The deep sea is a mysterious and fascinating place, with unique conditions that shape the marine life that inhabits it. One of the most intriguing aspects of the deep ocean is the carbonate compensation depth, a zone where high pressure and low temperature combine to dissolve calcium carbonate, the material used by marine animals to make their shells.
Located below 13,100 feet (4,000 meters) in the ocean, the carbonate compensation depth is expanding due to rising concentrations of carbon dioxide in the ocean. As the ocean absorbs more carbon dioxide from the burning of fossil fuels, its pH decreases, making it more acidic. This increase in acidity causes the deep-sea area where calcium carbonate dissolves to grow, creating a transition zone known as the lysocline.
Research has shown that the lysocline has already risen by nearly 100 meters since pre-industrial times and is projected to rise further by several hundred meters in this century. This rise in the lysocline can lead to large under-saturated (acidic) areas on the ocean floor, affecting millions of square kilometers of marine habitats.
The calcite saturation depth marks the upper limit of the lysocline transition zone, where seabed sediments are rich in calcium carbonate. Below this depth lies the calcite compensation depth, where seabed sediments contain little to no carbonate minerals. The area below the calcite compensation depth varies across different ocean sectors, with some regions experiencing a rise of more than 980 feet since the industrial revolution.
The expansion of the calcite compensation depth has significant implications for marine life. A recent study revealed that this boundary creates distinct habitats above and below it. In the northeast Pacific, organisms such as soft corals, brittle stars, and mussels thrive above the calcite compensation depth, while sea anemones, sea cucumbers, and octopus are more abundant below it. The expansion of the calcite compensation depth could limit life in vast areas of the ocean, impacting various species and ecosystems.
Furthermore, the effects of climate change, such as warming waters and declining oxygen levels, are also contributing to the shrinking of habitable spaces for marine species. As the calcite compensation depth rises and the ocean warms, marine habitats are being squeezed from both the bottom and the top, posing challenges for marine biodiversity.
Island nations are expected to be most affected by the expansion of the calcite compensation depth, with some countries facing significant losses in their exclusive economic zones. Countries with large continental shelves may experience proportionately less impact compared to oceanic and island nations.
In conclusion, the expansion of the deep-sea acidic zone due to the rising calcite compensation depth is a concerning trend with far-reaching consequences for marine habitats and biodiversity. Understanding these changes and their impacts on marine life is crucial for conservation efforts and sustainable management of ocean resources.
