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Salty Atlantic waters may have been seeping into the Arctic since the early 20th century, several decades earlier than previously believed. The Arctic is warming faster than any other part of the world and the increasing influence of water from the Atlantic Ocean, which is on average warmer and saltier than the Arctic Ocean, is likely to be leading to further ice loss.

This effect is known as “Atlantification”, says at the Italian National Research Council Institute of Polar Sciences. But it is hard to quantify because we only have 20 years of confirmed data about the interaction between these waters, he adds.

He and his colleagues studied the Fram Strait in the Arctic Ocean between Greenland and the Norwegian archipelago Svalbard. They collected a 112-centimetre sediment core from the bottom of one of Svalbard’s inlets to reconstruct the history of the strait.

“The rock is in the ocean,” says Tommaso. “What we see is a reflection of the water’s properties.”

The layers of the core correspond to sediments laid down over the past 800 years, which hold clues to the time they were deposited. “Every centimetre gave us climate information for about four to five years,” says Tommaso.

The team found that for the earliest 700 years or so, nothing changed in the composition of organic matter in the sediment. But in samples corresponding to the year 1907, they saw a sudden change in the oxygen isotopes in the organic matter. “This change suggests the waters became a lot warmer and saltier,” says Tommaso.

The team is unsure what caused this dramatic shift in temperature. “It could be a natural event that propagated from the subpolar regions to the gate of the Arctic Ocean,” says Tommaso.

More data and modelling are needed to gain a clearer picture of what caused this sudden change, he says.

“This early Atlantification is important as it will have pre-conditioned the Arctic to be susceptible to the more rapid change seen today,” says at Bangor University, UK.

Understanding the history of this effect can tell us about how the ecosystem may respond in the future, says at the Scottish Association for Marine Science. “The process of Atlantification continues across the Atlantic-Arctic under post-industrialisation climate change.”

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