The minimum of Arctic sea ice extent in the summer of 2007 was unprecedented in the historical record. A coupled ice-ocean model is used to determine the state of the ice and ocean over the past 29 years to investigate the causes of this ice extent minimum within a historical perspective. It is found that even though the 2007 ice extent was strongly anomalous, the loss in total ice mass was not. Rather, the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987. Since then, the simulated mean September ice thickness within the Arctic Ocean has declined from 3.7 to 2.6 m at a rate of -0.57 m/decade. Both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing. The combined impact of these two trends caused a large reduction in the September mean ice concentration in the Arctic Ocean. This created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the Pacific side to the Atlantic side of the basin and more than usual into the Greenland Sea. This exposed large areas of open water, resulting in the record ice extent anomaly.
The first and strongest signs of global-scale climate change exist in the high latitudes of the planet. Evidence is now accumulating that the Arctic is warming, and responses are being observed across physical, biological, and social systems. The impact of climate change on oceanographic, sea-ice, and atmospheric processes is demonstrated in observational studies that highlight changes in temperature and salinity, which influence global oceanic circulation, also known as thermohaline circulation, as well as a continued decline in sea-ice extent and thickness, which influences communication between oceanic and atmospheric processes. Perspectives from Inuvialuit community representatives who have witnessed the effects of climate change underline the rapidity with which such changes have occurred in the North. An analysis of potential future impacts of climate change on marine and terrestrial ecosystems underscores the need for the establishment of effective adaptation strategies in the Arctic. Initiatives that link scientific knowledge and research with traditional knowledge are recommended to aid Canada's northern communities in developing such strategies.
General circulation models (GCMs) are unanimous in projecting warmer temperatures in an enhanced CO2 atmosphere, with amplification of this warming in higher latitudes. The Hudson Bay region, which is located in the Arctic and subarctic regions of Canada, should therefore be strongly influenced by global warming. In this study, we compare the response of Hudson Bay to a transient warming scenario provided by six-coupled atmosphere-ocean models. Our analysis focuses on surface temperature, precipitation, sea-ice coverage, and permafrost distribution. The results show that warming is expected to peak in winter over the ocean, because of a northward retreat of the sea-ice cover. Also, a secondary warming peak is observed in summer over land in the Canadian and Australian-coupled GCMs, which is associated with both a reduction in soil moisture conditions and changes in permafrost distribution. In addition, a relationship is identified between the retreat of the sea-ice cover and an enhancement of precipitation over both land and oceanic surfaces. The response of the sea-ice cover and permafrost layer to global warming varies considerably among models and thus large differences are observed in the projected regional increase in temperature and precipitation. In view of the important feedbacks that a retreat of the sea-ice cover and the distribution of permafrost are likely to play in the doubled and tripled CO2 climates of Hudson Bay, a good representation of these two parameters is necessary to provide realistic climate change scenarios. The use of higher resolution regional climate model is recommended to develop scenarios of climate change for the Hudson Bay region.
Hudson Strait plays a crucial role for navigation into and out of Hudson Bay. The Strait is ice-covered for eight months of the year. We demonstrate the ability to forecast ice conditions, particularly ice formation and retreat, up to seven months in advance. Sea ice retreat and formation for three locations in Hudson Strait has been successfully forecasted for the years 2000-2003 using sea ice data collected from 1971 to 1999. On average, forecasts for the date of sea ice formation were within a week of the actual formation date, the temporal resolution of the sea ice data. Forecasts for the date of sea ice retreat were within the resolution of the sea ice data at the easternmost site and ±11 and 15 days at the middle and westernmost sites, respectively. Inclusion of the average air temperature of the preceding ice-free season improved the average forecast of ice retreat at the western site by six days while only marginally affecting the other two sites. This initial attempt exploits climate memory which may be applicable elsewhere.
The two polar regions have experienced remarkably different climatic changes in recent decades. The Arctic has seen a marked reduction in sea-ice extent throughout the year, with a peak during the autumn. A new record minimum extent occurred in 2007, which was 40% below the long-term climatological mean. In contrast, the extent of Antarctic sea ice has increased, with the greatest growth being in the autumn. There has been a large-scale warming across much of the Arctic, with a resultant loss of permafrost and a reduction in snow cover. The bulk of the Antarctic has experienced little change in surface temperature over the last 50 years, although a slight cooling has been evident around the coast of East Antarctica since about 1980, and recent research has pointed to a warming across West Antarctica. The exception is the Antarctic Peninsula, where there has been a winter (summer) season warming on the western (eastern) side. Many of the different changes observed between the two polar regions can be attributed to topographic factors and land/sea distribution. The location of the Arctic Ocean at high latitude, with the consequently high level of solar radiation received in summer, allows the ice-albedo feedback mechanism to operate effectively. The Antarctic ozone hole has had a profound effect on the circulations of the high latitude ocean and atmosphere, isolating the continent and increasing the westerly winds over the Southern Ocean, especially during the summer and winter.
