The climate change rates in the ocean depths worldwide could be seven times higher by the middle of this century compared to current levels, albeit emissions of greenhouse gases were cut dramatically, according to new research.
The uneven global heating at different depths could impact marine wildlife significantly, leading to disconnects as species dependent on each other are forced to move for survival.
Climate velocity is the measure scientists are looking at in this new research. It is the speed at which species would need to move to stay within their preferred range of temperatures when different ocean layers warm.
The study, published in the journal Nature Climate Change, found different parts of the ocean would change at varied rates as the extra heat generated from increasing greenhouse gas levels moved through the vast ocean depths.
By the second half of the century, the study found “a rapid acceleration of climate change exposure throughout the water column.”
The study first estimates the current rates of climate velocity at different ocean depths using climate models and then calculated future rates under three scenarios. First, where emissions started to fall right from now; second, where they began to fall by the middle of this century; and a third where emissions continued to rise until 2100.
Prof Jorge García Molinos, a climate ecologist at Hokkaido University and a co-author of the study, said: “Our results suggest that deep sea biodiversity is likely to be at greater risk because they are adapted to much more stable thermal environments.”
Recently, the global heating was already causing species to shift in all layers of the ocean from the surface to 4km and more down, but at different speeds.
If we assume a highly optimistic scenario, where emissions fell sharply right from now, climate velocity will change from about 6km per decade to 50km at the ocean’s mesopelagic layer from 200m to 1km down by the second half of the century. However, climate velocity would halve at the surface over the same period.
Even if emissions dropped sharply, climate velocity would triple current rates at depths of even between 1,000 and 4,000 meters.
Prof Anthony Richardson, of the University of Queensland and the CSIRO and one of the study’s 10 authors, told Guardian Australia: “What really concerns us is that as you move down through the ocean, climate velocity moves at different speeds.”
For species that rely on organisms in different layers, this could create a disconnect.
Richardson gave an example of tuna fish that lived in the mesopelagic layer between 200 and 1,000 meters deep; however, they relied on plankton species found near the surface.
According to him, as the oceans on this planet were so large and stored a huge amount of heat, “warming already absorbed at the ocean surface will mix into deeper waters.”
“This means that marine life in the deep ocean will face escalating threats from ocean warming until the end of the century, no matter what we do now.”
Isaac Brito-Morales, the study’s lead author and a researcher at the University of Queensland, said: “Because the deep ocean has a more stable temperature, any small increase will have an impact on species – they’re more at risk than those at the surface.”
Altogether, the matter was “concerning,” Richardson added, as their results showed different rates of climate velocity at different ocean depths, and also, the direction that species would need to move wasn’t uniform either.
The result is that marine park areas designed to protect different species or habitats failed to meet their objectives as species moved out of the protected areas into unprotected zones.
