MANGANESE IN THE EASTERN ATLANTIC-OCEAN - PROCESSES INFLUENCING DEEP AND SURFACE-WATER DISTRIBUTIONS

Samples collected at four vertical water column stations during the 19 90 IOC baseline survey cruise in the eastern Atlantic Ocean, were anal ysed for dissolved and total dissolvable manganese. The distributions show the elevated surface (0.90-2.12 nM) and low deep water (down to c a. 0.2 nM) concentrations typical of the oceanic distribution of this element. This new data in combination with literature data from elsewh ere in the Atlantic, Indian and Pacific Oceans, has allowed an examina tion of the large time and space scale removal of dissolved manganese from the water column. A first order scavenging removal model with a s teady state deep water concentration of 0.15 nM, and a removal rate co nstant of 0.015 yr(-1) leads to a consistent background Mn concentrati on after about 400 years. Suspended particulate matter in the water co lumn has a higher Mn to Al ratio than crustal material except where at mospheric inputs of crustal material are very high or significant bent hic sources exist. In the surface waters column, the role of atmospher ic dust inputs from the Sahara desert appear very important, and highe st Mn concentrations are generally associated with areas of highest du st input. However, closer to the African coast at about 12 degrees N, another source of manganese appears to be important, and may reflect b enthic sources and upwelling processes in the area. (C) 1998 Elsevier Science B.V.