Pedothem carbonates reveal anomalous North American atmospheric circulation 70,000–55,000 years ago

Abstract

Our understanding of climatic conditions, and therefore forcing factors, in North America during the past two glacial cycles is limited in part by the scarcity of long, well-dated, continuous paleoclimate records. Here, we present the first, to our knowledge, continuous, millennial-resolution paleoclimate proxy record derived from millimeter-thick pedogenic carbonate clast coatings (pedothems), which are widely distributed in semiarid to arid regions worldwide. Our new multiisotope pedothem record from the Wind River Basin in Wyoming confirms a previously hypothesized period of increased transport of Gulf of Mexico moisture northward into the continental interior from 70,000 to 55,000 years ago based on oxygen and carbon isotopes determined by ion microprobe and uranium isotopes and U-Th dating by laser ablation inductively coupled plasma mass spectrometry. This pronounced meridional moisture transport, which contrasts with the dominant zonal transport of Pacific moisture into the North American interior by westerly winds before and after 70,000–55,000 years ago, may have resulted from a persistent anticyclone developed above the North American ice sheet during Marine Isotope Stage 4. We conclude that pedothems, when analyzed using microanalytical techniques, can provide high-resolution paleoclimate records that may open new avenues into understanding past terrestrial climates in regions where paleoclimate records are not otherwise available. When pedothem paleoclimate records are combined with existing records they will add complimentary soil-based perspectives on paleoclimate conditions.

Seasonal Bias in Soil Carbonate Formation and Its Implications for Interpreting High‐Resolution Paleoarchives: Evidence From Southern Utah

“…This study also has implications for the use of laminated soil carbonate rinds as high‐resolution proxies for late Quaternary paleoclimate and ecosystem changes. Similar to the age models from the two published records (Oerter et al, ; Pustovoytov et al, ), radiometric dating at Torrey indicates laminated soil carbonates can be reliably dated. However, our results also highlight the utility of knowing the depth of formation as well as having extensive modern calibration data for interpreting soil carbonate formation conditions (Breecker et al, ; Burgener et al, ; Gallagher & Sheldon, ; Oerter & Amundson, ; Peters et al, ).…”

“…However, our results also highlight the utility of knowing the depth of formation as well as having extensive modern calibration data for interpreting soil carbonate formation conditions (Breecker et al, ; Burgener et al, ; Gallagher & Sheldon, ; Oerter & Amundson, ; Peters et al, ). Combining information on rinds from different depths (Oerter et al, ) is likely to obscure signals due to different infiltration, soil CO 2 , and temperature regimes (Burgener et al, ; Peters et al, ; Quade et al, ). In addition, the seasonality and mechanism of soil carbonate formation will need to be addressed through the duration of these records (e.g., with T (Δ 47 ) or other proxy information).…”

“…More recent work utilizes formation temperature estimates from clumped isotopes as an additional constraint (Quade et al, ), but this is not yet a routine measurement and can still yield nonunique results. Seasonality issues are especially critical in light of the potential for high‐resolution (hundreds of years) soil carbonate records, as demonstrated by pedogenic carbonate rinds from fluvial terraces in the Wind River Basin (Oerter et al, ) and archeological sites in the Fertile Cresent (Pustovoytov et al, ). These studies are intriguing because they suggest the possibility of long‐term, submillennial soil carbonate archives that can be used to investigate Quaternary timescales for which only a few proxies are available.…”

Global Isotope Hydrogeology―Review

“…The availability of deuterium excess values in fossil groundwater records provides an advantage over most other late‐Pleistocene isotopic records, which usually enable measurement of only one of O or H isotope systematics (e.g., solely δ 2 H data for leaf wax—e.g., Konecky et al, ; solely δ 18 O for lake sediment carbonate minerals—e.g., Mandl et al, ; solely δ 18 O for pedogenic carbonates—e.g., Oerter et al, ; and solely δ 18 O for most speleothems—e.g., Wang et al, ; cf. Porter et al, ).…”

The Sensitivity of Terrestrial δ18O Gradients to Hydroclimate Evolution

“…Additionally, in isotope‐enabled general circulation model simulations Poulsen and Jeffery () capture a decrease in the change in δ 18 O over mountain ranges in 2x‐ and 4x‐pCO 2 experiments. However, on geologic time scales other effects can amplify or overprint our predicted climate‐Δ δ 18 O relationship including vegetation and climate modifications to moisture recycling (Chamberlain et al, ; Mix et al, ; Winnick et al, ), and moisture source and atmospheric flow variability (Amundson et al, ; Edwards et al, ; Galewsky, ; Insel et al, ; Oerter et al, ; Poulsen et al, ; Rohrmann et al, ). In fact, through the cooling trend of the Neogene Chamberlain et al () suggest that isotope gradients became shallower, not steeper, due to enhanced moisture recycling and aridification.…”