North Atlantic meridional overturning circulation variations from GRACE ocean bottom pressure anomalie

Abstract:

The important role of the North-Atlantic Meridonal Overturning Circulation (AMOC) for regional as well as global climate is well recognized. Concerns about potential future AMOC changes imply the need for a continuous, large-scale observation capability to detect any such changes on interannual to decadal time scales. Here, we present the first measurements of lower North-Atlantic-Deep-Water (LNADW) monthly transport changes using only space-based time-variable gravity observations from Gravity Recovery and Climate Experiment (GRACE) satellites, continuously covering the time period from 2003 until now. Improved monthly gravity field retrievals allow the detection of North Atlantic interannual bottom pressure anomalies and yield LNADW transport estimates that are in good agreement with those from the ocean in-situ RAPID-MOCA array at 26.5N. Concurrent with the observed AMOC transport anomalies from late-2009 through early-2010, GRACE measured ocean bottom pressures changes in the 3000-5000 m deep western North Atlantic of -20 mm-H2O, implying a southward volume transport anomaly in that layer of approximately -5.5 Sv. Our results highlight the efficacy of space-gravimetry to observe and detect meridional ocean transport variations that can potentially be retrieved over all latitude ranges in the Atlantic.