Physics

Seasonality

Geology

Climate change

Meteorology

Archaeology

Cave

Speleothem

Mathematics

δ18O

Biology

Atmospheric sciences

Precipitation

Oceanography

Mathematical analysis

Monsoon

Westerlies

Geochemistry

Atmospheric circulation

China

Geography

Ecology

Stable isotope ratio

East Asian Monsoon

Plateau (mathematics)

Climatology

Quantum mechanics

Isotopes of oxygen

East Asia

Paleoclimatology

Environmental science

Proceedings of the National Academy of Sciences

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.

Enriched East Asian oxygen isotope of precipitation indicates reduced summer seasonality in regional climate and westerlies