Refining a High Resolution Climate Record from a Late Pleistocene New Zealand Speleothem: Stage 1 – Cross-Checking a Published Record

April 17th, 2004

Isotopic analysis and U-Th dating of New Zealand speleothem MD3 has yielded a 31,000-year record of climate change published by John Hellstrom in 1998 (Hellstrom et al., 1998). This is a particularly important climate record because the Southern Hemisphere is mostly marine, and thus there are very few places to obtain high-resolution climate information. But climatic information is attainable in the oxygen isotopic composition of speleothems. The oxygen isotopic ratio in speleothem calcite reflects the oxygen isotopic composition of precipitation which is a function of mean annual temperature (Dansagaard, 1964).

A quarter of the speleothem core was obtained from John Hellstrom. The core was fragmented and each piece was polished and mounted to a glass slide. Then the core was sampled at 5 mm intervals at the University of Iowa’s Paul H. Nelson Stable Isotope Laboratory. The microsampled powders were analyzed for oxygen and carbon stable isotopic ratios using a Finnigan-MAT 252 and a Kiel III automated carbonate device. The resulting isotopic curve was compared to the data compiled by John Hellstrom. The two isotopic curves matched well in all but a few areas, and MD3 is now ready to sample at high-resolution. High resolution sampling should allow sub-decadal resolution and thus the ability to investigate short duration climatic shifts.

Alexa Clements, ’05 Iowa City, IA
Majors: Religion and Geology

Sponsor: Rhawn Denniston

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