Influences On The Oceanic Biogeochemical Cycling Of The Hybrid Type Metals Cobalt Iron And Manganese

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.

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Cobalt is a necessary nutrient for many marine phytoplankton, but its hybrid-type nature results in small marine inventories that make it one of the scarcest bioactive trace metals in the oceans. This study examines the marine dissolved cobalt cycle in two regions: the Pacific Ocean and Antarctic coastal seas. In the North Pacific, elevated cobalt stoichiometries among phytoplankton were linked to nitrogen, iron and phosphate stress protein biomarkers at the boundaries of oceanographic provinces and upwelling zones, providing insight into the flexibility of cobalt stoichiometry. In both regions, perturbations to the marine cobalt cycle were either predicted or observed; in the equatorial Pacific, the dissolved cobalt inventory was predicted to increase by up to 28% due to the expansion of oxygen minimum zones in a warmer ocean, while in the Antarctic, melting ice shelves have the potential to shift the nutrient regime from iron limitation towards zinc and vitamin B12 limitation, resulting in higher cobalt demand and a lower dissolved cobalt inventory. When the global cobalt cycle was estimated throughout four of Earth's systems (the lithosphere, biosphere, hydrosphere and the anthroposphere - the human environment), it was determined that the scale of the cobalt flux through the anthroposphere is only one order of magnitude lower than the inventory of the entire hydrosphere (10(9) mol Co yr-1 and 10(10) mol Co, respectively), revealing a vulnerability to anthropogenic perturbation of the marine cobalt inventory through human mining, use and disposal of cobalt if appropriate pollution abatement, disposal and recycling infrastructure is not established. In light of observed and predicted changes to cobalt biogeochemistry, this research suggests that the marine cobalt cycle is particularly vulnerable to anthropogenic perturbation from both global climate change and pollution due to its low ocean inventory and interconnection to other nutrient biogeochemical cycles.

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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.

This book presents an up to date view of iron biogeochemistry in the ocean. It encompasses the description of iron speciation, the analytical methods used to measure the different iron forms in seawater and the different iron biogeochemical models.

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Highlighted in this compilation of papers is the role and importance of heavy metals in the environment. It provides up-to-date information in a field of active research and progress, where the focus is on effects and interactions between the environment and organisms, as well as contaminant dynamics. Several papers address the impact of heavy metals on our health. The influence of metals on plants is described in an exhaustive study on lichens, which have been widely used as biomonitors for environmental contamination by heavy metals. Metals are also accumulated by animals, as seen in a chapter which focusses on sediment/benthic organism interactions and biomonitoring in fish. Soil interactions are discussed, as well as regional studies of freshwater sediments and the marine environment. The final part of the book addresses a crucial problem: the management of stabilized municipal waste sludges. As a result, the most important and significant recent trends are included, emphasizing interactions with and impacts of heavy metals on humans, animals, plants and soils.

This volume presents state-of-the-art research about mineral dust, including results from field campaigns, satellite observations, laboratory studies, computer modelling and theoretical studies. Dust research is a new, dynamic and fast-growing area of science and due to its multiple roles in the Earth system, dust has become a fascinating topic for many scientific disciplines. Aspects of dust research covered in this book reach from timescales of minutes (as with dust devils, cloud processes and radiation) to millennia (as with loess formation and oceanic sediments), making dust both a player and recorder of environmental change. The book is structured in four main parts that explore characteristics of dust, the global dust cycle, impacts of dust on the Earth system, and dust as a climate indicator. The chapters in these parts provide a comprehensive, detailed overview of this highly interdisciplinary subject. The contributions presented here cover dust from source to sink and describe all the processes dust particles undergo while travelling through the atmosphere. Chapters explore how dust is lifted and transported, how it affects radiation, clouds, regional circulations, precipitation and chemical processes in the atmosphere and how it deteriorates air quality. The book explores how dust is removed from the atmosphere by gravitational settling, turbulence or precipitation, how iron contained in dust fertilizes terrestrial and marine ecosystems, and about the role that dust plays in human health. We learn how dust is observed, simulated using computer models and forecast. The book also details the role of dust deposits for climate reconstructions. Scientific observations and results are presented, along with numerous illustrations. This work has an interdisciplinary appeal and will engage scholars in geology, geography, chemistry, meteorology and physics, amongst others with an interest in the Earth system and environmental change. body>