Plio-Pleistocene Antarctic Bottom Water Production in the Ross Sea Reconstructed From Hillary Canyon Levee Turbidites

Dense shelf water (DSW) formed on Antarctica's continental shelves is a significant precursor for Antarctic Bottom Water (AABW), a critical component of global overturning circulation. We hypothesize that DSW cascades off the central Ross Sea shelf generated density currents that entrained sediment as they flowed down Hillary Canyon, resulting in turbidite deposits on adjacent levees. International Ocean Discovery Program Expedition 374 drilled two sites on the Hillary Canyon levee: Site U1525 at the base of the continental slope and Site U1524 on the rise. The more proximal Site U1525 yielded ∼160 m of Pleistocene sediment, and the more distal Site U1524 recovered ∼270 m of Late Pliocene to Pleistocene deposits. Within the muddy successions are distinct mm-scale silty layers interpreted as turbidites. We identified >3,300 turbidites at Site U1524 and >1,300 at Site U1525. At Site U1524, many outflow events occurred between the ∼3.3 and 2.1 Ma interval, except for a gap at ∼3.17 Ma, and declined through the Pleistocene. Between 2.1 and ∼1 Ma, turbidite frequency was similar at both sites. At ∼1 Ma, turbidite deposition ceased at both sites and then resumed at Site U1525 at ∼0.9 Ma. Longer-term variability in AABW outflow through Hillary Canyon was influenced by ice sheet extent and continental shelf area, whereas the shorter-term cessations in outflow are interpreted to correspond to anomalously warm interglacials.