The scientific party and crew are facing their final big challenge: a four day long dense sequence of CTDs, Ultra Clean CTDs (Fig. 1) as well as mooring recoveries and deployments.
The scientific party and crew are facing their final big challenge: a four day long dense sequence of CTDs, Ultra Clean CTDs (Fig. 1) as well as mooring recoveries and deployments.
A particular focus rests with the planned three fish moorings, which shall be deployed along this section. Our biologists would like to develop a method with which they can efficiently catch Antarctic toothfish (Dissostichus mawsoni) alive for scientific studies. Little is known about this species, which might reach an age of 50 years, knowledge that is urgently needed to protect it efficiently from a steadily growing commercial fishing industry, or at least to define regulations, which ensure its sustainability. However, for genetic and physiological studies it is mandatory to catch specimen and hold them in pens, one of which we set up especially for this expedition next to the fish lab. Unfortunately, the three fish moorings (Fig. 2) with which the fish shall be hoisted slowly and carefully from the depth, and which we had moored at 800, 1000 and 1200 for 24 hours each, turn out to be little effective. Not a single Antarctic toothfish is found hooked upon the mooring’s retrieval.
Our section ends at night with a Manta net (Fig. 3). Towing the net parallel to Polarstern, our Swiss colleagues sieve large amounts of water, searching for microplastic, meanwhile a nearly globally occurring trace of our civilization. At sea, only the larger particles may be detected and identified, but back home in the laboratories of their AWI partners on the island of Helgoland even the smallest particles will be analysed for their composition.
The final stations occur near Elephant Island. A last mooring with oceanographic and ocean acoustic instrumentation is recovered and redeployed, three further fish moorings are deployed and recovered a day later, time which we use for taking a quick group photo (Fig. 4) and a final RMT and Manta net casts. The NIOZ Ultra Clean CTD team samples their last incubator experiment on the sun-lit observation deck before starting dismantling their equipment. All across the ship scientists start packing up their gear and cleaning the labs, since, after being our homestead for nearly 8 weeks, we need to hand them over empty and clean to the next expedition as if nobody ever dwelled here before.
All that is left to do is to sum up what we achieved. Even though medical evacuation and logistic constraints caused significant delays, we were able to achieve most of our goals, not at least because the unusually low sea ice cover and storm activity allow for quick travelling between the stations. All oceanographic moorings and 8 fish moorings were retrieved or deployed as planned for (with the exception of one mooring that remained undeployed due to bad weather). More than 89 nets were cast, collecting a multitude of specimen for further analysis. The global fleet of profiling Argo floats was augmented by 22 floats and our understanding of the Southern Ocean was furthered by more than 80 CTD and UCC casts, which also served to deliver profiles of oceanic temperature and salinity. Water samples were drawn concurrently for various projects, analyzed on board or conserved for analysis in our home labs. Our bird and whale observers spent nearly 400 hours on the observation deck, weathering storm, snow and rain. And, last but not least, on 6 ice stations and 7 under ice ROV deployments the fauna directly under the ice was examined. This is, all in all, in spite of many hindrances, a noteworthy achievement, both due to a dedicated scientific team and outstanding crew and officers of Polarstern, all of which were highly committed to our common goal: Unveiling the secrets of this unique environment of our one and only home planet.
Science and ship wave good-bye to Antarctica, which sink below the horizon while bumping across Drake Passage – offering 8 Bft and 5m waves. We look forward to entering Magellan Strait and soon to arrive at this expedition’s final destination, Punta Arena. Seeing you soon!
Olaf Boebel
