Using NCAR CCSM3 to Explore how Future Environmental Stresses to Plant Physiology Affect the Ocean’s Global ‘Conveyor Belt’

Runoff in terrestrial ecosystems depends upon evapotranspiration, which we have shown decreases due to the response of vegetation to elevated CO2, increased nitrogen limitation, or rising surface ozone concentrations. Recent evidence indicates that there has been increased freshwater flux into the Arctic Basin since the early part of the 20th century, primarily from Eurasian rivers, due to warmer global temperatures and the resulting increased precipitation. We hypothesize that plant physiological considerations may increase the amount of freshwater input to the Arctic Basin by as much as 18%, thereby affecting the Meridional Overturning Circulation and production of North Atlantic Deep Water. Current river discharge to the Arctic Ocean is approximately 3238 km3yr-1, and it is thought that an additional 0.06-0.15 Sv (1892 — 4730 km3yr-1) to the North Atlantic is necessary to shut down the thermohaline circulation. We are using the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM3) to determine how the effect of elevated CO2, nitrogen-limitation, and ozone on terrestrial vegetation affects the ocean?s circulation. The CCSM3 is a fully coupled atmosphere, ocean, sea ice, and land model that is coupled with a biogeochemical model of terrestrial carbon and nitrogen dynamics. We are running this model on Lehigh’s new 9 node, 72 core Beowulf cluster. While the expected increase in runoff due to these stresses will likely be less than the total change in runoff due to warming and increased precipitation, it may still be as large as, or larger than, other components of the Arctic freshwater balance, such as melting from small glaciers or Greenland.