Oceanic and atmospheric methane cycling in the cGENIE Earth system model – release v0.9.14
2020
Abstract. The methane (CH 4 ) cycle is a key component of the Earth
system that links planetary climate, biological metabolism, and the global
biogeochemical cycles of carbon, oxygen, sulfur, and hydrogen. However,
currently lacking is a numerical model capable of simulating a diversity of
environments in the ocean, where CH 4 can be produced and destroyed, and
with the flexibility to be able to explore not only relatively recent
perturbations to Earth's CH 4 cycle but also to probe CH 4 cycling
and associated climate impacts under the very low-O 2 conditions
characteristic of most of Earth's history and likely widespread on other
Earth-like planets. Here, we present a refinement and expansion of the
ocean–atmosphere CH 4 cycle in the intermediate-complexity Earth system
model cGENIE, including parameterized atmospheric O 2 –O 3 –CH 4
photochemistry and schemes for microbial methanogenesis, aerobic
methanotrophy, and anaerobic oxidation of methane (AOM). We describe the
model framework, compare model parameterizations against modern
observations, and illustrate the flexibility of the model through a series
of example simulations. Though we make no attempt to rigorously tune default
model parameters, we find that simulated atmospheric CH 4 levels and
marine dissolved CH 4 distributions are generally in good agreement with
empirical constraints for the modern and recent Earth. Finally, we
illustrate the model's utility in understanding the time-dependent behavior
of the CH 4 cycle resulting from transient carbon injection into the
atmosphere, and we present model ensembles that examine the effects of
atmospheric p O 2 , oceanic dissolved SO 4 2 - , and the
thermodynamics of microbial metabolism on steady-state atmospheric CH 4
abundance. Future model developments will address the sources and sinks of
CH 4 associated with the terrestrial biosphere and marine CH 4 gas
hydrates, both of which will be essential for comprehensive treatment of
Earth's CH 4 cycle during geologically recent time periods.
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