Where is the twilight zone

Marine Research: Diving into the Twilight Zone

It is home to much of the marine fish biomass and helps remove an estimated four billion tons of carbon dioxide from the atmosphere annually. Scientists are now preparing to dive into the Twilight Zone. In the largely unexplored sea layer at a depth of 200 to 1000 meters, which is threatened by a changing climate and fishing.

In April, NASA will travel to the North Atlantic to study the movement of carbon between the atmosphere and the deep ocean. The mission costs $ 25 million. Others will join the expedition thanks to a collaborative project unveiled at the American Geophysical Union's ocean science meeting in San Diego, California in mid-February.

"This is literally the largest investment ever made in the Twilight Zone," said Dave Siegel, an oceanographer at the University of California, Santa Barbara. He heads the NASA mission called Export Processes in the Ocean from Remote Sensing, or EXPORTS for short. The network is designed to enhance data sharing and coordination with other research efforts around the world. "If we can band together, we can help each other."

Exploring the depths

The twilight zone begins where photosynthesis fails and extends to the point where there is no light at all. Here countless living things depend on pebbles and dead organisms that fall from above - typically called sea snow. Tiny grazers also soar into the upper ocean every night to hunt, making the largest migration of animals on earth. Larger predators such as whales and sharks often look for food in this area, and humans are also increasingly keeping an eye on the abundance of the animals. Commercial fisheries in Norway and other countries have already started harvesting krill, which prefer to live in the twilight zone.

Some scientists fear that the exploitation of this largely untapped protein store will increase in the future due to the increasing demand for food. That could have an impact on the marine food web and ultimately the climate, says Philip Boyd, a marine ecologist at the University of Tasmania in Hobart, Australia who leads a project that studies how much carbon falls into the abyss of the Southern Ocean.

The ocean is doing a vital service to humankind by removing carbon from the atmosphere, and that depends on what happens in the twilight zone, says Ken Buesseler, a marine radiochemist at the Woods Hole Oceanographic Institution (WHOI) in Massachusetts. "It's that simple," he says, "but it's not easy to measure."