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Geophysical, geochemical and geotechnical methods were used to investigate the spatial and temporal aspects of sediment distribution, accumulation, post-depositional alterations, and seafloor response and recovery to major events in a temperate, paraglacial, turbid outwash fjord. The goals of this study are to generate a complete geological model and compare the results to the global distribution of fjords. The over arching theme of this study is that the ratio of the area of the watershed to the area of the receiving basin can provide a first order indicator of many factors including glacial mass; the timing of glacial retreat; sediment input, accumulation, and preservation; and other factors. Temporal observations reveal the change of this fjord from a glaciated basin to and estuarine environment. These observations become important when viewed in the context of global climate change and the continued loss of ice. Preserved strata provide a 2800-year record of changing modes of sedimentation as the system evolved from a glaciated basin to a non-glaciated fjord revealing a detailed chronology of change between end-member systems which can be used to infer changes as glaciers retreat from other fjords. Short lived radio isotopes were used to investigate post-depositional alteration of modern sediments. Without an understanding of how biological and physical processes work to modify sedimentary fabric during preservation, changes seen in sediment and rock core data cannot be accurately resolved. Physical processes can cause erosion and lateral transport; winnowing and armoring; and instantaneous sedimentation, all of which may be preserved. Biological processes can modulate the preservation of strata by destroying sedimentary fabric and integrating signals. The final fundamental need is to investigate the seafloor response and recovery to these events. Massive earthquakes are frequent in the study area and cause perturbations to sediment input and preservation. By understanding how lakes and deltas modulate sediment discharge after the event; how shorelines are modified after the event; and where sediment is deposited we can determine the influence these changes have on the environment and on humans.
Geophysical, geochemical and geotechnical methods were used to investigate the spatial and temporal aspects of sediment distribution, accumulation, post-depositional alterations, and seafloor response and recovery to major events in a temperate, paraglacial, turbid outwash fjord. The goals of this study are to generate a complete geological model and compare the results to the global distribution of fjords. The over arching theme of this study is that the ratio of the area of the watershed to the area of the receiving basin can provide a first order indicator of many factors including glacial mass; the timing of glacial retreat; sediment input, accumulation, and preservation; and other factors. Temporal observations reveal the change of this fjord from a glaciated basin to and estuarine environment. These observations become important when viewed in the context of global climate change and the continued loss of ice. Preserved strata provide a 2800 yr record of changing modes of sedimentation as the system evolved from a glaciated basin to a non-glaciated fjord revealing a detailed chronology of change between end-member systems which can be used to infer changes as glaciers retreat from other fjords. Short lived radio isotopes were used to investigate post-depositional alteration of modern sediments. Without an understanding of how biological and physical processes work to modify sedimentary fabric during preservation, changes seen in sediment and rock core data cannot be accurately resolved. Physical processes can cause erosion and lateral transport; winnowing and armoring; and instantaneous sedimentation, all of which may be preserved. Biological processes can modulate the preservation of strata by destroying sedimentary fabric and integrating signals. The final fundamental need is to investigate the seafloor response and recovery to these events. Massive earthquakes are frequent in the study area and cause perturbations to sediment input and preservation. By understanding how lakes and deltas modulate sediment discharge after the event; how shorelines are modified after the event; and where sediment is deposited we can determine the influence these changes have on the environment and on humans.
