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Native arsenic at the Semenov-2 seafloor massive sulfide deposit (13°31′13 N, Mid-Atlantic Ridge) : an indicator of low-temperature, reducing, and acidic formation conditions
No full textNative arsenic, which is an extremely rare seafloor mineral, was found in opal-rich massive sulfide samples of the basalt-associated Semenov-2 seafloor massive sulfide (SMS) deposit (13°31′13 N, Mid-Atlantic Ridge) located on top of an oceanic core complex, which exposes mantle rocks on the seafloor. Native arsenic occurs in interstitial opal as small (<10 µm) subhedral to euhedral crystals and forms three mineral assemblages. In assemblage 1, native arsenic overgrows Se-bearing (up to 1.39 wt.% Se) galena and contains S (1.14–5.07 wt.%), Cu (0.42–1.09 wt.%), and Zn (0.90–1.32 wt.%). In assemblage 2, native arsenic forms euhedral crystals often arranged in stellar or elongated aggregates, hosts fine (∼1 µm) inclusions of Au-bearing native silver (50.31 wt.% Au = 0.35 apfu) in the center of the crystals, and is locally overgrown by rare argyrodite, Ag8GeS6. This native arsenic contains S (0.29–1.65%), Cu (0.38–1.85 wt.%), and Zn (0.58–1.86 wt.%). In assemblage 3, native arsenic overgrows and pseudomorphically replaces As-bearing (up to 18.01 wt.% As) pyrite (in most cases) and rarely sphalerite and contains S (0.11–3.99 wt.%), Fe (0.28–1.64 wt.%), Sb (0.48–1.05 wt.%), and, locally, Cu (0.29–0.37 wt.%) and Zn (0.54–0.65 wt.%). Thermodynamic modeling of the formation of native arsenic in the Selektor software shows that it forms after the interaction of a relatively low-temperature (∼100–150 °C) reducing (Eh120°C = −0.29 V) acidic (pH120 °C = 3.98) hydrothermal fluid with previously formed As-bearing sulfide minerals (As-rich pyrite in our case) rather than after the direct rock/seawater interaction. The formation of native arsenic from the hydrothermal fluid occurred within pores in late opal without mixing with seawater that was favorable for conductive cooling and reducing conditions. Our findings showed a potential for the precipitation of diverse late low-temperature ore minerals after the crystallization of late opal, which is ubiquitous in SMS deposits
Deglaciation history and relative sea level changes since the Last Glacial Maximum in the southern Gulf of St. Lawrence, Canada
No full textDuring the last glacial period, continents and surrounding shelves in high latitude regions of the Northern Hemisphere were covered by ice sheets. Their retreat during the late Pleistocene and Holocene resulted in isostatic adjustments of the previously glaciated landmass, which influenced post-glacial changes in relative sea level (RSL). Many questions, however, remain about the timing and impact of the ice retreat on the continental shelf environments and RSL after the Last Glacial Maximum, and of short-lived climatic events, such as the Younger Dryas. This study aims to reconstruct the deglaciation history and changes in RSL for the southern Gulf of St. Lawrence off Prince Edward Island on the eastern Canadian continental shelf for the past 14 ka, and to determine the influence of the Younger Dryas on the ice margin. Using information from sub-bottom profiles, sediment cores, and multibeam bathymetry, this study finds that most of the continental shelf was already flooded 13.6 ka ago, as evidenced by the presence of Bølling-Allerød marine sediments at a modern water depth of less than 50 m and ~15 km off the modern coastline. During the Younger Dryas cooling event, sedimentation rates increased from 0.1 to 1 cm a-1, likely as a consequence of readvancing ice masses. We observe an erosional truncation on top of the Younger Dryas sediment package, which presumably indicates a drop in RSL in the early Holocene. Based on our new data, we propose an updated RSL curve for the region that accounts for the presence of sea ice coverage rather than complete ice coverage as well as a geological model highlighting the sedimentation history over the past 14 ka and role of the Younger Dryas. The new paleo-environmental and RSL reconstructions shed light on the potential impact of short-lived climatic events at the former ice margin during deglaciation and reduce uncertainties for about past sea level changes
