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Validation of full resolution remote sensing reflectance from Sentinel-3 OLCI across optical gradients in moderately turbid transitional waters
Get PDFEstuarine and coastal transitional waters present a challenge for the interpretation of radiometric remote sensing. Neighbouring water masses have strongly contrasting optical properties at small spatial scales. Adjacency of land adds optical contaminations (adjacency effect) and further complicates satellite use in near-shore waters. In these areas, the lack of in situ observations has been the bottleneck for the characterisation of the uncertainty of satellite products. Radiometric underway measurements (e.g., ferries, ships of opportunity, autonomous vehicles) produce large volumes of in situ observations that can be used for radiometric validation. In this study, we evaluate the performance of the POLYMER atmospheric correction algorithm for the Ocean and Land Colour Instrument (OLCI) onboard Sentinel-3 (S3) for the retrieval of remote sensing reflectance R rs (λ) in the transitional waters of Plymouth, United Kingdom using hyperspectral radiometric underway measurements. We explored the effect of the selection of time window, averaged areas around the in situ measurement and quality control flags into the matchup procedure. We selected matchups only within 1 pixel and ±30 min of the satellite overpass. Accuracy (RMSD) decreased spectrally from blue to red wavelengths (from 0.0015 to 0.00025 sr −1 ) and bias (Median Percentage Difference) was mostly positive (up to more than 100%) in relation to in situ observations. We segregated the dataset with respect to optical water types and distance to shore. Although no statistically significant difference was observed among those factors on the measures of performance for the reflectance retrieval, RMSD was the most sensitive metric. Our study highlights the potential to use OLCI full resolution imagery in nearshore areas and the need for more in situ data to be collected in the more turbid waters
Development of a Maximum Specific Photosynthetic Rate Algorithm Based on Remote Sensing Data: a Case Study for the Atlantic Ocean
Get PDFNew regional empirical algorithms were developed to obtain maximum specific photosynthetic
rates of phytoplankton ( ) in the surface layer of the Atlantic Ocean. These algorithms were based on the
dependence of on seawater temperature. Sea Surface Temperature remote sensing data and the PANGAEA
global database of photosynthesis–irradiance parameters were used to test the algorithm. In addition, the
variability in , both spatially (from 60° S to 85° N) and seasonally, (2002–2013) was estimated. The highest
was obtained in December in areas of deep convection and the interaction between the Labrador Current
and the Gulf Stream, while minimum values were observed in the northern and equatorial–tropical parts of
the ocean during the time intervals between the phytoplankton blooms (March to September–October). In
addition, existing and algorithms used in primary production models, as well as the algorithm devel�oped using temperature and chlorophyll a data from AMT-29, which were then tested using the PANGAEA
dataset. The results show that the new algorithm developed using seawater temperature data with region�ally adjusted empirical coefficients correlated best with the in situ data
The genome sequence of the black-footed limpet, Patella depressa (Pennant, 1777)
No full textWe present a genome assembly from an individual Patella depressa (the black-footed limpet; Mollusca; Gastropoda; Patellogastropoda; Patellidae). The genome sequence is 683.7 megabases in span. Most of the assembly is scaffolded into 9 chromosomal pseudomolecules. Gene annotation of this assembly on Ensembl identified 20,502 protein coding gene
The structure and diversity of macroinvertebrate assemblages associated with the understudied pseudo-kelp Saccorhiza polyschides in the Western English Channel (UK)
No full textWe examined spatiotemporal variability in the structure of faunal assemblages associated with the warm-temperate pseudo-kelp Saccorhiza polyschides towards its range centre (Western English Channel, southwest UK), to better understand its role as a habitat-former in the northeast Atlantic. A total of 180 sporophytes and their associated fauna were sampled across three months, three sites, and two depths. Assemblage abundance and biomass varied markedly between three morpho-functional sporophyte components (i.e., holdfast, stipe, blade). We recorded rich and abundant macroinvertebrate assemblages, comprising nine phyla, 28 coarse taxonomic groups, and 57 species of molluscs, which consistently dominated assemblages. We observed pronounced seasonality in faunal assemblage structure, marked variability between sites and depths, and strong positive relationships between biogenic habitat availability and faunal abundance/biomass. S. polyschides sporophytes are short-lived and offer temporary, less-stable habitat compared with dominant perennial Laminaria species, so shifts in the relative abundances of habitat-formers will likely alter local biodiversity patterns
Comparison of ocean-colour algorithms for particulate organic carbon in global ocean
Get PDFIn the oceanic surface layer, particulate organic carbon (POC) constitutes the biggest pool of particulate material of biological origin, encompassing phytoplankton, zooplankton, bacteria, and organic detritus. POC is of general interest in studies of biologically-mediated fluxes of carbon in the ocean, and over the years, several empirical algorithms have been proposed to retrieve POC
concentrations from satellite products. These algorithms can be categorised into those that make use of remote-sensing-reflectance data directly, and those that are dependent on chlorophyll concentration and particle backscattering
coefficient derived from reflectance values. In this study, a global database of in situ measurements of POC is assembled, against which these different types of
algorithms are tested using daily matchup data extracted from the Ocean Colour Climate Change Initiative (OC-CCI; version 5). Through analyses of residuals, pixel-by-pixel uncertainties, and validation based on optical water types, areas for POC algorithm improvement are identified, particularly in regions underrepresented in the in situ POC data sets, such as coastal and highlatitude waters. We conclude that POC algorithms have reached a state of
maturity and further improvements can be sought in blending algorithms for different optical water types when the required in situ data becomes available. The best performing band ratio algorithm was tuned to the OC-CCI version 5
product and used to produce a global time series of POC between 1997–2020 that is freely available
