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Antarctic krill sequester similar amounts of carbon to key coastal blue carbon habitats
Get PDFThe carbon sequestration potential of open-ocean pelagic ecosystems is vastly under-reported compared to coastal vegetation ‘blue carbon’ systems. Here we show that just a single pelagic harvested species, Antarctic krill, sequesters
a similar amount of carbon through its sinking faecal pellets as marshes, mangroves and seagrass. Due to their massive population biomass, fast�sinking faecal pellets and the modest depths that pellets need to reach to achieve sequestration (mean is 381 m), Antarctic krill faecal pellets sequester
20 MtC per productive season (spring to early Autumn). This is equates USD$ 4 − 46 billion depending on the price of carbon, with krill pellet carbon stored for at least 100 years and with some reaching as far as the North Pacific. Antarctic krill are being impacted by rapid polar climate change and an expanding fishery, thus krill populations and their habitat warrant protection to preserve this valuable carbon sink
Biofouling and corrosion rate of welded Nickel Aluminium Bronze in natural and simulated seawater
Get PDFUpdated understanding on the effect of biofouling on corrosion rate is needed to protect marine structures as climate change is altering seawater physiochemistry and biofouling organism distribution. Multi-disciplinary techniques can improve understanding of biofouling development and associated corrosion rates on metals immersed in natural seawater (NSW). In this study, the development of biofouling and corrosion on welded Nickel Aluminium Bronze (NAB) was investigated through long-term immersion tests in NSW, simulated seawater (SSW) and air. Biofouling was affected by geographic location within the marina and influenced corrosion extent. The corrosion rate of NAB was accelerated in the initial months of exposure in NSW (1.27 mm.yr−1) and then settled to 0.11 mm.yr−1 (annual average). This was significantly higher than the0.06 mm.yr−1 corrosion rate measured in SSW, which matched published rates. The results suggest that corrosion rates for cast NAB should be revised to take account of biofouling and updated seawater physiochemistr
Eddy detection inverted from Argo profiles to surface altimetry
Get PDFArgo floats are widely used to characterize vertical structures of ocean eddies, yet their capability to invert sea surface features of eddies, especially those overlooked by available altimeters, has not been explored. In this paper, we propose an “interior-to-surface” inversion algorithm to effectively expand the capacity of eddy detection by estimating altimeter-missed eddies’ surface attributes from their Argo-derived potential density anomaly profiles, given that the interior property and surface signature of eddies are highly correlated. An altimeter-calibrated machine learning ensemble is employed for the inversion training based on the joint altimeter–Argo eddy data and shows promising performance with mean absolute errors of 5.4 km, 0.5 cm, and 14.3 cm2 s−2 for eddy radius, amplitude, and kinetic energy, respectively. Then, the trained ensemble model is applied to independently invert the properties of eddies captured by an Argo-alone detection scheme, which yields high spatiotemporal consistency with their altimeter-captured counterparts. In particular, a portion of Argo-alone eddies is ∼25% smaller than altimeter-derived ones, indicating Argo’s unique capability of profiling weaker submesoscale eddies. Sea surface temperature and chlorophyll data are further applied to validate the reliability of eddies identified and characterized by the Argo-only algorithm. This new methodology effectively complements that of altimetry in eddy detection and can be expanded to estimate other physical/biochemical eddy variables from a variety of in situ observations
Framework for Regional to Global Extension of Optical Water Types for Remote Sensing of Optically Complex Transitional Water Bodies
Get PDFWater quality indicator algorithms often separate marine and freshwater systems, introducing artificial boundaries and artifacts in the freshwater to ocean continuum. Building upon the Ocean Colour- (OC) and Lakes Climate Change Initiative (CCI) projects, we propose an improved tool to assess the interactions across river–sea transition zones. Fuzzy clustering methods are used to generate optical water types (OWT) representing spectrally distinct water reflectance classes, occurring within a given region and period (here 2016–2021), which are then utilized to assign membership values to every OWT class for each pixel and seamlessly blend optimal in-water algorithms across the region. This allows a more flexible representation of water provinces across transition zones than classic hard clustering techniques. Improvements deal with expanded sensor spectral band-sets, such as Sentinel-3 OLCI, and increased spatial resolution with Sentinel-2 MSI high-resolution data. Regional clustering was found to be necessary to capture site-specific characteristics, and a method was developed to compare and merge regional cluster sets into a pan-regional representative OWT set. Fuzzy clustering OWT timeseries data allow unique insights into optical regime changes within a lagoon, estuary, or delta system, and can be used as a basis to improve WQ algorithm performance
