Defective climate models? The Arctic Ocean started to warm decades earlier than expected

The Arctic Ocean has been warming since the start of the 20^e century – decades earlier than records suggest – due to the warmer water flowing into the delicate polar ecosystem from the Atlantic Ocean.

An international group of researchers has reconstructed the recent history of warming oceans at the gateway to the Arctic Ocean in a region called the Fram Strait, between Greenland and Svalbard.

Using chemical signatures found in marine microorganisms, researchers found that the Arctic Ocean began to warm rapidly at the turn of the last century as warmer, saltier waters poured in from the Atlantic – a phenomenon called atlantification – and that this change probably preceded warming. documented by modern instrumental measurements. Since 1900, the ocean temperature has risen by about 2 degrees Celsius, while the sea ice receded and the salinity increased.

The results, published in the journal Scientists progress, provide the first historical perspective on the Atlantic Ocean Atlantic and reveal a connection with the North Atlantic that is much stronger than previously thought. The connection is able to shape arctic climate variability, which could have important implications for sea ice retreat and sea level rise as polar ice caps continue to melt.

Using chemical signatures found in marine microorganisms, researchers found that the Arctic Ocean began to warm rapidly at the turn of the last century as warmer, saltier waters poured in from the Atlantic – a phenomenon called atlantification. Credit: Sara Giansiracusa

All of the world’s oceans are warming due to climate change, but the Arctic Ocean, the smallest and shallowest ocean in the world, is warming the fastest.

“The rate of warming in the Arctic is more than double the global average, due to feedback mechanisms,” said co-lead author Dr Francesco Muschitiello of the Cambridge Department of Geography. “Based on satellite measurements, we know that the Arctic Ocean has warmed steadily, especially over the past 20 years, but we wanted to put recent warming in a longer context. “

Atlantification is one of the causes of arctic warming, but instrumental recordings capable of monitoring this process, such as satellites, go back only about 40 years.

As the Arctic Ocean warms, the ice in the polar region melts, which in turn affects global sea level. As the ice melts, it exposes more of the Earth’s surface. ocean in the sun, releasing heat and raising the air temperature. As the Arctic continues to warm, it will melt permafrost, which stores huge amounts of methane, a greenhouse gas much more harmful than carbon dioxide.

Researchers have used geochemical and ecological data from ocean sediments to reconstruct changes in water column properties over the past 800 years. They accurately dated the sediments using a combination of methods and looked for diagnostic signs of Atlanticification, such as a change in temperature and salinity.

“When we looked at the entire 800-year timescale, our temperature and salinity records seem pretty constant,” said co-lead author Dr Tesi Tommaso of the Polar Science Institute. National Research Council of Bologna. “But all of a sudden at the beginning of the 20^e century you get this marked change in temperature and salinity – it really stands out. “

“The reason for this rapid Atlanticization at the gateway to the Arctic Ocean is intriguing,” said Muschitiello. “We compared our results with ocean circulation at lower latitudes and found that there is a strong correlation with the slowing of dense water formation in the Labrador Sea. In a future warming scenario, the deep circulation in this subpolar region is expected to decrease further due to the thaw of the Greenland ice sheet. Our results imply that we might expect a further Atlantic Atlanticization in the future due to climate change. “

The researchers say their findings also expose a possible flaw in climate models, as they do not replicate that early atlantification of the turn of the last century.

“Climate simulations generally do not reproduce this type of warming in the Arctic Ocean, which means that there is an incomplete understanding of the mechanisms behind atlantification,” Tommaso said. “We rely on these simulations to project future climate change, but the absence of any sign of an early warming of the Arctic Ocean is a missing piece of the puzzle.”

Reference: “Rapid Atlanticization along the Fram Strait at the beginning of the 20th century” by Tommaso Tesi, Francesco Muschitiello, Gesine Mollenhauer, Stefano Miserocchi, Leonardo Langone, Chiara Ceccarelli, Giuliana Panieri, Jacopo Chiggiato, Alessio Nogarotto, Jens Hefteros, Gsoianmarco Ingredients , Federico Giglio, Patrizia Giordano and Lucilla Capotondi, on November 24, 2021, Scientists progress.
DOI: 10.1126 / sciadv.abj2946

Francesco Muschitiello is a fellow of Sidney Sussex College, Cambridge.