Fischer, Gerhard¹, Gerold Wefer¹, Oscar Romero¹, Nicolas Dittert², Volker Ratmeyer¹ and Barbara Donner¹

¹Fachbereich Geowissenschaften, Klagenfurter Strasse, Universität Bremen, 28359 Bremen, Germany, Tel: 0049 (0)421 218 3588, Fax: 0049 (0)421 218 3116, E-mail: gerhard.fischer@allgeo.uni-bremen.de, and ²Institute Universitaire Européen de la Mer, Technopôle Brest-Iroise, Place Nicolas Copernic, F-29280 Plouzané, France

Transfer of particles into the deep Atlantic and the global ocean: importance of nutrient supply and ballast production

Particle fluxes from the deep Atlantic/Southern Ocean and the world ocean have been compiled to study the regional variations. It is shown that the supply of dissolved silicate to the surface waters plays a central role for opal fluxes, the BSi:Corg ratios, the BSi:carbonate ratios and the carbon rain ratios. The mean annual BSi:Corg ratio (mol/mol) normalized to 1000 m was 0.05 in the Atlantic, 0.4 in the Indian, 0.5 in the Pacific, and 0.1-3 in the Southern Ocean and follows the general path of the conveyor belt. A shift in the primary producer community from coccolithophorids to diatoms, reflected by an exponential increase of the annual BSi:carbonate flux ratios, occurs above a molar Si:N(250m) nutrient threshold of about 1.7. The surface sediment opal:carbonate ratios (%) versus the Si:N(250m) nutrient values give a threshold of 2-2.5. Our compilation of flux data also confirms the importance of mineral ballast (e.g., of carbonate) for the downward transport of particles. However, at certain sites, e.g., off NW Africa, lithogenic components were major particle carriers. There, relationships between carbonate/lithogenic/total ballast fluxes versus daily organic carbon fluxes may even vary from year to year. Off Cape Blanc, the carbonate-Corg-flux relationship is most significant during a strong coccolithophorid bloom in 1991, probably resulting in an efficient downward transfer of organic carbon.