Arctic Ocean temperature rose earlier than expected

Man-made climate change is ensuring that the world’s oceans are getting warmer and the poles are melting. In the Arctic Ocean, the problem is exacerbated by the influx of warm waters from the Atlantic Ocean. A new study now shows, based on analyzes of sediment over the past eight hundred years, that the so-called analysis of the Arctic Ocean may have actually begun at the beginning of the 20th century – decades earlier than previously assumed. The new findings also point to a gap in previous climate models.

Of all the world’s oceans, the Arctic Ocean is the hardest hit by global warming. Being the world’s smallest and flattest ocean, it is warming especially rapidly – with dire consequences not only for sensitive polar ecosystems, but also for the global climate. Due to rising water temperatures, the ice in the polar region is melting and sea level is rising. In addition, sunlight falling off the sea surface is reflected less strongly by ice, so more heat is absorbed and temperatures continue to rise. In addition, Arctic permafrost stores large amounts of greenhouse gas methane, which is released when permafrost thaws.

look at the past

The influx of warmer, higher salinity water from the Atlantic Ocean also plays a role in the warming of the Arctic Ocean. Automated records documenting this process, for example via satellite measurements, have only been around for about 40 years. A team led by Tommaso Tessi of the Polar Research Institute of the National Research Council in Bologna has taken a look back at the past. “We know from satellite measurements that the Arctic Ocean has been rising steadily, especially over the past 20 years, but we wanted to put the recent warming into a longer context,” says co-author Francesco Mochitello of the University of Cambridge.

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To do this, the researchers examined sediment samples from the Fram Strait region between Greenland and Svalbard, a link between the Atlantic Ocean and the Arctic Ocean. In sediment samples, covering a period of 800 years, Tessie and colleagues analyzed the chemical signatures of microorganisms such as foraminifera. Depending on the temperature and salinity of the water in which they live, these single-celled marine organisms store different oxygen isotopes in their dwellings, thus providing researchers with clues about the environmental conditions at the time the layer of sediment in question formed. The researchers combined this information with other data, including sediment lipid analyzes, local climate records and various dating methods.

Rapid heating at the beginning of the twentieth century

In this way, the scientists were able to trace the temperature and salinity of the transition between the Atlantic and Arctic oceans over centuries. The result: “If we look at the entire 800-year timescale, the temperature and salinity are fairly constant for a long time,” Tessie says. “But at the beginning of the twentieth century there was suddenly a significant change in temperature and salinity – and this is really noticeable. With regard to current reconstructions, our results show a rapid and early Atlantic analysis of the eastern Fram Strait at the beginning of the twentieth century.”

The researchers’ analyzes show that at this time the sea ice was receding rapidly, causing the plankton to bloom seasonally, the waters getting warmer, especially in summer, and the mixing of the water layers more in the winter. According to the researchers, a possible reason for the increase of the Atlantic at the beginning of the Industrial Age is that the Little Ice Age ended in the mid-19th century, after which the ocean circulation in the North Atlantic changed and enabled more efficient heat transfer. to the North Pole. “Our results suggest that we will have to account for more Arctic Atlantic in the future due to climate change,” Muschitiello says.

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Climate Models Gap

“Natural and anthropogenic effects on the North Atlantic system remain controversial,” the researchers wrote. They also suggest that their results point to a potential flaw in climate models. “Climate simulations cannot reproduce the kind of warming we observed in the Arctic Ocean, which means that understanding the mechanisms driving the Atlantic process is incomplete,” says Tessie. “We rely on these simulations to predict future climate change, but the lack of any evidence of early warming in the Arctic Ocean is a missing piece of the puzzle. Solving these modeling problems will be crucial to improving the accuracy of the prediction in space in response to future Arctic warming.”

Those: Tommaso Tesi (Institute of Polar Sciences, National Research Council, Bologna) et al., Science Advances, doi: 10.1126/sciadv.abj2946

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