The Atlantic Meridional Overturning Circulation at 35°N from deep moorings, floats, and satellite altimeter

Le Bras, I. A.-A., Willis, J., & Fenty, I., 2023. The Atlantic Meridional Overturning Circulation at 35°N from deep moorings, floats, and satellite altimeter. Geophysical Research Letters, 50(10), e2022GL101931. https://doi.org/10.1029/2022GL101931

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°N time series (magenta line) with a similar time series at 41°N (teal line) as well as the 26°N RAPID AMOC (orange line), 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. (The solid magenta line corresponds to the composite data product including the Line W mooring data, while the dotted line does not include the Line W data.) These observations suggest that AMOC decadal variability is meridionally coherent from 26°N to 41°N and that the DWBC may reflect this variability.  Figure provided by Isabela Le Bras.