Seiter¹, K., C. Hensen², M. Zabel¹ and J. Schröter¹

¹Bremen University, Dept. of Geosciences, Klagenfurterstr., D-28359 Bremen, Germany, Tel: +49-421-218 8933, Fax: +49-421-2184321, E-mail: kseiter@uni-bremen.de, and ²GEOMAR, Wischhofstr. 1-3, D-24148 Kiel, Germany,

A geostatistical approach for regionalization the TOC content in surface sediments - developing TOC-provinces on a global scale

Conventional global maps of the TOC content in surface sediments reflect the general distribution pattern of organic carbon and sedimentary processes. It is known, however, that the TOC content in surface sediments of the organic rich continental shelves and slopes is underestimated and regional underlying processes and trends are not reproduced in detail. This is caused by the type of statistical data distribution and the high TOC gradient between the coastal and the basin areas. The irregularly distributed data have the highest sampling site density on the continental shelves and slopes, especially along the west coasts of the continents. Summing up all basin areas against all coastal areas a data density ratio of 1/5 is given. This means that 80% of the TOC data is distributed at 12% of the global ocean area (shelves and slopes), whereas 88% (basins) of the global ocean area is covered by only 20% of the data. Thus, the relatively coarse data resolution in basin areas limits the processing of high-resolution TOC grids on a global scale. The objectives of our investigations are mainly to improve the information about the TOC distribution of surface sediments on large scales and in more detail. With the approach of the regionalization of the TOC content by discriminable benthic TOC provinces, suggested underlying local trends and anisotropies could be considered. The regional dependencies are expressed by variograms and are used to separate adjacent areas. The selection of the TOC data for modelling the variograms is coupled e.g. to oceanographic boundary conditions, the contour of the continental margins, the water depth, the distance to the coast and the terrestrial sedimentary input. For the processing of the distribution pattern of TOC in surface sediments on a global scale we compiled more than 5520 TOC surface data from individual sides. (The main part of the point data was inferred from the world data base Pangaea (www.pangaea.de) and adapted from published literature.) Despite a relatively rough grid resolution of 1°x1°, the discretization of the worlds ocean into separate provinces clearly improved the accuracy and reliability of the distribution maps. Increasing the grid-resolution in areas with high sample density, e.g. the Greenland sea or the south-west African coast, results in regional distribution patterns of TOC with much higher accuracy and increased significance. In these areas the influence of processes affecting the distribution and concentration of TOC in surface sediments can be properly quantified. First investigations of using this new global and high resolution TOC maps for calculation of benthic oxygen uptake and nutrient release rates show very promissing results which may lead to more reliable balancing of deep-sea benthic flux rates in the near future.