Stansell, Nathan D.
M.S. (Master of Science)
Department of Geology and Environmental Geosciences
Investigation of hydroclimate requires a higher level of spatial and temporal detail than what currently exists for Central America. High resolution lake sediment archives are critical to gaining a more complete understanding of late Holocene climate variability in the region. The climate of Central America is influenced by both tropical Atlantic and Pacific Ocean-atmosphere processes. A better understanding of how these processes have impacted regional hydroclimate is important as it will enable more accurate predictions of future climate changes associated with shifting conditions in a drought sensitive region. Here a 1,000-year carbonate oxygen isotope record is presented from Lake Asososca, located in western Nicaragua. In this record, high delta 18O values indicate drier conditions, while lower ?18O values indicate drier conditions. My data indicate wet conditions at the start of the Medieval Climate Anomaly (MCA) and a trend towards drier conditions until A.D. 1200. The transitional period between the MCA and the Little Ice Age (LIA) from A.D. 1200 - 1400 experienced a shift towards wetter conditions. The LIA from A.D. 1400 -- 1850 was a period of variable conditions. My record indicates a shift from wet to dry conditions from A.D. 1400 - 1600. A pronounced period of wetter conditions occurred from A.D. 1650-1700 during the Maunder Minimum solar event. From A.D 1700 -- 1800 the record indicates variable conditions that alternated between shifts towards dry and wet. After the LIA, the record indicates a trend towards drier conditions. The El Nino Southern Oscillation (ENSO), the North American Oscillation (NAO), and the Atlantic Multidecadal Oscillation (AMO), were often temporally correlated with the Lake Asososca record and suggest that these modes have impacted regional hydroclimate over the late Holocene. Correspondence between the Lake Asososca record and solar variability highlight a potential linkage. Climate models indicate that the Atlantic Meridional Overturning Circulation responds to changes in solar variability and can have impacts on Atlantic SSTs, and therefore may be provide a mechanism to amplify changes in solar variability to Central American hydroclimate. Comparison of the Lake Asososca delta18O record to regional hydroclimate proxies across show little correspondence over the past millennium. While some similarities exist between the Lake Asososca record and other regional proxies, the lack of a coherent hydroclimate signal over the late Holocene suggests temporally and spatially variability hydroclimate shifts. More hydroclimate reconstructions and modelling studies need to be performed in order to fully resolve hydroclimate variability in Central America over the past millennium. This record adds to the network of regional paleoclimate reconstructions in Central America and indicates that modes of variability in both the Atlantic and Pacific Ocean basins have impacted regional hydroclimate over the past millennium.
Perdziola, Stephen, "Late Holocene oxygen isotope record of hydroclimate variability in Nicaragua from Lake Asososca" (2018). Graduate Research Theses & Dissertations. 3763.
Northern Illinois University
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