Biogeochemical Cycling Of Metals In Redox Stratified Marine Environments

Volume 59 of Reviews in Mineralogy and Geochemistry ties together themes common to environmental microbiology, earth science, and astrobiology. The resesarch presented here, the associated short course, and the volume production were supported by funding from many sources, notably the Mineralogical Society of America, the Geochemical Society, the US Department of Energy Chemical Sciences Program and the NASA Astrobiology Institute.

Trace metal cycling is one of many processes that influence ocean ecosystem dynamics. Cobalt, iron, and manganese are redox active trace metal micro-nutrients with oceanic distributions that are influenced by both biological and abiotic sources and sinks. Their open ocean concentrations range from picomolar to nanomolar, and their bioavailabilities can impact primary production. Understanding the biogeochemical cycling of these hybrid-type metals with an emphasis on cobalt was the focus of this thesis. This was accomplished by determining the dissolved distributions of these metals in oceanic regions that were characterized by different dominant biogeochemistries. A large subsurface plume of dissolved cobalt, iron, and manganese was found in the Eastern South Atlantic. The cause of this plume is a combination of reductive dissolution in coastal sediments, wind-driven upwelling, advection, biological uptake, and remineralization. Additional processes that are discussed as sources of metals to the regions studied during this thesis include isopycnal uplift within cold-core eddies (Hawaii), ice melt (McMurdo Sound, Antarctica), riverine input (Arctic Ocean), and winter mixing (McMurdo Sound). The biological influence on surface ocean distributions of cobalt was apparent by the observation of linear relationships between cobalt and phosphate in mid to low latitudes. The cobalt:phosphate ratios derived from these correlations changed over orders of magnitude, revealing dynamic variability in the utilization, demand, and sources of this micronutrient. Speciation studies suggest that there may be two classes of cobalt binding ligands, and that organic complexation plays an important role in preventing scavenging of cobalt in the ocean. These datasets provided a basis for comparing the biogeochemical cycles of cobalt, iron, and manganese in three oceanic regimes (Hawaii, South Atlantic, McMurdo Sound). The relative rates of scavenging for these metals show environmental variability: in the South Atlantic, cobalt, iron, and manganese were scavenged at very different rates, but in the Ross Sea, mixing and circulation over the shallow sea was fast, scavenging played a minor role, and the cycles of all three metals were coupled. Studying the distributions of these metals in biogeochemically distinct regions is a step toward a better understanding of their oceanic cycles.

This book provides a detailed examination of the concentration, form and cycling of trace metals and metalloids through the aquatic biosphere, and has sections dealing with the atmosphere, the ocean, lakes and rivers. It discusses exchanges at the water interface (air/water and sediment/water) and the major drivers of the cycling, concentration and form of trace metals in aquatic systems. The initial chapters focus on the fundamental principles and modelling approaches needed to understand metal concentration, speciation and fate in the aquatic environment, while the later chapters focus on specific environments, with case studies and research highlights. Specific examples deal with metals that are of particular scientific interest, such as mercury, iron, arsenic and zinc, and the book deals with both pollutant and required (nutrient) metals and metalloids. The underlying chemical principles controlling toxicity and bioavailability of these elements to microorganisms and to the aquatic food chain are also discussed. Readership: Graduate students studying environmental chemistry and related topics, as well as scientists and managers interested in the cycling of trace substances in aqueous systems Additional resources for this book can be found at: www.wiley.com/go/mason/tracemetals.

Biological processes in the oceans play a crucial role in regulating the fluxes of many important elements such as carbon, nitrogen, sulfur, oxygen, phosphorus, and silicon. As we come to the end of the 20th century, oceanographers have increasingly focussed on how these elements are cycled within the ocean, the interdependencies of these cycles, and the effect of the cycle on the composition of the earth's atmosphere and climate. Many techniques and tools have been developed or adapted over the past decade to help in this effort. These include satellite sensors of upper ocean phytoplankton distributions, flow cytometry, molecular biological probes, sophisticated moored and shipboard instrumentation, and vastly increased numerical modeling capabilities. This volume is the result of the 37th Brookhaven Symposium in Biology, in which a wide spectrum of oceanographers, chemists, biologists, and modelers discussed the progress in understanding the role of primary producers in biogeochemical cycles. The symposium is dedicated to Dr. Richard W. Eppley, an intellectual giant in biological oceanography, who inspired a generation of scientists to delve into problems of understanding biogeochemical cycles in the sea. We gratefully acknowledge support from the U.S. Department of Energy, the National Aeronautics and Space Administration, the National Science Foundation, the National Oceanic and Atmospheric Administration, the Electric Power Research Institute, and the Environmental Protection Agency. Special thanks to Claire Lamberti for her help in producing this volume.

