Is the Global Conveyor Belt Threatened by Arctic Ocean Fresh Water Outflow?

Understanding climate and climate change is a main motive for determining fresh water budget of the Arctic Ocean, specifically the sources, distributions and pathways of fresh water. Most fresh water within the Arctic Ocean occurs as a result of there being more evaporation than precipitation in the Atlantic Ocean. Much of the excess evaporation from the Atlantic Ocean falls as rain into the Pacific Ocean and into river drainage basins that feed into both the Pacific and Arctic Oceans. The climate change concern is that, in returning to evaporation sites in the Atlantic Ocean, the fresh water passes through regions of deep convection in the Nordic and Labrador seas, the “headwaters” of the Global Conveyor Belt (Fig. 16.1). To quote Aagaard and Carmack (1989), “We find that the present-day Greenland and Iceland seas, and probably also the Labrador Sea, are rather delicately poised with respect to their ability to sustain convection.” Under climate change, we can anticipate changes in fresh water fluxes from the Arctic Ocean. A main motive for trying to determine Arctic Ocean fresh water sources and their distributions is to try to assess the vulnerability of the Atlantic thermohaline circulation to such changes. How the fresh water sources are redistributed within the Arctic Ocean together with the place and timing of their exit from the Arctic Ocean are of direct relevance to the development of models giving scenarios of changes, possibly abrupt, in the Atlantic thermohaline circulation (e.g., Rahmstorf 1996). Fortunately, tracers allow us to distinguish among the different sources of fresh water being exported from the Arctic Ocean thereby allowing changes in each to be separately accommodated in climate change model scenarios.