LATE HOLOCENE OXYGEN ISOTOPE RECORD OF HYDROCLIMATE VARIABILITY IN NICARAGUA FROM LAKE ASOSOSCA

Robust testing of hypotheses investigating ocean-atmosphere dynamics requires a higher level of spatial and temporal detail than what currently exists for Central America. Studying continuous, high resolution lake sediment archives is therefore crucial to gaining a fuller understanding of ocean-atmosphere dynamics in the region. The climate of Central America is influenced by both tropical Atlantic and Pacific ocean-atmosphere processes, with modes of variability such as the El Niño Southern Oscillation and the North American Oscillation driving changes. A better understanding of these systems is important as it will enable more accurate predictions of future climate changes associated with shifting conditions in a drought sensitive region.

Here we present a carbonate oxygen isotope record from the Late Holocene from Lake Asososca, a closed-basin crater lake in western Nicaragua. Oxygen isotope values from closed-basin lakes in this region are primarily controlled by the balance between evaporation and precipitation, as well as the isotopic composition of the precipitation. The isotopic composition of rainfall in this region is controlled by the amount effect, an inverse relationship between the δ¹⁸O values of precipitation and the amount of regional rainfall. Both factors work constructively to create more negative δ¹⁸O values during wetter conditions and more positive δ¹⁸O values during drier conditions.

By measuring δ¹⁸O values of endogenic carbonates from a 1.36 m composite sediment core, we can assess regional hydroclimate dynamics during the late Holocene. A 1.52 m near shore sediment core was also collected, containing multiple paleoshoreline facies. By comparing changes in δ¹⁸O values with changes in sediment facies, we will be able to better constrain the magnitude of lake level variations during the Late Holocene. The Lake Asososca record was dated using radiocarbon, as well as ²¹⁰Pb measurements. A total of 304 samples of endogenic carbonate, measured at a .2cm resolution, were analyzed. Palynology, loss on ignition, magnetic susceptibility, and X-ray fluorescence were also used to help characterize the sediment cores. The results from this study allow further insight into ocean-atmosphere dynamics in the region and past hydroclimate variability.