Today was –again- a great day for me on board Polarstern. It started in a bit of shock, as Bram, doing the early morning shift in counts of birds and mammals on top of the ship, woke me up by calling me via the stand-by mariphone in my cabin. He excitedly reported seeing “Brown Spots” which must sound weird and requires some explanation. Since my first marine science cruise on Polarstern, almost 20 years ago in 1988, I have been seeing occasional mysterious ‘brown spots’ while conducting the bird and mammal counts. They measure from several meters up to maybe a 100m in diameter. They are not easy to see if you’re not constantly on the lookout. Only with variable success I have been able to convince other people that indeed ‘something’ was there in the water. In my view, the spots had to be zooplankton swarms, but most others were rather sceptical and offered alternative explanations that ranged from cloud-shadows to whale-shit and accumulated algae in the water. Zooplankton was considered not to swarm so close to the surface during daylight hours.
Over the years I have tried many times to set up a way to have a closer look at the mysterious brown spots, but never managed because it’s not easy to change the planning of a big ship. But earlier on this voyage, we observed brown spots again, and this time from the helicopter. This led to a plan that abandoned the idea to use the ship to sample the spots, but instead aimed at using the helicopter! Chief scientist Uli Bathmann approved this ghost-hunt of a crazy Dutchman. So the IMARES team with the pilots and technicians of HeliTransair prepared a small net strong and heavy enough to be lifted as a sling-load under the heli. It sat waiting in the heli-hangar for a next opportunity.
And thus finally, this morning, that opportunity arrived. Around 09:00 we took off, flying to the last position on which Bram had seen the brown spots, and indeed we found them. Pilot Jürgen and technician Marcus skillfully manouvred the heli above the spot and lowerd the heli to about 5m above the water allowing the net to sink to about 15m depth. Then the heli slowly regained height to pull the net and its hopeful contents out of the water. I was so incredibly curious if our attempt had been successful, but had to be patient as flying back to the ship with a sling-load had to be done slow. The net was lowered to the helideck, and yes, only then I could see that indeed our out-of-the-ordinary plan had been a success: the orange shining of krill was visible through the gaze of the net. The swarm proved to consist of very young small krill. Why these animals swarm and why so close to the surface is somewhat of a mystery. And rather than helping us to solve the complex biology of the Southern Ocean, it makes our task more complicated. Important things are going on in the surface layer of the water that will need new approaches in future studies.
This first bit of an answer to a 20 year long puzzle in my life means that the 19th January 2008 has been indeed a great day for me. But there have been many good days. In spite of the considerable time that Polarstern had to spend on ‘logistic duties’ for Neumayer on this voyage, the Dutch IMARES team already now can look back on a successful expedition. We were able to collect extensive data on distributions of marine mammals and birds and had excellent results from the fishing with our “Surface and Under Ice Trawl (SUIT). The successful ‘Brown Spot’ action of today is the cream on the cake.
Jan van Franeker, Wageningen IMARES
the newly constructed Helinet hanging from the helicopter
Location: 66°S, 0°W
the first young krill ever flown in by a helicopter
Location: 66°S, 0°W
very young krill was caught with the first ever Helinet from the surface
Location: 66°S, 0°W
Photos: J. van Franeker and V. Wadley, Australian Antarctic Division
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Saturday, 19 January 2008 12:59
A mystery solved at 66°S-0°WWritten by Polarstern Expedition
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