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The combined role of near-bed currents and sub-seafloor processes in the transport and pervasive burial of microplastics in submarine canyons
Get PDFSubmarine canyons are important conduits for microplastic transport to the deep sea, but the processes involved in that transport and how faithfully seafloor deposits record trends in pollution remain unclear. We use sediment push-cores for microplastic and sediment grain-size analysis from two transects across the Whittard Canyon, UK, to investigate the roles of near-bed flows and sub-seafloor processes in the transport and burial of microplastics and semi-synthetic microfibres. Microplastic and microfibre pollution is pervasive across the canyon at both transects, from the thalweg and from 500 m higher on the flanks, despite turbidity currents being confined to the canyon thalweg. We calculate sediment accumulation rates from 210 Pb dating and show that microplastic concentrations remain similar at sediment depths down to 10 cm. Throughout the Whittard Canyon there is an observed uniformity in the gradual decline in microfibre concentration with sediment depth, despite the variable sample locations and marked variations in sediment accumulation rates. Furthermore, the huge global increase in plastic production rates over time is not recorded, and microplastics are present in sediments that pre-date the mass-production of plastic. The interaction of turbidity currents, deep tidally-driven currents, and sub-seafloor processes affects microfibre burial processes in the deep sea and shreds any potential signal that microplastics may provide as indicators of historical plastic production rates; complicating the use of microplastics as fully-reliable markers of Anthropocene onset
Detection of Genes Encoding for Absorption of Hydrocarbons Degradation by Bacteria Isolated from Antarctica, Malaysia, and Indonesia
No full textPetroleum spills pose a significant threat to ecosystems due to the presence of hydrocarbons, the primary toxic components. Bioremediation, particularly using hydrocarbon-degrading bacteria, offers an eco-friendly solution for mitigating this pollution. The present study aims to detect genes specifically the alkB gene associated with hydrocarbon degradation in bacterial strains isolated from oil-contaminated environments. Bacteria were successfully isolated from two distinct locations, Antarctica and Pulau Pinang. Molecular identification using 16S rRNA gene sequencing revealed the isolates as Brevibacterium casei with 92.85% similarity. The detection of the alkB gene in these strains suggests their potential use in cost-effective and efficient bioremediation strategies for hydrocarbon-contaminated environments
Evaluation of CryoSat-2 ocean products through routine monitoring and a 13-year long consistent time series dataset
No full textCryoSat-2 (C2) was launched in 2010 and has been retrieving values of sea surface height anomaly (SSHA), significant wave height (SWH) and wind speed (WSP) ever since. Although these oceanographic variables were secondary aims, an operational CryoSat Ocean Processor was implemented in 2014. This study provides details on the routine monitoring process for the various products alongside additional analyses using a 13-year dataset of quality-controlled Baseline C data. Most of this study focussed on Low Resolution Mode (LRM) data with some specific studies of Synthetic Aperture Radar (SAR) mode. No substantial issues with the data were observed but additional studies of SWH and WSP are recommended.
Global mean sea level (GMSL) from C2 has a trend of 4.2±0.3 mm/year which agrees, within uncertainties, from other data sources. Regionally the patterns in SSHA trend agree with other sources. SWH from similar analyses found no significant trend but WSP trend was 3.3±0.2 (cm/s)/year. For GMSL and WSP data from descending passes (C2 moving south) have non-significantly higher trends compared to data from ascending passes. Regionally, apart from a few, small areas (primarily around Southeast Asia), trends in C2 WSP are positive and agree with a previous study using multiple altimeters.
Biases have been identified including between LRM and SAR using successive differences in SSHA, SWH and WSP. Similarly, seasonally varying biases between ascending passes and descending passes are found, which in turn vary by hemisphere.
Comparisons were made between tide gauges based on data from the Permanent Service for Mean Sea Level (PSMSL) and gridded (1˚) SSHA from C2. For both LRM and SAR, the significant correlations were positive and similar, albeit slightly lower, to previous studies.
Routine reports compare C2 SWH to that from the WaveWatch3 model (WW3) with the latter on average (mean) ∼15 cm higher with a few exceptions. This was confirmed using WW3 and C2 SWH on the same monthly grid where the difference was found to be 10 to 20 cm, and all correlations were positive (∼0.8–0.9). There are strong differences between C2 SWH and WW3 by hemisphere (bias is greater in Southern Hemisphere) and the variability of correlations is greater in the Northern Hemisphere. The relationship is more complex as there is some evidence that at low SWH WW3 tends to be higher than C2 whereas at higher SWH C2 SWH is higher than WW3.
