A large proportion of the world’s freshwater lakes and ponds are in northern high-latitude regions, which are warming almost twice as fast as the global average. As temperatures increase, it is anticipated that lake methane production will also increase, resulting in a positive feedback to global warming. Palaeoenvironmental proxy data have shown substantial climate variation during the Holocene in Alaska, including a warmer-than-present Holocene Thermal Maximum (HTM) at c. 11 - 6 cal ky BP. By quantifying lake methane production under earlier warm periods, we can provide empirical data to validate future methane production scenarios. Past methane production can be estimated from changes in the composition of stable carbon isotopes (δ¹³C values) within different components of a lake ecosystem. As methane typically has characteristically highly negative δ¹³C values (-85 to -65‰), a methane signal can be traced through the ecosystem. We use δ¹³C values of aquatic invertebrate remains and specific biomarker proxies for methane-generating bacteria. The δ¹³C values measured on sedimentary remains of these proxies are lower when methane-derived carbon is an important part of the lake carbon cycle. Our proxy-based estimates of methane production from two lakes from boreal/ interior Alaska suggest that during the HTM, methane availability could have been 2-5 times higher than at present.

Primary Presenter: Roseanna Mayfield, Newcastle University (roseanna.mayfield@newcastle.ac.uk)

Authors:

Nichola Strandberg, University of Southampton  (N.A.Strandberg@soton.ac.uk)

Matthew Wooller, University of Alaska Fairbanks  (mjwooller@alaska.edu)

Simon Turner, University College London  (simon.turner@ucl.ac.uk)

Mary Edwards, University of Southampton  (m.e.edwards@soton.ac.uk)

Jessica Whiteside, University of Southampton  (J.Whiteside@soton.ac.uk)

Kim Davies, Bournemouth University   (daviesk@bournemouth.ac.uk)

Maarten van Hardenbroek van Ammerstol, Newcastle University  (maarten.vanhardenbroek@newcastle.ac.uk)