Description: Fragilariopsis kerguelensis is one of the most abundant diatoms in the sediments of the Southern Ocean. Its morphometric features have been proposed as proxies, based on links with, for example, iron availability, sea surface temperature and glacial/interglacial conditions. We investigated morphometric changes in F. kerguelensis valves in a well-studied sediment core record, focusing on transition periods between glacials and interglacials. By applying a high-throughput diatom imaging and morphometry workflow, we found two clearly distinct morphotypes which were differentiated by their rectangularity. One of them occurred preferentially in glacial samples, whilst the other persisted throughout. This indicates that their relative abundances depend on environmental conditions and thereby points to the possibility that paleo-proxies based on F. kerguelensis valve morphometric features might in the future benefit from differentiating these two morphotypes. As an initial exploration of this idea, we show that the abundance ratio of both morphotypes correlates well with paleo-temperatures which had been reconstructed using independent data from the same core. Distinguishing between the two morphotypes only became possible by image analysis for precisely measuring diatom valve outlines and area, highlighting the potential of such methods for diatom analyses.

Description: The planktonic diatom Fragilariopsis kerguelensis plays an important role in the biogeochemical cycles of the Southern Ocean, where remains of its frustules form the largest deposit of biogenic silica anywhere in the world. We assessed the genetic identity of 26 strains, from cells collected at various sites in the Southern Ocean, using three molecular markers, LSU and ITS rDNA and rbcL. The LSU sequences were identical among the tested strains, ITS sequences were highly similar, and only one base pair difference was detected among the rbcL sequences. These results, together with a large number of successful mating experiments demonstrated that the strains belong to a single biological species. We investigated the mating system and life cycle traits of F. kerguelensis. Cell size diminished gradually in clonal strains. Gamete formation only occurred when strains of opposite mating type - within a cell size range of 7-36 µm - were mixed together. Two binucleate gametes were formed in each gametangium and gamete conjugation produced a zygote that had four nuclei and was surrounded by thin siliceous scales. Two out of the four nuclei subsequently degenerated and the zygote expanded to form an auxospore surrounded by a transverse and a longitudinal perizonium. Staining with the fluorochrome PDMPO provided for the first time a clear demonstration that the longitudinal perizonium is formed after auxospore expansion is complete. Initial cells produced within the mature auxospores were 78-101 µm in length. Various authors have shown that the average valve size of F. kerguelensis varies in sediment samples collected in regions and seasons with different primary production regimes and this parameter has thus been proposed as a biological proxy for palaeo-productivity. A better understanding of the life cycle of F. kerguelensis should help the design of future investigations aimed at testing the link between cell size distribution in the natural environment and the role that environmental factors might have in the regulation of population cell size.

Description: Fragilariopsis kerguelensis is one of the most abundant diatoms in the sediments of the Southern Ocean. Its morphometric features have been proposed as proxies, based on links with, for example, iron availability, sea surface temperature and glacial/interglacial conditions. We investigated morphometric changes in F. kerguelensis valves in a well-studied sediment core record, focusing on transition periods between glacials and interglacials. By applying a high-throughput diatom imaging and morphometry workflow, we found two clearly distinct morphotypes which were differentiated by their rectangularity. One of them occurred preferentially in glacial samples, whilst the other persisted throughout. This indicates that their relative abundances depend on environmental conditions and thereby points to the possibility that paleo-proxies based on F. kerguelensis valve morphometric features might in the future benefit from differentiating these two morphotypes. As an initial exploration of this idea, we show that the abundance ratio of both morphotypes correlates well with paleo-temperatures which had been reconstructed using independent data from the same core. Distinguishing between the two morphotypes only became possible by image analysis for precisely measuring diatom valve outlines and area, highlighting the potential of such methods for diatom analyses.

Description: This open access book presents the results of three years collaboration between earth scientists and data scientists, in developing and applying data science methods for scientific discovery. The book will be highly beneficial for other researchers at senior and graduate level, interested in applying visual data exploration, computational approaches and scientifc workflows.

Description: EXECUTIVE SUMMARY Die vorliegende Studie untersuchte die mögliche Umsetzung und die dafür benötigten Steuerungsmechanismen und Instrumente für ein „Wissen Schafft Lebensraum“ (WSL) – Reallabor, welches den Aufbau und zur Etablierung nachhaltiger regionaler Lebensmittelwertschöpfungsketten in der Region Unterweser mit Bremerhaven als Oberzentrum als Kernziel hat. Mit qualitativen und quantitativen Methoden konnten erste Empfehlungen abgeleitet werden, welche als eine relative Bewertung entlang der gesamten Wirkungskette des WSL-Reallabores zu verstehen sind. Die möglichen Empfehlungen orientierten sich an den wissenschaftlichen Leitfragen für die Schaffung eines Reallabor und wurden in folgende Anwendungsmaßnahmen unterteilt: 1. Akteure und deren Interessensgewichtung 2. Beteiligungsgegenstand und –Ziele 3. Partizipationsprozesse 4. Erfolgsfaktoren Der Bericht enthält die Auswertung der Ergebnisse sowie Empfehlungen zu Akteurs-Auswahl und Stakeholder-Einbindung sowie Empfehlungen zum Ablauf der Partizipationsprozesse.

Description: The planktonic diatom Fragilariopsis kerguelensis plays an important role in the biogeochemical cycles of the Southern Ocean, where remains of its frustules form the largest deposit of biogenic silica anywhere in the world. We assessed the genetic identity of 26 strains, from cells collected at various sites in the Southern Ocean, using three molecular markers, LSU and ITS rDNA and rbcL. The LSU sequences were identical among the tested strains, ITS sequences were highly similar, and only one base pair difference was detected among the rbcL sequences. These results, together with a large number of successful mating experiments demonstrated that the strains belong to a single biological species. We investigated the mating system and life cycle traits of F. kerguelensis. Cell size diminished gradually in clonal strains. Gamete formation only occurred when strains of opposite mating type – within a cell size range of 7–36 μm – were mixed together. Two binucleate gametes were formed in each gametangium and gamete conjugation produced a zygote that had four nuclei and was surrounded by thin siliceous scales. Two out of the four nuclei subsequently degenerated and the zygote expanded to form an auxospore surrounded by a transverse and a longitudinal perizonium. Staining with the fluorochrome PDMPO provided for the first time a clear demonstration that the longitudinal perizonium is formed after auxospore expansion is complete. Initial cells produced within the mature auxospores were 78–101 μm in length. Various authors have shown that the average valve size of F. kerguelensis varies in sediment samples collected in regions and seasons with different primary production regimes and this parameter has thus been proposed as a biological proxy for palaeo- productivity. A better understanding of the life cycle of F. kerguelensis should help the design of future investigations aimed at testing the link between cell size distribution in the natural environment and the role that environmental factors might have in the regulation of population cell size.