There is a bias between C2 WSP and that from ERA5 that is negative (ERA5 WSP higher than C2 WSP) at higher WSP and a less pronounced positive bias at low WSP. Comparisons of trends in WSP from C2 compared to ERA5 are more complex and patterns in both do not fully match. These results are possibly as a result of altimeters being unable to resolve low WSP (<∼2 m/s)
Atmospheric forcing as a driver for ocean forecasting
Get PDFThe connection of the ocean component with the Earth system is subject to the way the atmosphere interacts with it. The paper illustrates the state of the art in the way atmospheric fields are used in ocean models as boundary conditions for the provisioning of the exchanges of heat, freshwater, and momentum fluxes. Such fluxes are typically based on numerical weather prediction (NWP) systems which ingest observations from remote sensing and in situ instruments. This study also discusses how the ocean–atmosphere fluxes are numerically ingested in ocean models from global to regional to coastal scales. Today's research frontiers on this topic are opening challenging opportunities for developing more sophisticated coupled ocean–atmosphere systems and improved ocean–atmosphere flux datasets
Summertime internal-wave properties along the SR1b section across Drake Passage
No full textThe Antarctic Circumpolar Current (ACC) connects all major oceans with a set of deep-reaching eastward frontal jets. When crossing large-amplitude topography the jets drive drive energetic internal waves, turbulence and mixing. Here we present an analysis of internal wave observations from 19 occupations of the SR1b repeat hydrography section across the ACC in the Scotia Sea. Internal-wave strength is quantified with vertical straining of the density stratification (strain), vertical shear of horizontal velocity (shear), vertical divergence of vertical velocity (divergence) and vertical kinetic energy (VKE). When temporally averaged, all four parameters show a consistent pattern with bottom-intensification over steep and rough topography but not elsewhere. Both the ACC jets and internal waves are anchored to seafloor topography. The internal waves are weak in the topographically smooth Ona Basin, even though the near-bottom currents there are stronger than where the ACC crosses the Scotia Ridge. Since vertical divergence, which has not been used in this context before, is both highly correlated with but also easier to measure than internal-wave shear, we propose the divergence-to-strain variance ratio as an alternative to the shear-to-strain variance ratio for quantifying the frequency content of the internal wave field. Along SR1b, both variance ratios, as well as the wavenumber spectral slopes of shear and VKE, show a consistent spatial pattern. Low values in the upper ocean along the entire section are associated with longer and higher-frequency waves. Highly variable and energetic waves are found in the deep ACC jets. Unexpectedly high variance ratios and spectral slopes, indicating preponderance of short, near-inertial waves in the deep Ona Basin, are attributed to critical layer absorption
Self-supervised learning with multimodal remote sensed maps for seafloor visual class inference
Get PDFSeafloor surveys often gather multiple modes of remote sensed mapping and sampling data to infer kilo- to mega-hectare scale seafloor habitat distributions. However, efforts to extract information from multimodal data are complicated by inconsistencies between measurement modes (e.g., resolution, positional offsets, geometric distortions) and different acquisition periods for dynamically changing environments. In this study, we investigate the use of location information during multimodal feature learning and its impact on habitat classification. Experiments on multimodal datasets gathered from three Marine Protected Areas (MPAs) showed improved robustness and performance when using location-based regularisation terms compared to equivalent autoencoder-based and contrastive self-supervised feature learners. Location-guiding improved F1 scores by 7.7% for autoencoder-based and 28.8% for contrastive feature learners averaged across 78 experiments on datasets spanning three distinct sites and 18 data modes. Location-guiding enhances performance when combining multimodal data, increasing F1 scores by an average of 8.8% and 37.8% compared to the best-performing individual mode being combined for autoencoder-based and contrastive self-supervised models, respectively. Performance gains are maintained over a large range of location-guiding distance hyperparameters, where improvements of 5.3% and 29.4% are achieved on average over an order-of-magnitude range of hyperparameters for the autoencoder and contrastive learners, respectively, both comparing favourably with optimally tuned conditions. Location-guiding also exhibits robustness to position inconsistencies between combined data modes, still achieving an average of 3.0% and 30.4% increase in performance compared to equivalent feature learners without location regularisation when position offsets of up to 10 m are artificially introduced to the remote sensed data. Our results show that the classifier used to delineate the learned feature spaces has less impact on performance than the feature learner, with probabilistic classifiers averaging 3.4% higher F1 scores than non-probabilistic classifiers
Predictive framework for estimating the risks to raptors from ecologically relevant exposure to second generation anticoagulant rodenticides
No full textGlobally, populations of many raptor species are declining for reasons including exposure to chemical contaminants. Second Generation Anticoagulant Rodenticide (SGAR) residues are commonly found in the livers of raptors, indicating dietary exposure and potentially secondary poisoning. There is a gap in our understanding of SGAR exposure for raptors at different life stages and under different usage regimes.
We develop a new modelling framework for non-target species to refine the commonly applied risk assessment using the common kestrel (Falco tinnunculus) as a case study. Our scenarios simulate high and low rodent consumption by raptors with high and low SGAR usage, of four different rodenticides at different raptor life stages. The risk to raptors was evaluated in reference to sublethal and lethal effect thresholds used by regulators.
