The Mayan ice cap: Glacial geology and paleoclimate of the northern Guatemalan highlands
The Sierra de los Cuchumatanes region of the northern Guatemalan highlands supported a large plateau ice cap with an area of ∼40 km2 along with a group of 5 cirque glaciers ∼1 to 2 km2 during the local last glacial maximum (LLCM). A comprehensive mapping reconstruction of the northern Guatemalan highlands is presented here, including glacial geology and an estimate of maximum ice limits from physical evidence and computer modeling. The glacial geologic map was produced via field mapping with global positioning system (GPS) surveying combined with aerial stereo photographic and topographic map analysis. This new field work on moraine limits expands upon previous reconnaissance-level studies and preliminary reconstruction efforts. Elevation of the northern Guatemalan highlands LLGMBR = 2.0 equilibrium line altitude (ELA) was estimated to be 3515 m for the cirque glaciers and an average of 3703 m for the plateau ice cap. Glacial evidence and regional climate data were employed as input to a physically based geographical information system (GIS) mass-balance model, developed by Plummer and Phillips (2003). Using the target ELA of the ice cap (3650 m) and cirque (3550 m) glaciers, the mass balance model results reveal that an average LLGM temperature depression was -5.0Ã‚Â°C from present day, accompanied by precipitation that was equal to 100% of present day totals. Using the present day Central American ELA of 4900 +/- 200 m, the glacial evidence shows 1197 +/- 200 m of ELA lowering for the plateau ice cap and 1385 +/- 200 m for the north facing cirques. When the amount of ELA lowering is multiplied by the Guatemalan temperature lapse rate of -5.3Ã‚Â°C km-1, an LLGM cooling is given as -7.4 +/- 1.1Ã‚Â°C for the cirques and a -6.4 +/- 1.1Ã‚Â°C average for the plateau ice cap. Although the physical evidence suggests a greater temperature reduction, during the LLGM of Guatemala, than the GIS model output, both methods place detailed constraints on Guatemalan highland paleoclimate and the LLGM ELA. Although the age of the Guatemalan glacial maximum is unconstrained, a qualitative assessment of moraine morphology suggests a correlation between the plateau moraines and the LLGM (20 to 17.5 ka) moraines of Mexico.