“The proposal required some changes in order to gain the unanimous support of all 25 CCAMLR members and the final agreement balances marine protection, sustainable fishing and science interests,” New Zealand Foreign Minister Murray McCully said.

“The boundaries of the MPA, however, remain unchanged.”

Moscow was the last government opposing the move, due to concerns over fishing rights, after China offered its support last year.

“When we came to Hobart we didn’t know the result and it was Russia that needed to come on board,” said Evan Bloom, head of the US delegation at the meeting.

“We had a lot of talks with them. Secretary (John) Kerry reached out to Russian President (Vladimir) Putin and (Foreign Minister Sergei) Lavrov and I think that helped a great deal to convince Russia to come on board.

“This decision is very important not just for the Antarctic but for efforts to promote world marine conservation,” he added.

But time ran out to reach agreement on a second proposed protected area on the meeting’s agenda -- the Australia and France-led East Antarctica sanctuary covering another one million square kilometre zone.

Both reserve proposals have been on the table since 2012 with CCAMLR - a treaty tasked with overseeing conservation and sustainable exploitation of the Antarctic Ocean, also known as the Southern Ocean.

Consensus is needed from all 24 member countries and the European Union.

A third German-proposed plan is also in the works to protect the Weddell Sea, which extends from the southeast of South America over an area of some 2.8 million square kilometres.

The Ross Sea is one of the last intact marine ecosystems in the world, home to penguins, seals, Antarctic toothfish, and whales. It is also 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”.

“Although there was not a decision on the proposed protection of the Weddell Sea and the East Antarctic this year, we are confident that these areas will be protected in the coming years, adding to the system of marine protected areas in the Southern Ocean.”

The agreement culminates years of pressure by conservationists, including a campaign by the global civic movement Avaaz which was kickstarted by Hollywood superstar Leonardo DiCaprio and supported by over two million signatures from across the world.

“There’s massive momentum in the world right now to protect our oceans,” said Avaaz campaign director Luis Morago.

“The Ross Sea is just the start.”