SEDIMENT RECORD DEMONSTRATES DYNAMICS OF DEGLACIATION IN THE HUGO ISLAND ANVERS TROUGH: A TEST OF CALVING BAY REENTRANT MODEL

The transition between the Last Glacial Maximum (LGM) and the Holocene is recorded by varved sediments deposited in a period of exceptionally high primary production in fjord-like settings along the western Antarctic Peninsula. Data from jumbo gravity cores retrieved from five sites along a North-South transect of the Hugo Island Anvers Trough record the deglaciation event in the early Holocene. Specifically, core lithology, water content and grain size data from cores collected by the R.V. Laurence M. Gould in 12-11 and 13-11 appear to correlate with other records, of note the 1998 Ocean Drilling Project Site 1098 and 1099 in Palmer Deep (PD), as they too capture the unique deglacial interface. Despite a series of projects in the region, poor core recovery interrupted the continuity of the time series. Thus, the Hugo Island Anvers Trough cores are crucial because they add to our estimation in the timing and rate of ice retreat along the western Antarctic Peninsula following a seemingly widespread, consistent response to ocean forcings at the end of the LGM.

Both the Palmer Deep and Hugo Island Anvers Trough sediment sequences contain almost identical varved intervals that were deposited under specific environmental conditions, when the site existed as a “calving bay reentrant”—an ice-walled fjord that formed as ice retreated in the deep, but remained grounded on the shallower shelf on the banks. Site 1098 contains ~176 couplets of diatom ooze siliciclastic-rich diatom mud spanning ~45m, suggesting that the calving bay environment was more of a permanent feature in PD. The same facies exists on a much smaller scale along the axis of the trough, spanning as little as half a meter with ~15 couplets in JGC-6 and ~14 couplets in JGC-4 suggesting the rapid recession of the calving bay model. The resulting calving bay reentrant facies that correlates along the Hugo Island Anvers Trough is also observed through spikes in water content and grain size. Increases in water content, ~30%, reflect the laminated diatom ooze and mud unique to the calving bay facies. Similarly, a grain size analysis of KC-6 and JGC-6 illustrates a distinct transition from silt and clay to a sandy clay rich mud at the reentrant facies. This study supplements our understanding of the calving bay reentrant model, and the nature of deglaciation at the end of the last glacial.