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  • 1
    Monograph available for loan
    Monograph available for loan
    Bremerhaven : Alfred-Wegener-Institut für Polar- und Meeresforschung
    Call number: AWI Bio-19-20533
    Type of Medium: Monograph available for loan
    Pages: 48 Seiten , Illustrationen
    Language: English
    Note: Content: Preface. - Polar ecosystems in a changing climate. - Ice edge blooms - Migrating oases in polar seas. - Antarctic: Krill has evolved adaptation strategies to its extreme environment. - Living at -20 degrees: why sea Ice algae don't freeze up. - ocean acidification and Iron deficiency affect Antarctic phytoplankton communities. - The oceans are acidifying: spIder crabs and Ice fIsh are feeling the repercussions of climate change. - melting glaciers - Changing coastal ecosystems in the West Antarctic. - In the service of science: elephant seals explore the Southern Ocean. - Ocean Acoustics - palaoa broadcasts live from the Southern Ocean. - When ice shelves disintegrate - diversity of life on the Antarctic seabed. - RV 'Polarstern' in Antarctica - observations in the ice. - deep-sea observatory in the Arctic: Climate change affects life on the ocean floor. - plankton rain in the vicinity of the Arctic HAUSGARTEN: What do sinking particles tell us?. - pelagic research in the Arctic faces new challenges. - fram observatory - live conference with the Arctic deep sea in preparation. - dom - the oceans' molecular memory. - siberian forests moving north - impact on the climate and biodiversity. - promoting young talent: High school pupils learn together with AWI scientists. - dream job- polar scientist - How a student achieved her goal over an icy path. - marIne biosciences in the scientific-societal context of the 21st. century. - Contact persons at the AWI. - Imprint. - geographic locatIons of the research reports of this brochure
    Location: AWI Reading room
    Branch Library: AWI Library
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  • 2
    Call number: ZS-090(551) ; ZSP-168-551
    In: Berichte zur Polar- und Meeresforschung
    Type of Medium: Series available for loan
    Pages: 259 S.
    ISSN: 1618-3193
    Series Statement: Berichte zur Polar- und Meeresforschung 551
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    D.3.
    Location: Lower compact magazine
    Location: Reading room
    Branch Library: GFZ Library
    Branch Library: AWI Library
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  • 3
    Call number: ZSP-168-121
    In: Berichte zur Polarforschung
    Type of Medium: Series available for loan
    Pages: II, 122 S. : graph. Darst., Kt.
    ISSN: 0176-5027
    Series Statement: Berichte zur Polarforschung 121
    Location: Reading room
    Branch Library: AWI Library
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  • 4
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    In:  (Doctoral thesis/PhD), Christian-Albrechts-Universität Kiel, Kiel, Germany, 93 pp
    Publication Date: 2018-02-21
    Type: Thesis , NonPeerReviewed
    Format: text
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  • 5
    Publication Date: 2014-07-30
    Description: Ikaite (CaCO3·6H2O) has only recently been discovered in sea ice, in a study that also provided first direct evidence of CaCO3 precipitation in sea ice. However, little is as yet known about the impact of physico-chemical processes on ikaite precipitation in sea ice. Our study focused on how the changes in pH, salinity, temperature and phosphate (PO4) concentration affect the precipitation of ikaite. Experiments were set up at pH from 8.5 to 10.0, salinities from 0 to 105 (in both artificial seawater (ASW) and NaCl medium), temperatures from 0 to −4 °C andPO4 concentrations from0 to 50 μmol kg−1. The results show that in ASW, calcium carbonate was precipitated as ikaite under all conditions. In the NaCl medium, the precipitates were ikaite in the presence of PO4 and vaterite in the absence of PO4. The onset time (τ) at which ikaite precipitation started, decreased nonlinearly with increasing pH. In ASW, τ increased with salinity. In the NaCl medium, τ first increased with salinity up to salinity 70 and subsequently decreased with a further increase in salinity; it was longer in ASW than in the NaCl medium under the same salinity. τ did not vary with temperature or PO4 concentration. These results indicate that ikaite is very probably the only phase of calcium carbonate formed in sea ice. PO4 is not, as previously postulated, crucial for ikaite formation in sea ice. The change in pH and salinity is the controlling factor for ikaite precipitation in sea ice. Within the ranges investigated in this study, temperature and PO4 concentration do not have a significant impact on ikaite precipitation.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
  • 7
    Publication Date: 2014-09-22
