Double Agent: The Arctic Ocean’s Role in Methane Emissions

Source Article: Ye W, Zhan L, Wu M, Liu J. Stable carbon isotopes of methane reveal that the central Arctic Ocean is a potential sink of atmospheric methane. Limnology and Oceanography. 2025 Dec 16;71(1). DOI: https://doi.org/10.1002/lno.70299

Liquids and (greenhouse) gases

Methane is a potent Greenhouse Gas (GHG) that boasts enough heat-trapping capabilities to put carbon dioxide to shame. As the threat of climate change looms over the planet, understanding the oceans’ role in it is crucial for paving a path forward. Until now, the oceans were confirmed to be mild, if under-explored, contributors to GHG emissions, especially methane, but novel research indicates that we are still missing important pieces of the puzzle.

Elevated marine methane concentrations have been observed around the globe, including in the Arctic. When the concentration of methane in the water is higher than that in the atmosphere, the methane molecules are prone to “jumping” to the air, increasing the atmospheric concentration. This accelerates global warming through the Greenhouse Effect, the process in which GHGs trap heat from the sun within the atmosphere and prevent it from dissipating in space.

However, the origins of these reported high levels are shrouded in mystery, as methane shouldn’t be produced in oxygen-rich surface waters. Commonly referred to as the “oceanic methane paradox”, this knowledge gap is especially prominent regarding the polar regions, as very few data exist for what happens at the frozen frontiers beyond their coastlines. Seeking answers, Ye’s team of scientists ventured to the Western Arctic Ocean in hopes of revealing the source of methane both near coast and at icy, offshore depths.

Leads and cracks in the ice cover of the Arctic Ocean north of Alaska, a potential pathway for methane release (Photograph by Eric Kort / NASA / NASA Earth Observatory, 2011. Public Domain).

Challenging the methane paradox: The arctic ocean can do both

How does one figure out where invisible molecules come from? Turns out, methane, depending on its source, has a distinct chemical “fingerprint” that can be measured with proper equipment that utilizes laser technology. Since the aim is to track these “fingerprints”, scientists take a page straight out of a detective novel and start investigating: where did those fingerprints come from and what happened to them afterwards -were they emitted in the atmosphere? Consumed by other microscopic organisms? Is the arctic ocean releasing methane into the air, or is it absorbing it instead?

In order to answer these questions, a detailed “methane budget” must be charted. To make that budget as trustworthy as possible, many different sites got sampled within the summer season, ranging from shallow, coastal areas to understudied, ice-covered deep waters. Alas, simple answers are scarce when looking at environments this vast: apparently, the arctic ocean is split. On one hand, the shallow areas (<100 m deep) are methane emitters. The waters there contain more methane than what would be in balance with the atmosphere, likely due to it being produced by microbes living on the seabed. On the other hand, deeper waters had lower methane levels than the atmosphere, indicating that they were ready to absorb methane gas instead. Curiously, some deeper parts that did have high concentrations also had an unconventional origin: the methane there was neither from the air nor form the seabed, but was likely produced right there in the open water by a fascinating phenomenon named “marine snow”: tiny, sinking particles in the water that host their own, equally tiny, microscopic communities.

Even more interestingly, the limited methane that was present deeper didn’t escape, but was either consumed by methane-eating bacteria (whose work always leaves some measurable “crumbs”) or mixed with deeper, methane-free water. Ice melting, while something we often dread to hear, actually helps this process by “covering” methane-rich waters, trapping the methane there until winter comes and forces it to mix with currents below. Thus, arctic waters are both a source and a surprising “sink” for this potent greenhouse gas.

The ocean is more than what meets the eye

While careful not to overstate the findings, as the methane sink discovered in the Arctic is quite small, the implications for how much we still have to learn about how oceans fit into climate change are vast. What makes the arctic ocean different is its ice-melting cycles, which, counterintuitively, help mitigate the climate threat of methane by putting a “lid” on top of oceanic emissions, a “lid” that the rest of the oceans lack. The shallow water emissions remain worrisome, but the fact that the vast expanse acts as a big methane filter is a testament to the complexity of and the delightful ways in which the oceans continue to turn the tables on us.

Cover Image: Blue sky begins to break through the clouds over Arctic Ocean ice on Sept. 9, 2009 (Photograph by Patrick Kelley, CC BY-SA 2.0, via Wikimedia Commons).

Massa Polasek

I’m an MSc candidate in Host-Microbe Interactions and a former researcher in microbial ecology. I have a BSc in Biochemistry and Biotechnology from the University of Thessaly and live in Skopelos, a small but beautiful Greek island. I’m passionate about the intersection of marine science and climate change and love to paint!