The Bjerknes Centre is a collaboration on climate research, between the University of Bergen, NORCE, the Institute of Marine Research, Nansen Environmental and Remote Sensing Centre.

Mountains separate Svalbard's glaciers today. Photo: Raymond S. Bradley

Moss in sediments suggests ice-free spot in ice age desert

In the coldest years of the last ice age, the ice cap reached the British Isles and Poland. New research has revealed a green patch much closer to the North Pole. Part of a peninsula in Svalbard was free from ice.

In a lake named Hajeren in the northwestern part of Spitsbergen, scientists have found fossils of mosses in sediments that are 20 to 30 thousand years old. At that time the ice cap over Northern Europe was at its greatest, covering all of Scandinavia, large parts of northern Europe and most of the British Isles. 

The results are presented in an article in the journal Science Advances today. Hajeren is located on the peninsula Mitrahalvøya, not far from the research station Ny-Ålesund on Spitsbergen. 

“It is incredible that a place so close to both the North Pole and big glaciers today, was ice-free during the coldest period of the last 100 000 years”, says Willem van der Bilt. 

Van der Bilt is a researcher at the Bjerknes Centre for Climate Research and the University of Bergen, and has led the study. 

The findings in Hajeren do not mean that the rest of Svalbard was free from ice. The ice cap reached north from Scandinavia and covered all of the Barents Sea, Novaya Semlya and Svalbard. It was much colder there than at the southern border through Poland. 

Huge glaciers or ice streams flowed from the ice cap through the fjords of Svalbard, ending at the continental shelf outside the western coast. Still, the new study indicates that there may have been ice-free and vegetated land between the fjords. 

Svalbard
Map of Svalbard showing the location of the lake and the extent of the ice age 20 and 30,000 years ago. From van der Bilt, 2019.

Life in an icy desert

«Svalbard was not really an island, but a continental, polar desert”, says Willem van der Bilt. “It was bone dry”. 

At the western coast, where Hajeren is located, the glaciers met sea ice. The islands were locked in the ice, and the air was dry. There was not much snow. Later, after 20,000 years ago, the glaciers expanded over the Mitrahalvøya peninsula, but in the period with the most extensive ice cover over Northern Europe, there may have been too little precipitation to maintain glaciers there.

“Clearly, temperature was not an issue”, says Willem van der Bilt.

The green patch was due to the lack of snow.

Volcanic ash sets the time

The fossils were found around three meters down in the lake sediments. At the same depth, the scientists found volcanic glass they could trace to an eruption on the Azores Islands around 23,000 years ago. 

The bottom of lake Hajeren builds up gradually by minerals and organic materials in the water draining into it. As a result, substances in the lake sediments can tell about things that have happened in the catchment, provided one knows when they were deposited.

Willem van der Bilt and his colleagues collected a sediment core from the bottom of the lake in 2012. They found fossil remains of mosses at three levels. Dating of the mosses and other organic material in the samples showed that the sediments were allowed to build up undisturbed, layer over layer, in the period from 30,000 to 20,000 years ago. 

Exact dates were complicated to obtain with the Carbon-14 method used. The method provided an estimate and showed that the age of the sediments increased evenly downward, but did not give the researchers an absolute age for each sediment layer. 

In a one-centimeter thick layer they knew was somewhere between 19 and 23,000 years old, they found volcanic glass – transparent shards about two hundreds of a millimeter in diameter.

Sediment core
Sediment core and fossilized moss. The graph in the middle shows the sediment age by depth, with markers representing the fossils. Ill.: Willem van der Bilt.

Chemically matched candidates

In this period, there were large eruptions from Etna and Vesuvius, as well as from volcanoes on Iceland and Ischia. Comparing the chemical composition of the shards from Svalbard with known characteristics of ashes from these volcanoes, the researchers excluded all of them as sources. 

The glass in Hajeren could only have come from the Azores Islands. With one volcano, the match was complete: Pico Alto on the island of Terceira. Indeed, this volcano did have a large, explosive eruption between 22,700 and 24,500 years ago. 

The volcanic glass helped the scientists set the time and also supported their theory that the catchment had been free from glaciers. That the glass from the ashes from the Azores was concentrated in such a thin and homogeneous layer, indicates that it must have fallen straight from the air, not taking the way through melting glacier ice. 

Return of the ice

Around 20,000 years ago, there was a full stop. The sediment layer above is only 11,000 years old, from the end of the ice age. Willem van der Bilt argues that the 9,000-year long hiatus means that no material was deposited in this period. The bottom of the lake stopped growing. 

This indicates that the entire area was glaciated and lake Hajeren frozen solid. As the sediment layers have not been destroyed, the ice must have been a so-called cold-based glacier, frozen to the base, with no melting there and without rapid movements that tear down everything below. 

Svalbard glacier
The ice is not far away, even today. Photo: Raymond S. Bradley

Present-time parallels

Today, Svalbard is gradually coming out of the ice. The glaciers on land are retreating, and there is much less sea ice around the islands than only a few decades ago. From the ice-free ocean, water evaporates, making the air more humid.

“This may have implications for the future response of ice sheets in a warmer world”, says Willem van der Bilt. 

He points to Antarctica and the northern part of Greenland as examples of regions that are shielded from humid ocean air today, like Svalbard was 20,000 years ago.

Finding out how much or how little snow that can have fallen from the dry air over western Spitsbergen at that time, will be one of his future tasks. 

He will also have a closer look at the mosses. The same species exist on Spitsbergen today, raising the question whether they may have survived througout the ice age or have returned at a later stage. If DNA from the fossils can be linked to mosses that grow in Svalbard today, it is likely that the plants that made Mitrahalvøya green between 20 and 30 000 years ago never were eradicated. 

Reference

van der Bilt, Willem G. M. & Lane, C. S. (2019): Lake sediments with Azorean tephra reveal ice-free conditions on coastal northwest Spitsbergen during the Last Glacial Maximum. Science Advances, 2019