Meridionally consistent decline in the observed western boundary contribution to the Atlantic Meridional Overturning Circulation

Despite numerous model-based analyses indicating a notable decline in the Atlantic Meridional Overturning Circulation (AMOC) in recent decades, robust, long-term evidence from multilatitudinal in situ observations remains limited. This study uses observational data from four mooring arrays, positioned along the western boundary of the North Atlantic (from 16.5°N to 42.5°N), to examine trends in the deep western overturning transports, derived from the cross-slope gradient in ocean bottom pressure or its equivalent, below and relative to 1000 meters that are linked to changing conditions at the western boundary. We identify a meridionally consistent decline in deep western overturning transport across these latitudes over the past two decades. This decline, observed at the western boundary, may serve as an effective indicator of AMOC weakening, despite the partial compensatory effect of overturn strengthening at the eastern boundary.