Water pH and temperature in Lake Biwa from MBT'/CBT indices during the last 280 000 years

T Ajioka,H Kitagawa,K Takemura,A Hayashida,M Yamamoto

doi:10.5194/cp-10-1843-2014

T Ajioka, H Kitagawa + Show 3 more

Open Access

https://doi.org/10.5194/cp-10-1843-2014

Copy DOI

Abstract

Abstract. We generated a 280 000 yr record of water pH and temperature in Lake Biwa, central Japan, by analysing the methylation index (MBT′) and cyclisation ratio (CBT) of branched tetraethers in sediments from piston and borehole cores. Our aim was to understand the responses of precipitation and air temperature in central Japan to the East Asian monsoon variability on orbital timescales. Because the water pH in Lake Biwa is determined by phosphorus and alkali cation inputs, the record of water pH should indicate the changes in precipitation and temperature in central Japan. Comparison with a pollen assemblage in a Lake Biwa core suggests that lake water pH was determined by summer temperature in the low-eccentricity period before 55 ka, while it was determined by summer precipitation in the high-eccentricity period after 55 ka. From 130 to 55 ka, the variation in lake pH (summer precipitation) lagged behind that in summer temperature by several thousand years. This perspective is consistent with the conclusions of previous studies (Igarashi and Oba, 2006; Yamamoto, 2009), in that the temperature variation preceded the precipitation variation in central Japan.

Highlights

The East Asian monsoon governs the climate of East Asia (Wang et al, 2003), and East Asian monsoon variability on orbital timescales has been the topic of many studies, which have revealed that it has responded to precession; the timing of monsoon variability continues to be debated
The pollen record in the north-western Pacific off central Japan shows that the East Asian monsoon has been strongest at the October–November perihelion in a precession cycle (Heusser and Morley, 1985; Igarashi and Oba, 2006)
We investigated branched Glycerol dialkyl glycerol tetraethers (GDGTs) in sediments from borehole BIW08-B and piston core BIW07-6 in

Summary

Introduction

The East Asian monsoon governs the climate of East Asia (Wang et al, 2003), and East Asian monsoon variability on orbital timescales has been the topic of many studies, which have revealed that it has responded to precession; the timing of monsoon variability continues to be debated. Kutzbach (1981) hypothesised that the Asian monsoon responds to insolation changes at low latitudes, which are regulated by precession. Kutzbach (1981) hypothesised that the Asian monsoon responds to insolation changes at low latitudes, which are regulated by precession. According to this hypothesis, the summer monsoon is maximal when Northern Hemisphere summer insolation is maximal in the precession cycle. Oxygen isotope records from cave stalagmites in China have demonstrated that summer monsoon variability was pronounced at the precession cycle and maximal at the July–August precession (e.g. Wang et al, 2001, 2008; Yuan et al, 2004; Dykoski et al, 2005). Clemens and Prell (2003) reported that Indian summer monsoon variability showed both precession and obliquity cycles and was maximal at the November perihelion on the precession band. The conclusions have varied according to the proxy record used

Objectives

Methods

Results

Discussion

Conclusion