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Accelerated warming in the Arctic has led to concern regarding the amount of carbon emission potential from Arctic water bodies. Yet, aquatic carbon dioxide (CO 2 ) and methane (CH 4 ) flux measurements remain scarce, particularly at high resolution and over long periods of time. Effluxes of methane (CH 4 ) and carbon dioxide (CO 2 ) from Toolik Lake, a deep glacial lake in northern Alaska, were measured for the first time with the direct eddy covariance (EC) flux technique during six ice-free lake periods (2010–2015). CO 2 flux estimates from the lake (daily average efflux of 16.7 ± 5.3 mmol m −2 d −1 ) were in good agreement with earlier estimates from 1975–1989 using different methods. CH 4 effluxes in 2010–2015 (averaging 0.13 ± 0.06 mmol m −2 d −1 ) showed an interannual variation that was 4.1 times greater than median diel variations, but mean fluxes were almost one order of magnitude lower than earlier estimates obtained from single water samples in 1990 and 2011–2012. The overall global warming potential (GWP) of Toolik Lake is thus governed mostly by CO 2 effluxes, contributing 86–93% of the ice-free period GWP of 26–90 g CO 2,eq m −2 . Diel variation in fluxes was also important, with up to a 2-fold (CH 4 ) to 4-fold (CO 2 ) difference between the highest nighttime and lowest daytime effluxes. Within the summer ice-free period, on average, CH 4 fluxes increased 2-fold during the first half of the summer, then remained almost constant, whereas CO 2 effluxes remained almost constant over the entire summer, ending with a linear increase during the last 1–2 weeks of measurements. Due to the cold bottom temperatures of this 26 m deep lake, and the absence of ebullition and episodic flux events, Toolik Lake and other deep glacial lakes are likely not hot spots for greenhouse gas emissions, but they still contribute to the overall GWP of the Arctic.
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Effects of long-term climate trends on the methane and CO2 exchange processes of Toolik Lake, Alaska
Methane and carbon dioxide effluxes from aquatic systems in the Arctic will affect and likely amplify global change. As permafrost thaws in a warming world, more dissolved organic carbon (DOC) and greenhouse gases are produced and move from soils to surface waters where the DOC can be oxidized to CO 2 and also released to the atmosphere. Our main study objective is to measure the release of carbon to the atmosphere via effluxes of methane (CH 4 ) and carbon dioxide (CO 2 ) from Toolik Lake, a deep, dimictic, low-arctic lake in northern Alaska. By combining direct eddy covariance flux measurements with continuous gas pressure measurements in the lake surface waters, we quantified the k 600 piston velocity that controls gas flux across the air–water interface. Our measured k values for CH 4 and CO 2 were substantially above predictions from several models at low to moderate wind speeds, and only converged on model predictions at the highest wind speeds. We attribute this higher flux at low wind speeds to effects on water-side turbulence resulting from how the surrounding tundra vegetation and topography increase atmospheric turbulence considerably in this lake, above the level observed over large ocean surfaces. We combine this process-level understanding of gas exchange with the trends of a climate-relevant long-term (30 + years) meteorological data set at Toolik Lake to examine short-term variations (2015 ice-free season) and interannual variability (2010–2015 ice-free seasons) of CH 4 and CO 2 fluxes. We argue that the biological processing of DOC substrate that becomes available for decomposition as the tundra soil warms is important for understanding future trends in aquatic gas fluxes, whereas the variability and long-term trends of the physical and meteorological variables primarily affect the timing of when higher or lower than average fluxes are observed. We see no evidence suggesting that a tipping point will be reached soon to change the status of the aquatic system from gas source to sink. We estimate that changes in CH 4 and CO 2 fluxes will be constrained with a range of +30% and −10% of their current values over the next 30 years.
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- PAR ID:
- 10400133
- Date Published:
- Journal Name:
- Frontiers in Environmental Science
- Volume:
- 10
- ISSN:
- 2296-665X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fenvs.2022.948529
