Material Fluxes on the Surface of the Earth (1994) / Chapter Skim
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In fact, although there have been major recent efforts to study natural systems, there remain many uncertainties about the base level of surficial processes and fluxes and their natural variability. Specifically, this study examines the following: · The state of knowledge of some of the most important processes, rates, and fluxes for Recent, Holocene, and late Pleistocene times; · the variability inherent in these processes, rates, and fluxes in relatively recent geologic times; · the extent to which modern measurements of these fluxes already incorporate anthropogenic effects; 1
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We recognize that, in the long term, catastrophic events might have a cumulative impact of the same order of magnitude as the more frequent and continuous processes, but the historical record contains an inadequate sampling of such events. Neither have we attempted to evaluate fluxes of volcanic gases, hydrothermal fluids, or the fluids expelled from sediments along subduction zones.
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From page 3... ...
In polar regions, the major meltwater flux of the spring-summer transition transports sediment at a time when direct observations are difficult because of lake- and sea-ice cover. Most glacial transport occurs beneath hundreds or thousands of meters of ice, precluding direct observation.
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Water budget of glaciers Sources of eolian material Chemical composition of eolian material Not well known Changes in dissolved or particulate fluxes with distance from source Chemical and physical controls of dissolved and particulate fluxes River fluxes fate of dissolved material and trace inorganic constituents at continent-ocean boundary Eolian fluxes Leaching from fresh lava Flux of volcanic ash to the atmosphere Fluxes from volcanic and hydrothermal areas on land (water, CO2, SO2, etc.) Diagenetic fluxes in terms of sediment types and accumulation rates Hydrothermal fluxes in the deep sea Silica budget in the ocean Not known River fluxes storage of particulate materials and trace organic constituents on land, slopes, floodplains, etc., on a global scale Sediment budget of glaciers on a global scale Effect of dissolution of glacially produced rock flour as it is transported to the ocean Groundwater fluxes Fluxes from nonchannelized runoff Rivers are the major natural transport mechanism responsible for moving detritus and dissolved solids on the land surface of the Earth.
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The effect of the sea-level rise has been to flood the nonglaciated continental margins, creating a fringe of estuaries and lagoons along many shores. These special shores provide a wide variety of habitats and a rich nutrient supply, and conses FIGURE 3 Modern lakes occupying basins excavated or dammed by drift left by the Laurentide Ice Sheet.
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From page 6... ...
During the sea-level fall that accompanied the growth of Northern Hemisphere ice sheets, the continental shelves beyond the ice margins were exposed to erosion, and large masses of sediment were transported downslope to the base of the continental rise and onto the abyssal plains. On glaciated shelves, the advance of the ice onto the shelf also shifted the locus of deposition toward the continental slope.
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From page 7... ...
Against a relatively constant background of erosion, transport, and deposition, large infrequent events result in step-function changes in material fluxes. Severe storms may breach the vegetation cover and expose previously stable slopes to erosion; deposition from streams overloaded with debris during extreme flood events may cause them to alter course; windstorms during periods of drought may strip the land of its soil; earthquakes may trigger landslides and submarine slumps; volcanic activity may result in massive ashfalls and mudflows that alter the character of the landscape.
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Very little is known about the magnitude and frequency of such episodes of rapid change. Catastrophic events can be defined as extremely rapid changes in environmental conditions; they commonly involve rapid dissipation of energy per unit area per unit time and/or a rapid rate of change of concentrations of materials or a rapid change in energy flow patterns.
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From page 9... ...
The late Pleistocene Missoula floods discussed by Baker (Chapter 6, this volume) are an example of flood events having a magnitude unknown in human history.
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Recent studies of ice cores from Greenland indicate that during deglaciation the CO2 content of the atmosphere changed significantly on time scales of a few decades. What natural processes were involved in such rapid changes of atmospheric CO2?
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From page 11... ...
Distribution of Sources and Sinks Prerequisites for studies of biogeochemical cycling are maps of sources and sinks of detrital and dissolved materials. These are essential to quantify global fluxes and to identify sensitive areas that are prone to rapid change.
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From page 12... ...
. The record of Late Pleistocene biogenic sedimentation in the eastern tropical Pacific Ocean, Paleoceanography 3, 39-59.
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