Trace metals in suspended particulate matter of Atlantic Ocean surface water (40 °N to 20 °S)

Abstract

In this synoptic study the distribution and trace element composition of oceanic suspended particulate matter (SPM) are presented. SPM was extracted from up to 1000 I of surface seawater by a continuous flow technique at 34 transects along the Atlantic Ocean. With an overall average of 27 μg/l, concentrations of SPM ranged from less than 1 μg/l in the southwestern Atlantic to a maximum of 115 μg/l in the open ocean off West Africa. Particulate concentrations of Al, Cd, Cu, Fe, Mn and Pb and distribution of particulate organic carbon (POC) were determined revealing significant and surprising spatial and seasonal variations: although sampling was performed on two cruises at different longitudes and seasons, particulate Al, Fe, Mn and Pb concentrations were very similar. Unlike these four elements, distinct seasonal differences in particulate Cd concentration were found and traced back to biological activity. Clearly distinguished peak concentrations for Al (7.1 n M ) and Fe (2.5 n M ) were found in the Intertropical Convergence Zone (ITCZ), while maxima for Cd (7.6 p M ), Cu (24 p M ) and Pb (1.1 p M ) were located further north in the subtropics. A significant correlation between POC and all six metals is further reported. SPM investigated in this study was found to consist mainly of phytoplankton. Corresponding dissolved Al, Cd, Cu and Pb concentrations in surface seawater are reported. Comparison with the particulate fraction shows that more than 90% of Cd, Cu and Pb and more than 80% of Al are localized in the dissolved state.