Evaluation of Tephra Found in the Law Dome Ice Core, East Antarctica

The presence of tephra in several sections of the Law Dome ice core, collected in East Antarctica, has enabled us to expand on the glaciochemical record of volcanic events detected in that core (Palmer et al., JGR, 2001). High snow accumulation, low summer temperatures that inhibit melting and relatively moderate winds that limit the amount of post-depositional mixing of snow at the coring site has helped produce a well-dated, and highly-resolved chronology of past volcanic activity. We expanded on this chronology by filtering continuous meltwater samples covering the last 700 years and by analyzing volcanic glass shards found in these sections with an electron microprobe with the objective of identifying the volcanic sources. We found rhyolitic glass in 15 different layers and are presently working on identification of the source volcanoes. The lack of significant populations of shards at many of these depths make the interpretation of these shards as time-stratigraphic makers equivocal. However, the compositions are not known to occur in Antarctica volcanic systems, thus we believe that they represent either southern hemisphere mid-latitude or equatorial eruptions. Several potential sources include rhyolitic volcanoes in New Zealand or South America. These results, in combination with the tephra analyses that we performed on the Antarctica Siple Dome and Taylor Dome ice cores, suggest that in addition to the stratospheric transport of volcanic debris from South America and New Zealand to Antarctica, tropospherically transported material may be another source of tephra particles found in Antarctica ice cores. Large particles sizes as well as thickness of the several tephra layers combined with results of satellite observations on propagation of volcanic clouds from recent eruptions of South American volcanoes allowed us to suspect this tropospheric mode of transport. This work provides interesting new evidence on past circulation patterns in the Southern Hemisphere and on the climatic-forcing capabilities of volcanic eruptions.