More than mud
Received from Daniella Gredin, The Swedish Polar Research Secretariat Edited by Jane Holst, GEUS
Edited by Jane Holst, GEUS, web-edition by Torsten Hoelstad, GEUS
30 August 2009
The icebreaker Oden
Position: 87°N 14°E
Weather: Sunny, temperature -6°C, wind 4 m/s
I have never given clay much thought before, let alone been fascinated by it. Some times I have come across colourful brochures trying to tempt me with spa-treatments, where the entire body is rubbed in some brown and sticky miraculous remedy, found at the bottom of the sea. But I have never bothered. At other times I have been annoyed when a fine sandy sea bottom turned into silt making my toes disappear. Then I prefer to dive into the sea from rocks. Once, during an adventurous lesson in biology, I studied bottom-living organisms near the Swedish coast. I don’t remember which species of larvae we found. So in spite of my sparse knowledge, I cannot help being fascinated by the clay lying in front of me. Each centimetre of this Arctic bottom sediment brings the researchers about 1000 years back in time.
During the LOMROG II expedition nine sediment cores have been taken along the Lomonosov Ridge both in the Eurasian and the American basins. The technique is called piston coring, where the core sampler is pushed into the sediment by releasing a weight from above. The first catch was meagre: only a small black stone. Since then one pipe after another filled with the much-coveted sediment has been brought up from depths of several thousand metres. The longest core is 7.87 m long, brought up from a depth of 3429 m.
When the 9 m long core sampler is brought out of the water onto the quarterdeck it is hosed down and winched into a steel cradle. Then the various sections are taken out of their plastic tubes and marked. Hopefully they are full of sediments. In the laboratory at the front of Oden, work is continued, the cores are examined in a machine, which calculates the samples’ density and how magnetic they are. The pipes are then divided in two parts. One of which is carefully packed in plastic ready to be filed without further interference in the cool archives at the University of Stockholm. The other half is examined on board.
The sea bottom of the Arctic Ocean can tell us much about the role of the Arctic in the global climate system in the past, the present and the future. By studying how the cores change in colour the researcher can get an understanding of previous climates. Dark-brown layers are evidence of warm periods with less ice. During periods with more open water the circulation and the oxygen content of the water are increased. This improves the living conditions for the fauna. Further down in the cores a marked grey layer is found. The layer is well known and is believed to be linked with lakes breaking out of their containment in the ice coursing under the ice sheet in Siberia approximately 50-60.000 years ago.
In the laboratory the researcher typically process one core per day. When the core has been registered and the archive part has been put aside, the surface of the work part is scraped with knife to remove any polluting objects. Then small plastic boxes are pressed into the core which are cut lose by nylon thread. These pieces of sediment are later sent to Germany to be X-rayed. On the X-ray pictures it is possible to see traces of how organisms have moved and how sea currents at the bottom have formed the sediment structures. Approximately 45 metres of core must be analysed during the expedition.