Strontium geochemistry in the estuarine mixing zone of the Mississippi River
Description
The geochemical behavior of Sr in the Mississippi River (MR) mixing zone is examined in an attempt to address the extent to which estuarine environments modify the fluvial flux of Sr on its way to the ocean Trace metal analyses show that particle-dynamic-related processes play an important role in the distribution of dissolved Fe, Mn and V. These same processes exert little effect on the dissolved U and Mo concentrations, as they do for Sr. Greater than 97% of the Sr in the water column is in the dissolved load and greater than 70% of Sr in the solid phase (particulates and sediments) is present in the residual, refractory fraction Sequential extractions indicate that particulates have concentrations of non-residual, labile Sr that are higher (30% of the total Sr is labile) than those in the sediments (15% of the total Sr is labile). Carbonate components seem to play an important role as carriers for labile Sr in particulates and sediments. Changes in the composition and content of the solid phase may significantly modify both the 87Sr/86Sr isotope ratio of the total labile fractions and that of the bulk components. However, such modifications normally do not influence significantly the Sr isotope composition of the dissolved phase The estuarine mixing patterns reveal slightly non-conservative behavior of Sr in the dissolved pool. The non-conservative patterns may result from: (1) redistribution of Sr between dissolved and particulate phases, (2) changes in the quantity and/or composition of colloidal material, (3) slight variations in the concentration of Sr in the high-salinity bottom waters of the mixing zone, and (4) particles which act as a sink for Sr in some high-salinity waters. The monthly measurements of the lower MR show that Sr input to the Gulf of the Mexico from the MR varies temporally in both elemental concentration and isotopic composition, and that the flux of Sr is largely a function of water discharge. The slightly non-conservative behavior of Sr during estuarine mixing does not affect the application of the Sr isotopic technique to studies of chemostratigraphic correlation