The twilight zone, an oceanic region that lies between 200 to 1,000 metres deep, is under threat from climate change, warn researchers. According to a study, published in the journal Nature, life in this region could decline by as much as 20-40 per cent by the end of the century. Furthermore, if high-emissions continue, the twilight zone could face severe depletion within the next 150 years, with no recovery for thousands of years.
The twilight zone is an area that receives little light from the sun, yet it is home to an abundant and diverse range of organisms. It is estimated that billions of tonnes of organic matter exist in this region, which is critical for the ocean’s food web and carbon cycle. The zone plays an important role in regulating the Earth’s climate by absorbing carbon dioxide from the atmosphere.
However, as the Earth’s climate changes, the temperature and chemistry of the ocean are also affected. The rising temperatures cause the water to become less dense, which reduces the amount of oxygen that can dissolve in it. This makes it harder for marine life to breathe, and it can also lead to the release of nutrients from the deep ocean to the surface, which can alter the balance of the ecosystem.
Furthermore, the changing ocean chemistry caused by increased levels of carbon dioxide is making it more acidic. This acidification can have negative impacts on the growth and development of marine organisms, especially those with shells or skeletons made of calcium carbonate, such as corals and shellfish.
The combination of these changes is causing a decline in the abundance and diversity of life in the twilight zone. This could have a significant impact on the ocean’s food web and carbon cycle, which could in turn affect the Earth’s climate.
The study’s lead author, Dr. Stephanie Dutkiewicz of the Massachusetts Institute of Technology, said, “The twilight zone is vast, and the consequences of losing this zone for both the ocean and society could be severe. We need to be paying more attention to the impacts of climate change on the ocean, particularly in regions that are often out of sight and out of mind.”
The researchers used a computer model to simulate the changes that could occur in the twilight zone under different scenarios of future emissions. The model predicted that if emissions continue to rise at their current rate, the amount of organic matter in the twilight zone could decline by 35-60 per cent by the end of the century. This could lead to a reduction in the number of species that can survive in the zone, as well as a decline in the size of the organisms that remain.
The researchers also found that if emissions are reduced, the twilight zone could recover some of its lost biodiversity within a few decades. However, if emissions continue to rise, the recovery could take thousands of years.
The study highlights the urgent need for action to reduce greenhouse gas emissions and limit the impacts of climate change on the ocean. It also underscores the importance of protecting the twilight zone, which plays a critical role in the ocean’s ecosystem and the Earth’s climate.