Intertidal seagrass extent from Sentinel-2 time-series show distinct trajectories in Western Europe
No full textIntertidal areas, which emerge during low tide, form a vital link between terrestrial and marine environments. Seagrasses, a well-studied intertidal habitat, provide a multitude of different ecosystem goods and services. However, owing to their relatively high exposure to anthropogenic impacts, seagrasss meadows and other intertidal habitats have seen extensive declines. Remote sensing methods that can capture the spatial and temporal variation of marine habitats are essential to best assess the trajectories of seagrass ecosystems. An advanced machine learning method has been developed to map intertidal vegetation from satellite-derived surface reflectance at a 12-band multispectral resolution and distinguish between similarly pigmented intertidal macrophytes, such as seagrass and green algae. The Intertidal Classification of Europe: Categorising Reflectance of Emerged Areas of Marine vegetation with Sentinel-2 (ICE CREAMS v1.0), a neural network model trained on over 300,000 Sentinel-2 pixels to identify different intertidal habitats, was applied to the open-access long term archive of systematically collected Sentinel-2 imagery to provide 7 years (2017–2023) worth of intertidal seagrass dynamics in 6 sites across Western Europe (471 Sentinel-2 Images). A combination of independently collected visually inspected Uncrewed Aerial Vehicle imagery and in situ quadrat images were used to validate ICE CREAMS. Having achieved a high seagrass classification accuracy (0.82 over 12,000 pixels) and consistent conversion into cover (19% RMSD), the ICE CREAMS model outputs provided evidence of site specific variation in trajectories of seagrass extent, when appropriate consideration of intra-annual variation has been considered. Inter-annual dynamics of sites showed some instances of consistent change, some indicated stability, while others indicated instability over time, characterised by increases and decreases across the time-series in seagrass coverage. This methological pipeline has helped to create up-to-date monitoring data that, with the planned continuation of the Sentinel missions, will allow almost real-time monitoring of these habitats into the future. This process, and the data it provides, could aid management practitioners from regional to international levels, with the ability to monitor intertidal seagrass meadows at both high spatial and temporal resolution, over continental scales. The implementation of Earth Observation for high-resolution monitoring of intertidal seagrasses could therefore allow for gap-filling seagrass datasets, and sustain specific and rapid management measure
Long-term changes in spatiotemporal distribution of Noctiluca scintillans in the southern North Sea
No full textTo assess the spatiotemporal evolution of the heterotrophic dinoflagellate Noctiluca scintillans in the North Sea, the Helgoland Roads time series and Continuous Plankton Recorder survey were analysed using generalized additive models. Over the last decades, blooms of N. scintillans have occurred more frequently and intensively in many regions. This harmful algal bloom forming species can alter food webs, reduce ecosystem productivity, and lead to economic losses while causing lower aquacultural yields. After the 1990s, N. scintillans abundances have significantly increased by 1.65-fold and a significant prolongation of the bloom window was found (from 27.5 to 98 days in recent decades) off the island of Helgoland, Germany. Significant correlations were found between bloom initiation and nutrients, as well as light availability since these factors lead to increased prey availability. Highest abundances of N. scintillans were associated with water temperatures around 17 °C and wind speed below 6 ms−1 causing dense surface accumulations. Solar radiation of more than 200 Wm−2 was identified as a main driver for post-bloom conditions as it can deteriorate the cells and lead to the decline of N. scintillans abundances. In the southern North Sea, N. scintillans occurrences have intensified and spread since the 1980s with hotspots identified as the coastal waters adjacent to the estuaries of the Elbe and Rhine river
Investigating the effects of mobile bottom fishing on benthic carbon processing and storage: a systematic review protocol
Get PDFBackground Marine sediments represent one of the planet’s largest carbon stores. Bottom trawl fisheries constitute
the most widespread physical disturbance to seabed habitats, which exert a large influence over the oceanic carbon
dioxide (CO2) sink. Recent research has sparked concern that seabed disturbance from trawling can therefore turn
marine sediments into a large source of CO2, but the calculations involved carry a high degree of uncertainty. This is primarily due to a lack of quantitative understanding of how trawling mixes and resuspends sediments, how it alters bioturbation, bioirrigation, and oxygenation rates, and how these processes translate into carbon fluxes into or out of sediments.
