Supply and removal of trace elements in the subtropical South Pacific

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With funding from this RAPID award, an American research team at the Lamont-Doherty Earth Observatory of Columbia University will study the supply and removal of trace elements in the South Pacific Subtropical Gyre (SPSG). This will be done in the context of an international program (UltraPac) under the direction of Dr. Tim Ferdelman of the Max Planck Institute in Breman, Germany, who has invited the Lamont-Doherty team to join the German scientists aboard their expedition on the Research Vessel Sonne (December 2015 - January 2016) between Antofagasta, Chile and Wellington, New Zealand. UltraPac is a coordinated interdisciplinary study of the SPSG, including research on microbiology, molecular biology, zooplankton, aerosols, trace metals, nitrogen fixation, carbon and nutrient biogeochemistry, among other topics. The American team will measure dissolved and particulate concentrations of long-lived, naturally-occurring radioisotopes in the uranium and thorium decay series that can be used to provide constraints on the rates of supply and removal of trace elements within this regime. The project will also provide education, training and professional development for two PhD students that would otherwise be unavailable through other aspects of their PhD research. It will also provide an opportunity for the students to network with foreign collaborators, which will be very beneficial to their long-term career development. This project will enable the Lamont-Doherty scientists to quantify the rates of supply and removal of trace elements in the severely undersampled SPSG, the ocean's largest biogeographic province, characterized by a hyper-oligotrophic (low biological productivity) ecosystem and ultra-low dust fluxes. Evaluating the supply of trace elements from dust provides critical information about sources of essential micronutrients that influence the ecology and biogeochemistry of the SPSG. The award will cover the travel expenses for two people to participate in the cruise, shipping to and from the cruise, and instrument fees to analyze samples collected on the cruise. Comparing scavenging results from the SPSG with results from recent studies of other biogeographic providences, including the North Pacific Subtropical Gyre, the Subarctic North Pacific, the North Atlantic Subtropical Gyre and the Eastern Tropical South Pacific, will build toward the team's long-range goal of characterizing the intensity of trace element removal from the ocean in terms of environmental, ecological and biogeochemical characteristics of ocean biogeographic provinces. The deep water column of the SPSG is influenced by the hydrothermal plume emanating from the East Pacific Rise. Comparing SPSG results with those from regions lacking significant influence by hydrothermal plumes will also enable them to constrain the role of these plumes in defining the global distribution of trace elements in the deep ocean. This effort should provide rates of supply and removal of biologically essential micronutrients, and of other trace elements, in an end-member ocean regime that is not scheduled for sampling by a GEOTRACES ocean section, thus filling a gap in the global database for trace elements and isotopes under development by GEOTRACES. Results will be obtained using GEOTRACES-compliant methods, and made available through the GEOTRACES database for use by investigators in other fields.