Weak 21st-century AMOC response to Greenland meltwater in a strongly eddying ocean model

TL;DR

This study uses a high-resolution ocean model to assess Greenland meltwater's impact on the Atlantic Meridional Overturning Circulation, finding its effect is small and largely independent of model resolution.

Contribution

First to quantify Greenland meltwater effects on AMOC in a strongly eddying ocean model under future climate scenarios.

Findings

Greenland meltwater causes a minor AMOC weakening of 0.6 Sv.

Model resolution has little impact on meltwater's effect.

Background ocean state influences meltwater impact more than resolution.

Abstract

Climate models project that the Atlantic Meridional Overturning Circulation (AMOC) will weaken in the 21st century, but the magnitude is highly uncertain. Some of this uncertainty is structural, as most climate models neglect increasing meltwater from the Greenland ice sheet and do not explicitly capture mesoscale ocean eddies. Here, we quantify the impact of Greenland meltwater on the AMOC until 2100 under SSP5-8.5 forcing for the first time in a strongly eddying (1/10{\deg} horizontal resolution) ocean model. The meltwater-induced additional AMOC weakening is small (0.6 $\pm$ 0.2 Sv) compared to the weakening due to warming alone, and similar at high and low resolution. The same meltwater would cause a stronger AMOC weakening under present-day climate conditions. We link both resolution-independence and state-dependence to large-scale controls of the AMOC. Our results demonstrate that the background ocean state is more important than resolution in determining how Greenland meltwater affects the AMOC.