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Late Quaternary diatom stratigraphy, paleoenvironments, and climate variability in Lakes Titicaca and Junin, tropical Andes (Peru and Bolivia)

Pedro Miguel Tapia, University of Nebraska - Lincoln

Abstract

Modern and fossil diatom assemblages from the quasi-endorheic lakes Junin (11°S) and Titicaca (17°S) in the tropical Andes were evaluated to infer past climates and their associated paleoenvironments. The diatom stratigraphy in Lake Titicaca indicates large-scale climatic variation during the past 30,000 years. Positive moisture balance is characteristic of Marine Isotope Satage 3 (MIS3), Last Glacial Maximum (LGM), and most of late-glacial times. This is followed by a period of large-amplitude lake-level fluctuations that ended with the onset of the Holocene. A short wet period in the early-Holocene ended by 8,000 cal yr BP, then extensive droughts dominated the region until ∼4,000 cal yr BP. At that time, increased precipitation produced a gradual lake-level rise, with the establishment of the modern diatom flora by ∼1,500 cal yr BP. Cyclotella andina is the most common planktonic diatom in Lake Titicaca in glacial and modern times. Combined morphological and biometric analyses permitted re-categorize this species into Cyclostephanos andinus (nov. comb.), and material from three Andean lakes demonstrates its distribution throughout the central Andes. The diatom record in Lake Junin suggest a freshwater shallow lake during MIS3, then a brief period of deeper freshwater conditions by ∼17,500 cal yr BP, and finally alkaline and shallow waters for the past ∼13,000 cal yr BP. The stable diatom flora during the Holocene differs from δ18Ocalcite interpretations that suggest a gradual increase of effective moisture in the basin. It seems that salinity and lake level was not sufficiently large to affect diatom composition. Evidence of a wet MIS3 and LGM period in the Lake Titicaca basin is contrary to the Refugia Hypothesis, which proposes and environments and rainfall contraction in Amazonia. The mid-Holocene was arid in the Altiplano and drier than in the glacial or today in Lake Junin. Orbital forcing associated with precessional cyclicity is the primary driver for millennial-scale climatic fluctuations in both basins.*^ *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Microsoft Office.^

Subject Area

Paleobotany|Geology|Paleoecology|Biology, Limnology

Recommended Citation

Tapia, Pedro Miguel, "Late Quaternary diatom stratigraphy, paleoenvironments, and climate variability in Lakes Titicaca and Junin, tropical Andes (Peru and Bolivia)" (2003). ETD collection for University of Nebraska - Lincoln. AAI3092612.
http://digitalcommons.unl.edu/dissertations/AAI3092612

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