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2. Wochenbericht FS Sonne Reise SO310
No full textFS Sonne Reise SO310 (S‐555),
20.02.25 – 22.03.25, Wellington – Wellington;
Quantifizierung der Rolle von Rutschungen in submarinen Canyons an aktiven und passiven Kontinentalrändern (MAWACAAP
How Phase Transitions Impact Changes in Mantle Convection Style Throughout Earth's History: From Stalled Plumes to Surface Dynamics
No full textMineral phase transitions can either hinder or accelerate mantle flow. In the present day, the formation of the bridgmanite + ferropericlase assemblage from ringwoodite at 660 km depth has been found to cause weak and intermittent layering of mantle convection. However, for the higher temperatures in Earth's past, different phase transitions could have controlled mantle dynamics. We investigate the potential changes in convection style during Earth's secular cooling using a new numerical technique that reformulates the energy conservation equation in terms of specific entropy instead of temperature. This approach enables us to accurately include the latent heat effect of phase transitions for mantle temperatures different from the average geotherm, and therefore fully incorporate the thermodynamic effects of realistic phase transitions in global-scale mantle convection modeling. We set up 2-D models with the geodynamics software Aspect, using thermodynamic properties computed by HeFESTo, while applying a viscosity profile constrained by the geoid and mineral physics data and a visco-plastic rheology to reproduce plate-like behavior and Earth-like subduction morphologies. Our model results reveal the layering of plumes induced by the wadsleyite to garnet (majorite) + ferropericlase endothermic transition (between 450 and 590 km depth and over the 2000–2500 K temperature range). They show that this phase transition causes a large-scale and long-lasting temperature elevation in a depth range of 500–650 km depth if the potential temperature of the mantle is higher than 1800 K, indicating that mantle convection may have been partially layered in Earth's early history.
Key Points
For a mantle potential temperature above 1800 K, the wadsleyite to garnet (majorite) + ferropericlase transition induces layering of plumes
The stalled plumes cause a long-lasting global temperature elevation at 500–650 km depth and reduce the vertical mass flux by up to 10%
As Earth cools down and transitions from a layering to a non-layering regime, the surface mobility increases
Plain Language Summary
Earth's mantle convects, cooling the planet and driving the tectonic plates that shape the surface of the Earth. However, it is still an open question how the pattern of mantle convection has changed throughout Earth's history. A key to answering this question might be the mineral assemblages in the mantle, which vary with depth due to changes in temperature and pressure. The transition between different mineral phases can affect the mantle flow and therefore the mantle convection style. For example, heat-absorbing transitions can result in denser mineral assemblages at higher temperatures, inhibiting mantle plumes—hot upwellings rising from the core-mantle boundary to the surface. Our research investigates the influence of phase transitions on mantle plumes and convection style throughout Earth's evolution through modeling. In the early stage of the Earth, when the mantle was hotter than today, different mineral phase transformations dominated the mantle. Our model shows that the transition from wadsleyite to garnet (majorite) + ferropericlase can stop upwelling plumes, leading to elevated temperatures in a depth range of 500–650 km in a mantle that is hotter than in the present day. These results imply that mantle convection may have been partially layered early in Earth's history
Symbionts of predatory protists are widespread in the oceans and related to animal pathogens
No full textHighlights
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Multiple uncultured bacterial lineages are symbionts of marine predatory protists:
• The symbionts are close relatives of animal symbionts that act as pathogens in humans
• Several unexpected proteins may modulate broader host-microbiome interactions
• Adaptions to conserved features of opisthokonts may open pathways for host expansion
Protists are major predators of ocean microbial life, with an ancient history of entanglements with prokaryotes, but their delicate cell structures and recalcitrance to culturing hinder exploration of marine symbioses. We report that tiny oceanic protistan predators, specifically choanoflagellates—the closest living unicellular relatives of animals—and uncultivated MAST-3 form symbioses with four bacterial lineages related to animal symbionts. By targeting living phagotrophs on ship expeditions, we recovered genomes from physically associated uncultivated Legionellales and Rickettsiales. The evolutionary trajectories of Marinicoxiellaceae, Cosmosymbacterales, Simplirickettsiaceae, and previously named Gamibacteraceae vary, including host-engagement mechanisms unknown in marine bacteria, horizontally transferred genes that mediate pathogen-microbiome interactions, and nutritional pathways. These symbionts and hosts occur throughout subtropical and tropical oceans. Related bacteria were detected in public data from freshwater, fish, and human samples. Symbiont associations with animal-related protists, alongside relationships to animal pathogens, suggest an unexpectedly long history of shifting associations and possibilities for host expansion as environments change
Record of Late Oligocene silicic volcanism in the Hrvatsko Zagorje Basin, Croatia: Insights from U-Pb zircon geochronology and volcanology
No full textThe Hrvatsko Zagorje Basin, represents a part of the Slovenian Strait, an Oligocene-Middle Miocene seaway connection between Central Paratethys and Mediterranean. Volcanic deposits within basin are key geochronological markers for understanding the evolution of this important segment of the Paratethyan realm. The timing, eruption styles, magma characteristics, and depositional environments of these events, however, remain poorly understood. In this study, we investigate volcaniclastic sequences from Donje Jesenje and Varaždinske Toplice using sedimentological, mineralogical, petrographical, geochemical, paleontological, and zircon U-Pb geochronological analyses. Zircon dating yielded 24.09±0.13 Ma for Donje Jesenje and 23.35±0.15 Ma for Varaždinske Toplice, corresponding to Late Oligocene. At both sites, the volcaniclastic deposits show evidence indicative of deposition from large explosive eruptions in a submarine environment. Post-depositional alteration processes have led to zeolitization of the glassy components in Donje Jesenje and alteration into clay minerals and silicification in Varaždinske Toplice, under burial diagenesis. Whole-rock geochemistry indicates rhyolitic, subduction-type volcanism, similar to older Periadriatic and younger Carpathian-Pannonian Region magmatism. The temporal and spatial position of Hrvatsko Zagorje Basin magmatism provides a link between these regional magmatic provinces. And allows us to hypothesise their geodynamic link during the Late Oligocene – Early Miocene tectonic reorganization of wider Alpine-Carpathian-Dinaride area
