9617430 Martin Dissolution of CACO3 will be measured in marine sediments of the eastern tropical Atlantic Ocean and western north Atlantic continental rise. The study areas have key characteristics for extending understanding of CaCO3 dissolution: (1) the range in saturation of bottom waters with respect to calcite, from CO32-=28 to =40, includes both substantial undersaturation -- ideal for constraining parameters in dissolution models -- and supersaturation, which is essential for the direct measurement of dissolution rates in sediments above the calcite lysocline; (2) the values of the important, dissolution-controlling Corg : CACO3 ratio in the material raining to the sea floor appear to be quite high, in some areas exceeding 2.5 mol/mol, in contrast to other above- saturation horizon regions that have been studied previously; (3) the area includes both a regions of high sediment O2 demand (the Cape Verde Plateau and western N. Atlantic margin) and one of lower demand, typical of non-upwelling, pelagic areas ( the Sierra Leone Rise); (4) the Sierra Leone Rise has been the site of extensive sedimentological and paleoceanographic investigation, resulting in a substantial set of ancillary data for the analysis of organic matter oxidation and CaCO3 dissolution, and allowing evaluation of the sedimentological indicators to above-saturation horizon dissolution; and (5) the study areas include high flux sites with low to moderate %CaCO3 (W.N. Atlantic margin) and with high %CaCO3 (Cape Verde Plateau, allowing evaluation of this factor as an explanation for discrepancies in dissolution rates measured by pore water and benthic chamber techniques. The examination of the variability in sedimentary oxidation and dissolution processes over the range of conditions on the sea floor is essential to accurate interpretations of the sedimentary record and to model-based predictions of the ultimate fate of anthropogenic CO2.
