Alfred Wegener Institute for Polar and Marine Research
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West Antarctic ice retreat and paleoceanography in the Amundsen Sea in the warm early Pliocene
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Mass loss from polar ice sheets is poorly constrained in estimates of future global sea-level rise. Today, the marine-based West Antarctic Ice Sheet is losing mass at an accelerating rate, most notably in the Thwaites and Pine Island glacier drainage basins. Early Pliocene surface temperatures were about 4 °C warmer than preindustrial and maximum sea level stood ~20 m above present. Using data from a sediment archive on the Amundsen Sea continental rise, we investigate the impact of prolonged Pliocene ocean warmth on the ice-sheet−ocean system. We show that, in contrast to today, during peak ocean warming ~4.6 − 4.5 Ma, terrigenous muds accumulated rapidly under a weak bottom current regime after spill-over of dense shelf water with high suspended load down to the rise. From sediment provenance data we infer major retreat of the Thwaites Glacier system at ~4.4 Ma several hundreds of km inland from its present grounding line position, highlighting the potential for major Earth System changes under prolonged future warming.</jats:p
Predictive links between microbial communities and biological oxygen utilization in the Arctic Ocean
Full text linkMicrobial metabolism influences rates of net community production (NCP), exerting a direct biological control on marine oxygen and carbon fluxes. In the Arctic, it is increasingly important to understand and quantify this process, as ecological and oceanographic conditions shift due to changing climate. Here, we describe potential ecological links between pelagic microbial diversity and an NCP precursor, biological oxygen utilization, using machine learning and paired observations of community structure and metabolic activity from a seasonally and spatially variable transect of the Arctic Ocean (2019–2020 MOSAiC Expedition). Community structure was determined using 16S (prokaryotic) and 18S (eukaryotic) rRNA gene amplicon sequencing, and metabolic activity was derived from ΔO2/Ar. Using self-organizing maps, we identified clear successional patterns in observed microbial community structure that were seasonally driven in the upper ocean and vertically stratified with depth. Metabolic activity was also stratified, with a primarily net heterotrophic water column (median −1.5% biological oxygen saturation), excepting periodic oxygen supersaturation (maximum: 13.6%) within the mixed layer. Using DNA sequences as predictor variables, we then constructed a random forest regression model that reliably reconstructed biological oxygen concentrations (root mean squared error = 4.14 μmol kg−1). Top predictors from this model were from heterotrophic (bacteria) or potentially mixotrophic (dinoflagellate) taxa. These analyses highlight biologically driven diagnostic tools that can be used to expand biogeochemical datasets and improve the microbial perspectives and metabolisms represented in ecological models of net productivity and carbon flux in a changing Arctic Ocean
Bioaccumulations and biotransformations of azaspiracids from Amphidoma languida in the mussel Mytilus edulis
Full text linkAzaspiracids are polyether marine algal toxins produced by several species of dinoflagellates from the family Amphidomataceae. Within the genus Amphidoma, Am. languida is the only species known so far to produce azaspiracids, while all the other toxin producers belong to the genus Azadinium. Strains of Am. languida collected in the Northeastern Atlantic have been found to produce AZA-38 and -39 as major metabolites. Cultures of Am. languida (24,000–30,000 cells mL−1) fed to mussels (Mytilus edulis), confirmed the bioaccumulation of AZA-38 and -39 in shellfish tissues. AZA-38 and -39 were found to reach a combined 75.2 μg kg−1 (AZA-1 equivalents) in mussel tissue. The tentative identification of new derivatives resulting from the biotransformation of AZA-38 and -39 in the shellfish tissue was performed by LC-HRMS/MS. Although toxin concentrations in the tissue never reached AZA-1 regulatory limits, the study demonstrates that toxins from Am. languida can readily bioaccumulate and biotransform in shellfish and the toxicity of AZA-38 and -39 and their products of biotransformation should now be assessed. Importantly, a snapshot of biotoxin data from the Irish monitoring program in 2020 also identified AZA-38 and -39 in some shellfish species, albeit at low levels, from locations around the Southwest coast of Ireland
Turbulent Mixing in the Upper Arctic Ocean Energized by Interactions of Tidally-Forced Waves With Mesoscale Shear
Full text linkAbstractHigh‐resolution observations in Fram Strait reveal complex interactions across scales, highlighting the role of internal waves in enhancing mixing within the meltwater halocline. A day‐long microstructure survey from drifting ice that traversed an anticyclone in summer shows rotating shear and straining in the halocline, resulting in low Richardson number layers coincident with turbulent patches and gradients in oxygen and chlorophyll. Year‐long data from an adjacent mooring demonstrate that increased shear variance can be related to upward‐propagating wave energy, generated by tidal forcing at the seafloor and amplified by mesoscale shear near the surface. These waves contain compound tides and overtones with spectral peaks at 3 and 4 cycles per day. Mesoscale variability modulates internal wave shear, influencing turbulent mixing and ecosystem dynamics. Our findings underscore the importance of cross‐scale interactions in driving turbulent mixing, with implications for water mass transformations, sea ice melt, and primary production in a changing Arctic.</jats:p
