A 1000-YEAR OXYGEN ISOTOPE RECORD OF SOUTH AMERICAN HYDROCLIMATE FROM LAKE JUNIN IN THE CENTRAL ANDES OF PERU

• Main Authors: Clark, Kaitlin, Abbott, Mark
• Format: Thesis
• Language: English
• Published: 2013
• Subjects: Austral; San Juan; North Atlantic
• Online Access: http://d-scholarship.pitt.edu/16722/; http://d-scholarship.pitt.edu/16722/1/ETD_KaitlinClark.pdf

The South American Summer Monsoon (SASM) provides the Peruvian Andes with precipitation during the austral summer. Over multidecadal timescales the SASM is influenced by sea surface temperature (SST) anomalies, land-sea temperature gradients, the El Nino Southern Oscillation (ENSO) and the location of the Intertropical Convergence Zone (ITCZ). Decadal to multi-decadal changes in SASM precipitation are documented by δ18O values of authigenic calcite precipitated from the waters of Lake Junin (11.0°S, 76.2°W), which is today a hydrologically open-basin lake system. This sediment record archives calcite-rich sediments that were used to determine the timing and magnitude of regional precipitation changes associated with variability of the SASM. Low δ18O values provide evidence for a strengthened monsoon system spanning the Little Ice Age (LIA) from AD 1250 to 1600. Following the LIA, higher δ18O values during the Current Warm Period (CWP) from AD 1850 to present are consistent with a time of decreased monsoon intensity. These data suggest that the SASM is sensitive to changes in the location of the ITCZ, which is influenced by Atlantic tropical SST anomalies controlled by Northern Hemisphere temperatures. The Junin sediment record deviates from other regional paleoclimate records in AD 1932, recording a sharp and sustained decrease of δ18O values. This event is attributed to the construction of the Upamayo Dam, which resulted in the impoundment of waters from the Rio San Juan in Lake Junin, delivering river waters with low δ18O meteoric rainwater to the lake. Trace metal data reveals a uniform and sustained enrichment of metal values beginning at 12 cm sediment depth (AD 1932), providing a reliable age-depth correlation between 12cm depth and the construction of the dam in 1932. This project demonstrates that SASM variability is sensitive to ITCZ location, which is dominantly controlled by Atlantic SST anomalies. This relationship suggests that a continued warming of the north Atlantic will prove to be detrimental ...