Plant wax isotopes in Greenland lakes record widespread CH4 uptake
during Holocene warming
Abstract
Methane (CH4) emissions from Arctic lakes are of global concern in a
warming world. Past Holocene warming provides an opportunity to examine
carbon-climate feedbacks that develop over hundreds to thousands of
years, but thus far records of past long-term changes in lake CH4
dynamics are rare. Here, we demonstrate for the first time that the
hydrogen stable isotopic composition of aquatic plant wax records
incorporation of CH4 in plant (aquatic moss) biomass. Trends in δ2H and
δ13C values of aquatic plant derived leaf waxes point to widespread and
sustained middle Holocene shifts in CH4 cycling at climatically diverse
sites across Greenland during millennia of elevated summer temperatures.
Independent proxies indicate concurrent increases in local primary
productivity and decreases in hypolimnetic oxygen. These data portend
that ongoing warming may promote an enduring shift towards conditions
that enhance methanogenesis in many Arctic lakes, including in lakes
where these conditions do not exist today. This work highlights a
previously unrecognized factor influencing δ2H values of aquatic leaf
waxes in some high-latitude lakes, and also draws attention to the role
of common aquatic mosses as a potentially important sink of lake CH4
across the Arctic that has yet to be quantified.