 64 days in the dark (α= 0.06; rETRmax=8). The reduction in these photo-physiological indices (a and rETRmax) after dark incubation was compensated with higher saturating irradiance (Ek), which we suspect to be a mechanism to optimize photochemical processes. But the PSII antenna was relatively light-sensitive because photosynthesis was already photoinhibited at half the photon flux density (≥ 585 μmol photons m–2 s–1) relative to light-adapted (≥ 972 μmol photons m–2 s–1) diatoms. We conclude that the benthic diatoms in our study were able to resume photosynthetic activity after 64 days in darkness and they were able to cope with relatively high intensities of UV radiation compared with their natural habitat.

Diversity and dynamics of Antarctic marine microbial eukaryotes under manipulated environmental UV radiation

In the light of the predicted global climate change, it is essential that the status and diversity of polar microbial communities is described and understood. In the present study, molecular tools were used to investigate the marine eukaryotic communities of Prydz Bay, Eastern Antarctica, from November 2002 to January 2003. Additionally, we conducted four series of minicosm experiments, where natural Prydz Bay communities were incubated under six different irradiation regimes, in order to investigate the effects of natural UV radiation on marine microbial eukaryotes. Denaturing gradient gel electrophoresis (DGGE) and 18S rRNA gene sequencing revealed a eukaryotic Shannon diversity index averaging 2.26 and 2.12, respectively. Phylogenetic analysis of 472 sequenced clones revealed 47 phylotypes, belonging to the Dinophyceae, Stramenopiles, Choanoflagellidae, Ciliophora, Cercozoa and Metazoa. Throughout the studied period, three communities were distinguished: a postwinter/early spring community comprising dinoflagellates, ciliates, cercozoans, stramenopiles, viridiplantae, haptophytes and metazoans; a dinoflagellate-dominated community; and a diatom-dominated community that developed after sea ice breakup. DGGE analysis showed that size fraction and time had a strong shaping effect on the community composition; however, a significant contribution of natural UV irradiance towards microeukaryotic community composition could not be detected. Overall, dinoflagellates dominated our samples and their diversity suggests that they fulfill an important role in Antarctic coastal marine ecosystems preceding ice breakup as well as between phytoplankton bloom events.

Spatial and temporal variability of sea ice in the southern Beaufort Sea and Amundsen Gulf: 1980–2004

Changing extent, location, and motion of the Arctic perennial pack affect the annual evolution of seasonal ice zones. Canadian Ice Service digital ice charts covering the southern Beaufort Sea and Amundsen Gulf are used to illustrate summer and winter conditions and trends between 1980 and 2004 for several sea ice stages of development. Results illustrate average sea ice conditions within the region in summer and winter for predominant sea ice types and changes in the relative concentration of sea ice types in summer and winter. In summer, a trend toward increased old sea ice concentration occurred near the mouth of Amundsen Gulf, with a trend toward decreasing summer first‐year sea ice farther west. In winter, increasing thick first‐year sea ice extent appears to be replacing young sea ice within the flaw lead system in the region. The dynamically driven breakup of sea ice in spring in the Amundsen Gulf is a highly variable event taking anywhere between 2 and 22 weeks to completely remove ice from the gulf. The timing and duration of the open water season depends upon the extent and timing of old ice influx. Freezeup occurs very quickly, proceeding from west to east with little temporal variability. The results of this paper are used to set the context for the Canadian Arctic Shelf Exchange Study (CASES) in terms of sea ice dynamic and thermodynamic processes.

Response to Dyck et al. (2007) on polar bears and climate change in western Hudson Bay

