Dependence of the cyclization of branched tetraethers on soil moisture in alkaline soils from arid–subhumid China: implications for palaeorainfall reconstructions on the Chinese Loess Plateau

H Wang,C L Zhang,W Liu

doi:10.5194/bg-11-6755-2014

Abstract

Abstract. The use of branched glycerol dialkyl glycerol tetraethers (bGDGTs) in loess–palaeosol sequences (LPSs) has shown promises in continental palaeotemperature reconstructions. Thus far, however, little is known about the effect of soil moisture on their distributions in the water-limited Chinese Loess Plateau (CLP). In this study, the relationships between environmental variables and the cyclization of branched tetraethers (CBT) were investigated in arid–subhumid China using 97 surface soils in the CLP and its vicinity, as well as 78 soils with pH > 7 which have been previously published. We find that CBT correlates best with soil water content (SWC) or mean annual precipitation (MAP) for the overall data set. This indicates that CBT is mainly controlled by soil moisture instead of soil pH in alkaline soils from arid–subhumid regions, where water availability is a limiting factor for the producers of bGDGTs. Therefore, we suggest that CBT can potentially be used as a palaeorainfall proxy on the alkaline CLP. According to the preliminary CBT–MAP relationship for modern CLP soils (CBT = −0.0021 × MAP + 1.7, n = 37, r = −0.93), palaeorainfall history was reconstructed from three LPSs (Yuanbao, Lantian, and Mangshan) with published bGDGT data spanning the past 70 ka. The CBT-derived MAP records of the three sites consistently show precession-driven variation resembling the monsoon record based on speleothem δ18O, supporting CBT as a reasonable proxy for palaeorainfall reconstruction in LPS. The direct application of CBT as a palaeorainfall proxy in corroboration with the bGDGT-based temperature proxy may enable us to further assess the temperature/hydrological association for palaeoclimate studies on the CLP.

Highlights

The deposits of wind-blown dust on the Chinese Loess Plateau (CLP; Fig. 1) are natural archives of past climate change
We have investigated the environmental controls on the distribution of branched glycerol dialkyl glycerol tetraethers (bGDGTs) for surface soils on the CLP and in other alkaline soils from arid–subhumid China
In contrast to most previous studies covering a large range of soil pH values, no obvious relationship was observed between soil pH and cyclization of branched tetraethers (CBT) for our alkaline soil data set

Summary

Introduction

The deposits of wind-blown dust (i.e. loess) on the Chinese Loess Plateau (CLP; Fig. 1) are natural archives of past climate change. The plateau consists of a sequence of alternating loess and palaeosol layers, which have accumulated at least since 2.6 Ma BP (before present; Liu, 1985; Liu and Ding, 1998), with the records extending back to late Oligocene (Heller and Liu, 1982; Guo et al, 2002; Qiang et al, 2011). The cyclic alternation of loess and palaeosol provides highly visible records of regional climate history resulting from changing monsoon intensity on glacial–interglacial timescales (An, 2000, and references therein; Porter, 2001). Since many proxies suffer from inherent weaknesses such as uncertainties of interpretation (e.g. controversy of precipitation-controlled vs. temperature-controlled) or sample unavailability (Yang et al, 2014a), the development of new palaeoclimatic proxies specific for temperature or precipitation is still necessary for this climatologically important region

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