This project investigates early Pliocene East Antarctic ice dynamics and paleoenvironmental conditions from variations in the production of ice-rafted debris and major element geochemistry of sediment cores collected during IODP Expedition 318 to the Wilkes Land margin of Antarctica. This portion of Antarctica carries the Wilkes and Aurora subglacial basins, where the East Antarctic Ice Sheet (EAIS) is grounded below sea level, and is potentially unstable. The early Pliocene is a known period of global warmth with sea surface temperatures ranging up to 5.5ºC higher than present in the Southern Ocean. The stability of the EAIS in this period of time is a major uncertainty and is considerably debated. Recent climate and ice-sheet modeling studies suggest that, in contrast to the West Antarctic Ice Sheet, the EAIS did not collapse during the Pliocene. However, the models do show that its margin retreated to within the present position and that the retreat generated a significant eustatic sea level component. The Wilkes Land margin is the location where the predicted retreat is the greatest. Here we collect a high-resolution record of IRD production, paleoproductivity, and changes in provenance, to 1) test the hypothesis of glacial retreat during early Pliocene warm periods; and 2) provide a record of sufficient resolution to correlate East Antarctic ice dynamics to global paleoclimatic proxies on 10kyr time scales. Two drillholes with well-dated early Pliocene intervals, Site U1358 on the continental shelf, and Site U1359 on the continental rise, are investigated. Ice-rafted debris (IRD) mass accumulation rates (MAR) will be determined in combination with bulk terrigenous grain-size analyses for Site U1359. Particle size analysis will also aid in the interpretation of the diamictites on the shelf at Site U1358. The sediments at both sites have > 5% terrigenous fraction, so that particulate scavenging by organisms on terrigenous sediment concentrations of Fe, Ti and Al is negligible and stable element ratios can be used to derive provenance information and local paleoproductivity and weathering proxies. The integrated datasets of IRD MAR, degree of chemical alteration through weathering, and paleoproductivity, will be used to assess variations in ice extent and paleoclimatic conditions along Wilkes Land and the adjacent ocean, through early Pliocene warm periods.
The Pliocene was the last epoch wherein the atmospheric pCO2 was similar to today?s partial pressure and global surface temperatures were higher than the modern with a larger than average degree of warming occurring at high latitudes. Tectonically and oceanographically the Earth was similar to today and the early Pliocene is, therefore, an excellent time interval to study the long-term stability of ice sheets in a world comparable to the present and the near future. The Antarctic ice sheets are important components of the global climate system, because of their high albedo and influence on sea ice formation, ocean circulation, and sea level. Satellite data suggest that the Antarctic ice sheets at present are losing mass and that mass loss has recently accelerated resulting in a present contribution to global sea level rise of ca. 0.3 mm/yr. Due to the short monitoring period, however, it is uncertain whether ice sheets are responding to the present warming or whether this is an expression of short-term perturbations in the icesheet system. Both short-term monitoring and the analyses of long-term trends in geological records are essential to provide a complete assessment of the state of the climate system. Important broader impacts of this work are further: 1) the availability of high resolution data on cryosphere dynamics for global climate studies, 2) the increased accessibility of the core material for other researchers who target short intervals with time intensive methods of analysis, 3) the PIs activities to inform researchers in urban and coastal management policy and the general public through lectures and local media outlets, and 4) education through research participation of two students of diverse backgrounds, which can be considered an importantlong-term benefit of this work.
|Effective start/end date||15/03/11 → 29/02/16|
- National Science Foundation: $183,565.00