The “viewpoint” article by Dyck et al. (2007) [Dyck. M.G., Soon, W., Baydack, R.K., Legates, D.R., Baliunas, S., Ball, T.F., Hancock, L.O., 2007. Polar bears of western Hudson Bay and climate change: are warming spring air temperatures the “ultimate” survival control factor? Ecol. Complexity 4, 73–84. doi:10.1016/j.ecocom.2007.03.002.] suggest that factors other than climate warming are responsible for a decline in the polar bear population of Western Hudson Bay. They propose: (1) that there is no evidence that the climate has warmed significantly in western Hudson Bay, (2) that any negative effects on the polar bear population likely result from interactions with humans (such as research activities, management actions, or tourism), (3) that studies suggesting climate warming could influence polar bear populations are confounded by natural fluctuations and (4) that polar bears will adapt to climate warming by eating vegetation, hunting other marine mammal species, and evolving new physiological mechanisms. In our examination of their alternative explanations, and the data available to evaluate each, we found little support for any. Research conducted since 1997 (when the last data were collected for the analyses in Stirling et al., 1999 [Stirling, I., Lunn, N.J., Iacozza, J., 1999. Long-term trends in the population ecology of polar bears in western Hudson Bay in relation to climate change. Arctic 52, 294–306.]) continues to be consistent with the thesis that climate warming in western Hudson Bay is the major factor causing the sea ice to breakup at progressively earlier dates, resulting in polar bears coming ashore to fast for several months in progressively poorer condition, resulting in negative affects on survival of young, subadult, and older (but not prime) adults and reproduction. When the population began to decline, the hunting quota for Inuit in Nunavut was no longer sustainable, which in turn probably resulted in the decline accelerating over time as a result of overharvesting (Regehr et al., 2007 [Regehr, E.V., Lunn, N.J., Amstrup, S.C., Stirling, I., 2007. Survival and population size of polar bears in western Hudson Bay in relation to earlier sea ice breakup. J. Wildl. Manage. 71, 2673–2683.]).

Effects of Earlier Sea Ice Breakup on Survival and Population Size of Polar Bears in Western Hudson Bay

ABSTRACT Some of the most pronounced ecological responses to climatic warming are expected to occur in polar marine regions, where temperature increases have been the greatest and sea ice provides a sensitive mechanism by which climatic conditions affect sympagic (i.e., with ice) species. Population‐level effects of climatic change, however, remain difficult to quantify. We used a flexible extension of Cormack‐Jolly‐Seber capture‐recapture models to estimate population size and survival for polar bears (Ursus maritimus), one of the most ice‐dependent of Arctic marine mammals. We analyzed data for polar bears captured from 1984 to 2004 along the western coast of Hudson Bay and in the community of Churchill, Manitoba, Canada. The Western Hudson Bay polar bear population declined from 1,194 (95% CI = 1,020‐1,368) in 1987 to 935 (95% CI = 794‐1,076) in 2004. Total apparent survival of prime‐adult polar bears (5–19 yr) was stable for females (0.93; 95% CI = 0.91‐0.94) and males (0.90; 95% CI = 0.88‐0.91). Survival of juvenile, subadult, and senescent‐adult polar bears was correlated with spring sea ice breakup date, which was variable among years and occurred approximately 3 weeks earlier in 2004 than in 1984. We propose that this correlation provides evidence for a causal association between earlier sea ice breakup (due to climatic warming) and decreased polar bear survival. It may also explain why Churchill, like other communities along the western coast of Hudson Bay, has experienced an increase in human‐polar bear interactions in recent years. Earlier sea ice breakup may have resulted in a larger number of nutritionally stressed polar bears, which are encroaching on human habitations in search of supplemental food. Because western Hudson Bay is near the southern limit of the species' range, our findings may foreshadow the demographic responses and management challenges that more northerly polar bear populations will experience if climatic warming in the Arctic continues as projected.

Detection of Coastal Region Sea Ice Decay from Orthorectified RADARSAT-1 ScanSAR Imagery: A Case Study of Bering Strait and Norton Sound, Alaska

Application of SAR images to detect the onset of breakup and dynamic decay process of coastal sea ice was investigated, using a time series of RADARSAT-1 C-band scanning SAR images of the areas around Seward Peninsula coastal region, Alaska, including Bering Strait and Norton Sound. Satellite image analyses mainly include a time series feature space images composed of radar backscattering coefficient versus look angle derived from RADARSAT-1 amplitude images covering both coastal sea and land area. It was found that the feature space images have a single mode before the decay and breakup of the coastal sea ice, and have multiple modes when large-scale open water first appears until the coastal sea ice disappears completely. The mode patterns in the feature space images can then be determined by the water surface roughness caused by the wind field. The single-mode phenomenon before ice melting is thought to be due to a similarity of the backscattering of snow cover on sea ice and land surface due to the common coverage by snow and ice. The appearance of multiple modes is due to the differences in backscattering of sea ice surface at various decaying stages or open water with different wave roughness due to wind effect, and the land surface with snow and ice cover with different melting conditions once the melting or decay starts and proceeds. The feature space images reported here can be used as a useful tool in detection of decay of coastal sea ice and landfast ice in the field of sea ice dynamics as the imaging radar technology is weather independent, providing information of coastal ice on a regular basis.

