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Author Krell, A.; Schnack-Schiel, S.B.; Thomas, D.N.; Kattner, G.; Zipan, W.; Dieckmann, G.S. url  openurl
  Title Phytoplankton dynamics in relation to hydrography, nutrients and zooplankton at the onset of sea ice formation in the eastern Weddell Sea (Antarctica) Type Journal Article
  Year 2005 Publication Polar Biology Abbreviated Journal Polar Biol  
  Volume 28 Issue 9 Pages 700-713  
  Keywords Weddell Sea; Asf; Hydrography; Phytoplankton; Seasonal change; Community composition; Primary production; Zooplankton  
  Abstract The quantitative and qualitative distribution of phytoplankton was investigated along five North–South transects in the eastern Weddell Sea during the transition from late autumn to winter. Relationships with the regional hydrography, progressing sea ice coverage, nutrient distribution and zooplankton are discussed and compared with data from other seasons. To the north of the Antarctic Slope Front (ASF) a remnant temperature minimum layer was found above the primary pycnocline throughout summer. Surface waters had not entirely acquired typical winter characteristics. While temperature was already in the winter range, this was not the case for salinity. Highest biomass of phytoplankton, with the exception of the first transect, was found in the region adjoining the ASF to the north. Absolute chlorophyll a (Chl a) concentrations dropped from 0.35 to 0.19 µg/1. Nutrient pools exhibited a replenishing tendency. Ammonium concentrations were high (0.75–2 µmol/1), indicating extensive heterotrophic activity. The phytoplankton in the ASF region was dominated by nanoflagellates, particularly Phaeocystis spp.. North of the ASF the abundance of diatoms increased, with Fragilariopsis spp., F. cylindrus and Thalassiosira spp. dominating. Community structure varied both due to hydrographical conditions and the advancing ice edge. The phytoplankton assemblage formed during late autumn were very similar to the ones found in early spring. A POC/PON ratio close to Redfield, decreasing POC concentration and a high phaeophytin/ Chl a ratio, as well as a high abundance of mesozooplankton indicated that a strong grazing pressure was exerted on the phytoplankton community. A comparison between primary production (PP) in the water column and the sea ice showed a shift of the major portion of PP into the ice during the period of investigation.  
  Address  
  Corporate Author Thesis  
  Publisher Springer-Verlag Place of Publication Heidelberg Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0722-4060 ISBN Medium  
  Area Expedition Conference  
  Notes (up) Isi:000231421200006 Approved no  
  Call Number refbase @ admin @ Krell++2005 Serial 747  
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Author Mock, T.; Dieckmann, G.S.; Haas, C.; Krell, A.; Tison, J.-L.; Belem, A.L.; Papadimitriou, S.; Thomas, D.N. url  openurl
  Title Micro-optodes in sea ice: a new approach to investigate oxygen dynamics during sea ice formation Type Journal Article
  Year 2002 Publication Aquatic Microbial Ecology Abbreviated Journal Aquat Microb Ecol  
  Volume 29 Issue 3 Pages 297-306  
  Keywords Fragilariopsis cylindrus; Oxygen; Methods; Micro-optodes; Sea ice; Biogeochemistry; Diatoms; Algae; Chlorophyll; Photosynthesis; Salinity effects; Sea water; Marine ecosystems; Chlorophylls; Dissolved oxygen; Gases; Epontic environment; Electrodes; Sensors; Brines; Ice-water interface; Ice formation; Bacillariophyceae  
  Abstract Oxygen micro-optodes were used to measure oxygen dynamics directly within the microstructure of sea ice by freezing the sensors into the ice during its formation. The experiment was conducted in a 4 m³ mesocosm filled with artificial seawater and inoculated with a unialgal culture of the common Antarctic ice diatom Fragilariopsis cylindrus (Bacillariophyceae) to a final chlorophyll a (chl a) concentration of 11 µg 1?¹. Ice growth was initiated 7 d after inoculation by reducing the air temperature to -10 plus or minus 2 degree C and terminated 17 d later. The final ice thickness was 27 cm. One optode was frozen into grease ice and 2 others into the skeletal layer of the growing ice sheet. Increasing oxygen concentrations during ice crystal formation at the water surface and the ice-water interface revealed a strong inclusion of oxygen, which was either physically trapped and/or the result of photosynthesising diatoms. The major portion of oxygen was present as gas bubbles due to super-saturation as a result of increasing salinity and oxygen production by diatoms. An increase in salinity due to a concurrent decrease in ice temperatures during subsequent sea ice development reduced the maximum concentration of dissolved oxygen within brine. Thus, dissolved oxygen concentrations decreased over time, whereas gaseous oxygen was released to the atmosphere and seawater. The sensors are a significant advance on more conventional microelectrodes, because the recordings can be temperature and salinity compensated in order to obtain precise measurements of oxygen dynamics with regard to total (dissolved and gaseous) and dissolved oxygen in sea ice. Optodes do not consume oxygen during measuremnet over a long period under extreme conditions, which is another advantage for long-term deployment in the field.  
