Sedimentary organic carbon budget of coastal sediments and the importance of benthic-pelagic coupling off Namhae Island in the South Sea of Korea

Abstract

We characterized the biogeochemical organic carbon cycles in the surface sediment layer (< 25 cm) in the coastal waters of Namhae off the South Sea of Korea. The total and diffusive sediment oxygen uptake rates were measured using an in situ benthic lander equipped with a benthic chamber and a microprofiler. The bottom water above the sediment-water interface was incubated to estimate the benthic flux of the dissolved inorganic nutrients and the total alkalinity using an in situ benthic chamber. In addition, the particulate materials vertically deposited onto the surface sediment and the sedimentation rates were quantified to calculate the sedimentary organic carbon budget. The total oxygen uptake rate was in the range 34.9 to 54.1 mmol O2 m-2d-1, which is about three times the diffusive oxygen uptake rate. An abnormal oxygen peak observed in the anoxic sediment layer suggests a higher bioirrigation activity in the sediment layer. The oxidation rate of organic carbon at the sediment surface showed a very narrow range (36 ± 7 to 37 ± 7 mmol C m-2d-1), and the burial flux into the sediment layer was in the range 3 to 13 mmol C m-2d-1, which accounted for 9% to 36% of the remineralization rate of the organic carbon. The N and P requirement fluxes for pelagic production could be supported by 29% and 42% of the benthic flux, respectively, which strongly suggests a benthic-pelagic coupling in the coastal area of the South Sea of Korea.