Expanding Deep Ocean Acidification is Shrinking Marine Habitats.
At a depth of 4,000 meters beneath the ocean, the combination of high pressure and low temperature creates an environment capable of dissolving calcium carbonate, the material that marine animals use to form their shells. This area, known as the calcium compensation depth, is increasingly expanding, according to a report by Live Science on August 13. The new research was conducted by expert Peter T. Harris from the GRID-Arendal center (Norway) along with colleagues and published in the journal Science Direct.
The expansion of the calcium compensation depth will impact marine life. (Photo: Stock colors).
The calcium compensation depth is distinct from the surface ocean acidification phenomenon—a phenomenon occurring due to the ocean absorbing CO2 from fossil fuel combustion. However, they are still interconnected. With rising CO2 levels, the ocean’s pH decreases (becoming more acidic) and the region of dissolved calcium carbonate is expanding from the ocean floor upwards.
The transitional zone where calcium carbonate becomes chemically unstable and begins to dissolve is referred to as the lysocline. Because the ocean floor is relatively flat, even a few meters rise in the lysocline can quickly create large acidic areas.
The new study indicates that this zone has risen nearly 100 meters since the pre-industrial period and is likely to rise hundreds of meters more in this century. Millions of square kilometers of the ocean floor will undergo rapid transformation, making calcium carbonate sediments chemically unstable and prone to dissolution.
The upper limit of the lysocline transitional zone is known as the calcite saturation depth, while the lower limit is the calcium compensation depth. The calcium compensation depth serves as a biological boundary with distinct habitats above and below.
In the northeastern Pacific Ocean, the most abundant benthic organisms that thrive above the calcium compensation depth include soft corals, brittle stars, clams, sea snails, chiton mollusks, and bryozoans, all of which possess calcium carbonate shells or skeletons.
However, below the calcium compensation depth, sea anemones, sea cucumbers, and octopuses are more prevalent. This acidic environment has restricted life over an area of 141 million square kilometers and could expand an additional 35 million square kilometers if the calcium compensation depth rises by 300 meters.
In addition to the expansion of the calcium compensation depth, some ocean regions at low latitudes are gradually losing species due to warming waters and decreasing oxygen levels caused by climate change. Consequently, the optimal living space for marine life is shrinking from both below (the rising calcium compensation depth) and above (increasing temperatures). The exclusive economic zones of some countries, especially island nations, are also affected.
