Paleoclimatic Inferences from an Isotopic Investigation of Groundwater in the Central San Juan Basin, New Mexico

1986 ◽  
Vol 26 (2) ◽  
pp. 179-193 ◽  
Author(s):  
Fred M. Phillips ◽  
Leslie A. Peeters ◽  
Michael K. Tansey ◽  
Stanley N. Davis
Keyword(s):  
New Mexico ◽  
Stable Isotope ◽  
Isotope Composition ◽  
Noble Gas ◽  
Winter Precipitation ◽  
American Southwest ◽  
San Juan ◽  
Mean Annual Temperature ◽  
San Juan Basin ◽  
Pleistocene Climate

Groundwater from the Ojo Alamo and Nacimiento aquifers in the central San Juan Basin. New Mexico, has yielded 14C ages ranging from modern to 35,000 yr B.P. The Pleistocene-age samples are characterized by a stable isotope content about 25‰ lighter in D and 3‰ lighter in 18O than modern precipitation and groundwater. We attribute this difference to a colder mean annual temperature and perhaps increased winter precipitation. Consideration of various factors controlling the stable isotope composition of the groundwater allows estimation of a 5° to 7°C temperature decrease during the late Wisconsin, accompanied by increased effective precipitation. A similar estimate of the temperature change is obtained from noble-gas paleothermometry. These data support a model of moderately cooler late Pleistocene climate in the American Southwest characterized by summers with less precipitation than today, but wetter winters.

A 30,000 yr Continental Paleotemperature Record Derived from Noble Gases Dissolved in Groundwater from the San Juan Basin, New Mexico

1995 ◽  
Vol 43 (2) ◽  
pp. 209-220 ◽  
Author(s):  
Martin Stute ◽  
Jordan F. Clark ◽  
Peter Schlosser ◽  
Wallace S. Broecker ◽  
Georges Bonani
Keyword(s):  
New Mexico ◽  
Gulf Of Mexico ◽  
Temperature Change ◽  
Noble Gases ◽  
Lapse Rate ◽  
Identical Result ◽  
San Juan ◽  
Mean Annual Temperature ◽  
The Holocene ◽  
San Juan Basin

AbstractPaleotemperatures for the last glacial maximum (LGM) have been derived from noble gases dissolved in 14C-dated groundwater of the Ojo Alamo and the Nacimiento formations in the San Juan Basin, northwestern New Mexico. The difference in mean annual (ground) temperature between the Holocene and the LGM was determined to be 5.5 ± 0.7°C. A practically identical result, 5.2 ± 0.7°C, has been obtained previously from the Carrizo aquifer in southern Texas. This suggests that the southwestern United States was uniformly cooler during the LGM and that the mean annual temperature gradient along a transect from the Gulf of Mexico to northwestern New Mexico has been unchanged since the LGM. The noble gas paleotemperatures are supported by paleoecological evidence in the region. The Holocene/LGM temperature difference of 5.4°C indicates that a simple lapse rate calculation may be applied to convert the 1000-m glacial depression of snowlines in the Colorado Front Range into a temperature decrease. A continental temperature change of 5.4 ± 0.7°C is inconsistent with a temperature change of about 2°C determined for the surface waters of the Gulf of Mexico.

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