  Address  
  Corporate Author Thesis  
  Publisher Inter-Research Place of Publication Oldendorf/Luhe Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0948-3055 ISBN Medium  
  Area Expedition Conference  
  Notes (up) Marine Approved no  
  Call Number refbase @ admin @ Mock++2002 Serial 749  
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Author Weykam, G.; Thomas, D.N.; Wiencke, C. openurl 
  Title Growth and photosynthesis of the Antarctic red algae Palmaria decipiens (Palmariales) and Iridaea cordata (Gigartinales) during and following extended periods of darkness Type Journal Article
  Year 1997 Publication Phycologia Abbreviated Journal Phycologia  
  Volume 36 Issue 5 Pages 395-405  
  Keywords Winter; Polar waters; Photosynthesis; Antarctic zone; Ice cover; Seaweeds; Light effects; Plant physiology; Growth; Palmariales; Gigartinales; Iridaea cordata; Palmaria decipiens; Ps; Antarctica  
  Abstract Physiological and developmental responses during and following long-term exposure to darkness were investigated in the Antarctic red algae Palmaria decipiens and Iridaea cordata. Thalli were kept in darkness for a period of 6 mo, simulating winter sea ice cover. Subsequently, they were grown illuminated under seasonally fluctuating Antarctic daylengths. During darkness, P. decipiens, an Antarctic endemic, rapidly lost its ability to photosynthesize although chlorophyll a content remained fairly constant. The amount of floridean starch decreased gradually in the dark, with a sudden drop simultaneous with the development of new blades. After reexposure to light there was a rapid increase in photosynthetic oxygen production, whereas the rate of carbon assimilation increased more slowly, resulting in high apparent photosynthetic quotients. The increase in growth rate showed a close relation to carbon assimilation, suggesting that carbon is utilized first for growth, then for floridean starch accumulation. In contrast to P. decipiens, the photosynthetic rate of the Antarctic cold-temperate I. cordata was still about half of the initial rate after a dark period of 6 mo, i.e. the alga maintained functionality of its photosynthetic apparatus during winter. After reexposure to light there was a continuous increase in specific growth rate due to increasing photosynthetic activity. Iridaea cordata also accumulated floridean starch during summer, although in smaller amounts than P. decipiens. Together with the ability to photosynthesize, starch accumulation facilitates survival during extended dark periods in winter. The early development of blade initials and the rapid increase in photosynthetic capability after illumination may permit P. decipiens to use the period of high water transparency optimally in Antarctic spring. Iridaea cordata seems better able to survive prolonged dark periods in areas with less predictable light conditions. Both physiological patterns are well suited to the highly seasonal light conditions in Antarctica.  
  Address  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0031-8884 ISBN Medium  
  Area Expedition Conference  
  Notes (up) Marine Approved no  
  Call Number refbase @ admin @ Weykam++1997 Serial 767  
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Author Mock, T.; Thomas, D.N. url  openurl
  Title Recent advances in sea-ice microbiology Type Journal Article
  Year 2005 Publication Environmental Microbiology Abbreviated Journal Environ Microbiol  
  Volume 7 Issue 5 Pages 605-619  
  Keywords  
  Abstract Over the past 50 years there has been much effort invested in the investigation of the ecology of sea ice. Sea ice is an ephemeral feature of the Arctic and Southern Oceans and smaller water bodies such as the Baltic and Caspian Seas. The semisolid ice matrix provides a range of habitats in which a diverse range of microbial organisms thrive. In the past 5 years there has been considerable steps forward in sea-ice research, in particular regarding the analysis of sea-ice microstructure and the investigation of the diversity and adaptation of microbial communities. These studies include: (i) controlled simulated and in situ studies on a micrometer scale to unravel the dynamic of the microhabitat with consequences for the organisms; (ii) the introduction of molecular approaches to uncover the diversity of uncultured still unknown microorganisms; and (iii) studies into the molecular adaptation of selected model organisms to the extreme environment. This minireview presents some of the most recent findings from sea-ice studies within the framework of these aims.  
