24 / 2022-03-04 10:33:56

Contrary Responses of the Gulf Stream and the Kuroshio to Arctic Sea Ice Loss

Arctic sea ice loss,western boundary currents,air-sea interaction,warming hole

As two important western boundary currents (WBCs), the Gulf Stream in the North Atlantic and the Kuroshio in the North Pacific play key roles during climate change. However, how Arctic sea ice loss leads to the variations in the Gulf Stream and Kuroshio remain uncertain. In this paper, the impact on the WBCs from Arctic sea ice loss is isolated using the Community Climate System Model version 4 (CCSM4) model. Results show that the Gulf Stream (Kuroshio) weakens (strengthens) in response to Arctic sea ice loss via ocean (atmosphere) adjustments. More precisely, the Kuroshio acceleration is mainly due to the anomalous wind stress over the North Pacific, while the ocean gyre adjustments in the Atlantic are responsible for the weakened Gulf Stream. As positive buoyancy fluxes induced by Arctic sea ice loss triggers a slowdown of the Atlantic Meridional Overturning Circulation (AMOC), the Gulf Stream moves much slower as well as its extension. The current speed decreases about 5-8 cm/s in the upper ocean. Resulted from less advection and horizontal diffusion in the temperature budget, less poleward warm water leads to a narrow sea surface cooling sandwiched between strong warming in the subpolar and subtropical Atlantic. Furthermore, colder surface decreases the upward heat flux (mainly latent heat flux) along the Gulf Stream Extension (GE) path, which leads to a warming hole in the atmosphere. The anomalous solar radiation flux also has a cooling effect on the sea surface temperature (SST), contributing to the warming hole formation.