October 17, 2007 WUN Virtual Seminar

Exploring high latitude climate from above and below: Altimetry to seagliders

Dr. Peter Rhines
University of Washington, Seattle

Global climate change is amplified at polar latitudes, with increasing imprint of human forcing. This is a ‘tall’ system in which important climate dynamics occurs from the stratosphere to the deep ocean, with strong up-down interactions characteristic of weakly stratified, rotating fluids. There are dramatic predictions of ice-free Arctic and declining oceanic overturning circulation. Much occurs in the subpolar Atlantic, where Arctic fresh-water outflow can condition oceanic deep convection.

New technologies can rise to the complexity and special physics of the subpolar oceans; here we describe results from Seagliders and satellite altimetry. Circulation and eddies observed in the Labrador Sea show the controlling effect of the buoyant, low-salinity water on both deep convection and spring plankton blooms. Intense eddies and jets carry the low-salinity cap from west Greenland boundary waters. Deep overflows spill unpredictably across the Iceland-Faroe Ridge: robotic Seagliders have begun surveying these thin bottom-hugging layers to establish pathways of both upper, warm and deep, cold branches at the headwaters of the global meridional overturning circulation. These processes also interact with the lateral gyre circulation. Since the early 1990s, altimetry and hydrography find the subpolar Atlantic gyre to be shrinking westward and decelerating, with enhanced penetration of the warm North Atlantic Current waters to the Nordic Seas.