Oceanic transport of subpolar climate signals to mid-depth subtropical waters

Abstract

The spatial distributions of certain sea-surface properties, such as temperature, fluctuate on timescales from months to decades and in synchrony with the main regional atmospheric patterns comprising the global climate system¹. 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 which water-mass circulation controls the timescales of climate fluctuations^2,3,4,5,6. Previously held notions of the immutability of the physical and chemical characteristics of deep water masses are changing as longer time series of ocean measurements indicate that the signatures of varying sea-surface conditions are translated to deep waters⁴,⁷. Here we use such time-series measurements to track signals ‘imprinted’ at the sea surface in the North Atlantic Ocean's subpolar Labrador Basin into the deep water of the subtropical basins near Bermuda, and infer 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 years⁸,⁹, and we predict that waters at these depths will continue to cool well into the next decade.