Montana Tech Research Activities in Antarctica: The International Polar Year and Beyond
by Professor Marvin Speece
Montana Tech researchers have participated in two recent research expeditions to Antarctica and plans are nearly complete for two additional trips to the Earth’s coldest continent. During the austral spring-summer, 2005, approximately 28 km of over-sea-ice seismic reflection data were recorded over Southern McMurdo Sound (SMS), Antarctica, in support of the ANtarctic geological DRILLing program (ANDRILL). ANDRILL is a consortium of four nations whose goal is to recover sediment cores from the Antarctic continental margin. These sediment cores will help earth scientists better understand Antarctica’s glacial, climate, and tectonic history for the past 50 million years.
Figure 1. Professor Marvin Speece (left) in Antarctica (photo by Marvin Speece). Former Montana Tech geophysical engineering graduate student Seth Betterly (right) in Antarctica (photo by Rich Levy).
Montana Tech professor Marvin Speece and Montana Tech graduate student Seth Betterly (Figure 1) helped plan this survey and collect these data. The 2005 ANDRILL Southern McMurdo Sound (SMS) seismic survey incorporated techniques that improved the quality of over-sea-ice seismic data (Speece et al., 2007; Betterly et al., 2007).
Previous over-sea-ice seismic experiments had limited success because of poor source coupling caused by thin sea ice, source bubble-pulse effects caused by explosive seismic sources placed in the water column, and ice flexural-mode noise caused by surface sources.
To mitigate these problems, a Generator-Injector (GI) air gun was used as the seismic source. The GI air gun was lowered into the water column through holes drilled through the sea ice. The GI air gun provided good source coupling and minimized the source bubble effects and flexural mode problems that had plagued previous over-sea-ice experiments in polar regions. These seismic data (Figure 2) were used to plan the location of the SMS Project drillsite. The SMS Project borehole was completed in 2007.
Figure 2. A fence diagram showing seismic data results collected in 2005. Colored lines overlie seismic reflectors that bound seismic units after the Harwood et al. (2004) interpretation. (After Betterly et al., 2008.)
Figure 3. Montana Tech graduate student Taylor Patterson (left) and Professor Marvin Speece (right) at field site in Granite Harbor, Antarctica (photo by Marvin Speece)
During the austral summer, 2007, Marvin Speece and Montana Tech graduate student Taylor Patterson helped conduct a Vertical Seismic Profile (VSP) seismic survey at the newly-drilled SMS Project borehole in collaboration with theANDRILL SMS Science Team. The VSP survey used an air-gun source and demonstrated that high-quality borehole seismic data could be collected in a sea-ice environment.
In addition, during 2007, Taylor and Marvin (Figure 3) helped collect approximately 20.5 km of high-quality seismic reflection data in Granite Harbor (Figure 4). This work was done in collaboration with researchers from Northern Illinois University. The focus of this study is to find Quaternary geological successions in the hope that these records can help decipher recent environmental changes.
The Mackay Sea Valley (MSV) is a deep trough thought to have been eroded beneath Granite Harbor by previous expansion of the Mackay Glacier. The seismic survey’s intent was to image recent sediment layers that accumulated in the MSV following erosion. The MSV seismic survey incorporated and refined techniques of over-sea-ice seismic data collection that had been used previously during ANDRILL SMS seismic site survey in 2005.
The MSV seismic survey was successful in locating a thin succession of low-amplitude reflections atop the higher-amplitude granite basement reflections in the deepest parts of the valley (Figure 5). The low-amplitude reflections are likely caused by layers of pelagic sediment. Future coring of these recent sediments could provide a high-resolution Quaternary climate record.
Figure 4. Mackay Sea Valley (MSV) seismic survey in Granite Harbor, western Ross Sea. An auger for drilling holes through the sea ice is shown in the background (on yellow sled). Air gun and seismic recording vehicle in foreground (orange). A snow streamer of gimbaled geophones was pulled behind the orange sled (photo by Luke Trusel).
In 2008, Montana Tech will embark on a third field season in Antarctica as part of a National Science Foundation (NSF) funded the International Polar Year (IPY) project. IPY is a large scientific program that is focused on the Arctic and the Antarctic from March 2007 to March 2009. It is the fourth polar year following those in 1882-3, 1932-3 and 1957-8. IPY involves over 200 projects, 60 nations and thousands of scientists. Montana Tech’s collaborators include scientists from Queens College, New York, and the University of Otago, New Zealand. Our project involves an over-sea-ice multi-channel seismic reflection survey in Offshore New Harbor (ONH) to investigate the stratigraphic and tectonic history of westernmost Southern McMurdo Sound during the Greenhouse World (Eocene) into the start of the Icehouse World (Oligocene). This project is expected to address two unresolved issues regarding Antarctica’s history: 1) the mid-Paleogene cryospheric development on Antarctica; and 2) the abrupt climate shift across the Eocene/Oligocene boundary. This planned seismic survey will use over-sea-ice seismic methods employed successfully by ANDRILL’s 2005 SMS and 2007 MSV surveys (Pekar et al., 2007).
Figure 5. Unprocessed single fold seismic reflection data from Granite Harbor showing low amplitude sediments overlying a high-amplitude granite basement. The high-amplitude reflection that appears to be a basement step could instead be caused by a terminal moraine. Trace spacing is 50 m.
In 2009, Montana Tech, in collaboration with the University of California at Santa Barbara and ANDRILL, plans to conduct a seismic survey on the Ross Ice Shelf at Coulman High as part of preparation for the next ANDRILL drilling project. This project will address topics such as the evolution and stability of Earth’s cryosphere, early Tertiary warm periods, and tectonics within the West Antarctic Rift System and the Transantarctic Mountains.
The National Science Foundation supports this work through research grants OPP-0342484 and ANT-0732875.
Betterly, S. J., Speece, M. A., Levy, R. H., Harwood, D. M., and Henrys, S. A., 2007, A novel over-sea-ice seismic reflection survey in McMurdo Sound, Antarctica, Terra Antartica, 14(2), 97-106.
Harwood, D. M, Florindo, F., Levy, R. H., Fielding, C. R., Pekar, S. F., Speece, M. A., and the SMS Science Team, 2005, ANDRILL Southern McMurdo Sound Project Scientific Prospectus, ANDRILL Contribution 5: ANDRILL Science Management Office, University of Nebraska-Lincoln, ISBN: 0-9723550-2-2, 32 pp.
Pekar, S. F., Speece, M. A., Harwood, D. M., Florindo, F., and Wilson, G., 2007, Using new tools to explore undiscovered country: understanding the stratigraphic and tectonic history of greenhouse to icehouse worlds of offshore New Harbor, Ross Sea, Antarctica: in Cooper, A. K. and Raymond, C. R. et al. (eds.)., A Keystone to a Changing World—Online Proceedings of the 10th ISAES, USGS Open-File Report 2007-1047, Extended Abstract 169, 4 pp.
Speece, M.A., Betterly, S. J., Levy, R. H., Harwood, D. M., and Pekar, S. F., 2007, An over-sea-ice seismic reflection survey in Antarctica using a GI air gun and a snowstreamer: SEG International Exposition and Seventy-Seventh Annual Meeting 2007 Technical Program Expanded Abstracts, 1-5.