Towards the Development of Magnetic Provenance Tracers in Antarctic Glacial Marine Sediments: A Pilot Study in the Antarctic Peninsula Region.

This award, provided by the Antarctic Geology and Geophysics Program of the Office of Polar Programs, provides funds for a pilot study designed to test the potential of using rock magnetic properties as sediment provenance tracers for Antarctic glacial marine sediment. A means of tracing sediment provenance would enable more meaningful interpretation of transport and depositional processes recorded in sediment cores. One could conceivably determine which parts of the continental ice sheet were advancing and supplying till, or disintegrating to create debris-laden icebergs. One could conceivably trace the paleocurrents that carried IRD-laden bergs, or identify wind patterns that carried the eolian material. Rock magnetic methods have the advantage of being inexpensive, rapid, non-destructive analyses using highly sensitive instrumentation capable of working with small amounts of material.

The chosen test area is the Antarctic Peninsula (AP) region. The AP region is the subject of intense interest to the paleoclimate-global change community in light of the recent warming trend, disintegration of ice shelves, and rapid ecological and physical changes presently taking place. The tectonic setting and petrology of the AP region have been studied extensively, and this region is site of on-going marine geology and LTER research. Thousands of pre-existing samples from the major rock types (and supporting published petrologic and chemical data) are housed at the Byrd Polar Research Center and are available for study.

Rock magnetic methods provide a rapid, sensitive, inexpensive means of identifying iron-bearing minerals in rocks and sediment. This project will systematically investigate the material properties and magnetic properties of the major bedrock formations exposed on the Antarctic Peninsula along with selected surface and historic sediment samples. The steps in developing reliable magnetic provenance tracers are:

o Confidently linking sediments with their source materials via their materials properties such as precise chemical composition, oxidation parameter, lattice parameter, and grain morphology

o Determining if a unique magnetic signature can be used to identify those material properties

o Testing if the magnetic signature is recognizable in the sediment, thus providing a rock magnetic means of tracing sediments back to their source rocks

o Verifying the success of the magnetic method by using existing petrologic and chemical data

Igneous rocks and sediment from Graham Land contain magnetite, titanomagnetite, and hematite. Initial studies indicate that the magnetite and titanomagnetite grains in the AP rocks are affected by varying degrees of oxidation and impurity content, which generates a reproducible, measurable magnetic signature. All magnetite is not the same. Even small deviations from metal-oxygen stoichiometry and deviations in cation distributions can have large effects on the physical and magnetic properties of metal oxides. This is the basis for suggesting that magnetic methods may be effective tracers. No single magnetic parameter is sufficient to uniquely characterize a sample or to serve as a link between sediment and source rock. Therefore, by following the steps outlined above it is hoped that a link based on quantifiable material properties can be established, and then magnetic signature of those properties can be determined. This work will test the concept that combinations of magnetic parameters can be used to identify material properties. If it can be demonstrated that distinctive magnetic properties in sediments are indicative of material states, and these states can be matched with their parent material, then rock magnetism may provide a rapid, inexpensive means of tracing sediment provenance.