UC San Diego

This thesis has been motivated by questions pertaining to the cycling of bioactive elements through the ocean on geological time scales. By definition, such questions cannot be addressed without understanding the organisms that mediate their fate, as well as the geological deposits in which they are deposited. I have further focused on metals, which have their own unique chemistry both in seawater and within the cell. This thesis is thus a highly interdisciplinary exercise. In chapter 2 I use a novel trace-metal clean and pH-controlled culturing technique to culture the coastal diatom Thalassiosira pseudonana under variable trace metal regimes. These experiments yield the first evidence for Cd incorporation into the diatom frusutle, for variability in frustular Cu incorporation, and I add nuance to previous observations of frustule-bound Zn. I evaluate existing paradigms for macronutrient and micronutrient cycling throughout the ocean in light of these data, and evaluate the potential for frustule-bound Cu, Zn, and Cd as paleoproxies. In chapter 3 I investigate the variability of polyphosphate in 4 species of diatom with the growth cycle and with variable Cu availability. I use a method that reports extractable polyphosphate (e-poly P) that does not include whole-cell P, but does include P bound in polyphosphate granules missed by some other methods. I find wide variability in e-poly P over the course of the growth cycle, over the range of [Cu²⁺] examined, and interspecific differences between the diatoms considered. In chapter 4 I report polyphosphate, Cu and Fe speciation, in situ phytoplankton community composition, macronutrient, and physical data from two cruises of opportunity in the Humboldt and California Currents. I use a sampling technique that enables quantification of all these parameters from a single 50 L sample of sea water processed using trace-metal clean techniques. I report some of the first particulate polyphosphate measurements from the ocean, I find no evidence for any of these parameters determining e-poly P, and I suggest that community growth cycle is the dominant determinant of poly P in situ