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3. Wochenbericht Reise SO312
No full textForschungsschiff SONNE Reise SO312, BRASS Brothers Volcano Seismic Structure, Auckland, 04.05.2025 - 31.05.2025.
3. Wochenbericht (19. - 25.05.2025
Hidden vortices: Near-equatorial low-oxygen extremes driven by high-baroclinic-mode vortices
No full textLong-term time series of dissolved oxygen (DO) measurements from the upper 500 m depth of the eastern tropical North Atlantic (ETNA), collected over a period of up to 15 years at three different mooring sites, reveal recurring extreme low-oxygen events lasting for several weeks. Similarly, observations from 15 individual meridional ship sections between 6° N and 12° N along 23° W show DO concentrations far below 60 µmol kg⁻¹ in the upper 200 m – significantly lower than the climatological values at this depth (>80 µmol kg⁻¹). Two-third of these low-oxygen events could be related with high-baroclinic-mode vorticies (HBVs) with their cores located well below the mixed layer. Despite the energetic equatorial circulation and the expected dominance of wave-like structures in the near-equatorial region, these HBVs persist as relatively long-lived and coherent features. Based on moored and shipboard observations from the ETNA, and supported by an eddy-resolving ocean-biogeochemistry model, we characterize their dynamics and DO distribution. Observed water mass properties and model analyses suggest that most HBVs originate from the eastern boundary and can persist for more than six months. As they propagate westward into regions of higher potential vorticity (PV), anticyclonic HBVs with low-PV cores remain more effectively isolated and have longer lifespans compared to cyclonic HBVs with high-PV core. The vertical structure of the dominant anticyclonic HBVs corresponds to baroclinic modes 4–10, with associated Rossby radii ranging from 34 km to 13 km, respectively. This is consistent with observed eddy sizes and is well below the corresponding 1st baroclinic Rossby radius of deformation (> 100 km). Since none of the observed HBVs exhibit a surface signature, a substantial portion of the near-equatorial eddy field may remain undetected by satellites, yet still exert significant influence on ocean ecosystems and biogeochemical cycles
Western boundary circulation, AMOC, Rain and Dust in the tropical Atlantic, Cruise No. M207, 04.01.2025 - 11.02.2025, Belém (Brazil) - Mindelo (Cape Verde)
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Strong Serpentinization and Hydration in the Subducting Plate of the Southern Mariana Trench: Insights From V p / V s Ratios
No full textThe southern Mariana subduction zone, home to the Challenger Deep—the deepest known point on Earth—poses significant challenges for studying the hydration of the subducting plate due to its extreme depth. This study uses S‐wave seismic tomography and V p / V s ratios to investigate hydration and serpentinization at the Challenger Deep. We observe a low V p and V s layer in the upper mantle with V p / V s ratios exceeding 1.8, reaching up to 1.95 at the Moho. These high ratios indicate a strong serpentinized layer (>15 vol%) with significant changes in the mechanical properties of the serpentinized peridotite. Additionally, V p / V s ratios in the crust and uppermost mantle increase from the outer rise to the trench axis, demonstrating that bending‐related faulting and hydration intensify as the plate approaches the trench. Our results suggest extensive faulting, hydration, and mantle serpentinization at the Challenger Deep, making this region an extreme example of water cycling in subduction zones.
Plain Language Summary
The southern Mariana Trench, containing the deepest point on Earth's surface, is where the old Pacific Plate (∼125 Ma) is subducting beneath the Philippine plate. Understanding the processes of bending‐related faulting and hydration of the incoming subducting plate has been challenging due to the limitations of using only P‐wave velocity ( V p ), which does not provide detailed lithological information. In this study, we identified valuable converted S‐wave arrivals from the incoming plate, allowing us to determine the S‐wave velocity ( V s ) structure and calculate the V p / V s ratios. Our results reveal that the low V p layer in the upper mantle is a strongly serpentinized layer. Compared to other subduction zones, the combination of lower V p and V s values with higher V p / V s ratios suggests more intense serpentinization within the incoming plate at the southern Mariana subduction zone. This study provides a clearer understanding of mantle hydration processes in extreme subduction environments and highlights how plate characteristics influence serpentinization intensity
Key Points
S‐wave tomography and V p / V s ratios reveal extensive serpentinization and hydration in the subducting plate of the southern Mariana Trench
V p / V s ratios in the crust and uppermost mantle increase toward the trench axis, indicating intensified hydration as the plate approaching
Challenger Deep is an extreme example of water cycling in subduction zone
Alkalinity and elemental cycles in present and past ocean: Insight from geochemical modeling and alkali and alkaline earth metal isotopes
No full textThis chapter provides an overview of near-surface geochemical processes operating on Earth, with special emphasis placed on (i) marine weathering such as alteration and dissolution of silicates, carbonates and terrigenous riverine particles in the ocean, complemented by (ii) reverse weathering reactions leading to marine authigenic clay formation, and the impact of these phenomena on ocean alkalinity budget and the chemical and isotope composition of seawater. Model simulations of the above processes provide estimates of the global marine fluxes of major cations (Na+, K+, Mg2+, Ca2+) and alkalinity in the ocean induced by silicate weathering and dissolution of terrigenous material in seawater. Additional constraints on silicate vs. carbonate weathering, oceanic/coastal CaCO3 cycling, and paleo-seawater reconstructions are provided via the stable and radiogenic isotope systems of alkali and alkaline earth metals (Li, K, Mg, Ca, and Sr isotopes) that are discussed within the context of marine and reverse weathering in the present and past ocean.
