Contrasting long‐term changes in lake trajectories linked to differences in wind‐induced mixing in the Peruvian Andes

Abstract

Abstract Historically, many high‐elevation lakes in the tropical Andes have been observed to mix frequently, with rare, brief periods of thermal stratification. As temperatures have risen in the Andes over the past several decades, thermistor data have shown that many lakes are now experiencing longer periods of thermal stratification with resultant ecological restructuring. Palaeolimnological studies from these lakes have recorded striking diatom assemblage shifts, coeval with recent changes in thermal stratification. Here, we analyse subfossil diatom assemblages from a wind‐sheltered lake, Laguna Yanacocha, in the Peruvian Andes. Thermistors deployed in the lake indicated that Laguna Yanacocha was more strongly thermally stratified and for longer periods than other nearby lakes. We hypothesised that, owing to its sheltered position, this lake is likely to have exhibited enhanced periods of thermal stratification even before the period of recent warming, and that these limnological conditions would be tracked in the subfossil diatom record. The diatom assemblages from Laguna Yanacocha recorded consistently high abundances of the obligate planktonic taxon Discostella stelligera over the last several centuries. This taxon is known to flourish with warming and has been shown to increase in abundance with the onset of thermally stratified conditions in other Andean waterbodies, as well as lakes globally. The dominance of D. stelligera throughout the entire sediment record suggests a long history of thermal stratification that is likely to be a consequence of the study lake's surrounding topography, which shelters it from wind mixing. The sub‐fossil assemblage data from Laguna Yanacocha contrasts with assemblages from previously studied wind‐swept lakes in the Andes, which primarily show low abundances of D. stelligera before well‐documented temperature increases. The fossil diatom record from Laguna Yanacocha may provide an indication of how other lakes from the region will respond to warming temperatures and enhanced thermal stratification.