Leaving the Arctic Behind – Of Polar Cod and Going Home

Quelle: blogs.helmholtz.de/polarstern/en/ 26 June 2015
Shannon MacPhee, Meri Korhonen, and Kirstin Werner
Only few days are left; we are approaching the end of the cruise. Last Wednesday we already entered the open ocean and left the Arctic sea-ice edge behind. On our way south, we passed an area inhabited by quite a few seals, and some of us were lucky enough to see whales. On Tuesday we had our last station; since then people have been busy with packing and cleaning the laboratories. The sudden emptiness of the labs seems somehow odd. While many of us will only be able to process their samples and generate data at our home institutions, we asked about some interesting things people have already noticed during the past few weeks. Many people had expected that the melt season would have already started and were thus surprised by the tough ice conditions. For example, the lack of meltponds, and that new ice, called grey or grease ice, was still forming as late as June 19th, was unexpected for many of us. On the other hand, the average ice thickness of 1.4 m was small compared to the ice thickness of 1.4 m usually observed in the Fram Strait by the end of the summer. Also related to sea ice, the team running the ROV has filmed brinicles, which are like icicles but under sea ice. These structures are formed when extremely saline water (so-called brines) drains from the sea ice and freezes the fresher water underneath. Formation of brinicles is possible because the saline brines remain liquid in lower temperatures than the fresher sea water. In addition, interesting features, such as deep scratches generated by icebergs have been seen on the seafloor using a multibeam mounted to the hull of the vessel. On our last ice station we were able to sample a meltpond where the algae Melosira arctica was found. Surprisingly for the trace gas team, it does not seem to emit much of the dimethylsulfide (DMS) relevant to clouds and therefore climate; on the contrary to another algae called Phaeocystis which the team found to produce lots of DMS. Being curious of what snow in the Arctic sea ice would contain, this group as well as other scientists filtered melted snow. From the darkness of the filters, they suspect high amounts of black carbon. Black carbon is usually produced by natural or anthropogenic combustion. Tracking it in Arctic snow might indicate long-range atmospheric transport, either from areas of natural wood burning, but possibly also due to industrial pollution. The foodweb ecology group was excited to find a lanternfish in their deepwater samples. They have also caught beautiful sea angels, ghost-like sea snails, and pteropods by the SUIT and RMT. This group was as well lucky to catch some individuals of polar cod. One of them was kept alive in an aquarium aboard. People could visit the fish, and quickly evolved some personal connection to it. The fish named Cindy soon became a new passenger on RV Polarstern. 'Polar cod is one of the two fish species in the Arctic Ocean that are specially adapted to live under sea ice', explains biologist Hauke Flores. Cindy was fed with copepods. To the dismay of several warm-hearted cruise participants Cindy finally returned into a sample number and was frozen for further analyses.   With these ambivalent emotions we are now leaving the Arctic Ocean. Though at times stressful, we eventually got into the working routine and could even feel home onboard. Spending six weeks on the research icebreaker within the Arctic sea ice was amazing, for some of us perhaps a once-in-a-lifetime-experience. Besides the scientific findings we also take home lots of memories. After having around us the beautiful colours of sea ice during the past weeks, we are now looking forward to meeting family and friends, and switching into the mid-latitude summer mode with green grass, flipflops, and maybe strawberries.