Key points
• Impact of weathering processes on marine elemental cycles and the ocean alkalinity budget.
• Alteration and dissolution of silicate minerals and riverine particles in the ocean quantified via thermodynamic equilibrium (PHREEQC) calculations, in seawater and top sediment settings.
• Estimates of global ocean fluxes of dissolved cations (Na+ , K+ , Mg 2+ , Ca2+ ) and alkalinity induced by alteration and dissolution of terrigenous material in seawater and marine sediments.
• Principles and mechanisms of isotope variability in nature (mass-dependent and radiogenic isotope effects) observed for
alkali and alkaline earth metals.
• Silicate vs. carbonate weathering and coastal carbon/carbonate cycling constrained via stable and radiogenic Ca and Sr, and Li isotopes.
• Oceanic processes, marine carbonate chemistry (alkalinization vs. acidification), and paleo-seawater reconstructions constrained via d44 Ca, d88
Sr, d26 Mg proxies and numerical (MATLAB) modeling.
• Emerging metal isotope proxies (d41
K) for silicate and reverse weathering in the ocean
The roles of celestine and barite in modulating strontium and barium water column concentrations in the northeast Pacific Ocean
No full textThe water column distributions of the alkaline earth metals strontium (Sr) and barium (Ba) were studied along a transect from Hawaii to Alaska. Despite similarity in the chemical properties of Sr and Ba, we find that changes in their concentrations along the transect are governed by different chemical and biological processes, meaning that these elements can be treated as independent variables in modern and ancient environments. Alaskan margin sediments are a particularly important source of dissolved Ba to the North Pacific, likely through a combination of saline submarine groundwater discharge and reductive dissolution of manganese (Mn) oxides. Abyssal North Pacific sediments are also a source of Ba to the bottom waters but a sink for Sr. We find that over 90 % of the water column variability in Sr concentrations is driven by precipitation and dissolution of the celestine (SrSO4) skeletons of Acantharia. However, the high Ba content of Acantharia celestine accounts for only 5–8 % of the global ocean variability in Ba concentrations in the water column. Similarly, the effects of barite (BaSO4) precipitation and/or dissolution on the marine Sr cycle is negligible, accounting for <1 % of the water column concentration structure for Sr and ∼3 % of the sedimentary Sr burial. The Sr-Ba-PO4 concentration distributions in the North Pacific are inconsistent with significant export of barite to the deep ocean and sediment. This suggests most of the barite formed at intermediate depths dissolves at similar horizons to its formation. The Ba content of phytoplankton organic matter is too low to constitute a major source for particulate Ba in the mesopelagic North Pacific, which suggests Ba is concentrated in marine aggregates by heterotrophic micro-organisms
Numerische Prozess-Simulation zur Bestimmung des statischen und dynamischen Speicherpotentials einer Speicherstätte im deutschen Sektor der Nordsee
No full textPhysical climate risk: Stock price reactions to the historically most extreme European and United States heat waves since 1979
No full textClimate change has heightened the need to understand physical climate risks, such as the increasing frequency and severity of heat waves, for informed financial decision-making. This study investigates the financial implications of extreme heat waves on stock returns in Europe and the United States. Accordingly, the study combines meteorological and stock market data by integrating methodologies from both climate science and finance. The authors use meteorological data to ascertain the five strongest heat waves since 1979 in Europe and the United States, respectively, and event study analyses to capture their effects on stock prices across firms with varying levels of environmental performance. The findings reveal a marked increase in the frequency of heat waves in the 21st century, reflecting global warming trends, and that European heat waves generally have a higher intensity and longer duration than those in the United States. This study provides evidence that extreme heat waves reduce stock values in both regions, with portfolio declines of up to 3.1%. However, there are marked transnational differences in investor reactions. Stocks listed in the United States appear more affected by the most recent heat waves compared to those further in the past, whereas the effect on European stock prices is more closely tied to event intensity and duration. For the United States sample only, the analysis reveals a mitigating effect of high corporate environmental performance against heat risk. This study introduces an innovative interdisciplinary methodology, merging meteorological precision with financial analytics to provide deeper insights into climate-related risks