| 1. |
- Douglas, Peter M. J., et al.
(författare)
-
Clumped Isotopes Link Older Carbon Substrates With Slower Rates of Methanogenesis in Northern Lakes
- 2020
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 47:6
-
Tidskriftsartikel (refereegranskat)abstract
- The release of long-stored carbon from thawed permafrost could fuel increased methanogenesis in northern lakes, but it remains unclear whether old carbon substrates released from permafrost are metabolized as rapidly by methanogenic microbial communities as recently produced organic carbon. Here, we apply methane (CH4) clumped isotope (Delta(18)) and C-14 measurements to test whether rates of methanogenesis are related to carbon substrate age. Results from culture experiments indicate that Delta(18) values are negatively correlated with CH4 production rate. Measurements of ebullition samples from thermokarst lakes in Alaska and glacial lakes in Sweden indicate strong negative correlations between CH4 Delta(18) and the fraction modern carbon. These correlations imply that CH4 derived from older carbon substrates is produced relatively slowly. Relative rates of methanogenesis, as inferred from Delta(18) values, are not positively correlated with CH4 flux estimates, highlighting the likely importance of environmental variables other than CH4 production rates in controlling ebullition fluxes. Plain Language Summary There is concern that carbon from thawed permafrost will be emitted to the atmosphere as methane (CH4). It is currently uncertain whether old organic carbon from thawed permafrost can be converted to CH4 as rapidly as organic carbon recently fixed by primary producers. We address this question by combining radiocarbon and clumped isotope measurements of CH4 from lakes in permafrost landscapes. Radiocarbon (C-14) measurements indicate the age of CH4 carbon sources. We present data from culture experiments that support the hypothesis that clumped isotope values are dependent on microbial CH4 production rate. In lake bubble samples, we observe a strong correlation between these two measurements, which implies that CH4 formed from older carbon is produced relatively slowly. We also find that higher rates of CH4 production, as inferred from clumped isotopes, are not linked to higher rates of CH4 emissions, implying that variables other than CH4 production rate strongly influence emission rates.
|
|
| 2. |
- Goodrich, Jordan P., et al.
(författare)
-
High-frequency measurements of methane ebullition over a growing season at a temperate peatland site
- 2011
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 38, s. L07404-
-
Tidskriftsartikel (refereegranskat)abstract
- Bubbles can contribute a significant fraction of methane emissions from wetlands; however the range of reported fractions is very large and accurate characterization of this pathway has proven difficult. Here we show that continuous automated flux chambers combined with an integrated cavity output spectroscopy (ICOS) instrument allow us to quantify both CH(4) ebullition rate and magnitude. For a temperate poor fen in 2009, ebullition rate varied on hourly to seasonal time scales. A diel pattern in ebullition was identified with peak release occurring between 20:00 and 06:00 local time, though steady fluxes (i.e., those with a linear increase in chamber headspace CH(4) concentration) did not exhibit diel variability. Seasonal mean ebullition rates peaked at 843.5 +/- 384.2 events m(-2) d(-1) during the summer, with a mean magnitude of 0.19 mg CH(4) released in each event.
|
|
| 3. |
- Jansen, Joachim, et al.
(författare)
-
Temperature Proxies as a Solution to Biased Sampling of Lake Methane Emissions
- 2020
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 47:14
-
Tidskriftsartikel (refereegranskat)abstract
- Lake emissions of the climate forcing trace gas methane (CH4) are spatiotemporally variable, but biases in flux measurements arising from undersampling are poorly quantified. We use a multiyear data set (2009-2017) of ice-free CH(4)emissions from three subarctic lakes obtained with bubble traps (n = 14,677), floating chambers (n = 1,306), and surface concentrations plus a gas transfer model (n = 535) to quantify these biases and evaluate corrections. Sampling primarily in warmer summer months, as is common, overestimates the ice-free season flux by a factor 1.4-1.8. Temperature proxies based on Arrhenius functions that closely fit measured fluxes (R-2 >= 0.93) enable gap filling the colder months of the ice-free season and reduce sampling bias. Ebullition (activation energy 1.36 eV) expressed greater temperature sensitivity than diffusion (1.00 eV). Resolving seasonal and interannual variability in fluxes with proxies requires similar to 135 sampling days for ebullition, and 22 and 14 days for diffusion via models and chambers, respectively.
|
|
| 4. |
- Olefeldt, David, et al.
