ALBERT

Description: Manganese (Mn) is an essential micro-nutrient that can limit or, along with iron (Fe), co-limit phytoplankton growth in the ocean. Glacier meltwater is thought to be a key source of trace metals to high latitude coastal systems, but little is known about the nature of Mn delivered to glacially-influenced fjords and adjacent coastal waters. In this work, we combine in-situ dissolved Mn (dMn) measurements of surface waters with Mn K-edge X-ray absorption spectroscopy (XAS) data of suspended particles in four fjords of West Greenland. Data were collected from transects of up to 100 km in fjords with different underlying bedrock geology from 64 to 70°N. We found that dMn concentrations generally decreased conservatively with increasing salinity (from 80-120 nM at salinity 〈8 to 〈40 nM at salinities 〉25). Dissolved Fe (dFe) trends in these fjords similarly declined with increasing distance from glacier outflows (declining from 〉20 nM to 〈8 nM). However, the dMn/dFe ratio increased rapidly likely due to the greater stability of dMn at intermediate salinities (i.e. 10 – 20) compared to rapid precipitation of dFe across the salinity gradient. The XAS data indicated a widespread presence of Mn(II)-rich suspended particles near fjord surfaces, with structures akin to Mn(II)-bearing phyllosilicates. However, a distinct increase in Mn oxidation state with depth and the predominance of birnessite-like Mn(IV) oxides was observed for suspended particles in a fjord with tertiary basalt geology. The similar dMn behaviour in fjords with different suspended particle Mn speciation (i.e., Mn(II)-bearing phyllosilicates and Mn(IV)-rich birnessite) is consistent with the decoupling of dissolved and particulate Mn and suggests that dMn concentrations on the scale of these fjords are controlled primarily by dilution of a freshwater dMn source rather than exchange between dissolved and particle phases. This work provides new insights into the Mn cycle in high latitude coastal waters, where small changes in the relative availabilities of dMn, dFe and macronutrients may affect the identity of the nutrient(s) proximally limiting primary production.

Description: The mesopelagic or ocean twilight zone (OTZ) in the ocean contains huge numbers of fish in a relatively pristine environment and may therefore attract interest as a commercial fishery. In this study we evaluate in economic terms, the likely trade-offs between the different services provided by the mesopelagic layer in the Bay of Biscay and the societal benefits of its commercial exploitation. Benefits arise mainly from the likely use of this group of species as raw material for producing fishmeal and fish oil. Costs are derived from the loss in climate regulating and cultural, services, but also from the loss in the provisioning service of other commercial species. To do so we compare the current non-exploited status with a situation in where mesopelagic fishes are harvested at levels capable of producing the Maximum Sustainable Yield. Results suggest that if mesopelagic fishes are harvested, a mean value of 1.2 million Euro loss in a year will be created in the Bay of Biscay, although in a range between 42 million Euro loss and 48 Euro million benefits. This uncertainty comes, mainly, from the limited existing knowledge of the mesopelagic fishes’ biomass but also from the uncertainty on the biomass of the rest of the species of the studied ecosystem. The large range indicates that a better understanding of the mesopelagic ecosystem is needed, however, results also show that ecosystem services under no exploitation provided by the OTZ could be more valuable than the fishmeal and fish oil that potentially could be obtained from the fishes harvested in this sea layer.

Description: Yedoma is a permafrost deposit widely distributed across the Arctic and found exclusively within the unglaciated regions in northern Siberia, Alaska, and the Yukon, which are the core regions of Beringia. Yedoma deposits accumulated during the late Pleistocene Stage and are characterized by their predominantly fine-grained texture and association with syngenetic perma-frost formation. The very high ground ice content is most commonly present as pore ice and wedge ice that formed contemporaneously with sediment deposition. In the last decade, research has transitioned from debates about the origin of the Yedoma deposits towards increasing attention on the large carbon and nitrogen pools in Yedoma, their vulnerability to thaw, and increasing mobilization as the climate has warmed across the Arctic. In addition to classical cryolithological and sedimentological research, new methods such as stable isotope paleoclimate reconstruction and ancient sedimentary DNA studies have been more widely applied to better understand the characteristics of Yedoma deposits and helped emphasize their value as archives of Quaternary climate and paleoecological conditions during Ice Age Beringia.