Predator Effect and Behavioral Patterns in Arctic Terns (Sterna paradisaea) and Sabine’s Gulls (Xema sabini) During a Failed Breeding Year

Abstract Little is known about the factors influencing the breeding decisions of Arctic breeding seabirds and their behavior in a failed breeding year. Here we present the behavioral patterns observed in a year with late sea ice break-up and regular predator visits to the colony. We found that breeding initiation of Arctic Terns and Sabine’s gulls was delayed until the breeding attempt was given up and the colony abandoned. However, the birds did not leave the region but returned to the colony soon after sea ice break-up continuing bonding behavior although egg-laying was not initiated. In 2006, the period 11-15 July seemed important for the breeding decision, as birds gradually gave up breeding and left the colony during that period.

Polar bears of western Hudson Bay and climate change: Are warming spring air temperatures the “ultimate” survival control factor?

Long-term warming of late spring (April–June) air temperatures has been proposed by Stirling et al. [Stirling, I., Lunn, N.J., Iacozza, J., 1999. Long-term trends in the population ecology of polar bears in western Hudson Bay in relation to climatic change. Arctic 52, 294–306] as the “ultimate” factor causing earlier sea-ice break-up around western Hudson Bay (WH) that has, in turn, led to the poorer physical and reproductive characteristics of polar bears occupying this region. Derocher et al. [Derocher, A.E., Lunn, N.J., Stirling, I., 2004. Polar bears in a warming climate. Integr. Comp. Biol. 44, 163–176] expanded the discussion to the whole circumpolar Arctic and concluded that polar bears will unlikely survive as a species should the computer-predicted scenarios for total disappearance of sea-ice in the Arctic come true. We found that spring air temperatures around the Hudson Bay basin for the past 70 years (1932–2002) show no significant warming trend and are more likely identified with the large-amplitude, natural climatic variability that is characteristic of the Arctic. Any role of external forcing by anthropogenic greenhouse gases remains difficult to identify. We argue, therefore, that the extrapolation of polar bear disappearance is highly premature. Climate models are simply not skilful for the projection of regional sea-ice changes in Hudson Bay or the whole Arctic. Alternative factors, such as increased human–bear interaction, must be taken into account in a more realistic study and explanation of the population ecology of WH polar bears. Both scientific papers and public discussion that continue to fail to recognize the inherent complexity in the adaptive interaction of polar bears with both human and nature will not likely offer any useful, science-based, preservation and management strategies for the species.

Fate of pelagic organic carbon and importance of pelagic–benthic coupling in a shallow cove in Disko Bay, West Greenland

Biomass and production of phytoplankton, bacteria, proto- and mesozooplankton to- gether with vertical flux of particulate organic carbon, sediment oxygen demand and biomass of macrozoobenthos were estimated over 2 wk in spring and 2 wk in autumn 2003 in a shallow cove in Disko Bay, West Greenland. In spring, bloom conditions were encountered with high phytoplankton concentrations of 20 to 30 mg chlorophyll a m -3 . The zooplankton community associated with the spring bloom could not control the developing bloom, which resulted in high sedimentation rates of 1438 mg C m -2 d -1 , of which 518 mg C m -2 d -1 could be related to chlorophyll a (chl a). The settling phytoplankton was ingested by filter-feeding as well as deposit-feeding bivalves. In autumn, the wa- ter column was stratified and nutrient levels reduced, resulting in a phytoplankton biomass below 0.5 mg chl a m -3 . The vertical flux of particulate carbon was reduced to 235 mg C m -2 d -1 . Compared to spring, benthic mineralisation rates had increased. Ingestion of chl a was reduced in filter-feeding and in deposit-feeding bivalves. The pronounced seasonal shift in production and mineralisation pathways clearly highlights the importance of the spring bloom in the costal waters of subarctic Greenland. Analysis of local sea ice conditions from 1979 to 2003 suggests that the mismatch between primary producers and copepods observed during 2 wk in spring could be related to an earlier than usual break-up of sea ice in 2003, which illustrates how climate can influence pelagic-benthic coupling.

