Annual CO2 flux in dry and moist arctic tundra: Field responses to increases in summer temperatures and winter snow depth

We examined the annual exchange of CO2 between the atmosphere and moist tus sock and dry heath tundra ecosystems (which together account for over one-t hird of the low arctic land area) under ambient field conditions and under increased winter snow deposition, increased summer temperatures, or both. O ur results indicate that these two arctic tundra ecosystems were net annual sources of CO2 to the atmosphere from September 1994 to September 1996 und er ambient weather conditions and under our three climate change scenarios. Carbon was lost from these ecosystems in both winter and summer, although the majority of CO2 evolution took place during the short summer. Our resul ts indicate that (1) warmer summer temperatures will increase annual CO2 ef flux from both moist and dry tundra ecosystems by 45-55% compared to curren t ambient temperatures; (2) deeper winter snow cover will increase winter C O2 efflux in both moist and dry tundra ecosystems, but will decrease net su mmer CO2 efflux; and (3) deeper winter snow cover coupled with warmer summe r temperatures will nearly double the annual amount of CO2 emitted from moi st tundra and will result in a 24% increase in the annual CO2 efflux of dry tundra. If, as predicted, climate change alters both winter snow depositio n and summer temperatures, then shifts in CO2 exchange between the biospher e and atmosphere will likely not be uniform across the Arctic tundra landsc ape. Increased snow deposition in dry tundra is likely to have a larger eff ect on annual CO2 flux than warmer summer temperatures alone or warmer temp eratures coupled with increased winter snow depth. The combined effects of increased summer temperatures and winter snow deposition on annual CO2 flux in moist tundra will be much larger than the effects of either climate cha nge scenario alone.