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The expedition ANT-XXVII/3 aimed at investigating the potential effects of climate change on biodiversity and ecosystem functioning in sub and high Antarctic regions. The expedition is part of the international SCAR program "Biodiversity and Evolution in the Antarctic: The response of life to change" (EBA). Based on data and results obtained during former expeditions (ANT-XV/3, ANT-XVII/3, ANT-XIX/5, ANT-XXI/2, ANT-XXIII/8) in the framework of EASIZ and EVOLANTA, this expedition was focusing on three main topics: 1. Zoogeography und biodiversity in the sub and high Antarctic and the genetic and physiological processes and characteristics determining species distribution. 2. Pelago-benthic coupling processes and the impact of climate change induced environmental alterations on food web structure. 3. Impact of changing shelf ice dynamics on the biodiversity of benthic and demersal fish communities on the shelf.

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According to the IPCC (Intergovernmental Panel on Climate Change) 2007 signs of climate change in the Antarctic are less pronounced as compared to the Arctic but in some parts of the Antarctic clear and significant temperature changes are detectable. Mean air temperatures at the Antarctic Peninsula and in the Bellingshausen Sea increased approximately by 1.5 °C since the 1950s, and by almost 3 °C within the last 100 years. Around South Georgia Island water temperatures increased by 3.3 °C in winter and by 0.9 °C in summer as compared to the early 20th century. The temperature rise entailed a drastic disintegration and reduction of various ice shelves along the Antarctic Peninsula; on the eastern side of the Antarctic Peninsula the Larsen A and B ice shelves, covering an area of approximately 80 x 80 km, broke away completely within the last 10 years. Both, changes in the temperature regime and changes of the shelf ice dynamics affect the marine living communities in these regions. In the long run, ongoing climate warming will most likely affect population dynamics and distributional ranges of species and finally might result in significant shifts in community composition due to extinction of endemic species and invasion of new species from adjacent northern regions. Such alterations in species composition will involve significant changes in the food web structure. Survival of particular endemic species and persistence of populations under altered abiotic conditions strongly depend on adaptability and physiological fitness and plasticity of individuals, as well as on the capacity of invasive species to build up competitive populations.

Former expeditions focusing on biogeography and biodiversity along the Scotia Arc and around Bouvet Island have shown that these islands in the South Atlantic might be important stepping stones for the colonization of Antarctic waters by northern alien species. During the expedition ANT-XIX/5 the discovery of reptant decapods around Bouvet Island provided first evidence that invasion via these islands might be already under way. However, whether these island shelves are also used by other taxonomic groups for invasion into Antarctic waters still needs to be verified.

Changes in shelf ice dynamics involve alterations in pelago-benthic flow patterns in the formerly ice-covered regions, and at the same time give rise to an increase in iceberg scouring events, which impacts the benthos and demersal fish communities on the shelf. The investigation of these effects was in the focus of several previous Antarctic expeditions between 1996 and 2006 (EASIZ I–III, BENDEX, LARSEN-A/B). These studies considerably improved our knowledge on the importance of pelago-benthic coupling processes and the significance of iceberg scouring events for benthic community structure and biodiversity. However, the timescales of recolonisation phases after disturbance are still completely unknown. To set a time stamp for the investigation of the recolonisation timescale, the artificial disturbance experiment BENDEX was initiated in 2003/04 on the north-eastern Weddell Sea shelf. During BENDEX the sea floor in a defined area was artificially disturbed to simulate an iceberg scour mark. This area was revisited during this expedition to document the recolonisation progress after 6 years. The consequences of the tremendous ice shelf disintegrations along the Antarctic Peninsula on biodiversity and community composition are so far unknown, as well. Some first studies focusing on benthic communities in the formerly ice-covered LARSEN A/B embayments were carried out during ANT-XXIII/8 in 2006/07; these studies were continued during this expedition.

