Alfred Wegener Institute for Polar and Marine Research
Electronic Publication Information CenterNot a member yet
52828 research outputs found
Sort by
Uncovering Fibrocapsa japonica (Raphidophyceae) in South America: First Taxonomic and Toxicological Insights from Argentinean Coastal Waters
Get PDFFibrocapsa 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
Seasonal recurrence and modular assembly of an Arctic pelagic marine microbiome
Get PDFDeciphering how microbial communities are shaped by environmental variability is fundamental for understanding the structure and function of ocean ecosystems. While seasonal environmental gradients have been shown to structure the taxonomic dynamics of microbiomes over time, little is known about their impact on functional dynamics and the coupling between taxonomy and function. Here, we demonstrate annually recurrent, seasonal structuring of taxonomic and functional dynamics in a pelagic Arctic Ocean microbiome by combining autonomous samplers and in situ sensors with long-read metagenomics and SSU ribosomal metabarcoding. Specifically, we identified five temporal microbiome modules whose succession within each annual cycle represents a transition across different ecological states. For instance, Cand. Nitrosopumilus, Syndiniales, and the machinery to oxidise ammonia and reduce nitrite are signatures of early polar night, while late summer is characterised by Amylibacter and sulfur compound metabolism. Leveraging metatranscriptomes from Tara Oceans, we also demonstrate the consistency in functional dynamics across the wider Arctic Ocean during similar temporal periods. Furthermore, the structuring of genetic diversity within functions over time indicates that environmental selection pressure acts heterogeneously on microbiomes across seasons. By integrating taxonomic, functional and environmental information, our study provides fundamental insights into how microbiomes are structured under pronounced seasonal changes in understudied, yet rapidly changing polar marine ecosystems
Future of coral bleaching research
Get PDFCoral bleaching is the largest global threat to coral reef ecosystem persistence this century. Advancing our understanding of coral bleaching and developing solutions to protect corals and the reefs they support are critical. In the present article, we, the US National Science Foundation-funded Coral Bleaching Research Coordination Network, outline future directions for coral bleaching research. Specifically, we address the need for embedded inclusiveness, codevelopment, and capacity building as a foundation for excellence in coral bleaching research and the critical role of coral-bleaching science in shaping policy. We outline a path for research innovation and technology and propose the formation of an international coral bleaching consortium that, in coordination with existing multinational organizations, could be a hub for planning, coordinating, and integrating global-scale coral bleaching research, innovation, and mitigation strategies. This proposed strategy for future coral bleaching research could facilitate a step-function change in how we address the coral bleaching crisis
PANGAEA Data Publisher for Earth & Environmental Science (Coordination Workshop SPP 1158, 2025)
Get PDF
Fjord sediments in southern Greenland reveal Holocene glacial activity and organic carbon sequestration dynamics
Get PDFSediments accumulating in Greenlandic fjords, situated between the ice sheet and the ocean, offer an excellent opportunity for investigating the environmental response to past climate variability and associated organic carbon sequestration processes. Our study focuses on a multiproxy approach of an almost undisturbed sedimentary record from Narsaq Sound in southern Greenland. A ~30-cm long multicore was collected on top of a ~11-m long gravity core during the MSM111 expedition in September 2022. Radiocarbon dating indicates a maximum age of approximately 12,000 years and a relatively constant sedimentation rate of ~1 m/kyr. A suite of whole-core analytical techniques was applied, including magnetic susceptibility measurements, X-ray fluorescence, and computer tomography scanning. Sediment samples were taken at intervals of 5–10 cm from the gravity core and at 1 cm intervals from the multicore. These samples were analyzed for total organic carbon, total nitrogen, stable isotopes of organic carbon and nitrogen, biomarkers (e.g., IP25), and organic carbon lability. Additionally, the elemental composition and dissolved organic carbon content of sediment pore-waters were assessed.Preliminary results show that sedimentological features such as IRD and bioturbation, as well as the elemental composition of the Narsaq record, reveal major changes related to the position of nearby glaciers and main climatic changes during the Holocene. Moreover, we found that the rather unusual element Niobium, derived from the surrounding drainage area, appears as a promising indicator of terrigenous sediment supply and past environmental change. Besides a clear change from predominantly terrestrial to more marine organic carbon during the transition from deglaciation to the thermal maximum era, the organic carbon is predominantly marine in origin during the entire Holocene. Our first results show that the investigated sediment cores from southern Greenland provide an excellent sedimentological and geochemical record reflecting past glacial activity and the impact of large scale climatic variability on local environmental changes since the last deglaciation
A simple physical model for glacial cycles
