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