The results of a study published in the journal Nature Communications by an international research group led by Katherine A. Crichton of the University of Exeter, in the United Kingdom, conducted simulations to evaluate possible future scenarios in the event of low carbon dioxide emissions, medium and high.
The results show that due to climate change by the end of the century we risk losing 20-40% of the life forms present in the twilight zone. In a high-emissions scenario, life in this part of the ocean could even disappear within 150 years, with effects that could last for thousands of years.
By the end of the century, climate change could drastically reduce the life forms present in the mesopelagic zone of the oceans, located between 200 and 1,000 meters deep and poorly illuminated by sunlight, home to the largest and least exploited fish stock in the world.
Study coordinator Paul Pearson of Cardiff University explained: 'We found that the twilight zone was not always a rich habitat for life. In these warm periods, far fewer organisms lived in the twilight zone, because much less food." Katherine A.
Crichton told: "We still know relatively little about the twilight zone of the oceans, but by studying the past we can understand what may happen in the future. The variety of life in the twilight zone has evolved over the last few million years, when the water of the oceans has cooled enough to act like a refrigerator, preserving food longer and improving the conditions that have allowed life to thrive." The team, made up of paleontologists and ocean modelers, examined ocean sediments for the remains of ancient life forms dating back to two warm periods in the past, corresponding to 15 and 50 million years ago.
The mesopelagic zone is the pelagic zone extended between 200 and 1000 meters below sea level. It is located between the photic epipelagic zone and the aphotic bathypelagic zone, where light is completely absent. While some light can reach these depths, it is not enough to allow photosynthesis.
Although the temperature varies less at any elevation than in the epipelagic zone, the mesopelagic zone is home to the thermocline and temperatures range from over 20°C in the upper reaches to 4°C at the boundary with the bathypelagic zone.
Animals such as swordfish, squid, wolf eels, cuttlefish and other semi-abyssal creatures live here. Also, enough light reaches it to make some animals, such as the reticulated dogfish, fluoresce. The deep reflective layer is almost always located in this area.