In addition to control by major nutrient elements (nitrogen, phosphorous, and silicon) growth and community composition of marine phytoplankton is also regulated by trace element nutrients (iron, copper, manganese, zinc, cobalt, nickel, and cadmium). Of these, iron is the most influential in the modern ocean, regulating phytoplankton growth and carbon export in high-nutrient low-chlorophyll regimes and exerting an important control on the marine nitrogen cycle through its role in di-nitrogen fixation. The distributions of these metals has the capacity to control primary production and phytoplankton community composition through differences in cellular quotas or metal sensitivities amongst species. The relationship between trace metal distributions and marine microorganisms is coupled; plankton and bacteria shape the distribution, speciation, and redox state of these metals through cellular uptake, recycling processes, and production of specific and non-specific metal chelators. The interplay between these chemical and biological processes has a profound influence on the modern ocean and global biogeochemical cycles. In this work the feedbacks between trace metal nutrients, natural metal-binding chelators, and marine microorganisms are examined in three distinct oceanic environments that encompass some of the major interfaces of trace metals to the ocean. In the upwelled waters of the California Current system field incubations examine the role of light on the uptake and speciation of metals; an important observation from this study was the increase in short-term Fe uptake rates for marine phytoplankton resulting from photochemical reactions of organically bound Fe, a process that may result in a competitive advantage for some phytoplankton species. In the surface waters of the West Florida Shelf a baseline study of the concentrations of bioactive trace metals and Fe-and-Cu binding organic ligands are reported between two seasons; the work identifies important regional and seasonal processes controlling the distributions of these metals and observed divergent mechanisms influencing the cycling of Fe-and-Cu-binding ligands that may act as a bottom-up control on phytoplankton communities in this region. In hydrothermal plumes along the Mid Atlantic Ridge field incubations examine the role of particles and Fe-binding ligands on the stabilization of dissolved Fe input from these vent systems; the experiments demonstrate the importance of colloids, exchange between particle phases, and Fe-binding ligand production in the stabilization of Fe far-field of these vent systems. The results of these studies present mechanistic frameworks to contextualize some of the basin-scale distributions of these metals generated from the GEOTRACES program. As the GEOTRACES program shifts progressively towards more process oriented studies this work may serve as a useful framework to test hypotheses and further characterize biogeochemical cycles of trace metals in these marine environments.

Building on the success of its 1993 predecessor, this second edition of Geochemistry, Groundwater and Pollution has been thoroughly re-written, updated and extended to provide a complete and authoritative account of modern hydrogeochemistry.Offering a quantitative approach to the study of groundwater quality and the interaction of water, minerals,

An important contribution to getting insight into processes of transport, transformation and accumulation of heavy metals in marine ecosystem lies on the understanding of the strategies developed during evolution by aquatic and terrestrial organisms to maintain equilibrated relations with heavy metal ions in the surrounding environment. This book presents a pioneering study on the workings of metal resistance systems in autotrophic protists and on their ecological significance, implementing the knowledge on chemical and biochemical mechanisms that regulate the bioavailability, accumulation and toxicity of heavy metals in the marine environment. The transboundary approach, which combines physical, chemical and biological competences, thus largely strengthening the methodological tools, allows to demonstrate the feasibility of using biochemical responses for the assessment of toxicity in ecosystems and, in particular, to give an important contribution to the understanding of mercury cycling in oceans. The book should be especially useful to anyone else who may be considering the assessment of the marine environment and in particular the study of biogeochemical cycles of heavy metals.