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Distinguish between feasibility and desirability when assessing climate response options
No full textThe current literature on assessing climate change response options does not sufficiently distinguish between assessing options in terms of their feasibility and in terms of their desirability. One example of this is the IPCC feasibility assessment framework. We argue that assessments of climate response options should indeed cover questions of desirability, but they should do so explicitly. Transparency about underlying normative standards is the key to a productive desirability assessment
Ein korrelationsbasierter Ansatz zur Vorhersage von DXA T-score Werten mittels des Calcium-Isotopen-Markers (CIM)
No full textEinleitung: Osteoporose Früherkennung ist entscheidend für den Erfolg präventiver Maßnahmen zur Vermeidung von Knochenbrüchen. Die Dual-Röntgen-Absorptiometrie (DXA) ist der Standard zur Bestimmung der Knochenmineraldichte (BMD), doch sie erfasst nicht die Dynamik des Calcium (Ca)-Stoffwechsels die zu Knochenbrüchen führen. Im Gegensatz dazu ermöglicht das Calcium-Isotopen-Verhältnis (⁴⁴Ca/⁴²Ca), bekannt als Calcium-Isotopen-Marker (CIM), eine nahezu Echtzeit-Erfassung des Gleichgewichts zwischen Knochenaufbau und -abbau, wenn es im Blut (CIM_serum) oder Urin (CIM_urin) gemessen wird.
Methode: Retrospektiv wurden Daten aus vier klinischen Studien mit 293 postmenopausalen Frauen (Alter: 25–81 Jahre), die weder an Niereninsuffizienz noch an Vitamin-D-Mangel (<25 nmol/L) litten. Die CIM-Werte (CIM_serum und CIM_urin) wurden mit den niedrigsten DXA-T-Scores (Hüfte oder Lendenwirbelsäule) verglichen.
Ergebnisse: Die Analyse ergab eine starke Korrelation zwischen CIM- und DXA-Werten (CIM_serum/DXA: r²=0,68, p<0,001; CIM_serum/CIM_urin: r²=0,54, p<0,001; CIM_urin/DXA: r²=0,43, p<0,001). Dies deutet darauf hin, dass Veränderungen des Ca-Isotopenverhältnisses eng mit Schwankungen der BMD verknüpft sind. Die Interpretation der Messwerte basiert auf in früheren Studien definierten CIM-Schwellenwerten von−0,85±0,06 ‰ für CIM_serum und 0,23±0,06 ‰ für CIM_urin. Werte außerhalb dieser Intervalle weisen auf eine positive oder negative Calcium-Bilanz im Knochen hin. Insbesondere Werte unterhalb der Schwellenwerte deuten auf ein erhöhtes Osteoporose Risiko hin.Die DXA-T-Scores für gruppierte Intervalle (Δ=1, Bereich: -4 bis 3) konnten entweder durch quadratische Regressionsmodelle mit CIM_serum oder CIM_urin (R²=0,35 bzw. R²=0,93) oder durch eine multiple lineare Regression (R²≈0,98), präzise approximiert werden. Der aus CIM abgeleitete DXA-Schwellenwert von -0,85±0,06 ‰ entsprach einem T-Score von ca. -1,2, höher als der aktuelle Grenzwert von -2,5.Eine Nachuntersuchung zu Osteoporose bedingten Frakturen zwei Jahre nach der OsteoGeo-Studie (Eisenhauer et al., 2019, 2024) bestätigte unsere Beobachtungen: Alle Fragilitätsfrakturen traten bei Personen mit CIM_serum-Werten unterhalb des Schwellenwerts auf, während nur ein Drittel der Frakturen im DXA-T-Score-Bereich der Osteoporose diagnostiziert wurden.
