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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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The Importance of Spring Mixing in Evaluating Carbon Dioxide and Methane Flux From a Small North‐Temperate Lake in Wisconsin, United States
Abstract In limnological studies of temperate lakes, most studies of carbon dioxide (CO2) and methane (CH4) emissions have focused on summer measurements of gas fluxes despite the importance of shoulder seasons to annual emissions. This is especially pertinent to dimictic, small lakes that maintain anoxic conditions and turnover quickly in the spring and fall. We examined CO2and CH4dynamics from January to October 2020 in a small humic lake in northern Wisconsin, United States through a combination of discrete sampling and high frequency buoy and eddy covariance data collection. Eddy covariance flux towers were installed on buoys at the center of the lake while it was still frozen to continually measure CO2and CH4across seasons. Despite evidence for only partial turnover during the spring, there was still a notable 19‐day pulse of CH4emissions after lake ice melted with an average daytime flux rate of 8–30 nmol CH4m−2s−1. Our estimate of CH4emissions during the spring pulse was 16 mmol CH4m−2compared to 22 mmol CH4m−2during the stratified period from June to August. We did not observe a linear accumulation of gases under‐ice in our sampling period during the late winter, suggesting the complexity of this dynamic period and the emphasis for direct measurements throughout the ice‐covered period. The results of our study help to better understand the magnitude and timing of greenhouse gas emissions in a region expected to experience warmer winters with decreased ice duration.
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- PAR ID:
- 10448110
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 126
- Issue:
- 12
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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