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Der Dorsch wird immer kleiner
No full textGeomar-Forscher legen Studie vor: Die jahrelange Überfischung der Ostsee hat das Erbgut der Tiere veränder
Brothers Volcano Seismic Structure, Cruise No. SO312, 04.05.2025 - 31.05.2025, Auckland (New Zealand) - Auckland (New Zealand), BASS
No full textCaldera collapse is an important geological process that shapes many of Earth’s volcanoes. The
structures that accommodate the collapse play a primary role in hydrothermal fluid circulation and
focus, and related mineralization. In addition, the collapse process and the associated volcanism can
pose a significant hazard to society. To understand caldera collapse and related hydrothermal
processes, three-dimensional (3D) investigation of the structural architecture and hydrothermal fluid
circulation are required. However, no 3D seismic data currently exist for any caldera in the world.
During SO312 we imaged Brothers Volcano - one of the best-studied examples of a submarine caldera
volcano in the world—to address three fundamental hypotheses: (1) that the caldera formation was
caused by a sudden collapse after an explosive eruption, rather than by incremental subsidence
associated with effusive eruptions; (2) that pre-existing zones of ‘volcanic weakness’ played a major
role in the collapse; and (3) that large-scale, seawater-dominated hydrothermal activity at Brothers
Volcano is intrinsically linked to caldera collapse structures. We conducted a major, high-resolution
3D seismic experiment that images the entire volcanic edifice of Brothers. In addition, we have
collected an ocean bottom seismometer dataset that will deliver a tomographic model of the upper 5
km beneath the volcano. The study will provide unprecedented insight into the geological processes
involved in submarine caldera collapse and will aid hazard assessment as well as mineral resource
assessment of similar volcanoes
Degrees of reversibility of ocean deoxygenation in an atmospheric carbon dioxide removal scenario
No full textOver the last century, increasing atmospheric carbon dioxide (CO2) concentrations, among other greenhouse gases, and resulting climate change have greatly impacted the ocean. Observed impacts include lower oxygen solubility and changes in ocean stratification, circulation and biological activity. To reduce the carbon burden in the atmosphere in the future and thereby mitigate anthropogenic climate change, carbon dioxide removal (CDR) techniques have been increasingly studied and tested. However, information on the impact of CDR on oceanic oxygen is still scarce. In the current study we explore dissolved oxygen responses from an idealized CDR implementation, with atmospheric CO2 ramp-up and ramp-down simulations following the CDR model intercomparison project protocol. We find that over the timescale of a few centuries, the degree of recovery of marine oxygen, after atmospheric CO2 has returned to pre-industrial levels, differs for different water depths. Oxygen concentrations strongly recover in the upper ocean, achieving a near reversibility within 97%-99% across models, and even overshoot pre-industrial levels at depths of 100-600 m. Conversely, oxygen responses show a long-lasting deoxygenation signal in the deep ocean, with a much smaller initial recovery signal by the end of the experiment. The main factor driving oxygen changes in the deep ocean is indicated by the apparent oxygen utilization, related to changes in circulation and ventilation, as inferred by the simulated age of deep water masses. According to our models and despite the effective recovery of oxygen in the upper ocean, the effects of time lags and hysteresis on deep ocean responses could lead to longstanding and deleterious impacts on redox-sensitive biogeochemical processes and on marine biota throughout the ocean
Freiwillige renaturalisieren Seegraswiesen
No full textIn Schleswig-Holstein hat die Pflanzsaison für ganz besondere Unterwassergärtner begonnen: Freiwillige Taucher bepflanzen in diesem Sommer erstmals wisenschaftlich ausgewählte Flächen, um Seegraswiesen in der Ostsee zu renaturiere
Disentangling upwelling: how light and nutrient supply shape primary producers and stoichiometry in the Humboldt upwelling system
No full textHighlights
• Light availability in the mixed layer plays a key role in explaining the seasonal mismatch between upwelling intensity and productivity in the Peruvian Humboldt upwelling system.
• Seasonal light limitation in the mixed layer inhibits particulate organic carbon accumulation and net primary productivity, despite ample nutrient supply from upwelling.
