The warm Pliocene: Bridging the geological data and modelling communities
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Water isotopic imprints of Pacific Walker Circulation responses to CO2 decline during the late Pliocene and early Pleistocene

Theodor Mayer1, Ran Feng1, Tripti Bhattacharya2, Erin McClymont3, Heather Ford4, and Sze Ling Ho5
Theodor Mayer et al.
  • 1Department of Geosciences, University of Connecticut , Storrs, United States of America (theodor.mayer@uconn.edu)
  • 2Earth and Environmental Science, Syracuse University, Syracuse, United States of America
  • 3Department of Geography, Durham University, Durham, England
  • 4School of Geography, Queen Mary University of London, London, England
  • 5Institute of Oceanography, National Taiwan University, Taipei City, Taiwan

Ocean-atmosphere coupled models predict pronounced weakening of the Pacific Walker Circulation (PWC) with increasing CO2 concentration associated with the enhanced tropospheric stability and reduced convective mass overturning. However, instrumental observations from the past few decades are inconsistent and do not support a clear weakening of the Walker circulation. The detection of the role of increasing CO2 is in part impeded by substantial internal variability and anthropogenic aerosol forcings. Here we explore the possibility of using a paleoclimatic analogue to understand the contemporary PWC sensitivity to CO2 changes. We focus on the interval from mid-Piacenzian (MP, 3.3 – 3.0 Ma) to early Pleistocene (~2.4 Ma). The MP had elevated CO2 concentrations (~400ppm) and geography, topology, and vegetation similar to today. Following the MP, global CO2 and temperature decreased, leading to the intensification of the Northern hemisphere glaciation. We seek to identify potential proxy constraints on model simulated PWC sensitivity to CO2 forcing by focusing on changes in the hydroclimatology during this time interval. We developed several sets of isotope-tracking enabled CESM version 1.2 simulations, which utilize pre-Industrial and mid-Piacenzian boundary conditions, different CO2 levels, and water tagging of several key oceanographic regions to track the life cycles of various water species (H216O, H218O and HD16O). Preliminary results show that Pliocene boundary conditions have little impact on the relationship between the CO2 forcing and the intensity of PWC. The precipitation δD contrast between the eastern and western tropical Pacific is linked to varying rates of moisture convergence change, and scales well with the PWC strength, suggesting high potential for developing PWC strengths proxy with precipitation isotopic records from both sides of the tropical Pacific. Our ongoing work will further identify physical processes responsible for the simulated precipitation isotopic signals: i.e., whether they reflect changes in the moisture source, moisture transport, or moist convection at the destination. Furthermore, coupled simulations are being carried out to understand seawater isotopic signatures of PWC related precipitation changes, and contributions from changing ocean dynamics to PWC changes during this interval.

How to cite: Mayer, T., Feng, R., Bhattacharya, T., McClymont, E., Ford, H., and Ling Ho, S.: Water isotopic imprints of Pacific Walker Circulation responses to CO2 decline during the late Pliocene and early Pleistocene, The warm Pliocene: Bridging the geological data and modelling communities, Leeds, United Kingdom, 23–26 Aug 2022, GC10-Pliocene-32, https://doi.org/10.5194/egusphere-gc10-pliocene-32, 2022.