Spatial and Temporal Distribution of Bioactive Trace-metals in the North Pacific: MESO-SCOPE, Gradients, and GP15
Seth John1, Paulina Pinedo-Gonzalez2, Nicholas Hawco3, Ruifeng Zhang4, Emily Seelen5, Rachel Lauren Kelly3, Shun-Chung Yang1, Xiaopeng Bian1, Jessica N Fitzsimmons6, Nathan Lanning6, Tim M Conway7 and Matthias Sieber8, (1)University of Southern California, Department of Earth Sciences, Los Angeles, United States, (2)Lamont -Doherty Earth Observatory, Geochemistry, Palisades, NY, United States, (3)University of Southern California, Earth Sciences, Los Angeles, CA, United States, (4)Shanghai Jiao Tong University, China, (5)University of Southern California, Earth Sciences, Los Angeles, United States, (6)Texas A&M University College Station, Oceanography, College Station, United States, (7)University of South Florida, College of Marine Science, St. Petersburg, United States, (8)ETH Swiss Federal Institute of Technology Zurich, Earth Sciences, Zurich, Switzerland
Abstract:
The North Pacific encompasses extreme gradients in trace-metal concentrations. The highest concentrations of zinc and cadmium (Zn and Cd) worldwide are found in the deep North Pacific, while surface concentrations of these elements in the overlying oligotrophic gyres can be nearly three orders of magnitude lower. The globally highest nickel and copper (Ni and Cu) concentrations are also found in the deep Pacific, yet these two elements are still present at quite high concentrations in surface waters. Iron (Fe) is the limiting nutrient for growth in the high-latitude North Pacific, yet in oligotrophic gyres Fe barely affects phytoplankton growth or ecology.
Three recent field campaigns provide unique and distinctive opportunities to understand how exactly biological processes give rise to these gradients in Zn, Cd, Ni, Cu, and Fe. The MESO-SCOPE cruise near Hawaii explored the biological and chemical cycling of trace-metals in nearby cyclonic and anticyclonic eddies, providing a constraint on the biological uptake and regeneration of metals over the weeks-long timescales of eddy formation, as higher metal concentrations from deeper waters are brought upwards towards the surface. Three Gradients cruises over the past several years provide an opportunity to understand the seasonal patterns in nutrient drawdown in the surface North Pacific, as spring and summer blooms push the nutrient-depletion front further northwards. Basic scale analyses of these metals from the GEOTRACES GP15 transect show how surface biological uptake is expressed in global ocean metal distributions.
Global biogeochemical models of trace-metal cycling provide a framework for synthesizing such disparate datasets, specifically here models of Zn, Cd, Cu, and Ni cycling built on the AWESOME OCIM platform. The datasets each provide unique constraints on biological metal uptake rates, which can then be tested and compared for the impact of this biological uptake on global metal distributions.
