MSI Technical Seminars

Wei-Jun Cai
Dept. of Marine Sciences, University of Georgia

Wednesday, April 4, 2007, 4:00 p.m.

"Synthesis of air-sea CO₂ exchange in a few western boundary current shelves"

One of the great uncertainties in identifying the “missing CO₂ sink^” in the atmosphere is inadequate knowledge of CO₂ uptake or release by coastal oceans, which link the atmosphere, land, and open ocean. Based on measurements primarily in the northern temperate zone, researchers have argued that the world’s continental shelf may absorb upper to 1.0 Pg/yr of atmospheric carbon. This CO₂ sink flux would change substantially the global carbon budget for land and oceans. However, contrasting and conflict results are also reported recently. A mechanistic study on how various shelves would behave is desirable. I will examine this issue by presenting CO₂ flux measurements from the U.S. South Atlantic Bight, Mid Atlantic Bight, and Gulf Coast as well as from the East and South China Seas. There is a latitudinal distribution of high CO₂ uptake in high and mid latitude shelves to less uptake or even release in low latitude shelves. Surface temperature, terrestrial input and shelf depth/stratification are identified as the most important factors in controlling shelf pCO₂.  I will also present a new estimate on global shelf CO₂ flux using a province-based approach (i.e., a smaller sink = 0.20±0.16 Pg C).  The CO₂ release at low latitudes, which offsets the uptake at mid-high latitudes, is consistent with the fact that low latitude shelves receive 60% of global terrestrial organic carbon supply and have a higher temperature. I will discuss the ramification of this finding on coastal ocean metabolism and carbon budget issues.