The Holocene paleolimnology of Lake Salpeten, Guatemala

Stratigraphic shifts in the oxygen isotopic (δ18O) composition of biogenic carbonate from tropical lake sediment cores are often interpreted as a proxy record of the changing relation between evaporation and precipitation (E/P). Holocene δ18O records from Lake Salpetén, Guatemala, were apparently affected by changes in drainage basin vegetation that influenced watershed hydrology, thereby confounding paleoclimatic interpretations. Oxygen isotope values in the lake were greatest between ∼9900 and 7500 cal yrs B.P., suggesting relatively high E/P, but pollen data indicate moist conditions and extensive forest cover in the early Holocene. The discrepancy between pollen and isotope-inferred climate conditions may be reconciled if the high early Holocene δ18O values were controlled principally by low surface run-off and groundwater flow to the lake, rather than high E/P. Dense forest cover in the early Holocene would have increased evapotranspiration and soil moisture storage, thereby reducing delivery of meteoric water to the lake.; Biogenic carbonate δ18O decreased between 7500 and 3300 cal yrs B.P. in Lake Salpetén. This decline coincided with palynologically documented forest loss that may have led to increased surface and groundwater flow to the lake. Minimum δ18O values occurred between 2400 and 1800 cal yrs B.P. Relatively high lake levels were confirmed by radiocarbon dated aquatic gastropods from subaerial soil profiles ∼1.0 to 7.5 m above present lake stage. High lake levels were a consequence of lower E/P and/or greater surface runoff and groundwater inflow related to watershed deforestation by the Maya. When the Maya population declined ∼1200 cal yrs B.P., δ 18O values increased as a consequence of reduced hydrologic input caused by increased E/P or forest recovery.; Model simulations incorporating pollen-derived deforestation rates can account for nearly 75% of the variance in the Lake Salpetén biogenic carbonate δ18O record, but do not reproduce the full magnitude of the δ18O minimum nor the abrupt changes observed in sediment cores. Minimum δ18O values were achieved only through combination of both a protracted ∼15% increase in precipitation and pollen-based estimates of vegetation cover change. Simulation of abrupt δ18O changes necessitated the rapid onset of precipitation decreases of at least 10% relative to modern.