Springtime Warming by Ocean Advection in the Gulf Stream

Abstract The Gulf Stream transports heat from the tropics poleward and is an integral part of how the planet redistributes heat. Studies of the variability of the Gulf Stream have suggested that the seasonal cycle of ocean mixed layer heat content in the Gulf Stream may be driven by the local net atmospheric heat flux or by oceanic advection of heat in the strong western boundary current. Here we use sustained underwater glider observations of the Gulf Stream from 80W to 67W during 2015–2023 to show that oceanic advection heats the ocean mixed layer in spring when the upper ocean switches from cooling to warming. Estimated terms of the mixed layer temperature budget demonstrate that the net atmospheric heat flux cools the upper ocean in all seasons except summer and that mixed layer warming in spring is due to ocean advection of heat from farther south.