South Georgia is a heavily glaciated sub-Antarctic island in the Southern Ocean. Cumberland Bay i... more South Georgia is a heavily glaciated sub-Antarctic island in the Southern Ocean. Cumberland Bay is the largest fjord on the island, split into two arms, each with a large marine-terminating glacier at the head. Although these glaciers have shown markedly different retreat rates over the past century, the underlying drivers of such differential retreat are not yet understood. This study uses observations and a new high-resolution oceanographic model to characterize oceanographic variability in Cumberland Bay and to explore its influence on glacier retreat. While observations indicate a strong seasonal cycle in temperature and salinity, they reveal no clear hydrographic differences that could explain the differential glacier retreat. Model simulations suggest the subglacial outflow plume dynamics and fjord circulation are sensitive to the bathymetry adjacent to the glacier. The addition of a postulated shallow inner sill in one fjord arm significantly changes the water properties in t...
Modelling the transport of microplastic pollution across the Antarctic Circumpolar Current
<p>Microplastic pollution is a ubiquitous marine environmental contaminant that is ... more <p>Microplastic pollution is a ubiquitous marine environmental contaminant that is found in all the world’s oceans. The Southern Ocean is not exempt from microplastic pollution, with numerous studies reporting microplastics to be present in the region, including south of the Antarctic Circumpolar Current (ACC). However, the challenges involved in collecting data on microplastic pollution in the Southern Ocean mean there are large areas of the Southern Ocean where microplastic pollution levels are largely unknown. In addition, the processes and resulting transport pathways that move microplastic pollution across the ACC into the highly sensitive Antarctic marine ecosystem are not yet well understood.</p> <p>To tackle these knowledge gaps, we use a modelling approach to simulate the transport pathways of microplastic in the Southern Ocean, with a specific focus on cross-ACC transport. Specifically, we use the Lagrangian particle tracking framework OceanParcels, forced with ocean velocity fields from a Southern Ocean configuration of NEMO-LIM3 with 1/12॰ horizontal resolution. This model set up, which includes the effect of Stokes drift and sub-grid scale diffusion alongside underlying ocean currents, has allowed us to identify key regions where surface microplastic pollution may cross the ACC and potential hotspots of microplastic accumulation along the Antarctic coastline. We describe seasonal and inter-annual variability in microplastic transport through analysis of 22 years of model output, and suggest potential drivers of this variability. The results of our study will inform future field research into microplastic pollution in the Southern Ocean.</p>
Physical Versus Anthropogenic Control of Nutrient Concentrations in the Irish Sea
Estuarine and Coastal Modeling (2003), 2004
The modeling study described in the paper has investigated the physical influences on salinity an... more The modeling study described in the paper has investigated the physical influences on salinity and nutrient concentrations in the Irish Sea, including the role of climate variability. Previous observational work had noted an inverse relationship between salinity and nitrate concentrations in the Irish Sea, and highlighted the effect of moving water mass boundaries on observations at a fixed sampling site. The process studies described here have demonstrated how high frequency pulses of lower salinity, high nutrient concentration waters could be observed at a fixed sampling site near the Isle of Man (the Cypris station), mainly through the effects of direct wind forcing. Far field forcing for the two arbitrary years used in the study acted to retain material in the western Irish Sea, thus providing a weak background concentration of nutrients to the sampling site. Although daily variability in river flows did not appear to have a significant influence on the high frequency variability at the Cypris station , an arbitrary doubling of river inflows caused a shift t the southwest of the water mass containing higher tracer concentrations. Thus longer term changes in freshwater inflows, for example through increases in precipitation in positive NAO years, could have a significant effect on the decadal scale salinity variability observed at the Cypris station by causing a westwards movement of the boundary between fresh and saltwater masses. To further investigate influences on the long term variability of salinity at the Cypris station, a 40 year hindcast simulation was completed for the period 1960-1999. A comparison of modeled temperatures with observed values from 5566 CTD profiles throughout the 40 years, demonstrated the ability to reproduce the observed seasonal and longer term cycles, with mean and RMS errors of 0.002 degrees Celsius and 0.773 degrees Celsius. The long term temperature variability at the Cypris station was also reproduced. These results suggest that observations taken at fixed sampling sites in active environments such as the Irish Sea should be treated with a degree of caution. Although anthropogenic loading undoubtedly has some influence on nutrient concentrations, much of the observed variability may be due to climate variability, in particular the combined effects of freshwater inflows (dependent on precipitation) and far field forcing of saltwater masses on the geographical position of the water mass boundary.
