• Assessment of the applicability of 3-hydroxy fatty acids as environmental proxies in lakes. • 3-Hydroxy fatty acids mainly produced in situ in lakes from France and Chile. • Specific 3-hydroxy fatty acid homologues indicators of lacustrine and soil settings. • First global calibration between 3-OH FAs and MAAT/pH in lakes using machine-learning. • Potential of 3-OH FAs as environmental proxies in lakes, complementarily with brGDGTs. Revealing high-resolution paleoclimate records in lakes is essential for our understanding of the climate system. To date, the ubiquitous branched glycerol dialkyl glycerol tetraethers (brGDGTs) are largely used to reconstruct for temperature and pH in continental settings. Recently, other bacterial membrane lipids – 3-hydroxy fatty acids (3-OH FAs) – have been proposed as independent temperature and pH proxies in soils, but their applicability in lakes remains poorly investigated. This study assessed the lipid origin of and key environmental influences on the 3-OH FAs in lakes, while establishing the first global dataset of lacustrine 3-OH FAs. Using 72 lake sediments in the French Alps and Chile, we showed that 3-OH FAs were mainly produced in situ . The distinct 3-OH FA signature in lakes and soils was highlighted at the global scale by combining all data available so far. Mean Annual Air Temperature (MAAT) and pH showed weak or no linear relationships with existing 3-OH FA based proxies in the available global lake dataset ( n = 92). This is likely due to the influence of confounding environmental factors, as suggested by the detailed study of 37 lakes in the French Alps. The complexity of factors influencing 3-OH FA distribution was taken into account through machine-learning algorithms, leading to strong correlations between 3-OH FAs and MAAT or pH lakes. Our study highlights the potential of 3-OH FAs as MAAT and pH proxies in lakes at the global scale and the complementarity with existing brGDGT proxies.
Ke et al. (2026) studied this question.