Alfred Wegener Institute for Polar and Marine Research
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Time-varying trends from Arctic ozonesonde time series in the years 1994–2022
Get PDFAbstractAlthough evidence of recovery in Antarctic stratospheric ozone has been found, evidence of recovery in Arctic ozone is still elusive, even though 25 years have passed since the peak in ozone depleting substances. Here we have used a Dynamic Linear Model to derive time-varying trends over 20-year periods in the Arctic ozone time series, measured in-situ by ozonesondes from 6 stations, from 1994 to 2022. The model accounts for seasonality, external forcing and 1st-order correlation in the residuals. As proxies for the external forcing, we have used tropopause pressure (replaced with Arctic Oscillation in the troposphere), eddy heat flux, the volume of polar stratospheric clouds multiplied by effective equivalent stratospheric chlorine, and solar radio flux at 10.7 cm for the 11-year solar cycle. Our results indicate that the ozone recovery in the lower Arctic stratosphere is not detectable. Though significant positive trends have been detected prior to 2017 at some stations, there are no statistically significant positive trends after 2017. Moreover, at a number of stations the trends after 2019 are rather negative and significant, varying between − 0.30 ± 0.25 and − 1.00 ± 0.85% per decade. Furthermore, the Arctic troposphere exhibited only statistically significant negative trends over 20-year periods ending in 2017 or later, varying between − 0.31 ± 0.27 and − 1.76 ± 0.41% per decade. These results highlight the importance of continued monitoring of the Arctic ozone.</jats:p
MODELING OF PATTERN FORMATION DURING BRINE CHANNEL FORMATION
Get PDFDuring the ice formation in the Arctic Ocean, small liquid-saline channels remain, which are colonised by various small microorganisms. The size of the ice domains separating regions of concentrated sea water depends on salinity and temperature and corresponds to the size of sea ice platelets obtained from a morphological stability theory for the solidification of salt water. We consider a pattern formation on the bases of the theory of phase transitions using the Landau-Ginzburg free energy. Instead of a reaction-diffusion kinetics with the formation of morphological Turing structures or the BCM-model modified thermodynamic approaches are considered. These are characterised by a total differential according to Schwarz’s theorem. We modify the original Kobayashi’s phase field model by including freezing point depression due to salt in order to describe the phase boundary of the fine network and cavities filled with brine which are formed during the freezing process in sea ice. A modified Cahn-Hilliard like model allows deeper supercooling temperatures than the modified Kobayashi approach and is therefore better suited for coupling to larger scales which can be realised by the extend Theory of Porous Media (eTPM). A linear stability analysis selects the parameter range that enables formation of structures. Initially, the diffusion parameter is time-dependent because of the changing porosity and tends towards a constant value at equilibrium
Biodiversity and Hemolytic Toxicity of the Genus Heterocapsa (Dinophyceae) in the Beibu Gulf, China.
