Mechanisms of Decadal Variability in the North Atlantic: The Thermohaline Circulation, Great Salinity Anomalies, and Gulf Stream Path

Princeton University, Princeton NJ

Investigators

Abstract

ABSTRACT OCE-0351383 The proposed research is to investigate the physical mechanisms of decadal variability in the North Atlantic ocean. Particularly, it focuses on exploring the hypothesis that Great Salinity Anomalies (GSAs) are a significant contributing factor to such variability, through their effect on the thermohaline circulation, deep western boundary current (DWBC), northern recirculation gyre (NRG) and the north-south shifts of the Gulf Stream path. Preliminary numerical experiments indicate that GSA events have as much if not more effect on decadal ocean variability than do changes in the wind forcing (e.g., variability in the North Atlantic Oscillation) and, on decadal timescales, have a much larger effect than do changes in radiative and surface heat flux changes due to increased greenhouse gases. Furthermore, the interaction between GSA events and the thermohaline circulation may lead to decadal variations of the cyclonic NRG, north-south shifts of the Gulf Stream path and thereby affect the climate of the east coast of the USA. The approach is to investigate these issues with a combination of numerical experimentation and theory, using both simplified and comprehensive numerical ocean models, coupled to slab sea-ice models and a simple model of the atmosphere. These numerical calculations will be supplemented by theoretical investigations of the nature of GSAs and how their interaction with the thermohaline circulation may lead to variations of NGR and north-south shifts of the Gulf Stream path, and hence decadal changes in the mid-latitude ocean circulation. In addition to climate variability, the proposed research addresses some physical-oceanographic problems of long-standing interest, namely the mechanism governing the Gulf Stream separation, the downstream path and the production of cyclonic NRG, and the importance (or otherwise) of the GSA events and their effect on the thermohaline circulation. In addition to an increased understanding of the fundamental nature and causes of ocean and climate variability, the research will lead to a better sense of whether and how high-latitude ocean monitoring is necessary in predicting and detecting decadal climate variability