RESPIRATION AND DISSOLUTION IN THE SEDIMENTS OF THE WESTERN NORTH-ATLANTIC - ESTIMATES FROM MODELS OF IN-SITU MICROELECTRODE MEASUREMENTS OF POREWATER OXYGEN AND PH

We present in situ microelectrode measurements of sediment formation f actor and porewater oxygen and pH from six stations in the North Atlan tic varying in depth from 2159 to 5380 m. A numerical model of the oxy gen data indicates that fluxes of oxygen to the sediments are as much as an order of magnitude higher than benthic chamber flux measurements previously reported in the same area. Model results require dissoluti on driven by metabolic CO2 production within the sediments to explain the pH data; even at the station with the most undersaturated bottom w aters >60% of the calcite dissolution occurs in response to metabolic CO2. Aragonite dissolution alone cannot provide the observed buffering of porewater pH, even at the shallowest station. A sensitivity test o f the model that accounts for uncertainties in the bottom water satura tion state and the stoichiometry between oxygen consumption and CO2 pr oduction during respiration constrains the dissolution rate constant f or calcite to between 3 and 30% day-1, in agreement with earlier in si tu determinations of the rate constant. Model results predict that ove r 35% of the calcium carbonate rain to these sediments dissolves at al l stations, confirmed by sediment trap and CaCO3 accumulation data.