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 to 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.

Causes of Interannual Variation of Summer Mean Alongshore Current Near the East Coast of Korea Derived From 16‐Year‐Long Observational Data

“…On the other hand, the coastal current can be influenced by offshore pressure forcing, particularly in the vicinity of the WBCs (Archer et al, 2017;Csanady, 1978;Kelly & Chapman, 1988;Liu et al, 2016;Xu & Oey, 2011). It has been suggested that interannual variations in the alongshore current near the coast are related to remote wind forcing (Bachèlery et al, 2016), cross-shore wind stress curl gradient (Davis & Di Lorenzo, 2015), and alongshore (Li et al, 2014) and cross-shore (Feng et al, 2016) wind stress.…”

Interannual surface salinity on Northwest Atlantic shelf

“…Sea level variations [Ezer and Atkinson, 2014], Gulf Stream position shifts [Andres, 2016], and a high recent rate in upper ocean heating [Gawarkiewicz et al, 2012;Mills et al, 2013] are all observed, with differing potential impacts on the circulation, ecosystems, and coastal populations. Regional salinity change is also under study [Townsend et al, 2015;Li et al, 2014;Feng et al, 2016], mainly using in situ observations, with ecosystem implications tied to changing nutrients and factors controlling ocean acidification rates. These studies identify the need for spatially resolved and shelf-wide salinity observations.…”

Assessing Coastal SMAP Surface Salinity Accuracy and Its Application to Monitoring Gulf of Maine Circulation Dynamics

“…It is transported southwestward down the coast within the Scotian Shelf Current (SSC, inshore branch). The variability of this coastal transport is an important factor controlling freshwater inflows into the GoM (Feng et al [3]). To assess this as a possible explanation for the observed SMAP SSSA data near buoys N01 and M01, we present climatological and anomalous ocean current and wind data for October and November 2016 in Figure 15.…”

“…The primary inflow to the GoM is through The dominance of subsurface GoM exchange pathways has, so far, limited the utility of surface remote sensing data for monitoring GoM dynamics. However, Feng et al [3] recently used altimeter data to demonstrate that seasonal and interannual variability in near-surface freshwater advection from the Scotian Shelf into the coastal GoM can be related to local wind-induced changes in the remote upstream coastal geostrophic currents. That study, amongst others cited, highlighted the need to resolve spatial information on surface salinity fields just offshore of and inside the GoM.…”

“…Key water mass inflows influencing this marginal sea include the upstream fresh/cold Scotian Shelf and Labrador Sea currents, and the adjoining salty/warm northwestern (NW) Atlantic shelf (Mountain [1]; Townsend et al [2]; Feng et al [3]; Peterson et al [4]). The primary inflow to the GoM is through The dominance of subsurface GoM exchange pathways has, so far, limited the utility of surface remote sensing data for monitoring GoM dynamics.…”