02 January 2001 - Science and the Festive Season
RRS James Clark Ross Diary
Noon Position : 55 degrees 42' South. 39 degrees 11' West.
Distance travelled since Grimsby: 15,321 nautical miles
Air temperature @ noon: 2.6 degrees Celsius
Sea temperature @ noon: 3.2 degrees Celsius
THE FESTIVE SEASON ENDS
The webpage is back again after a brief break over the festive period. Apologies to all those who have been looking out for the page recently, we are now back on our weekly schedule. The last few weeks have been busy with both science and a little bit of festive fun. The science plans have had to be flexible due to the very variable weather, mainly howling gales, but despite this the programme is now well under way. These changes meant that we found ourselves tied up to the Stromness Buoy on Christmas Eve, where we remained until Boxing Day. The main reason for going into the bay was to calibrate some of the science equipment, but it also meant that most people could get ashore and stretch their legs and enjoy the local scenery and wildlife. Most importantly it meant most people could relax and enjoy Christmas Day without the ship rocking and rolling!
Stromness Whaling Station.
Christmas Day visit by Hanseatic
Stromness is a disused whaling station that operated between 1912 and 1931, when it became a repair yard until it closed in 1961. It is named after the town in the Orkney Islands which was just one of the places that supplied the whaling industry in these parts with many workers. Stromness is probably most famous for it being the station where Sir Ernest Shackleton arrived after his epic journey across the previously unpenetrated mountains and crevassed glaciers of South Georgia, after the failed Endurance Expedition. The local wildlife is extensive and there to greet us on the beach were the local king penguins, gentoo penguins, fur seals and their new pups, and, slightly surprisingly, the resident reindeer.
Resident Reindeer with "Seasonal Cheer"
Christmas Day was pretty typical in that it involved excesses of everything, and a big thank you must go out to all the Galley staff and stewards who worked so hard to produce a fantastic lunch which they themselves probably never got to enjoy. Lunch was followed by the usual post prandial relaxation and a few games etc.. and then the compulsory James Bond movie to make us feel at home! As Christmas Eve had been a pretty epic night, most people required their beds at an uncharacteristically early hour. We also had a surprise visit from Hanseatic, a tour ship that had obviously the same idea as us in trying to get some shelter for Christmas lunch!
New Years Eve came around all too quickly and it was back to the over-indulging again. The New Year was brought in with what should have been the eldest (not Doug really - but he did a good job anyway) person on board ringing out the old year and the youngest (Gerry) ringing in the new year, up on the forecastle of the ship. It was then back indoors for further celebrations, not pictured.
After all the festivities it was back to the serious subject of science. We headed back into Cumberland Bay to continue with one of the fishing programmes, where we were treated to some spectacular weather and cloud formations.
Biological Sciences Cruise JR57: Core programme 6. (Principal Scientist: Peter Ward)
This year we are once again undertaking our annual survey of the waters surrounding the island of South Georgia where oceanographic conditions can vary considerably from year to year. Sometimes during the southern summer the seas in this northern part of the Southern Ocean are relatively warm (3-4 degrees C) and blooms of microscopic plant life (phytoplankton) are encountered, which in turn supports large amounts of animal life (zooplankton). At other times it can be cold (0-1 degrees C) with relatively little plankton present in the water. Many of the locally abundant dependent predators such as fish, birds and seals have life cycles that are closely synchronised with the short summer season, and depend heavily on food being available at this critical time. Fluctuations in the amount of krill and other zooplankton present close to the island can therefore have important repercussions on their reproductive success. This cruise forms part of a long-term study designed to monitor oceanographic variation in the region and ultimately to understand its causes.
This year has seen us get off to a slow start because of the adverse weather we experienced at the start of the cruise. Gale force winds and rough seas prevented us from running our survey lines in the planned order, and we have mainly concentrated our efforts on near-shore elements of the programme where we get some shelter from the prevailing westerly winds, with a view to running the main transect lines later in the cruise. A three day lull did however allow us to complete a number of stations on a line extending 180 km offshore aimed at assessing the importance of different water masses in transporting krill to the Island from further south. Both of these areas of science are outlined in more detail below.
