Alfred Wegener Institute for Polar and Marine Research
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Effects of Temperature, Salinity and CO2 Concentration on Growth and Toxin Production of the Harmful Algal Bloom species Alexandrium pseudogonyaulax (Dinophyceae) from the Danish Limfjord
Get PDFOrbitally forced and internal changes in West African rainfall interannual-to-decadal variability for the last 6000 years
Get PDFRecent variability in West African monsoon rainfall (WAMR) has been shown to be influenced by multiple ocean–atmosphere modes, including the El Niño Southern Oscillation, Atlantic Multidecadal Oscillation and the Interdecadal Pacific Oscillation. How these modes will change in response to long term forcing is less well understood. Here we use four transient simulations driven by changes in orbital forcing and greenhouse gas concentrations over the past 6000 years to examine the relationship between West African monsoon rainfall multiscale variability and changes in the modes associated with this variability. All four models show a near linear decline in monsoon rainfall over the past 6000 years in response to the gradual weakening of the interhemispheric gradient in sea surface temperatures. The only indices that show a long-term trend are those associated with the strengthening of the El Niño Southern Oscillation from the mid-Holocene onwards. At the interannual-to-decadal timescale, WAMR variability is largely influenced by Pacific–Atlantic – Mediterranean Sea teleconnections in all simulations; the exact configurations are model sensitive. The WAMR interannual-to-decadal variability depicts marked multi-centennial oscillations, with La Niña/negative Pacific Decadal Oscillation and a weakening and/or poleward shift of subtropical high-pressure systems over the Atlantic favoring wet WAMR anomalies. The WAMR interannual-to-decadal variability also depicts an overall decreasing trend throughout the Holocene that is consistent among the simulations. This decreasing trend relates to changes in the North Atlantic and Gulf of Guinea Sea Surface Temperature variability
Recent emergence of Arctic atlantification dominated by climate warming
Get PDFThe Arctic Ocean’s Eurasian Basin underwent notable atlantification during the 2010s, characterized by warming of the Atlantic Water layer and increased upper ocean salinity. Despite profound implications for the Arctic climate system and marine ecosystems, the primary drivers of this process remain debated. One hypothesis suggested that alternating phases of the atmospheric Arctic Dipole may have mitigated recent atlantification. Here, we use high-resolution model simulations to disentangle the main contributors to atlantification in the Arctic basin. We show that the decline in Arctic sea ice was the dominant driver, while wind variability associated with the Arctic Dipole played a minor role, contributing slightly rather than mitigating the process. The positive phase of the Arctic Oscillation also made a relatively small contribution. Although recent changes in atmospheric circulation over the Greenland Sea tended to reduce warm water inflow through the Fram Strait, this cooling effect on the Arctic Atlantic Water layer was outweighed by the warming induced by sea ice decline.</jats:p
Greenhouse Gas Production and Microbial Response During the Transition From Terrestrial Permafrost to a Marine Environment
Get PDFArctic permafrost coasts, affected by rising sea levels and increasing coastal erosion in a warming climate, undergo significant changes. Simulating how permafrost is impacted by inundation with fresh, brackish and marine water enhances our understanding of permafrost carbon stock responses to increasingly marine conditions. We investigated CO2 and CH4 production during key transitions in a coastal thermokarst landscape on the Bykovsky Peninsula, Siberia, assessing short- and long-term microbial responses to varying salinities in anaerobic 1-year incubation experiments. Initially, CO2 production from saltwater-inundated permafrost was low due to the low abundance of salt-tolerant microbial communities. Over the long term, after simulated lagoon formation and the growth of sulfate-reducing bacteria, CO2 production surpassed that of the terrestrial sites by 8 times. CO2 and CH4 production was lowest under fully marine conditions, suggesting incomplete adaptation of microbes. Rapid ecosystem changes stress microbial communities, with greenhouse gas production highest under near-natural conditions. With an increase in lake drainage events and rising sea levels, thermokarst lagoon distribution on Arctic coasts will escalate, resulting in a further increase of carbon mineralization and CO2 release. With this study, we provide first estimations on greenhouse gas production during the transition from terrestrial to submarine conditions in permafrost-affected aquatic systems
Towards semi-quantification of DOM: isomer separation with LC-FT-ICR-MS combined with a post-column infusion of standard.
Get PDF10.1039/D4AN00119
Lack of Hematodinium microscopic detection in crustaceans at the northern and southern ends of the Wadden Sea and an update of its distribution in Europe
Get PDFHematodinium is a parasitic dinoflagellate with a wide distribution along the European coastline. We investigated whether Hematodinium occurs in the Wadden Sea, a large tidal flat system spanning the Netherlands, Germany, and Denmark, where to date no records exist. In total, we investigated eight different species from six sites at the southern (Texel, the Netherlands) and northern (Sylt, Germany) ends of the system. Based on microscopic hemolymph screening, we did not detect Hematodinium in any of the 1252 investigated individuals. An extensive additional literature review revealed 1489 Hematodinium records in Europe from 14 crustacean species, most locally occurring at high prevalence. This makes our finding of lack of Hematodinium infections surprising and suggests that environmental factors such as a lower salinity may limit the distribution of Hematodinium at the investigated locations at both ends of the Wadden Sea. However, whether the entire Wadden Sea represents a distributional gap for Hematodinium remains to be investigated
Evidence for immune priming specificity and cross-protection against sympatric and allopatric Vibrio splendidus strains in the oyster Magalana (Crassostrea) gigas
Get PDFInfections with pathogenic Vibrio strains are associated with high summer mortalities of Pacific oysters Magalana (Crassostrea) gigas, affecting production worldwide. This raises the question of how M. gigas cultures can be protected against deadly Vibro infection. There is increasing experimental evidence of immune priming in invertebrates, where previous exposure to a low pathogen load boosts the immune response upon secondary exposure. Priming responses, however, appear to vary in their specificity across host and parasite taxa. To test priming specificity in the Vibrio - M. gigas system, we used two closely related Vibrio splendidus strains with differing degrees of virulence towards M. gigas. These V. splendidus strains were either isolated in the same location as the oysters (sympatric, opening up the potential for co-evolution) or in a different location (allopatric). We extracted cell-free haemolymph plasma from infected and control oysters to test the influence of humoral immune effectors on bacterial growth in vitro. While addition of haemolypmph plasma in general promoted growth of both strains, priming by an exposure to a sublethal dose of bacterial cells lead to inhibitory effects against a subsequent challenge with a potentially lethal dose in vitro. Inhibitory effects and immune priming was strongest when oysters had been primed with the sympatric Vibrio strain, but inhibitory effects were seen both when challenged with the sympatric as well as against allopatric V. splendidus, suggesting some degree of cross protection. The stronger immune priming against the sympatric strain suggests that priming could be more efficient against matching local strains potentially adding a component of local adaptation or co-evolution to immune priming in oysters. These in vitro results, however, were not reflected in the in vivo infection data, where we saw increased bacterial loads following an initial challenge. This discrepancy might suggests that that it is the humoral part of the oyster immune system that produces the priming effects seen in our in vitro experiments