Gulf of Maine salinity variation and its correlation with upstream Scotian Shelf currents at seasonal and interannual time scales

Abstract

In the Gulf of Maine (GoM), a network of buoy hydrography measurements collected since 2001 provide a subsurface salinity time series showing a strong seasonal cycle and interannual variations that are both consistent with remote forcing of Gulf hydrography by upstream advection. These long-term mooring data are combined with satellite altimeter estimates of upper ocean current anomaly on the adjoining Scotian Shelf (SS) in a new attempt to use disparate regional observations as proxies to detect and evaluate remote forcing of water mass change inside the Gulf from 2002-2015. Focusing on buoys moored along the Maine coastal current (MCC), lagged cross correlations with upstream altimeter-derived SS current anomalies are found to be as high as 0.84 and explain 50-70% of variance in the MCC subsurface salinity data at both seasonal and interannual time scales. Significant MCC freshening in 2004-2005 and 2010-2011 follow SS velocity strengthening, while salting events in 2002-2004 and 2012-2015 are associated with relaxation of SS currents. Estimated time lags translate to advective SS inflow velocity estimates of 6±2 cm/s that are consistent with past modeling and observational work. Investigation of wind stress control on SS velocity anomalies indicates that wind directions away from the along-shore can factor into flow modulation. Overall, the study findings are consistent with past freshwater flux observations and modeling examining southwest SS inflow to the GoM, provide a new empirical means to diagnose GoM hydrographic change, and point to one potential application of an altimeter measurement record that extends from 1992 into the future. This article is protected by copyright. All rights reserved.