Get PDFAbstract. Glacial cycles are the norm in Pleistocene climate variability. Models of varying degree of complexity have been used to answer the question of what causes the nonlinear response of the climate system to the periodic forcing from the Sun. At one end of the complexity spectrum are comprehensive models which aim to represent all involved processes in a realistic manner. However, their high computational cost precludes their use in the very long simulations needed. At the other end are conceptual models which are computationally far less demanding. Most of them capture well the shape and patterns of glacial cycles as indicated by the geological record, but they generally lack a physical basis, thus making it very difficult to identify the underlying mechanisms. Here we present a conceptual model that aims to physically represent the interaction between the climate and the Northern Hemisphere ice sheets while eliminating spatial dimensions in some of the fundamental ice-sheet thermodynamic and dynamic equations. To this end, we describe the Physical Adimensional Climate Cryosphere mOdel (PACCO) from its simplest to its most complex configuration. We discuss separately the implications of different fundamental mechanisms such as ice-sheet dynamics and thermodynamics, glacial isostatic adjustment, and ice-sheet albedo aging for our model. We conclude that ice-sheet dynamics and a delayed isostatic response are sufficient to produce resonance around periodicities of 100 kyr, despite the fact that the forcing has a spectrum concentrated around lower values. In addition, ice-sheet thermodynamics and ice aging separately enhance the model nonlinearities to provide 100 kyr periodicities in good agreement with reconstructions. Overall, PACCO is a valuable tool for analyzing the different hypotheses present in the literature
Diagnosing the Atlantic Meridional Overturning Circulation in density space is critical in warmer climates
Get PDFThe Atlantic Meridional Overturning Circulation (AMOC) plays a crucial role in shaping the global climate system by redistributing heat and influencing large-scale climate patterns. Utilizing the AWI-CM3 model, we investigate the AMOC sensitivity to an abrupt climate change scenario (abrupt-4xCO2) with respect to pre-industrial climate (PI), comparing the AMOC diagnosed in depth (z-AMOC) and density (ρ-AMOC) space. Water mass transformations are assessed to analyze the impact of background climate on surface-forced and interior-mixing-induced transformations. We find that both the location and magnitude of AMOC maximum are directly affected by the framework choice. In PI, the ρ-AMOC maximum is substantially stronger than that of the z-AMOC, while at 26° N the two diagnostics are nearly equivalent. Consequently, the variability of the z-AMOC maximum correlates only with that at 26° N, reflecting isopycnal flattening into constant depth levels in the subpolar North Atlantic inherent to these diagnostics. Strong AMOC weakening is observed under 4xCO2 forcing in both frameworks until simulation year 75. Subsequently, both diagnostics reveal a weaker AMOC with an approximate strength of 7.1 Sv, although with z-AMOC displaying a slight recover towards the end of the simulation and ρ-AMOC oscillating steadily around 5 Sv. At 26° N, variability patterns remain comparable to PI, albeit with an additional ρ-AMOC weakening of approximately 2 Sv, indicating divergence between the representation of AMOC dynamics in the subtropical Atlantic within both frameworks in comparison to PI. The diagnostics in density space allow for the attribution of this further ρ-AMOC weakening to increased entrainment of fresher overflows from amplified GIN seas overturning and reduced deep convection in the Labrador and Irminger Seas. In contrast, the diagnostics in depth space only reveals reduced downwelling around the southwestern Greenland coast and along the path of the Gulf Stream, features that are more challenging to evaluate against available observations. Thus, the comparison between z-AMOC and ρ-AMOC indicates that diagnosing the AMOC in density space provides more physically meaningful information regarding the state of the water mass transformations and their contribution to ocean circulation regimes across the entire Atlantic basin, not only the subpolar North Atlantic, and especially as the climate continues to warm. These findings emphasize the importance of diagnosing AMOC in density space to better understand water mass transformations, which are concealed in depth space and to capture AMOC variability in warmer climates, across all latitudes
The colors of proxy noise
Get PDFAbstract. The complex biological and physical processes that preserve paleoclimate information over centuries or longer introduce variations in proxy time series that are unrelated to the true climate. These non-climatic variations act on different timescales and are often referred to as “noise” of a specific color, based on similarities between a time series' power spectrum and the electromagnetic spectrum of light. For example, “white noise” equally affects all timescales, where “red noise” dominates only on long timescales, similar to longwave red light. Noise spectra in proxy records have far-reaching implications in paleoclimate research, but noise characteristics are often assumed based on first principles rather than estimated directly, risking either inflating or underestimating error at particular frequencies. Here, we provide concrete definitions of the various types of timescale-dependent errors that are present in proxy data, and review the literature on methods for quantifying noise terms. We then synthesize the results of several published studies that use a common empirical approach for estimating the noise spectrum in ice-core, coral, and tree-ring data. We posit that the colors of proxy noise are archive-specific, with white noise dominating in depositional archives such as ice cores and marine sediment cores, while red noise is more common in biological archives such as tree rings and corals. Our synthesis supports assigning specific colored noise terms in proxy system models, data assimilations and other experiments