2002-2003 Science Planning Summary

Geology & Geophysics

Dr. Scott Borg
Program Manager

GO-092-O

NSF/OPP 99-09665
Station: RV Laurence M Gould
RPSC POC: Don Michaelson
Research Site(s): Andvord Bay, Lallemand Fjord, Brialmont Cove, King George Island

Development of a luminescence dating capability for antarctic glaciomarine sediments: Tests of signal zeroing at the Antarctic Peninsula
Dr. Glenn W. Berger
Desert Research Institute
Earth and Ecosystem Sciences
gwberger@dri.edu
Dr. Eugene Domack
Hamilton College

Deploying Team Members: Emily Backman . Glenn W Berger . Emily Constatine . Sarah Doane . Eugene W Domack . Sara E Draucker . Robert Gilbert . Amy R Leventer . Susan Morgan . Zack Norcross . Dave Tewksbury . Trevor Tompkins
Research Objectives: Paleoclimatology, the study and reconstruction of ancient weather, climate and their likely effects, is not an exact science. Climatic indicators, such as marine sediments that have been abundantly deposited in Antarctica over the last 2 million years, provide useful information about such phenomena as the waxing and waning of ice sheets but only to the extent that these fossils can be accurately dated.

Traditionally, radiocarbon dating with the naturally occurring isotope 14C (carbon 14) has proved reliable for specimens as old as 40,000 years, perhaps even up to 70,000 years, though problems such as the "reservoir effect" can also limit its reliability and range. However, increasing amounts of 14C in the atmosphere have compromised its precision. A more recently developed method, photon-stimulated-luminescence sediment dating (photonic dating), has been used in temperate latitudes for eolian and waterlain deposits and proved reliable over a larger span of Quaternary time -- from decades to hundreds of thousands of years. Can this method be reliably used in polar regions?

Marine sediments in and around Antarctica pose special difficulty because polar conditions can limit the sunlight that detrital grains are exposed to. Since the thermoluminescent test involves reflecting the last time a sample was exposed to light (what is known as the clock-zeroing process), antarctic glaciomarine depositional settings and processes could undermine the potential reliability of photonic dating of antarctic marine sediments, and ages could be overestimated if grains were not exposed to daylight before deposition. Other processes could also compromise photonic dating. For example, transport of terrigenous suspensions by neutrally buoyant "cold-tongue" (mid-water) plumes may be common around Antarctica, yet the effect of such transport on luminescence zeroing is unknown. Typical marine cores taken near Antarctica may contain an unknown fraction of detrital grains from cold-tongue and near-bottom suspensions.

Project team members will collect detrital grains from a variety of "zero-age" (modern) marine depositional settings within the Antarctic Peninsula, where representative antarctic depositional processes have been documented and where logistics permit access.

By systematically studying the effectiveness of luminescence-clock-zeroing in antarctic glaciomarine settings researchers hope to determine whether photonic dating can be reliably applied to antarctic marine sediments in the future. In the process, scientists expect to develop refined sedimentological criteria for selecting future samples. If photonic dating can be validated in this environment, scientists would gain a numeric geochronometer extending well beyond the age range of 14C dating, and be better able to answer a number of broader questions about the timing and extent of past glaciations near and on the antarctic shelves.


Field Season Overview:
On this 18-day cruise researchers will investigate luminescence dating of silt-sized feldspar grains from representative glacio-marine deposits. Working aboard the R/V Laurence M. Gould, researchers will:

- Obtain water-column profiles of the conductivity, temperature, and depth using CTD casts,

- Collect sediment-suspension samples,

- Recover sediment-trap moorings from Brialmont Cove and Andvord Bay in the Antarctic Peninsula,

- Collect Kasten core samples from Brialmont Cove,

- Conduct bottom camera photography in Brialmont Cove,

- Collect sediment-suspension samples from Admiralty Bay,

- Collect core-top sediments and sediment-suspension samples from Lallemand Fjord (ice conditions prevented this on an earlier cruise).

- Obtain a Smith-MacIntyre (SM) grab (core-top) sample.