Emission of methane (CH and CO2. In situ mole
fractions of CH4 and CO2 were measured
in the subglacial air at a subglacial river outlet where emissions of
CH4 and CO2 had been identified. Water
samples were analysed for dissolved CH4 and
CO2 concentrations. CH4 and
CO2 in gas and water samples were analyzed for their
isotopic composition of 13C and 2H.
Close correlation between gaseous and dissolved CH4 and
CO2, respectively, show degassing of CH4
and CO2 from the subglacial meltwater. The diurnal
variability of in situ mole fractions of CH4 and
CO2 in subglacial air was related to meltwater runoff.
Maximum in situ mole fractions decreased after the peak of the
melt season, but estimated net emissions increased because the size of
the subglacial river outlet increased. The isotopic signature of
CH4 in the subglacial air, estimated with a Keeling
plot, indicated that subglacial CH4 likely originated
from acetoclastic methanogenesis. Isotopic signatures of gaseous
CO2 indicate that both microbial oxidation of
CH4 in the subglacial system and remineralization of
carbon in subglacial sediments contribute to subglacial
CO2.