Carbonate chemistry dynamics and carbon dioxide fluxes across the atmosphere–ice–water interfaces in the Arctic Ocean: Pacific sector of the Arctic

Climatic changes in the Northern Hemisphere have led to remarkable environmental changes in the Arctic Ocean, which is surrounded by permafrost. These changes include significant shrinking of sea-ice cover in summer, increased time between sea-ice break-up and freeze-up, and Arctic surface water freshening and warming associated with melting sea-ice, thawing permafrost, and increased runoff. These changes are commonly attributed to the greenhouse effect resulting from increased atmospheric carbon dioxide (CO 2) concentration and other non-CO 2 radiatively active gases (methane, nitrous oxide). The greenhouse effect should be most pronounced in the Arctic where the largest air CO 2 concentrations and winter–summer variations in the world for a clean background environment were detected. However, the air–land–shelf interaction in the Arctic has a substantial impact on the composition of the overlying atmosphere; as the permafrost thaws, a significant amount of old terrestrial carbon becomes available for biogeochemical cycling and oxidation to CO 2. The Arctic Ocean's role in determining regional CO 2 balance has been ignored, because of its small size (only ∼ 4% of the world ocean area) and because its continuous sea-ice cover is considered to impede gaseous exchange with the atmosphere so efficiently that no global climate models include CO 2 exchange over sea-ice. In this paper we show that: (1) the Arctic shelf seas (the Laptev and East-Siberian seas) may become a strong source of atmospheric CO 2 because of oxidation of bio-available eroded terrestrial carbon and river transport; (2) the Chukchi Sea shelf exhibits the strong uptake of atmospheric CO 2; (3) the sea-ice melt ponds and open brine channels form an important spring/summer air CO 2 sink that also must be included in any Arctic regional CO 2 budget. Both the direction and amount of CO 2 transfer between air and sea during open water season may be different from transfer during freezing and thawing, or during winter when CO 2 accumulates beneath Arctic sea-ice; (4) direct measurements beneath the sea ice gave two initial results. First, a drastic pCO 2 decrease from 410 μatm to 288 μatm, which was recorded in February–March beneath the fast ice near Barrow using the SAMI-CO 2 sensor, may reflect increased photosynthetic activity beneath sea-ice just after polar sunrise. Second, new measurements made in summer 2005 beneath the sea ice in the Central Basin show relatively high values of pCO 2 ranging between 425 μatm and 475 μatm, values, which are larger than the mean atmospheric value in the Arctic in summertime. The sources of those high values are supposed to be: high rates of bacterial respiration, import of the Upper Halocline Water (UHW) from the Chukchi Sea (CS) where values of pCO 2 range between 400 and 600 μatm, a contribution from the Lena river plume, or any combination of these sources.

Autonomous detection of cryospheric change with hyperion on-board Earth Observing-1

On-board detection of cryospheric change in sea ice, lake ice, and snow cover is being conducted as part of the Autonomous Sciencecraft Experiment (ASE), using classifiers developed for the Hyperion hyper-spectral visible/infrared spectrometer on-board the Earth Observing-1 (EO-1) spacecraft. This classifier development was done with consideration for the novel limitations of on-board processing, data calibration, spacecraft targeting error and the spectral range of the instrument. During on-board tests, these algorithms were used to measure the extent of cloud, snow, and ice cover at a global suite of targets. Coupled with baseline imaging, uploaded thresholds were used to detect cryospheric changes such as the freeze and thaw of lake ice and the formation and break-up of sea ice. These thresholds were used to autonomously trigger follow-up observations, demonstrating the capability of the technique for future planetary missions where downlink is a constrained resource and there is high interest in data covering dynamic events, including cryospheric change. Before upload classifier performance was assessed with an overall accuracy of 83.3% as measured against manual labeling of 134 scenes. Performance was further assessed against field mapping conducted at Lake Mendota, Wisconsin as well as with labeling of scenes that were classified during on-board tests.

