Siberian-Arctic shelf surface-sediments: sources, transport pathways and processes, and diagenetic alteration Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/k930c044g

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  • This thesis investigates lithogenic sediments on the Siberian Arctic shelf, their sources, modes of dispersal, transport pathways and post-depositional diagenetic alteration. Working with cores collected from the Chukchi, East Siberian and Laptev Seas, we characterize surface-sediment elemental chemistry and clay mineralogy. We identify five regions with endmember sedimentary compositions. Comparing these data with a variety of geological, physical oceanographic and other environmental observations, we conclude that endmember formation is controlled by a complex combination of sediment provenance and various physical processes. Average sediment transport pathways are inferred from gradients in geochemical endmember flux distributions. On the Chukchi shelf sediment movement is primarily offshore. In the alongshore direction, available data suggest that sediment dispersal is predominately to the east in both the Chukchi and Laptev Seas. These results corroborate the limited observations of shelf currents and suggest circulation is key in determining dominant sediment transport pathways. In the Laptev Sea, offshore sediment movement is limited compared to alongshore sediment movement. This sedimentation pattern may be controlled by currents, or by removal of sediment from the central Laptev shelf via ice rafting. A fraction of the material deposited on the shelf is recycled to overlying waters by sediment diagenesis. Chukchi surface sediments are typically depleted in Mn and Co relative to values predicted based on sediment source rock geology. Evaluating these metal depletions in the context of shelf primary production gradients and surface sediment color observations, we conclude they are caused by dissolved metal fluxes from suboxic surface sediments to overlying waters. We estimate that sediments within our Chukchi study area release 4.5-6.1 x 1O⁴ tons/yr of dissolved Mn. Less than 1/20th of this Mn is sequestered as reactive Mn in lower Chukchi slope and Canadian basin sediments. Reactive Mn deposition throughout the Amerasian Arctic at depths >1000 m can potentially account for only about half of this Mn, indicating additional sinks exist for the dissolved Mn released from shelf sediments. Possible fates include 1) deposition as reactive Mn in upper slope sediments and 2) export from the region dissolved in Amerasian Arctic waters.
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