Western Divide West Antarctic Ice Cores (WAISCORES) Site Selection
Bookmarks: NSF Proposal Summary:The Western divide, between the Ross Sea Embayment and the Amundsen Sea, has been identified as the region for the next deep ice core by the West Antarctic Ice Cores (WAISCORES) community. The Ice Core Working Group (ICWG) has developed a planning document (WAISCORES: Science and Implementation Plan, 2000), which outlines the objectives of the proposed drilling and the physical and chemical properties of the core necessary to achieve those objectives. The divide region spans more than 40,000 km 2 and preliminary site selection using airborne geophysical methods is now underway. This work has identified several potential drill sites within this large region where the climate record should be best preserved throughout its long history of ice dynamics. Here we propose a suite of ground-based geophysical measurements to map in detail spatial variations of ice flow, accumulation rate, internal layering and ice thickness at two of the most promising sites. Our main investigative tools are high- and low-frequency ice penetrating radar to image the topography of internal layers and the bed, repeat GPS surveys to calculate the present-day surface velocity field, SAR interferometry to calculate the regional velocity field, and short firn cores to calculate present-day accumulation rates.Beyond the initial mapping and interpretation of internal layers and surface velocity, the measurements will be used to constrain our ice flow modeling effort. In particular, we will use the measurements and models to identify the specific site that is most likely to satisfy the following ICWG criteria: (1) minimal disturbance due to ice flow; (2) a record that extends to at least 50,000 years BP; (3) countable annual layers back to 20,000 years BP. A fourth criterion (good preservation of chemical species) will be addressed by others. The first criterion (minimal disturbances) will be evident directly from the patterns of radar-detected internal layers. To address the other two criteria, we will use the measurements as input for time-dependent ice flow and temperature models that predict depth variations of age, layer thickness, and temperature. As well as yielding an estimate of expected conditions before drilling, the mismatch between the model prediction and data eventually recovered from the core will help infer thinning and climate (accumulation and temperature) histories for the region. Our three year study is a collaboration among PI's at the University of Washington and the University of Texas at Austin. We will contribute information about the physical properties and dynamics of the ice that will help guide the Western Divide WAISCORES site selection. 2002/03 Field SeasonThe objective of the field season was to survey the two preferred core site candidates (B and E) using the UW ground-based radar as well as to install ice motion marker poles. The field party, led by H. Conway, traversed by skidoo from the Byrd camp, profiling with the radar along the way. This will allow us to map the timescale of the Byrd Core to corresponding internal layer depths in the divide region. Here where it all happened:
Figure 1: Heavy black lines give the paths of radar surveys collected in 2002/03. These surveys follow the paths of earlier airborne radar sounding profiles (red lines) that parallel the local ice flow direction. Candidate core sites B and E are shown along with the locations of a University of Wisconsin weather station (Noel) and 100 m firn core collected as part of the US ITASE traverse.
The Western Divide Core SiteThe Washington crew have now completed two field season and analyses of the results are underway. Our interest is focused on the two westernmost red lines if Figure 1. Turns out site "E" has a bedrock peak and trough upstream (Figure 2) and the internal layering shows a local accumulation rate variation associated with it that propagates to the core site, resulting in a wrinkle in the timescale/layer thickness profile. Fearing such complexity, we've shifted our happy-place for the core to the next line west and a bit upstream, to the site shown as "WDC" in Figure 3.
Figure 2: Airborne radar cross section crossing the Ross/Amundsen ice flow divide, passing through candidate core site "E". Green lines are identified ice surface and ice bed horizons.
Figure 3: Airborne radar cross section crossing the Ross/Amundsen ice flow divide, passing through the new preferred core site "WDC". Green lines are identified ice surface and ice bed horizons. Headed up by Howard Conway, several of us are preparing a manuscript that describes the merits of the new site: View a pdf of version 3. . | |||||||||
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