Modeling the Freshening and Cooling Event in the Subpolar North Atlantic Ocean and its Impact on Thermohaline Circulation

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

ABSTRACT OCE-0351055 Large-scale and full-depth cooling and freshening have occurred in the subpolar North Atlantic Ocean in the last four decades. This was accompanied by a reduction of the Nordic Seas overflow through the Faroe Bank Channel, a key process for the NADW formation. Observations indicated that interaction between the Nordic Seas and the Atlantic Ocean may have played a key role in the development of this event. The PI proposes to use numerical models to study mechanisms and interactions that give rise to the observed changes, and to assess their impacts on the thermohaline circulation (THC) and on ocean circulations in the tropical and subtropical Atlantic Ocean. Since the dynamics and scales inherent to such exchanges are very different from that of the general circulation over the open ocean, most ocean general circulation models (OGCMs) are not yet adequate for modeling interactions between the Nordic Seas and the Atlantic Ocean. Supported by a previous NSF grant, the PI and Dr. Jim Price have developed a coupled OGCM/marginal-sea model with the specific purpose of applying it in the subpolar North Atlantic Ocean. This coupled model represents a state of the art numerical tool for studying interactions among the Nordic Seas overflow, the density current entrainment at shelf breaks, and open ocean processes. The model will be used to address (1) how the sustained positive state of North Atlantic Oscillation in the last 4 decades a?ected the fresh water budget in the Nordic Seas; (2) how the overflow through the Denmark Strait and Faroe Bank Channel responded to the fresh water forcing in the Nordic Seas; (3) how the freshening of the overflowed source water a?ected the entrainment rate at shelf breaks and thus the property and production of NADW; (4) how the THC responded to changes in NADW production; (5) what role the wind-driven circulation played in this cooling and freshening event; (6) how the circulation in the low-latitude ocean responded to the NADW and THC changes.