Frozen ponds: production and storage of methane during the Arctic winter in a lowland tundra landscape in northern Siberia, Lena River delta

[摘要] Lakes and ponds play a key role in the carbon cycle of permafrost ecosystems,where they are considered to be hotspots of carbon dioxide CO₂ andmethane CH₄ emission. The strength of these emissions is, however,controlled by a variety of physical and biogeochemical processes whoseresponses to a warming climate are complex and only poorly understood. Smallwaterbodies have been attracting an increasing amount of attention sincerecent studies demonstrated that ponds can make a significant contribution tothe CO₂ and CH₄emissions of tundra ecosystems. Waterbodiesalso have a marked effect on the thermal state of the surrounding permafrost;during the freezing period they prolong the period of time during whichthawed soil material is available for microbial decomposition.

This study presents net CH₄ production rates during the freezingperiod from ponds within a typical lowland tundra landscape in northernSiberia. Rate estimations were based on CH₄ concentrations measuredin surface lake ice from a variety of waterbody types. Vertical profilesalong ice blocks showed an exponential increase in CH₄ concentrationwith depth. These CH₄ profiles were reproduced by a 1-D mass balancemodel and the net CH₄ production rates were then inferred throughinverse modeling.

Results revealed marked differences in early winter net CH₄production among various ponds. Ponds situated within intact polygonal groundstructures yielded low net production rates, of the order of 10^-11 to10^-10 molm^-2 s^-1 (0.01 to 0.14 mg_CH4 m^-2 day^-1). In contrast, ponds exhibitingclear signs of erosion yielded net CH₄ production rates of the orderof 10^-7 mol m^-2 s^-1 (140 mg _CH4 m^-2 day^-1). Ourresults therefore indicate that once a particular threshold in thermalerosion has been crossed, ponds can develop into major CH₄ sources.This implies that any future warming of the climate may result in nonlinearCH₄ emission behavior in tundra ecosystems.

[学科分类] 地球化学与岩石