Get PDFThe dinoflagellate genus Heterocapsa includes several widely distributed and potentially toxic species associated with Harmful Algal Blooms (HABs), particularly affecting the Western Pacific Ocean. To reveal the biodiversity of Heterocapsa in Beibu Gulf, six strains were morphologically characterized using light and scanning electron microscopy, while large subunit rDNA (LSU rDNA) and internal transcribed spacer (ITS) were sequenced for phylogenetic analysis through maximum likelihood and Bayesian inferences. Two strains (BGERL169, BGERL170) were identified as Heterocapsa philippinensis ribotype I, three (BGERL171-BGERL173) as a new Heterocapsa philippinensis ribotype II, and one strain (BGERL174) as Heterocapsa pseudotriquetra. Cells of H. philippinensis were ovoid to spherical, yellowish-brown, with reticulate chloroplasts, and had a sausage-shaped nucleus positioned longitudinally along the dorsal side of the cell, and the theca was arranged in Po, cp, X, 5′, 3a, 7″, 6c, 5s, 5‴, 2⁗. Additionally, BGERL169 and BGERL171 showed no hemolytic toxicity in rabbit erythrocyte lysis assays. To the best of our knowledge, this research provides the first morphological and phylogenetic analysis of H. philippinensis, including the identification of a new ribotype, as well as the discovery of H. pseudotriquetra in Chinese waters. The findings contribute to the understanding of Heterocapsa species biogeography and toxicity in Chinese waters, offering valuable data for future HAB monitoring in Beibu Gulf.</jats:p
Weddell seals and shelf ice-associated cryo-benthos at the Ekström and Riiser-Larsen ice shelves
Get PDFIncidences of cryo-benthic communities beneath ice shelves are rare and recent discoveries. Combined seal- and ROV-borne imagery and novel sampling technologies allowed for a comparative assessment and augmentation of earlier findings on cryo-benthic communities being attached head-down to the underside of floating shelf ice beneath Ekström (Atka Bay) and neighbouring Riiser-Larsen ice shelves (Drescher Inlet; eastern Weddell Sea). These “hanging gardens” represent a food horizon where seals could benefit from a local hotspot of enhanced biological activity, and could probably be indicative for increased abundances of seals at the interface between shelf and sea ice. Here we compile local physical, biological, and biogeochemical data and discuss their relevance in the wider regional context for this faunal hotspot. These include data on shelf-, sea- and platelet ice, seafloor topography, hydrography and water chemistry, as well as associated pelagic and benthic marine life, in particular affinities of the cryo-benthic isopod community to related fauna occurring in nearby seabed communities using molecular barcoding. In view of the vast but almost entirely unsampled habitat of >1.5 million square km in the entire Southern Ocean, the magnitude of the carbon stored is a significant gap in our knowledge of the Southern Ocean food web. This unique ecosystem is endemic to the Antarctic and under severe threat due to climate warming
Marine particle microbiomes during a spring diatom bloom contain active sulfate-reducing bacteria
Get PDFPhytoplankton blooms fuel marine food webs with labile dissolved carbon and also lead to the formation of particulate organic matter composed of living and dead algal cells. These particles contribute to carbon sequestration and are sites of intense algal-bacterial interactions, providing diverse niches for microbes to thrive. We analyzed 16S and 18S ribosomal RNA gene amplicon sequences obtained from 51 time points and metaproteomes from 3 time points during a spring phytoplankton bloom in a shallow location (6-10 m depth) in the North Sea. Particulate fractions larger than 10 μm diameter were collected at near daily intervals between early March and late May in 2018. Network analysis identified two major modules representing bacteria co-occurring with diatoms and with dinoflagellates, respectively. The diatom network module included known sulfate-reducing Desulfobacterota as well as potentially sulfur-oxidizing Ectothiorhodospiraceae. Metaproteome analyses confirmed presence of key enzymes involved in dissimilatory sulfate reduction, a process known to occur in sinking particles at greater depths and in sediments. Our results indicate the presence of sufficiently anoxic niches in the particle fraction of an active phytoplankton bloom to sustain sulfate reduction, and an important role of benthic-pelagic coupling for microbiomes in shallow environments. Our findings may have implications for the understanding of algal-bacterial interactions and carbon export during blooms in shallow-water coastal areas
A song for Pelagibacter. Using creative improvisation as a tool for novel science communication through the Ocean Science Jam
