September 19, 2019 @ 4:00 pm - 5:00 pm CDT
Current Research in EEPS Seminar: Dr. Samantha Stevenson – University of California, Santa Barbara
How Oxygen Isotopes Can Help Us Understand Past and Future Climate Variability
Year-to-year variations in climate are hugely important in many contexts, from water management to ecosystem services among other applications. The El Nino/Southern Oscillation (ENSO) is particularly important, as it drives the majority of interannual climate variability. However, climate model projections disagree widely on estimates of future changes to ENSO – and the observational record is too short to reliably distinguish ‘good’ from ‘bad’ model ENSO representations. Paleoclimate information provides an invaluable way to extend our observational baseline, and many proxy data are collected in the form of oxygen isotopes (d18O); however, since many processes affect d18O variations, interpreting the climate signals recorded in d18O can be quite complex. Here we present the first look at isotopic expressions of ENSO in the Community Earth System Model (CESM), using newly completed, isotope-enabled members of the Last Millennium Ensemble (LME). CESM does quite well at capturing the large-scale structure of isotopic variations, although it appears that anthropogenically forced changes to ENSO over the last millennium are relatively small in this model. We therefore explore the ENSO response to volcanic eruptions as a check on model behavior, since volcanic eruptions are the largest natural perturbation to the climate. In the LME, large eruptions lead to changes in d18O over land and ocean, and the responses are highly sensitive to eruption latitude. In fact, this sensitivity enables isotopes to serve as ‘fingerprints’ of eruption latitudinal structure; the dominant hemisphere of most high-latitude eruptions can be correctly identified based on anomalies in precipitation d18O alone. This work shows the potential for isotopes to serve as new, powerful constraints on the properties of past volcanic eruptions and their influence on the climate system.