Our model suggests exposure to Brodifacoum exceeds the threshold for lethal and sublethal effects. Breeding adults and nestlings are at risk of sublethal effects from Difethialone and the mixture of Bromadiolone and Difenacoum exposure. This is concerning because Brodifacoum and Difethialone usage seems to be rising globally due to increased resistance of rodents to other SGARs. Difethialone represents cumulative risk in scenarios previously not a risk, reaching the threshold in a week Avoiding SGAR usage during the raptor breeding season would reduce the likelihood and impact of secondary SGAR poisoning. Our framework can be used to assess different exposure scenarios for SGARs and raptors in ecological meaningful contexts to guide SGAR usage and regulation
Catalyzing change: a literature review on the implementation of the Nature Futures Framework
Get PDFThe Nature Futures Framework (NFF), developed under the Intergovernmental Science–Policy Platform on Biodiversity and Ecosystem Services (IPBES), serves as a catalyst for advancing new scenarios and models focused on biodiversity and ecosystem services within the broader research community. In particular, the framework facilitates the development of scenarios and models that can help guide change processes toward desirable futures for nature and people. This paper assesses 31 studies that have engaged with the NFF since its introduction in 2020, aiming to identify which research areas have been addressed, and where development needs remain. The applications exhibit a large diversity in terms of locations, spatial scales, methods, outputs, and stakeholder involvement. The most common use of the framework has been in developing visions and scenarios. Nearly all studies engaged with diverse values of nature through the framework’s fundamental value perspectives: ‘ Nature for Society ’, ‘ Nature for Natur e’, and ‘ Nature as Culture / One with Nature ’. While the framework is generally perceived as useful, challenges remain in integrating the NFF across multiple scales and fully incorporating plural values, particularly in measuring relational aspects and avoiding Western-centric biases. Future research priorities include developing integrated, quantitative studies and exploring transformative pathways to enhance the framework's effectiveness in driving sustainable outcomes. Overall, the growing body of work using the NFF provides a strong foundation for distilling best practices, facilitating large-scale applications, and achieving the framework's objectives
Extensive fluvial surfaces at the East Antarctic margin have modulated ice-sheet evolution
Get PDFAntarctic bed topography influences how the overlying ice sheet responds to climate change and provides a record of long-term glacial history. However, knowledge of the processes that governed the development of the landscape before glacial inception and how this modulated subsequent ice-sheet evolution remains limited. Here we use radio-echo sounding to reveal extensive flat surfaces beneath the ice margin between Princess Elizabeth Land and George V Land, East Antarctica. When their elevations are isostatically adjusted for unloading of the present-day ice load, these surfaces cluster at 200–450 metres above sea level and dip gently in an offshore direction. We show that the surfaces are fragments of a once-contiguous coastal plain formed by fluvial erosion, which dates from between the separation of East Antarctica from Australia (~100–80 Ma) and the onset of Southern Hemisphere ice-sheet glaciation (~34 Ma). The preservation of these landforms indicates a lack of intense, selective erosion of the surfaces throughout Antarctica’s glacial history. Fast-flowing ice has instead been directed through inherited tectonic structures and fluvial valleys, leading to the incision of overdeepened subglacial troughs between the flat surfaces and thus modulating the responsiveness of the ice sheet to climate change
Ancient environmental DNA indicates limited human impact on marine biodiversity in pre-industrial Iceland
Get PDFHuman activities are affecting marine biodiversity globally by accelerating extinction rates, altering ecosystem conditions and changing community structures. These changes can only be understood through establishing the ecosystem state prior to significant anthropogenic impact and by disentangling the anthropogenic effect from natural climatic changes. Here, we reconstruct marine biodiversity in Iceland across three millennia (1315 BCE–1785 CE), encompassing periods of climatic fluctuation and human settlement, to explore the comparative effect of natural and anthropogenic forces on marine biodiversity. We performed 18S metabarcoding of ancient environmental DNA from two sediment cores collected from northern Icelandic shelf seas, integrating local climatic records, population estimates and zooarchaeological remains from published sources to estimate the influence of climatic and anthropogenic impacts. Against the backdrop of increasing human populations and marine exploitation, we observe no large-scale taxonomic shifts or anthropogenic biodiversity changes across the period. In contrast, we found a positive correlation between herring ( Clupea harengus ) detection rates and proxy-reconstructed sea surface temperature, suggesting a role for climate in shaping marine biodiversity. Overall, our data suggest that despite impacts on terrestrial ecosystems and the development of a substantial export fishery across the study period, Icelandic society may have had a limited effect on marine biodiversity.
This article is part of the theme issue ‘Shifting seas: understanding deep-time human impacts on marine ecosystems’
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