Paleoclimate
Climate variability in North America during the last 120,000 years
revealed by carbon, oxygen and uranium isotopes in pedogenic carbonate
This work presents a continuous record of paleoclimate in mid-continent North America for the last 120,000 years based on micro-analyses of laminated pedogenic carbonate coatings (pedothems, from Greek: πέδον, pedon, "soil"; and θέμα, théma, "deposit") formed on soil stones. Modern micro-analytical techniques allow the carbonate layers to be dated and to be analyzed for stable O and C isotopes, which are related to the climatic conditions in which they formed. The resulting dataset and paleoclimate record is the first of its kind, with a continuity and detail that rivals currently existing paleoclimate records and adds to our understanding of North America climate history during the most recent ice ages.
Reflected light photomicrographs of pedogenic carbonate rind (pedothem) from Wind River Basin, Wyoming: A) LA-ICPMS time transgressive analysis transect across pedogenic carbonate laminations; B) 230Th/U powder calibration sample taken from white oval; C) Magnified area of box in (B) showing arrangement of paired C and O analysis spots, vertically transects are along age axis, horizontal are synchronous along carbonate lamination; D) Magnified area of box in (C) showing spatial arrangement of C, O and U analysis spots.
Oerter, E, W Sharp, J Oster, A Ebeling, J Valley, R Kozdon, I Orland, J Hellstrom, J Woodhead, J Hergt, O Chadwick, R Amundson, 2016, Pedothem carbonates reveal anomalous North American atmospheric circulation 70,000 to 55,000 years ago. Proceedings of the National Academy of Sciences of the United States of America, v. 113, no. 4, p. 919-924, doi: 10.1073/pnas.1515478113. pdf
Paleoclimate in the Atacama Desert, Chile
The Atacama Desert of northern Chile and southern Peru is a fascinating place, partly because of the fact that it has never rained in some places (during human history). This project examines soils that formed from 20 to 10 million years ago in climates that oscillated from rainy and humid to dry and desert-like. There were periods of high rainfall that formed clay minerals that alternated with drier periods that lead to the formation of carbonate and therefore a record of climate and atmospheric circulation.
The Atacama Desert of northern Chile and southern Peru is a fascinating place, partly because of the fact that it has never rained in some places (during human history). This project examines soils that formed from 20 to 10 million years ago in climates that oscillated from rainy and humid to dry and desert-like. There were periods of high rainfall that formed clay minerals that alternated with drier periods that lead to the formation of carbonate and therefore a record of climate and atmospheric circulation.
Oerter, E, R Amundson, A Heimsath, M Jungers, G Chong, P Renne, 2016, Early to middle Miocene climate in the Atacama Desert of northern Chile. Palaeogeography, Palaeoclimatology, Palaeoecology, v. 441, p. 890-900. pdf
We studied a soil on a late Tertiary to early Quaternary alluvial fan that exhibits evidence of an initial wetter period (secondary clay formation) followed by a period dry enough to form secondary carbonate accumulations, sometimes as dense pedothems on soil gravels. C stable isotope values show a ~4‰ increase in δ13C values through time, reflecting a change towards aridification with decreasing plant density and soil respiration. O stable isotope values show a more complex pattern along the same time axis with variability of up to 10‰. Together this evidence records a shift towards drier climate conditions and reveal a fascinating change over time that appears to be associated with the rise of the Andes Mountains.
Ebeling, A, E Oerter, J Valley, R Amundson, 2016, Relict soil evidence for profound Quaternary aridification of the Atacama Desert, Chile. Geoderma, v. 267, p. 196-206., doi: 10.1016/j.geoderma.2015.12.010. pdf
We studied a soil on a late Tertiary to early Quaternary alluvial fan that exhibits evidence of an initial wetter period (secondary clay formation) followed by a period dry enough to form secondary carbonate accumulations, sometimes as dense pedothems on soil gravels. C stable isotope values show a ~4‰ increase in δ13C values through time, reflecting a change towards aridification with decreasing plant density and soil respiration. O stable isotope values show a more complex pattern along the same time axis with variability of up to 10‰. Together this evidence records a shift towards drier climate conditions and reveal a fascinating change over time that appears to be associated with the rise of the Andes Mountains.
Ebeling, A, E Oerter, J Valley, R Amundson, 2016, Relict soil evidence for profound Quaternary aridification of the Atacama Desert, Chile. Geoderma, v. 267, p. 196-206., doi: 10.1016/j.geoderma.2015.12.010. pdf