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Spatiotemporal scales of mode water transformation in the Sea of Oman
No full textIn the Sea of Oman, mode water forms at the surface and is trapped under a warm stratified layer in summer. This capped and well-mixed oxygenated layer decouples the oxygen minimum zone from ocean surface processes and provides a space for remineralisation, reducing oxygen demand in the deeper oxygen minimum zone. Several physical processes, from isopycnal and diapycnal mixing to advection, transform mode water and change its properties. Using monthly climatologies derived from profiling floats and high-resolution underwater glider observations, we perform a volume budget analysis to investigate the mechanisms driving mode water volume change in the Sea of Oman from monthly to 3-day temporal scales. Isopycnal and diapycnal water-mass transformations are estimated in a density-spice framework. Mode water predominantly transforms along isopycnals, yet strong but transient diapycnal transformation occurs at shorter timescales. Moreover, fluxes between the mode water layer and its surroundings are highly sensitive to the presence of mesoscale eddies. Across eddies, diapycnal and isopycnal transformations intensify by 61 % and 45 % respectively, compared to non-eddy conditions, indicating that eddies are drivers of both lateral and vertical water mass exchanges. This study provides a new methodological approach to understanding water mass transformation using high-resolution underwater gliders, and shows that this water mass transformation framework can be used at higher resolution than traditional climatological products or models. By comparing monthly climatological products to the high-resolution glider data, we estimate that the climatological estimates are outside of the high-resolution glider mean ± standard error 40 % of the time for diapycnal and 60 % of the time for isopycnal transformation. These results highlight the intense variability occurring at small scales and can serve to inform future estimates of water mass transformation uncertainty from coarser products
The Rainer Froese Award
No full textThe 19th Hellenic Conference of Ichthyologists, held in Ioannina, Greece from October 30 to November 2, 2025, celebrated the forefront of ichthyology and fisheries science. Among the highlights was the inaugural presentation of the Rainer Froese Award, established to honor the legacy of Dr. Rainer Froese (GEOMAR Helmholtz Centre for Ocean Research Kiel), co-creator and long-term coordinator of FishBase and the lead author of the innovative stock assessment method for data-limited fisheries, CMSY++.
Dr. Froese’s pioneering contributions to ichthyology and fisheries biology have profoundly influenced modern fisheries science, earning international recognition including an honorary award at the 16th Hellenic Conference of Ichthyologists in Kavala, Greece (October 6, 2016). At that time, Dr. Froese delivered the inaugural invited talk, with Dr. Kostas Stergiou—former director of the Laboratory of Ichthyology at Aristotle University of Thessaloniki and a long-standing member of the FishBase Consortium—delivering the laudatio. Among his other prestigious honors are the 2017 Le Cren Medal from the Fisheries Society of the British Isles and the 2020 Ocean Awards for Conservation Science from the Blue Marine Foundation and BOAT International
Der Polarbär kommt nicht allein
No full text17 Holzskulpturen im Stadtgebiet: Bildhauer Marcus Meyer will mit einer Ausstellung Meeresschutz erfahrbar mache
Survival of zooplankton communities in ships’ ballast water tanks
No full textGlobal maritime transport is a major pathway for the unintentional spread of non-native species, particularly via the uptake and discharge of ballast water. Zooplankton are among the most frequently transported taxa and can alter recipient ecosystems when released. This study examined short-term changes in zooplankton communities and environmental conditions inside two ballast water tanks on the RV Alkor. Three independent 10-day experiments were conducted in Kiel, Germany (October 2017, November 2017, February 2018), with tanks filled from Kiel Fjord and sampled on Day 0, Day 5, and Day 10. Zooplankton abundance and composition were assessed from three 1 m³ replicates per tank and environmental parameters were measured. Generalized linear mixed-effects models revealed significantly lower abundances in tanks immediately after filling compared to pier water, with an overall ~74 % reduction. PERMANOVA confirmed significant community differences between pier and tank samples at Day 0 and pronounced temporal shifts within tanks. SIMPER analysis identified the taxa contributing most to initial differences and to the marked temporal shifts in community composition. Environmental fitting (nMDS + envfit) indicated that dissolved oxygen, temperature, salinity, and trace metals significantly correlated with community trajectories. The findings show that ballast water conditions rapidly restructure zooplankton communities through selective survival, even over short holding times, highlighting the ecological risks and the need for fine-scale monitoring to guide management
Micro-Seismicity to the South of the Louisville Ridge-Tonga Trench Collision Zone: New Insight into Processes Controlling Seismic Gaps and Subduction Erosion
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The chromosomal genome sequence of the sponge Cliona cf. orientalis Thiele (1900) and its associated microbial metagenome sequences
No full textWe present a genome assembly from a specimen of Cliona cf. orientalis (Porifera; Demospongiae; Clionaida; Clionaidae). The genome sequence has a total length of 217.17 megabases. Most of the assembly (98.28%) is scaffolded into 19 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 19.63 kilobases in length. Gene annotation of this assembly on Ensembl identified 25,502 protein-coding genes. Furthermore, three prokaryotic binned genomes were generated, including a high-quality metagenome-assembled genome (MAG) of the family Parvibaculaceae. Although Symbiodiniaceae sequences were also identified, a complete genome assembly could not be generated due to low coverage
Supplementary Data to: River discharge impacts coastal Southeastern Tropical Atlantic sea surface temperature and circulation: a model-based analysis
No full textLocalized nutrient colimitation of phytoplankton growth rates across the subtropical South Pacific Ocean
No full textThe simultaneous depletion of multiple nutrients in seawater potentially leads to colimitation of phytoplankton growth across large oceanic extents. Single limitation versus colimitation carries implications for mathematically predicting growth, its response to environmental forcing, and evaluating biogeochemical feedbacks. However, identifying colimited growth has proved challenging due to a lack of appropriate methods. Here, we present the results of 12 experiments conducted across the South Pacific that used a matrix of nutrient additions to strongly diluted surface seawater. Dilution restricted both grazing rates and nutrient drawdown due to phytoplankton accumulation. We find that despite simultaneous depletion of nitrate, phosphate, and iron concentrations throughout the oligotrophic gyre, community-level phytoplankton growth rates were only constrained by nitrogen. In contrast, zones of colimitation and serial limitation by nitrogen and iron were found along the eastern gyre margin. At the nitrogen-iron co-/serially limited sites, growth response surfaces to nutrient additions varied, suggesting the need for dynamic models to accurately represent colimited phytoplankton growth in the ocean.
Significance
Oceanic phytoplankton support marine food webs and influence global climate. Their growth typically depends on the availability of nutrients; principally nitrogen, phosphorus, and iron. An ongoing conundrum is whether multiple nutrient depletion leads to nutrient “colimitation” of phytoplankton growth rates. This has been difficult to address due to a lack of appropriate methods. Here, we use a different type of experiment to show that even when all three nutrients were simultaneously depleted across large extents of the South Pacific, phytoplankton growth was limited by nitrogen alone. However, we also found a zone where phytoplankton growth rates were robustly colimited by nitrogen and iron. Our initial findings suggest that alternative phytoplankton models might be needed to better understand ocean productivity