It’s understandable that, when it comes to the oceans, we mainly think about what’s happening up at the surface. Grim stories of the epic scale of plastic pollution often dominate the headlines, particularly when the world seems to react too slowly, or too feebly, to the crisis at hand.
A new, comprehensive review in the journal Science has pointed out, in no uncertain terms, that another catastrophe is unfolding deep below those blue crests and troughs. Our oceans are being somewhat suffocated by our behavior; its deep reserves of oxygen are disappearing at a breakneck speed, and Earth's biosphere will soon begin to suffer the consequences if nothing is done to reverse the trend.
The study concludes by suggesting that, “in the longer term, these conditions are unsustainable and may result in ecosystem collapses, which ultimately will cause societal and economic harm.”
The review, the largest of its kind, was led by an enormous international team of researchers collectively known as the Global Ocean Oxygen Network, or GO2NE. It makes for an unquestionably upsetting read.
The study notes that oxygen concentrations in large swaths of the ocean – including both the wide expanse far from land, and along coastal regions – has declined precipitously since the 1950s.
Oxygen-minimum zones, sometimes referred to as “dead zones”, aren’t a new phenomenon; they've been around for hundreds of millions of years. However, today, they’re proliferating and expanding rapidly, and they aren't being driven by natural processes.
Since the middle of the 20th century, those in the open ocean have quadrupled in size, whereas those along the coast have experienced a 10 times increase.
To put it another way, the open ocean oxygen minimum dead zones have expanded in size by 4.5 million square kilometers (1.7 million square miles), which the authors compares to “the size of the European Union.” That is roughly 46 percent of the area of the US, or 18.5 times the size of the UK.
It's worth pointing out, as the new study does, that oxygen-deficient oceans in warmer climates are often associated with major extinction events. Previous studies have noted that the sudden appearance of dead zones within the oceans – sometimes called anoxic events – devastated life in the Cretaceous Period. One naturally-occurring event back then killed off 27 percent of all marine invertebrates.
Although there are plenty of extremophiles in the oceans that can live perfectly happily without oxygen, it’s a necessity for a plethora of life. Without it, they die, food chains collapse, and – considering how much humanity relies on the oceans – we will pay a price too high to handle.
It’s not just the destruction of life that’s emerging from recent studies. The ocean is a chemistry experiment; as one element is added, another ingredient is lost, and vice versa. In this case, the disappearance of oxygen has led to an increased production of N2O, a rarely spoken about but incredibly potent greenhouse gas.
Although it’s not as long-lived as carbon dioxide, which can spend centuries in the atmosphere, nitrous oxide traps heat 265–298 times more effectively than the more famous greenhouse gas. That makes it an incredibly effective catalyst for climate change, and the deoxygenation of the oceans is triggering that.
There is one benefit to all this chaos, though. Fish escaping the underwater apocalypse will swim up to the surface to try and escape, and as a result, they’ll be easier to catch. Not exactly a fair trade-off for the near-inexorable demise of plenty of life within our oceans, though.
This deoxygenation, without a shadow of a doubt, it caused by us.
When it comes to coastal regions, the chemical runoff from agriculture and industry is causing small-scale biological revolutions. Nitrate and phosphorous-rich pollution trigger a boom in phytoplankton populations. When they inevitably die off in vast numbers, they sink, and the bacteria that break them down consume enormous amounts of oxygen.
In the open ocean, climate change is the primary antagonist. Although it has plenty of effects, the most problematic issue is that warmer waters contain less oxygen.
“We will be late in reacting to the clearly identified threat, and our inaction will make the situation less manageable for the future generations,” Vladimir Ryabinin, executive secretary of the Intergovernmental Oceanographic Commission, told IFLScience via email.
Ryabinin emphasized that he is “deeply troubled by the evidence that almost all of the known trends are in the direction of negative influence on ocean ecosystems.”
“It is engagement of people, governments and private sector that, in the shorter run, may help to reduce nutrient pollution of the ocean, which in turn may partially help to cope with some areas of deoxygenation near the coast,” he added, noting that we need to adapt to this worrying new world at the same time.
“Establishment of scientifically designed marine protected areas would also be an efficient measure for protection of biodiversity.”
Make no mistake: we rely on our oceans more than we realize. Not only are they an incredible carbon sink, but they also provide the world with half of all its oxygen.
Unless climate change and pollution are stamped out, we might be heading into a bleaker future, one where parts of our oceans will transform from cornucopias of life to graveyards that we can only describe in elegiac terms.