Late Pleistocene and early Holocene climate and limnological changes in the Sierra Nevada, California, USA inferred from midges (Insecta: Diptera: Chironomidae)

Chironomid and stratigraphic analyses of a lake sediment core recovered from a high-elevation lake in the central Sierra Nevada, California, USA, was undertaken to assess chironomid community development during the Pleistocene–Holocene transition and to quantitatively reconstruct the thermal regime that existed during this interval. Between 14 800 cal yr BP and 13 700 cal yr BP the chironomid community consisted almost exclusively of Heterotrissocladius, suggesting this period was characterized by extremely cold climatic conditions. Evidence of post-glacial climatic amelioration, as manifested by increases in thermophilous chironomid taxa, head capsule concentrations, and taxon richness and diversity, commenced at approximately 13 300 cal yr BP. In order to quantify the magnitude of the water temperature changes associated with post-glacial climatic amelioration, a recently developed chironomid-based inference model for surface water temperature was applied to the subfossil chironomid assemblages. The one-component, weighted-averaging partial least squares (WA-PLS) model has an r2jack=0.72, RMSEPjack=1.1°C and a maximum bias of 1.24°C. The reconstructed surface water temperatures suggest a minimum warming of approximately 4.7°C occurred during the Pleistocene–Holocene transition. However, warming during this interval may not have been monotonic. Evidence of the Younger Dryas has been previously discovered in the study area and adjacent regions; Our research indicates that changes in chironomid community composition and an inferred short-term cooling event occurred between 12 000 cal yr BP and 11 500 cal yr BP, which may represent a local manifestation of the Younger Dryas. Chironomid community development during the Pleistocene–Holocene transition appears to primarily reflect the influence of changing climate conditions.