This project studies marine sediment cores from the Antarctic peninsula to determine whether the current decay of ice shelves there is caused by global warming or another cycle. A comprehensive set of core analyses?from radiocarbon to biostratigraphy?will be performed to characterize ice-shelf status during the last 20,000 years. The project?s goal is to assess ice-shelf response to environmental drivers such as ocean temperature, precipitation, and sea ice extent. The study benefits from two, recent, NSF-supported expeditions to the area, including ShalDril, in which lengthy sediment cores were collected. These cores will support development of a high-resolution picture of the peninsula?s glacial, climactic, and oceanographic history.
The broader impacts of this project include graduate and undergraduate participation in research, support for early career researchers, collaboration with primarily undergraduate institutions, and international collaboration with scientists in the UK and Poland. There are also implications for society?s understanding of climate change, since this work improves our understanding of the behavior of ice sheets and their links to global climate.
To assess the significance of modern-day trends of warming in the Antarctic Peninsula, it is necessary to compare to the climate and glacial history since the last glacial maximum. If the present decay of valley glaciers in the Antarctic Peninsula region is unprecedented for the Holocene, the sedimentological manifestation of this modern event will stand out as unique in the sedimentary record of the bays and fjords of the region. In each study area we have paid particular attention to the most recent sedimentary layers so that we can compare characteristics of the modern to the rest of the Holocene record and assess the records’ variability through time. Because we have samples from 11 different study areas, we have also assessed areal variability. We expected that the timing and magnitude of glacial change will vary from north to south and on either side of the peninsula due to latitudinal differences and orographic effects. This being the case, it is likely that tidewater glacier advance and retreat across the region was asynchronous in the past. Our broad scale results have shown that the retreat of ice across the Antarctic Peninsula during the Holocene was dramatically asynchronous. This suggests that the modern change, retreat across the peninsula simultaneously, is not the norm. Our current work is aimed at better proving the asynchronous nature of the retreat by better constraining the chronostratigraphy in each area. Our work has now turned to focus on the cores from the Bransfield Basin in the north and Beascochea Bay at the southern end of the study. In Bransfield, which sits between Maxwell and Firth of Tay, our C and N records have shown a significant shift towards warmer water at 1600 years BP. The timing of this change is between that of Maxwell and Firth of Tay, suggesting a gradual progression of warming events across the region. In Beascochea Bay, which is on the Graham Land Coast and receives ice draining from the Bruce Plateau, we have documented a Little Ice Age response in the bay as well as advance of ice during what is typically considered a warming period. This suggests that ice advance in this portion of the peninsula is controlled by precipitation, not temperatures. Finally, our latest results focus on comparison of ramped pyrolysis radiocarbon dates to carbonate radiocarbon dates, the first time such a comparison has been made. Our original results suggested that dates from mixed foram assemblages might be biased towards older material, even though they have been considered the 'gold standard' in the past. We have recently done several repeat analyses to confirm this surprising result. The repeat measurements show less of a dramatic difference, yet nonetheless older results from mixed foram assemblages. This project has directly supported three graduate students and two undergraduate students, all of whom have continued to work as geologists and educators.