Get PDFSharing complex oceanic research in an accessible way with the public is being identified by scientific institutions, universities, governmental departments, and NGOs as a critical intervention in promoting better engagement with the sea. Art–science collaborations play an integral role in this. Traditionally, these involve pairing artists and marine scientists to work on a project which is then presented to an audience. Increasingly however more interactive relationships with the public are being seen as a beneficial way to merge art and scientific data. The Ocean Science Jam is such a project that brings musicians, artists, dancers, performers, and the public together to respond creatively in real time to visual and audio cues based on a theme related to marine scientists’ work. By mixing creativity with science in an integrative way the Ocean Science Jam not only acts as tool for public communication but also opens new ways for scientific data to be interpreted by non-scientists. This paper will explore this initiative from design to delivery highlighting the results of facilitating with the public moments where new responses to ocean science can be created through art. It will do so by combining the reflections of the creator of the Ocean Science Jam as well as feedback from the scientists and public who have participated. It will argue for the benefits of using improvisation and artistic co-creation for developing moments of embodied oceanic exchange and connection.</jats:p
Winter distribution of zooplankton and ichthyoplankton assemblages in the North Sea and the English Channel
Get PDFAlthough zooplankton were extensively studied in the North Sea, knowledge about winter zooplankton assemblages is still scarce, despite potential influence of zooplankton overwintering stocks on seasonal plankton succession and productivity. Furthermore, several economically and ecologically important fish species reproduce during winter contributing to the zooplankton community as passive members (eggs) or predators (larvae). To elucidate on winter zooplankton distribution, abundance and composition in the Southern North Sea and Eastern English Channel, we defined assemblages based on mesozoo- and ichthyoplankton data sampled between January and February 2008 using fuzzy-clustering and indicator species. Mesozoo- and ichthyoplankton (eggs+larvae) were integrated in a common analysis by using a spatial grid adapted to the datasets and defined by means of a geostatistical method developed in agronomics. Potential environmental drivers of assemblage distribution were evaluated by means of GLMM and comparison with data from 2022 facilitated insight about the inter-annual representativeness of the assemblages. Five zooplankton assemblages were found varying with regard to total zooplankton abundance, dominant and indicator taxa. Spatial variability of abiotic (dissolved nutrients, salinity, depth, temperature, organic matter in suspension, chlorophyll a), biotic variables (phyto- and microplankton composition), water masses and fish spawning grounds were revealed as potential drivers of assemblage distribution. Assemblages off the Rhine-Scheldt estuary and in the German Bight harbored the biggest zooplankton overwintering stocks that might influence the grazing pressure on phytoplankton spring production. Assemblages off the Rhine-Scheldt estuary and covering the English Channel and the Southern Bight were found to be of high importance for herring and plaice larvae. Although further analyses suggested inter-annual representativeness of the assemblages found (2008 vs 2022), the assessment of further years would be necessary to account for potential inter-annual variability. Future studies could profit from the assessment of microzooplankton facilitating insight in fish larvae feeding potential and zooplankton overwintering strategies
Southern Ocean and Southern African Monsoon Forcing of the Subtropical Indian Ocean Early Pliocene “Biogenic Bloom”
Get PDFThe Pliocene epoch emerges as a pivotal juncture in Earth's climatic evolution, characterized by pronounced warmth and elevated atmospheric carbon dioxide compared to contemporary levels. While the broader climatic context of the Pliocene has garnered attention, there remains an outstanding gap in detailed paleoclimate reconstructions of the early Pliocene, a new potential target for data-model intercomparison. Addressing this, we investigate the drivers of the early Pliocene ?Biogenic Bloom? and implications for nutrient dynamics and climate. By analyzing high-resolution biotic assemblage and geochemical records from the Agulhas Plateau, southwestern Indian Ocean (International Ocean Discovery Program, IODP Site U1475), we aim to elucidate the forcing and feedback mechanisms driving the early Pliocene marine ecosystems. We identify a distinct shift in coccolithophore assemblages at ?4.6 million years ago, characterized by a notable change in dominance between the larger and smaller Reticulofenestra and high abundances of Noelaerhabdaceae < 5 µm. Our findings confirm the adaptive strategies of coccolithophore communities to prevailing environmental conditions, underscoring their evolutionary resilience by producing smaller coccoliths while increasing their abundances in a nutrient-replete ocean. Surface water dynamics, particularly the subtropical front migration and expansion of Southern Ocean waters, in combination with the southern African monsoon variability, emerge as key drivers of phytoplankton productivity during the early Pliocene. We posit that a weakened biological carbon pump, due to increased phytoplankton production driven by intense ocean circulation and mixing during the early Pliocene, served as a potential precursor to the subsequent middle Pliocene abrupt climate extremes