DIEL TRACE METAL VARIATIONS IN THE NORTH PACIFIC SUBTROPICAL GYRE
During the C-MORE/SCOPE cruise HOE-Legacy-2 (Summer 2015), we undertook Lagrangian sampling in a weakly anti-cyclonic eddy, about 250 km northeast of Station ALOHA, to investigate possible diel changes in bioactive trace metal (Fe, Mn, Zn, Ni, Cu, Cd) concentrations. We sampled for both dissolved and particulate phases in mixed layer waters at unprecedented temporal resolution (sunrise and sunset for 9 days). We additionally sampled thorium isotopes to track scavenging effects (Th-230) and lithogenic element supply (Th-232). In initial results, for most dissolved metals, with the possible exception of Fe, there was no discernible diel variation. Biological uptake and regeneration are likely tightly coupled to minimize the loss of dissolved metals during the daytime growing period. Some elements did display significant weekly-scale trends, however. Most notably, dissolved Zn steadily increased by a factor of 2 (from ~0.5 nmol/kg to 1.0 nmol/kg) over the course of the cruise. This does not correlate with a change in thorium scavenging or supply and could possibly be related to the progression of phytoplankton senescence. With this data we constrain expected variability in daily-weekly scale trace metal concentrations, informing seasonal to annual studies relying on the representativeness of 1 particular sampling day.
Hayes, C. T., University of Southern Mississippi, USA, firstname.lastname@example.org
Fitzsimmons, J. N., Texas A&M University, USA, email@example.com
Morton, P. L., Florida State University, USA, firstname.lastname@example.org
McGee, D., Massachusetts Institute of Technology, USA, email@example.com
Boyle, E. A., Massachusetts Institute of Technology, USA, firstname.lastname@example.org
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