47242 research outputs found
Sort by
Dark ocean archaeal and bacterial chemoautotrophs drive vitamin B1 production in oxygen minimum zones
No full textVitamin B1 (thiamine) is essential for all cells, yet many marine microbes cannot synthesize B1 de novo. Dissolved thiamine and its related chemical congeners (TRCs) concentrations are not well characterized beyond the surface ocean, where they are typically low. Here, we observed unexpected enrichment of TRCs in regions of low dissolved oxygen levels (9.4 < O2 < 12.5 μmol kg-1) across vertical profiles in Monterey Bay and Pacific waters 145 km offshore (Station 67-70). TRC concentrations ranged from fM to pM, with 1.1 to 4.5 fold increases from near-surface waters to the mesopelagic Oxygen Minimum Zone (OMZ). Notably, at 67-70, dissolved B1 increased 3.5-fold within the mesopelagic OMZ. Paired metagenomic analysis suggests that chemoautotrophic ammonia-oxidizing Archaea (AOA) and Thioglobaceae, alongside nitrite-oxidizing Nitrospina, are important B1 producers in OMZs. Metagenome-assembled genomes indicate that Nitrospina may alternate between B1 biosynthesis and energy-preserving salvage pathways in synergy with co-occurring AOA. Re-analysis of metatranscriptomic reads from a previous study established Thioglobaceae can be dominant expressors of key de novo B1 biosynthesis genes in Monterey Bay. These findings suggest that deep ocean chemoautotrophs are B1 prototrophs in OMZs, analogous to photoautotrophs in the epipelagic ocean, and provide the foundation for B1 trafficking
Benthic POC cycling in the Skagerrak basin: The role of lateral POC input
No full textHighlights
• The POC rain rate in the Skagerrak basin is 10.9 mmol m-2 d-1, of which 60% is recycled back to the water column and 40% remains permanently buried in the sediment
• Local primary production contributes 18±6% to the sedimentary POC pool, while the majority of 82±6% is transported laterally into the Skagerrak basin
• POC burial fluxes in the Skagerrak basin declined substantially over the last ∼100 years, suggesting considerable variability in the North Sea POC cycle
Abstract
The burial of particulate organic carbon (POC) on continental margins represents a major long-term sink for atmospheric carbon. Hence, accurate descriptions of the benthic marine POC cycle are necessary for understanding the ocean’s CO2 uptake capacity. Here, benthic POC cycling is examined in the Skagerrak basin, the largest depocenter for POC in the North Sea. POC burial fluxes, benthic dissolved inorganic carbon (DIC) fluxes, POC rain rates and burial efficiencies (CBE) are reported at six stations based on porewater, solid phase and in-situ benthic flux measurements. On average, 10.9 mmol m-2 d-1 of POC rains onto the seafloor, of which 6.6 mmol m-2 d-1 is recycled back into the water column as DIC and 4.3 mmol m-2 d-1 is permanently buried in the sediment, resulting in a CBE of 40%. The data indicate that the mass accumulation rate (MAR), faunal activity and the quality of the settling POC are key driving mechanisms for the benthic POC cycle. Three independent approaches are used to distinguish between the contributions of autochthonous and allochthonous POC to the total sedimentary carbon pool. On average, 18±6% of POC originates from local production, while 82±6% is transported laterally into the Skagerrak basin. Considering previously reported MARs, the temporal evolution of POC burial in the Skagerrak basin shows a substantial decline over the last ∼100 years, indicating variability in the lateral POC input. Possible reasons for the POC burial decline are qualitatively discussed, including changes in sediment cycling and primary production in the North Sea
Relating Atlantic meridional deep-water transport to ocean bottom pressure variations as a target for satellite gravimetry missions
No full textThe Atlantic Meridional Overturning Circulation (AMOC) is a salient feature of the climate system that is observed with respect to its strength and variability using a wide range of offshore installations and expensive sea-going expeditions. Satellite-based measurements of mass changes in the Earth system, such as from the Gravity Recovery and Climate Experiment (GRACE) mission, may help monitor these transport variations at the large scale, by measuring associated changes in ocean bottom pressure (OBP) at the boundaries of the Atlantic remotely from space. However, as these signals are mainly confined to the continental slope and are small in magnitude, their detection using gravimetry will likely require specialised approaches. Here, we use the output of a fine-resolution (1/20°) regional ocean model to assess the connection between OBP signals at the western boundary of the North and South Atlantic to changes in the zonally integrated meridional deep-water transport. We find that transport anomalies in the∼1–3 km depth range can be reconstructed using OBP variations spatially averaged over the continental slope, with correlations of 0.75 (0.72) for the North (South) Atlantic and root-mean-square errors of ∼1 Sv (sverdrup; 10^6 m^3 s^−1), on monthly to inter-annual timescales. We further create a synthetic data set containing OBP signals connected to meridional deep-water-transport anomalies; these data can be included in dedicated satellite gravimetry simulations to assess the AMOC detection capabilities of future mission scenarios and to develop specialised recovery strategies that are needed to track those weak signatures in the time-variable gravity field
