Response of the North Atlantic jet to LGM ice sheets and sea ice

The North Atlantic jet in the modern climate is relatively weak and tilted northeastward, while Last Glacial Maximum (LGM) simulations using high-end estimates of the Laurentide ice sheet elevation show a much more intense and zonally-oriented jet. Here, we explore this response using a sequence of LGM simulations spanning a broad range of ice sheet elevations. We find that increasing ice sheet height favours planetary wave breaking and nonlinear reflection in the subtropical North Atlantic. This entails a zonalisation of the stationary wave phase lines and thus of the midlatitude jet. At the same time, increasing ice sheet elevation promotes southward migration of the sea-ice margin, which helps further zonalise the jet and elongate it eastward.