3 January - 10 January 2008

We received offspring. Polarstern took 25 new passengers on board, for one night only, but it was strange enough to see new faces at the dinner tables and in the halls and gangways. We realise that our expedition has already become an entity during the last 6 weeks, united by matching scientific programmes, logistics tasks and unforeseen events. On Polarstern’s way to Neumayer we received a call from the South African ship Agulhas asking whether we could pick up 25 construction workers who were supposed to fly by helicopter to Neumayer. Bad weather and low cloud ceiling prevented long flights, and so we used the two Polarstern helicopter’s to pick up the people and luggage. As I write this, the group is already on its way to Neumayer station, while we dock close to the Naja Arctica in Atka Bay to investigate the ice situation that has not been this strong for 15 years. The massive and stable sea ice barrier is lasting long into the Antarctic summer.

The decision to interrupt the scientific work was not easy, taken on 7 Jan after we had received all the necessary information about sea ice conditions, weather and logistic constrains for Neumayer III. Polarstern’s ice breaking capacities are urgently needed and that is why science again has to step aside. We lost the chance to collect essential information about hydrography and krill in the southeast corner of our investigation area.

Before starting our route west to Neumayer, we managed to accomplish the calibration of the SIMRAD EK 60 fish, krill and zooplankton echo sounder system. Everybody knows the party game of a ball hanging from a rope which is tied around a person’s waist, and the person tries to fit the ball into a small glass standing between his or her feet. Echo sounder calibration is quite similar. The waist of Polarstern is 25 m wide with a 30 m nose and a 90 m tail. We used three ropes instead of one. The little copper spheres (in fact we needed four) for calibration with diameters between a tennis ball and a big pea, hang 15 m below the ship i.e. in 25 m water depth. Now the task is to centre one sphere in the beam of the appropriate echo sounder that at this depth is about 2 m wide. For 21 hours scientists took 1-hour shifts to roll the rope in and out, just to circle the spheres in the appropriate positions. Once in vision of the system, the operator can see the sphere as a marked backscatter signal on the control monitor. Thereafter the spheres are positioned in the 4 quarters of the beam to allow the system to pick up signals evenly spread over the entire recording beam area. Calibration tells you something about the particular properties of an instrument, which is necessary because each instrument is different regarding not only the transformation of electrical energy into sound, but also the transformation of the intensity of the echo into the actual signal. The four different spheres are used because the zooplankton echo sounder works with four different frequencies. Such copper spheres with well-defined acoustic properties are used for calibration on research vessels worldwide.

The hull-mounted acoustic measuring system EK60 from SIMRAD allows detection of zooplankton and krill in the water column of several hundred meters beneath the steaming ship. Vertically directed, narrow acoustic beams of four different frequencies send out pulses in regular intervals of about 2.5 seconds and the reflecting echo from particles is passively recorded and analysed. Each zooplankton group, each species or even different developmental stages, of e.g. krill has a typical reflection pattern (backscatter). These species perform rather distinct vertical migrations on a daily basis but also in an annual pattern. These migrations are regulated by ocean physics (e.g. light, temperature, currents) and ocean biology (e.g. presence of prey and predators, reproduction cycle). By means of the under water acoustics we attempt not only to study the vertical migration pattern but also to estimate the biomass of single groups of zooplankton, krill and fish. All of these are prey for whales, seals, penguins and flying birds. Many of these species feed on the ocean surface during nighttime when the prey appears in the uppermost water layers. These acoustic measurements are performed in the international context of the Convention for Conservation Antarctic Marine Living Resources (CCAMLR).  During this expedition the underwater acoustic system has detected a pronounced echo layer between 500 and 800 m water depth. Several other backscattering layers occurred in the layer 400m to surface. In 50 m water depth every now and then, larger groups of organisms (krill), which did not show any dial vertical migration pattern, passed.

Marine birds and mammals are amongst the top predators harvesting krill and fish. The abundance of these vertebrates is estimated based on band-transect counts during helicopter flights and from observation posts on the flying bridge. From densities per square km, biomass and daily food consumption can be calculated. Thanks to good weather in the ice-areas, 25 helicopter flights have covered a survey area of 1369 km2 with good coverage of the two transect legs completed. From the top deck, 1078 ten-minute counts covering 1246 km2 have been performed in the all-lasting daylight of the southern summer. We saw a wide selection of species in the area of sea-ice: the most numerous were Crabeater Seals, Emperor and Adélie Penguins and Snow and Antarctic Petrels. Minke Whales are regularly seen, but appear somewhat less abundant than during the previous cruise in mid-winter 2006. Possibly, many are feeding now near the outer ice edge. Amazingly, the normally ‘rare’ Ross Seal is frequently seen with a record of 10 individuals during the last helicopter survey. The numbers of top predators indicate considerable food supplies of krill, fish and other types of prey even in early summer when ice concentrations decrease from 100% ice-cover down to open water.  The pattern of overall abundance of marine mammals and birds suggests enriched waters in the heavy sea-ice north of the ice-shelf, in a central area around 66°S west of seamount Maud Rise and in the outer ice edge.

As we are waiting for the logistic duties of Polarstern to be accomplished, people are working on their data, analysing samples or simply enjoying the sunny, calm Wednesday afternoon. I will just provide another Internet link (URL) for those of you who would like to read more about our expedition and its relation to the International Polar Year

www.polarjahr.de/Expedition-ANT-XXIV-2.475+M52087573ab0.0.html

Have fun surfing
Uli Bathmann