No abstract

During the last decade, the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in lacustrine sediments has been widely used to reconstruct past variations in lake temperature. A prerequisite for the application of brGDGTs to lacustrine paleoclimate reconstructions is to understand the sources of brGDGTs in lake systems and the processes that influence their distribution. In this study, we investigated the distribution of brGDGTs in core-top sediments from 35 lakes across China, with a broad mean annual air temperature (MAAT) range but a constrained pH range, to explore the effect of temperature. The results reveal a contrasting response of MBT'5ME and MBT'6ME to temperature in lake environments compared to that in soils. The sedimentary distributions of 5-and 6-methyl brGDGTs exhibit different relationships with temperature, with most of the latter being correlated to MAAT while the former responding to temperature by only hexamethylated compounds. In both global and Chinese soils, most 6-methyl brGDGTs have no relationship with MAAT but the distribution of 5-methyl brGDGTs is correlated with MAAT. The different behaviors suggest that both 5-and 6methyl brGDGTs-producing communities might be different in lakes and soils. In addition, in lakes from cold regions (MAAT < 5 °C), the brGDGT distribution correlates only with warm season temperatures (April to October) but exhibits no correlation with cold seasons, suggesting a seasonal bias in brGDGT production in these lakes. This bias towards the warm season is not found in lakes from warmer regions (MAAT > 5 °C). Based on these results we propose new temperature calibrations for paleotemperature reconstructions in Chinese alkaline lakes. Highlights 5-and 6-methyl brGDGTs measured in 35 Chinese lakes Seasonal bias towards warm months in cold region lakes Different responses to temperature between lakes and soils Highlights (for review)

No abstract

No abstract

The distributions of microbial tetraether lipids, i.e. glycerol dialkyl glycerol tetraethers (GDGTs), were investigated in a variety of Chinese soils featured by a wide range of pH values in different climate zones. The bacterial branched GDGTs and archaeal isoprenoid GDGTs were found to be widely distributed in Chinese soils and their relative abundance was controlled primarily by soil pH. The bacterial bGDGTs usually dominate over archaeal iGDGTs in abundance when the soil pH is below 8.0. However, archaeal iGDGTs become dominant and the abundance of halophilic archaea characterized by GDGT V without cyclopentyl ring increases dramatically in the alkaline soil with pH greater than 8.0. The relative abundance of archaeal iGDGTs to bacterial bGDGTs was defined here as RAI index. The RAI index decreases with elevated soil pH and a linear correlation is found between them, indicating that the relative abundance of archaeal iGDGTs to bacterial bGDGTs increases with increased pH. The RAI index thus could be a novel proxy of the pH values of paleosol. The terrestrial input index, BIT (Branched and Isoprenoid Tetraethers Index), decreases with increased soil pH, suggesting that soil pH should be taken into consideration when the terrestrial contribution to marine sediments is estimated by BIT index. Moreover, the TEX 86 index cannot be used to reconstruct sea surface temperature in the sediments featured by a large terrestrial input. GDGTs, Archaea, BIT index, soil pH Citation:Yang H, Ding W H, Wang J X, et al. Soil pH impact on microbial tetraether lipids and terrestrial input index (