The Impact of Greenland Tip Jets on the Eastern Irminger Sea: Insights from Ocean Moorings.

Abstract

The Irminger Current (IC) flows north-eastward along the western slope of the Reykjanes Ridge, transporting and transforming relatively buoyant Irminger Subpolar Mode Water (SPMW) in its upper branch. Thereby, its buoyancy and water mass transport are important to the circulation in the North Atlantic subpolar gyre (NASPG) and the Atlantic Meridional Overturning Circulation (AMOC). The area is under the atmospheric influence of Greenland tip jets, which are intense (up to ~28 m/s), short-lived (up to ~3 days), mesoscale westerly wind events. These winds precondition waters for deep convection and cause wind-driven surface transport in the central and western Irminger Sea. However, their impact on the IC is still not well understood, despite the IC’s relevance to the overturning circulation. Using hourly ERA5 reanalysis data, I detected tip jet hours in the eastern Irminger Sea. Combined with observations from the IC moorings of the Overturning Subpolar North Atlantic Program (OSNAP) East array (2014-2022), I investigated the influence of these tip jet hours on upper ocean velocities and transport, net surface heat flux (Q), and water mass properties of the IC. Most tip jet hours occurred during boreal winter (December–March), particularly in 2015 and 2022 when there was a strong positive NAO. I found that tip jet forcing disrupts the vertical coherence of IC velocities and reduces the northward volume transport. Therefore, it temporarily weakens the volume transport of the IC between 65 and 455m by altering the direction of upper water column velocities. Tip jets are associated with strong heat loss events and winters with strong tip jet forcing have a large cumulative cooling of the water column, densifying the Irminger SPMW. I detected vertical mixing down to ~460m in multiple years, but strong stratification and buoyant surface anomalies can inhibit convection, even under intense surface forcing. These results suggest that both atmospheric forcing and hydrographic structure regulate the contribution of the IC to overturning across OSNAP East.