The predominance of young carbon in Arctic whole-lake CH4 and CO2 emissions and implications for Boreal yedoma lakes

Clayton Drew Elder, Jet Propulsion Laboratory, cdelder@uci.edu (Presenter)
Xiaomei Xu, University of California, Irvine, xxu@uci.edu
Jennifer Walker, University of California, Irvine, jclehman@uci.edu
Katey Marion Walter Anthony, University of Alaska, Fairbanks, kmwalteranthony@alaska.edu
John Pohlman, USGS, jpohlman@usgs.gov
Chris Arp, University of Alaska, Fairbanks, cdarp@alaska.edu
Benjamin Gaglioti, Lamont-Doherty Earth Observatory, gaglioti@ldeo.columbia.edu
Amy Townsend-Small, University of Cincinnati, townseay@ucmail.uc.edu
Hinkel Kenneth, Michigan Technological University, kmhinkel@mtu.edu
Claudia Czimczik, University Of California, Irvine, czimczik@uci.edu

Lakes in Arctic and Boreal regions are hotspots for atmospheric exchange of the greenhouse gases CO2 and CH4. Thermokarst lakes are a subset of these Northern lakes that may further accelerate climate warming by mobilizing ancient permafrost C (> 11,500 years old) that has been disconnected from the active C cycle for millennia. Northern lakes are thus potentially powerful agents of the permafrost C-climate feedback. While they are critical for projecting the magnitude and timing these feedbacks from the rapidly warming circumpolar region, we lack datasets capturing the diversity of northern lakes, especially regarding their CH4 contributions to whole-lake C emissions and their ability to access and mobilize ancient C.

We measured the radiocarbon (14C) ages of CH4 and CO2 emitted from 60 understudied lakes and ponds in Arctic and Boreal Alaska during winter and summer to estimate the ages of the C sources yielding these gases. Integrated mean ages for whole-lake emissions were inferred from the 14C-age of dissolved gases sampled beneath seasonal ice. Additionally, we measured concentrations and 14C values of gases emitted by ebullition and diffusion in summer to apportion C emission pathways.

Using a multi-sourced mass balance approach, we found that whole-lake CH4 and CO2 emissions were predominantly sourced from relatively young C in most lakes. In Arctic lakes, CH4 originated from 850 14C-year old C on average, whereas dissolved CO2 was sourced from 400 14C-year old C, and represented 99% of total C flux. Although ancient C had a minimal influence (11% of total emissions), we discovered that lakes in finer-textured aeolian deposits (Yedoma) emitted twice as much ancient C as lakes in sandy regions.

In Boreal, yedoma-type lakes, CH4 and CO2 were fueled by significantly older sources, and mass balance results estimated CH4-ebullition to comprise 50-60% of whole-lake CH4 emissions. The mean 14C-age of Boreal emissions was 6,000 14C-years for CH4-C, and 2,400 14C-years for CO2-C. Seasonal differences in dissolved CH4 revealed a clear influence of trapped ebullition dissolving into the water below lake ice in Boreal, but not Arctic lakes. Together, our data demonstrate that regional surficial geology exerts a larger control than climate on C ages and gas emission pathways from lakes.

Associated Project(s): 

• Miller-C-05

Poster Location ID: 7

Session Assigned: Carbon Dynamics