Synthesis & Modeling Project
The cycling of organic carbon and calcium carbonate
in marine sediments: Determination of parameters for use in global models
NSF OCE-9876533 03/99-02/01
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.
|DATA:||Patterns in Organic Matter Oxidation Kinetics in Sediments (data from Sierra Leone Rise)|
|PUBLICATIONS:||- no publications listed -|
- no related projects listed -
William R. Martin
Mail Stop 8
Department of Marine Chemistry and Geochemistry
Woods Hole Oceanographic Institution
Woods Hole, MA 02543-1050
tel: (508) 289-2836