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THE EUROPEAN POLARSTERN STUDY : A MULTIDISCIPLINARY COLLABORATIVE EUROPEAN ENTREPRISE IN ANTARTIC MARINE ECOLOGY AND SUPPORTING DISCIPLINES

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A series workshops were set up under the European Polarstern Study (EPOS) in which the following data on hydrological parameters, hydrochemical parameters and chlorophyll were discussed.

The transition from open water to 100% ice covered water was abrupt. The sea ice had a very sharp edge, from 0 to 100% coverage with broken ice (floes of a few metres in thickness) within a few 100 m. This suggested that it was an icefield that had drifted already for a long time. The general flow direction of this ice field was north east east (60 degrees). It drifted with a velocity of 0.12 ms{-1}. Current meters moored south of Elephant Island showed the same direction and velocity. During the entire investigation period the sea ice had no influence on the water column below. This became evident by looking at the isolines of physical and chemical parameters which were often perpendicular to teh ice edge. 3 different water masses were found at the surface in the investigation area. The stability. Maximum concentrations (in average 1.56 mg chlorophyll a m{-3} in the surface) were found at stations 49 to 63 which were located in summer modified surface water of the Weddell Sea.

A series of workshops were set up under the European Polarstern Study (EPOS) in which the following meteorological, hydrographical and nutrient results were discussed.

Between Elephant Island and the South Orkneys, wind directions along theice edge changed from north east through north, north west to south west in the period from December 29 to January 13; winds from west and north west prevailed. Average wind speed was 3 to 7.6 ms{-1}. Between 60 degrees to 61 degrees south at the ice edge, wind direction changed from 225 degrees to 270 degrees with wind speeds ranging from 4.6 to 7.6 ms{-1}. At the latitudes 48 degrees to 51 degrees south ('Polarstern') wind directions were 300 degrees to 240 degrees and wind speeds were 10 to 14.4 ms{-1}. These differences in wind speeds at the different latitudes south may have been the main cause of anticyclonic eddies at the ice edge.

Comparison of the nitrate and silicate data collected by Dr Francisco Gomez Figueiras and coworkers, Institute de Investigacion Marinas, 36208, Vigo, Spain with those collected during EPOS for this region showed that the data compared quite well.
Preliminary results indicate that at about 52 degrees west a watermass with high salinity, high nitrate and high silicate was flowing northward and later eastward. This could very well explain the variations in chemical parameters that were encountered at 49 degrees west.

A series of workshops were set up under the European Polarstern Study (EPOS) in which the following data on phytoplankton and zooplankton were discussed.

Different regional and seasonal distribution patterns of major phytoplankton groups were found. The investigation period from November to January covered the main growth season, spring and summer, for Antarctic phytoplankton. Factors influencing the different patterns found were the different water masses in the investigation area as well as the receding ice edge. Bottom topography, the shelf of the South Orkney Islands may also have influenced phytoplankton distribution either due to a different movement of water masses induced by a shallower bottom and/or due to an Islands effect itself. In general highest biomass was found in the waters of the Weddell-Scotia-Confluence int he marginal ice zone. The studies revealed 2 assemblages, one in the north dominated by diatoms in spring and another one in the south dominated by Cyptomonas species in summer.

During EPOS Leg 1 a phytoplankton bloom was found in early November in the area of the outer marginal ice zone in waters of the Weddell-Scotia-Confluence. The phytoplankton biomass was dominated by diatoms such as Thalassiosira 'gravida' forming large colonies and small Chaetoceros species mainly C neglectum. Very low abundances of phytoplankton were observed in the water column under the pack ice in the southernmost stations. This assemblage consisted mainly of nanoflagellates and pennate diatoms (Nitzschia cylindrus, other pennate diatoms). A lot of empty diatoms frustules were found. During EPOS leg 2 along a transect at 49 degrees west, the diatom bloom consisting of almost the same dominant species continued until the end of November. However, in January in the north another bloom of diatoms was found dominated by cylindrus. This dominance remained until EPOS leg 3 in late January, numbers decreased towards the south. In early January in the south (Polish da ta) cylindrus dominated near ice edge with numbers decreasing towards the open waters. This suggested 2 sources of N cylindrus, 1 in the oceanic waters in the north, another being an inoculum from the melting pack ice which contained at that time N cylindrus as the dominant species. In December and January along transect 47 degrees west and 49 degrees west (combined 'Polarstern' and 'Siedledki' data) a completely different phytoplankton assemblage was encountered dominated by cryptophytes Cryptomonas assemblage was encountered dominated by cryptophytes Cryptomonas species and diatoms decreased in numbers. Cryptomonas species increased from Elephant Island towards the South Orkneys.
Some species such as Corethorn criophilum for instance showed a distinct pattern throughout the entire investigation. A patch of this species was always related to the maximum diatom occurrence dominated by Thalassiosira 'gravida' and C neglectum. Another maximum of this species appeared in the southwest of the South Orkneys.

