In the Arctic marine sediments was found cosmic dustremnants of stellar explosions from Space, which it reveals how extensive the sea ice was in this area in the past. Researchers at the University of Washington made the discovery, who published it in a study in the journal Science. Cosmic dust, which regularly falls on Earth, provides this important information because where sea ice is absent it manages to accumulate in ocean sediments, while where it is present it is blocked on the surface. By measuring the amount of space dust in the sediments, the researchers reconstructed the extent of Arctic sea ice in the United States last 30,000 years. Studying its evolution helps to understand how this behaves in relation to climate change.
How cosmic dust allows us to tell the story of the evolution of ice in the Arctic
When stars explode or when comets and asteroids collide with each other, the so-called cosmic dust. This dust, passing close to the Sun, is enriched with a rare form of helium, called helium-3. Its particles fall at a regular rate to the Earth and then to the bottom of the oceans, where they add to the dust of terrestrial origin. To distinguish space dust from terrestrial dust in Arctic marine sediments, the researchers used the isotope helium-3. Measuring the quantity in sediment cores allows us to understand where sea ice was once found: when the sea surface is covered with ice, dust cannot settle on the seabed, but when it is absent it can. The researchers took sediment cores in three different sites: one near the North Pole, which remains covered by sea ice year-round; one located along the edge of the sea ice during its seasonal minimum extent; one that is now ice-free for much of the year. By measuring the quantity of cosmic dust in the carrots it was thus possible to reconstruct theevolution of sea ice over the last 30,000 years. During the Last Ice Age the central Arctic Ocean was always covered with sea ice throughout the year, as demonstrated by the absence of dust on the seabed, while around 15,000 years ago the ice began to retreat and the dust reappeared.
What is the connection between changes in Arctic ice and nutrient consumption?
The researchers’ attention was also focused on shells of very small organisms called foraminiferacontained in the sediments. Their composition reveals the amount of nutrientsin particular nitrogen, which organisms used while alive. By comparing these values with sea ice extent data, it was discovered that the nutrient consumption it was highest when sea ice cover was low and decreased when it increased. This indicates that the ongoing retreat of Arctic ice due to climate change will be accompanied by increased nutrient consumption by the phytoplanktonmade up of microscopic organisms that use them for photosynthesis in surface waters. In turn, phytoplankton is eaten by other organisms, so this alteration has consequences for the entire food chain. Further research is needed to understand why ice variation affects nutrients. For example, a smaller amount of ice might encourage photosynthesis on the surface, increasing the absorption of nutrients.
