Mountain flowers during the last Ice Age

Fjellvalmue-ingress
08.09.2016
Was our country completely covered by ice during the last ice age? Or did there exist ice-free nunataks (isolated peaks of rock) where certain hardy plants were able to survive? This has long been discussed by biologists and geologists, but the mystery remains unsolved.

In this first article about mountain plants, I have benefited from the botanical expertise of Kristine Bakke Westergaard.

 

By Fridtjof Riis
This article was previously published on www.geoforskning.no


Cartography: Fridtjof Riis

A number of  between 50 and 100 flowering plants with a  bicentric or unicentric distribution grow in the northern and southern culmination of the Scandinavian mountain range.
Cartography: Fridtjof Riis

 

When the inland ice receded from Scandinavia, the mountain plants rapidly followed. They established themselves in various colonies in locations where they could thrive. Botanists are able to trace their migration routes from the south and east.

However, the situation is more complex in some mountain regions in the northern and southern culmination of the Scandinavian mountain range. Between 50 and 100 flowering plants grow here, which are what we call bicentric or unicentric.

Some grow in just one, or just a few locations. Around 30 of them are west-arctic – apart from here, they are found only on Iceland, Greenland and in North America. They are all hardy, although some of them require conditions that are not extremely harsh, and they do not have fruit and seeds that are designed to spread very far. How can we explain the migration history of these species? When and how did they cross the Atlantic Ocean?

Botanists Sernander and Blytt launched the overwintering theory in the 1890s. They believed that such isolated species in Scandinavia must have survived the maximum glaciation during the last Ice Age, either on nunataks or in ice-free areas along the coast.

The overwintering theory was rejected by geologists, who had long claimed that absolutely all of Scandinavia had been covered by a thick layer of ice in the Late Weichsel. The alternative hypothesis was that the plants must have migrated in from areas outside of the Scandinavian ice sheet after the cold period that occurred between 25,000 and 18,000 years ago (the Last Glacial Maximum).

Summer 1977: Field research with bedrock mapping for NGU (the Geological Survey of Norway) south of the Lyngen Alps in Troms. We tackled one mountain every day, 1500 metres up ice-scoured mountainsides with good profiles through the thrust nappes on the way up to an entirely different landscape – let's call it Norway's roof.

Norway's roof consists of sloping ridges and mountain plateaus with blockfields and some solifluction (creeping soil), no solid bedrock, no ice-scouring to be seen. On Russetind, the highest small mountain plateau, surrounded by wide, deep valleys, between the patches of snow, there, and there only, blooms the yellow mountain poppy.

The mountain poppy is a hardy plant. Together with Purple saxifrage, it grows along the earth's northernmost fixed point, Kaffeklubben Ø in the Arctic Ocean north of the Greenland inland ice. The Scandinavian variety of the mountain poppy is found here in Norway, as well as on Iceland and the Faroe Islands.

There are quite a few isolated colonies in the mountainous areas in both the north and south. Each area has its own variety which differs slightly from the other forms of the same species.

I had studied plant geography as a young student, but it was right then and there, in 1977, that I understood what overwintering really meant. Why should we construct a long migration path for these plants, which are designed to live on windblown peaks? Could it be possible that the ice wasn't actually that thick after all?

About a decade later, around 1990, I worked with Willy Fjeldskaar to understand the large-scale glaciation of Scandinavia, glacial erosion in the Barents Sea and on the mainland, and the deposit of sediments on the Shelf. We enjoyed close contact with the Quaternary geology communities in Norway.

How thick was the maximum ice sheet? Both very thick and very thin ice models have been proposed in literature. Because the ice cap creeps outward and breaks up where it meets the deep sea, the surface height of the ice can be modelled.

Not all of the parameters were well-known, but the ice cap in Fjeldskaar's updated models was thinner over the mountains in western Norway than was indicated by the thickest model, and the top was not very much higher than the highest mountaintops.

 

DNA provides new answers

A small, isolated plant colony will gradually develop genetic dissimilarities. The degree of difference between several such plant colonies tells us how long they have been isolated, but cannot provide an accurate absolute age.

Extensive use of DNA surveys in recent years has given botanists new insight and facts that can help determine whether the overwintering theory can be supported .

For example, studies of mountain poppies reveal that, even though the various stands have somewhat different appearance, the genetic variation is not so great that it could not have developed after the last glacial maximum. The genetics of mountain poppies can neither prove, nor disprove, the overwintering theory.

Kristine Bakke Westergaard has studied genetic variation in arctic plants living in Scandinavia, Iceland, Greenland, North America and on Svalbard.

Studies like these indicate that even plants with seeds that are not normally transported far can spread surprisingly fast, e.g. on drift ice and with the wind over ice-covered areas. In an article in Science, Alsos et.al. (2007) have documented spread over to Svalbard from other land areas.

The DNA studies in the west-arctic plants which were examined by Kristine reveal genetic lines that have spread over the Atlantic Ocean after the last glacial maximum, both to the east and to the west.

Kristine concludes both that long-range spread has occurred, and that species may have survived in areas that lie within the maximum extent of the ice cap. The method does not determine exactly where these areas were located, but provides indications as to which direction the spread has taken.

 

Many signs pointing towards Andøya

2009-2010: In the Norwegian Petroleum Directorate, we evaluated the shelf off Lofoten and Vesterålen. The shallow layers are important in the understanding of petroleum geology. Andfjorden and Vestfjorden are large glacially formed troughs.

