Temporal variations in the concentrations of some particulate elements in the surface waters of the Sargasso Sea and their relationship to deep-sea fluxes

The concentrations of particulate Ca, Al, Ba, Sr, Mn, Mg, V and I have been measured in the upper 200 m of the water column of the Sargasso Sea at approximately monthly intervals over a 4-year period. Biogenic particles dominate the composition of the particulate matter and show a seasonality related to the cycle of primary productivity, with concentration maxima in spring. Particulate Ca, Sr and I follow this pattern. Particulate Al concentrations (presumed to be associated with clays) in the shallowest samples show a maximum in summer, which is suggested to be associated with aeolian inputs to waters above the seasonal thermocline. Particulate V and Mg behave similarly to Al. The different seasonalities in Ca and Al concentrations lead to a seasonality in Ca/Al ratios which can also be seen in sediment-trap material collected in this area. In general, particulate trace element concentrations decrease with depth over the upper 200 m but Mn, by contrast, increases, probably because of in situ scavenging of dissolved Mn.