Preindustrial atmospheric ethane levels inferred from polar ice cores: A constraint on the geologic sources of atmospheric ethane and methane

Ethane levels were measured in air extracted from Greenland and Antarctic ice cores ranging in age from 994 to 1918 Common Era (C.E.) There is good temporal overlap between the two data sets from 1600 to 1750 C.E. with ethane levels stable at 39728 parts per trillion (ppt) (2standard error (s.e.)) over Greenland and 1039ppt over Antarctica. The observed north/south interpolar ratio of ethane (3.90.1, 1 sigma) implies considerably more ethane emissions in the Northern Hemisphere than in the Southern Hemisphere, suggesting geologic ethane sources contribute significantly to the preindustrial ethane budget. Box model simulations based on these data constrain the global geologic emissions of ethane to 2.2-3.5Tgyr(-1) and biomass burning emissions to 1.2-2.5Tgyr(-1) during the preindustrial era. The results suggest biomass burning emissions likely increased since the preindustrial period. Biomass burning and geologic outgassing are also sources of atmospheric methane. The results place constraints on preindustrial methane emissions from these sources.