    Description: Antifreeze proteins (AFPs) from polar and cold-tolerant organisms are able to control ice growth as a result of their adsorption on the ice crystal surface. The proteins bind to selected crystallographic planes, which are characteristic for each kind of AFP. As a consequence of the adsorption, the freezing point of the solution is locally lowered below the melting point, following the Gibbs-Thomson equation. Within the difference between the melting and the freezing point (hysteresis gap), the macroscopic growth of the crystals is arrested. Below the freezing point, crystals grow with a burst of determined shapes. Their habit is dominated by the crystallographic planes inhibited by the proteins, due to the geometric adsorption selectivity as well as to the adsorption rate of the proteins. Most of the well-studied fish AFPs do not bind to the basal plane, therefore crystals burst as needles parallel to the c-axis. At strong supercoolings the protein adsorption rate is not fast enough to balance radial growth due to heat dissipation, and crystals develop dendrites. However, data about the shape of the crystals after the burst, and well below the freezing point, are still scarce, resulting in an incomplete understanding of the growth inhibition mechanisms by the different AFP types. Here we present ice growth experiments in the presence of AFPs from the polar diatom Fragilariopsis cylindrus, a dominant microalga in sea ice assemblages. The protein was recombinantely expressed and purified from E. coli. Ice grain habit was observed at light microscopy in a dish, from the hysteresis gap until growth into a solid sample of polycrystalline ice. Crystals grew with an expansion of the basal plane area, but a suppressed development parallel to the c-axis compared to negative controls, resulting in thin ice “sheets”. A slow three- dimensional growth was revealed by the formation of characteristic features as pits and groves. Dendritic growth was limited, presumably among others an effect of the rapid heat dissipation through the thin sheet. The effect of the AFPs was still evident hours after the initial burst, as shown by analyses of the fully frozen polycrystalline block. Microtomed ice observed through crossed polarizers revealed marked microstructural features, which confirm a freezing history as a process of sheet after sheet freezing. Our results suggest that proteins bind, among others, to the basal plane of crystals, as also proposed in previous studies. Analyses of the habit showed a crystal shape relatively stable over time, and explain the microstructural features in the polycrystalline sample. Furthermore, the studies about this kind of AFP contribute to complete the puzzle of growth inhibition by AFPs.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 8
    Publication Date: 2018-08-10
    Description: Germany intends to present the Scientific Committee the background document that provides the scientific basis for the evaluation of marine protected areas (MPAs) in the Weddell Sea. Please note, that the current state of the background document presents a comprehensive yet incomplete first version concerning chapters that have to be (further) developed or revised. The contents and structure of the document reflect also its main objectives, i.e. (i) to set out the general background and context of the establishment of MPAs, (ii) to describe the boundaries of the Weddell Sea MPA Planning Area, (iii) to inform on the data retrieval process, (iv) to provide - for the first time- a comprehensive, yet succinct, general description of the Weddell Sea ecosystem to reflect the state of the science, and additionally to present the results of the various preliminary scientific analyses that were carried out so far within the framework of the MPA Weddell Sea project, and finally (v) to describe future work beyond the development of the scientific basis for the evaluation of a Weddell Sea MPA.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Miscellaneous , NonPeerReviewed
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  • 9
    Publication Date: 2015-04-13
    Description: Due to the unique and extreme physico-chemical conditions in sea ice, i.e. the high salinity and the icy matrix, it constitutes a favourable habitat for the production of high levels of dimethylsulfoniopropionate (DMSP) by the inhabiting microalgae. High concentrations of DMSP and DMS (dimethylsulfide) are frequently found in sea ice during spring and summer. Records of production during winter are still scarce, but first evidence indicates the potential importance for global budgeting. Our study presents profiles of DMS(P) in sea ice cores collected during the AWECS (Antarctic Winter Ecosytem Climate Study) cruise on RV Polarstern (ANT29-6) in the Weddell Sea. Results show that significant DMS(P) production also occurs during winter in sea ice of the Weddell Sea. This stands in contrast to previous measurements in Arctic winter sea ice (CFL-IPY cruise in the Circumpolar Flaw Lead Polynya), where DMS(P) concentrations were very low. Possible explanations for the differences between DMS(P) levels in the Arctic and Antarctic might be the different snow cover and thus insulation, light regimes and also microbial community structure within the ice. The DMS profiles mirrored the permeability of the sea ice, following elevated DMSP levels in the impermeable areas while showing losses to the ice surface and ice-water interface in the more permeable regions. DMS(P) levels were generally correlated with chlorophyll A concentrations, although the details are complex and seem to be influenced by species composition and species specific DMSP/Chla ratios. Three mayor trends determined in situ reflect values of 136 (±93), 32 (±15) and 5 (±2) mmol DMSP/g Chla resembling published values for cultures of dinoflagellates, haptophytes and diatoms. Preliminary microscopy data confirm that dinoflagellate dominated sea ice layers display higher DMSP/ChlA ratios than diatom dominated ones.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 10
    Publication Date: 2014-12-10
    Description: We investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of −14 °C for 14 days after which ice decay was induced by increasing the air temperature to −1 °C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicates that there was two main stages in the brine dynamics: bottom convection during ice growth, and brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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