Carbon isotopes record lake water anoxia and methanogenesis under warm and cold climate conditions at Lake El’gygytgyn, Far East Russia

Abstract:

As the climate warms due to anthropogenic climate change, the sensitive ecosystems in and around Arctic lakes are expected to be significantly impacted. These changes will likely influence lacustrine primary production and carbon cycling, with potential implications for regional and global climate. Here, we present a record of stable carbon isotopes (𝛿¹³C) of bulk sediment from Lake El’gygytgyn, a meteorite impact crater lake in NE Siberia. Throughout the 3.4 Ma record, 𝛿¹³C values average -28‰, reflecting a dominantly terrestrial organic matter source. Fluctuations occur periodically throughout the record with negative 𝛿¹³C excursions to values of -37‰. These depleted 𝛿¹³C values are present during glacial and interglacial periods, and likely occur as a result of methanogenesis during prolonged lake anoxia. While bottom water anoxia has previously been linked to cold glacial periods with perennial lake ice cover at Lake El’gygytgyn, the occurrence of negative 𝛿¹³C excursions during warm intervals provides an additional pathway, increased lacustrine productivity, as a driver of anoxia and methanogenesis. To support interpretation of the 𝛿¹³C record, we utilize previous work from Lake El’gygytgyn, including records of percent biogenic silica, total organic carbon, sediment facies, and pollen and biomarker based temperature reconstructions. Our results indicate that changes in lacustrine carbon cycling occur under warm and cold climate conditions and have implications for the role Arctic lakes may play in the global carbon cycle.