Collaborative Research: RUI: Obliquity vs precession effects in Antarctic ice margin dynamics inferred from ice rafted debris in the Southern Indian Ocean at ODP Site 745

About This Grant

When glaciers scrape across Antarctica, they pick up rock fragments and incorporate them into their bottom layers while transporting them toward the coast. There, icebergs break off, drifting towards lower latitudes and warmer waters. Along the way the icebergs melt and the rock fragments sink to the seafloor, leaving behind a trail of these rock fragments called ice rafted debris. Ice rafted debris accumulates at the bottom of the ocean and over time preserves a record of activity at their source, the Antarctic ice sheet. In this study investigators will use sediment cores recovered in the Indian Ocean by the Ocean Drilling Program to reconstruct the accumulation of ice rafted debris over time. The drill site is about 500 miles north of the Antarctic continent, and in the path of the ice bergs that it sheds. When looking at the variations in ice rafted debris over time, the team will obtain a record of changes in the glacial activity of the Antarctic ice sheet through time. The study is motivated by the mystery surrounding changes in glacial activity in response to changes in the shape of Earth’s orbit around the sun, the wobble of its axis, and the degree of the tilt of the Earth’s axis, the so-called Milankovitch cycles. For a period of time between about 1.2 and 1.6 million years ago, it is not clear if ice sheet growth and melt responded to changes in incoming solar energy related to changes in the shape of the orbit or to changes in its tilt toward or away from the sun. This study will contribute data to help understand how these external mechanisms cause variations in the size and behavior of Antarctic ice sheets. Investigators will conduct this research alongside a number of undergraduate students and one graduate student. Records of ice rafted debris provide an ideal teaching tool as they are reasonably easy to assemble by students independently (after initial training) and thus provide students with a sense of self-reliance and self-confidence, increasing their motivation to remain in a STEM related field. Thus, ice rafted debris is an ideal proxy to teach students about paleoclimate and paleoceanography. Broader impacts activities include training and mentoring undergraduate students and a graduate student, outreach with a local middle school, and efforts to expand access in STEM. Legacy Ocean Drilling Program Site 745B - drilled during Leg 119 in 1988 south of the polar front in the Indian Ocean sector of the Southern Ocean - provides a rare opportunity to study paleoclimate at the full orbital scale back into the late Miocene (Shipboard Scientific Party, 1989) in a vastly understudied region of the world ocean. Investigators propose to construct records of ice rafted debris (IRD) to infer Antarctic ice margin dynamics during the early Pleistocene (~1.1-1.8 Ma) and during specific late Pleistocene interglacial intervals (Marine Isotope Stages 1,5, 7, 11, and 15). Recently, orbital-scale resolution records of biogenic opal and magnetic susceptibility have been tuned to the Lisiecki and Raymo (2005) oxygen isotope stack unlocking the site’s full potential for paleoceanographic reconstructions. With the early Pliocene record, the team will test the hypothesis that the dominance of 41 kyr ice volume fluctuations observed during this interval of time is an artifact of the oxygen isotope proxy. Precession-related variations in the IRD record would support interhemispheric cancellation of the precession signal in oxygen isotope records. Dominance of obliquity would suggest that fluctuations in marine-terminating ice sheets did occur on this time scale. With the late Pleistocene interglacial intervals, which correspond to different amplitudes of obliquity versus precession in insolation forcing, investigators will examine the response of marine terminating ice margins under these different conditions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.