Isotopic composition of dissolved and particulate Cu in the North Atlantic: Constraining the atmospheric deposition of aerosol Cu

Cu is an essential micronutrient required in various phytoplankton metalloenzymes, but can also be a potential toxin at sufficiently high concentrations. The Cu stable isotope composition (δ⁶⁵Cu) of seawater has been employed to constrain sources of Cu to the global ocean. However, the biogeochemical cycling of Cu isotopes in the modern ocean is still poorly understood. Dedicated sampling for dissolved and particulate Cu concentrations and stable isotope composition was carried out along CLIVAR meridional Atlantic section A16N in 2013 to address previous studies that have reached contradictory conclusions about the effects of both active biological uptake of Cu by phytoplankton and passive adsorption of Cu onto particles on δ⁶⁵Cu values. Stations sampled span diverse geochemical provinces with varying levels of primary production and both natural lithogenic and anthropogenic aerosol Cu inputs. Paired analyses of dissolved and particulate fractions of open-ocean Cu pools will better constrain the effects of biological uptake, particle scavenging, and aerosol source on Cu isotopic composition in the North Atlantic. Data will be used to refine an isotopic mass balance for global ocean Cu to better constrain atmospheric Cu inputs, as current estimates range over two orders of magnitude.