U.S. GLOBEC: Georges Bank PHASE III Modes of Circulation and Mixing on Georges Bank -- Quantifying Source Water Using the Oxygen Isotope Tracer

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9806542Fairbanks Georges Bank is the most studied ocean region in the world. However, more than a century of biological and physical oceanographic measurements have not yet lead to a predictive model of Georges Bank biological variability. This is a goal of U.S. GLOBEC: Georges Bank to which this project seeks to make a contribution. Circulation over Georges Bank can be described by two modes: (i) the canonical mode is an anticyclonic gyre with source waters originating in the coastal Gulf of Maine and, (ii) the "shunt mode" which is characterized by direct injection of Scotian Shelf Water across Northeast Channel onto the south flank of Georges Bank. The primary objective of this study is to make a quantitative assessment of the amount of the biological variance explained by these two circulation modes. This project is to continue use of the oxygen isotope tracer H 19 0 which has demonstratedthe unique ability to distinguish local and upstream freshwater sources. It has revealed significant inter-annual variations in the percent of freshwater on the Bank derived from local river sources. Although the details of the mixing processes responsible for exchanging water onto the Bank are not yet clearly understood, these results demonstrate the existence of distinct modes of circulation and mixing. Assessing the sensitivity of these modes to variations in external forcing and the consequences for the flux of particle and dissolved constituents onto Georges Bank is the primary objective. The significance of this project is to bring a quantitative assessment of the influence of local and far-field water sources on the Georges Bank environment. The water molecular isotope composition provides a tracer linking modern climate processes (e.g., runoff, sea ice, ice sheet, and marine precipitation) and Georges Bank source waters. The water molecular isotope tracer is among the best monitors of the impact of changing climate on Georges Bank mass origins and their variability. The research will contribute directly to modeling studies to understand the physical and biological processes controlling the early life stages and recruitment of fish and zooplankton stock on Georges Bank as well as provide a baseline for monitoring the influences of any future climate change.