Production rates and radiocarbon signatures of greenhouse gases from incubations of thermokarst lake sediments in Kuujjuarapik

This dataset presents results from anoxic incubations of thermokarst lake surficial sediments from northern Quebec (Kuujjuarapik) across a range of temperatures (4, 12, and 22˚C). We measured methane (CH4) and carbon dioxide (CO2) production rates and associated radiocarbon values.

In the summers of 2019 and 2021, sediment samples were collected from five lakes two different sites. The first lake (KWK1), located in the KWK valley, was formed due to mineral soil permafrost collapse. The remaining four lakes are situated in the SAS2 peatland. Permafrost in this region is found in palsa permafrost mounds, while permafrost-free areas consist of bogs with peat moss and sedges, along with numerous thermokarst lakes. The lakes sampled include SAS2X, SAS2C, SAS2A, and SAS2B. Sampling involved collecting the upper 5–10 cm of surface sediments from the central regions of the lakes using an Eckman dredge. In 2019, samples were stored in sealed 0.5 L Nalgene bottles, while in 2021, Whirlpak bags were used. The sediments were stored at 4 °C until utilized for the subsequent incubation experiments.

Experiments were prepared by combining ~10 grams of homogenized sediment from the sites with 20 mL of M9 growth medium in anaerobic conditions. The slurries were sealed in serum bottles, flushed with pure Nitrogen, and incubated at three temperatures (4 °C, 12 °C, and 22 °C) with duplicates or triplicates for each site. Controls were added to assess abiotic CH4 production and verify the absence of CH4 sources other than sediment. Incubations were terminated when there was sufficient CH4 for radiocarbon measurements, approximately 1 mg of carbon or 3% CH4 in the headspace.

Three sets of incubations were conducted. The first involved sediment collected in August 2019 from SAS2B, SAS2C, and KWK1 lasting 105 days. The second set, assembled eight months later due to COVID-19 restrictions, used the same sediment and extended the incubation to 219 days. The third set utilized sediment collected in August 2021 from SAS2X, SAS2C, and SAS2A for 260 days.

Results in this dataset include then, production rates of CH4 and CO2, radiocarbon values of CH4 and CO2, and geochemical and isotopic characteristics of the sediment used for the incubations.