Trace Elements in Seawater and Marine Productivity

Research Project , Research Report 2001

Yoshiyuki NOZAKI The Ocean Research Institute, the Univ. of Tokyo
Dia Sotto ALIBO Graduate School of Science, the Univ. of Tokyo
Hajime OBATA The Ocean Research Institute, the Univ. of Tokyo(Research Partners)
Edward A. BOYLE Department of Earth, Atmospheric, and Planetary Sciences, MIT, USA

Abstract

The marine geochemistry of refractory metals, such as Al, In and Ce, has been poorly understood because of their low concentrations in seawater and contamination problems. These metals are insoluble in seawater and have relatively short mean residence time as compare to the ocean mixing time of ~103 years. This leads these metals to be sensitive and useful tracers for lithogenic substance in the ocean. We present here the distributions of dissolved surface Al, In and Ce in the eastern Indian Ocean. The latitudinal distributions of these metals are compared with that of 228Ra (with half life, 5.7 years), derived fluvially and/or coastally. The trend of the surface Al is similar to that of 228Ra, which implies that the mean residence time of Al in the surface is shorter than 5.7 years if additional sources of Al exist except the river and coastal sediment. The ratios of surface Al/210Pb, derived atmospherically with a half life, 22.3 years, are also calculated. These ratios are within the range of the Al/210Pb ratio in the air. This indicates that the mean residence time of Al is similar to that of 210Pb. The mean residence time of Al (0.5-3 years) estimated from the dust flux supports the similarity of Al and 210Pb in the oceanic surface.

Keywords:

trace elements, aluminum, indium, cerium, seawater, productivity, Indian Ocean