OCEANIC TRANSPORT OF SUBPOLAR CLIMATE SIGNALS TO MID-DEPTH SUBTROPICAL WATERS

The spatial distributions of certain sea-surface properties, such as t emperature, fluctuate on timescales from months to decades and in sync hrony with the main regional atmospheric patterns comprising the globa l climate system(1). Although it has long been assumed that the ocean is submissive to the dictates of the atmosphere, recent studies raise the possibility of an assertive, not merely passive, oceanic role in w hich water-mass circulation controls the timescales of climate fluctua tions(2-6). Previously held notions of the immutability of the physica l and chemical characteristics of deep water masses are changing as lo nger time series of ocean measurements indicate that the signatures of varying sea-surface conditions are translated to deep waters(4,7). He re we use such time-series measurements to track signals 'imprinted' a t the sea surface in the North Atlantic Ocean's subpolar Labrador Basi n into the deep water of the subtropical basins near Bermuda, and infe r an approximately 6-year transit time, We establish a geographic and temporal context for a portion of the long-term warming trend reported for mid-depth subtropical waters over the past 40 or so years(8,9), a nd we predict that waters at these depths will Continue to cool well i nto the next decade.