Sediment-water column fluxes of carbon, oxygen and nutrients in Bedford Basin, Nova Scotia, inferred from 224Ra measurements

[摘要] Exchanges between sediment pore waters and the overlying water column play asignificant role in the chemical budgets of many important chemicalconstituents. Direct quantification of such benthic fluxes requires explicitknowledge of the sediment properties and biogeochemistry. Alternatively,changes in water-column properties near the sediment-water interface can beexploited to gain insight into the sediment biogeochemistry and benthicfluxes. Here, we apply a 1-D diffusive mixing model to near-bottomwater-column profiles of ²²⁴Ra activity in order to yield vertical eddydiffusivities (K_Z), based upon which we assess the diffusive exchangeof dissolved inorganic carbon (DIC), nutrients and oxygen (O₂), acrossthe sediment-water interface in a coastal inlet, Bedford Basin, Nova Scotia,Canada. Numerical model results are consistent with the assumptionsregarding a constant, single benthic source of ²²⁴Ra, the lack ofmixing by advective processes, and a predominantly benthic source and sinkof DIC and O₂, respectively, with minimal water-column respiration inthe deep waters of Bedford Basin. Near-bottom observations of DIC, O₂and nutrients provide flux ratios similar to Redfield values, suggestingthat benthic respiration of primarily marine organic matter is the dominantdriver. Furthermore, a relative deficit of nitrate in the observed fluxratios indicates that denitrification also plays a role in the oxidation oforganic matter, although its occurrence was not strong enough to allow us todetect the corresponding A_T fluxes out of the sediment. Finally,comparison with other carbon sources reveal the observed benthic DIC releaseas a significant contributor to the Bedford Basin carbon system.

[学科分类] 地球化学与岩石