Description: Sea-level rise submerges terrestrial permafrost in the Arctic, turning it into subsea permafrost. Subsea permafrost underlies ~ 1.8 million km2 of Arctic continental shelf, with thicknesses in places exceeding 700 m. Sea-level variations over glacial-interglacial cycles control subsea permafrost distribution and thickness, yet no permafrost model has accounted for glacial isostatic adjustment (GIA), which deviates local sea level from the global mean due to changes in ice and ocean loading. Here we incorporate GIA into a pan-Arctic model of subsea permafrost over the last 400,000 years. Including GIA significantly reduces present-day subsea permafrost thickness, chiefly because of hydro-isostatic effects as well as deformation related to Northern Hemisphere ice sheets. Additionally, we extend the simulation 1000 years into the future for emissions scenarios outlined in the Intergovernmental Panel on Climate Change’s sixth assessment report. We find that subsea permafrost is preserved under a low emissions scenario but mostly disappears under a high emissions scenario.

Description: Fault creep along the lower eastern flank of Mt. Etna volcano has been documented since the end of the 19th century and significantly contributes to the surface faulting hazard in the area. On 29 October 2002, during a seismic swarm related to dyke intrusions, two earthquakes caused extensive damage and surface faulting in an area between the Santa Venerina and Santa Tecla villages. On the same day after the two earthquakes, an episodic aseismic creep occurred along the Scalo Pennisi Fault close to the Santa Tecla coastline. On 8 February 2022, during another aseismic creep event along the Scalo Pennisi Fault, we observed the reopening of the pre existing 2002 ground ruptures mostly as pure dilational fractures. We mapped the 2002 and 2022 surface ruptures, and collected data on displacement, length, and pattern of ground breaks. Ground ruptures affected structures located along the activated fault segments, including roads, walls and buildings. The 2002 surface faulting propagation can be ascribed to a sliding of the Mt. Etna eastern flank toward the SE, as also suggested by the related shallow seismicity, and InSAR and geodetic data between 2002 and 2005. For the 2022 event, dif ferential InSAR data, acquired in both descending and ascending views, allowed us to decompose Line of Sight (LOS) displacement into horizontal and vertical components. We detect a ~ 700 m long and ~ 500 m wide deformation zone with a downward and eastward motion (max displacement ~1,5 cm) consistent with a normal fault. We inverted the InSAR–detected surface deformation using a uniform-slip fault model and obtained a shallow detachment for the causative fault, located at ~300 m depth, within the volcanic pile. This is the first in depth study along the Scalo Pennisi Fault to suggest a shallow faulting that accommodates Mt. Etna E flank gravitational sliding.

Description: Published

Description: 229829

Description: JCR Journal

Description: In this article the author name Matthew Mazloff was incorrectly written as Matthew Mazloeff. The original article has been corrected.

Description: Correction to: Scientific Data, published online 22 June 2023 The original version showed the wrong image for Figure 3, with the image for Figure 4 used for both. This has been corrected in the pdf and HTML versions of the article, with the correct version of Figure 3 replacing the duplicated figure. The dates in the figure captions were also incorrect and have been amended as follows: Figure 3 caption: “from 2019-10-25 - 2020-07-30” modified to “from 2019-10-25 - 2020-05-15” Figure 4 caption: “from 2020-02-25 - 2020-07-30” modified to “from 2020-06-13 - 2020-07-30”.

Description: Snow plays an essential role in the Arctic as the interface between the sea ice and the atmosphere. Optical properties, thermal conductivity and mass distribution are critical to understanding the complex Arctic sea ice system’s energy balance and mass distribution. By conducting measurements from October 2019 to September 2020 on the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we have produced a dataset capturing the year-long evolution of the physical properties of the snow and surface scattering layer, a highly porous surface layer on Arctic sea ice that evolves due to preferential melt at the ice grain boundaries. The dataset includes measurements of snow during MOSAiC. Measurements included profiles of depth, density, temperature, snow water equivalent, penetration resistance, stable water isotope, salinity and microcomputer tomography samples. Most snowpit sites were visited and measured weekly to capture the temporal evolution of the physical properties of snow. The compiled dataset includes 576 snowpits and describes snow conditions during the MOSAiC expedition.

