| Summary: | Concerns about North Atlantic Meridional Overturning Circulation (NAMOC) changes imply the need for a continuous, large-scale observation capability to detect changes on interannual to decadal time scales. Here we present the first measurements of Lower North Atlantic Deep Water (LNADW) transport changes using only time-variable gravity observations from Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 until now. Improved monthly gravity field retrievals allow the detection of North Atlantic interannual bottom pressure anomalies and LNADW transport estimates that are in good agreement with those from the Rapid Climate Change-Meridional Overturning Circulation and Heatflux Array (RAPID/MOCHA). 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 on the order of 20 mm-H₂O (200 Pa), implying a southward volume transport anomaly in that layer of approximately −5.5 sverdrup. Our results highlight the efficacy of space gravimetry for observing AMOC variations to evaluate latitudinal coherency and long-term variability. We thank Elanor Frajka-Williams for her helpful discussions about the RAPID-MOCHA measurements, and Don Chambers and an anonymous reviewer for their very constructive comments. This work represents one phase of research carried out at the Jet Propulsion Laboratory/California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The JPL-RL05M GRACE solutions are available via the Physical Oceanography Distributed Active Archive Center (PODAAC) as well as the GRACE Tellus websites (www.grace.jpl.nasa.gov). RAPID is funded by the Natural Environment Research Council in the UK and the National Science Foundation and National Oceanic and Atmospheric Administration in the United States. Data are freely available from http://www.rapid.ac.uk. The Editor thanks Don Chambers and an anonymous reviewer for ...
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