The Atlantic Meridional Overturning Circulation at 35 degrees N From Deep Moorings, Floats, and Satellite Altimeter

From 2004 to 2014, the Line W moorings measured a 0.7 Sv yr(-1) slowing of the deep western boundary current (DWBC) offshore of Cape Cod. Here, we combine these deep mooring observations with float and satellite altimeter data and find that this DWBC change corresponded to a slowing of the cross-basin Atlantic Meridional Overturning Circulation (AMOC) of about 0.3 Sv yr(-1). Our AMOC transport time series corresponds well with the Estimating the Circulation and Climate of the Ocean state estimate, particularly when the Line W mooring data influences our volume closure. We compare our 35 degrees N time series with a similar time series at 41 degrees N as well as the 26 degrees N RAPID AMOC, and find AMOC declines across datasets from 2004 to 2014. However, when we extend our analysis to 2004-2019, there are no significant trends at any latitude. These observations suggest that AMOC decadal variability is meridionally coherent from 26 degrees N to 41 degrees N and that the DWBC may reflect this variability. Plain Language Summary The Atlantic ocean hosts an overturning circulation that is thought to be an important piece of our climate system. This circulation pattern spans the width of the basin, making it difficult and costly to measure, so direct observations of the overturning circulation are scarce. In this study we combine existing mooring, float, and satellite altimeter observations to estimate the overturning circulation at a new latitude (35 degrees N), and compare it to existing estimates at 26 degrees N and 41 degrees N as well as the ECCO ocean state estimate. We find that the long term (about 10 year) AMOC variability is consistent across latitudes and data products. While we cannot rule out a decreasing AMOC trend during the 20th century, we find that natural variability is too large to detect a net AMOC decrease in direct observations since 2004.