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Exploring Silicon Isotope Fractionation by Silicoflagellates: Results from a KOSMOS Experiment off Peru
No full textThe Peruvian Upwelling is known for its exceptionally high surface water productivity and the presence of one of the world’s largest Oxygen Minimum Zones. The upwelling of silicate-rich subsurface waters typically supports diatom-dominated primary productivity in this region. However, warmer surface waters and subsequent changes in stratification and nutrient supply can cause a shift in plankton communities from diatoms to dinoflagellates and silicoflagellates, which affects the silicon (Si) and carbon (C) cycles.
In 2017, we investigated the Si cycle in a field experiment off the coast of Peru. Pelagic mesocosms (~55,000 L) were deployed for 50 days from February to April to simulate upwelling conditions, which coincided with a coastal El Niño. This unique setting allowed us to study the evolution of stable silicon isotopes in seawater (δ30SidSi) and its direct comparison to the produced biogenic material (δ30SibSi) without the influence of unaccountable water mass mixing. On day 12, approximately 40 % of the surface water of the mesocosms was replenished with nitrate-depleted deep water (low N:Si and N:P ratios), which strongly influenced the phytoplankton community. Prior to the addition of the deep water, the phytoplankton community was dominated by diatoms but shifted towards a pronounced dominance of flagellates, including silicoflagellates. At the beginning of the experiment, when diatoms dominated the phytoplankton community, the δ30SidSi distribution in the surface water (+1.4 ‰ to +2.5 ‰) was within the same range as observed in previous seawater studies in the Peruvian upwelling. After deep water addition, low N:Si (0.02 to 0.2 mol/mol), strongly deviating from the preferred 1:1 ratios for diatoms, favored silicoflagellate (and dinoflagellate) growth and resulted in higher δ30SidSi values (up to +4.1 ‰) in the surface waters. The strong increase in δ30SidSi was associated with low δ30SibSi values (-0.26 to +0.65 ‰) caused by high fractionation factors of stable silicon isotopes between seawater and silicoflagellates. For the first time, the field experiment allowed us to determine the Si isotope fractionation factor for silicoflagellates (ε30silico = -3.63 ‰), which is remarkably high compared to diatoms (-1.1 ‰) and offers a novel tool to study changes in the present and past marine silicon cycle
Ocean-bottom seismometers document how submarine landslides develop and grow
No full textSubmarine landslides reshape seafloor geomorphology, transport sediment and carbon to the deep-sea, and can trigger tsunamis or damage valuable seabed infrastructure. Yet, submarine landslides have never been directly observed in action. Here, we present the most detailed measurements yet of an ongoing submarine landslide using high-frequency (1-10 Hz) ground motions captured by an ocean-bottom seismometer placed in the vicinity of the slide's source region. We tracked a similar to 0.00423 km(3) flank collapse in the Congo Canyon, and reveal its triggers and chronology of movement, thereby testing fundamental landslide models. A powerful turbidity current undercut the canyon wall, and landslide failure initiated at the base-of-slope. The landslide retrogressed 1.3 km upslope for 15 minutes in 1-2 min pulses, interspersed with brief downslope movement. Retrogression speeds ranged from 1.6 to 5.8 m/s, and downslope movement speeds from 0.8 to 3.3 m/s. Once the failure reached its upslope limit, the landslide transitioned into 1.5 hours of pulsed sediment transport, which fed a turbidity current along the canyon-axis. These observations show seismic monitoring can produce major advances in the understanding of submarine landslides. They challenge simple "toe-backward" and "head-forward" collapse models, revealing a hybrid, bottom-up retrogressive process that only released sediment after climbing far upslope
Quaternary deep-thermocline cooling enhanced by southern Pacific Ocean tunnelling
No full textTropical climate is considered to be one of the decisive keys to global climate dynamics. The extent to which extratropical forcing mechanisms contributed to changes of tropical heat and thus global changes in the climate system, however, is only poorly understood. Here, we reconstruct early Quaternary hydrographic variability of the tropical deep thermocline of the eastern margin of the West Pacific Warm Pool using magnesium to calcium and oxygen isotope ratios of surface and deep-dwelling foraminifera. This approach allows to determine past ocean temperatures and relative salinity changes likely related to extratropical oceanographic reorganisations. Our proxy records point to a freshening of the tropical Pacific deep-thermocline and exhibit a strong coupling to the volume increase of the Antarctic ice shield and cooling of high/mid latitude surface water masses at 1.5 Ma. This temporal coincidence is accompanied by the progressive increase in Earths obliquity amplitude and suggests high latitude climate impact via ocean tunnelling of southern-sourced sub-surface water masses towards the equatorial Pacific. We hypothesize that ocean tunnelling of mid-latitude Southern Ocean/South Pacific water to the West Pacific Warm Pool effectively contributed to global climate between 1.7 Ma and 1.2 Ma prior the Mid-Pleistocene-Transition, particularly through changes in oceanic heat budget across vast latitudinal ranges
