Observed Transport Decline at 47°N, Western Atlantic

Abstract

AbstractDespite the importance of the large‐scale Atlantic circulation for the climate system and sea level, most of the interior flow field is only known qualitatively, and neither the mean nor the variability and trends are quantified. We investigate the meridional flow field in the western Atlantic at 47°N between 44°W and 31°W, combining moored pressure inverted echo sounders and current meter moorings with lowered acoustic Doppler current profiler and Argo data. Correlations with altimetry are used to extend each of the transport time series back to 1993. At the Canadian continental margin the boundary current exports −23.1 ± 1.5 Sv to the south. Nearby, the northward flowing North Atlantic Current (NAC) imports 105.9 ± 3.4 Sv into the subpolar gyre. Constrained mainly by topography, about half of that flow recirculates in close proximity to the NAC (−58.8 ± 3.9 Sv). NAC and recirculation are significantly anticorrelated. The flow east of 37°W (−27.8 ± 2.1 Sv) has no permanent regional features and is not correlated to the NAC. The sum of the interior components (19.3 ± 3.3 Sv) shows a significant trend in the time period 1993–2018 of −0.60 Sv/year. This decline is dominated by the significant increase of the southward flow east of 37°W (−0.44 Sv/year). The trends of the other individual components are not significant, but the sum of the interior and boundary current transport is (−0.71Sv/year). The trends are most likely caused by regionally different warming.