9 January 2008Called back to the icePolarstern ANT–XXIV–2The stations selected for our sampling provide a comparison between areas of high and low surface production; we follow its path down to the deep seafloor. So far, we have sampled going north to 62° S along the 3° W transect, then south on 3° E. The pelagic gear — Rectangular Midwater Trawl, multinets and under-ice net — caught mainly krill, with the occasional small squid and pelagic worm. As expected, the krill Euphausia superba was dominant but in some trawls the related species Thysanoessa macrura also appeared in reasonable numbers.
On each transect, we took underway measurements and water samples. At every degree of latitude, deep Conductivity Temperature Depth casts went down to the seafloor, alternately with ‘shallow’ casts to 1,000 m on the half degree. The deep casts take an hour to reach the bottom at about 5,000 m. The physical characteristics of the water mass tell us about the habitat of the pelagic animals. A special water sample catches the larval stages of the copepod crustacean Oithona similis; they are too small to be held in our smallest .055 mm multinet mesh. Krill eat these and other species of copepods.
We completed a comprehensive sampling station at Maud’s Rise, position 62° S 3° W. This seamount has a plateau at 2,200 m, emerging from the abyssal plain at 5,300 m. The seafloor video hovered over many metres of mud — exciting to us but not likely to be a best seller! The sediment looked suitable for our sampling gear, so during the next 48 hours we sent down two multiple corers, a box corer and the Lander sediment profiler with attached scavenger trap. Each gear brought back perfect samples and some amazing animals — thank you, Maud!
Echinoderms dominated the catch of the Agassiz trawl on Maud’s Rise. The holothurians were huge; the largest purple specimen weighed 3.6 kg. This ugly sea cucumber eats detritus (compost) on the sediment to maintain its massive size. What a life in the deep, dark ocean! Two other species were common — in total the holothurians weighed 11.5 kg. Brittle stars were abundant; they also feed on detritus near the surface of the sediment. The trawl caught a few ice fish, specially adapted so that their blood does not freeze in the sub-zero water temperatures.
The voyage Polarstern ANT 24-2 has logistic as well as a scientific responsibilities. We have been called to assist the freighter Naja Arctica. Stuck in the heaviest ice for the last 15 years, she cannot deliver the important cargo of construction materials to build the permanent base Neumayer III. The Polarstern is an impressive 118 m long with displacement 17,277 tonnes. Rated ARC 3, the second-highest ice class, she has double steel hulls, each 58 mm thick at the water line and a special deep 11.2 m draft for ramming ice. The extreme thick ice in Atka Bay will test her strength.
Victoria Wadley |
|
