Arctic Ocean started to warm decades earlier than scientists thought

The Arctic Ocean has been warming since the beginning of the 20th century, fueled by a process known as Atlantification, according to a study published Wednesday in the journal Science Advances.

The new research highlights the connection between the North Atlantic and Arctic between Greenland and Svalbard, a region known was Fram Strait, where warmer, saltier water from the south has been steadily infiltrating northern waters.

"Pinpointing the exact timing of the onset of Atlantification in the Arctic can give us some important clues as to the exact driving mechanisms behind this phenomenon," study co-lead author Francesco Muschitiello told UPI in an email.

A more precise Arctic warming timeline will also allow scientists to compare the history of climate change in the Arctic to changes in volcanism, solar activity, freshwater, greenhouse gases, aerosols and more.

"[This] will ultimately help better quantifying the sensitivity of Arctic warming to natural versus anthropogenic forcing," said Muschitiello, a marine scientist with the University of Cambridge's Department of Geography.

For decades, scientists have noted changes in Arctic climate patterns. The atmosphere and ocean near the poles are warming at a rate double the global average, ocean waters continue to grow saltier and sea ice remains on the retreat.

But the mechanisms driving these accelerated changes remain a point of contention among Arctic researchers.

"There is some ongoing debate in our community as to what drives the recent rapid sea ice retreat in the Atlantic portion Arctic," University College London climate scientist Michel Tsamados told UPI in an email.

The drivers of Arctic warming and sea ice loss either are oceanic or atmospheric or some combination of the two.

"Some of the recent views are that most of the variability is atmospheric-driven, with winds and temperature driving sea ice variability that in turns imprints the ocean temperatures," said Tsamados, who was not involved in the new study.

"Others have hypothesized regional mechanisms by which localized tipping points in sea ice decline are driven by the combined effect of the thinning sea ice cover and Atlantic warm current influxes in the region," Tsamados said.

To figure out exactly when and how the Arctic Ocean began warming at an accelerated rate, researchers studied chemical changes in the fossil shells of microorganisms from ocean sediments.

The seafloor sediment cores provided researchers with geochemical and ecological data stretching back 800 years.

For most of those 800 years, researchers noted the Arctic Ocean's temperature and salinity were relatively stable. But the geochemical signatures began to shift around the beginning of the 20th century, revealing a significant uptick in temperature and salinity.

When scientists compared their updated warming timeline with records of ocean circulation at lower latitudes, they found the shift corresponded with a slowdown of dense water formation in the Labrador Sea.

Scientists expect deep water circulation within this subpolar region to decelerate as the planet warms and temperature differences between polar and mid-latitude regions decrease. As result, researchers predict climate change will continue to spur Atlantification in the Arctic Ocean.

"Establishing accurate timing between events in the Arctic proper and sub-Arctic areas is critical for understanding linkages and causation of changes observed in the polar basins," University of Alaska atmospheric scientist Igor Polyakov told UPI in an email.

"Various temporal and spacial scales of processes involved in communication of the Arctic Ocean with lower latitude basins make this analysis very difficult and each new study is a welcome addition to the previous efforts," said Polyakov, who has studied Atlantification in the Arctic, but was not involved in the most recent paper.

Perhaps most importantly, Muschitiello and his colleagues were able to show that most climate models fail to identify this early period of warming surrounding the Fram Strait, which suggests simulations don't fully account for the mechanisms driving Atlantification in the Arctic.

The climate models used to predict how Arctic systems will behave in the future -- and influence climate systems all over the globe -- must rely on accurate reconstructions of past climate change, researchers said.

"[Pinpointing the exact timing of the onset of Atlantification in the Arctic] also provides an important 'observational' benchmark to improve historical climate model simulations and highlight physical processes that are potentially under-represented in climate models," Muschitiello said.

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