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Sediments Beneath Multi-Year Sea Ice: Delivery By Deltaic and Eolian Processes
Little is known about land-to-sea sediment transport and deposition in polar regimes with multi-year sea ice such as at the mouth of the Taylor Valley, one of the Dry Valleys in Antarctica. This study integrates textural analysis of 574 coastal subaerial and nearshore submarine sediment samples with data from sediment traps and with published grain-size analyses of offshore sea-ice surface and submarine sediments to reconstruct transport and depositional processes from the shoreline to ∼ 8 km offshore.
Sediment, primarily sand sized, is transferred into the marine environment via two processes: 1) erosion, transport, and deposition of till by ephemeral meltwater streams that deliver sediment to the subaqueous part of the delta built over the last ∼ 7,500 years, and 2) onshore to sea-ice sediment transport by wind during rare but powerful foehn wind events. Because the distributaries flow into quiet water beneath the sea ice, most of their load is dropped close to shore, but a small amount of fine-grained sediment, mostly silt, is carried kilometers offshore, probably by low-density, low-salinity plumes.
Wind deposits sediment on the sea ice with median grain size decreasing from medium to fine sand within 1.5 km of the shoreline; even offshore sea-ice sediment contains very little silt and almost no clay. Nearshore the sea-ice sediment is coarser than that on the underlying seafloor, but in a few kilometers offshore the median grain sizes of the seafloor and sea-ice sediments are similar; this reflects a mixture of sea-ice-rafted eolian sediment and fine-grained delta-derived sediment transported beneath the sea ice.
This system is unusual in the relative effectiveness of the transport systems. The feeble distributaries deposit their sediment load immediately upon entering the quiet water, and only a minor amount of silt and clay is carried seaward under the ice. In contrast, winds deposit coarser sediment on the nearshore sea ice and carry fine sand > 7 km offshore, although the amount and grain size of sediment is attenuated within 1.5 km of shore. Melting of the sea ice drops sediment onto the seafloor, where it mixes with the delta-derived silt and clay. Similar combinations of eolian and fluvial transport processes may have operated in polar regimes dominated by multi-year sea ice in the past. Understanding of the modern processes in Explorers Cove may aid recognition of ancient sediments deposited under multi-year sea ice, as well as help predict future changes in processes around Antarctica as the distribution of multi-year sea ice shifts in response to climate change.
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