Ice-ocean interactions remain poorly understood despite the growing recognition that they play significant roles in the complex behavior of glaciers that reach the oceans, which is of broad interest because it contributes substantially to the challenge of predicting global sea-level rise. This research focuses on the dynamics of sediment accumulation near the calving fronts of tidewater glaciers across a climatic continuum from polar to temperate conditions. Rates and spatial patterns of sediment accumulation merit close attention because they can affect glacier stability by reducing the water depth that controls the calving rate, the surface area available for submarine melting, and the ability of tidewater glaciers to advance into deep water. The sediments produced by these glaciers are also of considerable interest because they record changes in glacial, environmental, and tectonic conditions. In light of the recent, well documented changes in climate and glacier extent along the Antarctic Peninsula through much of the last century, a detailed study was developed to understand how modern sediments have recorded these regional changes. Sediment accumulation rates for sixteen cores collected in fjords across a 15° N-S transect from the Antarctic Peninsula to southern Chile were calculated using the decay of naturally occurring radioisotope 210Pb. Records from the Antarctic Peninsula show surprisingly constant rates of sediment accumulation (1-7 mm/yr) throughout the past century despite rapid warming, increase in surface melt, and glacial retreat. Cores from the South Shetland Islands, on the other hand, reveal accelerated sediment accumulation over the past few decades, likely due to warming and an increase in surface melt in this region, which straddles the boundary between subpolar and temperate conditions. In the temperate fjords of southern Chile, sediment accumulates faster (11-24 mm/yr). This increase in sediment accumulation with decreasing latitude reflects the gradient from subpolar to temperate climates, and is consistent with glacial erosion being much faster in the very wet, temperate climate of southern Chile than along the colder Antarctic Peninsula. Links between rates of glacier retreat, ice motion, sediment flux, and the evolution of glacial sediment deposits in a temperate setting are explored using a large existing dataset for Columbia Glacier, Alaska and new oceanographic data from the fjord recently exposed by its retreat. High-resolution seismic data indicate that 3.2 x 108 m3 of sediment has accumulated over the last three decades; this volume corresponds to erosion at 5.1 ± 1.8 mm/yr averaged over the entire ~1000 km2 area of the glacier. A numerical model is developed to relate known patterns of sedimentation and changes in the glacier terminus position to the accumulation of sediment in the fjord during the 30-year period of retreat. The model, which represents both primary sedimentation and secondary reworking, is used to produce a history of the sediment flux from the glacier that is compatible with the observed post-retreat sediment deposit thickness and architecture. The bathymetric history and model results corroborate that the sediment flux increased sixfold within the 1997-2000 period; interestingly this increase is not correlated with concurrent changes in glacier dynamics. It is suggested that the increase resulted from the sediment transport capacity of subglacial rivers increasing due to the retreat-related steepening of the glacier surface over a deep subglacial basin. That major variations in the sediment flux can be controlled by changes in subglacial sediment storage, in addition to changes in climate and the erosion rate, adds richness and complexity to the interpretation of the glacimarine sediment record. The sediment-flux model is also applied to Jorge Montt Glacier, a Patagonian tidewater glacier with very similar behavior to Columbia Glacier, but without the detailed record of its retreat history and other complementary glaciological data. Sediment volume calculations for both glaciers indicate that the effective erosion rate necessary to sustain the mean sediment fluxes during their respective periods of retreat is surprisingly similar, ~5 mm/yr, despite differences in the geographic, tectonic, and geologic settings. For both rapidly retreating glaciers, the numerical model yields a sediment-flux history that produces sediment packages generally consistent with observed bathymetry and internal stratigraphic architecture. On the time scale of retreat, temporal variations in the modeled sediment flux from both glaciers are not related to concurrent variations in ice velocity, as expected. Rather, changes in the sediment flux are attributed to the tendency for sediment to be flushed from subglacial basins due to the progressive steepening of the glacier terminus during retreat. In both fjords, model results corroborate that sediment accumulates rapidly (>1 m/yr) near the ice front. In addition, the model suggests that gravity-driven processes are essential for delivering and redistributing sediment within the fjords to create the observed bathymetry and internal stratigraphic architecture.
All over the world, the awareness of the increasing pollution of rivers, estuaries and the sea with its associated impact on these ecosystems, its effect on organisms, food-chains, water supply and finally on man himself is growing. Estuaries form a link between the limnetic and marine environments, characterized by a variety of complex processes. Most of these phenomena are not yet sufficiently understood, making efficient water quality management a difficult task. The volume has two main objectives: to present the latest information on current estuarine research and to elaborate fundamentals and criteria for planners and decision-makers in water quality management.