• Phytoplankton in winter exhibits photoacclimation, but this does not translate into higher carbon fixation rates
• Higher nutritional quality of the phytoplankton community, caused by reduced carbon uptake rates under light limitation, may contribute to the exceptionally high trophic transfer efficiency observed in the Humboldt upwelling system
Abstract
The Humboldt upwelling system (HUS) is known for its extraordinary productivity due to wind-driven upwelling of nutrient-rich deep water, resulting in the highest fish catches per unit area worldwide. However, contrary to other Eastern boundary upwelling systems, upwelling intensity is highest in winter, while primary productivity reaches its peak during the summer months. Our current understanding of the counterintuitive relationship between upwelling intensity and productivity is insufficient to predict the consequences of climate change on this ecosystem. To elucidate the drivers of the upwelling-productivity relationship in the HUS, we tested the hypothesis that low light availability limits primary productivity in winter despite strong upwelling intensity supplying plenty of nutrients into the surface layer, while light availability in the shallower mixed layer in summer enables an effective use of the upwelled nutrients. To disentangle the interactive effects of light and nutrients on primary production and carbon cycling, we enclosed natural plankton communities off the coast of Callao (Peru) during a 35-day mesocosm experiment by recreating summer-time high light and winter-time low light conditions under different upwelling intensities (0%, 15%, 30%, 45% and 60%). Primary productivity and phytoplankton biomass scaled with both nitrate and light availability. Comparing the same upwelling intensity at different light levels, our data confirmed the hypothesis that light limitation due to deepening of the mixed layer is a key driver for the out-of-phase observations in primary productivity in the Humboldt upwelling system. Under light limiting conditions phytoplankton had low POC:Chla ratios indicating photoacclimation and low POC:PON ratios indicating light limitation of nitrate uptake which leads to increased food quality for grazers in winter. Our study indicates that small seasonal changes in phytoplankton biomass (estimated using Chla) might hide larger changes in primary productivity (carbon uptake), and highlights the importance of combining satellite studies with in situ observations and experimental studies to predict the fate of upwelling systems in a changing ocean. Increased stratification caused by global warming in upwelling systems such as the HUS would lead to less phytoplankton biomass with higher POC:Chla and POC:PON ratios. This phytoplankton community would have lower food quality for grazers and might lead to a decline in the transfer to higher trophic levels, but at the same time might lead to increased CO2 drawdown in an otherwise CO2 emitting ecosystem. Understanding the unique relationship between upwelling intensity and productivity in the HUS contributes to predicting the reaction of this valuable ecosystem for fisheries to the impacts of climate change
University Bremen Student Training Cruises: Advanced Marine Geophysical Survey Project, Marine Geophysical Field Exercise, September 16 2023 – September 30 2023, Kiel (Germany) – Kiel (Germany), GeophysPracUB, Cruise No. AL602
No full textThe Cruise AL602/Leg 1 took place from September 16th 2023 to September 20th 2023 in the
south-western Baltic Sea near Rügen. The starting point was Kiel and the destination was Sassnitz,
Rügen. The aim of the cruise was to train students by collecting marine geophysical data in the
Baltic Sea, especially in a prospective wind farm area. The areas examined included the Bay of
Kiel, Fehmarn Belt, the Bay of Luebeck, the Bay of Mecklenburg and the Tromper Wiek in the
Pommerian Bay. The methods used to collect data were: 2D reflection seismic,
sediment-echosounding, multibeam-sounding and sidescan-imaging.
The 2nd Leg of Cruise AL602 on RV ALKOR took place from 21st of September to 26th of
September 2023. The leg started and finished in the harbor of Sassnitz on Ruegen island. The
cruise is offered as part of the master’s program "Marine Geosciences" at the University of
Bremen. The data collected also serves the purpose of complimenting the existing data sets.
From a student’s point of view, the cruise serves as a fundamental introduction to the
geophysical methods used in marine geological research and provides an opportunity to get hands-on experience with a wide variety of equipment. During the cruise, various data acquisition
methods were used. Ship mounted instruments running nearly the full duration of the cruise
included: a sediment echosounder (SES) imaging of the uppermost tens of meters of sediments, a
multibeam echosounder (MBES) imaging the seafloor, and an EK80 high resolution echosounder
serving the purpose of water column imaging. As towed equipment, a high-resolution multichannel
seismic (MCS) system was used to image the subsurface, and a Sidescan Sonar was used to acquire
seafloor backscatter data. Finally, CTD casts was used to characterize the water properties,
Students were involved in planning, data acquisition, data processing and interpretation in the 24-
hour shift work that is common on research vessels
Seismic structure and the variation of magmatic budget in the Southwest Sub-Basin of the South China Sea
No full textThe oceanic lithospheric structure is key to understanding the processes related to the interplay between tectonics and magmatism from the end of rifting to the onset and cessation of seafloor spreading. In the oceanic basin of the South China Sea (SCS), the Southwest Sub-basin (SWSB) is the last-opening segment before the abandonment of seafloor spreading. The SWSB shows a V-shaped geometry associated with the SW-ward propagation of the spreading center during the opening. Here, we present a 540-km-long wide-angle seismic profile along a seafloor-spreading flow-line in the central sector of the SWSB. A joint refraction and wide-angle reflection travel-time tomography provides a P-wave velocity (Vp) model of the crust and uppermost mantle. Continental break-up produced asymmetric conjugate margins, abutted by a typical oceanic crust with a two-layer Vp structure. The distinct vertical velocity gradients in the upper and lower crust, and a clear Moho, indicate a magmatically-dominated oceanic system. In contrast, oceanic crust <19.2 Ma displays no Moho interface and a Vp structure indicating reduced magmatism and increased tectonic extension. Anomalously slow Vp structure under the median valley indicates serpentinized mantle resulting from enhanced faulting during the final opening phase. The spatial variation in Vp structure reflects two main temporal stages of the SWSB seafloor spreading before cessation. Previous results of plate kinematics reconstructions appear to support that the transition from magmatically robust to increased tectonics and final cessation of seafloor spreading in the SWSB might relate to the subduction of the proto-SCS.
