CICS/Princeton Research Highlights Northern Hemisphere-Southern Ocean Climate Link

Surface warming in the Northern Hemisphere, particularly amplified at high latitudes, could reduce the formation of cold deep water (primarily in the North Atlantic), significantly altering the oceans’ ability to moderate global climate variability and change. Using a simplified configuration of an ocean general circulation model developed at NOAA’s Geophysical Fluid Dynamics Laboratory (GFDL), Neven S. Fuckar at the Cooperative Institute for Climate Science (CICS) at Priceton University and Geoffrey K. Vallis at GFDL show that Northern Hemisphere surface warming, and the induced weakening of the deep inter-hemispheric Meridional Overturning Circulation (MOC), may produce substantial changes in the Southern Ocean. Strikingly, the Antarctic Circumpolar Current (ACC) could become much stronger. This, possibly paralleled with the intensification of the Southern Ocean overturning circulation, could increase the inter-basin exchange and the ventilation rate of waters in the Southern Hemisphere. Hence, this strengthening of zonal and meridional flow around the Antarctica could have an important impact on the oceans’ capability to moderate global climate variability and change. The study appears in the July 24, 2007 issue of the journal Geophysical Research Letters.

Background: The critical role of the ocean in climate dynamics stems from its enormous capacity to absorb heat, freshwater and chemical substances (i.e., tracers) and the global redistribution of these tracers on times scales of 100-1000 years. Such long duration, from the formation at the surface and sinking, to ventilation (i.e., rising to the surface) of the deep and abyssal waters, generates a mechanism for climate moderation. The MOC has an important role in the transport of tracers (primarily in the north-south direction). However, a truly global character of the oceans’ tracer transport is made possible by the zonally unobstructed flow around the Antarctica with the significant climatic relevance due to the associated ventilation of the deep and abyssal waters in the Southern Ocean. A change in the MOC-ACC interaction has a potential to modify the oceans’ ability to stabilize climate.

Significance: The dependence of the ACC zonal transport and the Southern Ocean overturning circulation on the northern hemisphere surface temperature, demonstrated in this study, enhances our understanding of the large-scale ocean circulation and the ocean’s role in climate. This research supports NOAA Mission Goal 2 – Understand Climate Variability and Change to Enhance Society's Ability to Plan and Respond.