Variations of phytoplankton productivity and community evidenced by sterol records in Lake Tuofengling, a crater lake in northeast China, during the last 25,000 years

Abstract

Knowledge regarding phytoplankton productivity and community structures under past warming scenarios is crucial for assessing the responses of aquatic ecosystems to global warming. This study presents high-resolution sterol records from Lake Tuofengling, a crater lake in northeast China, offering new insights into the evolution of lake productivity and algal community since the Last Glacial Maximum. The sedimentary record reveals abundant sterols, including cholesterol, brassicasterol, stigmasterol, sitosterol, and dinosterol, which serve as valuable paleolimnological proxies. A significant decline in the sitosterol/stigmasterol ratio since the Bølling-Allerød interstadial indicates a substantial increase in autochthonous contributions, coinciding with rising lake levels. A notable increase of the productivity of dinoflagellates relative to diatoms occurred around 10.5 cal ka BP, as indicated by sharp decrease in biogenic silica content and increase in dinosterol/sitosterol. This ecological shift was likely driven by changes in growing season temperatures and nutrient availability. The period between ∼6–4.2 cal ka BP was marked by significantly higher sterol abundances, indicating elevated lake productivity that was probably linked to increased precipitation during the mid-Holocene. Subsequently, around 4.2 cal ka BP, there was a sudden decrease in sterol concentrations and corresponding lake primary productivity, which can be ascribed to a sensitive response of the lake ecosystem to the 4.2-ka millennial event. Since approximately 3 cal ka BP, intensified human activities and increased dust deposition in northern China have significantly impacted the lake's ecological dynamics, resulting in high-amplitude fluctuations in sterol concentrations and a gradual increase in abundance of brassicasterol relative to dinosterol. The observed decoupling between diatom-dinoflagellate relative abundances and overall lake productivity demonstrates the complex responses of aquatic ecosystems to both natural and anthropogenic environmental changes.