MODERN CLIMATE-SENSITIVE SEDIMENTARY SEQUENCE DEPOSITED AT MOUTH OF LONG-TERM GLACIAL VALLEY/FJORD: EXPLORERS COVE, ANTARCTICA

The Taylor Valley, unique among Antarctica’s large ice-free valleys in opening directly into McMurdo Sound, and its offshore extension has been a glacial valley/fjord for > 20 MY. It has served as a conduit and repository for glacial and glaciomarine sediments emanating from both onshore and offshore. During the LGM the Ross Ice Sheet advanced into the Taylor Valley from McMurdo Sound, depositing moraines that dammed a large, deep lake. Since retreat of the ice sheet ~8200 years ago, the meltwater fed Wales Stream has built a delta into nearly perennially sea-ice covered Explorers Cove (EC).

The complex interplay between ample sediment source, fluvio-deltaic and aeolian transport, multi-year sea ice, and biological and taphonomic processes results in a distinctive sedimentary package in EC. Significant ingredients include: 1) Multi-year sea ice that melts out completely once ~10 yr^-; 2) Large supply of unvegetated (mostly sand-sized) sediment; 3) Ephemeral streams and distributaries that drop load in shallow quiet water under sea ice; 4) Foehn wind events that blow sediment onto sea ice, which eventually reaches the seafloor through cracks; 5) Very low productivity because of low light levels under thick sediment-laden sea ice; 6) Intense diffuse sediment disruption by suspension-feeding scallops whose “claps” resuspend sediment and by highly mobile generalist feeding epifaunal ophiuroids; 7) Survival of thin-shelled scallop and epifuanal ophiuroid because of sea-ice induced quiet water conditions and absence of fast predators; 8) Enhanced dissolution of ophiuroid ossicles and possibly scallop shells during long residence time in the taphonomically active zone.

The resulting sedimentary package is massive sand, homogenized by an epifauna that may not be preserved as body fossils or discrete trace fossils. Although cryptic, this massive sand facies is probably a temporally and spatially widespread record of nearshore deposition under climate-sensitive multi-year sea ice.