Climate change: life in ocean ‘twilight zone' at risk from warming

Scientists caution that the amount of life in the deepest, sunlight-accessible portions of our seas might drastically decrease due to climate change.

By the end of the century, global warming may have reduced life in the so-called twilight zone by as much as 40%.

Between 200 meters (656 feet) and 1,000 meters (3,281 feet) is the twilight zone.

Researchers discovered that while it is teeming with life, warmer times in Earth's past were home to fewer creatures.

Researchers from the University of Exeter examined data from tiny shells that were preserved to study two warm eras of Earth's history that occurred around 50 million years ago and 15 million years ago.

They discovered much fewer organisms were in the zone at these times because less food from the surface entered the twilight zone as a result of faster bacterial food degradation.

Dr. Katherine Crichton, from the University of Exeter, was the study's lead author. "The rich variety of twilight zone life evolved in the last few million years, when ocean waters had cooled enough to act rather like a fridge, preserving the food for longer, and improving conditions allowing life to thrive," she said.

The disphotic zone, commonly referred to as the twilight zone, is an important habitat for marine life. According to the Woods Hole Oceanographic Institution, it is too dark for photosynthesis to take place yet is home to more fish than the rest of the ocean combined as well as a diverse spectrum of life, including bacteria, plankton, and jellies.

As a carbon sink, it also plays a crucial role in the ecosystem by removing gases that warm the globe from our atmosphere.

The scientists created computer simulations of current and potential twilight zone events as a result of global warming. They said that their research indicated important changes could already be under progress.

According to Dr. Crichton, "Our study is a first step to determining how vulnerable this ocean habitat may be to climate warming."

"This could result in the disappearance or extinction of much twilight zone life within 150 years, with effects spanning millennia thereafter, unless we rapidly reduce greenhouse gas emissions," according to the report.