SIMULATION OF O-2, PO4 AND ORGANIC-CARBON BEHAVIOR DURING A BENTHIC CHAMBER EXPERIMENT ON THE DEEP-SEA FLOOR

Using a time-dependent model for organic matter mineralization by oxygen and the resulting phosphate production in deep-sea sediments, the progress of a benthic chamber experiment is simulated. Assuming a known steady state as starting condition, the vertical distribution of chemical species in the sediments, pore water and solids, and the concentrations in the benthic chamber are calculated. Compared to previous approaches, the computation scheme utilized here considers explicitly a coupled and non-linear kinetic formulation of organic carbon oxidation and oxygen reduction. The purpose of this modeling approach is to assess the validity of conventional interpretations of benthic chamber experimental data. The results of the calculations show that the concentration gradients of solutes at the sediment-water interface and the penetration depth of O-2 in the sediment undergo important changes during the deployment of a benthic chamber. On the contrary, the particulate phase distribution (organic carbon) is only slightly modified. The model is further used to perform numerical experiments and the different techniques used to calculate fluxes (linear regression, zero-order model) are compared. Differences exist between the different ways of calculating the chemical fluxes. It is shown that a systematic bias, ranging from 10 to 20 %, is introduced by the linear regression technique, On the other hand, calculations performed with a simple zero-order model agree within 2 to 5 % with our calculations and therefore provide a very good estimate of the solute fluxes.