Transform Faulting in the Northern Red Sea Revealed by Ocean Bottom Seismometers Deployed in the Zabargad Fracture Zone
No full textThe Zabargad Fracture Zone (ZFZ), the largest rift‐axis offset in the Red Sea, extends from 23.5°N to 26°N. It is covered by thick sedimentary layers that have hindered the ability of geophysical data sets to image the geometry of the normal faults and any potential transform faults. Passive seismology observations in the region have been limited to onshore recordings, leading to high uncertainty in earthquake locations and hampering detailed seismicity analyses. To address this limitation, we deployed a network of ocean bottom seismometers (OBSs) and land‐based stations for a duration of 12 months. From these data, we built the first high‐resolution earthquake catalog for this region of the Red Sea by applying a deep‐learning‐based algorithm to automatically detect earthquakes and pick P‐ and S‐phases. To obtain reliable earthquake locations, we derived a 1‐D seismic velocity model of the ZFZ. We established a calibration between measured on land and on OBSs to overcome magnitude overestimation using the OBS data alone. Additionally, we computed focal mechanisms of selected events using waveform polarities and amplitude ratios. The hypocenter distribution reveals two major seismicity clusters, the North and South clusters. The North cluster highlights NW–SE trending normal faults reflecting the extensional tectonics of the Red Sea. In the South cluster, we discover a NE–SW transform fault, possibly in its early development stage and NW–SE normal faults. The depth of seismicity reveals variations in the brittle‐ductile transition zone depth, with shallow depth in the north indicating higher shallow lithospheric temperature.
Plain Language Summary
The Red Sea is a young ocean where tectonic plates slowly pull apart, and a new oceanic floor emerges. In its northern region, thick layers of sedimentary rocks obscure the ocean floor, complicating observations and leading to different views on the shape of the plate tectonic boundaries. A key area of interest is the Zabargad Fracture Zone (ZFZ), the largest plate boundary offset in the Red Sea. To study the tectonics of the ZFZ, we placed ocean‐bottom seismometers on the seafloor to record earthquakes for a period of 12 months. We used advanced techniques, including machine learning, to obtain the first detailed map of earthquakes in the ZFZ, revealing hidden fault structures. We identify two main zones: in the northern ZFZ, seismically active faults are primarily influenced by the opening of the Red Sea and in the southern ZFZ, seismic activity reveals that tectonic plates slide past each other along a transform fault. We observed differences in how deep earthquakes occur, revealing the physical properties of rocks in the region. This research helps us understand the complex geological processes shaping this region and highlights the importance of assessing earthquake hazards for the communities and infrastructures along the Red Sea coast.
Key Points
Ocean Bottom Seismometer data reveal earthquakes associated with spreading segments and an emerging transform in the Zabargad Fracture Zone
Event depth variations reveal shifts in the brittle‐ductile transition, with shallower depths northward suggesting hotter crustal conditions
Our study enhance understanding on faulting in young oceanic basins and stress the need for better seismic hazard assessment in the regio
Over 1200 Non‐Native Species Are Established in the Iberian Peninsula
No full textAim:
As a consequence of globalisation, biological invasions have become an increasing concern due to multifaceted ecological and socio-economic impacts on biodiversity and ecosystem services. Despite the increasing availability and accessibility of data, a comprehensive assessment of established non-native species and their distribution in the Iberian Peninsula has not been conducted so far.
Location:
Iberian Peninsula, including Spain, Portugal, Andorra, and Gibraltar.
Methods:
We compiled a harmonised dataset of 1273 established non-native species from multiple regional, national, and global sources. We analysed taxonomic composition, introduction pathways, and native biogeographic realms. Temporal patterns were assessed using first-record data, while spatial patterns were mapped using high-resolution occurrence data from GBIF and national databases.