Throughout all the ice ages over the last 2.7 million years, ice streams in these troughs have transported and deposited erosion material out to the shelf edge and on the slope to the deep sea. The rest of the shelf edge between Vestfjorden and Andøya received little Quaternary sediments, because the mountain ridges in Lofoten and Vesterålen steered the huge ice streams toward the north and south.

From Andøya, it is just 15 kilometres to the shelf edge where the ice stream from Andfjorden calved. The mountaintops had local cirque glaciers that have created alpine landscape features, and contributed to the formation of the strandflat.

The sea level was low during the glacial maximum, and the shallowest banks may have been exposed. The data may indicate that the ice sheet was separate from the inland ice in the shelter of the Lofoten mountains, but does not reveal whether parts of the banks may have been ice-free.

Research conducted at the University of Tromsø shows that the oldest sediments in lakes and marshes on Andøya date back more than 20,000 years. An article by Parducci et al. (2012) in Science interprets findings of DNA from spruce and pine in material from these old deposits. It's not a long way from Andøya to the northern centre for rare mountain plants.

One special variety of the tundra vole lives here. This is a good starting point for botanists, zoologists and geologists searching for traces of life during the last glacial maximum.

We see a similar geometry on the Møre coast with high mountains and alpine formations near the deep sea. The largest ice streams were deviated to the north and south of the highest mountains, and the banks are shallower than is otherwise the case on the Shelf.

 

Spotlight on beryllium

Small quantities of Beryllium-10 form in quartz grains that are exposed to cosmic radiation. Measuring beryllium isotopes in quartz grains from surface samples tells us how long they have been exposed.

Surveys of 10Be in block fields in the high mountains over the last ten years have yielded a better understanding of the thickness of the ice sheet during the last glacial maximum and have revealed that the block fields on Norway's roof may be extremely old.

The mountain landscape in the coastal areas west of the Svartisen glacier is marked by ice erosion. I know of just one mountain that stands out: Helgelandsbukken, which towers over the other mountains and is situated between two deep fjords. Henriette Linge et al. (2007) conducted a number of beryllium analyses from Helgelandsbukken, from other mountains and from the lowlands west of Svartisen.

They write that, while all other mountaintops are ice-scoured, Helgelandsbukken is covered by block fields, seemingly unaffected by ice. A small remnant of Norway's roof. The beryllium ages correspond with this, being situated at approx. 15,000 years in most of the locations, while Helgelandsbukken gives 30,000 to 50,000 years.

 

Fjellvalmue er vanlig i Arktis, dette er varianten svalbardvalmue (Longyearbyen).

The Arctic poppy is common in the Arctic, this is the Svalbard poppy
(Longyearbyen) variety.

 

A feature that is not mentioned in the article is that Helgelandsbukken area is the only locality for a specific form of mountain poppy called Svartisen poppy. It is a protected species, and a symbol for Meløy municipality. Do the beryllium ages mean that Helgelandsbukken was ice-free during the glacial maximum, a nunatak? Not necessarily.

An ice sheet that merely rests on top of the block field without eroding or moving it will not re-set the beryllium ages. This can happen with cold ice that has frozen to the underlying base. The article also states that modelling has been created for the movement of the ice from Svartisen and down into the fjords, and that the maximum top of the ice might have been around 90 metres above the mountaintop.

In the seedbank on Svalbard, seeds are stored in a dry environment at a temperature of 18 degrees below zero Celsius. Michael Heim has made me aware that under such conditions some seeds can germinate after several thousand years, and that may be a factor that has helped mountain plants to survive.

The only location of the Svartisen poppy  is found on Helgelandsbukken. It is protected, and is a symbol of Meløy municipality.

 

Utsikt fra Helgelandsbukken mot Engabreen og Svartisen.

View from Helgelandsbukken towards Engabreen and Svartisen. The glaciers erode sharply in valleys and canyons, but the block field on the mountain plateaus lies untouched.

 

What are you doing here in the crater?

Summer 2006: Fieldwork on the Ritland structure in Rogaland county alongside geologists from the University of Oslo. A couple of colonies of field locoweed (Oxytropis campestris) grow in a warm, sunny pasture above the treeline.

In Norway, this plant is only found in a few places in the mountains in Hjelmeland municipality, with the closest occurrence being in Scotland. Hjelmeland and the neighbouring municipality of Suldal have three mountain plants, with isolated occurrences of this type.

They are not nearly as hardy as the mountain poppies, and there have been no nunataks in the area. Only the Norwegian trench separates them from what was once large areas of land in the North Sea during the last ice age.

Kristine Bakke Westergaard has studied genetic material from other mountain plants in Scotland, and suggests that they came from Central Europe after the ice started to recede. The field locoweed has not yet been analysed; perhaps it has a similar history.

 

A force that cannot be modelled

We still don't have a satisfactory explanation for the mystery of the mountain plants. There are various, co-existing hypotheses.

However, with the knowledge we have today, it should be possible to arrive at a broad understanding of the ice conditions and the climate in Scandinavia during the glacial maximum, and the conditions this posed for various types of life.

In any event, the spread of these mountain plants illustrates the powerful force of life: Species survive and spread under extreme conditions where it seems unlikely that anything could survive.

Vitality - a factor that cannot be modelled, and that helps plants and animals adapt to even the most extreme climate changes.


Topics: Geology