Publication Date:
2019-07-13
Description:
Speleothem records from the South Asian summer monsoon (SASM) region display variability in the ratio of O-18 and O-16 ( 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 O-18. However, neither the amount effect nor temperature differences are responsible for the majority of the SASM O-18 variability. Instead, changes in the relative moisture contributions from different source regions drive much of the SASM 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 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.
Keywords:
Meteorology and Climatology
Type:
GSFC-E-DAA-TN58219
,
Journal of Geophysical Research: Atmospheres (ISSN 2169-897X) (e-ISSN 2169-8996); 123; 11; 5927-5946
Format:
text
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