This award supports a project to investigate the sensitivity of the Antarctic ice sheet (AIS) to global climate change over the last two Glacial/Interglacial cycles. The intellectual merit of the project is that despite its importance to Earth's climate system, we currently lack a full understanding of AIS sensitivity to global climate change. This project will reconstruct and precisely date the history of marine-based ice in the Ross Sea sector over the last two glacial/interglacial cycles, which will enable a better understanding of the potential driving mechanisms (i.e., sea-level rise, ice dynamics, ocean temperature variations) for ice fluctuations. This will also help to place present ice?]sheet behavior in a long-term context. During the last glacial maximum (LGM), the AIS is known to have filled the Ross Embayment and although much has been done both in the marine and terrestrial settings to constrain its extent, the chronology of the ice sheet, particularly the timing and duration of the maximum and the pattern of initial recession, remains uncertain. In addition, virtually nothing is known of the penultimate glaciation, other than it is presumed to have been generally similar to the LGM. These shortcomings greatly limit our ability to understand AIS evolution and the driving mechanisms behind ice sheet fluctuations. This project will develop a detailed record of ice extent and chronology in the western Ross Embayment for not only the LGM, but also for the penultimate glaciation (Stage 6), from well-dated glacial geologic data in the Royal Society Range. Chronology will come primarily from high-precision Accelerator Mass Spectrometry (AMS) Carbon-14 (14C) and multi-collector Inductively Coupled Plasma (ICP)-Mass Spectrometry (MS) 234Uranium/230Thorium dating of lake algae and carbonates known to be widespread in the proposed field area. The broader impacts of this work are that it fits well within the West Antarctic Ice Sheet initiative and complements the ANDRILL program. In addition, the PIs are committed to and have a long record of student education and outreach at all levels. A number of students (4-6) will be mentored in this project. The PI regularly visits classrooms to talk about Antarctica and communicates with students from the field and participates in local outreach efforts to attract girls to earth science.
The intellectual merit of this work concerns the behavior of the Antarctic ice sheet and its possible relationship to past and future sea-level change. When we began this project several years ago, our primary goal was to determine when ice sheets in Antarctica reached their maximum level during both the last and penultimate ice ages. We were interested particularly in the Ross Sea region, because this area was occupied by a large ice sheet that was an appendage of both the West Antarctic Ice Sheet (WAIS) and the larger East Antarctic Ice Sheet (EAIS). By understanding the history of the ice sheet in the Ross Sea region, we can gain knowledge about the mechanisms that controlled ice-sheet behavior in the past and that may drive ice-sheet trajectories in the future. Because the WAIS is thought to be a likely contributor to sea level under global warming scenarios, understanding the factors that control its behavior is key for predictions. We produced detailed geologic maps of areas in the Royal Society Range formerly covered by the Ross Sea ice sheet. We used these maps, as well as surveying control, to determine former ice elevations. Study of landform shape and composition allowed us to reconstruct former ice-marginal environments. These data afforded the foundation for interpretation of numerous dates that allowed us to put ice-level changes in chronological context. One main result of our work was the determination of the elevation and the timing of the maximum of the last ice age in the Royal Society Range. More than 200 dates place the maximum at roughly 13,000-19,000 years before present. This information suggests that deglaciation of ice in Antarctica was delayed compared to other parts of the world. For example, ice retreat in New Zealand to the north of our field area began at ~17,500 years ago. The delayed retreat until after 13,000 years ago suggests that the Ross Sea sector of the Antarctic ice sheet was not a primary contributor to a prominent rise in sea level at ~14,500 years ago. Rather, the ice sheet survived most of the sea-level and temperature change of the last deglaciation relatively intact until ~13,000 years ago, when it began to thin rapidly. Final deglaciation to the present-day position is thought to have been accomplished through the ocean, either by accerated calving of icebergs or melting from warm ocean water. Our work affirms the importance of marine mechanisms for causing ice-sheet recession both in the past and likely in the future. The broader impacts of this work include not only those of a scientific nature but also of education and training of young scientists. We feel that the training of the next generation of scientists is one of the greatest broader impacts we can make. Four graduate students and five undergraduates carried out research related to this project and participated in field work. Four of the undergraduates have since gone on to graduate school and the fifth is employed by the mining industry. All of the graduate students are still involved in the field; one is a postdoctoral researcher, two are Ph.D. students, and one works as a glacial geologist for a state geological survey. We also contributed to the education of students at the K-12 level, through classroom visits and correspondence with students while in the field.