Polish zooplankton results (Professor Siedleck) correspond to the EPOS zooplankton results (clusters) from the Weddell Sea both with regard to species composition and to quantity. These similarities are mainly noticeable for the group Calanoida. In the case of Cyclopoida (Oithona), the Polish counts are lower than those obtained during EEPOS. This difference could be attributed to the different nets used.

A series of workshops were set up under the European Polarstern Study (EPOS) in which the following data on krill were discussed.

Netcatches and acoustic data were compared in order to calibrate and match trends and patterns found. Both acoustic data sets match very well. Swarms parameters (ie length and thickness) show the same frequency distributions with only a minor shift that is either due to differences in gainsetting of the sounders or to the fact that different areas were covered. The trend that swarm sizes increase in size and time and distance from the ice edge (towards the north) occurs in both data sets. EPOS data show that further northward sizes decrease again. EPOS data also show that in time a similar trend exists: number of swarms decrease with time while their sizes increase, while during the last transect there is again a decrease in size.
The fact that in EPOS data no diel patterns were found can be related to the mixed structure of the krill populations (small and large ones occurred in most of the stations where krill catches were made). The Polish data show that different behaviour and diel distribution are related to differences in size and life stages. This could not be confirmed by the EPOS data set as the few stations where 'unipeaked' size frequencies were found did not have matching acoustic sets. Despite the small differences in space and time in general netcatch data and distributions of krill seem to agree between the 2 expeditions. During EPOS leg 1 (end of October beginning of November) only small sized krill were found in the southern part of the area studies. In the beginning of EPOS leg 2 (end of November and December) there were still small krill near the ice edge, while bigger ones occurred in the north in the confluence area. Later during leg 2 both in the north. When comparing this with the Polish data set (end of December) we see that there are extensive stocks of large krill in the western part of the transect, near Ele phant Island, and in the Eastern part of the South Orkney Islands with the smaller ones in the centre. This may explain why near the end of EPOS leg 2 larger krill appeared near the ice as they probably drifted in from the west with the east flowing currents. So the 2 factors play a role here: passive drifting krill with the currents and active migration (in general towards the north) in search for food.

One objective of EPOS 3 was to investigate the biological, physical and chemical characteristics of the high Antarctic water column during summer. Transects were sampled to obtain quantitative profiles of the major oceanographic parameters. The long on continuous daylight is a marked feature of high Antarctic environment during the summer and it might be assumed that there would be little variability among parameters mediated by light. However it was considered as important to address this question and investigate whether short term variability was significant.

Results showed that there was marked variability in many of the physical, chemical and biological parameters in the water column over a 24h cycle. The greatest amplitude in variability was found in the upper strata of the water column and many of the parameters measured had distribution patterns that conformed with a diurnal cycle. Such patterns were not necessarily directly synchronized with the irradiance curve. Modification of the temperature profile conformed directly with the diurnal irradiance cycle and so this introduces an alternative interpretation for the diurnal changes that were observed. It was concluded that the results obtained were the combined result of diurnal biogenic effects and sampling across a small eddy in the East Wind Drift.

It was also concluded that the experiment had achieved its original objective and demonstrated marked variability among components of the pelagic marine ecosystem in the high Antarctic during summer. These observations suggested that comparisons of oceanographic data collected without replication and without regard to diurnal processes should be treated with caution. The magnitude in variation attributed to geography or seasonal time scales may actually lie within the range occurring over diurnal time scales.
The European "Polarstern" Study (EPOS) is a co-operative European venture to investigate the ecology of plankton, benthos and sea ice communities of the Weddell Sea and adjacent regions. The expedition will be carried out during the austral summer 1988/89 on the research icebreaker Polarstern which is being put at the disposal of the scientific community of Europe by the Alfred Wegener Institute for Polar and Marine Research (AWI) in Bremerhaven, F.R.G. Well over hundred scientists from eight EEC countries, three further European countries and Israel will participate in the scientific programme, which will be divises into three legs and last from October 1988 to March 1989. More than two additional years will be necessary for the work-up of cruise results, review and publication activities to be completed.

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Letzte Aktualisierung: 24 November 1989

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Permalink: https://cordis.europa.eu/project/id/SC1*0075/de

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