Key Points
A seismic tomographic Vp model constrains the crustal structure across the southwest sub-basin (SWSB) of the South China Sea (SCS)
Two stages of seafloor spreading are proposed and related to the reduction of magmatic budget due to change in mantle properties
Regional kinematics of proto-SCS subduction are suggested to govern the onset and cessation of SWSB
Plain Language Summary
The structure of oceanic lithosphere holds important clues about how magmatic and tectonic processes interact at the mid-ocean ridges where the seafloor spreads. Using a method called travel-time tomography, a P-wave velocity (Vp) structure is obtained along a seismic survey line crossing the whole basin of Southwest Sub-basin (SWSB) of the South China Sea (SCS). The Vp structure reveals two distinct oceanic regions formed during different stages of seafloor spreading: (a) a region dominated by magmatic activity and (b) a region controlled by tectonic processes. Notably, the shift in Vp structure coincides with the timing of a geological transition from subduction to collision, related to the northward subduction of proto-SCS. We propose that the termination of the ancient subduction event likely caused the seafloor spreading style of SWSB to change from being magmatic-dominated to tectonic-dominated
Combining Multibeam and Single beam echosounders for quantifying gas bubble release from the seafloor
No full textMarine gas bubble release is a worldwide phenomenon that impacts the local marine ecosystem and contributes to carbon fluxes with respect to global warming. It is still challenging to assess gas flow for large seep areas (tens of km2), but recent advances in calibrating and processing multibeam echosounder (MBES) data make this problem approachable. A recently published method called “echo grid integration” describes the computation of aggregated backscattering cross-sections of bubble stream layers from calibrated MBES data. Here, we use this method combined with methods for bubble stream detection, acoustic inversion, cross-calibration and dissolution modeling to create a full gas flow quantification workflow. A simultaneously recording scientific single beam echosounder (SBES) is used to acoustically (cross-) calibrate the MBES. The final result of the presented workflow is a map showing the distribution and estimated gas flow of 10 bubble seep clusters and > 50 individual seeps in a 5 × 7 km wide area on the Black Sea shelf. It is shown that the MBES gas flow estimates correlate linearly with estimates from the SBES and are consistent over depth and at different beam angles. Multibeam echosounder data thereby provided 10 times the areal coverage per survey line compared to the scientific SBES. Our results highlight a heterogeneous picture of gas release in the area, where 10% of the flares are responsible for ~ 80% of the overall gas flow (~ 260–780 tons of methane per year). According to bubble dissolution modeling, this free methane dissolves in the water before reaching the surface
FS Alkor Reise AL637 (GPF 24-2/014), 11.08.25 – 19.08.25, Kiel – Kiel, 1. und letzter Wochenbericht, 11.08. – 17.08.2025
No full textSeegeophysikalisches Praktikum der Christian-Albrechts Universität zu Kie
The Eocene–Oligocene Transition in the Paratethys: boreal water ingression and its paleoceanographic implications
No full textThe Eocene–Oligocene Transition (EOT) represents a pivotal period in Earth's climatic history, marked by the onset of Antarctic glaciation and global cooling. While deep-sea records have extensively documented this transition, its impacts on marginal and epicontinental seas remain less understood. This study investigates the impacts of the EOT in the Karaburun composite section, located in the Eastern Paratethys. Using a multidisciplinary approach that integrates biostratigraphy, geochemistry, geochronology, and sequence stratigraphy, a robust chronostratigraphic framework for the latest Eocene to early Oligocene was established. The stable isotopic shifts observed in benthic and planktic foraminifera δ18O and δ13C records at Karaburun align with global patterns but also reveal regional effects, such as freshwater influx and basin restriction, specific to the semi-restricted Paratethys. The abrupt negative δ18O shift across the Eocene–Oligocene Boundary (EOB) in the Paratethys reflects boreal water ingressions driven by the onset of anti-estuarine circulation between the Nordic Seas and the Atlantic and the closure of the Arctic–Atlantic gateway, which redirected cold, low-salinity boreal waters through interconnected basins towards the Paratethys. These findings highlight the interplay between global climate drivers and regional hydrological dynamics, providing critical insights into the evolution of marginal marine environments during the EOT. Our results underscore the significance of the Paratethys as a unique archive for studying the onset of global icehouse climate conditions and regional responses