Thermokarst lakes accelerate deep permafrost thaw and the mobilization of previously frozen soil organic carbon. This leads to microbial decomposition and large releases of carbon dioxide (CO₂) and methane (CH₄) that enhance climate warming. However, the time scale of permafrost-carbon emissions following thaw is not well known but is important for understanding how abrupt permafrost thaw impacts climate feedback. We combined field measurements and radiocarbon dating of CH₄ ebullition with (a) an assessment of lake area changes delineated from high-resolution (1–2.5 m) optical imagery and (b) geophysical measurements of thaw bulbs (taliks) to determine the spatiotemporal dynamics of hotspot-seep CH₄ ebullition in interior Alaska thermokarst lakes. Hotspot seeps are characterized as point-sources of high ebullition that release ¹⁴C-depleted CH₄ from deep (up to tens of meters) within lake thaw bulbs year-round. Thermokarst lakes, initiated by a variety of factors, doubled in number and increased 37.5% in area from 1949 to 2009 as climate warmed. Approximately 80% of contemporary CH₄ hotspot seeps were associated with this recent thermokarst activity, occurring where 60 years of abrupt thaw took place as a result of new and expanded lake areas. Hotspot occurrence diminished with distance from thermokarst lake margins. We attribute older ¹⁴C ages of CH₄ released from hotspot seeps in older, expanding thermokarst lakes (¹⁴C_CH4 20 079 ± 1227 years BP, mean ± standard error (s.e.m.) years) to deeper taliks (thaw bulbs) compared to younger ¹⁴C_CH4 in new lakes (¹⁴C_CH4 8526 ± 741 years BP) with shallower taliks. We find that smaller, non-hotspot ebullition seeps have younger ¹⁴C ages (expanding lakes 7473 ± 1762 years; new lakes 4742 ± 803 years) and that their emissions span a larger historic range. These observations provide a first-order constraint on the magnitude and decadal-scale duration of CH₄-hotspot seep emissions following formation of thermokarst lakes as climate warms.

Thermokarst lakes, formed by permafrost thaw, are an important source of atmospheric methane (CH4), a powerful greenhouse gas. Ebullition (bubbling) is often the dominant mode of lake CH4 emission. Because extrapolating spatially limited field measurements of CH4 ebullition induces large uncertainties in regional emission estimates, there is a need for remote sensing based approaches to detect and quantify CH4 ebullition at larger spatial scales in lakes. We examined the relationship between spaceborne synthetic aperture radar (SAR) pixel values of lake ice and biogeochemical field measurements of CH4 ebullition on ten lakes on the northern Seward Peninsula. Among lakes, ebullition ranged from low to high. We found that both the area of ice-bound ebullition-bubble clusters and the bubbling rates that generated the clusters were correlated with L-band single-polarized (HH) SAR (R2 = 0.70, p = 0.002, n = 10) and with the “roughness” component of a Pauli decomposition of L-band quad-polarized SAR (R2 = 0.77,... Les lacs thermokarstiques, formés par le dégel du pergélisol, sont une source importante de méthane atmosphérique (CH4), un puissant gaz à effet de serre. L’ébullition (formation de bulles) est souvent le principal mode d’émission de CH4. Puisque l'extrapolation à partir de mesures d’ébullition de CH4 prises sur le terrain et limitées dans l'espace induit un haut degré d'incertitude dans l'estimation des émissions régionales, des approches basées sur la télédétection pour détecter et quantifier l’ébullition de CH4 sur des espaces à plus grande échelle dans les lacs sont nécessaires. Nous avons examiné la relation entre les valeurs de pixels de glace lacustre provenant d'un radar à synthèse d'ouverture (SAR) spatioporté et les mesures biogéochimiques d’ébullition de CH4 prises sur le terrain de dix lacs de la partie Nord de la péninsule de Seward. Parmi les lacs, l’ébullition allait de faible à élevée. Nous avons déterminé que les régions de grapes de bulles d’ébullition prises dans la glace ainsi que le t...

Thermokarst lakes are prevalent in Arctic coastal lowland regions and sub‐lake permafrost degradation and talik development contributes to greenhouse gas emissions by tapping the large permafrost carbon pool. Whereas lateral thermokarst lake expansion is readily apparent through remote sensing and shoreline measurements, sub‐lake thawed sediment conditions and talik growth are difficult to measure. Here we combine transient electromagnetic surveys with thermal modeling, backed up by measured permafrost properties and radiocarbon ages, to reveal closed‐talik geometry associated with a thermokarst lake in continuous permafrost. To improve access to talik geometry data, we conducted surveys along three transient electromagnetic transects perpendicular to lakeshores with different decadal‐scale expansion rates of 0.16 m yr^‐1, 0.38 m yr^‐1, and 0.58 m yr^‐1. We modeled thermal development of the talik using boundary conditions based on field data from the lake, surrounding permafrost and a borehole, independent of the transient electromagnetics. A talik depth of 91 m was determined from analysis of the transient electromagnetic surveys. Using a lake initiation age of 1400 years before present and available subsurface properties the results from thermal modeling of the lake center arrived at a best estimate talk depth of 80 m, which is on the same order of magnitude as the results from the transient electromagnetic survey. Our approach has provided a non‐invasive estimate of talik geometry suitable for comparable settings throughout circum‐Arctic coastal lowland regions.

Vast mosaics of lakes, wetlands, and rivers on the Arctic Coastal Plain give the impression of water surplus. Yet long winters lock freshwater resources in ice, limiting freshwater habitats and water supply for human uses. Increasingly the petroleum industry relies on lakes to build temporary ice roads for winter oil exploration. Permitting water withdrawal for ice roads in Arctic Alaska is dependent on lake depth, ice thickness, and the fish species present. Recent winter warming suggests that more winter water will be available for ice- road construction, yet high interannual variability in ice thickness and summer precipitation complicates habitat impact assessments. To address these concerns, multidisciplinary researchers are working to understand how Arctic freshwater habitats are responding to changes in both climate and water use in northern Alaska. The dynamics of habitat availability and connectivity are being linked to how food webs support fish and waterbirds across diverse freshwater habitats. Moving toward watershed-scale habitat classification coupled with scenario analysis of climate extremes and water withdrawal is increasingly relevant to future resource management decisions in this region. Such progressive refinement in understanding responses to change provides an example of adaptive management focused on ensuring responsible resource development in the Arctic.