Alfred Wegener Institute for Polar and Marine Research
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Author Correction: Deglacial release of petrogenic and permafrost carbon from the Canadian Arctic impacting the carbon cycle
Get PDFRefining Zooplankton Diet Composition Studies Over Short and Long Time Scales by Combining 18S Metabarcoding With Fatty Acid Analyses
Get PDFUnderstanding diet composition is essential for unravelling trophic interactions in aquatic ecosystems. DNA metabarcoding, utilising various variable regions of the 18S rRNA gene, is increasingly employed to investigate zooplankton diet composition. However, accurate results depend on rapid inactivation of digestive enzymes and DNA nucleases through proper sample processing and preservation. In this study, we compare the prey communities of Antarctic krill retrieved from the 18S variable regions V4 and V7 and assess how different processing treatments affect the detected prey composition of both krill and salps. Our findings highlight the critical importance of prompt sample processing for species with highly efficient digestive enzymes, such as krill, to preserve rapidly digested prey, including gelatinous plankton. Comparative analyses of the V4 and V7 regions revealed significantly different prey communities within the same krill samples, indicating that these regions may not be suitable for direct comparisons within or across studies. To complement molecular approaches, we also analyse fatty acids (FA) as trophic markers which provide insights into dietary habits over both short and long time scales. By comparing FA signals from stomach and tissue samples of the same krill and salp individuals, we identified significant differences in trophic markers representing different plankton groups. These findings emphasise the necessity of separating digestive tract from tissue to distinguish between short- and long-term diet signals. Furthermore, integrating FA analysis with metabarcoding offers valuable insights into zooplankton digestion efficiency across taxonomic levels. This combined approach enhances our understanding of zooplankton feeding ecology and trophic interactions in marine ecosystems
Uncovering Fibrocapsa japonica (Raphidophyceae) in South America: First Taxonomic and Toxicological Insights from Argentinean Coastal Waters
No full textFibrocapsa japonica (Raphidophyceae) is a cosmopolitan species frequently associated with harmful algal blooms (HABs) and fish mortality events, representing a potential threat to aquaculture and coastal ecosystems. This study provides the first comprehensive morphological, phylogenetic, pigmentary, and toxicological characterization of F. japonica strains isolated from Argentina. Light and transmission electron microscopy confirmed key diagnostic features of the species, including anterior flagella and the conspicuous group of mucocyst in the posterior region. Phylogenetic analysis based on the LSU rDNA D1–D2 region revealed monophyletic relationships with strains from geographically distant regions. Pigment analysis by HPLC identified chlorophyll-a (62.3 pg cell−1) and fucoxanthin (38.4 pg cell−1) as the main dominant pigments. Cytotoxicity assays using RTgill-W1 cells exposed for 2 h to culture supernatants and intracellular extracts showed strain-specific effects. The most toxic strain (LPCc049) reduced gill cell viability down to 53% in the supernatant exposure, while LC50 values ranged from 1.6 × 104 to 4.7 × 105 cells mL−1, depending directly on the strain and treatment type. No brevetoxins (PbTx-1, -2, -3, -6, -7, -8, -9, -10, BTX-B1 and BTX-B2) were detected by LC–MS/MS, suggesting that the cytotoxicity may be linked to the production of reactive oxygen species (ROS), polyunsaturated fatty acids (PUFAs), or hemolytic compounds, as previously hypothesized in the literature. These findings offer novel insights into the toxic potential of F. japonica in South America and underscore the need for further research to elucidate the mechanisms underlying its ichthyotoxic effect
Skyglow increases cyanobacteria abundance and organic matter cycling in lakes
Get PDFArtificial light propagating towards the night sky can be scattered back to Earth and reach ecosystems tens of kilometres away from the original light source. This phenomenon is known as artificial skyglow. Its consequences on freshwaters are largely unknown. In a large-scale lake enclosure experiment, we found that skyglow at levels of 0.06 and 6 lux increased the abundance of anoxygenic aerobic phototrophs and cyanobacteria by 32 (±22) times. An ecosystem metabolome analysis revealed that skyglow increased the production of algal-derived metabolites, which appeared to stimulate heterotrophic activities as well. Furthermore, we found evidence that skyglow decreased the number of bacteria-bacteria interactions. Effects of skyglow were more pronounced at night, suggesting that responses to skyglow can occur on short time scales. Overall, our results call for considering skyglow as a reality of increasing importance for microbial communities and carbon cycling in lake ecosystems
