Rapid barotropic sea level rise from ice sheet melting

Sea level rise associated with idealized Greenland and Antarctic ice sheet melting events is examined using a global coupled ocean sea-ice model that has a free surface formulation and thus can simulate fast barotropic motions. The perturbation experiments follow the Coordinated Ocean-ice Reference Experiment (CORE) version III. All regions of the global ocean experience a sea level rise within 7-8 days of the initialization of a polar meltwater input of 0.1 Sv (1 Sv = 106 m3 s-1). The fast adjustment contrasts sharply with the slower adjustment associated with the smaller steric sea level evolution that is also connected with melt events. The global mean sea level rises by 9 mm yr-1 when this forcing is applied either from Greenland or Antarctica. Nevertheless, horizontal inter-basin gradients in sea level remain. For climate adaption in low-lying coastal and island regions, it is critical that the barotropic sea level signal associated with melt events is taken into consideration, as it leads to a fast sea level rise from melting ice sheets for the bulk of the global ocean. A linear relation between sea level rise and global meltwater input is further supported by experiments in which idealized melting occurs only in a region east or west of the Antarctic Peninsula, and when melting rates are varied between 0.01 Sv and 1.0 Sv. The results indicate that in ocean models that do not explicitly represent the barotropic signal, the barotropic component of sea level rise can be added off-line to the simulated steric signal.