Seasonal to Multi‐Year Variability of Upwelling Along Southwest Greenland and the Role of Atmospheric Circulation

Abstract Upwelling along southwest Greenland plays an important role in modulating shelf‐basin exchange and influencing deep convection in the Labrador Sea. Here we investigate its seasonal and interannual variability using the Overturning in the Subpolar North Atlantic Program West Greenland mooring observations and atmospheric reanalysis fields. Over the decade 2014–2024 we identified 142 upwelling events. During this time the number of events increased, primarily due to summer events, whereas the mean duration of events decreased for the first 7 years and then rebounded, largely reflecting winter variability. The latter is consistent with the winter North Atlantic Oscillation (NAO), whereas the relationship between the number of summer events and the summer NAO is counterintuitive. Two distinct atmospheric patterns were identified. Most events are associated with forward Greenland tip jets, whereby low‐pressure systems deepen in the vicinity of southeast Greenland resulting in enhanced northwesterly winds along southwest Greenland. In contrast, a large number of the summer events are shown to be related to an alternative atmospheric scenario characterized by a weak, distant low‐pressure system located south of Iceland coexisting with a high‐pressure system over the Labrador Sea. The tracks of these storms are typical of low‐NAO conditions, thus explaining the above‐noted counterintuitive relationship. Using a proxy we demonstrate that there was a regime shift in 1990/91 after which this type of summer upwelling became more common. Our results highlight a previously underappreciated role of high‐pressure systems in driving upwelling variability and provide new insights into the factors controlling upwelling along southwest Greenland.