The expedition ANT-XXVII/3 aimed at investigating the potential effects of climate change on biodiversity and ecosystem functioning in sub and high Antarctic regions. The expedition is part of the international SCAR programme “Biodiversity and Evolution in the Antarctic: The response of life to change” (EBA). Based on data and results obtained during former expeditions (ANT-XV/3, ANT-XVII/3, ANT-XIX/5, ANT-XXI/2, ANT-XXIII/8) in the framework of EASIZ and EVOLANTA, this expedition was focusing on three main topics:

1. Zoogeography und biodiversity in the sub and high Antarctic and the genetic and physiological processes and characteristics determining species distribution.

2. Pelago-benthic coupling processes and the impact of climate change induced environmental alterations on food web structure.

3. Impact of changing shelf ice dynamics on the biodiversity of benthic and demersal fish communities on the shelf.

The studies concentrated on shelf and upper slope communities down to about 600 m water depth. Study areas included the sub Antarctic islands in the Scotia Sea and Bouvet Island, as well as high Antarctic shelf areas in the western and eastern Weddell Sea. In all areas studies on biogeography, genetics, ecology and physiology of zooplankton, benthos and fishes were carried out.

The 3rd leg of the Polarstern expedition ANT-XXVII started on the 8th of February 2011 at 20:00 in Punta Arenas, Chile (see Fig. 1.1). Under good weather conditions the ship sailed towards the first sampling location on Burdwood Bank, where scientific work started at the 11th of February. Further stations were located around South Georgia and the South Orkneys. The sampling schedule in the Scotia Sea could be completed successfully and Polarstern reached the Dallmann Laboratory at Jubany Station (King George Island) on the 22nd of February. During the day some logistic operations were carried out including personnel exchange (two geophysicists from board / one biologist on board). After two days of field work off King George Island, Polarstern steamed through the Antarctic Sound and reached the former Larsen A/B ice shelf areas on February the 26th. Here, on the east Antarctic Peninsula shelf, an extensive sampling programme was processed. Almost all stations that were sampled during a previous expedition in 2006/07 could be resampled. Additionally two new sites at the edge of the Larsen C ice shelf were sampled. During our work in the Larsen embayments we experienced exceptional weather phenomena, namely foen situations with air temperatures of up to +9 °C. During helicopter monitoring flights progressive melting of the residual shelf ice, indicated by large lakes on the ice shelf and water run offs from the ice edge, were observed (Fig. 1.2).

The Larsen C area was characterized by a very poor benthic community. In Larsen B benthic community structure did not differ from what was found during the last visit in 2006. In the area of Larsen A, where the benthic realm is free from shelf ice for longer time, few early successional stages could be identified. On the 13th of March we finished our work at Larsen and Polarstern moved towards the eastern part of the Weddell Sea. On the 20th of March we arrived at the BENDEX site in the vicinity of Austasen and another extensive working programme was immediately started. Video observations by ROV and the video-equipped multicorer revealed some signs of first slow recolonisation of the sea floor after the artificial disturbance in 2003, although a rich benthic community is present directly adjacent to the experimental site. As also observed in the Larsen embayments recolonisation of the sea floor seems to be a very long lasting process in high Antarctic waters. On the 26th of March the working programme at the BENDEX site was interrupted for one day in order to supply the Neumayer III station in Atka Bay. Continuing the work from previous expeditions, the edge of the ice shelf between Atka Bay and Kapp Norvegia was surveyed by helicopter GPS. A comparison with data from 1996, 2000 and 2003 showed a highly dynamic ice shelf situation. In some areas the ice shelf decreased between 1996 and 2000, but increased again between 2000 and 2011.

During our work in the eastern Weddell Sea the air temperature declined drastically down to -27 °C (wind chill -53 °C), making the working conditions on deck quite difficult and unpleasant for crew and scientists. The rapid development of fast ice demanded the nautical skills of the ship’s guidance. On the 5th of April the work in the eastern Weddell Sea was successfully completed. After one more plankton station at 2,000 m on the 6th of April Polarstern headed towards Bouvet Island, where the scientific programme had be reduced to one CTD and two bottom trawls due to stormy weather conditions. A storm with hurricane wind force, approaching the area of Bouvet, forced us to leave the area immediately. On the 18th of April 2011 in the early morning hours the 3rd leg of ANT-XXVII finished with the arrival of Polarstern in Cape Town, South Africa.

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