(författare)
-
Net carbon accumulation of a high-latitude permafrost palsa mire similar to permafrost-free peatlands
- 2012
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39, s. L03501-
-
Tidskriftsartikel (refereegranskat)abstract
- Palsa mires, nutrient poor permafrost peatlands common in subarctic regions, store a significant amount of carbon (C) and it has been hypothesized their net ecosystem C balance (NECB) is sensitive to climate change. Over two years we measured the NECB for Stordalen palsa mire and found it to accumulate 46 g C m(-2) yr(-1). While Stordalen NECB is comparable to nutrient poor peatlands without permafrost, the component fluxes differ considerably in magnitude. Specifically, Stordalen had both lower growing season CO2 uptake and wintertime CO2 losses, but importantly also low dissolved organic carbon exports and hydrocarbon (mainly methane) emissions. Restricted C losses from palsa mires are likely to have facilitated C accumulation of unproductive subarctic permafrost peatlands. Continued climate change and permafrost thaw is likely to amplify several component fluxes, with an uncertain overall effect on NECB - highlighting the necessity for projections of high-latitude C storage to consider all C fluxes.
|
|
| 5. |
- Prytherch, John, et al.
(författare)
-
Direct determination of the air-sea CO2 gas transfer velocity in Arctic sea ice regions
- 2017
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 44:8, s. 3770-3778
-
Tidskriftsartikel (refereegranskat)abstract
- The Arctic Ocean is an important sink for atmospheric CO2. The impact of decreasing sea ice extent and expanding marginal ice zones on Arctic air-sea CO2 exchange depends on the rate of gas transfer in the presence of sea ice. Sea ice acts to limit air-sea gas exchange by reducing contact between air and water but is also hypothesized to enhance gas transfer rates across surrounding open-water surfaces through physical processes such as increased surface-ocean turbulence from ice-water shear and ice-edge form drag. Here we present the first direct determination of the CO2 air-sea gas transfer velocity in a wide range of Arctic sea ice conditions. We show that the gas transfer velocity increases near linearly with decreasing sea ice concentration. We also show that previous modeling approaches overestimate gas transfer rates in sea ice regions.
|
|
| 6. |
- Thornton, Brett F., et al.
(författare)
-
Climate-forced changes in available energy and methane bubbling from subarctic lakes
- 2015
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:6, s. 1936-1942
-
Tidskriftsartikel (refereegranskat)abstract
- Strong correlations between seasonal energy input and methane (CH4) bubbling (ebullition) in northern lakes suggest that energy proxies might provide a constraint on the magnitude of future CH4 emissions. Ebullition is a major pathway for transporting anaerobically produced CH4 from lake sediments to the atmosphere and represents a large unquantified CH4 source. In high-latitude, postglacial lakes during the ice-free season, solar shortwave energy input can constrain CH4 productivity via control of sediment temperature. Utilizing long-term climatic predictors, we calculate CH4 ebullition from three subarctic lakes in northern Sweden over the period of 1916-2079. Using observed energy trends, the seasonal average lake CH4 ebullition is predicted to increase by 80% between the 1916-1926 decade and the 2040-2079 period. Present-day seasonal average methane ebullition is estimated to have already increased 24% since the 1916-1926 decade.
|
|
| 7. |
- Thornton, Brett F., et al.
