TY - JOUR
T1 - Haline Сontrol of Unusually Deep Winter Mixing in the Gulf of Maine Investigated Using a Regional Data-Assimilative Model
AU - Levin, J. C.
AU - Grodsky, S. A.
AU - Vandemark, D.
AU - Wilkin, J. L.
N1 - Funding Information:
Doppio model 4D‐Var development was supported by DOC NOAA Research Award # NA16NOS0120020 and the NASA Earth Science Division Award # NNX17AH58G (for JL and JW), while analysis of model and observational data for this research was funded by NASA Earth Science Division Awards # 80NSSC20K0878 (for JL, SG, and DV) and # NNX17AK02G (for JL).
Publisher Copyright:
© 2022. The Authors.
PY - 2022/11
Y1 - 2022/11
N2 - An unusually large positive salinity anomaly was observed across the eastern Gulf of Maine in winter 2017–2018. Buoy measurements in Jordan Basin found this anomaly extended down to at least 100 m, the deepest mixing observed in the past 19 years. Similarly, this is the strongest positive regional salt anomaly ever observed in sea surface salinity (SSS) satellite observations. To determine the source waters driving this event and to diagnose the relative importance of forcing processes, passive tracer adjoint sensitivity experiments are performed using a data assimilating version of the Regional Ocean Modeling System. The model suggests that northeastward Scotian Shelf wind anomalies is one factor in the dramatic decrease in freshwater transport to Jordan Basin, which leads to an early winter upper water column salinity surplus. This salinity change weakens the normally haline-controlled vertical stratification across the eastern Gulf. Modeled upper ocean density and vertical diffusivity from 2007 to 2021 both show a maximum in January 2018. Winter 2017–2018 is the only period where the enhanced winter mixing extends below 100 m. Thus, anomalous vertical entrainment of saltier subsurface Gulf water is the major factor driving the extreme positive satellite-observed SSS anomaly across the eastern Gulf including Jordan Basin. Other factors, including a modest increase in wind-forced slope water transport, and positive fall 2017 salinity anomalies on the Scotian Shelf and Slope Sea, appear to play lesser roles in the observed salinification. The adjoint sensitivity analysis demonstrates its utility for back tracing transport pathways for periods of several months.
AB - An unusually large positive salinity anomaly was observed across the eastern Gulf of Maine in winter 2017–2018. Buoy measurements in Jordan Basin found this anomaly extended down to at least 100 m, the deepest mixing observed in the past 19 years. Similarly, this is the strongest positive regional salt anomaly ever observed in sea surface salinity (SSS) satellite observations. To determine the source waters driving this event and to diagnose the relative importance of forcing processes, passive tracer adjoint sensitivity experiments are performed using a data assimilating version of the Regional Ocean Modeling System. The model suggests that northeastward Scotian Shelf wind anomalies is one factor in the dramatic decrease in freshwater transport to Jordan Basin, which leads to an early winter upper water column salinity surplus. This salinity change weakens the normally haline-controlled vertical stratification across the eastern Gulf. Modeled upper ocean density and vertical diffusivity from 2007 to 2021 both show a maximum in January 2018. Winter 2017–2018 is the only period where the enhanced winter mixing extends below 100 m. Thus, anomalous vertical entrainment of saltier subsurface Gulf water is the major factor driving the extreme positive satellite-observed SSS anomaly across the eastern Gulf including Jordan Basin. Other factors, including a modest increase in wind-forced slope water transport, and positive fall 2017 salinity anomalies on the Scotian Shelf and Slope Sea, appear to play lesser roles in the observed salinification. The adjoint sensitivity analysis demonstrates its utility for back tracing transport pathways for periods of several months.
KW - Regional Ocean Modeling System (ROMS)
KW - Soil Moisture Active Passive (SMAP) satellite mission
KW - adjoint sensitivity analysis
KW - salinity anomalies in Gulf of Maine
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U2 - 10.1029/2021JC018281
DO - 10.1029/2021JC018281
M3 - Article
AN - SCOPUS:85142653751
SN - 2169-9275
VL - 127
JO - Journal of Geophysical Research: Oceans
JF - Journal of Geophysical Research: Oceans
IS - 11
M1 - e2021JC018281
ER -