Results:
The majority of established non-native species are vascular plants and insects, specifically of the classes Magnoliopsida and Insecta and the families Asteraceae and Formicidae, respectively. Overall, the most common pathways of introduction were escapes from human facilities and transport-related mechanisms (contaminant and stowaway), but their importance varies among countries. Established non-native species were mostly native to the other regions within the Palearctic, followed by the Nearctic and Neotropical realms. Regarding the time of introduction, first records increased steadily until the last decades of the 20th century, when the introduction rate slowed down; yet new introductions persist. Finally, our spatial analysis identified that areas with high human population density and coastal zones recorded the highest number of established non-native species.
Main Conclusion:
The Iberian Peninsula hosts a high number and diversity of established non-native species. Given the ongoing rise in cumulative introductions and the role of unintentional human-driven pathways, strengthening prevention measures is vital to reduce future invasions. However, with many non-native species already established, effective management efforts are equally crucial to curb further spread and mitigate consequent impacts, especially in areas of conservation interest
From Microscale to Microbial Insights: Validating High-Throughput Microvolume Extraction Methods (HiMEx) for Microbial Ecology
No full textExtracting and directly amplifying DNA from small-volume, low-biomass samples would enable rapid, ultra-high-throughput analyses, facilitating the study of microbial communities where large-volume sample collection is challenging. This can aid where ‘conventional’ filtration-based methods miss capturing smaller microbes, or where microscale variability matters, such as the ocean. Here, we develop and validate physical and chemical-based DNA extractions from microvolumes with universal rRNA gene amplicons and metagenomic sequencing of all domains and viruses, on natural surface seawater and experimentally manipulated marine waters. Compared to 500-mL filter-based extraction, direct PCR of 3 μL of lysate from seawater microvolume extractions ranging from 100-1000 μL consistently captured comparable microbial community composition and diversity, with reliable amplification and little to no contamination. Metagenomic results of 10 μL lysates from 15 microvolume samples (100 μL) captured 83 high- and draft-quality, diverse bacterial genomes and 430 complete, high and medium quality viral contigs. Our approach enables scaling of rRNA gene sequencing and metagenomic library prep for high-throughput experimentation for a fraction of the cost of conventional methods and builds upon existing microvolume approaches by removing unnecessary expenses, like excess plasticware and expensive bead clean-up. The method expands opportunities for more comprehensive microbial community monitoring and controlled laboratory experiments by facilitating higher sample numbers and lowering sample volume needs. However, its potential bias against Gram-positive bacteria should be considered when applying to environments where these taxa are abundant
Nearshore Macroalgae Cultivation for Carbon Sequestration by Biomass Harvesting: Evaluating Potential and Impacts with An Earth System Model
No full textThis study assesses an ocean-based carbon dioxide removal (CDR) approach: Nearshore Macroalgae Aquaculture for Carbon Sequestration (N-MACS). By cultivating macroalgae in nearshore areas, N-MACS aims to sequester atmospheric through subsequent carbon storage. Using an Earth System Model of intermediate complexity, we evaluate its CDR potential and impacts on the global carbon cycle, marine biogeochemistry, and ecosystems. Our results show that N-MACS could sequester 0.7–1.1 gigatonnes of carbon annually. However, it significantly reduces marine phytoplankton productivity due to nutrient uptake and canopy shading. The CDR efficiency—defined as the increase in air–sea
flux relative to carbon fixed in harvested macroalgal biomass—is approximately 65%, with primary offsets from ocean carbon backflux and suppressed phytoplankton growth. Reduced surface NPP lowers carbon export from the euphotic zone, increasing dissolved oxygen and decreasing denitrification in modern oxygen minimum zones. Biogeochemical effects linked to phosphorus removal via harvesting persist for centuries after N-MACS ends.
Plain Language Summary
Our study explores the Nearshore Macroalgae Aquaculture for Carbon Sequestration (N-MACS) as a potential marine carbon dioxide removal strategy. This approach uses ocean-based seaweed farming to capture carbon dioxide—the main greenhouse gas causing global warming—and permanently stores it post harvesting through biomass processing and carbon storage. Our simulations indicate that N-MACS has the potential to remove substantial quantities of carbon dioxide every year. Nonetheless, harvesting will also remove oceanic nutrients and decrease open ocean primary production. At the same time, N-MACS can beyond mitigate ocean oxygen depletion and ocean acidification. Those impacts on the oceanic ecosystem and marine biogeochemistry could potentially persist for centuries, upon the cessation of N-MACS.
