Abstract:
A stalagmite (sample OCNM8-02A) collected from Oregon Caves National Monument (OCNM) was sampled for stable isotope ratios in order to develop a record of Pacific Northwest climate history. Nine U-series dates indicate that the record spans the time period - 13.5 - 9.5 ka. The stalagmite growth rate varied from 0.85 to 2.0 mm per 100 years. Measurements along a single stalagmite growth ring found no correlation between 813C and5180, indicating that the stalagmite was deposited under isotopic equilibrium conditions, a primary requirement for using 818OC in speleothems as a climate proxy. A numerical model that evaluated the net effects of the potential climatic variables on 818O, from OCNM indicated that atmospheric temperature variations above the caves propagate into a measurable signal in 81800 in OCNM speleothems. The isotope record from stalagmite OCNM8-02A indicates that the climate of the Pacific Northwest during the last deglaciation changed synchronously with climate elsewhere in the Northern Hemisphere. Paleotemperature estimates derived from 5180
measurements imply - 4 °C cooling during the Younger Dryas period, followed by a -3.5 °C warming leading into the early Holocene. 513CC measurements indicate increasing biomass over the caves through the recent deglaciation. Forest development stalled over a period slightly lagging the Younger Dryas, possibly implying that regional vegetation responded to the millennial scale cold event.
