Our DNA analysis of 75,000-year-old bones in Arctic caves reveals how animals responded to changing climates

While the Arctic warms faster than everywhere else on earth, the animals that have evolved to survive the cold face unprecedented challenges. While scientists learn more about how modern fauna reacts to environmental change, we still know about how species faced in the past.

Our new study studies the oldest diversified animal community in the European Arctic, dating from 75,000 years. Preserved at the bottom of a cave in northern Norway, it offers a rare overview of the operation of Arctic ecosystems for a slightly warmer phase of the last glacial period.

The Arctic region has undergone progress and repeated pensions of ice cream through the last glacial period (118,000 to 11,000 years ago) – a sequence of colder glacial conditions (stadials) and warmer phases (Intersadials), during which the glaciers have withdrew into higher elevations. These fluctuating conditions have led to successive migration and retraction of animals and plants, ultimately shaping the animal communities that we see today.

A consequence of being in an ice age is that sediment deposits are easily destroyed, while glaciers sculpt through the landscape and the cast iron rinses naked caves. This left very few animals and ecosystems records before the end of the last ice age, about 11,000 years ago.

But remarkably, a sediment deposit survived intact for more than 75,000 years in Arne Qvamgrotta, a branch of the largest system of Karst caves in Starsteinhola in Norway.

This cave is hidden just in the Arctic circle in the shade of the Norway National Mountain, Stetind, on the outskirts of the small coastal town of Kjøpsvik, Northland. The region is home to thousands of karst caves formed by dissolving water the underlying foundation, causing dramatic landscapes and breathtaking above and below.

The intact sediment deposit with preserved bones of Arne Qvamgrotta was discovered for the first time in the early 1990s, during the industrial mining activity for limestone. In 2021 and 2022, our team – led by the University of Oslo – returned to the cave to explore these sediments and to search and recover bone material, to better understand the diversity of species in this unusual deposit. Our analyzes provide a rare ecological snapshot of the last glacial period.

We have recovered more than 6,000 bone fragments, on which we used comparative osteology (comparing the bone form and structure to identify species) and the metabarcoding of ancient DNA (identifying the fragmented bones by analyzing the DNA strands and making them correspond to a species database). Using these techniques, we have identified 46 different types of animals (at family, gender and species levels), including mammals, birds and fish living on land and sea.

These species include the third oldest polar bear ever discovered, as well as walrus, archers’ whale and sea birds such as King Eider and Puffin. We found fish, including Arctic Grisling and Atlantic Cod. One of the most important discoveries is now extinguished necklace lemming, an animal that had not been identified before in Scandinavia.

We used various dating techniques that show that bones are about 75,000 years old – restoring a slightly warmer (interstadial) phase of the last ice age.

The animals that we found show that, during this period in this part of Norway, the coastal land was without ice – allowing the easy movement towards the north of migratory reindeer and freshwater fish, for example. We have also found a rich mixture of sea and coastal animals that support the presence of seasonal sea ice.

This animal community is clearly different from the most popular icy megafauna. These include woolly mammoth and musk beef which are generally associated with Mammoth steppe – the cold and dry meadows which extended in a large part of Europe, North America and North Asia during the last glacial period.

This difference probably reflects the single coastal frame and the landscape surrounding Arne Qvamgrotta, which would have supported another type of ecosystem.

Other analyzes of the ancient DNA of certain bones reveal that the lines of the polar bear, the lemming to collar and the arctic fox of this time and the place are now extinct. This suggests that these animals could not follow the changing habitats or find refuge during the subsequent cold periods of the last glacial period – clarification how vulnerable nature can be in changing climatic conditions.

This article is republished from the conversation under a Creative Commons license. Read the original article.