Diskussion: Unsere Studie zeigt, dass CIM-Werte mit DXA-T-Scores korrelieren und unterstreicht das Potenzial von CIM als nicht-invasives, laborbasiertes Verfahren zur frühzeitigen Risikoerkennung und Therapiekontrolle bei Osteoporose. Der CIM-Ansatz bietet somit einen wesentlichen diagnostischen Fortschritt gegenüber der herkömmlichen DXA-Messung, da er die mit den Veränderungen in der Knochendichte einhergehenden Veränderungen des Knochenstoffwechsels früher erfasst und zukünftig eine statistische Frakturvorhersage ermöglicht
New Insights into SMS Deposits: How Microbial Activity and Oxygen Levels Shape Metal Preservation
No full textSeafloor massive sulfide (SMS) deposits form on the modern ocean seafloor at active hydrothermal vent systems through mixing of mineral-rich, hydrothermal fluids with ambient oxygenated seawater. Once hydrothermal activity ceases, oxygenated seawater infiltrates these deposits, fostering to abiotic oxidative weathering. Microbial activity considerably accelerates this transformation, driving sulfide mineral breakdown, thus enhancing metal transport. Under conditions, restricting oxygen entrainment, low-oxygen zones form below the surface, shielding SMS deposits from oxidative weathering, potentially extending their preservation. SMS deposits are valuable sources of metals governing the interest of their lifespan.
In this study, we explore the impact of microbial activity on SMS transformation and mineral dissolution under oxic and low-oxygen conditions. We incubated sulfide minerals, i.e. pyrite and chalcopyrite for four years on the seafloor at active and inactive vent sites along the Indian Ridge. These sulfide minerals were then used for metagenomics, microscopy, microbial enrichment experiments, physiological studies, and geochemistry to identify the key microbial agents driving mineral transformation and metal release. Scanning electron microscopy (SEM) reveals diverse mineral structures, such as twisted stalks and nanowires, suggesting various Fe-oxidizing microbes as well as those involved in extracellular electron transfer. Preliminary metagenomic analyses provide insights into the presence of genes associated with iron oxidation and reduction. Laboratory cultivation experiments mimicked different temperature, oxygen, and pH conditions of hydrothermal vent fluids admixed to distinct degrees with ambient seawater and suggest faster microbially mediated mineral dissolution under oxic conditions and of pyrite as opposed to chalcopyrite. By assessing turnover rates of mineral transformations, we aim to predict how microbial activity affects SMS deposit longevity under varying oxygen conditions
Geothermal gas geochemistry in Southeast Tibetan Plateau margin influenced by magma chambers and fractures
No full textHydrothermal gases play a pivotal role in elucidating the cycling of deep materials and subsurface processes. Here, we analyzed the chemical and isotopic compositions of 40 gas samples and compiled geochemical data on >280 samples discharged from the Tengchong hydrothermal field, located on the Southeast Tibetan Plateau margin. Helium isotopes span from 0.13 Ra (the 3He/4He ratio of air) to 5.91 Ra, indicating a mixing between mantle-derived helium and crustal components. Spatial distributions of helium isotopes are closely associated with the locations of magma chambers beneath the Tengchong field. N2/Ar ratios and nitrogen isotopic compositions suggest that N2 and Ar were primarily contributed by atmospheric sources and groundwater, with minor N2 contributions from mantle-derived materials. CO2 was mostly originated from the thermal decomposition of limestone and magma degassing, with a few samples affected by secondary processes like carbonate precipitation. The chemical and carbon‑hydrogen isotopic compositions of alkanes indicate that methane was mainly sourced from thermogenic processes. The central magma chamber and its adjacent faults are characterized by the most intensive magmatic activity and the closest connection to deep materials. A gas migration and diffusion model using a crustal 3He endmember of 6 × 10−9–9 × 10−8 (volume ratio of 3He to total gases) well explains the decreasing 3He concentrations with the distance from magma chambers. Hence, the highly penetrable helium in quiescent regions like Tengchong could migrate through overlying rocks without the need of gas channeling along faults. Similarly, our model can also explain the relationships between Ar concentrations and the distance from springs to faults and magma chambers. In contrast, the geochemical characteristics of other gas components (e.g., CO2, N2) are closely associated with the location of major faults. This study offers valuable insights into the spatial relationships between gas geochemistry and subsurface magmatism and fault distribution, highlighting the influence of hydrothermal processes on diverse patterns of gas migration and source in hydrothermal fields
Lessons Learned from Marine Refraction Seismic Experiments in the Ligurian Sea
