C037-0007
Sedimentary record of Antarctic Bottom Water (AABW) outflow in the Ross Sea since 3.3 Ma (IODP Sites U1524 and U1525)
Friday, 11 December 2020
Poster
Natalia Varela, Virginia Tech, Geosciences, Blacksburg, VA, United States, Brian Romans, Virginia Tech, Geosciences, Blacksburg, United States, Molly O'Rourke Patterson, Binghamton University, Binghamton, NY, United States, Jeanine L Ash, Rice University, Earth, Environmental and Planetary Sciences, Houston, TX, United States, Denise K Kulhanek, T, International Ocean Discovery Program, College Station, TX, United States, Laura De Santis, Ist Nazionale Oceanografia, Sgonico, Italy, Robert M Mckay, Victoria University of Wgtn, Wellington, New Zealand and IODP Expedition 374 Scientists
Abstract:
The Ross Sea is a key area for Antarctic Bottom Water (AABW) formation in West Antarctica, due to the interannual variability of water density and temperature and driven by the sea ice formation during the winter. However, the AAWB response to major climatic transitions for the past few million years is uncertain. For example, what is the relationship of AABW outflow to warmer periods of the Pliocene and how did it change at the Pliocene-Pleistocene transition? To understand the West Antarctic Ice Sheet (WAIS) evolution and its feedback with AABW outflow over the Neogene and the Quaternary, IODP Expedition 374 drilled five sites in the eastern Ross Sea, from the outer continental shelf to the rise. This study is focused on Sites U1524 (-74.0507°, -173.6335°; 2394 m water depth) and U1525 (-75°0.06′, -173°55.20′; 1776 m water depth), which are both located on a sedimentary ridge adjacent to Hillary Canyon, a large submarine canyon-channel system (40 km wide by 500 m deep) and one of the principal conduits for
AABW outflow. Here, we propose that these overbank deposits are, in part, a product of lateral overspill of turbidity currents transported through Hillary Canyon,
triggered by dense shelf-water cascading from the shelf edge down to the deep ocean and, therefore representing a record of pulsed AABW outflow.
The ~158 m of Pleistocene sediments recovered at the more proximal Site U1525 shows massive to stratified diamict, sand, mud, and layers with variable diatom content, which combined with the presence of ice-rafted debris reveal the influence of glaciomarine processes. The more distal Site U1524 is a ~270 m Plio-Pleistocene succession that represents a combination of hemipelagic and turbiditic mud, coarse silt to very fine sand beds, and diatom-bearing mud layers. Our sedimentological analyses on the turbidite beds showed a similar average thickness (~1.5 mm) at both sites. Bed counting for U1525 (from 55.7 m to 116.5 mbsf) reveals 1,350 turbidite beds and >3,300 for U1524. Our grain-size analysis targeted a subset of these silty to very fine-grained sand beds and the mud-dominated intervals that overlie them. These parameters will allow us to characterize the turbidity currents in terms of flow height and volume, which can be used to estimate changes in AABW outflow over the last 3.3 Myr.
