1. Interpreting Precession‐Driven δ 18 O Variability in the South Asian Monsoon Region
- Author
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Jesse Nusbaumer, M. P. Erb, Zhengyu Liu, Bette L. Otto-Bliesner, David Noone, Clay R. Tabor, Jiang Zhu, Tony E. Wong, and Esther C. Brady
- Subjects
Atmospheric Science ,geography ,geography.geographical_feature_category ,010504 meteorology & atmospheric sciences ,δ18O ,Northern Hemisphere ,Speleothem ,010502 geochemistry & geophysics ,Monsoon ,01 natural sciences ,Geophysics ,Space and Planetary Science ,Climatology ,Paleoclimatology ,Soil water ,Earth and Planetary Sciences (miscellaneous) ,Precession ,Environmental science ,Precipitation ,0105 earth and related environmental sciences - Abstract
Speleothem records from the South Asian summer monsoon (SASM) region display variability in the ratio of O-18 and O-16 (δ O-18) in calcium carbonate at orbital frequencies. The dominant mode of variability in many of these records reflects cycles of precession. There are several potential explanations for why SASM speleothem records show a strong precession signal, including changes in temperature, precipitation, and circulation. Here we use an Earth system model with water isotope tracers and water-tagging capability to deconstruct the precession signal found in SASM speleothem records. Our results show that cycles of precession-eccentricity produce changes in SASM intensity that correlate with local temperature, precipitation, and δ O-18. However, neither the amount effect nor temperature differences are responsible for the majority of the SASM δ O-18 variability. Instead, changes in the relative moisture contributions from different source regions drive much of the SASM δ O-18 signal, with more nearby moisture sources during Northern Hemisphere summer at aphelion and more distant moisture sources during Northern Hemisphere summer at perihelion. Further, we find that evaporation amplifies the δ O-18 signal of soil water relative to that of precipitation, providing a better match with the SASM speleothem records. This work helps explain a significant portion of the long-term variability found in SASM speleothem records.
- Published
- 2018