Flood detection and monitoring with the Autonomous Sciencecraft Experiment onboard EO-1

In this paper, we present a new way of detecting and monitoring flooding through the Autonomous Sciencecraft Experiment (ASE) [Chien, S. T., Debban, C., Yen, R., Sherwood, R. Castano, B., & Cichy, A. G. et al. (2001). ASC Science Study Report, available from http://ASE.jpl.nasa.gov], which is part of the Space Technology 6 effort under NASA's New Millennium Program. Recent autonomy experiments conducted on Earth Observing 1 (EO-1) using the ASE flight software have demonstrated the ability of several science algorithms to successfully classify key features including flood-induced changes, in hyperspectral images captured by the EO-1 Hyperion instrument. Furthermore, onboard science analysis on the classified images has been performed, and then used to modify an operational plan without interaction from the ground (Sherwood, R., Chien, S., Tran, D., Cichy, B., Castano, R., Davies, A., et al. (2004). Preliminary results of the autonomous sciencecraft experiment. In: Proceedings of the IEEE Aerospace Conference, Big Sky, MT). These algorithms are used to downlink science data only when change occurs, and to detect features of scientific interests such as flooding, volcanic eruptions, and the formation and breakup of sea ice. The purpose of this paper is to demonstrate the success of ASE and its implications on detecting, mapping, and monitoring transient processes such as flooding autonomously from space. Mapping of water inundation and its change through time is part of our focus in studying transient processes from space. In 2004, hyperspectral data were acquired from the Hyperion instrument for target areas around the world that have a high potential for flooding to develop and test floodwater classifiers. In addition, classifier thresholds were determined from both normal flows and possible flood conditions. The paper introduces the development, testing, and success of the ASE software in detecting and reacting to flooding in near real-time. ASE is now operational and flight-tested, and, thus, ready to use for space-borne reconnaissance. Successful demonstration of the floodwater classifiers includes the capture of a rare flooding event of the Australian Diamantina River during ground testing in February 2004, and the detection of flood-related changes along the Brahmaputra River in Bangladesh and the Yukon River in Alaska during onboard testing on EO-1 in 2005. Both of these detections led to triggered responses onboard the spacecraft, which included acquiring additional Hyperion scenes. These results pave the way for future smart reconnaissance missions of transient processes on Earth and beyond. It is hoped that ASE will become a default in future missions to increase the science return by introducing spacecraft autonomy for detection and monitoring of science events, which otherwise would be discovered too late or altogether missed.

Particle fluxes and geochemistry on the Canadian Beaufort Shelf: Implications for sediment transport and deposition

Biogeochemical data from four sequential sediment traps deployed for one full year (April 1987–March 1988) at the shelf edge (200 m isobath) of the Canadian Beaufort Sea are presented. In addition, multi-traps and Kenney traps, which collect material suspended near the bottom, provided data from the inner shelf for short intervals in spring and summer. A novel aspect of this work is the discrimination of biogenic and terrigenous contributions to the total carbon using a relationship between terrigenous carbon and aluminum (Al). The vertical flux in the Beaufort Sea derives primarily from three sources: marine biological production, the Mackenzie River Plume, and coastal and seabed erosion. The material trapped at all shelf edge sites was predominantly biogenic and the seasonal fluxes of both biogenic and terrigenous matter varied with geographical location. In open-water conditions, deposition of terrigenous material can be attributed at various times and places to (1) transport by the Mackenzie Plume to the shelf edge during freshet; (2) resuspension of sediment during north-westerly gales; and (3) erosion of steep coastlines during south-easterly gales followed by northward transport. On the west side of the shelf, the biogenic and terrigenous fluxes were highest in summer and were primarily influenced by the Mackenzie River freshet, increased solar flux, available nutrients, sea ice break-up, and water column stability. On the east side of the shelf, biogenic and terrigenous fluxes were highest in the fall and the most important controlling factors were the extensive open water, intense resuspension events accompanying storms from the northwest, and the flow of the fresh, warm, turbid waters of Mackenzie River to the northeast. There was strong evidence of sediment transport in mid-water and bottom layers, but the mechanisms involved cannot be inferred from this study. Stable isotopes of carbon and nitrogen, C/N ratios, biogenic silica, and chlorophyll a measurements help to distinguish between marine autotrophic production and heterotrophic production, of which the latter appears to dominate in the fall and continue beneath the ice into the polar night. Al and iron correlate strongly and are primarily associated with the terrigenous fraction whereas calcium and phosphorus have both terrestrial and biogenic associations.

