oa Distribution of 3-OH FAs and brGDGTs in Lakes of the French Alps and Chile: Implications for Palaeoclimate Reconstructions

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) remain the only organic proxy for temperature and pH reconstructions in continental settings, with however high residual error (RMSE ∼ 4 °C). Recently found 3-hydroxy fatty acids present potential as independent and complementary paleoclimate proxies. Previous soil studies proposed indices based on 3-OH FA distributions that linearly correlate with mean annual air temperature (MAAT) and pH. Here, we aim to evaluate the applicability of 3-OH FAs in the lacustrine environments, in comparison to the conventional brGDGT proxies. Two study sites of contrasting climates are selected, the French Alps and Southern Chile. We first detected autochthonous source, i.e., in situ productions, of the lacustrine 3-OH FAs, with significantly higher concentration of 3-OH FAs in lake surface sediments than in soils. Later on, with 11 collected environmental factors, we found mild influence from temperature and pH on the 3-OH FA distributions, while brGDGTs display the opposite. However, with higher-complexity Random Forest and Multilinear algorithms, the predictions of MAAT and pH based on lacustrine 3-OH FAs are strongly correlated with observations. These findings highlighted the potential of 3-OH FAs as environmental proxies in lakes, and could be further evaluated by larger datasets.