Constraints on the Origin of Paleolake Expansions in the Central Andes

Abstract

During the late Pleistocene, at least one episode of lake expansions occurred in the internally draining high plateau region of Bolivia. Some researchers have advocated that a wetter climate associated with a change in atmospheric circulation caused the development of the large paleolakes, while others have hypothesized that deglaciation contributed to the water source for the expanding lakes. From estimates of the potential meltwater stored in the glaciers during their maximum extents, we conclude that insufficient meltwater was available to fill the large paleolakes. However, the meltwater hypothesis remains viable south of the main plateau region where, in five small drainage basins, the volume of available glacial meltwater was 3 to 16 times greater than the volume of water in the paleolakes. Pollen, dunes, and other eolian features indicate that the region surrounding the Altiplano was much drier during at least one interval of the Late Pleistocene. Although the timing of the dry period with respect to the paleolakes is still unknown, a pluvial explanation for the existence of paleolakes seems unlikely. Decreased evaporative loss, however, remains a possible explanation. To understand what factors could have been associated with a decrease in evaporation rates over the drainage basin, an evaporation model is developed based on the energy balance and bulk-transfer methods. The model indicates that a 10 °C drop in air temperature or a doubling in cloudcover could have caused the paleolakes to reach their highest levels. Alternatively, a 50% increase in precipitation rate could have also maintained the paleolakes.

An energy-balance hydrologic model for the Lake Malawi Rift Basin, East Africa

“…Lake surface area varies with changing lake-level, thereby changing the spatial extent of over land versus over water evaporation. The evaporation subcomponent of the energy-balance hydrologic model can be expressed by simultaneously solving the energy-balance equations for evaporation and the bulk transfer formula for evaporation (Brutsaert, 1982) to determine surface temperature (T s ) for both land and water (Blodgett et al, 1997) (Fig. 6, Table 1).…”

“…To simulate the Malawi historical lake-level record, the energybalance hydrologic model is used with a monthly time step (Blodgett et al, 1997) (Fig. 6, Table 1).…”

“…Lake water budget models have helped assess the causative mechanisms behind large magnitude lake-level changes in a variety of tropical lacustrine basin settings. In South America, Blodgett et al (1997) examined the climate conditions required to form and expand paleo-lakes in the Central Andes, by estimating evaporation through simultaneously solving the energy-balance equations and the bulk transfer formula for evaporation (Brutsaert, 1982). Bookhagen et al (2001) modeled the conditions required to form a landslide-dammed lake in northwest Argentina~30 000 14 C yr BP.…”

Pronounced occurrence of long-chain alkenones and dinosterol in a 25,000-year lipid molecular fossil record from Lake Titicaca, South America

“…Modeling of basin hydrology suggests that relatively modest changes in precipitation, temperature, and cloudiness result in large impacts on the water balance of Lake Titicaca (Rowe and Dunbar, 2004) and the greater Altiplano region (Hastenrath and Kutzbach, 1985;Blodgett et al, 1997) over century to millennial time periods. During the latest Pleistocene, when glacial conditions prevailed, the lake was at a relative highstand and the Altiplano was wet (Baker et al, 2001).…”

Effects of climate variability on lake evaporation: Results from a long-term energy budget study of Sparkling Lake, northern Wisconsin (USA)

“…Yu and Knapp, 1985;Ikebuchi et al, 1988;Laird and Kristovich, 2002) as a result of its ease of application and suitability for modeling (e.g. Hostetler and Bartlein, 1990;Blodgett et al, 1997). Water balance studies, on the other hand (e.g.…”