Assessing the potential of bacterial and archaeal membrane lipids (GDGTs) to reconstruct Late Pleistocene and Holocene climatic changes in the Canary Islands

Sedimentary records covering the Late Pleistocene show glacial-interglacial and millennial temperature changes accompanied with, for instance, rainfall and vegetation changes at the global and regional scales. However, such records are missing for the islands of Macaronesia. Here we generate three sedimentary records over the last 10,000 to 45,000 years from the islands of Tenerife, Gran Canaria, and La Gomera using glycerol dialkyl glycerol tetraethers (GDGTs). At the global scale, air temperature and soil pH influence GDGT distributions in soils, although these biomarkers also react to other environmental factors (e.g., land use, vegetation, and soil moisture and chemistry) and shifts in bacterial and archaeal communities. Accordingly, we examined several GDGT-based proxies, notably those using bacterial branched GDGTs (brGDGTs), to assess their applicability in the Canary Islands. Our preliminary results show drastic downcore and inter-site changes in GDGT distributions, with brGDGT-based air temperature ranges larger than 10 °C over the last 10,000 to 45,000 years when applying global calibrations at the three study sites. Air temperatures and soil pH inferred from brGDGTs decrease in Tenerife and La Gomera over the end of the African Humid Period, which suggests an effect of reduced rainfall on brGDGTs, possibly accompanied with a shift in bacterial communities. Air temperatures inferred from brGDGTs show a general increase over the last 27,000 years in Gran Canaria, whereas cyclization and isomerization indices of brGDGTs suggest typically opposite changes in soil pH, in disagreement with global-scale patterns from surficial soils. Our GDGT-based records also show a few drastic increases in archaeal GDGT abundances relative to the full GDGT pool after the Last Glacial Maximum, notably in Gran Canaria and La Gomera, partly related to the rainfall increase during the African Humid Period. Our preliminary application of GDGT-based proxies in the Canary Islands reveals complex environmental influences on soil bacterial and archaeal lipids, which may also be related with local climate and vegetation dynamics. Our preliminary study also motivates a follow-up GDGT study in surficial soils from the Canary Islands to establish, for instance, a brGDGT-temperature calibration suitable for this archipelago.