Hydrographic Transect to the Northeast of South Georgia
(Mike Meredith, Sally Thorpe, Sharon Grant and Nathan Cunningham)
The krill population at South Georgia is not self-sustaining and consequently, knowledge of the pathways, rates and variability of transport of krill into the area is of prime importance in understanding the local ecosystem dynamics. It is thought that one of the main physical processes supplying krill to the South Georgia region is advection along the path of the Southern Antarctic Circumpolar Current Front (SACCF). This is a relatively narrow, fast-moving jet that flows across the Scotia Sea from the vicinity of the Antarctic Peninsula and loops anticyclonically around South Georgia. We have been measuring physical parameters such as temperature and salinity to the full depth of the ocean along a transect to the northeast of South Georgia to identify the position of the front whilst others in the group have been studying associated biological processes.
The temperature along the transect is shown in Figure 1. The SACCF is apparent through the steeply sloping temperature contours near 53.7 degrees S. Also clear is another manifestation of the front near 53.4 degrees S. Here the contours slope with the opposite sense, indicating that the current flow is in the reverse direction: the SACCF has retroflected northwest of the transect. This contraflow arrangement is more readily seen in Figure 2, which shows current speeds measured relative to the flow at the seabed.
The SACCF close to South Georgia is narrow and has high velocities (around 30 cm/s), whereas the flow further offshore is broader and more sluggish (although still high relative to the general levels away from the front). These velocities were obtained by considering the flow due only to horizontal density gradients in the water; we intend also to include the other component of flow, due to slopes in the sea surface, by including direct velocity measurements from the Acoustic Doppler Current Profiler. The potential biological significance of the SACCF can be glimpsed by observing that the highest current velocities in the front close to South Georgia coincide very well with high values of fluorescence (a measure of phytoplankton abundance: Figure 3). Further occupations of this transect during the coming years will reveal the coupling of the physical and biological components of the South Georgia ecosystem, and the degree of variability resulting from physical forcing.
Studies of mackerel icefish larvae and their copepod prey in Cumberland East Bay,
(Tony North and Rachael Shreeve)
Mackerel icefish, Champsocephalus gunnari, are regularly fished around South Georgia by Russian and Polish ships under licence from the Government of South Georgia within quotas set by the Commission for the Conservation of Antarctic Marine Living Resources. Adult icefish are krill predators and, in turn, are eaten by fur seals and gentoo penguins. The icefish taste good, and they occasionally appear on the slab at supermarket fish counters.
From regular zooplankton sampling around much of South Georgia over the last twenty years we know that Cumberland East Bay is one of the main nursery grounds for the mackerel icefish. The adults spawn eggs, 3-4 mm diameter, nearshore in April-May. The larvae hatch in September at around 13 mm long and grow relatively slowly so by late December they are about 30 mm long. On Christmas Eve and December 30, we sampled in the bay to catch larval icefish, and their main prey, the copepod Drepanopus. When data on the abundance and size of the icefish are analyzed it tells us if it is a good or bad year for them. Hopefully, such data may be used to indicate potential recruitment in 2-3 years time when they have grown up and become the bulk of the fishable population. We want to see if there is any relationship between their growth performance and environmental factors, such as the abundance of their copepod prey and sea temperature. Furthermore, we hope to link with studies of icefish larvae planned for the new Applied Fisheries Research Laboratory at King Edward Point in Cumberland East Bay.
From our previous work we know that the larval icefish are found in the upper 20 m of the water column during the day and then migrate to between 60 and 100 m depth by midnight. Many of the larvae manage to avoid the net during daylight and so we sample at night. The water column was sampled by towing an 8-m square net in the upper 3 to 100 m of the water column and a neuston sea surface sledge in the upper 1 m. Samples from the upper layer contained larvae of another common fish, the humphead notothen Gobionotothen gibberifrons, which as adults are a by-catch in the fishery. Our previous work has found that the growth rate of larval humphead varies interannually. Growth rate and the size attained by mid-January was greater in colder years, perhaps indicating poorer feeding conditions in warm years.