Radiocarbon chronology of ross sea drift, eastern taylor valley, antarctica: evidence for a grounded ice sheet in the ross sea at the last glacial maximum

Abstract

More than 250 radiocarbon dates of lacustrine algae and marine shells afford a chronology for Ross Sea drift in eastern Taylor Valley. Dates of algae that lived in ice‐dammed Glacial Lake Washburn show that grounded Ross Sea ice blocked the mouth of Taylor Valley between 8340 and 23,800 14C yr bp. Ross Sea ice was at its maximum position at the Hjorth Hill moraine between 12,700 and 14,600 14C yr bp and was within 500m distance of this position as late as 10,794 14C yr bp. The implication is that the flow line of the Ross Sea ice sheet which extended around northern Ross Island and across McMurdo Sound to Taylor Valley must have remained intact, and hence that a grounded ice sheet must have existed east of Ross Island as late as 8340 14C yr bp. Evidence from ice‐dammed lakes in Taylor Valley and from shells from McMurdo Sound suggests grounding‐line retreat from the vicinity of Ross Island between 6500 and 8340 14C yr bp. If this is correct, then most recession to the present‐day grounding line on the Siple Coast took place subsequently in the absence of significant deglacial sea‐level rise. Rising sea level may have triggered internal mechanisms within the ice sheet that led to retreat, but did not in itself drive continued ice‐sheet recession. Ice retreat, once set in motion, continued in the absence of sea‐level forcing. If correct, this hypothesis implies that the grounding line could continue to recede into the interior reservoir of the West Antarctic Ice Sheet.

Stratigraphy of Lake Vida, Antarctica: hydrologic implications of 27 m of ice

“…However, the radiocarbon dates impart a maximum age constraint on the ice, as it is almost impossible that samples were contaminated by young carbon, and indicate the top 27 m of ice formed after 6300 14 C yr BP. This aligns with the geomorphic reconstructions that indicate that Victoria Valley was filled with a deep (> 200 m) glacial lake prior to 8600 yr 14 C BP (Hall et al, 2002(Hall et al, , 2010, and the Ross Ice Shelf retreated from the mouth of the dry valleys between 6500 and 8340 14 C yr BP (Hall and Denton, 2000). Furthermore, it may be that the ice cover originated much later, as radiocarbon dates of the dissolved organic carbon fractions in the Lake Vida brine date between 2955 and 4150 14 C yr BP (Murray et al, 2012).…”

The Saline Lakes of the McMurdo Dry Valleys, Antarctica

“…Lake Fryxell has also undergone an evolutionary history of changing size as the climate has varied. It had decreased in size from a large mega-lake, Glacial Lake Washburn, which had occupied all of Taylor Valley during the last glacial period into the early Holocene (Hall and Denton 2000). Lyons et al (1998a) pointed out that *1 kyr ago the lake was a playa-like entity with a brine saturated with NaCl.…”

Lake-ice conveyor deposits: Geomorphology, sedimentology, and importance in reconstructing the glacial history of the Dry Valleys

“…Dates of actual moraines on the headlands indicate that Ross Sea ice did not start to thin until after 12,700 14 C years B.P. (Hall and Denton, 2000a). Related work indicates that grounding-line recession in the Ross Sea occurred well after the major eustatic sea-level rise associated with the last deglaciation (Conway et al, 1999).…”

“…Stuiver et al (1981) also noted difficulties in reconstructing ice retreat, because the ages of the cross-valley ridges were not showing the pattern expected for a receding ice margin. Moreover, deltas were present in locations that should have been covered with grounded ice (Hall and Denton, 2000a). By the new, lake-ice con- .…”

“…A huge ice sheet, fed from both East and West Antarctica, expanded into the Ross Sea Embayment and blocked the mouths of the valleys adjacent to McMurdo Sound (Denton and Marchant, 2000;Hall and Denton, 2000a). This Ross Sea ice sheet reached 350 m elevation at the eastern end of Taylor Valley.…”