Differences in the Response of the Atlantic Ocean Circulation to Greenland Freshwater Input Using High- and Low-Resolution Models
The sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to high-latitude freshwater input is a key uncertainty in the climate system. Considering the importance of the AMOC for global heat transport and the vulnerability of the Greenland Ice Sheet to global warming, assessing this sensitivity is critical for climate change projections. A unique set of computational experiments were conducted at Los Alamos National Laboratory to investigate the adjustment of the AMOC to enhanced melt water from the Greenland Ice Sheet under present-day conditions. This is the first time that the response of a global, high-resolution strongly-eddying ocean model was systematically compared to that of a typical coarser-grid ocean Intergovernmental Panel on Climate Change-class climate model. The overall decline of the AMOC on decadal time scales is quantitatively similar (<10%) in the two configurations. However, the time-varying transient response is significantly different; the AMOC decline and reduction during wintertime convection is markedly more gradual and persistent in the strongly-eddying configuration. The strongly-eddying ocean model also responds more strongly to a traditional, single dump of freshwater, in contrast to the low-resolution model, in which the spatial distribution of the freshwater flux anomaly does not matter for the AMOC response. This study reveals the conditions under which climate projections based on coarse models need to be revisited with higher-resolution investigations.
Weijer, W., M. E. Maltrud, M. W. Hecht, H. A. Dijkstra, and M. A. Kliphuis. 2012. “Response of the Atlantic Ocean Circulation to Greenland Ice Sheet Melting in a Strongly-Eddying Ocean Model,” Geophysical Research Letters 39, L09606. DOI: 10.1029/2012GL051611