The polar regions of the earth have long been the focus of geopoliticians, explorers and scientists. In the present era of global climate change, interest in the Arctic region has grown, particularly in response to the recent summertime opening of the fabled "northwest passage." Expansion of sovereignty claims into the deep Arctic Ocean, and competition for the exploitation of significant oil, natural gas and mineral reserves have increased the focus. Environmental change in the Arctic not only has profound implications and consequences for the peoples and societies of the north, but also for the global community through climate impacts.

In recent years, scientific research has shown significant warming over land and sea in the Arctic, and increased sea-ice loss in the Arctic Ocean. The Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment, released in 2007, reported that average air temperatures in the Arctic have increased over the last century at nearly twice the global average. Since 1978, sea ice extent decreased on average by 2.7% per decade. However, over the last several years, the pace of decline has accelerated beyond model predictions and in summer 2007, sea-ice extent declined by 20-25% with an additional loss of ~1.2 million km². Much of this loss occurred over the polar continental shelves and Makarov and Canada Basins of the Arctic Ocean. This led to the opening of the "northwest passage" across the Arctic. A couple of years ago, summertime sea-ice free conditions across the Arctic Ocean were predicted by 2030-2040. Recent studies suggest sea-ice free conditions could occur by 2013. Given the pace of change and revised predictions of summer sea-ice free conditions, it has become critical to gain a better understanding of the interactions between freshwater, heat and sea-ice dynamics, carbon cycle, climate and greenhouse gases in the Arctic region.

The Arctic region has a critical role in the global freshwater cycle, Atlantic overturning circulation, and biogeochemical cycling of carbon, nutrients, and climate forcing gases such as carbon dioxide (CO₂), methane (CH₄) and dimethylsulphide (DMS). Due to complex interactions and feedbacks, this region is particularly sensitive to albedo and heat budget changes, low-frequency modes of atmosphere-ocean-sea-ice forcing, and ecosystem changes associated with warming temperatures and sea-ice loss.

Arctic carbon cycle research is a central goal of the U.S. Climate Change Science Program's (CCSP) research priorities and it has been recognized that "while considerable progress has been made in the study of Arctic carbon, ecosystem and ocean dynamics, significant gaps and uncertainties remain that limit our understanding of carbon sources and sinks and the linkages and feedbacks between carbon and climate". In this edition of Meridian, Dr. Michael Lomas describes a new research project that is focused on the Bering Sea. We also briefly detail in this edition of Meridian two other research projects that are focused on the Chukchi Sea and Arctic Ocean.

The Bering Sea and Chukchi Sea are highly productive marine ecosystems that support important human socio-cultural and economic activities. Physical processes and seasonal sea ice cover play a major role in shaping the ecosystems of the Bering Sea and Chukchi Sea. The southeast Bering Sea, particularly along the coastal "green belt", extending northwards along the continental shelf, plankton primary production supports a large population of seabirds, and marine mammals, >50% of commercial fish and shellfish landings in the U.S., and traditional use of marine resources by the native peoples of Alaska and eastern Siberia. The character of the marine ecosystem productivity in the Bering Sea has undergone dramatic change over the past decade, the domination of cold-water, Arctic species replaced by organisms more indicative of temperate zones. For example, large, sweeping populations of jellyfish have come and gone, and previously infrequent coccolithophorid blooms have become regular features.

In the Chukchi Sea, during the brief "summertime" period of seasonal sea-ice melt and retraction toward the pole, the flow of nutrient-rich Pacific and Alaskan coastal waters from the Bering Sea through the Bering Strait into the Chukchi Sea supports a brief but intense plankton primary production in the seasonally sea-ice free regions of the Chukchi and Beaufort Seas and Canada Basin. In the Chukchi Sea, this primary production supports substantial pelagic and benthic biomass that, in turn, supports fish, bird and mammal populations. The planktonic foundation for support of migrating whale and resident walrus populations in the Chukchi Sea is highly important for the peoples of Alaska.

At the Bermuda Institute of Ocean Sciences (BIOS), two new research projects are focused on the Arctic Ocean. Despite the importance and highly dynamic physical and biological nature of the Arctic, there are very few studies of carbon cycling in the region. The carbon cycle and CO₂ are highly influenced by seasonal light and temperature changes, seasonal sea-ice dynamics, and biological production influence inorganic nutrient and carbon dynamics in the Arctic Ocean. Between 2002 and 2004, observations made by our group at BIOS in the Canada Basin indicated that the Arctic Ocean has a strong potential to be a sink for atmospheric CO₂, although, at present, suppressed by perennial sea-ice cover. The reduction of sea-ice has tripled the uptake of atmospheric carbon dioxide (CO₂) in the region over the last few decades. With sea-ice extent and volume in the Arctic Ocean decreasing over the last few decades and expected to decrease further over the next few decades, it has been predicted that the Arctic Ocean region may absorb much larger amounts of CO₂, but release methane from permafrost from sediments in the coastal seas of the Arctic. Thus, as part of a joint U.S.-Russian research project titled, Russian-American Long-term Census of the Arctic (RUSALCA), and funded by the National Oceanic and Atmospheric Administration (NOAA), BIOS scientists will join cruises to the Arctic Ocean aboard Russian research vessels over the next few years. This summer, research specialist Marlene Jeffries will join a Russian vessel in Alaska for a survey of the Arctic Ocean in the region of the extreme sea-ice loss in the Makarov and Canada Basins of the Arctic observed in 2007. Observations of the carbon cycle and CO₂ will be made in a region where little or no data exists.

