Description:
<jats:p>Pore water data from surface sediments and bottom water data at 180 locations were used to create distribution maps of diffusive benthic release rates of nitrate, phosphate, and silicate in the southern Atlantic Ocean for water depths ≥1000 m. Geostatistical methods of variogram analysis and kriging were used for data interpolation. Since benthic fluxes are controlled by organic matter degradation and dissolution processes and therefore by the supply of organic matter to the sediment surface, the distribution pattern of all investigated constituents should reflect a general coupling to surface water productivity. This seems to be true for the most part of the oligotrophic central South Atlantic and the upwelling area off southwest Africa. Striking regional differences in this regard, however, exist for the eastern equatorial region where unexpectedly low fluxes were calculated and the Argentine Basin where benthic fluxes are very high. The Argentine Basin obviously receives a higher input of degradable/dissolvable material, whereas in the eastern equatorial region the low benthic fluxes are possibly due to intense nutrient recycling within the water column. Estimated fluxes vary considerably over the entire region: NO<jats:sub>3</jats:sub>, 10–180 mmol m<jats:sup>−2</jats:sup> yr<jats:sup>−1</jats:sup> PO<jats:sub>4</jats:sub>, (−2)−11 mmol m<jats:sup>−2</jats:sup> yr<jats:sup>−1</jats:sup> and Si, 0–0.65 mol m<jats:sup>−2</jats:sup> yr<jats:sup>−1</jats:sup>. Areas of highest release rates are the continental margins off southwest Africa and off Argentina. The investigated area comprises a total of approximately 32×10<jats:sup>6</jats:sup> km<jats:sup>2</jats:sup> between 8°N and 40°–50°S. Our estimations reveal benthic release rates of 1.55×l0<jats:sub>12</jats:sub> mol NO<jats:sub>3</jats:sub> yr<jats:sup>−1</jats:sup>, 3.5×l0<jats:sup>10</jats:sup> mol PO<jats:sub>4</jats:sub> yr<jats:sup>−1</jats:sup> and 2.1×10<jats:sup>12</jats:sup> mol Si yr<jats:sup>−1</jats:sup>. Open ocean areas with middle to low fluxes contribute about 70–80% of the total estimated fluxes. The release of phosphate is probably underestimated because of core recovery artifacts and is therefore based on the assumption that fluxes are not lower than 0.25 mmol m<jats:sup>−2</jats:sup> yr<jats:sup>−1</jats:sup> at any location of the studied area. The investigated area represents about one tenth of the world deep ocean (without the Arctic Ocean). Assuming the South Atlantic to be representative, we calculate annual global release rates of 15×l0<jats:sup>12</jats:sup> mol NO<jats:sub>3</jats:sub>, 32×l0<jats:sub>10</jats:sub> mol PO<jats:sub>4</jats:sub> and 20×10<jats:sup>12</jats:sup> mol Si. If our estimates are correct, about 4–6% of silicate, 3–4% of nitrate, and 1% of phosphate annually produced in the surface waters are remineralized in surface sediments from water depths ≥ 1000 m.</jats:p>