Sediments Beneath Multi-Year Sea Ice: Delivery By Deltaic and Eolian Processes

Abstract

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 finegrained 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.

Glacial-Marine Sedimentation

“…Analysis of sedimentary matter obtained by melting of sea ice gives important materials also. These studies made possible to reveal one unexpected source of glacial sediments -aeolian (Darby et al, 1974;Lisitzin, 2002;Shevchenko et al, 2002;Shevchenko, 2010;Chewings et al, 2014;Miller et al, 2015). The main feature of aeolian supply here is that aeolian material is deposited mostly during polar winter at low temperatures.…”

“…The dominant sedimentary process in most fjords is sedimentation from the brackish plumes rich in suspended particulate matter that emerges from either glacier-fed river mouths or tidewater cliff. Modern glacial-marine environments are widely spread in the Antarctic, Alaska, Greenland, Baffin Island, British Columbia, Svalbard, Norway, Novaya Zemlya, and Severnaya Zemlya (Drewry and Cooper, 1981;Elverhøi et al, 1983;Molnia, 1983;Cowan and Powell, 1991;Syvitski et al, 1996;Gilbert et al, 2003;Kehrl et al, 2011;Politova et al, 2012;Szczucinski and Zajaczkowski, 2012;Chewings et al, 2014;Miller et al, 2015).…”

BIOTURBATION BY THE COMMON ANTARCTIC SCALLOP (ADAMUSSIUM COLBECKI) AND OPHIUROID (OPHIONOTUS VICTORIAE) UNDER MULTI-YEAR SEA ICE: ECOLOGIC AND STRATIGRAPHIC IMPLICATIONS

“…1), typically is covered with multi-year sea ice~4 m thick that melts completely about every 10 years (Gooday et al 1996). During the summer, a moat commonly forms alongside the shoreline, the sea ice becomes ungrounded, and an ephemeral melt-water stream delta transports sediment to the seafloor where sedimentation rates are low and ocean currents are minimal (Murray et al 2013;Miller et al 2015).…”

“…Consequently, Antarctic scallops could survive with thinner, lighter valves, resilient hinge material, and low area-to-weight ratios compared to temperate scallops, allowing for clapping with reduced metabolic demand (Bailey et al 2005;Denny and Miller 2006). The delta in Explorers Cove delivers the sand-size fraction of sediment preferred by the scallops, and average low rates of sedimentation prevent scallop burial (Fan et al 2012;Miller et al 2015). This grain size typically accumulates in areas of relatively high currents or waves (Stokesbury and Himmelman 1993) that would be destructive to the thin scallop shells.…”

“…This study is part of a larger integrated investigation aimed at providing baseline data and models to recognize past and present sedimentologic and taphonomic processes on the shallow Antarctic seafloor under multi-year sea ice in this climatically sensitive setting Murray et al 2013;Walker et al 2013;Miller et al 2015). The purpose of this study was to constrain under laboratory conditions the styles and rates of bioturbation of the two dominant epifaunal animals on Antarctic soft substrates and to interpret the ecologic, taphonomic, sedimentologic, and stratigraphic implications of this bioturbation.…”