LARGE HOLOCENE LAKES AND CLIMATE CHANGE IN THE CHIHUAHUAN DESERT, MEXICO

Lake-level chronologies from Laguna El Fresnal and Laguna Santa María (31^o10’N, 107^o30’W) in the Chihuahuan Desert, Mexico reveal episodic Holocene lake highstands in currently dry basins. Situated about 70 km south of the U.S.-Mexico international border, lakes occupying these internally drained basins combined during episodes of wetter than modern climate conditions to form pluvial Lake Palomas. At roughly 60,000 km², the Palomas watershed drains the largest area in the Chihuahuan desert. This simple drainage system, which receives hydrological input from only groundwater discharge, precipitation, and runoff, responded rapidly to climatically driven changes in effective moisture.

Constructional beach ridges dated at 221 ± 33 and 435 ± 39 14C years before present (¹⁴C yr B.P.) (Little Ice Age), 3815 ± 52 to 4251 ± 59 ¹⁴C yr B.P. (early Neoglacial), 6110 ± 80 to 6721 ± 68 ¹⁴C yr B.P. (middle Holocene), and 8269 ± 64 and 8456 ± 97 ¹⁴C yr B.P. (early Holocene) provide the first detailed Holocene lake record for northern Mexico. Distinct pluvial episodes during the early Holocene and prior to the early Holocene are marked by two shorelines above an intrabasin sill. At these times, conditions were wet enough to form one large lake that encompassed all of the sub-basins. We estimate that the largest spatial extent of this combined lake covered approximately 7030 km² during maximum pluvial conditions, probably during the late Pleistocene. In addition, this lake-level record shows unambiguous evidence for wetter than present conditions during the middle Holocene, a time that is widely considered to have been relatively dry in this region. These lake highstands correlate with other records of millennially spaced wet and (or) cold events in the northern hemisphere, and are inferred to be driven by a greater frequency of winter storms over the southwestern U.S. and northern Mexico.