http://hdl.handle.net/1957/12776 Search the Channel search http://ir.library.oregonstate.edu/jspui/simple-search http://hdl.handle.net/1957/12853 Title: Effect of iron limitation on the cadmium to phosphorus ratio of natural phytoplankton assemblages from the Southern Ocean<br/><br/>Authors: Cullen, Jay T.; Chase, Zanna; Coale, Kenneth H.; Fitzwater, Steve E.; Sherrell, Robert M.<br/><br/>Abstract: There is considerable interest in the biogeochemical cycling of cadmium (Cd) and phosphate (PO4) in surface waters, driven in part by the ongoing development of a paleonutrient proxy that utilizes Cd preserved in fossil planktonic foraminifera to determine past PO4 utilization efficiencies in ocean surface waters. The present article reports the results of a field study into the effects of Fe limitation on the Cd : P composition of natural assemblages of marine phytoplankton in the Antarctic Zone of the Pacific sector of the Southern Ocean. Iron enrichment to shipboard incubation bottles led to increases in community growth rate and final biomass. After 10.7 d of incubation, the climax community was dominated by large diatoms of the genus Fragillariopsis, Pseudonitzschia, and Nitzschia. Direct measurements of phytoplankton metal : P ratios from controlled shipboard experiments indicate that Cd : P, Co: P, and Zn : P ratios decreased from control values with increasing initial dissolved Fe concentrations in the incubation bottles, by factors of ~2–10 at highest Fe additions. We suggest that the effect of Fe limitation on resident diatoms is to decrease growth rate, leading to elevated cellular Cd content. The dissolved Cd : P ratio in iron-limited surface waters of the Southern Ocean may, therefore, respond to the supply of Fe to the resident phytoplankton community, which has implications for the developing paleonutrient proxy. We suggest that the biological uptake of Cd and P is independent of the dissolved Cd: PO4 ratio. As a consequence, the results argue against the use of empirical Rayleigh fractionation models or models with fixed phytoplankton uptake ratios to account for regional variability in surface water dissolved Cd : PO4. Tue, 29 Oct 2002 22:58:59 GMT http://hdl.handle.net/1957/12852 Title: Metabolic consequences of iron deficiency in heterotrophic marine protozoa<br/><br/>Authors: Chase, Zanna; Price, N. M.<br/><br/>Abstract: Iron is recognized as a key element regulating primary production in large regions of the ocean, but nothing is known of its direct effect on higher trophic levels. Two species of heterotrophic protozoa were thus fed iron-rich and iron-poor bacterial prey and their growth and metabolism examined. Maximum growth rates of Paraphysomonas imperforata and Paraphysomonas butcheri were observed only when iron quotas of bacterial prey were >70 μmol Fe mol C-l. At lower Fe : C ratios, but at constant prey biomass, both species grew significantly slower. Iron quotas of the flagellates at these slow growth rates (-10 μmol Fe mol C-l) were similar to those of iron-limited phytoplankton and bacteria. Growth rate reduction was likely the result of direct, elemental limitation by iron, judging from the positive response of the protozoa to iron addition and their biochemical characteristics. Filtration and carbon ingestion rates increased under iron limitation, but gross carbon growth efficiency (GCGE) decreased when P. imperforata consumed iron-poor bacteria. Ammonium regeneration efficiency was also reduced. The decrease in GCGE was a consequence of reduced activity of the iron-dependent electron transport system, greater dissolved organic carbon excretion, and greater CO, evolution by iron-limited protozoa. P. imperforata excreted iron, even when limited by this element, and retained less of the ingested ration than when consuming iron-rich bacteria. Coupled with recent measurements of biogenic Fe : C in the subarctic Pacific, our results suggest that heterotrophic bacterivorous flagellates may experience iron limitation in remote oceanic regions. Tue, 29 Oct 1996 22:58:59 GMT