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