Tracing East Asian Monsoon precipitation using Mg isotopic composition of the loess leaching fraction
Abstract
East Asian Monsoon (EAM) precipitation, transported from the tropic ocean to Asian inland, influences billions of human beings and the sustainable development of the environment. As the results of EAM, the thick and continuous Chinese loess deposits contain a detailed record of precipitation changes in East Asian monsoon climate. However, since the moister and heat are always simultaneously transported by EAM and both recorded in loess deposits during pedogenic process, it is not straightforward to separate and extract precipitation signals from the loess deposits by using traditional monsoon proxies. As a major and mobile element in Chinese loess carbonate, Mg isotopes in loess carbonate may provide an opportunity to trace EAM precipitation.
In order to systemically characterize the loess carbonate Mg isotopic behavior during pedogenic processes and explore its potential as a reliable proxy for East Asian Monsoon precipitation, we measured both elemental and Mg isotopic composition (δ26Mg) of the weak acid leaching fractions from loess potential source regions, spatial Holocene sites and the last glacial-interglacial loess sequence. Our results show that δ26Mg of leaching fractions were relative constant between different source regions, gradually increases from northwest to southeast Chinese Loess Plateau, and gradually decreases from last interglacial to last glacial. Due to the source regions with relative constant Mg isotopic composition and the only separation of fine-grained loess, the δ26Mg variations in loess leaching fraction were attributed to pedogenic weathering (temperature and precipitation). Positive relationship of δ26Mg and modern mean annual precipitation (MAP) suggests that δ26Mg in loess leaching fractions is mainly controlled by MAP and is a reliable proxy to reconstruct the EAM precipitation. We explore that MAP influences δ26Mg values through changing the carbonate content. To validate this loess-based proxy, MAP during last glacial-interglacial was estimated. The estimated MAP shows more abundant during last interglacial than last glacial, similar trend but larger glacial-interglacial fluctuation compared with previous results using different proxies.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP22C..04M
- Keywords:
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- 9340 Indian Ocean;
- GEOGRAPHIC LOCATIONDE: 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGEDE: 1807 Climate impacts;
- HYDROLOGYDE: 4904 Atmospheric transport and circulation;
- PALEOCEANOGRAPHY