Hamish Harding, a British businessman and explorer, was among those aboard the submersible that went missing in the North Atlantic on Sunday, according to Mark Butler, the managing director of Mr. Harding’s company, Action Aviation.

Mr. Harding, 58, who holds several Guinness World Records, including one for the longest time spent traversing the deepest part of the ocean on a single dive, wrote on his Facebook page on Saturday that he was proud to finally announce that he had joined OceanGate’s mission “on the sub going down to the Titanic.”

Mr. Harding is the chairman of Action Aviation, a sales and air operations company based in Dubai. He had previously flown to space on a mission by Jeffrey P. Bezos’s Blue Origin rocket company. He also took part in a mission for reintroduction of cheetahs to India, and holds a world record for the fastest circumnavigation of Earth via both the geographic poles by plane.

In an Instagram post on Saturday with pictures of the submersible and of him signing a flag for the Titanic mission, he wrote that the group had sailed from St. Johns, Newfoundland, Canada, on Friday, and was planning to start dive operations around 4 a.m. on Sunday.

The post included a reference to P.H. Nargeolet as a member of the submersible team. Paul Henry Nargeolet is a French authority on the Titanic wreck and has made numerous submersible dives to its site.

Despite the winter being particularly hard in Newfoundland this year, “a weather window has just opened up,” he added.

“More expedition updates to follow,” he wrote. “IF the weather holds!”

On Monday, the president of The Explorers Club, a New York-based organization of which Mr. Harding was a board member, alerted the club’s membership to the disappearance of the submersible on which Mr. Harding, along with four other people, were attempting to reach the Titanic.

“When I saw Hamish last week at the Global Exploration Summit,” wrote the official, Richard Garriott de Cayeux, “his excitement about this expedition was palpable. I know he was looking forward to conducting research at the site.

“We all join in the fervent hope that the submersible is located as quickly as possible and the crew is safe.”