The distribution of dissolved copper in the tropical-subtropical north Atlantic across the GEOTRACES GA03 transect

Dissolved copper (Cu) was determined in the tropical-subtropical North Atlantic Ocean along the GEOTRACES GA03 transect that covers a number of this basin's key regions. In the surface water, dissolved Cu concentration shows a strong shelf input from North American and European continents, and a significant depletion in the productive zone off Mauritania coast. Dissolved Cu concentration in the surface water of the western margin anti-correlates linearly with salinity suggesting an inefficient surface removal of dissolved Cu relative to the rate of lateral mixing in this region. The depletion of dissolved copper near the Mauritanian shore, in contrast, indicates an efficient scavenging of dissolved Cu onto the biogenic particles which precludes the observation of the shelf input. In general, dissolved Cu concentration strongly correlates with silicate. A similar deep water accumulation for dissolved Cu and silicate was observed along the GA03 transect. The Southern Ocean may be the major source of dissolved copper along our transect, because silicate distribution in the North Atlantic is mainly controlled by the Southern Ocean sources through mixing and due to the strong correlation between dissolved Cu and silicate in the Atlantic sector of that basin. However, the ratio of copper to silicate was much larger during our study than that found for the Southern Ocean (Heller and Croot, 2015), suggesting the presence of additional Cu sources in our study region. One of such Cu sources may be from the benthic sediments, as suggested by previous studies. In addition, subsurface enrichment and seaward decrease of dissolved Cu were observed at the western and northeastern part of our transect. Near the Strait of Gibraltar a hotspot of copper was observed within the influence zone of the Mediterranean Outflow Water (MOW). Copper does not show an anomaly within the oxygen minimum zone (OMZ) off the slope of Mauritania, indicating an insignificant net effect of Cu remineralization relative to scavenging in this region. In this zone, dissolved copper variability, instead, is found mainly near the slopes of Mauritania and Cape Verde Islands, suggesting an influence by sedimentary Cu source. Hydrothermal field on the axis of the Mid-Atlantic Ridge is observed as a sink for the dissolved copper. (C) 2015 Elsevier B.V. All rights reserved.