Lima, Ivan, Luanne Thompson, Steven Emerson and Paul Quay

School of Oceanography, University of Washington, P.O. Box 355351, Seattle, WA 98195, USA, E-mail: ivan@ocean.washington.edu

Thermocline ventilation and apparent oxygen utilization in the North Pacific: a numerical modeling investigation

The ocean plays a fundamental role in the global carbon cycle and climate system as a major sink for anthropogenic carbon from fossil fuel burning and land use change. Our current inability to predict the ocean response to and feedbacks on anthropogenic perturbations is one of the major uncertainties for projecting future climate change. There is strong observational evidence that the apparent oxygen utilization (AOU) in the subtropical North Pacific has increased in the 1990s. This could be the result of either an intensification of the carbon pump or a decrease in ventilation. As a first step in understanding the physical controls of carbon uptake and export in the subtropical North Pacific, biogeochemical tracers have been incorporated into an ocean general circulation model (OGCM) to investigate the effects of historical wind and surface heat forcing on thermocline ventilation rates and apparent oxygen utilization. The coupled model is based on the Hallberg Isopycnal Model (HIM), with 16 layers and horizontal resolution of 2 degrees, and includes CFC11, CFC12, dissolved oxygen and an ideal age tracer. The depth dependent oxygen utilization rate (OUR) function of Jenkins (1982) is applied below the euphotic zone. The CFCs are used to estimate apparent ages and ventilation rates and AOU is calculated from the dissolved oxygen. Model experiments using historical and climatological forcing are compared to determine if the observed increase in AOU during the 1990s can be explained by interannual changes in the historical wind and heat forcing. We are presently interpreting these results. The poster focuses on the interannual variability of the thermocline ventilation and its implications for apparent oxygen utilization and the inferred export of organic carbon.