Date of Award

12-2002

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

Supervisor

Dr. Henry P. Schwarcz

Co-Supervisor

Dr. Derek C. Ford

Abstract

Prediction of future climate change relies on the accuracy of models that can be calibrated using paleoclimate proxy data. The longest and most continuous records are based on marine sediment and ice cores, but cannot be dated using absolute radiometric techniques. Analyses of speleothems from western North America were used to develop well-dated isotope records for Quaternary paleoclimate reconstructions. This research uses the oxygen and carbon isotope records of speleothems from Reed's Cave, in the Black Hills of South Dakota, to determine the presence of high resolution and long-term climate cycles. δD analyses of fluid inclusion water extracted from speleothem were used to estimate absolute paleotemperature change.

Oxygen and carbon isotope analysis of two Winsconsin age speleothems shows different δ18Oct (δ18O of calcite) records for their coeval period of growth. The growth rates for the speleothems also differ and suggest that local environmental factors may have produced the divergent isotopic variation. Spectral analysis of the oxygen isotope record reveals the presence of millennial-scale cycles and Heinrich events. Good correlation with speleothem isotope records from Missouri and Israel confirm that global climate is being recorded.

Three mid-Pleistocene speleothems from Reed's Cave grew from 550,000 to 150,000 years ago have divergent isotope records but show evidence of global climate change. Local differences in hydrology and topography are attributed to the different records. Two speleothems show large isotopic variation during marine isotope stages (MIS) 11 and 13. These results show the sensitivity of the speleothem isotope record to climate change on the continents. There is evidence that MIS 13 was warmer than MIS 11, information that rejects the theory that MIS 11 was the warmest Quaternary interglacial.

The measurement of δD variations in speleothem fluid inclusion water gives a record of paleopreciptitation for two sites in western North America. The temperatures calculated show large magnitude changes in temperature during the Wisconsin glacial period of up to 10 °C. The temperature shift for the coeval period of the growth for the two speleothems shows sychronous warming and cooling events between 60 and 55 ka BP. Results of δD analyses of a speleothem from the central California coast show Holocene cooling that was initiated at approximately 8 ka BP and may be evidence of the hypsithermal.

This research was initially intended to develop paleoclimate records for western North America but also succeeded in providing additional insight on speleothem geochemistry. Divergent isotope records in coeval speleothems is not necessarily evidence of non-equilibrium deposition. We found corresponding differences in the deposited calcite and the fluid inclusion water, which is likely a preserved sample of the original dripwaters. Therefore it is possible to uncover global climate signals in speleothems with divergent δ18Oct records. The influence of local, small scale variables on the isotope record has been underestimated. There is stron evidence that terrestrial proxies record high resolution paleoclimate that cannot be captured by the marine and ice core records.

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