Climate variability and its magnetic response recorded in a lacustrine sequence 
in Heqing basin at the SE Tibetan Plateau since 900 ka

Hu, Shouyun; Goddu, Srinivasa Rao; Herb, Christian; Appel, Erwin; Gleixner, Gerd; Wang, Sumin; Yang, Xiangdong; Zhu, Xiuhua

doi:10.1093/gji/ggv033

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Climate variability and its magnetic response recorded in a lacustrine sequence in Heqing basin at the SE Tibetan Plateau since 900 ka

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Gleixner, Gerd
Molecular Biogeochemistry Group, Dr. G. Gleixner, Department Biogeochemical Processes, Prof. S. E. Trumbore, Max Planck Institute for Biogeochemistry, Max Planck Society;

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Citation

Hu, S., Goddu, S. R., Herb, C., Appel, E., Gleixner, G., Wang, S., et al. (2015). Climate variability and its magnetic response recorded in a lacustrine sequence in Heqing basin at the SE Tibetan Plateau since 900 ka. Geophysical journal international, 201(1), 444-458. doi:10.1093/gji/ggv033.

Cite as: https://hdl.handle.net/11858/00-001M-0000-0027-A39D-5

Abstract

The lacustrine deposits in Heqing basin provide an excellent archive for long-term highresolution palaeoclimate studies in the monsoon-dominated southeastern Tibetan Plateau region. In this study, we investigate the climatic significance of magnetic parameters for analysing the variability of the past climate. For this, we performed comprehensive time-series and statistical analysis on previously published proxy data from a 168-m-long drill core (Core- HQ) that spans ∼900–30 ka, comprising mainly magnetic parameters and carbonate content (CC). Moreover, we investigated magnetic properties of modern soil in the catchment that predominantly formed on limestone bedrock. Key findings are: (1) modern soils and sediments of Core-HQ both contain a mixture of magnetite (Mt), maghemite (Mgh) and hematite (Ht), but magnetic concentration of the soils is one order higher; (2) a superparamagnetic (SP) fraction of Mt/Mgh dominates in the soils whereas in Core-HQ the SP contribution is generally very low; (3) a larger grain-size fraction of Mt/Mgh and Ht is also present in the soils. We explain variations of magnetic concentration and CC in Core-HQ by an increased wind transport of soil and a decreased surface water transport of carbonate and soil in less humid periods. Low-temperature oxidation of magnetite in the catchment is as another crucial process that reflects weathering conditions and is likely sensitive to humidity; the degree of LTO can be semi-quantified by the magnetic parameters ARM/SIRM and S-ratio. Combining CC, ARM/SIRM and S-ratio values, we derive a weathering intensity (WI). The WI index variation along Core-HQ shows strong fluctuations on a 100-kyr eccentricity scale in the lower part, especially during ∼630–380 ka, followed by a long period (∼320–80 ka) of persistently weaker weathering (drier?) conditions with low variability, and a rapid return of much stronger weathering (wetter?) conditions at ∼80 ka. We suggest that a reduced influence of the Indian summermonsoon accounts for less moisture supply to the region and lower climatic variability.