The effect of ocean alkalinity enhancement on pelagic bacterial communities: focus points derived from a mesocosm experiment
Get PDFAnthropogenic climate change caused by CO2 emissions forces humanity to reduce the usage of fossil fuels. Along with the task of emission reduction, societies face the task of removing excess CO2 from the atmosphere by using negative emission technologies (NETs). Ocean alkalinity enhancement (OAE) is a proposed NET, aiming at increasing oceanic CO2 uptake through the addition of alkaline substances. This is an anthropogenically accelerated version of rock weathering, a natural global process for atmospheric CO2 regulation. The environmental impacts of OAE remain poorly understood. This study was part of a comprehensive OAE-mesocosm experiment in the North Sea (RETAKE), and focused on the effects of OAE on the pelagic bacterial community during the experiment. We assessed changes in bacterial community structure with 16S rRNA amplicon sequencing and abundance with flow cytometry, to evaluate responses to alkalinity addition. Beta diversity analysis showed that sampling time was the primary driver for community variation, with only marginal structural differences linked to alkalinity treatments. PERMANOVA tests conducted on predictions of functional metabolic pathways of the community revealed significant differences between treatments and baseline controls. A deeper analysis of the identified metabolic pathways revealed little evidence for alkalinity-induced changes. In contrast, total bacterial cell counts were influenced by alkalinity additions, showing delayed abundance peaks at higher concentrations and a non-linear response threshold between 500–750 µmol/L. These dynamics were linked to shifts in chlorophyll concentrations, suggesting an indirect effect of OAE on bacteria mediated by phytoplankton derived resources. This study is one of the first to assess ecological impacts of OAE on bacteria. Our findings highlight a structural resilience of bacterial communities to OAE but also show a quantitative response. By discussing our findings, this study aims to provide focus points, such as a threshold for save levels of alkalinity addition, to direct future research
Interstadial diversity of East Asian summer monsoon linked to changes of the Northern Westerlies
Get PDFDuring the last glacial period, the iconic Greenland ice-core records provide evidence of interstadial warmings with various durations ranging from a century to millennia. However, whether differences in interstadial duration are mirrored by distinct hydroclimate responses in the tropics remains unclear. Here we present four speleothem δ18O records from the Indian summer monsoon (ISM) and East Asian summer monsoon (EASM) regions, spanning both short and long interstadials during the last glacial period. Greenland and ISM records show broadly similar isotopic responses across events, however, the EASM records exhibit markedly different δ18O depletions between short and long interstadials. Using an isotope-enabled climate model, we attribute these differences to a further northward shift of the Northern Westerlies during short interstadials, driven by intensified high-latitude warming. This shift promoted the northwestward expansion of Western Pacific Subtropical High and hence the delivery of isotopically enriched near-sourced vapor to eastern China, dampening δ18O depletion during stadial-to-interstadial transitions. Our findings highlight a previously unrecognized sensitivity of EASM precipitation δ18O to nuanced meridional shifts in the Northern Westerlies in contrast to the uniform responses of the ISM during interstadials
Processes and Palaeo‐Environmental Changes in the Arctic from Past to Present (PalaeoArc) – introduction
No full textEnvironmental controls of rapid terrestrial organic matter mobilization to the western Laptev Sea since the Last Deglaciation
Get PDFAbstract. Arctic permafrost stores vast amounts of terrestrial organic matter (terrOM). Under warming climate conditions, Arctic permafrost thaws, releasing aged carbon and potentially impacting the modern carbon cycle. We investigated the characteristics of terrestrial biomarkers, including n-alkanes, fatty acids, and lignin phenols, in marine sediment cores to understand how the sources of terrOM transported to the ocean change in response to varying environmental conditions, such as sea-level rise, sea-ice coverage, inland climate warming, and freshwater input. We examined two sediment records from the western Laptev Sea (PS51/154 and PS51/159) covering the past 17.8 kyr. Our analyses reveal three periods with high mass accumulation rates (MARs) of terrestrial biomarkers, from 14.1 to 13.2, 11.6 to 10.9, and 10.9 to 9.5 kyr BP. These terrOM MAR peaks revealed distinct terrOM sources, likely in response to changes in shelf topography, rates of sea-level rise, and inland warming. By comparing periods of high terrOM MAR in the Laptev Sea with published records from other Arctic marginal seas, we suggest that enhanced coastal erosion driven by rapid sea-level rise during meltwater pulse 1A (mwp-1A) triggered elevated terrOM MAR across the Arctic. Additional terrOM MAR peaks varied regionally. Peaks from the Beaufort Sea during the Bølling–Allerød coincided with a freshwater flooding event, while peaks from the Laptev Sea and the Fram Strait during the Preboreal/early Holocene coincided with periods of enhanced inland warming and prolonged ice-free conditions. Our results highlight the influence of regional environmental conditions, in addition to global drivers, which can either promote or preclude regional terrOM fluxes
