Benthic carbon mineralization in the Atlantic: a synthesis based on in situ data from the last decade

Abstract

Benthic oxygen uptake rates quantified by the use of microsensors and flux chambers over a period of approx. 10 yr were compiled and used to assess the organic carbon mineralization in the central and South Atlantic (35°N–50°S). Measurements were performed in situ and in the laboratory on recovered sediment cores. In contrast to the laboratory data, both the in situ diffusive (DOU) and total oxygen uptake (TOU) decreased with increasing water depth. The data demonstrated that sediment recovery alter the O 2 microdistribution and affect the measured O 2 uptake rates. The ratio between TOU and DOU, a measure of the benthic fauna-mediated oxygen uptake, decreased from 3 to 4 in shallow and productive areas to around 1 at the deeper sites. The in situ oxygen uptake rates (both diffusive and total) also correlated with the oceanic primary production. Based on the compiled in situ measurements an empirical relation between the surface water primary production (PP, g C m −2 yr −1), water depth ( z, m) and benthic mineralization deduced from the TOU and DOU was established (C-DOU=PP 0.7358 z −0.3306 (g C m −2 yr −1); C-TOU=PP 1.0466 z −0.4922 (g C m −2 yr −1)). These equations were extrapolated to the entire investigated area of the Atlantic. The mineralization mimicked the surface water primary production, with high consumption rates in the upwelling areas. For the entire area (water depth⩾1000 m) the benthic carbon mineralization was between 134 and 168×10 12 g C yr −1 (from C-DOU and C-TOU, respectively), which equals 1.7–2.1% of the surface water primary production. These rates are higher than previous estimates of benthic carbon mineralization in deep-sea sediments. Integrated for the investigated area of the Atlantic the benthic fauna-mediated carbon mineralization accounted for 35×10 12 g C yr −1 (or 21% of the total mineralization rate). Using our relations to calculate the organic carbon flux through the 1000 m depth horizon revealed that between 212 and 333×10 12 g C yr −1 sink below this depth horizon, of which 63% and 51% is remineralized in the sediments. Particulate organic carbon fluxes obtained from sediment trap data cannot support either the measured or extrapolated benthic mineralization. The areal distribution of the oxygen penetration depth (OPD) for the investigated area of the Atlantic was estimated from the relation between the in situ C-DOU and OPD measurements (OPD=114,6968 C-DOU −0.7541 (mm)).