Key Points
Nearshore marcoalgae cultivation for carbon dioxide removal has a global potential of gigatonne scale
Partition of marine net primary production shifts from phytoplankton to macroalgae due to shading and nutrient robbing
Macroalgae-induced reduction in open-ocean net primary production reduces the oxygen deficient zone
UV Weathering Alters Toxicity and Chemical Composition of Consumer Plastic Leachates
No full textHighlights
• UV weathering increased the toxicity of specific plastic leachates
• Cell-based bioassays revealed plastic- and cell-specific toxic effects
• LC-HRMS identified (un)known plastic-associated chemicals
• Toxicity was linked to the formation of bioavailable transformation products
• Microplastics and metals showed weaker links to bioassays effects than organics
Abstract
Plastics release complex mixtures of partially toxic substances into the environment, particularly following UV-induced weathering. Using integrated chemoassays, cell line bioassays, and chemical profiling, we assessed leachates from eight types of consumer plastic products following accelerated UV weathering equivalent to eight months of natural solar weathering in temperate regions to identify key contributors to leachate toxicity. Chemoassays, used as proxies for protein damage, showed UV-induced reactive toxicity, which increased by up to 82% depending on plastic type. Cell-based bioassays revealed that UV exposure enhanced cytotoxicity up to 13-fold, especially for polyethylene leachates, in liver, skin, lung, and breast cancer cell lines, reflecting cell-specific vulnerabilities. UV exposure substantially altered the chemical composition of leachates shown by liquid chromatography -high resolution mass spectrometry (LC-HRMS) screening which identified 11 target-, 12 suspect-, and 90 non-target chemicals. Furthermore, UV exposure promoted the formation of more bioavailable and hazardous transformation products compared to the dark controls. The increased toxicity was primarily linked to the release and transformation of organic plastic-associated chemicals rather than microplastics or metal(loid)s. Overall, these findings highlight UV weathering as a critical driver of enhanced plastic leachate toxicity and emphasize the need for comprehensive chemical and toxicological assessments in environmental risk evaluations of plastics
Analysis of microbially induced iron corrosion inside monopiles of offshore wind turbines - methods for in situ experiments
No full textOffshore wind turbines are exposed to extreme environmental conditions inside monopiles where microbially induced corrosion (MIC) occurs. In this study, microbial in situ incubation experiments were carried out at different water depths inside a monopile. First results indicate that water depth-related seasonal stratification of the inner water column clearly influences microbial consortia and the grade of corrosion. At a water depth of 6 m, iron-oxidizing microbes dominate under aerobe conditions, while sulphate-reducing and methanogenic microbes are prevailing close to the sea bed at 21 m in temporarily anoxic and sulfidic bottom water. The S355 steel specimens show significant corrosion after several months of in situ incubation, however pronounced pitting was not observed. The focus of this study is the development of long-term in situ observation methods of MIC inside offshore monopiles to finally test adapted corrosion mitigation strategies
Reconstruction of South China Sea Deep Water Salinity During the Last Glacial Maximum (LGM)
No full textReconstructing the deep water salinity during the Last Glacial Maximum (LGM, 26.5~19 ka BP), corresponding to Marine Isotope Stage 2, the most recent and coldest period, is crucial for understanding glacial deep ocean circulation variation and its effect on the climate. The South China Sea (SCS) is one of the largest marginal seas in the western Pacific Ocean, where LGM deep water salinity reconstruction remains unexplored. This study employs pore water [Cl−] profiles acquired from boreholes of Site U1499 of IODP Expedition 367 and Sites U1431 and U1433 of IODP Expedition 349 to reconstruct the LGM salinity in the deep SCS. Utilizing a one-dimensional diffusion-advection numerical model, the LGM salinity of the deep northern SCS is determined to be 35.68 ± 0.04 g/kg, and that of the deep central SCS is 35.61 ± 0.03 g/kg, revealing an intra-basin salinity gradient of ~0.07 g/kg. LGM salinity gradients within the SCS were reduced relative to modern ones, indicating attenuated deep circulation within the SCS during the LGM. Furthermore, a diminished salinity gradient (Δ = 0.02 g/kg) across the Luzon Strait between the SCS and Pacific and an enhanced vertical stratification between Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) collectively support a sluggish deep Pacific circulation during the LGM