A recent decline in North Atlantic subtropical mode water formation

Type Article
Date 2020-04
Language English
Author(s) Stevens Samuel W.1, 2, Johnson Rodney J.2, Maze GuillaumeORCID3, Bates Nicholas R.2, 4
Affiliation(s) 1 : Earth, Ocean and Atmospheric Sciences Department, University of British Columbia, Vancouver, British Columbia, Canada
2 : Bermuda Institute of Ocean Sciences, St. George’s, Bermuda
3 : Ifremer, University of Brest, CNRS, IRD, Laboratoire d’Océanographie Physique et Spatiale (LOPS), IFREMER, Brest, France
4 : Ocean and Earth Science Department, University of Southampton, Southampton, UK
Source Nature Climate Change (1758-678X) (Springer Science and Business Media LLC), 2020-04 , Vol. 10 , N. 4 , P. 335–341
DOI 10.1038/s41558-020-0722-3
WOS© Times Cited 5
Abstract

As a manifestation of mixing dynamics in the upper ocean, interannual and decadal variability of subtropical mode water (STMW) properties in the North Atlantic Ocean provides a valuable insight into ocean–atmosphere interaction in a changing climate. Here, we use hydrographic data from the Bermuda Atlantic Time-Series Study and Hydrostation S sites near Bermuda, as well as various ocean reanalysis products, to evaluate the modern variability of STMW properties. Our study finds an 86–93% loss of STMW thickness at these sites between 2010 and 2018 and a comparable loss throughout the western subtropical gyre, culminating in the weakest STMW pentad on record. We correlate this decline with a reduction in the annual outcropping volume and northward excursions of the formation region, suggesting a gyre-wide signal of weakening STMW generation. The outcropping volume of STMW is anti-correlated with surface ocean heat content, foreshadowing future STMW loss in the face of continued warming.

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