Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Enriched East Asian Oxygen Isotope of Precipitation Indicates Reduced Summer Seasonality in Regional Climate and Westerlies

TitleEnriched East Asian Oxygen Isotope of Precipitation Indicates Reduced Summer Seasonality in Regional Climate and Westerlies
Publication TypeJournal Article
Year of Publication2020
JournalProceedings of the National Academy of Sciences
Volume117
Number26
Pages14745-14750
Abstract / Summary

Speleothem oxygen isotope records over East Asia reveal apparently large and rapid paleoclimate changes over the last several hundred thousand years. However, what the isotopic variation actually represent in terms of the regional climate and circulation is debated. We present an answer that emerges from an analysis of the interannual variation in amount-weighted annual δ18O of precipitation over East Asia as simulated by an isotope-enabled model constrained by large-scale atmospheric reanalysis fields. 18O-enriched years have reduced summer seasonality both in terms of precipitation isotopes and in the large-scale circulation. Changes occur between June and October, where the δ18O of precipitation (δ18Op) transitions from the isotopically heavier winter to the lighter summer regime. For 18O-enriched years, this transition is less pronounced. Variations in precipitation amount alone are insufficient to explain the amount-weighted annual δ18Op between 18O-enriched and 18O-depleted years. Reduced summer seasonality is also expressed in the low-level monsoonal southerlies and upper-level westerlies; for the latter, the northward migration across the Tibetan Plateau in the summer is less pronounced. Our result thus implicates the westerlies across the plateau as the proximate cause of East Asian paleomonsoon changes, manifested as a modulation of its summer peak.

URLhttp://dx.doi.org/10.1073/pnas.1922602117
DOI10.1073/pnas.1922602117
Journal: Proceedings of the National Academy of Sciences
Year of Publication: 2020
Volume: 117
Number: 26
Pages: 14745-14750
Publication Date: 06/2020

Speleothem oxygen isotope records over East Asia reveal apparently large and rapid paleoclimate changes over the last several hundred thousand years. However, what the isotopic variation actually represent in terms of the regional climate and circulation is debated. We present an answer that emerges from an analysis of the interannual variation in amount-weighted annual δ18O of precipitation over East Asia as simulated by an isotope-enabled model constrained by large-scale atmospheric reanalysis fields. 18O-enriched years have reduced summer seasonality both in terms of precipitation isotopes and in the large-scale circulation. Changes occur between June and October, where the δ18O of precipitation (δ18Op) transitions from the isotopically heavier winter to the lighter summer regime. For 18O-enriched years, this transition is less pronounced. Variations in precipitation amount alone are insufficient to explain the amount-weighted annual δ18Op between 18O-enriched and 18O-depleted years. Reduced summer seasonality is also expressed in the low-level monsoonal southerlies and upper-level westerlies; for the latter, the northward migration across the Tibetan Plateau in the summer is less pronounced. Our result thus implicates the westerlies across the plateau as the proximate cause of East Asian paleomonsoon changes, manifested as a modulation of its summer peak.

DOI: 10.1073/pnas.1922602117
Citation:
Chiang, J, M Herman, K Yoshimura, and I Fung.  2020.  "Enriched East Asian Oxygen Isotope of Precipitation Indicates Reduced Summer Seasonality in Regional Climate and Westerlies."  Proceedings of the National Academy of Sciences 117(26): 14745-14750.  https://doi.org/10.1073/pnas.1922602117.