The processes associated with the release of CH 4 and CO 2 from sub-permafrost groundwaters are considered through a year-long monitoring investigation at a terrestrial seepage site in West Spitsbergen. The site is an open system pingo thought to be associated with the uplift of a former sea-floor pockmark in response to marked isostatic recovery of the coastline following local ice sheet loss over the last 10,000 years. We find that locally significant emissions of CH 4 and (less so) CO 2 to the atmosphere result from a seepage <1 L s −1 that occurs all year. Hydrological and meteorological conditions strongly regulate the emissions, resulting in periodic outbursts of gas-rich fluids following ice fracture events in winter, and significant dilution of the fluids in early summer by meltwater. Evasion of both gases from a pond that forms during the 100 days summer (45.6 ± 10.0 gCH 4-C m −2 and 768 ± 211 gCO 2-C m −2) constitute between roughly 20 and 40% of the total annual emissions (223 gCH 4-C m −2 a −1 and 2,040 gCO 2-C m −2 a −1). Seasonal maximum dissolved CH 4 concentrations (up to 14.5 mg L −1 CH 4) are observed in the fluids that accumulate beneath the winter ice layer. However, seasonal maximum dissolved CO 2 levels (up to 233 mg L −1) occur during late summer. Differences between the δ 13 C-CH 4 composition of the winter samples [average 58.2 ± 8.01‰ (s.d.)] and the late summer samples [average 66.9 ± 5.75‰ (s.d.)] suggest minor oxidation during temporary storage beneath the winter ice lid, although a seasonal change in the methane source could also be responsible. However, this isotopic composition is strongly indicative of predominantly biogenic methane production in the marine sediments that lie beneath the thin coastal permafrost layer. Small hotpots of methane emission from sub-permafrost groundwater seepages therefore deserve careful monitoring for an understanding of seasonal methane emissions from permafrost landscapes.
Geodetic volume estimates of Storglaciären in Sweden suggest a 28% loss in total ice mass between 1910 and 2015. Terrestrial photographs from 1910 of Tarfala valley, where Storglaciären is situated, allow for an accurate reconstruction of the glacier's surface using Structure-from-Motion photogrammetry, which we used for past volume and mass estimations. The glacier's yearly mass balance gradient and net mass balance was also estimated back to 1880 using weather data from Karesuando, 170 km northeast of Storglaciären, through neural network regression. These combined reconstructions provide a continuous mass change series between the end of the Little Ice Age and 1946, when field data become available. The resultant reconstruction suggests a state close to equilibrium between 1880 and the 1910s, followed by drastic melt until the 1970s, constituting 76% of the 1910-2015 ice loss. More favourable conditions subsequently stabilized the mass balance until the late 1990s, after which Storglaciären started losing mass again. The 1910 reconstruction allows for a more accurate mass change series than previous estimates, and the methodology can be used on other glaciers where early photographic material exists.
Photogrammetric reconstructions of the Aldegondabreen glacier on Svalbard from 17 archival terrestrial oblique photographs taken in 1910 and 1911 reveal a past volume of 1373.7 ± 78.2 · 106 m3; almost five times greater than its volume in 2016. Comparisons to elevation data obtained from aerial and satellite imagery indicate a relatively unchanging volume loss rate of − 10.1 ± 1.6 · 106 m3 a−1 over the entire study period, while the rate of elevation change is increasing. At this rate of volume loss, the glacier may be almost non-existent within 30 years. If the changes of Aldegondabreen are regionally representative, it suggests that there was considerable ice loss over the entire 1900s for the low elevation glaciers of western Svalbard. The 1910/11 reconstruction was made from a few of the tens of thousands of archival terrestrial photographs from the early 1900s that cover most of Svalbard. Further analysis of this material would give insight into the recent history and future prospects of the archipelago's glaciers. Photogrammetric reconstructions of this kind of material require extensive manual processing to produce good results; for more extensive use of these archival imagery, a better processing workflow would be required.
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