Combined effects of glacial retreat and penguin activity on soil greenhouse gas fluxes on South Georgia, sub-Antarctica.

The effects of soil succession after glacial retreat and fertilisation by marine animals are known to have major impacts on soil greenhouse gas (GHG) fluxes in polar terrestrial ecosystems. While in many polar coastal areas retreating glaciers open up new ground for marine animals to colonise, little is known about the combination of both factors on the local GHG budget. We studied the magnitude of GHG fluxes (CO2, CH4 and N2O) on the combined effect of glacial retreat and penguin-induced fertilisation along a transect protruding into the world's largest King Penguin (Aptenodytes patagonicus) colony at Saint Andrews Bay on sub-Antarctic South Georgia. GHG production and consumption rates were assessed based on laboratory incubations of intact soil cores and nutrients and water additional experimental incubations. The oldest soils along the transect show significant higher contents of soil carbon, nutrients and moisture and were strongly influenced by penguin activity. We found a net CH4 consumption along the entire transect with a marked decrease within the penguin colony. CO2 production strongly increased along the transect, while N2O production rates were low near the glacier front and increased markedly within the penguin colony. Controlled applications of guano resulted in a significant increase in CO2 and N2O production, and decrease in CH4 consumption, except for sites already strongly influenced by penguin activity. The results show that soil microbial activity promptly catalyses a turnover of soil C and atmospheric methane oxidation in de-glaciated forelands. The methane oxidizers, however, may increase relatively slowly in their capacity to oxidise atmospheric CH4. Results show also that the increase of nutrients by penguins reduces CH4 oxidation whereas N2O production is greatly increased. A future expansion of penguins into newly available ice-free polar coastal areas may therefore markedly increase the local GHG budget.