A comparison of benthic nutrient fluxes from deep-sea sediments off Namibia and Argentina

Benthic fluxes of nitrate, phosphate, silicate, and oxygen, estimated C(org) input to the sea floor, and C(org) content of surface sediments at various stations in the Argentine Basin and the Cape Basin (South Atlantic) were used to characterize the benthic mineralization pattern in these areas. Diffusive benthic fluxes across the sediment-water interface reveal very intense subsurface biodegradation of organic matter and dissolution of biogenic silica, Across the Namibian continental margin diffusive benthic fluxes generally decrease with increasing water depth, but a considerable site-to-site variation exists along the 1300 m isobath. Mineralization patterns indicate that the input flux of organic matter seems to be significantly controlled by vertical transport through the water column. A nearly reverse pattern can be observed in the western Argentine Basin. Intense nutrient release is observed even at locations on the deeper slope. For this whole area a dependence of nutrient release and water depth is not observed. An exception is the Rio de la Plata region, where stations between 1800 and 3500 m water depth reveal the highest nitrate and phosphate fluxes, decreasing towards the shelf and into the deeper basin. Silicate fluxes off the Rio de la Plata increase continuously with water depth. Below 4000 tn water depth this is probably due to the input of Antarctic diatoms by the Antarctic Bottom Water. Mineralization processes on the continental margin of the Argentine Basin do not correlate with the estimated organic matter input from surface waters. In accordance with previous sedimentological studies, we conclude that intense sediment mass flows from the shelf are the main source for the input of reactive organic matter to the deeper parts of the continental margin. (C) 2000 Elsevier Science Ltd. All rights reserved.