Date of Award

6-2010

Document Type

Union College Only

Degree Name

Bachelor of Arts

Department

Environmental Science and Policy

First Advisor

Donald Rodbell

Language

English

Keywords

Peru, geology, sediment, isotope, record, enrichment

Abstract

Laguna Piuray is a carbonate lake in the Urubammba Province of southern Peru. The lake is formed in a glacial valley and surrounding the present-day shoreline are deposits ~4 m thick of calcite (CaCO3) rich sediments (marl) that record an interval of higher than present lake levels in the past. An intact 3.2 meter-long sample of the lake sediments was taken in 2008. Charcoal subsamples were obtained from the sediments and used for radiocarbon dating. The results indicate that the sediments contain an ~14.2 kyrs record, which includes the late-glacial; a period of dramatic climate change in Peru and globally. The sample was further subsampled every 0.5 cm and the resultant sediment samples were analyzed for organic and inorganic carbon, and sieved to isolate the <75 µm fraction what contains the authigenic calcite that precipitated in equilibrium with the lake water. The oxygen stable isotope composition shows highly depleted values from 14.2-11.3 kyrs BP including a small depletion coeval with the onset of the north Atlantic Younger Dryas (YD). A rapid 5‰ enrichment event, identical in magnitude to other regional isotope records, occurred 11.3 kyrs BP and indicates the climate became warmer and dryer from the end of the YD to the early Holocene. This shows the YD was felt in the southern tropics. On comparison with Antarctic and Greenland isotope records the Piuray archive, and a few other tropical isotope records, seem to indicate the southern tropics to have experienced bipolar climatic forcing associated with polar climate oscillations. This is evident in the Piuray isotope record, which seems to indicate the region to be following an Antarctic signal prior to the start of the YD.

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