The encroaching dark and cold drizzle in Vineyard Sound provided the perfect backdrop Wednesday evening for a lecture on the mid-water depths of the ocean, a place called the Twilight Zone.

The talk at the Black Dog Tavern was given by Simon Thorrold, PhD, a senior scientist at the Woods Hole Oceanographic Institution (WHOI). Its full title was The Ocean Twilight Zone: New Discoveries from the Earth’s Last Frontier.

Mr. Thorrold was hosted by Sail MV as part of their 2024 winter lecture series, which was held in person for the first time this year since the beginning of the Covid-19 pandemic. Wednesday’s gathering was the last installment of this season’s series.

The Twilight Zone — also referred to as the mesopelagic zone — begins at around 650 feet below the surface and extends to 3,000 feet. It gets its name from the fact that these waters are out of sunlight’s reach. This region is home to at least a gigaton (a billion metric tons) of creatures, Mr. Thorrold said, including iconic bioluminescent oddities such as anglerfish and lanternfish.

It is also a key component in maintaining the earth’s climate, Mr. Thorrold said.

A large portion of the fish that live in the Twilight Zone are responsible for ferrying carbon deeper into the ocean on a daily basis. As the sun sets, these fish rise to surface waters to feed. Part of their meals include phytoplankton, which consume carbon dioxide through photosynthesis. When the fish return to deeper waters during the day, the carbon goes with them. When the fish aspirate and defecate in the deep, they release the carbon, where it remains for a longer time than it would on the surface, before dissolving back into the atmosphere.

“The lungs of the planet are actually this movement,” Mr. Thorrold said, emphasizing the importance of trapping carbon deep below the surface as the climate continues to warm.

“What happened in 2023 was actually pretty frightening, and, unfortunately, it looks like 2024 is going to be worse,” he said, referring to the warming planet.

Currently, WHOI’s Twilight Zone project is made up of 12 scientists, including Mr. Thorrold. The group aims to conduct more research, develop new technology and, in general, raise awareness for the public and policymakers.

Mr. Thorrold said the group has expanded on his earlier research about sharks. He had intended to study the horizontal movement of sharks, but found that they dove deeper than expected.

Mr. Thorrold added that commercial fisheries have begun to show an increased interest in these waters. He hopes that the research coming out of WHOI will help inform the potential impact of fishing the Twilight Zone.

“It’s for us as a society to decide what we value,” Mr. Thorrold told the audience, “It is my job as a scientist to explain the trade offs.”