Plio-Pleistocene Antarctic Ice-Ocean Interactions in the Ross Sea

• Main Author: Prunella, Catherine
• Format: Thesis
• Language: unknown
• Published: Digital Commons @ University of South Florida 2020
• Subjects: Foraminifers; Geochemistry; Mg/Ca; Paleoclimate; Stable isotopes; Climate; Geology; Antarctic; Ross Sea; Southern Ocean; Antarc*; Ice Sheet
• Online Access: https://digitalcommons.usf.edu/etd/8581; https://digitalcommons.usf.edu/context/etd/article/9778/viewcontent/Prunella_usf_0206M_16475.pdf

Warm, intermediate-depth Southern Ocean waters are implicated in recent Antarctic ice mass loss. Direct observations of Antarctic Ice Sheet (AIS) retreat are temporally limited, necessitating paleoceanographic records of ocean-ice interactions during past warm climate intervals. Deepsea and ice-proximal sediments record orbitally-paced glacial-interglacial fluctuations in AIS volume during the Plio-Pleistocene (last 5 million years; Ma), but the total contribution of the AIS and the role of ocean heat in these fluctuations remain unresolved. To address the response of Antarctica’s ice sheets to changing ocean temperatures during the Plio-Pleistocene, International Ocean Discovery Program (IODP) Expedition 374 recovered sediments from the Ross Sea outer-shelf at Site U1523. Site U1523 is close to the shelf break and sensitive to incursions of warm intermediate-depth Southern Ocean waters. Site U1523 sediments include foraminifer-bearing/rich sands and muds, which enable development of benthic (Trifarina sp.) and planktic (N. pachyderma sinistral) foraminifer stable oxygen (δ18O) and carbon (δ13C) isotope records. Here we present foraminifer δ18O, δ13C, and Mg/Ca records from the upper 90 m of U1523, which spans the late Pliocene to Holocene (last 3.1 Ma). We provide a new chronology for the U1523 Pleistocene sedimentary sequence by correlating diatom-bearing muds with low magnetic susceptibility (MS) to interglacial periods of the last 0.65 Ma. Benthic and planktic foraminifer δ18O values increase by ~1.5‰ up-section, which reflects long-term global cooling and ice growth, with orbital-scale ice volume and temperature variability superimposed. Our isotope records include an abrupt shift at 16 m CCSF, which we interpret as a hiatus due to an increase in ice-volume and bottom water production during the mid-Pleistocene transition. To separate the ice volume and temperature signals contained in the δ18O signal, we analyzed Mg/Ca in benthic and planktic foraminifers. Our Mg/Ca records reveal a 4.4°C and 4.8°C cooling ...