Greenland tip jet and deep convection in the Irminger Sea: disentangling the roles of heat loss and wind stress

Abstract. The strength of the Atlantic Meridional Overturning Circulation (AMOC) depends on deep-water formation in the Subpolar Gyre, particularly in the Irminger Sea, where convection is strongly modulated by short-lived but intense Greenland tip jet. These mesoscale westerlies induce substantial surface heat loss and impose wind stress on the ocean, jointly influencing convective intensity. Using the high-resolution Parallel Ocean Program (POP) within the Community Earth System Model (CESM), we disentangle the thermal and mechanical effects of tip jet on mixed layer deepening through three ensemble experiments: full-forcing (heat loss + wind stress anomalies), heat-only, and wind-only, each compared to a climatological control run. All forced cases show a significant December–April deepening of the mixed layer relative to the control. The heat-only and full-forcing experiments produce similar mixed layer depth (MLD) increases (+1200 m; reaching ~1800 m), confirming that surface heat loss is the primary driver of deep convection. The wind-only case shows a smaller but still significant increase (+400 m; MLD ~1000 m), associated with enhanced early-winter mixing and wind-driven salinity increases in the upper ocean. This wind stress forcing erodes the fresh surface layer, reduces buoyancy, and promotes shear-driven mixing in December so that climatological winter heat loss can deepen the mixed layer more efficiently. Because wind stress is not projected to weaken under future warming, its mechanical influence may help delay or modulate the decline of convection in the Irminger Sea as surface heat loss decreases.