Projecting the impacts of climate change in the Atlantic Ocean: a global ocean downscaling approach
No full textThe latest generation CMIP6-class Earth system models (ESMs) are a great tool for projecting climate variability on multi-centennial and global scales as they are designed to explicitly represent the process-coupling amongst the different Earth system components (atmosphere, ocean, land, cryosphere, biosphere) and prioritise system robustness such as minimisation of drift. However, CMIP6-ESMs do not accurately represent the fine-scale circulation and water-masses in ocean margins and shelf seas since by design: (i) their resolution is too coarse and so they only implicitly include regional-scale processes or even exclude these processes (particularly shelf-seas related processes); and (ii) their initialisation from a steady state leads to their divergence from reality and present-day conditions. To address these shortcomings and project the impacts of climate change in the Atlantic Ocean with focus on regional scales, we downscale globally an ensemble of future ocean projections with a NEMO-ERSEM coupled hydrodynamic-ecosystem model. Here, we discuss the design-methodology for our global ocean downscaling experiment: (i) selection of future scenarios, (ii) initialisation from “real” ocean conditions, (iii) selection of the CMIP6-ESMs atmospheric conditions to force our model based on their realism and uncertainty span, and (iv) treatment of the river runoffs as to impose both a realistic rivers state and a future trend consistent with CMIP6-ESMs. Comparisons of our global ocean downscaling simulations to CMIP6-ESMs during the historical period demonstrate their added value in terms of representation of physical ocean conditions and circulation in the Atlantic Ocean. We also present preliminary analysis in terms of future trends in temperature, salinity and circulation patterns in the Atlantic Ocean, with focus on regional features like changes in the Gulf Stream and trends in coastal regions
Catch yield and selectivity of a modified scallop dredge to reduce seabed impact
Get PDFGlobal scallop fisheries are economically important but are associated with environmental impacts to seabed communities resulting from the direct physical contact of the fishing gear with the seabed. Gear modifications attempting to reduce this contact must be economically feasible such that the catch numbers for the target species is maintained or increased. This study investigated the outcome of reducing seabed contact on retained catch of scallops and bycatch by the addition of skids to the bottom of the collecting bag of scallop dredges. We used a paired control experimental design to investigate the impact of the gear modification in different habitat types. The modified skid dredge generally caught more marketable scallops per unit area fished compared with the standard dredge (+5%). However, the skid dredge also retained more bycatch (+11%) and more undersize scallops (+16%). The performance of the two dredges was habitat specific which indicates the importance of adjusting management measures in relation to habitat type. To realize the potential environmental benefits associated with the improvement in catchability of this gear modification, further gear modification is required to reduce the catch of undersize scallops and bycatch. Furthermore we advocate that technical gear innovations in scallop dredging need to be part of a comprehensive and effective fisheries management system
Exceptional atmospheric conditions in June 2023 generated a northwest European marine heatwave which contributed to breaking land temperature records
Get PDFThe Northwest European shelf experienced unprecedented surface temperature anomalies in June 2023 (anomalies up to 5 °C locally, north of Ireland). Here, we show the shelf average underwent its longest recorded category II marine heatwave (16 days). With state-of-the-art observation and modelling capabilities, we show the marine heatwave developed quickly due to strong atmospheric forcing (high level of sunshine, weak winds, tropical air) and weak wave activity under anticyclonic
weather regimes. Once formed, this shallow marine heatwave fed back on the weather: over the sea it reduced cloud cover and over land it contributed to breaking June mean temperature records and to enhanced convective rainfall through stronger, warmer and moister sea breezes. This marine heatwave was intensified by the last 20-year warming trend in sea surface temperatures. Such sea surface temperatures are projected to become commonplace by the middle of the century under a
high greenhouse gas emission scenario
Seasonal patterns of microbial diversity across the world oceans
Get PDFUnderstanding the patterns of marine microbial diversity (Bacteria + Archaea) is essential, as variations in their alpha‐ and beta‐diversities can affect ecological processes. Investigations of microbial diversity from global oceanographic expeditions and basin‐wide transects show positive correlations between microbial diversity and either temperature or productivity, but these studies rarely captured seasonality, especially in polar regions. Here, using multiannual alpha‐diversity data from eight time series in the northern and southern hemispheres, we show that marine microbial community richness and evenness generally correlate more strongly with daylength than with temperature or chlorophyll a (a proxy for photosynthetic biomass). This pattern is observable across time series found in the northern and southern hemispheres regardless of collection method, DNA extraction protocols, targeted 16S rRNA hypervariable region, sequencing technology, or bioinformatics pipeline
A global overview of marine heatwaves in a changing climate
No full textMarine heatwaves have profoundly impacted marine ecosystems over large areas of the world oceans, calling for improved understanding of their dynamics and predictability. Here, we critically review the recent substantial advances in this active area of research, including the exploration of the three-dimensional structure and evolution of these extremes, their drivers, their connection with other extremes in the ocean and over land, future projections, and assessment of their predictability and current prediction skill. To make progress on predicting and projecting marine heatwaves and their impacts, a more complete mechanistic understanding of these extremes over the full ocean depth and at the relevant spatial and temporal scales is needed, together with models that can realistically capture the leading mechanisms at those scales. Sustained observing systems, as well as measuring platforms that can be rapidly deployed, are essential to achieve comprehensive event characterizations while also chronicling the evolving nature of these extremes and their impacts in our changing climat