Observed mechanisms triggering the recent warming in the eastern subpolar North Atlantic since 2016
Event: 2023 Ocean Surface Topography Science Team Meeting
Session: Science II: Large Scale Ocean Circulation Variability and Change
Presentation type: Type Oral
Contribution: PDF file
The overturning circulation of the subpolar North Atlantic (SPNA) plays a fundamental role in Earth's climate variability and change. Here, we demonstrate, based on observations, that the recent warming period since about 2016 in the eastern SPNA involves an increased western boundary density at the intergyre boundary due to enhanced buoyancy forcing as a response to the strong increase in the North Atlantic Oscillation in the preceding years. As these positive density anomalies spread southward along the western boundary, they enhance the North Atlantic Current and associated meridional heat transport at the intergyre boundary, leading to an increased influx of subtropical heat into the eastern SPNA, as confirmed by a Lagrangian analysis based on altimetry-derived geostrophic velocities. This increased heat transport can mainly be explained by the gyre circulation, as shown in a range of ocean reanalyses, and it has a specific large-scale sea-surface height imprint in the North Atlantic Ocean that will be discussed further.