Controls on brGDGT Production in the Seasonally Anoxic Water Column and Sediments of Rotsee (Lake Rot)

Journal article

Plain Language Summary: Understanding past climate change relies on chemical “proxies” that record environmental conditions. One such proxy, the MBT'5ME index, is based on special bacterial lipids (brGDGTs) preserved in lake sediments. However, the processes controlling these lipids are still debated. We studied Rotsee, a small Swiss lake that develops warm surface waters and cold, oxygen‐poor bottom waters each summer. Over 1 year, we collected monthly water samples from both layers, along with sediments and nearby soils. We measured bacterial lipids and DNA and compared them with environmental factors such as temperature, oxygen, and pH. In surface waters, MBT'5ME responded only weakly to summer warming, but another measure, the isomer ratio (IR), tracked temperature more clearly. The two indices were also strongly linked, suggesting IR can help identify lipids that truly reflect surface water signals. In deep waters, MBT'5ME was instead influenced by pH, while IR reflected oxygen availability. DNA analysis showed that not only Acidobacteria but also several different bacterial groups potentially contribute to brGDGT production. Overall, our findings show that lake mixing and stratification shape these lipid signals. This can improve the reliability of brGDGTs as tools for reconstructing past climates from lake sediments.

Authors: Ajallooeian, F; Dubois, N; Ladd, SN; Lever, MA; Schubert, CJ

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Geophysical Union
• Journal: Journal of Geophysical Research: Biogeosciences
• Volume: 130
• Issue: 12
• Article number: e2025JG009132
• Publication date: 2025-12-07
• Acceptance date: 2025-11-18
• DOI: 10.1029/2025jg009132
• EISSN: 2169-8961
• ISSN: 2169-8953
• Language: English
• Keywords: paleothermometry; microbial lipids; lake stratification; biomarkers; anoxic water column; brGDGTs