Marine Biogeochemical Cycling of Carbon and Cadmium

Abstract/nMarine Biogeochemical Cycling of Carbon and Cadmium/nby/nHannah Bourne/nDoctor of Philosophy in Earth and Planetary Science/nUniversity of California, Berkeley/nProfessor James Bishop, Chair/nThe actions of single celled organisms living in the surface ocean drive the distribution/nof many elements in the ocean - both vertically and horizontally across the ocean surface,/ndetermining global chemical signatures. Autotrophs fix CO2 and dissolved nutrients into/ntheir cells, building biomass that forms the base of the food chain, providing the energy/nsource for all higher trophic levels. The subsequent export of fecal pellets produced by/nzooplankton and small particles aggregated into larger particles drive the biological pump./nThe magnitude and processes of biomass export from the surface determines distributions/nof elements and the partial pressure of CO2 near the surface, which ultimately affects global/nclimate.While the spatial distribution of near-surface biomass is well quantified through high/nfrequency satellite observations, observations of the vertical distribution and the processes/ndetermining these distributions are relatively few./nIn the first section, I present a model predicting the horizontal global distribution of Cd,/na toxic trace metal, in particles in the surface ocean. Particulate Cd concentrations is higher/nin HNLC environments with cold temperatures and low dissolved silica levels than in warm,/noligotrophic regions. I hypothesize that this is due to inadvertent uptake of cadmium by/ntransporter cells outside of cells targeting other divalent trace metals such as iron and zinc./nIn regions with low concentrations of bioavailable necessary divalent trace metals, Cd is more/nlikely to be accidentally taken up by cells. Another finding in this study is that particulate/nP occurs in two forms with different labilities. One phase, such as phosphorus in DNA, is/nmore labile than Cd while the other phase, such as P bound in phospholipids, is less labile/nthan Cd. These differences in remineralization lead to subsurface Cd:P peaks occurring near/nthe euphotic zone depth./n2/nIn the second part, I present the development of a novel in-situ sampling system which/nwas integrated with robotic profiling floats called Carbon Flux Explorers. We built two of/nthese integrated CFEs, which are called CFE-Cals. The CFE-Cals are capable of collecting/nparticles in-situ while drifting with currents at depth. During a 30 day research expedition/nin June 2017 off the coast of California, I deployed the CFE-Cals 15 times. With samples/ncollected during the expedition, I successfully calibrated the CFEs optical measurements of/nparticle flux in terms of carbon and nitrogen. This translates sensor images into biogeochemical/nterms, and is an important step forward in the advancement of autonomous optical/ncarbon export observations for quantifying processes in the carbon pump. Samples were/ncollected in varied environments - from very productive near shore regions where export/nwas dominated by large anchovy fecal pellets to low nutrient, low flux offshore waters dominated/nby small particles. Regression slopes for the optical properties measured by the CFE,/nVolume Attenuance (VA), to concentrations of particulate organic carbon and particulate/nnitrogen (units mATN-cm2: mmol; R2, n, p-value in parentheses) were 10:07103 (0.86, 12,/n5:7 10-8), 10:05 104 (0.87, 15, 5:2 10-10) respectively./nIn the last section, I examine carbon export beneath a highly productive filament of/nnutrient rich upwelled water in dynamic waters off the coast of California. In this study,/nexport is relatively high and increases with depth, contrary to typical observations of export/nmagnitude rapidly attenuating with depth. These observations indicate that in coastal regions,/nefficient export by filtering organisms and lateral transport of material facilitate high/nlevels of carbon export.

Advisor: Bishop, James