Impact of Greenland Ice Sheet disintegration on atmosphere and ocean disentangled
No full textWe analyze the impact of a disintegrated Greenland Ice Sheet (GrIS) on the climate through steady-state simulations with the global Max Planck Institute for Meteorology Earth System Model (MPI-ESM). This advances our understanding of the intricate feedbacks between the GrIS and the full climate system. Sensitivity experiments enable the quantification of the individual contributions of altered Greenland surface elevation and properties (e.g., land cover) to the atmospheric and oceanic climate response. Removing the GrIS results in reduced mechanical atmospheric blocking, warmer air temperatures over Greenland and thereby changes in the atmospheric circulation. The latter alters the wind stress on the ocean, which controls the ocean-mass transport through the Arctic gateways. Without the GrIS, the upper Nordic Seas are fresher, attenuating deep-water formation. In the Labrador Sea, deep-water formation is weaker despite a higher upper-ocean salinity, as the inflow of dense overflow from the Denmark Strait is reduced. Our sensitivity experiments show that the atmospheric response is primarily driven by the lower surface elevation. The lower Greenland elevation dominates the ocean response through wind-stress changes. Only in the Labrador Sea do altered Greenland surface properties dominate the ocean response, as this region stores excessive heat from the Greenland warming. The main drivers vary vertically: the elevation effect controls upper-ocean densities, while surface properties are important for the intermediate and deep ocean. Despite the confinement of most responses to the Arctic, a disintegrated GrIS also influences remote climates, such as air temperatures in Europe, the Atlantic Meridional Overturning Circulation (AMOC) and the subtropical gyre. These interactions and feedbacks between ice sheets and the other climate components highlight the necessity of including dynamic ice sheets in climate models that are used for future projections
2. Wochenbericht SO314
No full textForschungsfahrt des FS SONNE SO 314: T-SECTOR Southeast Pacific Rise:
13.08.2025 (Papeete/Tahiti) – 05.10.2025 (Antofagasta/Chile
Sediment Biogeochemistry Model Intercomparison Project (SedBGC_MIP): motivation and guidance for its experimental design
No full textBenthic biogeochemical models are critical for understanding and predicting seafloor processes that regulate ocean chemistry, carbon sequestration, benthic habitat conditions, and climate feedbacks. However, current sediment models have limited predictive capabilities with widely variable complexity, structure, and underlying assumptions, highlighting a lack of consensus on essential process representations. To address this issue, this paper introduces the Sediment Biogeochemistry Model Intercomparison Project (SedBGC_MIP), a community-driven initiative aimed at systematically comparing existing benthic models against available observational constraints to refine key parameterizations and assess structural uncertainties. We review the state of sediment biogeochemical modeling, highlighting discrepancies in the representation of carbon cycling, burial, and redox remineralization processes across different model complexities. Through case studies, we demonstrate how varying model structures and ecosystem dynamics create uncertainty in global predicted biogeochemical feedbacks. We outline the objectives of SedBGC_MIP, including the need for standardized benchmarking, observational datasets, and cross-disciplinary collaboration to improve model skill and integration into Earth System Models. Ultimately, SedBGC_MIP aims to advance our ability to simulate benthic processes with greater accuracy, enhancing projections of ocean biogeochemistry under climate change scenarios with new capacity to address emerging living marine resource and geoengineering applications
Direct cooling effect of artificial upwelling dominates over its marine carbon dioxide removal potential.