Chronic Wasting Disease Research in North America: A systematic review highlighting species-wise and interdisciplinary research trends
Full text linkChronic Wasting Disease (CWD) research has experienced significant growth, spanning diverse disciplines such as genetics, immunology, modelling, and behaviour. To gain a broad understanding of the changes in CWD research focusing cervids, we analysed temporal trends in study location, species, genus investigated, infection types, and population type since the discovery of CWD in 1980s. Our findings indicate that Colorado, USA, published the highest number of articles, followed by Wisconsin, and publication numbers correlated with reported CWD cases in states/provinces. Odocoileus emerged as the most studied genus. Wild populations are studied more commonly than captive populations. Keyword analysis of transmission types shows the discovery of novel transmission modes in the recent past. We also used a novel approach to categorize studies into five themes: field-based, lab-based, math/analytics/modelling-based, management-based, and human dimensions. Overall, most studies captured had a lab-based component. The interdisciplinary or transdisciplinary nature of major disciplines and evolving trends in keywords, particularly the increased reliance on genetics/genomics, accentuate the beginning of using genomics to under and tackle CWD at a fundamental scale. Encapsulated in our analysis, these dynamic changes offer valuable insights for navigating CWD through scientifically informed proactive management decisions in conjunction with existing surveillance efforts not only for the commonly studied species but also for potentially susceptible species
Optimizing Phaeodactylum tricornutum cultivation: integrated strategies for enhancing biomass, lipid, and fucoxanthin production
Full text linkBackground: Phaeodactylum tricornutum is a versatile marine microalga renowned for its high-value metabolite production, including omega-3 fatty acids and fucoxanthin, with emerging potential for integrated biorefinery approaches that encompass biofuel and bioproduct generation. Therefore, in this study we aimed to optimize the cultivation conditions for boosting biomass, lipid, and fucoxanthin production in P. tricornutum, focusing on the impacts of different nutrient ratios (nitrogen, phosphorus, silicate), glycerol supplementation, and light regimes. Results: Optimized medium (− 50%N%, + 50% P, Zero-Si, 2 g glycerol) under low-intensity blue light (100 μmol m⁻2 s⁻1) improved biomass to 1.6 g L⁻1, with lipid productivity reaching 539.25 mg g⁻1, while fucoxanthin increased to 20.44 mg g−1. Total saturated fatty acid (ΣSFA) content in the optimized culture increased approximately 2.4-fold compared to the control F/2 medium. This change in fatty acid composition led to improved biodiesel properties, including a higher cetane number (59.18 vs. 56.04) and lower iodine value (53.96 vs 88.99 g I2/100 g oil). The optimized conditions also altered the biodiesel characteristics, such as kinematic viscosity, cloud point, and higher heating value. Conclusion: Our optimization approach reveals the significant potential of P. tricornutum as a versatile microbial platform for biomass, lipid, and fucoxanthin production. The tailored cultivation strategy successfully enhanced biomass and lipid accumulation, with notable improvements in biodiesel properties through strategic nutrient and light regime manipulation. These findings demonstrate the critical role of precise cultivation conditions in optimizing microalgal metabolic performance for biotechnological applications
Shared preferences along stress gradients: how a growth-tolerance trade-off drives unimodal diversity and trait lumping
Full text linkEnvironmental gradients are pervasive across ecosystems and play a fundamental role in structuring species distributions and community dynamics. While ecological theory mainly focuses on species with distinct preferences for specific niches along the gradient, many natural communities follow an alternative pattern of shared preferences. In such systems, all species prefer the same optimal conditions but differ in their tolerance to harsher environments, according to a growth-tolerance trade-off. Here, we develop a trait-based metacommunity model, based on integrodifference equations, to investigate the development of community structure along a one-dimensional stress gradient with shared preferences. We demonstrate how species interactions, driven by competition, dispersal, and a growth-tolerance trade-off, lead to the emergence of patterns such as unimodal diversity distributions and trait lumping. Our model provides a conceptual framework for exploring the processes that shape metacommunities across spatial gradients characterized by shared preferences, offering new insights into this underrepresented class of ecological systems
Characterizing organisms from three domains of life with universal primers from throughout the global ocean
