ROLE OF GROUNDING ZONE WEDGES IN GROUNDING LINE STABILIZATION: CASE STUDY FROM ROSS SEA

An analysis of post-Last Glacial Maximum grounding zone wedges (GZWs) in the Ross Sea was conducted using an extensive grid of multibeam profiles acquired during multiple cruises. This study has yielded important insights into grounding line dynamics and the role of GZWs in stabilizing ice sheet grounding lines. GZWs vary widely in size, with relief ranging from less than ten meters to a few hundred meters and lengths ranging from hundreds of meters to tens of kilometers. Some GZWs exhibit foreset strata that downlap onto glacial unconformities and/or they are overprinted by glacial lineations. These features are evidence that the grounding line position stabilizes and even advances during landform construction. Sinuosity of GZWs varies widely, ranging from relatively straight small-scale (<10 m in amplitude) to highly sinuous GZWs with deep embayments associated with meltwater channels that terminate at the grounding line. In general, sinuosity increases with GZW size and is attributed to lateral in sediment supply and accumulation along the grounding line. In eastern Ross Sea, large GZWs (> 50 m in amplitude) are restricted to four paleo-glacial troughs and are separated by tens of kilometers stretches of sea floor with pristine mega-scale glacial lineations. This reflects step-wise retreat of the WAIS grounding line, with each trough exhibiting a different number and spacing of GZWs indicative of variable ice stream behavior. In western Ross Sea, where the EAIS drained, closely spaced GZWs and recessional moraines indicate short-lived grounding line stability with steps in grounding line retreat over distances of hundreds of meters. Given limited constraints on ages and sediment flux measurements for GZW formation, the duration of grounding line stability and shifts in grounding line position in the western Ross Sea occurred mainly at decadal time scales. The different styles and rates of grounding line retreat across Ross Sea are consistent with a lower profile West Antarctic Ice Sheet and higher profile East Antarctic Ice Sheet, but also reflect differences in sea floor bathymetry and, to some degree, sea floor geology.