Responses of primary producers, anoxia, and chemical feedback to Late Glacial climate change: Insights from a paired lake approach

Abstract Worldwide, lacustrine ecosystems are threatened by eutrophication and deoxygenation. Both processes are driven by the combined effects of human activities and climate change. Understanding the pre‐anthropogenic nexus between warming, eutrophication, deoxygenation, and related feedback is essential to determine how lakes respond to rapid climate change. We investigate the responses of primary producers, stratification, and nutrient cycling in a small Central European lake (Übeschisee, Swiss Plateau) to rapid climate change during Late Glacial times (17–11 ka). After 16.2 ka (Heinrich Stadial; HS1) and during the Bølling/Allerød interstadial, Übeschisee experienced natural eutrophication following summer warming and vegetation development in the catchment. Anoxia events with blooms of sulfur bacteria systematically established during colder periods of HS1 (16.5 ka), the Older Dryas (14 ka), the Gerzensee Oscillation (13.2 ka), and the Younger Dryas (12.7–11.7 ka). Anoxia events also caused reductive dissolution of Mn; labile P was always efficiently recycled. Algal communities responded to anoxia events, but the excursions of community composition were reversible. Ti follows NGRIP Dust, suggesting that Übeschisee provides a continuous record of dust deposition with high rates during colder periods. The paired lake approach with adjacent Amsoldingersee shows that the results are robust and regionally reproducible, and that common drivers influenced both lakes simultaneously.