Arctic Forests: What the Svalbardian rocks tell us about past climate and future warming

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This was written by guest contributors Thomas Frank and Stan Schouten

Barren lies the tundra right outside the northernmost city in the world, Longyearbyen. As the winter approaches, strong winds and cold temperatures make this place truly hostile. The darkness of the winter months adds to that, allowing only very specialist forms of life to survive here high above the Arctic circle.

While the fauna has managed to sustain even large species such as the polar bear, the flora is limited to flat vegetation with hard leaves creeping on the cold ground. It is impossible for any bigger plants to survive in such a cold environment with only very short growth seasons. Indeed, it is very hard to imagine that this climatic setting could have been different in the past – and yet it´s true.

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The continent configuration 60 million years ago with Svalbard (small yellow circle) still attached to Greenland (own figure). Illustration by Thomas Frank and Stefan Schouten.

The plant fossils that can be found in abundance in the moraines around the mountain Sarkofagen right at the very edge of Longyearbyen; bear witness to a once very green and vivid Svalbard. But what factors contributed to such a big change? And could this past climate be a blueprint for the future given recent rises in global temperatures? The answer to that, with implications far beyond the coastlines of Svalbard, could be hidden in the rocks right around Longyearbyen and is subject to extensive research efforts.

Going back 60 million years, a climate much warmer than to today reigned over the earth. Ocean temperatures on the equator of 36°C, thunderstorms of incredible strength and heat waves hotter than the warmest temperatures measurable presently created a hothouse climate beyond imagination.

A human civilization under those conditions? Impossible! Similar to the rest of the planet, the polar areas were much warmer than they are today, and lush forests were dwelling on both Antarctica and the land masses surrounding the Arctic Ocean. Metasequoia, a huge coniferous tree related to the present day giant redwood trees of California, dominated the Svalbardian woods. Besides, large-leafed deciduous trees flourished in the undergrowth. Little ponds and ferns added to the picture of a dense green landscape. The climate was moist and damp with only small changes between the seasons. Even in the wintertime, the temperature did not fall below zero, allowing large reptiles to live above the Arctic Circle.

Hard to imagine now, but an alligator fossil has been excavated as far north as Ellesmere Island in the Canadian Arctic. In Svalbard, the fossil record is also dominated by warmth-loving creatures. Footprints of a Pantodont, a horse-like herbivore, were found in Gruve 7 (known in English as Mine 7). Such an animal eating grass and leaves could, under no circumstances, survive even one year in the current Svalbard climate.

Looking back so far in time means looking at a historic Earth almost as alien to us as a distant planet. The land distribution was completely different from today as were the oceans and the atmosphere. The Atlantic Ocean was just about to open up completely, Antarctica was attached to South America, and what is now central Europe and Russia was divided by a shallow but wide ocean strait. The Arctic Ocean was an almost entirely closed basin with only very little exchange of water with the rest of the world´s seas. Svalbard was at that time at 80°N and still attached to Greenland, but an eastward movement of this little patch of Earth along developing faults foreshadowed the coming divorce.

This shearing eventually started to build up a mountain chain in eastern Svalbard which would later – shaped by the elements through many million years – form the sharp tops visible today along western Spitsbergen. Due to the buildup of those mountains in the east, heavy load was put on the earth crust in that area. And similar to how the surface of an air balloon forms a depression when pressing with a fingertip, a little basin slowly developed to the west of that mountain chain. As the mountains grew, they simultaneously started to erode, leading to more and more sediment being produced and deposited in the depression in the west. In the beginning being a marine basin below the sea surface, eventually the whole depression was filled up until a land surface was established. This basin has become central Svalbard and now, after having undergone uplift and extensive erosion including several cycles of glaciation, forms the landscape around Longyearbyen. Like baking a layer cake for several million years, sedimentary layer upon sedimentary layer had been deposited, until the cavity was filled to the top.

For geologists, such a setting is like winning the jackpot. Every climate change, every variation in biology has the potential to be recorded somewhere in the sediment if the record isn´t disrupted by gaps. Regarding the last 60 million years, this is the case for Svalbard’s rocks and they therefore constitute a world-class geological location. As a result, research institutes from the whole world come to Svalbard every year. The question that drives them all: What makes the earth warm up so extremely that even the polar regions accommodate temperate rain forests? And is this a possible scenario for the future?

To answer this, particular focus has been laid on a period about 55 million years ago that can be studied in the Svalbardian sedimentary rocks. During that time, a sharp temperature increase has been detected called Paleocene-Eocene Thermal Maximum (PETM) that stands out above the already warm climate before and after this event. Temperature skyrocketed even more and subtropical droughts, wide ocean circulation alternations and large-scale migration of animals are associated with this warming event. It is now believed to be a consequence of increases in atmospheric greenhouse gases that provided the initial spark. This signal was then amplified by positive feedback mechanisms and so the Earth maneuvered itself into an overheated state.

This might well look like an analogy for what we are experiencing currently and, indeed, some similarities are present. Just like back then we observe changes in weather patterns and the behavior of animals. And just like back then CO2 levels are clearly rising at a rate unmatched by any other time in Earth’s history, leading to a steady increase in global temperature. However, an important difference is that we do not yet observe direct triggering of these large-scale feedback responses by greenhouse gasses. The background temperature and the CO2 levels were much higher back then, so the fragility of the climate was different, perhaps more susceptible to changes. The main cause for the PETM temperature rise is assumed to have been methane release from the ocean bottom as a result of water temperatures exceeding a certain threshold. As those were much higher than today already at the beginning of this thermal maximum, this scenario might be less likely to occur in the near future.

In any case, both the past and present are characterized by high greenhouse gas concentrations. For the past, scientists estimate the CO2 level at 800-1600 ppm. That seems to be far away from our current values of 400 ppm but, worryingly, when continuing our current emissions we might arrive there as early as 2085. Uncertainties in the models that predict climate change impacts are still present as the complex nature of the earth system makes it hard to reliably predict the future.

However, there is no doubt that CO2 plays a major role in trapping heat which is proven both on a theoretical level and with the evidence of the past. Therefore, an analogy between the Eocene and the present can certainly be seen, even though it is unlikely that we will experience forests in Svalbard anytime soon. A lesson that we can learn from studying the past is however very important: If the climate system has started to move into a state of increasing warmth, feedback mechanisms will probably amplify that signal considerably. But in order to understand what that really means and which mechanisms are at play, more research is needed and Svalbard is a perfect location to do that.

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Thomas Frank of Germany and Stan Schouten of Utrecht University were guest researchers in Arctic Geology at The University Centre in Svalbard in the spring of 2018.

 

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