Snowline Altitude and Climate in the Peruvian Andes (5-17° S) at Present and during the Latest Pleistocene Glacial Maximum

Abstract

The present snowline in the Peruvian Andes (5-17°S), rises from as low as 4.7±0.1km on the eastern (windward) to more than 5.3 ± 0.1km on the western (leeward) side of the central Andes. The effect of temperature on snowline altitude is isolated from the effect of precipition by subtracting the altitude of the mean annual 0°C isotherm from the altitude of the snowline. This difference, defined as the normalized snowline altitude, increases with decreasing precipitation.
The lowest late Pleistocene snowline rose from east to west and ranged in altitude from 3.2 to 4.9 (±0.1) km. Both the present and lowest late Pleistocene snowlines indicate that moisture at both times was derived principally from tropical easterly winds. An east-west precipitation gradient steeper than present is inferred for the eastern slopes of the centralAndes from the steeper late Pleistocene snowline gradient. Mean annual temperatures were 10±1.9°C cooler that today at 3.52 km, as calculated from a late Pleistocene snowline as much as 1.4±0.2 km lower than today. Mean annual precipitation was 25 to 50% less than today along the eastern side, and more than 75% less on the western side of the central Andes. These estimates of lower temperature and decreased precipitation are more extreme than previous estimates. They imply that the amount of glacial-age cooling elsewhere, such as in western North America, may also have been underestimated by previous researchers because they did not adequately consider the effect of reduced ice-age precipitation on snowline lowering.