Description: The spatial pattern of Antarctic surface air temperature variability on multi–decadal to multi–centennial time scales is poorly known because of the short instrumental records, the relatively small number of high–resolution paleoclimate observations, and biases in climate models. Here, changes in surface air temperature over Antarctica are reconstructed over the past two millennia using data assimilation constrained by different ice core water isotope records in order to identify robust signals. The comparison between previous statistically based temperature reconstructions and simulations covering the full Common Era driven by natural and anthropogenic forcings shows major discrepancies occurring in the period 1–1000 CE over East Antarctica, with the reconstructions displaying a warming over 1–500 CE that is not reproduced by the simulations. This suggests that the trends in the first millennium deduced from the statistically based reconstructions are unlikely to be entirely forced by external forcings. Our reconstructions show the high sensitivity of the 500-year temperature trend in Antarctica and its spatial distribution to selection of the records for the reconstructions, especially during 1–500 CE. A robust cooling over Antarctica during 501–1000 CE has been obtained in three data assimilation–based reconstructions with a larger magnitude in the WAIS than elsewhere over Antarctica, in agreement with previous estimates with the larger changes than simulated in climate models. The reconstructions for atmospheric circulation indicate that the pattern of temperature changes over 501–1000 CE is related to the positive trend of Southern Annular Mode and a deepening of Amundsen Sea Low. This confirms the role of internal variability in the temperature trends on multi–centennial scales.

Description: Nominally anhydrous minerals (NAMs) may contain significant amounts of water and constitute an important reservoir for mantle hydrogen. The colloquial term ‘water’ in NAMs is related to the presence of hydroxyl-bearing (OH􀀀 ) point defects in their crystal structure, where hydrogen is bonded to lattice oxygen and is charge-balanced by cation vacancies. This hydrous component may therefore have substantial effects on the thermoelastic parameters of NAMs, comparable to other major crystal-chemical substitutions (e.g., Fe, Al). Assessment of water concentrations in natural minerals from mantle xenoliths indicates that olivine commonly stores ~0–200 ppm of water. However, the lack of samples originating from depths exceeding ~250 km coupled with the rapid diffusion of hydrogen in olivine at magmatic temperatures makes the determination of the olivine water content in the upper mantle challenging. On the other hand, numerous experimental data show that, at pressures and temperatures corresponding to deep upper mantle conditions, the water storage capacity of olivine increases to 0.2–0.5 wt%. Therefore, determining the elastic properties of olivine samples with more realistic water contents for deep upper mantle conditions may help in interpreting both seismic velocity anomalies in potentially hydrous regions of Earth’s mantle as well as the observed seismic velocity and density contrasts across the 410-km discontinuity. Here, we report simultaneous single-crystal X-ray diffraction and Brillouin scattering experiments at room temperature up to 11.96(2) GPa on hydrous [0.20(3) wt% H2O] Fo90 olivine to assess its full elastic tensor, and complement these results with a careful re-analysis of all the available single-crystal elasticity data from the literature for anhydrous Fo90 olivine. While the bulk (K) and shear (G) moduli of hydrous Fo90 olivine are virtually identical to those of the corresponding anhydrous phase, their pressure derivatives K′ and G′ are slightly larger, although consistent within mutual uncertainties. We then defined linear relations between the water concentration in Fo90 olivine, the elastic moduli and their pressure derivatives, which were then used to compute the sound velocities of Fo90 olivine with higher degrees of hydration. Even for water concentrations as high as 0.5 wt%, the sound wave velocities of hydrous and anhydrous olivines were found to be identical within uncertainties at pressures corresponding to the base of the upper mantle. Contrary to previous claims, our data suggest that water in olivine is not seismically detectable, at least for contents consistent with deep upper mantle conditions. In addition to that, our data reveal that the hydration of olivine is unlikely to be a key factor in reconciling seismic velocity and density contrasts across the 410-km discontinuity with a pyrolitic mantle.

Description: Published

Description: 107011

Description: JCR Journal