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Climate: Arctic Ocean has been warming since the beginning of the 20th century


An analysis of drill cores shows that temperatures in the Arctic Ocean rose earlier than expected. However, the study should by no means be interpreted as a doubt about the climate models, the researchers write.

Enlarge image

Iceberg in front of Svalbard

Photo: AGAMI / P.

Morris / IMAGO

The Arctic is a region of great global interest.

On the one hand, climate change has a particularly strong impact, for example with the melting of the glaciers in Greenland and the sea ice.

The consequences of this have an impact on other regions.

Global ocean currents may change.

Scientists have therefore now studied the warming of the Arctic Ocean.

According to a new study, it started much earlier than previously assumed.

Using drill core analyzes, an international team reconstructed the sea temperature on the west coast of the Spitzbergen archipelago over the past 800 years.

The scientists write that since the beginning of the 20th century, more warm and salty water flowed from the Atlantic into the Arctic Ocean.

The study by the team led by Tommaso Tesi from the Istituto di Scienze Polari in Bologna in Italy and Francesco Muschitiello from the University of Cambridge in Great Britain was published in the journal »Science Advances«.

The researchers see their publication as a suggestion to improve climate prognoses, but in no way as a doubt about the climate models in general.

"The rate of warming in the Arctic is more than twice as high as the global average due to feedback mechanisms," Muschitiello is quoted in a communication from his university.

One of these feedback loops is the difference between ice and open water: While the light ice reflects most of the incoming sun rays (high albedo), the darker water absorbs more solar energy and warms up faster.

The more the ice melts, the more dark ocean surface becomes free.

Since around 1900 the Arctic Ocean has become about two degrees Celsius warmer.

Drill core off Spitsbergen

For around 40 years, modern measuring instruments, including satellite measurements, have been registering a rise in temperature in the Arctic Ocean. But Tesi, Muschitiello and colleagues wanted to know when this development began. They concentrated on the eastern part of the Fram Strait, the sea area between Svalbard and Greenland. One of the northernmost foothills of the Gulf Stream runs along there, the West Spitsbergen Stream. It is considered to be the main source of salt and heat in the Arctic Ocean.

The scientists used a drill core from the Kongsfjord on Spitsbergen, which they examined for various chemical-physical markers. Most importantly, they analyzed the amount of microscopic living things, mainly foraminifera. Due to their preferences for certain environmental conditions, these single-cell organisms show how warm, salty and nutrient-rich the water was in which they lived. In this way, the researchers reconstructed the development of these water properties.

For most of the 800 years the values ​​were fairly constant. "But at the beginning of the 20th century you suddenly get this significant change in temperature and salt content - that really stands out," says Tesi. He and his colleagues see a connection to the end of the Little Ice Age at the end of the 19th century. The rising temperatures around the turn of the 20th century would also have had an impact on ocean currents. The sub-polar eddy south of Greenland has weakened, so that warmer and salty Atlantic water reached the Arctic Ocean. The year 1907 emerges as the turning point from the various series of measurements.

The researchers tried to find this turning point using simulations in the latest global climate models, but they did not succeed.

This means that the understanding of the mechanisms that drive the warming of the Arctic Ocean by Atlantic water is incomplete in the climate modeling, emphasizes Tommaso and adds: “We rely on these simulations to predict future climate change, but the lack of any signs early warming in the Arctic Ocean is a missing piece of the puzzle. "

joe / dpa

Source: spiegel

All tech articles on 2021-11-25

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