Contribution of North Atlantic Intermediate and Deep water Masses to the Earth’s Heat Balance

The Intergovernmental Program on Climate Change (IPCC, 1996) and the WCRP CLIVAR Program (CLIVAR, 1995)have identified the ocean as being critical to understanding the earth’s climate system and how climatic conditions may change with time. We quantify for the first time the contribution of the entire North Atlantic Ocean, from the surface through 3000 m depth, the interannual-to-decadal variability of the heat storage of this ocean.

We present results that quantify the rate of heat storage for the North Atlantic Ocean for depths below 500 m for the period from 1970-74 through 1988-92. Cooling occurred throughout the subarctic gyre with the maximum rate of heat storage exceeding 6 W/M-2 in the Labrador Sea. Most of these changes occurred below depths of 500 m. Warming occurred in the midlatitudes and subtropics with values exceeding 6 W/M-2 in the western midlatitudes of the North Atlantic. Most of this change occurred in the upper 1000 m of the water column. The changes in the Labrador Sea are consistent with changes associated in convective activity of the North Atlantic. Water mass properties associated with the Mediterranean Outflow at 1750 m depth are oppositely correlated with changes induced by the renewal of deep convection in the Labrador Sea. The observed decadal changes in the heat storage of the Atlantic are comparable to similar changes in the upper ocean and changes in both regions are comparable in magnitude to the climatological annual cycle of heat storage in the upper ocean which is driven directly by solar heating ocean.