JR157: Seabed biology of Marguerite Bay, Antarctica


 JR157



Cruise Diary


Date: Friday 2 Febrary 2007
Position: 68o44.9’ S, 69o34.2’ W, Bourgeois Fjord, Antarctic Peninsula

Chris writes:

"Since my last entry we have found ourselves somewhat thwarted by the Antarctic weather, although we are genuinely very grateful for the calm conditions we have had for science since 18 January. On Wednesday night (31 January) we attempted to head back out into Marguerite Bay to visit another site on the shelf break. However, as we headed out the sea conditions worsened and in the small hours of Thursday morning the Captain, in agreement with the lead PI, decided that it would be unsafe to launch and recover Isis in such rough conditions.

As an alternative we headed to what has become our final science site. We have moved inside Adelaide Island and have steamed up the Bourgeois Fjord, past Pourquois Pas Island and to the snout of the Pernatz Glacier. We have come here to investigate the effects of recent cycles of glacial advance and retreat on both the seabed geology and biology, in contrast to the older sites we explored in deeper water earlier in the trip.

Once again the scenery has been spectacular and those that were not immediately involved in science spent most of Thursday out in the biting wind taking photographs of the mountains and icebergs which have carved off from the numerous glaciers and which litter the fjord. The high mountains surrounding the fjord have, however, blocked our satellite links to the outside world. This has meant we have had had no email or internet access for the first time on this trip, hence the delay in sending this diary entry. For some this has been quite a relief whilst for others amongst it has proved quite a frustration! It is interesting to realize how dependent we have become on satellite communications and email access in the modern world.

In the end we spent all of Thursday running swath bathymetry from the ship as essentially we are now working in uncharted waters; possibly even redrawing the coastline on charts as a result of this survey. The fjord is approximately 600m deep in the centre but has numerous ledges rising up to 200m along its length. At its farthest point the RRS JCR was a mere 150m from the end of the glacier. A combination of strong and gusty catabatic winds, of up to 60 knots, and a poor satellite-derived position fix in amongst these high mountains meant that we were unable to launch the ROV Isis. Swath bathymetry using the ship system and gravity coring took place throughout the evening of Thursday 1st February.

At lunch time on Friday, after a reassessment of the conditions, we were able to put Isis into the water to run a video transect up from about 400m to the snout of the glacier. The images sent back were most interesting. The seabed in deeper water consists mostly of flat mud and drop stones but the fjord is crisscrossed with numerous small ridges a few metres in height. At this early stage there is some discussion as to whether these small ridges represent glacial moraines or iceberg scour marks. The biological community was also different to that we have seen before. In the water column there were very few krill and these seemed to have been replaced by juvenile fish – do Antarctic fjords provided nursery grounds for pelagic species? On the sea bed in deeper water the community was dominated by sponges, starfish, sea stars and bryozoans; however, we did not find any brittlestars which have been numerous at other sites. As we moved into the shallows the biological community became both less diverse and less abundant until we came to a scree slope almost underneath the snout of the glacier that seemed almost totally barren. Theories to explain these observations were the topic of conversation amongst the scientists in the bar on Friday night.

Having completed the video transect, and after taking another gravity core, Isis was reconfigured to run high resolution swath bathymetry to map the features we had seen on Friday. This swath transect was run through Friday night and into Saturday..."


Pourquoi Pas Island on the west
side of the Bourgeois Fjord


The snout of the Perutz glacier at the head of the fjord

Isis preparing to dive in the Bourgeois Fjord

Juvenile fish in the fjord

Sponges on the side of one of the ridges

Sponges

Crinoids on a drop stone

Boulder scree near the snout of the glacier



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January 2007
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