Observed storminess patterns and trends in the circum-Arctic coastal regime

Storm event statistics for the open-water season (June–October) were extracted from the terrestrial-based observational record throughout the circumpolar coastal regime over the period 1950–2000. The Barents/Norwegian and Kara regions exhibited an active spring/quiet summer signature typical of the mid-latitudes. The Kara and Laptev Sea regions had a strong June peak possibly associated with early sea ice breakup. The Chukchi sector exhibited large storm power values (defined as speed2*duration). Storm counts declined from 1950 to 1970, shifted rapidly from 1970 to 1974 to a level of greater mean activity and greater inter-annual variability, and declined after 1988.

CLIMATE CHANGE AND RINGED SEAL (PHOCA HISPIDA) RECRUITMENT IN WESTERN HUDSON BAY

Climate warming is predicted to reduce the extent of ice cover in the Arctic and, within the Hudson Bay region, the annual ice may be significantly decreased or entirely lost in the foreseeable future. The ringed seal (Phoca hispida), a key species that depends on sea ice, will likely be among the first marine mammals to show the negative effects of climatic warming. We used 639 ringed seals killed by Inuit hunters from western Hudson Bay (1991–1992, 1999–2001) to assess trends in recruitment relative to snow depth, snowfall, rainfall, temperature in April and May, North Atlantic Oscillation (NAO) from the previous winter, and timing of spring break-up. Snowfall and ringed seal recruitment varied from lower than average in the 1970s, to higher in 1980s and lower in 1990s. Prior to 1990, seal recruitment appeared to be related to timing of spring ice break-up which was correlated with the NAO. However, recent 1990–2001 environmental data indicate less snowfall, lower snow depth, and warmer temperatures in April and May when pups are born and nursed. Decreased snow depth, particularly below 32 cm, corresponded with a significant decrease in ringed seal recruitment as indicated by pups born and surviving to adults that were later harvested. Earlier spring break-up of sea ice together with snow trends suggest continued low pup survival in western Hudson Bay.

Reproductive rates of ringed seals and survival of pups in Northwestern Hudson Bay, Canada, 1991?2000

Reproductive parameters were determined from a sample of ringed seals collected by Inuit hunters during their annual open water harvest in autumn at Arviat, Nunavut, on the western coast of Hudson Bay, Canada, in 1991–1992 and 1998–2000. Ovulation rates of adult females were high and similar to rates recorded from studies of ringed seals in other geographic areas. However, pregnancy rates averaged only 55% and were significantly lower than in other studies, and the proportions of young-of-the-year were only 4.8, 4.2, 7.5, 4.1, and 23% for the mentioned years, respectively, instead of being >30% as expected. These results appear to indicate that reproductive parameters of ringed seals and survival of their young are exhibiting long-term shifts rather than short-term fluctuations, and that the trend is downward. Furthermore, these downward trends in reproduction, in conjunction with changes in the proportions of different seal species in the diet of polar bears, climatic warming in western Hudson Bay, and progressively earlier breakup of sea ice over the last 25 years, suggest that major changes are occurring in the marine ecosystem of Hudson Bay. The pathways involved are poorly understood and merit further study.

In situ Sea Ice Experiments in McMurdo Sound: Cyclic Loading, Fracture, and Acoustic Emissions

The breakup of first-year sea ice plays an important role in the dynamics and thermodynamics of polar ice covers. A recent research program has studied the in situ mechanical properties of the annual ice in Antarctica to support the development of physically based models of the breakup process. As part of this effort, two field trips were conducted to McMurdo Sound, and the present paper describes the experimental work and presents selected results. The in situ experiments investigated the constitutive and fracture behavior of edge-notched, square plate specimens of first-year ice and involved a detailed characterization of the physical properties and thermal state of the ice. Acoustic emissions, which are generated by microcracking, were monitored in the crack tip vicinity and provide insight regarding the size of the process zone. The paper describes the physical properties and microstructure of the sheet, the cyclic-loading response, and the acoustic emissions activity from an extensive series of experiments conducted on one of the in situ specimens. Varying the cyclic-loading frequency and amplitude provided a means to examine rate effects on the anelastic and viscous components of strain and the extent of microcracking near the crack tip. The viscous deformation rate estimated from the experiments exhibited an increasing power-law exponent with values between one and three. Acoustic emissions monitoring indicated that microcracking occurred in a process zone near the crack tip, and the size of the process zone increased with decreasing cyclic loading frequency. Practical aspects of the experiments are considered, and the results are put into context with the overall modeling goals of the project.