The case for Ross Bank ice rises since the middle Miocene

Many tens of ice rises exist at the marine margins of the Antarctic Ice Sheet.  Isle-type ice rises in particular are those where an ice shelf is pinned to an underlying submarine bank.  Recent and ongoing studies show that Ross Bank, on the middle continental shelf of central Ross Sea, was the former site of an important Ross Ice Shelf ice rise during the advance and retreat of the West Antarctic Ice Sheet (WAIS) in the last glacial cycle.  Ross Bank is a broad and anomalously shallow water platform whose crest rises to 150 m water depth. Despite its importance as a buttressing site, little is known about how, when and why such submarine banks formed. Here, we use a grid of seismic data acquired during expedition NBP2301/2 to reconstruct how Ross Bank morphology evolved.  Our seismic-based correlations and mapping show that Ross Bank overlies the western flank of the Central High, a large basement horst created during the rifting of Ross Sea.  Seismic correlation to lithologic and chronologic control at IODP expedition 374 sites U1521 and U1522 indicates that thick grounding zone wedges were deposited at the site of Ross Bank during the early Miocene.  Intermittent advance of erosive ice streams deeply eroded those wedges and produced approximately 400 meters of relief at Ross Bank prior to the middle Miocene.  The complete absence of middle Miocene strata at Ross Bank suggests significant intervals of subglacial erosion associated with glacial stages of the Middle Miocene Shift.  In the time since, relatively minor aggradation on the crest of Ross Bank occurred during parts of the late Miocene, Pliocene and Pleistocene. Our analyses make the case that a shallow submarine area existed at Ross Bank since the middle Miocene.  The bank would have been the site of ice rises that influenced the advance and retreat of the WAIS in central Ross Sea over the past 14 Myr.