Is climate warming causing eutrophication and anoxia? Lessons learned from Late-Glacial sediments of Lakes Amsoldingen and Soppen, Switzerland.

The Soppensee pigment record responded to the initial Bølling warming (14.6 cal. kyr. BP) by developing eutrophic conditions in a stratified lake with hypolimnetic anoxia and redissolution of redox sensitive phosphorous, iron and manganese. In Amsoldingersee, pigment data shows clear anoxic events that pre-date the Bølling warming and relate consistently to the colder phases within the Late-Glacial (GS-2/Heinrich Event 1, GI-d, GI-c3, and GS-1). In contrast to Soppensee, total chlorophyll, and carotenoids peaked when the climate was cool and dry, advocating for substantial aquatic production during cold periods.