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• 3-OH FAs and brGDGTs analyzed in soils from an altitudinal transect in the French Alps. • Investigation of the environmental factors controlling the distribution of bacterial lipids. • Influence of soil traits predominant over MAAT. • Statistical identification of the individual bacterial lipids influenced by MAAT/pH required. • Development of local calibrations with MAAT and pH based on such identification. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are a family of bacterial lipids widely used for temperature and pH reconstructions in terrestrial settings. 3-hydroxy fatty acids (3-OH FAs) with 10–18 carbon atoms, produced by Gram-negative bacteria, have been recently proposed as independent and complementary proxies of temperature and pH in terrestrial environments. Nevertheless, the correlations between mean annual air temperature (MAAT)/pH and bacterial lipid (brGDGTs/3-OH FAs) distributions show a large degree of scatter, as the relative abundance of these lipids is influenced by factors other than temperature and pH. A full understanding of the environmental parameters influencing bacterial lipid distribution in soils is required to increase the reliability of the temperature and pH proxies based on these compounds in terrestrial environments. The aim of this work was to determine and quantify the cumulative effect of environmental parameters on the distribution of both brGDGTs and 3-OH FAs along a well-documented composite altitudinal transect in the French Alps (234–2748 m). Redundancy analysis revealed that the influence of local parameters (pH and to a lesser extent, soil moisture and grain size, related to vegetation and soil types) on brGDGT and 3-OH FA distributions amounted to 48.1% and 26.1%, respectively, and was predominant over MAAT. This likely explained the weak or lack of relationships between MAAT and brGDGT-/3-OH FA-based indices in this region. The identification of lipids whose fractional abundance is correlated with MAAT or pH allowed the development of local calibrations with MAAT/pH applicable in the French Alps, which are representative of highly contrasted microenvironments, reflecting different types of soil and vegetation. The present study highlighted the importance of constraining the environmental factors affecting the distribution of 3-OH FAs and brGDGTs in terrestrial settings prior to any paleoenvironmental reconstruction. Such an approach should be reproduced in other sites, where local factors could also strongly influence the bacterial lipid distribution. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lipid biomarkers from loess-paleosol sequences inform on palaeoenvironmental changes. • Shrub versus grass cover shifts suggested by n -alkyl compounds and triterpenoids. • Regional temperature variations suggested by bacterial membrane lipids. • Distinction between anthropogenic and climate impacts on local vegetation cover. • Significant impacts of reindeer herders on vegetation in sub-Arctic environment. Arctic reindeer herders demonstrate resilience to climate fluctuations by adjusting their pastoral practices to changing environments. The multiple phases of occupation at one of the oldest identified reindeer-herding sites, I A ^ rte 6 on the I A ^ mal peninsula, northwest Siberia, are thought to be linked to its local vegetation cover. Here we provide information on local palaeovegetation and climate shifts which occurred between the 7th and the 11th century CE based on lipid biomarkers. Aliphatic compounds, pentacyclic triterpenoids, branched glycerol dialkyl glycerol tetraethers (brGDGTs) and other lipids were analysed in four separate palaeosols from two loess-palaeosol sequences at the site. Based on different indices, the impact of human- or root-derived lipids and post-depositional microbial degradation on the signature of the studied pedosequences seem limited, which indicates that palaeobiomarkers are well preserved and representative of the analysed compounds. n -Alkanes, n -carboxylic acids, n -aldehydes and pentacyclic triterpenoids point to the progressive colonization of grasses, sedges and herbs at the site, which can be attributed to the regional decrease in temperature suggested by bacterial-derived brGDGTs. During the last phase of occupation, however, when proxies point to increasing temperatures, and shrubs would normally be expected to return, the shrub cover continued to decrease, probably due to the impact of camping and holding reindeer at the site. The decoupling trends observed for particular pentacyclic triterpenoids as potential dwarf birch biomarkers could suggest a preferential shift of species within shrubs, probably influenced by human activities. Multi-family lipid biomarker analysis therefore made it possible to distinguish anthropogenic impacts on the local vegetation cover from regional climatic changes, and show how significant the impacts of humans on local vegetation can be, even in extreme environments where such activities are limited. [ABSTRACT FROM AUTHOR]