H11 meltwater and standard 127 ka Last Interglacial simulations suggest more modest peak temperatures for both Greenland and Antarctica: a multi-model study of water isotopes
Get PDFThe Last Interglacial (LIG) period, approximately 130 000 to 115 000 years ago, represents one of the warmest intervals of the past 800 000 years. Here, we simulate water isotopes in precipitation over Antarctica and the Arctic during the LIG, using three isotope-enabled atmosphere–ocean coupled climate models: HadCM3, MPI-ESM-wiso, and GISS-E2.1. These models were run following the Paleoclimate Modelling Intercomparison Project phase 4 (PMIP4) protocol for the LIG at 127 ka (kiloyears ago), supplemented by a 3000-year Heinrich Stadial 11 (H11) experiment using HadCM3. The long H11 simulation applies Northern Hemisphere meltwater to the North Atlantic, causing large-scale changes in ocean circulation – including cooling in the North Atlantic and Arctic and warming in the Southern Ocean and Global Ocean. While the standard 127 ka simulations do not capture the observed Antarctic warming and sea ice reduction in the Southern Ocean and Antarctic regions, they do capture around half of the warming in the Arctic. The H11 simulations align more closely with observations than the 127 ka simulations. H11 captures more than 80 % of the warming, sea ice loss, and δ18O changes for both Greenland and Antarctica. Decomposition of seasonal δ18O drivers highlights the dominant role of sea ice retreat and associated changes in precipitation seasonality in influencing isotopic values across all simulations, alongside a smaller common response to orbital forcing. We use the H11 and multi-model 127 ka simulations together to infer LIG surface air temperature (SAT) changes based on ice core measurements. The peak inferred LIG Greenland SAT increase is +2.89±1.32 K at the NEEM ice core site – less than half the previously inferred warming. Peak inferred LIG Antarctic SAT increases are +4.39±1.45 K at EDC, dropping to +1.67±3.67 K at TALDICE. These calculated warming values reflect climate effects alone and do not account for any ice-flow- or site-elevation-related impacts. Coastal sites in Greenland and Antarctica appear to have experienced less warming compared with higher central regions
Identifying common factors resulting in hatchery crashes during the production of Ostrea edulis for ecological restoration in Europe
Get PDFThe European flat oyster, Ostrea edulis , once formed extensive reefs along European coasts. These reef ecosystems are now functionally extinct, but support for their restoration is rapidly growing. Efforts are currently limited by a bottleneck in O. edulis supply. O. edulis is a challenging species to produce in a hatchery. Currently unknown causes of high mortality and hatchery crashes must be addressed to meet the increased demand for spat from the ecological restoration sector. Here we present the results of a collaborative effort between nine European hatcheries and marine research laboratories to share recent experiences, as well as production and protocol-related data. We found that crashes were widespread and suspected to be caused by diverse culprits, including Vibrio species, predatory zooplankton, and poor water quality. A Boruta regression analysis of production data identified eleven factors including water temperature in the larval tank, broodstock origin, and number of broodstock as being potentially important in explaining crashes during the larval growth phase. Eight factors including duration of larval growth stage and larval density at transfer to the settlement tank, were identified as potentially important in explaining crashes during the settlement phase. When applied to larval mortality data of batches that did not crash, the Boruta analysis identified 13 factors, including water temperature, broodstock and larval densities and broodstock origin in determining larval mortality during the larval growth stage and two factors, number of larvae in the initial larval release and broodstock origin, during the larval settlement phase. This research highlights the value of knowledge exchange between hatchery facilities in overcoming spat production problems, identifies factors that may contribute to increased larval mortality and the risk of larval crashes, as well as the importance of developing collaborative research programmes to provide for greater commonality in data collection for future coordination and production analysis