Top image: Old seabed peeks out on the sandbanks of Torskevatnet. Photo: Malin Daase (UiT).
Rijpfjorden not only holds a very special place in the story of how the weather station Haudegen housed the last armed German soldiers towards the end of World War II. It is also home to a much older and equally important story – a story that stretches several thousand years back in time and has not yet been really told. This is a story told by the “cod lake” (Torskevatnet).
18 September 2018
Text: Professor Jørgen Berge (UiT, the Arctic University of Norway, UNIS and NTNU).
Beyond Vindbukta on the east coast of Rijpfjorden, is Torskevatnet (Cod lake). This lake has gotten its name after it was found cod there in the 1990s. The cod now seems to have disappeared, but the name remains. But the history of Torskevatnet does not start there. It starts many thousands years ago, at a time when the sea level was much higher than today. At that time there was a fjord where Vindbukta is today – a fjord with a relatively shallow threshold and a pool within which was 50-60 meters deep. Along the banks of this fjord there were many organisms that we still can find in Rijpfjorden today, such as wrinkled rock-borer (Hiatella arctica) and truncate softshell (Mya truncata). But there were also other species not found today in Rijpfjorden (and hardly anywhere else in Svalbard). Blue mussels are perhaps the best known example; another is saltwater clams (Mya).
It gives a very special feeling to go across the valley from Vindbukta towards Torskevannet. It’s not a long walk, barely 1 kilometer. But it really feels like going back in time. The tundra is meager and one can only feel sorry for the poor Svalbard reindeer that go down the slope and look for something green to eat. And here, six thousand years ago, there was a fertile seabed.
Particularly in the sand banks around Torskevatnet there are clear traces of the seabed that once was here, both in the form of shells in small streams where melting water has dug into the ground and not least the areas where the old seabed is almost untouched. In the picture we see an example of the seabed – here are soft-shell clams (Mya arenaria) half buried in the ground in exactly the position they lay in when they died. Soft-shell clams are a species we today only rarely see in Svalbard, but they are very common further south. Both these and the blue mussels tell a clear story about a climate that was significantly warmer than today. And when you see the shells exposed like this, it’s really not hard to imagine how they lived a few thousand years ago!
But it’s not just shells that testify to a bygone era. The lake has also two other time witnesses who tell a story. Along the southwestern bank there is a whale skeleton, according to the size and how the bones are spread out, possibly a Fin whale or Blue whale? In the sandbank a little above the lake we find remains of the jaw and some vertebrae, while in the water there are more bones. This whale must have strayed into the fjord before the fjord was cut off from the rest of Rijpfjorden. It has probably sunk down on the bottom and been eaten by amphipods, snails and fish before it has been covered by sediments from melting glaciers. Today, rain and meltwater have uncovered the skeleton again.
In the water we also find another time witness of a bygone era. Those who would like to dive down to about 12 meters will see something that is both quite special and actually a bit scary when you see it with your own eyes; while the upper 12-13 meters are freshwater, there is a salty, dark and totally lifeless layer at the bottom. This is simply old sea water that has got a layer of fresh water at the top. The water is what we call for ‘meromictic’. While the Torskevatnet was still a fjord, there would have been a continuous exchange of water masses with Rijpfjorden, largely driven by the melting water from surrounding glaciers. But after the fjord was turned into a lake, this fresh water has been like a lid over the old salty water. And this is where the cod in the “Cod lake” comes from.
I have never caught cod in Torskevatnet, but I have colleagues who have. For instance, professor Svein Østerhus who accompanied us to Rijpfjorden this summer. He says that they caught cod here for a period of 4-5 years in the 1990s. The special thing about this cod was that it lived in the fresh water layer, not in the salt water. The cod must simply have been caught in the lake through some event that has caused seawater and fish to have entered the lake or the lagoon below. And just the fact that there has been cod there helps to explain why the deep layer in the water is so much saltier than normal seawater. When the cod has successfully entered the lake, it is likely that such events have occurred both before and later. Throughout the last thousands of years, sea ice and/or seawater from the Polar Ocean and Rijpfjorden have provided an extra salt water supply. In this way, the salty layer at the bottom has become extra salty and eventually also completely free of oxygen. Today, there is only life in the upper freshwater layer, and the only fish we have found since 2003 are char and humpback salmon. But that’s another story.