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

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 higheccentricity 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.

A refined paleotemperature calibration for New Zealand limnic environments using differentiation of branched glycerol dialkyl glycerol tetraether (brGDGT) sources

“…Copyright # 2016 John Wiley & Sons, Ltd. season of brGDGTs in temperate lakes. Applying a reconstruction restricted to MST might thus result in missing potential in situ bio-production during other times of the year and it also needs to be considered that brGDGTs from paleo-records comprise a mixed signal over longer time periods less specific to seasonal growth periods (Schoon et al, 2013;Ajioka et al, 2014). However, in regimes with a long period of ice cover on lakes, such as in the Arctic or Antarctic, microbial productivity is shifted to the summer season and hence in such cases summer temperature should be preferred for correlation (e.g.…”

“…These authors subsequently proposed that the methylation index of branched tetraethers (MBT) and cyclization index of branched tetraethers (CBT) together enable the reconstruction of mean annual air temperature (MAT) in terrestrial environments such as soils and peat bogs. As brGDGTs also occur ubiquitously in lake sediments, the MBT/CBT index has been used to determine variation in continental climates in several paleoenvironmental studies (Tierney and Russell, 2009;Tierney et al, 2010;Pearson et al, 2011;Loomis et al, 2012;Niemann et al, 2012;Ajioka et al, 2014;Colcord et al, 2015). Many of those studies, however, have shown that the application of temperature calibrations derived from the distribution of brGDGTs in soils generally results in reconstructed MAT values that underestimate actual temperature trends.…”

Branched GDGT variability in sediments and soils from catchments with marked temperature seasonality

“…Given the temperature and pH dependence of brGDGT indices in soils and peats, they are used as proxies for these parameters in loess-palaeosol, peat and sedimentary records (e.g. Weijers et al, 2007;Schouten et al, 2008;Rueda et al, 2009;Ballantyne et al, 2010;Bendle et al, 2010;Tyler et al, 2010;Fawcett et al, 2011;Peterse et al, 2011;Gao et al, 2012;Niemann et al, 2012;Zech et al, 2012;Ajioka et al, 2014b;Sanchi et al, 2014;Cao et al, 2017;Wang et al, 2017a). However, brGDGTs are also argued to be produced in situ within the water column or the sediments of aquatic settings (e.g.…”