The development and release of iCESM1.2

Because of the pervasive role of water in the Earth system, the relative abundances of stable isotope tracers of water are valuable for understanding atmospheric, oceanic, and biospheric processes, and for interpreting paleoclimate proxy reconstructions. They are transported by both large‐scale and turbulent flows, and the ratio of heavy to light isotopologues changes due to fractionation that can accompany condensation and evaporation processes. Correctly predicting the isotopic distributions requires resolving the relationships between large‐scale ocean and atmospheric circulation and smaller‐scale hydrological processes, which can be accomplished within a coupled climate modeling framework.

A schematic of iCESM1 showing the five major model components and all of the major intercomponent fluxes that impact the water isotope tracers
Figure: A schematic of iCESM1 showing the five major model components (iCAM, iCLM, iRTM, iPOP, and iCICE) and all of the major intercomponent fluxes that impact the water isotope tracers. It should be noted that although some of these fluxes are only shown once, they occur for multiple components.

The water isotope‐enabled version of the Community Earth System Model version 1 (iCESM1.2) was a community effort, including researchers at NCAR, University of Colorado, Oregon State University, University of Wisconsin, and Ohio State University. The iCESM1, which simulates global variations in water isotopic ratios in the atmosphere, land, runoff, ocean, and sea ice, was released to the community on github (Brady et al., 2019). It is poised to be a vital community resource for ongoing model development with both modern and paleoclimate applications. It has already been applied to the Last Millennium (Stevenson et al., 2019), Holocene (Thompson et al., 2019), Last Glacial Maximum (LGM, Zhu et al., 2017), Early Eocene Climatic Optimum (Zhu et al., 2019), and Carboniferous (Macarewich et al., 2019).

Changes in variance of the simulated oxygen isotopic ratios between the LGM and Preindustrial
Figure: Changes in variance of the simulated oxygen isotopic ratios between the LGM and Preindustrial (PI), illustrating how at certain core locations (*) the interannual and total variance can differ in sign. This has implications for reconstructing ENSO during the LGM using foraminifera records. Differences insignificant at the 95% confidence level are dotted.

References

  • Brady, E.C., S. Stevenson, D. Bailey, Z. Liu, D. Noone, J. Nusbaumer, B.L. Otto-Bliesner, C. Tabor, R. Tomas, A. Wong, J. Zhang, and J. Zhu, 2019: The connected isotopic water cycle in the Community Earth System Model, version 1. Journal of Advances in Modeling Earth Systems, 11. https://doi.org/10.1029/2019MS001663
  • Macarewich S., C. Poulsen, and I. Montanez, 2019: Constraining seawater conditions in ancient epicontinental seas with iCESM: Implications for oxygen isotope secular curves. 24th Annual CESM Workshop, Boulder.
  • Stevenson, S., B.L. Otto-Bliesner, E.C. Brady, J. Nusbaumer, C. Tabor, R. Tomas, D. Noone, and A. Liu, 2019: Volcanic eruption signatures in the isotope-enabled Last Millennium Ensemble. Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2019PA003625
  • Thompson, A., C. Tabor, and C. Poulsen, 2019: Model-proxy comparison of precipitation and hydrogen stable isotopes in mid-Holocene Northern Africa with iCESM. 24th Annual CESM Workshop, Boulder.
  • Zhu, J., Z.Y. Liu, E.C. Brady, B.L. Otto-Bliesner, S.A. Marcott, J. Zhang, A. Wang, D. Noone, R. Tomas, J. Nusbaumer, T. Wong, A. Jahn, and C. Tabor, 2017: Reduced ENSO variability at the LGM revealed by an isotope-enabled Earth system model. Geophysical Research Letters, 44, 6984-6992.
  • Zhu, J., Poulsen, C. J., Otto-Bliesner, B. L., Liu, Z., Brady, E. C., Noone, D. C., 2019: Simulation of early Eocene water isotopes using an Earth system model and its implication for past climate reconstruction. Earth and Planetary Science Letters. under review.