In a separate but complimentary project funded by the National Science Foundation (NSF), our team at BIOS has been funded to answer two main questions: "What are the present stocks and controls of carbon in the Arctic Ocean and adjacent polar seas?" and, "How will climate change (i.e., sea-ice reduction, changes in stratification, production and freshwater/materials inputs) affect the carbon cycle of the Arctic Ocean and adjacent polar seas?" In this project (and in collaboration with scientists at University of Alaska Fairbanks, Rosenstiel School of Marine and Atmospheric Sciences (RSMAS) and University of Rhode Island (URI)), a synthesis and modeling study will improve our knowledge of the carbon and air-sea CO₂ exchanges across the entire Arctic region.

This research contributes to understanding how climate variability over multiple time scales influences the coupled physical, chemical, and biological processes of the arctic shelf-basin systems. It will also provide basic information that allows scientists to assess how changes in these processes affect the broader Arctic system.

Global industrialization - while having many social benefits - has resulted in the ever increasing consumption of fossil fuels to support the demand for energy and transportation. Associated with this increase in fossil fuel consumption has been a drastic increase in the rate of carbon dioxide accumulation in the atmosphere, the likes of which have not been seen in the past 600 million years (Siegenthaler et al. 2005). The Fall 2007 issue of the Meridian focused on the role of carbon dioxide in ocean acidification and the ramifications for Bermuda's corals; but elevated carbon dioxide levels has other impacts on marine ecosystems. As a greenhouse gas, carbon dioxide has strong and predictable correlations with global temperatures which have increased by ~0.7oC over the past century. This relatively small increase in global temperature, along with changes in Arctic weather patterns, has had a disproportionately large effect on the spatial distribution and dynamics of Arctic/sub-Arctic sea ice. In the past, Arctic sea ice would melt in the summer and refreeze in the winter. However, for the past several years the extent of summer sea ice extent has been even lower than predicted - suggesting that Arctic sea ice melting has reached (or perhaps passed) a 'tipping point' into an irreversible phase of increased warming and continued melting. While this loss of Arctic sea ice will not contribute directly to global sea level rise, the loss of sea ice could further accelerate global warming, as white-colored ice tends to deflect heat. Darker-colored water, however, absorbs heat, leading to further melting of land-based ice which will lead to an increase in surface sea level. Beyond the global impacts of polar sea ice loss, the loss of sea ice will also have a profound impact on polar ecosystems, potentially altering critical U.S. fisheries and threatening 'charismatic megafauna' such as polar bears, seals and other sea life.

I, in collaboration with Dr. Brad Moran at the Graduate School of Oceanography - University of Rhode Island, have recently begun a four year, U.S. National Science Foundation (NSF) funded project on the eastern Bering Sea Shelf. The first cruise is underway aboard the U.S.C.G. Icebreaker Healy (http://bsierp.nprb.org/cruises/index.html) while this issue of Meridian is in press. Our project is part of a much larger program called the Bering Sea Ecosystem Study (BEST) (http://bsierp.nprb.org/index.htm), with the goal of improving our scientific understanding of the entire Bering Sea ecosystem - from nutrients to walruses and native peoples - and how the ecosystem as a whole may respond to climate change. The climate change-related driver in the eastern Bering Sea is sea ice extent and, while a four year study is unlikely to be able to detect definitive responses to climate change, we will be able to observe strong interannual variability in sea ice extent

Interannual changes in southward ice edge extent in April in the eastern Bering Sea (Figure provided by Rodionov et al., 2007).

and make more educated predictions about future responses to climate change. Our specific contributions to the larger program are to quantify phytoplankton primary production and its fate within the eastern Bering Sea ecosystem in response to interannual variability in wintertime sea ice extent.

The eastern Bering Sea shelf is an ocean region bounded by the Alaskan coastline and the Aleutian archipelago. This region has an area of approximately two million square kilometers, or roughly half again larger than the state of Alaska. Much of the eastern Bering Sea is characterized by a relatively shallow shelf (<70m) but has a sharp drop off to depths >200m at its western boundary. The eastern Bering Sea alone accounts for ~55% of all U.S. fisheries landings from crustaceans to pelagic fishes like pollock and salmon, and as such has a huge impact on the U.S. food supply and economy of the region (dockside landings valued at over two billion dollars). The eastern Bering Sea, due to its shallow nature, has a biologically active and diverse benthic (seabed) habitat as well as a pelagic (water column) habitat. These habitats differ not only in the organisms that occupy them (crustaceans and flat fishes in the benthic habitat and pollock, salmon and other predatory fish in the pelagic habitat) but also upon the mechanisms by which they derive their nutrition. The benthic habitat is fueled by phytoplankton primary production that occurs near the ice-edge and that directly sinks to the benthos and is consumed by crustaceans, mollusks and other benthic infauna. Many marine mammals (e.g., walruses, grey whales and seals) are benthic feeders living off these mollusks and benthic infauna. In the pelagic habitat phytoplankton primary production occurs in open water, away from the ice-edge, and is efficiently grazed by zooplankton that in turn are fed upon by predatory pelagic fishes. This bifurcation in the flow of carbon through the eastern Bering Sea ecosystem may be a very important control point, as this partitioning of phytoplankton primary production between benthic and pelagic habitats is temperature dependent, due primarily to differences in temperature-related growth responses of phytoplankton and zooplankton. Phytoplankton, which divide by mitosis, are able to grow at lower temperatures than zooplankton due to the fact that lower temperatures reduce egg development and larval growth rates in zooplankton.