No full textWide-angle refraction seismic experiments are generally executed along 2D profiles. In this study, we investigate the potential and limitations of using adjacent 2D wide-angle seismic profiles for 3D tomography. From this, we provide suggestions on best practices when designing new offshore experiments so that the data can be used for both 2D and 3D tomography. We use two example experiments from the Ligurian Sea, the 2006 SARDINIA Experiment and the 2017/8 AlpArray—LOBSTER Experiment, to highlight the benefits and pitfalls of two common station-shot geometries: parallel 2D seismic profiles and crossing seismic profiles through a network of Ocean Bottom Seismometers (OBS). We interpolate the lateral resolution of these experiments, and compare this with the potential resolution that could be achieved by the strategic addition of shots or stations. The synthetic results show that when two parallel 2D seismic profiles are shot (Sardinia Experiment), the resolution can be equally improved by the addition of a line of shots between profiles as by a line of stations between profiles. For an OBS network (AlpArray—LOBSTER Experiment), the synthetic results show that additional shot lines throughout the network are necessary to resolve the network area. One major difficulty with this specific area, is the complex geological structure of the Liguro-Provençal Basin, especially the presence of a Messinian evaporite layer that interferes with and scatters the seismic signal. The resolution achieved by these different network geometries shows that while these experiments alone were not sufficient for 3D tomography, they could both have been made suitable for 3D tomography by the addition of shot profiles, which are cost-effective and easier to add than stations. This workflow for estimating the lateral resolution of a 3D seismic refraction experiment can be applied to any tectonic setting, and should be considered when planning offshore experiments to enable 2D and 3D tomography and increase the output of this valuable data
Environmental controls of rapid terrestrial organic matter mobilization to the western Laptev Sea since the Last Deglaciation
No full textArctic 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
Ocean alkalinity enhancement (OAE) does not cause cellular stress in a phytoplankton community of the subtropical Atlantic Ocean
No full textA natural plankton community from oligotrophic subtropical waters of the Atlantic near Gran Canaria, Spain, was subjected to varying degrees of ocean alkalinity enhancement (OAE) to assess the potential physiological effects in the context of the application of ocean carbon dioxide removal (CDR) techniques. We employed nine mesocosms with sediment traps attached to the bottom, each enclosing a volume of 8.3 m3, to create a gradient in total alkalinity (TA). OAE was based on the addition of carbonates (NaHCO3 and Na2CO3). The lowest point on this gradient was 2400 µmol L−1, which corresponded to the natural alkalinity of the environment, and the highest point was 4800 µmol L−1. Over the course of the 33 d experiment, the plankton community exhibited two distinct phases. In phase I (days 5–20), a notable decline in the photosynthetic efficiency () was observed. This change was accompanied by substantial reductions in the abundances of picoeukaryotes, small-size nanoeukaryotes (nanoeukaryotes-1), and microplankton. The cell viability of picoeukaryotes, as indicated by fluorescein diacetate hydrolysis by cellular esterases (FDA green fluorescence), slightly increased by the end of phase I, whilst the viability of nanoeukaryotes-1 and Synechococcus spp. did not change. Reactive oxygen species levels (ROS green fluorescence) showed no significant changes for any of the functional groups. In contrast, in phase II (days 21–33), a pronounced community response was observed. Increases in in the intermediate OAE treatments of Δ900 to Δ1800 µmol L−1 and in chlorophyll a (Chl a), chlorophyll c2 (Chl c2), fucoxanthin, and divinyl Chl a were attributed to the emergence of blooms of large-size nanoeukaryotes (nanoeukaryotes-2) from the genera Chrysochromulina, as well as picoeukaryotes. Synechococcus spp. also flourished towards the end of this phase. In parallel, we observed a significant change of 20 % in the overall metaproteome of the phytoplankton community. This is considered a significant alteration in protein expression, having a substantial impact on cellular functions and the physiology of the organisms. Medium levels of ΔTA showed more upregulated and less-downregulated proteins than higher ΔTA treatments. Under these conditions, cell viability significantly increased in pico- and nanoeukaryotes-1 at intermediate alkalinity levels, while in Synechococcus spp., nanoeukaryotes-2 and microplankton remained stable. ROS levels did not significantly change in any functional group. The pigment ratios DD+DT : FUCO and DD+DT : Chl a increased in medium ΔTA treatments, supporting the idea of nutrient deficiency alleviation and the absence of physiological stress. When all data are taken together, this study shows that OAE did not cause cellular stress in the phytoplankton community studied, and physiological fitness was not impaired. The drawdown in phytoplankton cell numbers that was observed at times seemed to have been most likely caused by nutrient limitation
Dynamics of dissolved trace metals, rare earth elements and Pb isotopes across the eastern margins of the Mediterranean Sea
No full textHighlights
• Intermediate nepheloid layers are a source of Zn and Cd and a sink for Pb
• The impact of the margins over TM inventories is detected up to 500 km from shore
• Historical anthropogenic Pb modulates deep-water Pb inventories
• Dynamic inputs result in temporal variability of Zn, Pb, and Pb isotopes
Abstract
Continental margins support marine primary productivity by transferring nutrients and micro-nutrients (trace metals) from the coast to the oceans. Yet, the mechanisms governing the delivery of trace metals across the land-sea continuum, and how they vary temporally, are still poorly constrained. Here, we report high spatial resolution depth profiles of dissolved trace metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb), rare earth elements (REEs), nutrients (PO4, TON, and SiOH4) and Pb isotopes from two transect cruises in the oligotrophic eastern Mediterranean Sea.
