Abstract

Monitoring the cold and productive waters of the Gulf of Maine and their interactions with the nearby northwestern (NW) Atlantic shelf is important but challenging. Although remotely sensed sea surface temperature (SST), ocean color, and sea level have become routine, much of the water exchange physics is reflected in salinity fields. The recent invention of satellite salinity sensors, including the Soil Moisture Active Passive (SMAP) radiometer, opens new prospects in regional shelf studies. However, local sea surface salinity (SSS) retrieval is challenging due to both cold SST limiting salinity sensor sensitivity and proximity to land. For the NW Atlantic, our analysis shows that SMAP SSS is subject to an SST-dependent bias that is negative and amplifies in winter and early spring due to the SST-related drop in SMAP sensor sensitivity. On top of that, SMAP SSS is subject to a land contamination bias. The latter bias becomes noticeable and negative when the antenna land contamination factor (LC) exceeds 0.2%, and attains maximum negative values at LC = 0.4%. Coastward of LC = 0.5%, a significant positive land contamination bias in absolute SMAP SSS is evident. SST and land contamination bias components are seasonally dependent due to seasonal changes in SST/winds and terrestrial microwave properties. Fortunately, it is shown that SSS anomalies computed relative to a satellite SSS climatology can effectively remove such seasonal biases along with the real seasonal cycle. SMAP monthly SSS anomalies have sufficient accuracy and applicability to extend nearer to the coasts. They are used to examine the Gulf of Maine water inflow, which displayed important water intrusions in between Georges Banks and Nova Scotia in the winters of 2016/17 and 2017/18. Water intrusion patterns observed by SMAP are generally consistent with independent measurements from the European Soil Moisture Ocean Salinity (SMOS) mission. Circulation dynamics related to the 2016/2017 period and enhanced wind-driven Scotian Shelf transport into the Gulf of Maine are discussed.

Highlights

  • Monitoring interactions between the cold and productive waters of the Gulf of Maine (GoM) and the adjoining northwestern Atlantic shelf is an important yet challenging regional need, with seasonal and longer timescale change impacts that affect ecosystem, fishery, and coastal management efforts

  • This paper addresses several challenging issues related to satellite ocean salinity data accuracy and application within the challenging salinity remote sensing domains of both cold and coastal waters

  • The focus region is the Gulf of Maine and the adjoining Scotian Shelf and NW Atlantic shelf break, where upstream fresh coastal subarctic waters are advected into a region that includes high salinity Gulf Stream eddies

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Summary

Introduction

Monitoring interactions between the cold and productive waters of the Gulf of Maine (GoM) and the adjoining northwestern Atlantic shelf is an important yet challenging regional need, with seasonal and longer timescale change impacts that affect ecosystem, fishery, and coastal management efforts. 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 remoTtehesednosminignadnactae foofrsmubosnuirtofarcinegGGooMMexdcyhnaanmgiecsp.aHthowwaeyvsehr,aFs,ensog featr,alli.m[3i]terdectehnetluytiulisteydoaflstiumrfeatceer rdeamtaotteo sdeenmsionngsdtraattaeftohramt soenaistoonrianlgaGndoMintdeyrannanmuiacsl.vHaroiwabeivlietyr, iFnenngeaert‐saul.r[f3a]cerefcreensthlwy uatseerdaadlvtiemcteitoenr dfraotma tothdeeSmcootniastnraStheetlhfaitnstoeatshoenacloaanstdalinGteorMancnaunalbvearreialabtielditytoinlonceaalr-wsuinrfda‐cinedfruecsehdwcahtearngadesveinctitohne frreommottheeuSpcsotrteiaanmSchoealfstinaltogethoestcrooapshtaicl cGuorMrenctasn.

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