Major nations announced the creation of the world's largest protected ocean reserve around Antarctica on October 27 after Russia dropped previous objections to the treaty.
Officials credited the efforts of U.S. Secretary of State John Kerry, a passionate advocate for the reserve, who aides said pressed hard to persuade Russian President Vladimir Putin to go along with the pact this year.
The final deal creating a 1.55 million square kilometer reserve the size of Britain, Germany, and France combined in Antarctica's Ross Sea included changes to address Russian concerns by allowing sustainable fishing in a small part of the reserve, officials said.
"We had a lot of talks with them. Secretary Kerry reached out to Russian President Putin and [Foreign Minister Sergei] Lavrov, and I think that helped a great deal to convince Russia to come on board," said Evan Bloom, head of the U.S, delegation in Hobart, Australia, where the agreement was announced.
In a statement, Kerry said the agreement "will safeguard one of the last unspoiled ocean wilderness areas on the planet -- home to unparalleled marine biodiversity and thriving communities of penguins, seals, whales, seabirds, and fish."
Andrew Cavanagh of The Pew Charitable Trusts said the reserve had become a passion project for Putin's former chief of staff, Sergei Ivanov.
The Ross Sea is one of the last intact marine ecosystems in the world. It is considered critical for scientists to study how marine ecosystems function and to understand the impacts of climate change on the ocean.
"For the first time, countries have put aside their differences to protect a large area of the Southern Ocean and international waters," said Mike Walker, project director of the Antarctic Ocean Alliance, calling the outcome "momentous."
Reaching the deal required a consensus between 24 countries and the European Union charged by treaty with protecting Antarctica. That consensus had been elusive to reach in the past, despite years of negotiations.
