Benthic Fluxes and Sediment Irrigation on the Continental Margin, N.W. Atlantic

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9503562 MARTIN Benthic fluxes and pore water concentrations of carbon and related solutes will be determined on a depth transect of the continental margin in the northwest Atlantic ocean. The proposed study area is the depth interval from 100-2000m at 71 W, a region that is physically representative of much of the margin. A complete depth transect in this region will significantly advance our ability to incorporate margin processes in quantitative models of global chemical cycles. The proposed measurements will differ from previous flux determinations on margins in several respects. (1) Flux chamber deployments will be 4 days long, 2-3 times longer than most deployments in rapidly accumulating, high-flux sediments. This increased length will define several processes important in sediments of this type. In situ measurements will be made of solute transport by macroninfaunal irrigation in offshore margin sediments. Significant improvements in the signal-to-noise ratio in alkalinity, dell-13C (totalCO2), and dissolved organic carbon fluxes will be achieved thus providing new information on the contributions of DOC and above-saturation horizon dissolution of CaCO3 to the benthic carbon cycle. (2) Flux experiments will be carried out in duplicate at each of 8 sites, and will be accompanied by extensive, in situ microelectrode profiling and both high-resolution and "standard" pore water sampling. Flux chamber and coring operations will be carried out via submersible, allowing the combination of measurements to be made in a relatively small, visually homogeneous area. The number an combination of measurements will allow improved evaluation of intra-site variability over what has been possible in past experiments, increasing confidence in trends of flux vs. water column depth. (3) At shallower sites (100-1000m), the increased length of flux chamber deployments would lead to extensive depletion of O2 in chamber water. To counteract this effect (with its potentia l undesirable consequences are designed to maintain the O2 in chambers are designed to maintain the O2 level close to that of ambient bottom water.