Multidecadal landscape studies of methane fluxes in a high Arctic valley

Abstract:

The carbon balance of high-latitude terrestrial ecosystems plays an essential role in the atmospheric concentration of trace gases, including carbon dioxide and methane. Increasing levels of atmospheric methane have contributed to c. 20 percent of the observed global warming since the pre-industrial era, and rising temperatures in the Arctic are expected to promote the release of methane from Arctic ecosystems. Existing methane collection efforts are sparse and highly scattered, and further attempts to assess the landscape fluxes over multiple years are needed. Here we compile data from systematic campaigns between 2006 and 2019 conducted using automated flux chambers in a fen area in Zackenberg Valley, northeast Greenland. Measurements of methane were highly variable with July-August mean fluxes varying from 0.26 to 3.41 mg m^-2 h^-1. Other methane flux measurement campaigns were carried out in the area between 1997-2013. This study assesses the variability in methane fluxes between these different campaigns as they represent fluxes from the different common land cover types in the valley and represent the interannual variability of fluxes. The automated chamber time series and a 2007 study are combined to provide flux estimate at the landscape scale, and the temporal dynamics are calculated to estimate the development of fluxes in the valley. Valley-wide fluxes are highly variable, but lower than estimated in previous studies, ranging between a source of 0.06 and 0.83 mg m^-2 h^-1 between 1996 and 2019. A recent 2018 thermokarst event indicates that some fen and grassland areas in the valley are becoming unstable after a prolonged period of permafrost warming, and it is shown that although such physical disturbances in the landscape can disrupt the ecosystem-atmosphere flux pattern, future thermokarst areas in the valley are unlikely to cause significant impacts on a landscape scale. The results show that methane fluxes may well be challenging to model from environmental factors and stresses the need for long-term measurements in the Arctic.