Varying anthropogenic inputs resulted in inter-cruise variations in Zn and Pb concentrations and Pb isotopes. In contrast, low temporal variability was registered for PO4, SiOH4, Cu, and Co. The isotopic composition of Pb in the eastern Mediterranean Sea (206Pb/207Pb = 1.161–1.173 and 208Pb/206Pb = 2.085–2.101) is controlled by advected Atlantic surface water and anthropogenic inputs delivered via continental runoff (terrestrial) or atmospheric shuttles. The deep-water inventory of Pb is partially controlled by historical anthropogenic sources. An enrichment in Zn and Cd (81 and 17 %, respectively) and a 50 % depletion in Pb relative to open-waters was observed in Intermediate Levantine Waters, in tandem with terrestrial Pb isotopic signatures, light REE depletion (shale-normalized Nd/Yb < 0.22) and a strong Ce anomaly (Ce/Ce* < 0.20). These are driven by intermediate nepheloid layers from the margins, which act as both a source and a sink for trace metals through release and scavenging, evident 300–500 km away from the shore. This study highlights the dynamic role of continental margins in modulating terrestrial and anthropogenic inputs to the oceans
Uncertainty evaluation of the AMOC transport calculation at 11°S
No full textThe Atlantic meridional overturning circulation (AMOC) is a key feature of the global ocean circulation and has a big impact on regional weather and global climate. To project future AMOC variability, it is vital to understand and properly assess the past variability. The AMOC transport and in particular its geostrophic component is measured at several latitudes by specific observing systems. However, the transport can be calculated using multiple combinations of instruments which complicates both the comparison of the observed AMOC at different latitudes and to model transports.
Here, we present results from a systematic comparison of methods to compute the upper branch of the AMOC at 11°S, utilizing data from the Tropical Atlantic Circulation and Overturning at 11°S (TRACOS) array. The TRACOS array comprises 10 years of observations, including data from Pressure Inverted Echo Sounders, tall moorings, and ship sections at the eastern and western boundaries as well as supplementary data from Argo floats and satellites. By subsampling the observational setup in two ocean models (INALT20 and VIKING20X, both based on NEMO), we quantify uncertainties in AMOC transport estimates on different time scales.
We find that bottom pressure measurements, despite being prone to sensor drifts, effectively capture the seasonal variability. The largest potential source of error lies in the choice of vertical structure between the measurement points. Longer-term variability assessments based on moored density measurements require particularly high vertical resolution in the upper 500m. For both methods, the error associated with replacing the eastern boundary data with a climatological seasonal cycle is small, indicating low uncertainty resulting from loss of instruments in that region. We also consider uncertainties in the Ekman transport, which has a magnitude of about one-third of the geostrophic transport at 11°S. Ekman transport estimates vary by a few Sverdrups depending on the choice of wind stress product or drag coefficient used. All in all, we find that the TRACOS array can assess AMOC signals but we also show potential improvements in the array design to reduce uncertainties regarding longer-term variability