  Address  
  Corporate Author Thesis  
  Publisher Blackwell Publishing, Inc. Place of Publication Oxford Editor  
  Language Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 1462-2912 ISBN Medium  
  Area Expedition Conference  
  Notes (up) Minireview Approved no  
  Call Number refbase @ admin @ Mock+Thomas2005 Serial 750  
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Author Brierley, A.S.; Thomas, D.N. openurl 
  Title Ecology of southern ocean pack ice Type Journal Article
  Year 2002 Publication Advances in marine biology Abbreviated Journal Adv Mar Biol  
  Volume 43 Issue Pages 171-276  
  Keywords Animals; Antarctic Regions; Birds; Crustacea; Ecology; *Ecosystem; Environment; Fishes; *Ice; *Marine Biology; Oceans and Seas; Phytoplankton; Population Dynamics; Research Support, Non-U.S. Gov't; Seasons; *Seawater; Water Microbiology; Whales  
  Abstract Around Antarctica the annual five-fold growth and decay of sea ice is the most prominent physical process and has a profound impact on marine life there. In winter the pack ice canopy extends to cover almost 20 million square kilometres--some 8% of the southern hemisphere and an area larger than the Antarctic continent itself (13.2 million square kilometres)--and is one of the largest, most dynamic ecosystems on earth. Biological activity is associated with all physical components of the sea-ice system: the sea-ice surface; the internal sea-ice matrix and brine channel system; the underside of sea ice and the waters in the vicinity of sea ice that are modified by the presence of sea ice. Microbial and microalgal communities proliferate on and within sea ice and are grazed by a wide range of proto- and macrozooplankton that inhabit the sea ice in large concentrations. Grazing organisms also exploit biogenic material released from the sea ice at ice break-up or melt. Although rates of primary production in the underlying water column are often low because of shading by sea-ice cover, sea ice itself forms a substratum that provides standing stocks of bacteria, algae and grazers significantly higher than those in ice-free areas. Decay of sea ice in summer releases particulate and dissolved organic matter to the water column, playing a major role in biogeochemical cycling as well as seeding water column phytoplankton blooms. Numerous zooplankton species graze sea-ice algae, benefiting additionally because the overlying sea-ice ceiling provides a refuge from surface predators. Sea ice is an important nursery habitat for Antarctic krill, the pivotal species in the Southern Ocean marine ecosystem. Some deep-water fish migrate to shallow depths beneath sea ice to exploit the elevated concentrations of some zooplankton there. The increased secondary production associated with pack ice and the sea-ice edge is exploited by many higher predators, with seals, seabirds and whales aggregating there. As a result, much of the Southern Ocean pelagic whaling was concentrated at the edge of the marginal ice zone. The extent and duration of sea ice fluctuate periodically under the influence of global climatic phenomena including the El Nino Southern Oscillation. Life cycles of some associated species may reflect this periodicity. With evidence for climatic warming in some regions of Antarctica, there is concern that ecosystem change may be induced by changes in sea-ice extent. The relative abundance of krill and salps appears to change interannually with sea-ice extent, and in warm years, when salps proliferate, krill are scarce and dependent predators suffer severely. Further research on the Southern Ocean sea-ice system is required, not only to further our basic understanding of the ecology, but also to provide ecosystem managers with the information necessary for the development of strategies in response to short- and medium-term environmental changes in Antarctica. Technological advances are delivering new sampling platforms such as autonomous underwater vehicles that are improving vastly our ability to sample the Antarctic under sea-ice environment. Data from such platforms will enhance greatly our understanding of the globally important Southern Ocean sea-ice ecosystem.  
  Address Gatty Marine Laboratory, School of Biology, University of St Andrews, Fife, KY16 8LB, UK. andrew.brierley@st-andrews.ac.uk  
  Corporate Author Thesis  
  Publisher Place of Publication Editor  
  Language English Summary Language Original Title  
  Series Editor Series Title Abbreviated Series Title  
  Series Volume Series Issue Edition  
  ISSN 0065-2881 ISBN Medium  
  Area Expedition Conference  
  Notes (up) PMID:12154613 Approved no  
  Call Number refbase @ user @ Serial 317  
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