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

Abstract

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.

Noble gases, stable isotopes, and radiocarbon as tracers of flow in the Dakota aquifer, Colorado and Kansas

“…The differences are based on only two samples and may have a large uncertainty associated with them. However, the Holocene to LGP change in the noble gas temperature agrees well with other records from the southern United States (Stute et al, 1992a;1995a and b;Clark et al, 1997) O compositions were about -3‰ in the San Juan Basin (Phillips et al, 1986;Stute et al, 1995a) and greater than ϩ 1‰ in the Carrizo aquifer (M. Stute, personal communication). The positive change in d…”

“…Pearson and White, 1967;Winograd and Friedman, 1972;Rozanski, 1985;Phillips et al, 1986;Siegel, 1991;Davisson and Criss, 1993;Dutton, 1995;Rose and Davisson, 1996). 14 C is the most reliable chronometer of moderately old groundwater (5-30 kyr) although corrections must be made to account for water-rock interactions.…”

Aspect‐related microclimatic influences on slope forms and processes, northeastern Arizona

“…Annual air temperatures on south‐facing canyon slopes in the study area were 1.4–2.1°C warmer than north‐facing slopes (Table 1), and differences in winter were 2–3°C warmer (Figure 8). Modern vertical temperature gradients in the southern Colorado Plateau are 5–6°C/1000 m [ Stute et al , 1995], thus air temperature differences among aspects (Table 1) are roughly analogous to elevation differences of about 230–600 m. Paleoclimatic reconstructions for the southern Colorado Plateau and adjacent areas indicate a 2–4°C range of mean annual temperatures in the Holocene, and late Pleistocene temperatures 4–6°C cooler than present [ Phillips et al , 1986; Cole , 1990; Davis and Shafer , 1992; Anderson , 1993; Stute et al , 1995; Zhu et al , 1998]. Temperature differences between north‐ and south‐facing slopes thus approach long‐term differences in Holocene mean temperatures, but both analogies are limited.…”

Isotopic evidence for widespread cold‐season‐biased groundwater recharge and young streamflow across central Canada

“…However, few studies have explicitly quantified seasonal groundwater recharge ratio biases, and fewer still have quantified large‐scale spatial distributions of recharge‐seasonality biases (e.g., Sánchez‐Murillo & Birkel, ). Understanding the spatial patterns and variability of recharge ratios is important in order to help predict how groundwater recharge may respond to climatic shifts or to decadal‐scale changes to seasonal water balances, and to interpret the many isotope‐based records of quaternary climate such as speleothems and fossil groundwater (e.g., Bertrand et al, ; Chen et al, ; Clark, Stute, Schlosser, Drenkard, & Bonani, ; Darling, Edmunds, & Smedley, ; Edmunds & Wright, ; Jasechko et al, ; Phillips, Peeters, Tansey, & Davis, ; Plummer, ; Wagner et al, ; Wang et al, ; Wang et al, ).…”