Evidence for centennial-scale Mid-Holocene episodes of hypolimnetic anoxia in a high-altitude lake system from central Tian Shan (Kyrgyzstan)

Few sedimentary archives of lake meromixis are available in palaeolimnological records, because long-term observations limited time and indisputable sediment proxies hypolimnetic anoxia still scarce. Here we use visible near infrared (VNIR), short-wave infra-red (SWIR) hyperspectral imaging combined with geochemical analyses to reconstruct stratification history, redox status mixing conditions the water column Lake Son Kol (Kyrgyzstan) Central Tian Shan during last 8500 years. In particular, detection Bacteriopheophytin a (Bphe a), pigment produced by anoxygenic phototrophic bacteria at chemocline meromictic lakes, emphasizes episodes multi-decadal centennial Kol. Phases inferred from deposition dark organic sediments within stratified system, which occurred periods increased snowmelt (and solid winter precipitation) warmer spring/summer temperatures that promoted floods export terrestrial material catchment. Prolonged euxinic bottom waters (involving development stable chemocline) reported around 8500, 8400, 8200–7800, 7700–7500, 7300–7000, 6500–6100, 6000–5700 5500–5250 cal yr BP. At ca. 5250 BP, abruptly vanished as tipped into regime predominantly cooler well-mixed (predominance oxygenic phototrophs), coeval higher levels. The disappearance coincides strengthened wind imply enhanced overturning upward nutrients column. This study reveals strong potential imaging, combination more classical approaches, trophic history explore controlling mechanisms work on decadal timescales. Our results outline how abrupt ecosystem changes may occur even absence anthropogenic climate change.