The term "abyssal ocean" conjures up ominous images, and rightly so — the literal deep sea abyss is extremely dark, at or near freezing temperatures, and full of peril. In the deepest parts of the abyssal ocean, which is defined as the ocean layer between 4,000 to 6,000 meters deep, light is so limited that photosynthesis is not even possible, meaning there are no plants. Because the animals which live there must survive in harsh conditions, they have evolved otherworldly, bizarre adaptations.
The study is "yet another example of the unanticipated ways that our greenhouse gas emissions is affecting global processes."
But the most terrifying thing about the abyssal ocean may be the fact that normal life on Earth is dependent on the way water moves through it. If that circulation changes, the repercussions could be devastating for all life on Earth: food chain disruptions, weather patterns drastically changing, and ocean life finding itself suddenly unbalanced.
Now a new study from the scientific journal Nature reveals that this scenario may soon come to pass. Climate change is melting ice in the Antarctic; that, in turn, is slowing down the circulation of deep ocean water within this region. If this process continues at its current pace for another 30 years, it will wreak havoc on Earth.
Using a sophisticated computer model developed over three years, the scientists led by researchers at the University of New South Wales calculated the impact of melting Antarctic ice on deep ocean currents within the abyssal layer. Using a transient forced high-resolution coupled ocean–sea-ice model, they found that if climate change continues at its current pace, abyssal warming would "accelerate over the next 30 years."
The technical reason has to do with the melting ice around Antartica. That water descends into the sea and opens a pathway that scrambles existing currents, sending warmer waters to the abyssal oceans.
To be exact, the model estimates that the abyssal layer currents will slow by roughly 42% by the year 2050. This is because the increased amount of cold water dumped into this system by the melting Antarctic ice winds up "freshening" that water — that is, making it warmer and less salty so it does not sink to the bottom of the ocean as it used to. This means that it will not move north, carrying increasing amounts of carbon, oxygen and nutrients to sea life in higher layers of the ocean.
"We know that nutrients exported from the Southern Ocean in other current systems support about three quarters of global phytoplankton production – the base of the food chain," the report's co-author, Steve Rintoul from Australia's Commonwealth Scientific and Industrial Research Organisation, told CNN. "We've shown that the sinking of dense water near Antarctica will decline by 40% by 2050. And it'll be sometime between 2050 and 2100 that we start to see the impacts of that on surface productivity."
This development will also exacerbate the climate change-related problem of sea level rise.
"The main near-term risk is in relation to sea-level rise, which accelerates due to amplifying feedbacks when deep ocean warming increases at the ice margin," report co-author Matthew England told Salon by email. "Another detrimental impact is on nutrient resupply to the ocean surface, which would be weakened significantly if the overturning slows down as projected."
"What happens in the surface waters of the Southern Ocean can have a huge influence on global scale processes."
Dr. Ken Caldeira from the Carnegie Institution for Science, who was not involved in the study, praised the study in an email to Salon as "yet another example of the unanticipated ways that our greenhouse gas emissions is affecting global processes."
"Changes in ocean circulation can affect uptake of both heat and carbon dioxide over many thousands of years," Caldeira continued. "The decisions we make about energy systems and deforestation over the next years will affect Earth's climate for many millennia in ways that are now poorly understood."
He also noted that over 20 years ago he and his colleagues wrote a paper on how brine is rejected from Antarctic sea ice (as opposed to glacial ice in this case). This water "is important in structuring the global ocean," he said. "Southern Ocean surface waters are on the fast track to the deep ocean, and what happens in the surface waters of the Southern Ocean can have a huge influence on global scale processes over many millennia."
Not every scientist was impressed with the modeling in the study.
"The study is based on a model which is unlikely to be very close to reality," Dr. Kevin Trenberth of the National Center for Atmospheric Research (NCAR) told Salon by email. Trenberth said that the abstract noted they had "limited measurements" that affected their ability to link the change to specific "drivers."
"There are big issues in getting the modeling right, including how much snow falls on Antarctica and actually builds up the ice sheet, as is happening in East Antarctica," Trenberth continued. "That snow has its origins in the so-called melt water through evaporation from the strong southern ocean winds."
"Models do not do this well," he concluded.
Other oceanic currents are being disrupted by climate change too. In 2021, a study in the journal Paleoceanography and Paleoclimatology that the Kuroshio Current and Extension (KCE) is warming, adjusting its latitudinal position northward, and possibly increasing the amount of warm water that it moves north in the process as a result of climate change. The KCE forms the main western boundary current as part of the North Pacific ocean gyre (meaning a large system of circulating currents) that spans from the North American Pacific Coast to Polynesia.
"The Kuroshio Current Extension is home to some of the highest biodiversity (number of organisms) in the world ocean today," Adriane R. Lam, a paleoceanographer and Binghamton University postdoctoral fellow who co-authored the study, wrote to Salon at the time. "This is one reason why Japan's fishing industry is so robust." These fisheries would be severely and negatively affected by a disruption to KCE.
Similarly, the Atlantic Meridional Overturning Circulation (AMOC) for short was found by a recent study to be at its weakest in 1,600 years. If AMOC shuts down, temperatures will drop all over Europe as the number of storms increases; rising sea levels along the North American eastern seaboard will cause millions to flee their homes; and changing weather conditions will lead to food shortages in India, West Africa and South America.
