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

Delta(14)C 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 sedimentwater interface (-263parts per thousand) to 10 cm depth (-446parts per thousand) 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 C-14 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 Delta(14)C 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. (C) 2002 Elsevier Science Ltd. All rights reserved.