Megadunes and Geologic Maps of Snow/Firn of East Antarctica: Implications for Major Climatic Change, Accumulation Rates, Ice Flowage, and Bedrock Structures

Recent satellite mosaics of East Antarctica (EA) contradict current megadune origin models based on modern wind patterns, sastrugi, and slow, snow/firn accumulation rates. The images invariably show older megadune fields buried by younger snow/firn or cut by younger structures with sastrugi as surface decorations. An alternative model proposes these enigmatic, 2-4 km spaced, zebra-striped, snow ripple marks are relics of a past climate wherein summer glaze preserved winter antidunes that grew at rates 10 to 50 times present values. This requires an earlier Holocene, warm climatic excursion with extremely rapid snow accumulation from moisture- rich air off more open winter seas. Following this, present-day snow/firn has slowly accumulated over about 2/3 of EA. This, plus limited apparent erosion / ablation of megadune areas, implies relatively minor, net accumulation over the post-megadune surface, now collapsing from deeper, bedrock-controlled outflow. A new type of snow/firn geologic map supports these interpretations using the Megadune Formation (MF) as a basal unit. A new class of transitional high relief dunes helps define the MF. These "Duke of York" (DOY) dunes (after that nursery rhyme of uphill-downhill marches) marks the top of the MF, transitional from uphill-migrating, upper flow regime antidunes into overlying, downhill-migrating, modern- style, lower flow regime dune fields and smooth snow/firn deposits. The MF crops out flowing over bedrock highs and disappears into snow basins above bedrock lows. One map suggests flowage over a 900 km-long, bedrock, fault-line scarp passing nearly under the South Pole. An opposite facing partner forms a bedrock horst, blocking drainage of a stagnant basin now filled as the large, flat area E of the pole. A map of Argus Dome, highest divide of the plateau, suggests high relief DOY dunes formed a walled, shallow basin around a former divide. That basin, now completely filled with firn, forms the present crest, with trend changed by about 45 degrees. These models, geologic maps, and their interpretations may be "outrageous hypotheses" but at least they are testable by correlation with shallow ice cores and radar traverses.