ANT-XXVII/3, Weekly Report No. 5
7 March - 13 March 2011 (CAMBIO)
In the Antarctic the time flies by. With astonishment we state that at this time, after the fifth week, half our expedition time is over. The weather has been less kind to us, however, as we have had problems with bad visibility rather than with the sea-state. Miserable sight condition due to fog or heavy snow impedes reconnaissance and slows down our steaming through the ice-fields, making it impossible to find lagoons in the ice where we can work. Thick ice-fields and drifting growlers endanger wires, cables and instruments. High swell brings water on deck and lets gear, such as the multicorer (MUC) or Dieter’s magic gear (MG), swing dangerously on the winch cable. The bongo or light plankton nets can fly like kites in the high winds. Heavy pitching of the aft deck impedes work with the MUC and ROV as the ship’s movement causes their position to vary in relation to the seafloor. Although the weather impedes regular work on “Polarstern” less than on other ships it has to be taken into account as it is still a serious factor under Antarctic conditions.
At the beginning of the week we continue our catches and ROV video transects in the Larsen B area. We find a conspicuous contrast between the miserable catches of the AGTs, which are largely full of mud and stones with the only noticeable animals being brittlestars and shells of small scaphopods, and the ROV pictures from 160 m. The ROV moves along the coralline and ground shell substrate with many larger stones that have obviously been there quite some time. They are colonised over and over with pink and white hydrocorals, bryozoans, gorgonians resembling bottle-brushes, worm tubes and grey encrusting sponges. Upon these organisms, and even on ascidians, sit isopods keeping their legs with the filter combs into the current to catch particles. In the lights of the ROV we see quince yellow and vivid green sponges amongst the shell and debris between the stones, and once the lights of the ROV pick up an octopus coloured the same pink as many of the hydrocorals. The motile crinoids here have extended their arms and tube dwelling worms have extended their tentacle crowns to filter food from the current. Different sea urchins, of the short and long-spined type, and ophiuroids are sitting in large numbers between the stones. A large sea star is spotted eating an adult sea urchin.
Why is this community so diverse and others at a short distance so very poor? One reason seems to be that this coral community was never covered by the ice shelf. However, that is true also for the poor community in Larsen C. Dieter will try to find out whether there have been long-term differences in the sea-ice cover in the past.
On Tuesday thick grey clouds are hanging above the almost complete sea-ice cover that surrounds us at 800 m depth. It is predominantly multi-year ice of considerable thickness with a snow layer up to 1 m. After a reconnaissance flight of the helicopter it is clear that the only things we can use here are the corers. Several multicorers are coming up with holothurians, and the video of the multibox corer shows on a light, soft bottom these 'sea-pigs' and other holothurians, polychaetes and ophiuroids. A bit further north we find open water for the towed gear, but the station B north that we planned we have to cancel as towards the weekend a storm is to come from the south-westerly direction and this might trap us in the ice. An AGT comes up with a torn cod-end from the deep, and Henri looses his Rauschert dredge, of which only the hanepot is left attached to the cable. The bentho-pelagic trawl is deployed for the third time and catches, beside several kilograms of ice-krill, some dozen juvenile silverfish (Pleuragramma) of 8 cm length. The weather on Ash Wednesday fits the day. It is foggy and once again the light has difficulty penetrating the clouds. The ice rain at night, which makes the deck dangerously slippery, changes to snow, although it does become a little warmer. We steam northward through giant icebergs which were probably formerly part of the Larsen ice shelf, and which are often higher than the ship including the chimney and mast. To the front visibility is very poor, sometimes the size of the icebergs can be estimated only at the last moment, but Captain Pahl and his Mates always find a lead.
On Thursday morning we are back in Larsen A. It is even darker than on the previous days. It is snowing heavily but the storm that was announced to us seems to have changed its mind. We lie close to the shore between islands, whose steep slopes resemble those of Norwegian fjords. Because of the snow cover it is not always clear what is land and what is iceberg; also on the icebergs there is often sediment or stones.
The large AGT gets stuck on the seafloor and pulls wire from the winch, but comes free and the net remains intact, although with only 10 animals, mostly brown echiurids. The yield of organisms is once again extremely low. The small AGT is deployed immediately afterwards and brings up from 300 m a tonne of mud and stones which cost us 2 hr of washing and sieving, but which also yield a more representative catch of organisms. The young researchers are sieving the material with great enthusiasm, interrupted with occasional snowball fights. Echiurids, small bivalves and tube-dwelling polychaetes dominate the catch. Organismic density this close to glaciers is extraordinarily low. We see that also on the video of the MG from 200 m, which shows fine, grey sediment from the glaciers’ abrasive action on the bedrock, and many stones. The holes in the sediment with an earth-wall around are likely to be the dwellings of echiurids, which throw out the digested sediments. The storm remains absent. The explanation of the meteorologists is that we are in the eye of the low-pressure system. The snow ceases, the sea around us is covered with a thin layer of new ice with snow cover on top.
On Friday there is more light and it remains quiet. We conduct a ROV at 140 m at the station Larsen A south, close to the shore, which replaces the ROV that was cancelled due to weather the week before. Close to the seafloor a lot of krill is observed swimming around the lights. The community is similar to the previous station at Larsen B, but medium sized glass sponges are more common, with some younger ones seen less frequently. However the stalked ascidians, which Julian found here a couple of years ago as an almost mono-specific community have practically disappeared. In general this community has reached 1.5 decades after the collapse of the ice shelf a fairly high state of development, showing considerable biodiversity. Special attention finds a demersal yellow ctenophore which is fishing plankton with long tentacles. Its relatives all have a pelagic lifestyle.
On Saturday we experience the edge of the storm. In our lagoon we face a choppy sea and it is extraordinarily cold in the wind. The deck has a thin layer of snow and ice. We are fishing with the large bentho-pelagic net. The success is low – a few dozen Pleurogramma of different size, some ice fish and a few kilograms of ice krill. There is really not much in the way of fish in the pelagic zone. At the bottom there seems to be more life as observed on the video pictures.
On our farewell from Larsen we have the pleasure to have one of those Antarctic days one will never forget. At about 09:00 the sun climbs out of the sea like a fireball in the east, painting the new ice areas around the ship and the snow and ice-covered mountain chain of the Peninsula to the west into quickly changing colours from red, via pink, to white. As then the orange/red buoys of Dieter’s moorings come to the surface without problems, our luck seems perfect. However, there is a bitter aftertaste to the sweet success of the recovery as only the pelagic sediment trap has worked while the benthic sediment trap has not.
The last AGT is taken from 170 m from where the ROV had recently taken the video. It contains many live fish which go straight to the aquarium, lots of medium sized sponges, sea urchins, gorgonians, ophiuroids and ascidians. On the whole it is fairly diverse. In the afternoon we carry out an emergency polar baptising of Stephanie on the working deck. The whole group is participating. Stephanie has to be flown out via the Chilean station Frei, due to a health problem which cannot be treated on “Polarstern”. After the baptism we have our obligatory group photo on the helideck.
With that we are finished at Larsen. In the most beautiful sunshine we steam for the north and pass the remains of the ice shelf for several hours. In distances of a few hundred meters there are again and again small waterfalls of meltwater, and in other places these waterfalls have frozen to cascades of icicles. A breathtaking landscape in front of the mountain chain of the Peninsula! Everybody who is not occupied is meeting on the helideck. What great luck for us to be allowed to be here today.
We on board greet those at home from the temporarily sunny Antarctic.
Rainer Knust - Chief Scientist Wolf Arntz - Rapporteur