The chromosomal genome sequence of the Maltese sponge, Agelas oroides (Schmidt, 1864), and its associated microbial metagenome sequences
No full textWe present a genome assembly from a specimen of Agelas oroides (Maltese sponge; Porifera; Demospongiae; Agelasida; Agelasidae). The genome sequence has a total length of 260.66 megabases. Most of the assembly (98.43%) is scaffolded into 23 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 22.44 kilobases in length. Gene annotation of this assembly on Ensembl identified 23,435 protein-coding genes. The metagenome of the specimen was also assembled, and 138 binned bacterial genomes were identified, including 82 high-quality MAGs that were representative of a typical high microbial abundance sponge and included besides the phyla Thermoproteota (Cenarchaeum), Chloroflexota (Dehalococcoidea), Acidobacteriota (Vicinamibacterales), Alpha- and Gammaproteobacteria (Pseudomonadota) and others, also several candidate phyla (Candidatus Paceibacterota, Poribacteria, Binatia and Latescibacteria)
The chromosomal genome sequence of the marine sponge Diacarnus erythraeanus Kelly-Borges & Vacelet, 1995, and its associated microbial metagenome sequences
No full textWe present a genome assembly from an individual Diacarnus erythraeanus (sponge; Porifera; Demospongiae; Poecilosclerida; Podospongiidae). The genome sequence has a total length of 140.86 megabases. Most of the assembly (98.57%) is scaffolded into 18 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 19.34 kilobases in length. Sixty-four binned genomes were generated from the metagenome assembly, of which 46 were classified as high-quality metagenome assembled genomes (MAGs). The microbial signature is typical of HMA sponges, including the Pseudomonadota, Chloroflexota and Acidobacteriota as dominant phyla and several candidate phyla (Poribacteria, Binatota, Latescibacterota) as well as the archaeal clade Nitrosopumilaceae in lower abundance
Nitrous oxide (N 2 O) in the sea surface microlayer and underlying water during a phytoplankton bloom: a mesocosm study
No full textNitrous oxide (N2O) is an important climate-relevant atmospheric trace gas. The open and coastal oceans are a major source for atmospheric N2O. However, its production and consumption pathways in the ocean are not well-known and its emissions estimates are associated with a high degree of uncertainty. Potential N2O production pathways in the oxic surface ocean include microbial nitrification, release from phytoplankton and photochemodenitrification. In order to decipher the effect of a phytoplankton bloom on dissolved N2O concentrations, N2O was measured – for the first time – in the sea surface microlayer (SML, i.e. the upper 1 mm of the water column) and in the corresponding underlying water (ULW) during a mesocosm study with Jade Bay (southern North Sea) water from 16 May to 16 June 2023. N2O concentrations were slightly enriched in the SML compared to the ULW although the difference of the mean N2O concentrations between the ULW and SML was statistically not significant. However, the enrichment of N2O in the SML was most probably underestimated due to the loss of N2O during sampling with the glass plate method. N2O was supersaturated (100 %–157 %) in the ULW and SML during the course of the study which indicated an in-situ production of N2O. N2O in-situ production was most probably driven by photochemodenitrification in combination with the release from phytoplankton whereas microbial production of N2O via nitrification appeared to be of minor importance. N2O concentrations in both the ULW and the SML were remarkably constant over time and were apparently not affected by irradiation and a phytoplankton bloom which was triggered by nutrient additions. We therefore conclude that the N2O in-situ sources were balanced by the release of N2O to the atmosphere resulting in a steady state of the system. Our results indicate that the role of the SML for N2O cycling in the surface ocean and its emissions to the atmosphere has been overlooked so far. Moreover, our results are in line with results from field studies which showed that phytoplankton blooms in the ocean do not result in temporarily enhanced N2O concentrations in the ocean surface layer
Ocean Turbulent Heat Flux Responses to Sea Surface Salinity Variability During Benguela Niños and Niñas
No full textBenguela Ni & ntilde;o and Ni & ntilde;a events are episodes of extreme warming and cooling off Angola with impacts on fisheries, ecosystems, and rainfall in southwest Africa. They are typically forced remotely or locally by variations in equatorial or alongshore winds, respectively. We use an extensive in-situ data set to show that sea surface salinity (SSS) changes can also act as a local forcing that amplifies these extreme warm and cold events by altering the water column stratification and consequently the impact of subsurface mixing. The mixed layer turbulent heat loss during an extreme warm episode with unusually low SSS in 1995 is nearly 3x lower than during a cold event with high SSS in 1997. We also demonstrate that interannual turbulent heat flux variability in early boreal spring off Angola is strongly impacted by salt advection fluctuations, and that this turbulent mixing is significant for altering mixed layer temperatures and restoring its salinities.
