The Labrador Sea
The Labrador Sea as a "Vital Organ" in the Earth System
The Labrador Sea, off the east coast of Canada, is one of the few oceanic regions where the deep ocean exchanges gases such as oxygen and carbon dioxide (CO2) directly with the atmosphere (Clarke and Coote, 1988; Azetsu-Scott et al., 2003; DeGrandpre et al., 2006). This gas exchange, driven by wintertime deep convection is the ocean's "deep breathing" and the Labrador Sea can be viewed as a lung in the Earth System. Localized deep convection releases large amounts of heat to the atmosphere (Lazier et al. 2002) and the resulting Labrador Sea Water contributes to the global ocean thermohaline circulation that redistributes heat from low latitudes to the poles. Deep water formation in the Labrador Sea is one of several tipping points in the Earth.s climate system (Lenton et al. 2008). Convection also drives a large flux of oxygen and anthropogenic CO2 into the North Atlantic, oxygenating subsurface layers and slowing the accumulation of CO2 in the atmosphere (Steinfeldt et al. 2009), but exacerbating ocean acidification along Canada's sensitive eastern continental margin (Azetsu-Scott et al. 2010). The combined action of convection and horizontal circulation redistributes nutrients and contaminants (e.g. from future deepwater oil production along the deep Labrador slope) potentially affecting ocean productivity and marine ecosystem health (Carmack 2007). These globally significant processes of direct importance to Canada are regionally localized, temporally variable, and sensitive to the effects of ongoing climate changes.
Gas uptake and redistribution processes ("breathing and circulation") are expected to respond to and feedback on climate change, as the hig h latitude warming surrounding the Labrador Sea increases stratification (Dickson et al. 2007). Stratification changes may come from direct surface warming as well as the enhanced freshwater input from the melting of snow, multi-year sea ice and glaciers in Greenland and Canada . In either case, enhanced stratification will likely lead to a decline in deep water oxygen (Keeling et al. 2010) and anthropogenic CO2 sequestration (Steinfeldt et al. 2009). With the accelerating rate of warming in the hig h North (Gillett et al. 2008), multiple sources of freshwater now converge on the Labrador Sea (Dickson et al. 2007), with the potential to disrupt deep convection, meridional ocean heat transport, climate, and ocean biogeochemistry at regional and global scales (Stouffer et al . 2006). A present concern, which still requires evaluation, is that a slowdown in deep water formation will cut off the source of oxygen a nd .suffocate. the deep ocean, and reduce a critical sink of anthropogenic CO2. Thus, it is essential that "breathing and circulation" processes be represented properly in coupled ocean-ice-atmosphere climate models. Currents bringing low-oxygen and high biological CO2 wate r from the Arctic and subtropics are analogous to the .veins. of the system. Regional mixing and biogeochemical processes within the Labrad or Sea transform the source waters within the basin. Advective-diffusive export pathways ("arteries") connect the oxygenated and transformed water masses to the Atlantic Ocean interior.
Labrador Sea and Canada
The Labrador Sea and surrounding shelves are critical for the ecological, economic, and societal health of North America and Europe. Canada has a national investment in offshore fisheries and transportation within this basin, and a growing presence as resource exploration and exploitation moves northward and farther offshore. Eastern Canada's weather and climate are also strongly influenced by the Labrador Sea (Dickson 1997). The Labrador Sea is important strategically as the Canadian gateway to the Arctic. It is therefore critical that Canada, as the only G8 nation that borders this important basin, has a strong voice on the world stage about events occurring in this basin. Canada also has a long tradition of scientific firsts in this globally important region in climate studies, including the earliest recognition of the variability of Labrador Sea Water formation (Lazier, Clarke), and the first process-oriented and tracer studies of deep convection (Clarke and Gascard 1983) and ocean acidification (Azetsu-Scott et al., 2010). This proposal announces our intent to leverage Canada's academic expertie and to build on the long-term monitoring program of Fisheries and Oceans Canada (DFO) and previous studies carried out intermittently by German, U.S. and the UK. VITALS will consider the role of the Labrador Sea in the global thermohaline circulation and high latitude climate, its influence on deep ocean biogeochemistry and atmospheric CO2 levels, and its accurate representation in numerical models, with an end goal of their accurate representation in Canadian coupled climate models, used by Canadian governmental agencies.