An Atlantic wide assessment of marine heatwaves beyond the surface in an eddy-rich ocean model
No full textPeriods of prolonged anomalously high temperatures in the ocean, known as marine heatwaves (MHWs), can have devastating effects on ecosystems. While MHWs are extensively studied in the near-surface ocean, little is known about MHWs at depth. As continuous observations in space and time are very sparse away from the surface, basin wide studies on MHWs at depth have to rely on models. This introduces additional challenges due to the long adjustment timescale of the deep ocean, resulting in a long-term drift following the model’s initialisation. This unrealistic model drift dominates the MHW statistics below approximately 100 m when a fixed baseline is used. As a result, MHW studies at depth require a long model spin-up, or have to apply a linear baseline removing temperature trends. Based on a comparison of two model configurations with eddy-permitting and eddy-rich horizontal resolution, we show that the representation of mesoscale dynamics leads to pronounced differences in the characteristics of MHWs, in particular along the boundaries and along pathways of highly variable currents. Our results highlight the importance of horizontal and vertical heat transport within the ocean on sub-surface, but also on near-surface, MHWs. By investigating the vertical coherence of MHWs in an example region, here the Cape Verde archipelago, we show that MHWs are coherent over layers of a few 100 to 1000 m thickness, independent of the baseline used. These ranges are closely related to the vertical structure of the temperature field
Student Cruises: Advanced marine geophysical survey project Seegeophysikalische Geländeübung - Marine Geophysical Field Exercise, Cruise No. AL566/Leg1+2+3, 02.10.2021 – 15.10.2021, Kiel (Germany) – Kiel (Germany), GeophysPracUniBremen
No full textThe student training cruises of the Faculty of Geosciences at the University of Bremen took place
in 2021 during the Cruise AL566. The cruise was dedicated to master and bachelor students. The
master students took part in the frame of the course “Advanced marine geophysical survey project”,
which is part of the module “Field and Lab Practice” within the internationally oriented postgraduate study program Master of Science "Marine Geosciences". The module is mandatory for students in the first year of the curriculum. The data collected during the cruise are used for small
scientific projects carried out by the students after the cruise. Additionally, the collected data are
available for master theses.
For the bachelor students, the cruise is the “Seegeophysikalische Geländeübung” as part of the
module “Projektkurs”. This module is mandatory for students in their third academic year. The
“Seegeophysikalische Geländeübung” is addressed to students which enrolled the core subject
“angewandte Geophysik”. Within this core subject, the module “Marine Geophysik” is a major
component of the second academic year of the students, and the content communicated in the
module „Marine Geophysik“ should be applied during the cruise. The collected seismic data are
used by the participating students in the third academic year in the courses “Seismische Exploration” and “Seismisches Datenprozessing”.
During the cruise, seismo-acoustic data were collected by means of a multichannel seismic
system, a multibeam system, a sidescan sonar, and the hull mounted echosounders SES2000 and
EK80. Additionally, magnetic data were gathered along profiles, and CTD measurements were
carried out during stations
Dynamics of Surface Cold Patch off the Korean Peninsula Cape: Driven by Upwelling
No full textKey Points:
- A surface cold patch (SCP) is persistently present offshore of the Korean Peninsula Cape (KPC) during the summer season
- The SCP off the KPC is dominated by upwelling, which induces a thermocline ventilation effect
- Tides and background currents collectively facilitate the formation of upwelling
Surface cold patches (SCPs) are important hydrological phenomena in the Yellow Sea (YS). We investigate the dynamics behind the appearance of the SCP off the Korean Peninsula Cape during summer. The numerical model results revealed that upwelling is the primary mechanism of SCP formation in this region. On one hand, the 3D vorticity balance of the dynamic processes of the SCP indicated that the combined effect of the tides and the baroclinic pressure gradient enhances dissipation in the bottom boundary layer, leading to seawater convergence in the bottom layer west of the tidal front and divergence east of the tidal front, forming a stable frontal secondary circulation and resulting in the formation of upwelling. On the other hand, the offshore transport, which is triggered by the Jeju Warm Current and persists throughout the year in the strait, leads to a divergence of seawater within the region. The joint effect of the above two processes ultimately contributes to the generation of upwelling. The presence of upwelling forces the thermocline to be changed. Strong tidal upwelling triggers the upward ventilating of the thermocline, which can bring cold water to the surface, and the dome-like upwarp of the thermocline isotherms caused by the current-induced upwelling, together lead to the formation of the SCP
Continuous thermosalinograph oceanography along RV METEOR cruise track M207
No full textUnderway temperature and salinity data was collected along the cruise track with two autonomous thermosalinograph (TSG) systems, each consisting of a SBE21 TSG together with a SBE38 Thermometer. Both systems worked independent from each other throughout the cruise. While temperature is taken at the water inlet in about 5 m depth, salinity is estimated within the interior TSG from conductivity and interior temperature. No correction against independent data was performed for temperature. Salinity was calibrated against independent water samples. Finally, TSG1 was chosen for publication. For details to all processing steps see Data Processing Report
2. Wochenbericht SO316 CAVA Tephras
No full textFS SONNE Ausfahrt SO316 - CAVA Tephras,
21.11. – 26.12.2025, Balboa (Panama) – San Diego (USA