Key Points:
- Anomalous sea surface salinity can amplify Benguela Niño and Ninã events via changes in stratification and in turbulent heat fluxes
- Stratification anomalies led to nearly three times more cooling from turbulent heat fluxes during the 1997 cold event in comparison to the 1995 warm episode
- For constant dissipation rates of turbulent kinetic energy, anomalous salt advection drives 53% of Angola's spring heat flux variabilit
Ecological and Evolutionary Dynamics of Invasive Species Under Global Change
No full textThe Anthropocene is characterized by accelerating changes in climate, land use, pollution, and global connectivity, largely reshaping ecosystems across spatial and temporal scales (Keys et al. 2019; Willcock et al. 2023). These rapid transformations frequently outpace the adaptive capacity of native species, contributing to widespread biodiversity loss and, possibly, to a 6th mass extinction (Barnosky et al. 2011; Hoffmann and Sgrò 2011). In contrast, invasive species often thrive in disturbed environments, thereby further exacerbating ecological disruptions across diverse ecosystems (Gu et al. 2023). As such, biological invasions have emerged not only as a consequence of global change but also as a significant driver of further environmental degradation (Sage 2020). Increasingly, evidence indicates that the interactions between biological invasions and other global change drivers are complex, nonlinear, and can often produce unexpected economic, ecological, or evolutionary outcomes (Ricciardi et al. 2021; Hu et al. 2025). For example, global change-induced environmental extremes can result in rapid evolution in invasive species, which can enhance the probability of invasion success and alter species interactions and ecosystem functioning (Moran and Alexander 2014; Borden and Flory 2021). Thus, there exists an urgent need to deepen our understanding of the complex ecological and evolutionary dynamics underlying interactions between biological invasions and global change, and, more importantly, to develop effective management solutions
Coupling hydrodynamic drifting simulations and seasonal demographics to unmask the drivers of jellyfish blooms
No full textAbstract
Although jellyfish are an important component of coastal marine communities, their public perception is often tainted by their proclivity for aggregating in vast numbers, known as jellyfish blooms. Jellyfish blooms occur worldwide and are associated with major economic ramifications, particularly throughout the fisheries, aquaculture and tourism sectors. Predicting jellyfish blooms is crucial for managing and mitigating their ecological and economic impacts, but the complex life cycles and cryptic life stages exhibited by most jellyfish species largely preclude accurate predictions of their temporal and spatial occurrence.
Here, we introduce a framework, combining state-of-the-art hydrodynamic simulations and periodic population modelling approaches, to simulate spatial and temporal patterns in the formation of jellyfish blooms. While this framework is sufficiently flexible for accommodating various bloom-forming jellyfish species and impacted coastal regions worldwide, we focus on moon jellyfish (Aurelia aurita) populations within the Baltic Sea as an illustrative example.
We emphasise how this framework can provide valuable insights for resolving key gaps in our understanding of the drivers of bloom events. Indeed, by doing so, this tool will help to guide the future collection of data needed to predict the locations and timings of their formation.
Synthesis and applications. Crucially, the framework we present here offers an approach for identifying the, to date, unknown locations of polyp beds; a key parameter in enhancing our capacity to accurately predict the occurrence of jellyfish blooms. Accordingly, this framework represents a key decision-support tool for mitigating the socio-economic impacts of bloom formation