(författare)
-
Double-counting challenges the accuracy of high-latitude methane inventories
- 2016
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:24, s. 12,569-12,577
-
Tidskriftsartikel (refereegranskat)abstract
- Quantification of the present and future contribution to atmospheric methane (CH4) from lakes, wetlands, fluvial systems, and, potentially, coastal waters remains an important unfinished task for balancing the global CH4 budget. Discriminating between these sources is crucial, especially across climate-sensitive Arctic and subarctic landscapes and waters. Yet basic underlying uncertainties remain, in such areas as total wetland area and definitions of wetlands, which can lead to conflation of wetlands and small ponds in regional studies. We discuss how in situ sampling choices, remote sensing limitations, and isotopic signature overlaps can lead to unintentional double-counting of CH4 emissions and proposethat this double-counting can explain a pan-Arctic bottom-up estimate from published sources, 59.7 Tg yr-1(range 36.9–89.4 Tg yr-1) greatly exceeding the most recent top-down inverse modeled estimate of thepan-Arctic CH4 budget (235 Tg yr-1).
|
|
| 8. |
- Thornton, Brett F., et al.
(författare)
-
Methane fluxes from the sea to the atmosphere across the Siberian shelf seas
- 2016
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:11, s. 5869-5877
-
Tidskriftsartikel (refereegranskat)abstract
- The Laptev and East Siberian Seas have been proposed as a substantial source of methane (CH4) to the atmosphere. During summer 2014, we made unique high-resolution simultaneous measurements of CH4 in the atmosphere above, and surface waters of, the Laptev and East Siberian Seas. Turbulence-driven sea-air fluxes along the ship's track were derived from these observations; an average diffusive flux of 2.99mgm(-2) d(-1) was calculated for the Laptev Sea and for the ice-free portions of the western East Siberian Sea, 3.80mgm(-2)d(-1). Although seafloor bubble plumes were observed at two locations in the study area, our calculations suggest that regionally, turbulence-driven diffusive flux alone accounts for the observed atmospheric CH4 enhancements, with only a local, limited role for bubble fluxes, in contrast to earlier reports. CH4 in subice seawater in certain areas suggests that a short-lived flux also occurs annually at ice-out.
|
|
| 9. |
- Wik, Martin, et al.
(författare)
-
Biased sampling of methane release from northern lakes : A problem for extrapolation
- 2016
-
Ingår i: Geophysical Research Letters. - : AMER GEOPHYSICAL UNION. - 0094-8276 .- 1944-8007. ; 43:3, s. 1256-1262
-
Tidskriftsartikel (refereegranskat)abstract
- Methane emissions from lakes are widely thought to be highly irregular and difficult to quantify with anything other than numerous distributed measurement stations and long-term sampling campaigns. In spite of this, a large majority of the study sites north of 50°N have been measured over surprisingly short time periods of only one to a few days. Using long-term data from three intensively studied small subarctic lakes, we recommend that measurements of diffusive methane flux and ebullition should be made over at least 11 and 39 days scattered throughout the ice-free season using depth-stratified sampling at 3 and 11 or more locations, respectively. We further show that low temporal and spatial resolutions are unlikely to cause overestimates. Therefore, we argue that most sites measured previously are likely underestimated in terms of emission potential. Avoiding these biases seen in much of the contemporary data is crucial to further constrain large-scale methane emissions from northern lakes and ponds.
|
|
| 10. |
- Wik, Martin, et al.
(författare)
-
Energy input is primary controller of methane bubbling in subarctic lakes
- 2014
-
Ingår i: Geophysical Research Letters. - : Wiley-Blackwell. - 0094-8276 .- 1944-8007. ; 41:2, s. 555-560
-
Tidskriftsartikel (refereegranskat)abstract
- Emission of methane (CH4) from surface waters is often dominated by ebullition (bubbling), a transport mode with high-spatiotemporal variability. Based on new and extensive CH4 ebullition data, we demonstrate striking correlations (r(2) between 0.92 and 0.997) when comparing seasonal bubble CH4 flux from three shallow subarctic lakes to four readily measurable proxies of incoming energy flux and daily flux magnitudes to surface sediment temperature (r(2) between 0.86 and 0.94). Our results after continuous multiyear sampling suggest that CH4 ebullition is a predictable process, and that heat flux into the lakes is the dominant driver of gas production and release. Future changes in the energy received by lakes and ponds due to shorter ice-covered seasons will predictably alter the ebullitive CH4 flux from freshwater systems across northern landscapes. This finding is critical for our understanding of the dynamics of radiatively important trace gas sources and associated climate feedback.
|
|
