The ocean makes me feel uneasy in a quiet way. It looks like nothing is happening at first glance—sunlight spreading out across huge, uninterested waves. But deep down, at the microscopic level, things are happening that could change how quickly the Earth warms up. They are still hard for scientists to understand, and the picture they are painting is not a good one.
A group from the University of Rochester published their findings earlier this year in the Proceedings of the National Academy of Sciences. They found a specific mechanism that makes methane in the open ocean. Scientists in the ocean have been trying to figure out this mystery for decades. Seawater at the surface has a lot of oxygen in it, while methane is usually found in places with no oxygen, like swamps, deep sediments, and the mucky bottom of a lake. But methane has been seen to be released into the air by ocean water at the surface for a long time. How was always the question.
It turns out that phosphate is the answer. Methane is made by some bacteria when they break down organic matter, but only when there isn’t enough phosphate available. The study’s leader, associate professor Thomas Weber, put it simply: the lack of phosphate is essentially what controls the production of methane in the open ocean. When these microbes don’t have enough phosphate, they switch to a metabolic pathway that makes methane. At the cellular level, it’s just a small change. When you look at the whole ocean, the effects are not small.
What comes next as the planet warms up makes this discovery feel even more important. Because of climate change, the ocean is getting warmer from the top down. This makes the difference in density between the warmer water on top and the colder water below bigger over time. Vertical mixing, the process that normally brings nutrients like phosphate up from the deep, is slowed down by that gap. When there is less mixing, phosphate doesn’t get to the surface as much. When there is less phosphate, more of these bacteria that make methane do what they do when they don’t have enough food. More methane makes it warmer. When it warms up, there is less mixing. It goes around and around itself in a way that is, to use a word scientists use carefully, creepy.
It’s interesting that this feedback isn’t included in the main climate models we use to make predictions right now. That isn’t a criticism of the scientists who made those models; they only use what they know. In this case, this mechanism wasn’t known in this form. But it makes me wonder what else might be in those waters, working on timescales and scales that aren’t yet accounted for in the equations we use to make predictions.
The story of the ocean methane isn’t the only one. In the background, a different line of research has been growing around Antarctica, where another missing feedback is starting to show up. Recent studies have shown that meltwater flowing off of ice shelves changes the ocean in ways that make melting happen faster. This is a physical feedback that, like the methane loop, hasn’t been taken into account in most predictions of sea level rise. When meltwater discharge was taken into account, it was found that the Denman and Scott glaciers in East Antarctica could pass a critical retreat threshold about 25 years earlier than models had predicted. No, that’s not a small change. Twenty-five years is a generation.
You should pay attention to this pattern. The most important processes are often the ones that are just on the edges of what can be measured. For example, microbial metabolism in water that doesn’t have enough nutrients, meltwater changing the density of the ocean near the base of a glacier, and carbon stirring in coastal sediments as sea levels rise are all examples of these. Modeling is easier for things that are big and easy to see. Most of the time, surprises are found in the small, linked details.
It’s easy to think that this whole thing is always bad. Not quite. It looks like science is doing what it’s supposed to do: researchers are finding gaps, filling them, and making the models stronger. Weber’s team said that this work can help climate predictions take into account interactions that weren’t thought of before. That’s important. But it also means that the time frame for change might be shorter than what we think now, and we need to speed up how we understand and deal with that change.
For a long time, the ocean has been taking in heat, carbon, and the effects of people. It’s becoming more and more clear that it’s been talking back in a quiet way.