Sea ice is an integral part of the marine ecosystem in the Arctic and important habitat for ringed seals and polar bears. To study changes in sea ice characteristics indicative of ringed seal habitat (and linked, through predator/prey relationships, to polar bear habitat), we examined historical changes in sea ice concentration and type within M'Clintock
Channel and the Gulf of Boothia, two regions of the Canadian Arctic Archipelago, during 1980-2000. Results suggest large interannual variability in winter ice conditions over the 21-year study period. In M'Clintock Channel, first-year ice types
dominated consistently, while in the Gulf of Boothia, thick ice types dominated in some years. For breakup and consolidation, the regional spatial patterns differed significantly, occurring in opposite directions (N-S vs. S-N) in the two regions. The dates showed considerable interannual variability in both regions, suggesting no clear pattern of either earlier breakup or later consolidation. Analysis of satellite data confirmed the results obtained from digital ice charts. Ringed seal habitat suitability indices (HSI) indicate that both regions contained primary, secondary, and tertiary HSI classes. No trends were evident in the secondary or tertiary classes, but changes in the primary class were evident in M'Clintock Channel over the five-year period 1997-2001. Dynamic and thermodynamic sea ice processes are important to ringed seal habitat (and
ultimately, polar bear habitat) at regional and hemispheric scales in the current context of climate variability and change.
Global climate changes is expected to have an effect on the physical and ecological characteristics of the Baltic Sea. Estimates of future climate on the regional scale can be obtained by using either statistical or dynamical downscaling methods of global AOGCM scenario results. In this paper, we use 2 different coupled ice-ocean models of the Baltic Sea to simulate present and future ice conditions around 100 years from present. Two 10-year time slice experiments have been performed using the results of atmospheric climate model simulations as forcing, one representing pre-industrial climate conditions (control simulation), and the other global warming with a 150% increase in CO2 greenhouse gas concentration (scenario simulation). Present-day climatological ice conditions and interannual variability are realistically reproduced by the models. The simulated range of the maximum annual ice extent in the Baltic in both models together is 180 to 420 x 10(3) km2 in the control simulation and 45 to 270 x 10(3) km2 in the scenario simulation. The range of the maximum annual ice thickness is from 32 to 96 cm and from 11 to 60 cm in the control and scenario simulations, respectively. In contrast to earlier estimates, sea ice is still formed every winter in the Northern Bothnian Bay and in the most Eastern parts of the Gulf of Finland. Overall, the simulated changes of quantities such as ice extent and ice thickness, as well as their interannual variations are relatively similar in both models, which is remarkable, because the 2 coupled ice-ocean model systems have been developed independently. This increases the reliability of future projections of ice conditions in the Baltic Sea.
Arctic sea ice can incorporate sediment and associated chemical species during its formation in shallow shelf environments and can also intercept atmospherically transported material during transit. Release of this material in ice ablation areas (e.g. the Fram Strait) enhances fluxes of both sediments and associated species in such areas. We have used a suite of natural (7Be, 210Pb) and anthropogenic (137Cs, 239Pu, 240Pu) radionuclides in sea ice, sea-ice sediments (SIS), sediment trap material and bottom sediments from the Fram Strait to estimate transit times of sea ice from source to ablation areas, calculate radionuclide fluxes to the Fram Strait and investigate the role of sea-ice entrained sediments in sedimentation processes. Sea ice intercepts and transports the atmospherically supplied radionuclides 7Be and 210Pb, which are carried in the ice and are scavenged by any entrained SIS. All of the 7Be and most of the excess 210Pb measured in SIS collected in the Fram Strait are added to the ice during transit through the Arctic Ocean, and we use these radionuclides as chronometers to calculate ice transit times for individual ice floes. Transit times estimated from the 210Pb inventories in two ice cores are 1?3 years. Values estimated from the 7Be/210Pbexcess activity ratio of SIS are about 3?5 years. Finally, equilibrium values of the activity ratio of 210Pb to its granddaughter 210Po in the ice cores indicate transit times of at least 2 years. These transit times are consistent with back-trajectory analyses of the ice floes. The latter, as well as the clay-mineral assemblage of the SIS (low smectite and high illite content), suggest that the sampled sea-ice floes originated from the eastern Siberian Arctic shelf seas such as the eastern Laptev Sea and the East Siberian Sea. This result is in agreement with the relatively low activities of 239,240Pu and 137Cs and the 240Pu/239Pu atom ratios (_0.18, equivalent to that in global fallout) in SIS, indicating that prior global atmospheric fallout, rather than nuclear fuel reprocessing facilities, forms the main source of these anthropogenic radionuclides reaching the western Fram Strait at the time of sampling (1999). Transport of radionuclides by sea ice through the Arctic Ocean, either associated with entrained SIS or dissolved in the ice, accounts for a significant flux in ablation areas such as the Fram Strait, up to several times larger than the current atmospheric flux in the area. Calculated fluxes derived from sea-ice melting compare well to fluxes obtained from sediment traps deployed in the Fram Strait and are consistent with inventories in bottom sediments. 240Pu/239Pu atomic ratios lower than 0.18 in bottom sediments from the Fram Strait provide evidence that plutonium from a source other than atmospheric fallout has reached the area. Most likely sources of this Pu include tropospheric fallout from atomic weapons testing of the former Soviet Union prior to 1963 and Pu released from nuclear reprocessing facilities, intercepted and transported by sea ice to the ablation areas. Future work is envisaged to more thoroughly understand the actual mechanisms by which radionuclides are incorporated in sea ice, focusing on the quantification of the efficiency of scavenging by SIS and the effect of melting and refreezing processes over the course of several years during transit.