Abstract
Methane (CH4) emissions from Arctic lakes are of global concern in a
warming world. Holocene warming provides an opportunity to examine
carbon-climate feedbacks that develop over hundreds to thousands of
years of warming, but thus far records that document changes in lake CH4
dynamics in the Arctic are limited. Here, we show that Holocene warming
led to widespread increases in CH4 in Greenland lakes during the middle
Holocene driven by increases in primary production and decreases in
oxygen in hypolimnetic water due to stratification. We infer changes in
CH4 dynamics using δ2H values of sedimentary moss biomarkers which
demonstrate at multiple sites on Greenland a several-thousand-year
period during which δ2Hmoss values are consistent with uptake of
CH4-derived H, likely via intracellular H2O and NH4+ supplied by
endophytic methanotrophic bacteria that dominated in increasingly
stratified lakes. These data indicate ongoing warming will promote an
enduring shift towards conditions that enhance methanogenesis and
increase CH4 in warming Arctic lakes whose geometries are prone to
thermal stratification even in lakes where these conditions do not exist
today. This work also draws attention to a likely role of common aquatic
mosses as an important sink of CH4 in lakes across the Arctic.