Full text linkWe introduce the Global rRNA Universal Metabarcoding Plankton database (GRUMP), which consists of 1194 samples that were collected from 2003–2020 and cover extensive latitudinal and longitudinal transects, as well as depth profiles in all major ocean basins. DNA from unfractionated (>0.2 µm) seawater samples was amplified using the 515Y/926 R universal three-domain rRNA gene primers, simultaneously quantifying the relative abundance of amplicon sequencing variants (ASVs) from bacteria, archaea, eukaryotic nuclear 18S, and eukaryotic plastid 16S. Thus, the ratio between taxa in one sample is directly comparable to the ratio in any other GRUMP sample, regardless of gene copy number differences. This obviates a problem in prior global studies that used size-fractionation and different rRNA gene primers for bacteria, archaea, and eukaryotes, precluding comparisons across size fractions or domains. On average, bacteria contributed 71%, eukaryotes 19%, and archaea 8% to rRNA gene abundance, though eukaryotes contributed 32% at latitudes >40°. GRUMP is publicly available on the Simons Collaborative Marine Atlas Project (CMAP), promoting the global comparison of marine microbial dynamics
Extensive Oxygen Consumption in the Intertidal Infiltration Zone of Beach Aquifers—The Impact of Seasonal Input Filtration Efficiency and Morphodynamics
Full text linkAbstract Seawater infiltration into the permeable sands of beach aquifers creates a high input of biogeochemical reactants driven by tides and waves. The upper sand layer acts as a filter, retaining particulate organic matter (POM), which is degraded by bacteria under predominantly oxic conditions. The seasonal variation of seawater POM and oxygen (O 2 ) entering the infiltration zone, combined with the POM filtration efficiency of the highly morphodynamic upper layer, determines the organic matter turnover and subsequent redox gradients along porewater flowpaths. We investigated these effects by quantifying the seasonal O 2 consumption rates directly from the incubations of sediments taken along a transect in the seawater infiltration zone at Spiekeroog Beach, Germany. We carried out a two‐monthly year‐long sampling campaign with high spatial resolution measurements down to 1 m depth. In summer, O 2 consumption rates of up to 106 μM hr −1 were found in the first decimeters with a significant decline over depth, indicating efficient retention of reactive POM in the surface layer. Seasonal variation in organic carbon of the sand's suspendable particulates indicates rapid turnover and little storage. In winter, rates decreased significantly to below 11 μM hr −1 . Integrated over the investigated oxic layer, the estimated carbon mineralization varies between 15 (winter) and 143 (summer) mmol C m −2 d −1 with a yearly average of 73 mmol C m −2 d −1 . The yearly CO 2 production of 35 kg per meter shoreline characterizes the beach as a high‐throughout system with rapid OM remineralization in the retention layer, especially in summer, but with little OM storage.
Plain Language Summary On the coast, sandy beaches act as a filter for seawater. Seawater seeps into the sand, and organic particles such as algae remains are trapped between the sand grains. Bacteria live on the surface of the sand grains and use the oxygen dissolved in seawater to break down the organic material. We investigated how seasonal changes from spring to winter, and the particle filtration affects the oxygen consumption by bacteria. Our study found that oxygen consumption follows the availability of fresh algal material during the year and is greatest in summer, when temperatures are high and algal blooms are intense. This cycle determines when and where in the sediment bacteria are active and controls the breakdown of the organic algae material to carbon dioxide (CO 2 ). We found that overall bacteria in the beach sands degrade a high amount of organic matter compared to other sandy seabeds. Our findings therefore give valuable information on bacterial activity present in beach sands, which impacts the breakdown of organic material and determines the quality of the beach groundwater that ultimately flows back into the ocean. These processes impact the health of coastal ecosystems and have consequences for human activities, such as fisheries or recreation.
Key Points Seasonal variations in organic matter inputs and temperature regulate oxygen consumption in intertidal beach aquifers Retention of fresh particulate organic matter in the sand body in summer leads to a highly reactive top layer in the beach infiltration zone Seasonal variations of organic carbon content in the fine fraction of the sediments indicate rapid organic matter turnover and low storag
Sentinel-3 Altimetry Thematic Products for Hydrology, Sea Ice and Land Ice
Full text linkThis paper presents the Copernicus Sentinel-3 level-2 altimetry Hydro-Cryo “Thematic Products”, operationally generated by ESA since September 2023. In comparison to previous product versions, the level-2 processing is now performed through three independent chains, generating three families of “Thematic Products”, for measurements acquired over hydrological, sea ice and land ice areas, respectively. Prior to the operational deployment, a full mission reprocessing was achieved with the thematic processors, providing a complete and harmonised dataset to the users. In this paper, the new architecture of the ground segment processing is presented, along with the major algorithmic developments. The main data content of the Thematic Products is also described, to indicate the key product variables for the end users. The Thematic Products have been evaluated by the Sentinel-3 Mission Performance Cluster (MPC) experts. The major results and outcomes are presented, showing the significant performance improvement achieved in comparison to previous processing versions