Dataset: Diagnostic box model results of interannual to decadal variability in the carbon cycle at stations BATS and ALOHA, 2004 (U.S. JGOFS Synthesis & Modeling Phase project results)

The prediction of future atmospheric CO2 concentrations requires an in depth understanding of the feedbacks that operate between the physical, biological and chemical components of the global climate system.  One of the few means to study these feedbacks is the investigation of the observed variability in the past.  Variability in the marine carbon cycle has been studied most thoroughly in the tropical Pacific in connection with ENSO. By contrast, little is known about the contribution of the subtropical and subpolar gyres to atmospheric CO2 variations, despite the fact that these gyres cover more than half of the world's ocean.  This study addresses this gap and pursues the following goals:

1. to quantify the variability in the marine carbon cycle in the subtropical and subpolar gyres on the interannual to decadal time scale and to determine the role of these oceanic regions for the observed temporal and spatial variability in atmospheric CO2
2. to evaluate and quantify the contributions from biological and physical processes to the observed variability;
3. to work toward a better understanding of the complex feedbacks that operate between the physical, chemical and biological processes in the ocean.

This proposal addresses these objectives by combining a detailed analysis of two long time series observations in the subtropical gyres of the North Atlantic and North Pacific with three-dimensional ocean biogeochemistry modeling studies.  We will make use of the inorganic carbon system observations made by C.D. Keeling since 1983 near Bermuda and since 1988 near Hawaii and combine them with the U.S. JGOFS sponsored inorganic carbon observations made by N. Bates at BATS and C. Winn at HOT.  These combined observations form the longest record available for inorganic carbon variability and allow quantification of the variability on scales from seasons to decades.  The contribution of air-sea gas exchange, mixing and biological production to the observed variability will be analyzed using a simple inverse box model constructed on the basis of the concurrent isotopic observations made by C.D. Keeling.  Results from this local studies will be put into a three-dimensional context and scaled up by running and analyzing simulations of the carbon variability in a state-of-the-art ocean biogeochemistry model on the basis of the Upper Ocean Model (UOM) developed by Gokhan Danabasoglu and Jim McWilliams.  Our research will be guided by the hypothesis that variations in the strength of the winter time convection is the primary mechanism that controls interannual variability in the subtropical and subpolar gyres.  We will specifically test the hypothesis that the response of the subtropical and subpolar gyres to variability in winter time convection is fundamentally different, but may lead to a coordinated response to large-scale climate forcing, such as the North Atlantic Oscillation.