No abstract

Inputs of pollutant lead to the Gulf of Mexico from the Mississippi River have declined by about 40 percent within the past decade. This decrease has been determined from annual lead loads of the Mississippi River and from the lead record in Mississippi Delta sediments. The observed trend is consistent with reduced consumption of lead in gasoline in the United States. More than 90 percent of the riverborne lead is associated with suspended sediments. Most of this particle-bound lead is deposited within 50 kilometers of the river mouth and is not easily leached at pH values above 3.

Concentrations of trace metals in Fe‐ and Cl‐rich hydrothermal solutions from the southern Juan de Fuca Ridge (SJFR) have been determined and corrected for residual precipitates formed in the sampler. Precipitate corrections for Ag, Cd, Cu, Mo, Pb, Sb, and Zn were variable, contributing an average of 20% to total solution concentrations whereas corrections for Co averaged less than 5% and essentially no corrections were required for Fe and Mn. Values for Cu, Co, and Mo in these solutions showed a strong dependence on temperature with sharp decreases in concentrations as temperatures decreased to less than 320°C. In addition, and unlike most other metals studied, all vent fluids from the SJFR were almost completely depleted in Mo relative to seawater values of about 110 nmol kg−1. In contrast to the Cu‐Co‐Mo group, concentrations of Ag, Cd, Sb, and Pb correlated well with those for Zn and are presumed to follow a distribution that is influenced less by temperature over the 246 to 332°C range encountered in this study and more by the combined chemical processes that control Zn levels along the transport pathway from the deep reaction zone to the vent orifice.

No abstract

MThee intense halocline and redoxcline in the Orca Basin, northwest Gulf of Xico, induce dramatic water column profiles for manganese, iron, and SUspended particulates. Within a 17 m interval, the salinity of the basin ~'ater increases from 66 to -~260%~ and dissolved oxygen decreases to zero.Midway through this transition zone, concentrations of suspended matter Peak at ~900 i~g/liter. Dissolved iron and manganese concentrations in the an0xic brine increase from oceanic values to maxima of 1.6 and 22 n~g/liter, respectively. Upward migration of dissolved manganese from the bnne leads to production of manganese-rich particles in the slightly oxygenated overlying water.