Sensitivity of Stationary Wave Amplitude to Laurentide Ice Sheet Topography and the Interpretation of the Heinrich Event Climate Record

Charles S Jackson (NOAA/GFDL, P.O. Box 308, Princeton, NJ 08542; ph. 609-452-6566; fax 609-987-5063; Internet: csj@gfdl.gov)

The geologic record of the last ice age indicates the Laurentide ice sheet periodically discharged large volumes of ice into the North Atlantic ocean as icebergs. There is yet no adequate explanation

for why these discharge events precede the atmosphere's warming over Greenland or why the long trends in Greenland climate are framed by the removal of ice covering Hudson Bay. Since ice sheets can only affect climate indirectly, there is a need to find out how the Laurentide ice sheet was able to communicate with climate. I consider how the atmosphere's stationary waves could serve as a means to translate changes in ice sheet topography to climate.

I use one-and two-layer models of the atmosphere to assess the relative influence of various portions of the Laurentide ice sheet's topography on the atmosphere's stationary wave amplitude. The two models isolate various factors thought to be important to stationary wave sensitivity to topography. These factors include the spherical shell domain, realistic Glacial Maximum topography, zonally varying mean winds, and transient eddies.

I present the idea that small changes in ice volume can lead to significant changes in stationary wave amplitude by way of stationary wave interference. I illustrate the development of `sweet spots' on the Laurentide ice sheet which are areas whose topographic alteration leads to significant changes in stationary wave amplitude over what may be expected if stationary wave amplitude scales with ice volume.

Simulations of Heinrich discharge events, represented by the removal of 3 percent ice volume from the Hudson Bay ice dome, show a 13 percent increase in stationary wave amplitude over the North Atlantic and enhanced poleward heat transport leading to a 3 degree Celsius warming of high northern latitudes. Results from the Heinrich experiment suggest the observed atmospheric warming that occurs over Greenland after a Heinrich discharge event may be related to the atmosphere's response to the altered topography of the Laurentide ice sheet. I also suggest that Greenland's long-term climate trends could be following the atmosphere's response to changes in the Laurentide ice sheet's topography created by the periodic discharge of ice volume to the North Atlantic ocean and gradual recovery.