Find in Library

<p>The methane (CH<span class="inline-formula">₄</span>) 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<span class="inline-formula">₄</span> can be produced and destroyed, and with the flexibility to be able to explore not only relatively recent perturbations to Earth's CH<span class="inline-formula">₄</span> cycle but also to probe CH<span class="inline-formula">₄</span> cycling and associated climate impacts under the very low-O<span class="inline-formula">₂</span> 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<span class="inline-formula">₄</span> cycle in the intermediate-complexity Earth system model cGENIE, including parameterized atmospheric O<span class="inline-formula">₂</span>–O<span class="inline-formula">₃</span>–CH<span class="inline-formula">₄</span> 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<span class="inline-formula">₄</span> levels and marine dissolved CH<span class="inline-formula">₄</span> 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<span class="inline-formula">₄</span> cycle resulting from transient carbon injection into the atmosphere, and we present model ensembles that examine the effects of atmospheric <span class="inline-formula"><i>p</i></span>O<span class="inline-formula">₂</span>, oceanic dissolved SO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">4</mn><mrow><mn mathvariant="normal">2</mn><mo>-</mo></mrow></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="13pt" height="17pt" class="svg-formula" dspmath="mathimg" md5hash="9def59c1763723bf85d4c029a1ebd14e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="gmd-13-5687-2020-ie00001.svg" width="13pt" height="17pt" src="gmd-13-5687-2020-ie00001.png"/></svg:svg></span></span>, and the thermodynamics of microbial metabolism on steady-state atmospheric CH<span class="inline-formula">₄</span> abundance. Future model developments will address the sources and sinks of CH<span class="inline-formula">₄</span> associated with the terrestrial biosphere and marine CH<span class="inline-formula">₄</span> gas hydrates, both of which will be essential for comprehensive treatment of Earth's CH<span class="inline-formula">₄</span> cycle during geologically recent time periods.</p>