Zinc, chromium, vanadium and iron in the Mediterranean Sea

Abstract

Mediterranean surface waters contain elevated levels of zinc and chromium and slightly lower levels of vanadium compared to similar nutrient-depleted open ocean waters. A detailed mapping of surface concentrations in the Alboran Sea (immediately east of the Strait of Gibraltar) reveals that maximum total dissolvable concentrations of Zn (9.4 nmol kg −1, Cr (3.9 nmol kg −1), V (35 nmol kg −1) and total Fe (53 nmol kg −1) occur in the core of the Atlantic inflow jet. These distributions imply that a portion of Mediterranean trace metal enrichment occurs during passage of surface water through the coastal region and into the Strait, as observed previously for Cu and Cd. Mass balance indicates that about half of the Mediterranean Zn enrichment, and most of the Cr enrichment, is due to sources within the basin itself. High concentrations of particulate Fe in the Alboran Sea suggest eolian input or recent sediment resuspension, but in general metal sources are difficult to identify and could be fluvial or anthropogenic as well as eolian and sedimentary. Chromium and V levels in Mediterranean deep water are similar to surface water concentrations near deep-water formation regions, but Zn is enriched in deep water, implying some vertical transport by biological cycling. A simple steady-state box model indicates that about 30% of the Zn transport is particulate and that the Zn: nutrient ration in sinking particulate matter is similar to that in open ocean particulates.