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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.
