Winter surface salinity in the northeastern Gulf of Maine from five years of SMAP satellite data

Type Article
Date 2021-04
Language English
Author(s) Grodsky Semyon A.1, Vandemark Douglas2, Reul NicolasORCID3, Feng Hui2, Levin Julia4
Affiliation(s) 1 : Department of Atmospheric and Oceanic Science, University of Maryland, College Park, USA
2 : University of New Hampshire, Durham, USA
3 : IFREMER, University Brest, CNRS, IRD, Laboratoire d'Oceanographie Physique et Spatiale (LOPS), IUEM, Brest, France
4 : Rutgers University, New Brunswick, NJ, USA
Source Journal Of Marine Systems (0924-7963) (Elsevier BV), 2021-04 , Vol. 216 , P. 103508 (15p.)
DOI 10.1016/j.jmarsys.2021.103508

Wintertime freshwater transport into the Gulf of Maine (GoM) is typically controlled by a seasonal velocity increase in the fresh upstream Nova Scotia Current (NSC). Repeat satellite observations from the Soil Moisture Active Passive mission have mapped significant GoM surface salinity anomalies in four of five recent winters. These satellite data are used in combination with Jordan basin buoy and model datasets to investigate the likelihood that variable wind-forcing of the NSC contributed to these anomalies. This stems from regional ocean circulation studies suggesting that strengthening of alongshore southwesterly winds on the Scotian shelf weakens NSC transport into the GoM, while cross-shore southeasterly winds may also contribute to NSC weakening, and vice versa. A 17-year time series analysis of GoM buoy and satellite data shows that near-surface salinity in the eastern GoM can indeed be modulated by both alongshore and cross-shore winds through their impact on the NSC. The NSC geostrophic current modulation correlates with buoy-observed surface salinity anomalies when using a one month advective lead time. For a shorter 5-year period, a SMAP-derived salinity anomaly index in the eastern GoM indicates a similar relation to NSC variation and also correlates with Scotian Shelf wind anomalies. The relationships between winter wind and NSC transport variability are confirmed using output from a 19-year high resolution global ocean simulation. Attribution of these local wind anomalies to basin-scale atmospheric patterns shows that most years with strong winter GoM freshening coincide with weakening of a North Atlantic Oscillation-like wind pattern. But its reversals do not always correspond with a saline GoM. This contrast suggests that wind forcing more directly controls fresh winter GoM anomalies but not salty. Instead, they are partly due to density-driven advection from neighboring warm and saline Atlantic slope water including episodic Gulf Stream instabilities.

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