Award: OCE-1233733

Copper is a trace metal of interest in the marine environment because it can affect the health of marine microbes, for example phytoplankton at the base of the marine food web. Copper can be toxic to phytoplankton at elevated concentrations, and can also act as a limiting nutrient in ocean regions where its concentrations are very low. The biological impact and cycling of copper are largely controlled by the interaction of copper with dissolved organic ligands in seawater, which bind to (i.e. form complexes with) the copper and affect its biological availability and particle reactivity, among other properties. In this study we applied a competitive ligand exchange voltammetric technique to learn about the organic complexation of dissolved copper along the GEOTRACES Eastern tropical Pacific GP16 transect. The data set that we have produced is the largest data set thus far produced on the chemical species of copper in the ocean. Our data indicate that ligands occur in excess of copper throughout the transect, keeping the levels of biologically available free copper below toxicity, especially in surface waters. In the far eastern, iron-limited surface waters of the transect, free copper is extremely low, which may be related to the iron limitation of phytoplankton in that region. Free copper levels are also very low in the low productivity western surface waters of the transect. Highest levels of free copper are found in the deepest parts of the water column, in water that has been isolated from the surface for hundreds of years. Free copper concentrations in these deep waters do approach levels that are toxic to some sensitive microorganisms. The presence of copper binding ligands in deep waters is likely important in controlling the concentration of total dissolved copper. Our data set has greatly expanded the amount of data available on copper chemistry in ocean waters. In addition to producing a valuable dataset this project also funded the PhD research of graduate student Angel Ruacho, an under-represented minority student. The PI also participated in a collaborative webinar series on GEOTRACES sponsored by the Center for Ocean Sciences Education Excellence-Ocean Systems (COSEE-OS) group based at the University of Maine. Last Modified: 06/27/2018 Submitted by: Katherine Barbeau