Dataset: Parameterizations for Organic Matter Oxidation Kinetics, 2007 (U.S. JGOFS Synthesis & Modeling Phase project results)

Research topic: the cycling of organic carbon and calcium carbonate in marine sediments: Determination of parameters for use in global models

Models attempting to explain past climate change and to predict changes in atmospheric composition and climate on time scales of 100 years or longer need to consider carbon cycling at the surface of marine sediments.  Given the large CO₂ neutralization capacity of marine sediments, which is due to their high CaCO₃ content, it is particularly important to consider reactions affecting the preservation of calcite.  The most important of these reactions are the oxic decomposition of organic matter and the calcite dissolution driven by benthic metabolism and by bottom water undersaturation.  Through the efforts of JGOFS and other programs, a large data set describing reactions in the upper millimeters to centimeters of the sediment column has been created.  This data set has not yet been examined to produce parameters that accurately describe organic matter decomposition and calcite dissolution.  The work we propose is designed to use this new data set to generate parameters that can be used in models allowing extrapolation from studied areas to the global ocean.  The ultimate result will be a substantially firmer foundation for global carbon mass balances.

Our proposed approach to quantifying the role of benthic fluxes of organic carbon and CaCO₃ in the marine carbon cycle is to develop diagenetic models that describe organic matter degradation and CaCO₃ dissolution in sediments at the limited number of sites/regions where adequate data sets are available and to extrapolate the results from these sites to regional and global scales with the models generated.  We have selected nine regions that best meet our data criteria and represent a wide range of environmental conditions in the oceans.

Our parameterization of remineralization reactions will proceed in several steps.  First, we will characterize the depth scales of organic matter oxidation within the sediments.  The parameters resulting from this effort can be used directly to assess the role of metabolic acids in the dissolution of CaCO₃ at the sea floor.  Second, at the more limited set of sites with high resolution pore water data as well as solid phase organic carbon and radiotracer data for bioturbation rate estimates, we can determine the time scales of organic matter decomposition.  The latter results will then be used, in conjunction with the depth scale parameterization, to expand the geographic scope of our time scale determinations.  Finally, we propose to examine the current parameterization of the rate law for calcite dissolution in sediments.  In particular, we propose to carry out new experiments to determine the power of the dependence of dissolution rate on degree of saturation with respect to calcite.  The end result of this data synthesis and parameterization effort will be greatly improved constraints on global estimates of the rate of carbon cycling at the sea floor.