No full textArtificial upwelling (AU) is investigated as a marine carbon dioxide removal (CDR) method with a strong focus on its potential impact on Earth’s carbon cycle, in particular enhanced air-sea CO2 flux. The overarching goal of marine CDR methods is to contribute to offsetting remaining CO2 emissions as a means to stabilize global mean surface air temperature (SAT). However, AU also directly affects ocean heat uptake (OHU) through the upwelling of cold ocean interior water to the surface and the simultaneous backflow of warm surface water into the ocean interior. In this study, we challenge the carbon centered perception of AU. We simulate large-scale AU in an Earth system model of intermediate complexity between the years 2025 and 2100 with and without its direct impact on OHU under low, medium and high future CO2 emission scenarios. Thus, we can quantify the individual contributions of AU-induced carbon and heat effects to changes in global mean SAT. We find the direct impacts of AU on OHU to be key for a significant reduction in global mean SAT and the atmosphere’s CO2 concentration under all simulated future CO2 emission pathways. If AU directly impacts OHU, we can attribute only 17 % under RCP 2.6 to 27% under RCP 8.5 of the reduction in global mean SAT (-0.17 to -0.27˚C) until the end of the century to the reduction in the atmosphere’s CO2 inventory (-5.9 to -31.2 Pg C). Our findings lead us to challenge the classical view of AU as primarily a marine CDR method. Instead, we propose to consider AU as a method to enhance OHU and thereby reduce global mean SAT, with secondary effects on the carbon cycle that result in some CDR
The coupled oxygen and carbon dynamics in the subsurface waters of the Gulf and Lower St. Lawrence Estuary and Implications for Artificial Oxygenation
No full textThe Gulf and Lower St. Lawrence Estuary have experienced major environmental change over the past century, including the development of hypoxic bottom waters and their simultaneous warming and acidification. Here, we use biogeochemical observations collected during the 2021–2023 TReX project as well as historical data, combined with a tracer-calibrated 1D Advection-Diffusion model with variable boundary conditions to represent dissolved oxygen (DO) and dissolved inorganic carbon (DIC) dynamics within the core of the oxygen minimum zone (27.15–27.3 kg m-3 isopycnals) of the Laurentian Channel. The rate of in-channel oxygen utilization in the deep layer was nearly invariant from 2003 to 2023 at 21.1 ± 2.5 µmol kg-1 yr-1 and the DIC accumulation rate was estimated to be 18.3 ± 2.5 μmol kg-1 yr-1. Using δ13CDIC data, we assess the effect of microbial organic matter remineralization processes and dilution of the 13CDIC pool (−6.6×10-3 ‰ per μmol of added metabolic DIC). These data and the use of a tracer-calibrated model to resolve advection and mixing dynamics reconcile differences in prior estimates of biogeochemical transformation rates. Finally, we apply the model to the mitigation scenario proposed by Wallace et al. (2023) for artificial re-oxygenation of the Laurentian Channel bottom waters using pure oxygen. We estimate that the injection of ~8.3 × 105 tonnes yr-1 of oxygen, equivalent to an additional 55 μmol kg-1 relative to the 2023 boundary concentration proximal to the Cabot Strait, would be required to achieve and maintain above hypoxic levels (>62.5 μmol kg-1) at the head of the Laurentian Channel. Using the model, we estimate the time required to re-establish steady-state along-channel distributions of DO and DIC following a change in offshore boundary conditions to be about 10 years, or twice the along-channel transit time
Technical Report for Raw 2D MCS Reflection Data, R/V Sonne Cruise 301, Port Louis – Port Louis (Mauritius), 22/11/23 – 04/01/24
No full textThe raw 2D multichannel seismic reflection data presented in this report were acquired during expedition SO301 north of the Rodrigues Triple Junction. Data collection targeted the Central Indian Ridge, including the 25°S Oceanic Core Complex (OCC) and the Kairei hydrothermal field, to investigate crustal structure and faulting processes at a slow spreading ridge. A total of 29 seismic lines were recorded using an 8 km, 756-channel streamer and an air gun source array. The dataset covers approximately 1871 line kilometers and includes profiles across ridge segments, the OCC, and conjugate flanks. The data are provided in raw SEG-D format with associated navigation and standardized metadata. Detailed information on the acquisition can be found in the SO301 cruise report (https://doi.org/10.48433/cr_so301). This technical report provides further information on the acquisition of the 2D multichannel seismic reflection data set
Data-driven approaches to Eastern Boundary Upwelling Systems
No full textEastern Boundary Upwelling Systems (EBUS) are among the most productive
marine ecosystems and provide substantial socio-economic value to
coastal states. The Canary Current Upwelling System located along the
north-west African coast is one of them. There, the north-east trade winds
and their seasonal north-south migration drives o↵shore Ekman transport
with a pronounced seasonality. The o↵shore Ekman transport is compensated
by upward motion of water from subsurface layers. Several indices
have been defined in order to quantify upwelling and describe its spatial and
temporal variability. Here, a machine learning-based prediction system for
coastal upwelling is implemented and tested. By using a local coordinate
system aligned to the coast, the complexity of the prediction resulting from
the geometry of the coast was reduced and the generalisability improved.
The ML model trained on VIKING20X ocean hindcast simulations could be
transferred to observational data. It is shown that a strong decrease of the
prediction skill can be prevented by small admixtures of observation data
during the training