Methods The primary question addressed by this review protocol is: how does mobile bottom fishing affect benthic
carbon processing and storage? This question will be split into the following secondary questions: what is the effect
of mobile bottom fishing on: (i) the amount and type of carbon found in benthic sediments; (ii) the magnitude and
direction of benthic-pelagic carbon fluxes; (iii) the biogeochemical, biological, and physical parameters that control the fate of benthic carbon; and (iv) the biogeochemical, biological, and physical parameters that control the fate of resuspended carbon. Literature searches will be conducted in Web of Science, SCOPUS, PROQUEST, and a range of grey and specialist sources. An initial scoping search in Web of Science informed the final search string, which has been formulated according to Population Intervention Comparator Outcome (PICO) principles. Eligible studies must contain data concerning a change in a population of interest caused by mobile bottom fishing. Eligible study designs are Before and After, Control and Impact, and Gradient studies. Studies included at full-text screening will be critically appraised, and study findings will be extracted. Extracted data will be stored in an Excel spreadsheet. Results will be reported in narrative and quantitative syntheses using a variety of visual tools including forest plots. Meta-analysis will be conducted where sufficient data exist
Enhanced ocean CO2 uptake due to near-surface temperature gradients
Get PDFThe ocean annually absorbs about a quarter of all anthropogenic carbon dioxide (CO2) emissions. Global estimates of air–sea CO2 fuxes are typically based on bulk measurements of CO2 in air and seawater and neglect the
efects of vertical temperature gradients near the ocean surface. Theoretical and laboratory observations indicate that these gradients alter air–sea CO2 fuxes, because the air–sea CO2 concentration diference is highly temperature sensitive. However, in situ feld evidence supporting their
efect is so far lacking. Here we present independent direct air–sea CO2 fuxes alongside indirect bulk fuxes collected along repeat transects in the Atlantic Ocean (50° N to 50° S) in 2018 and 2019. We fnd that accounting for vertical temperature gradients reduces the diference between direct
and indirect fuxes from 0.19 mmol m−2 d−1 to 0.08 mmol m−2 d−1 (N = 148). This implies an increase in the Atlantic CO2 sink of ~0.03 PgC yr−1 (~7% of the Atlantic Ocean sink). These feld results validate theoretical, modelling
and observational-based eforts, all of which predicted that accounting for near-surface temperature gradients would increase estimates of global ocean CO2 uptake. Accounting for this increased ocean uptake will probably require some revision to how global carbon budgets are quantife
Dimethyl sulfide (DMS) climatologies, fluxes, and trends – Part 1: Differences between seawater DMS estimations
Get PDFDimethyl sulfide (DMS) is a naturally emitted trace gas that can affect the Earth's radiative budget by changing cloud albedo. Most atmospheric models that represent aerosol processes depend on regional or global distributions of seawater DMS concentrations and sea–air flux parameterizations to estimate its emissions. In this study, we analyse the differences between three estimations of seawater DMS, one of which is an observation-based interpolation method following Hulswar et al. (2022) (hereafter referred to as H22) and two of which are proxy-based parameterization methods following Galí et al. (2018) (hereafter referred to as G18) and Wang et al. (2020a) (hereafter referred to as W20). The interpolation-based method depends on the distribution of observations and the methods used to fill data between observations, while the parameterization-based methods rely on establishing a relationship between DMS and environmental parameters such as chlorophyll a, mixed-layer depth, nutrients, sea surface temperature, etc., which can then be used to predict DMS concentrations. On average, the interpolation-based methods show higher DMS values compared to the parameterization-based methods. Even though the interpolation method shows higher values than the parameterization-based methods, it fails to capture mesoscale variability. The regression-based parameterization method (G18) shows the lowest values compared to other estimations, especially in the Southern Ocean, which is the high-DMS region in austral summer. The parameterization-based methods suggest positive long-term trends in seawater DMS (3.82±0.79 % per decade for G18 and 2.13±0.32 % per decade for W20). Since large differences, often more than 100 %, are observed between the different estimations of seawater DMS, the derived sea–air fluxes and, hence, the impact of DMS on the radiative budget are sensitive to the estimate used
Channels of evolution: unveiling evolutionary patterns in diatom Ca2+ signalling
No full textDiatoms are important primary producers in marine and freshwater environments, but little is known about the signalling mechanisms they use to detect changes in their environment. All eukaryotic organisms use Ca2+ signalling to perceive and respond to environmental stimuli, employing a range of Ca2+-permeable ion channels to facilitate the movement of Ca2+ across cellular membranes. We investigated the distribution of different families of Ca2+ channels in diatom genomes, with comparison to other members of the stramenopile lineage. The four-domain voltage-gated Ca2+ channels (Cav) are present in some centric diatoms but almost completely absent in pennate diatoms, whereas single-domain voltage-gated EukCatA channels were found in all diatoms. Glutamate receptors (GLRs) and pentameric ligand-gated ion channels (pLGICs) also appear to have been lost in several pennate species. Transient receptor potential (TRP) channels are present in all diatoms, but have not undergone the significant expansion seen in brown algae. All diatom species analysed lacked the mitochondrial uniporter (MCU), a highly conserved channel type found in many eukaryotes, including several stramenopile lineages. These results highlight the unique Ca2+-signalling toolkit of diatoms and indicate that evolutionary gains or losses of different Ca2+ channels may contribute to differences in cellular-signalling mechanisms between specie