Δ14C of the organic matter in sediments from the Antarctic Polar Front: origin and dynamics of sedimentary organic carbon

Δ14C of sedimentary organic matter was measured on one sediment core from the deep-sea below the Subantarctic Front of the Indian Ocean using acceleration mass spectrometry. In the mixed layer, values decrease from the sediment–water interface (−263‰) to 10 cm depth (−446‰) with a sharp gradient in the first 2 cm. This indicates the loss of organic younger fractions due to mineralization of labile organic matter during bioturbation and burial in the upper sediment layer. A previously published model (Limnol. Oceanogr. 43(1998)420), combined with suppositions concerning the 14C content of each organic carbon fraction, produces a good agreement with the radiocarbon data. Our data set supports a strong biogeochemical coupling between the pelagic zone and the sediment in this region. The low Δ14C values found at depth in the sediment point to a particular source of the refractory organic matter. It could originate from adsorption of “old” deep-sea dissolved organic carbon on falling particles (Nature 347(1990)172) and contribute largely to the burial of organic carbon in this type of sediment.