To study the transport of plaice (Pleuronectes platessa L.) eggs and larvae in the eastern Irish ... more To study the transport of plaice (Pleuronectes platessa L.) eggs and larvae in the eastern Irish Sea, we constructed a 3D-baroclinic physical model and coupled it to a particle-tracking scheme that allowed aspects of larval behaviour to be simulated. Starting positions for eggs were based upon data from a series of ichthyoplankton surveys and final positions were compared with results of settled plaice distributions from two beam trawl surveys conducted on beaches around the eastern Irish Sea. If simulated larval behaviour was limited to passive drift or horizontal swimming, the particles diffused away from the spawning areas but failed to reach nursery grounds in significant numbers (85-90% remaining offshore). In contrast, switching on circatidal vertical swimming significantly increased the numbers of larvae reaching the coast (only 23-30% remained offshore). Particles tended to accumulate in bays and estuaries and this pattern compared well with the distribution of settled plaice from the field surveys. Studies in the southern North Sea (where spawning and nursery grounds are widely separated) have also demonstrated the importance of selective tidal stream transport for successful recruitment of settling plaice to nursery grounds. Although our understanding of the ontogeny of this behaviour is still poor, the model results presented suggest that this aspect of behaviour is a key factor influencing plaice settlement success.
Three-dimensional curvilinear modelling of wind-induced flows through the North Channel of the Irish Sea
PROC INT CONF ESTUARINE COAST …, 2000
Three-dimensional curvilinear modelling of wind-induced flows through the North Channel of the Ir... more Three-dimensional curvilinear modelling of wind-induced flows through the North Channel of the Irish Sea. Emma F Young, John N Aldridge, Juan Brown PROC INT CONF ESTUARINE COAST MODEL,, 549-563, 2000. A three ...
Quantifying the level of population connectivity within and between geographically separated sing... more Quantifying the level of population connectivity within and between geographically separated single-species deep-water fisheries stocks will be vital for designing effective management plans to preserve such populations. Despite this, stock structure in many fisheries is still poorly described and, at best, subject to precautionary management. Here we use rapidly evolving mitochondrial genes and microsatellite markers to investigate population connectivity patterns in commercially targeted Hyperoglyphe antarctica populations between four seamounts within the Tristan da Cunha Exclusive Economic Zone (EEZ). We find little evidence of population genetic structure between fished populations, with both mtDNA and microsatellite markers showing that there is low genetic population diversity (reflecting substantial gene flow) across the four seamounts. We also find little genetic differentiation between H. antarctica across the wider Southern Hemisphere. Such results support the role for co...
This is an open access article under the terms of the Creative Commons Attribution License, which... more This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Seamounts have long been recognised as hotspots for pelagic productivity and diversity in the wor... more Seamounts have long been recognised as hotspots for pelagic productivity and diversity in the world’s open ocean habitats. Recent studies have suggested that productivity may vary greatly between different seamounts, depending on complex interactions between the bathymetric features and local oceanography. These processes may enhance local primary production which support elevated biomass at higher trophic levels. In addition to enhancing local biomass, seamounts may also act as aggregative features, attracting pelagic species from the surrounding waters. Such characteristics make seamounts attractive targets for fisheries. However, as these unique habitats are localised and relatively small, they are vulnerable to overexploitation, which may have detrimental impact on the wider region. Mapping and quantitative assessments of the fish biomass at different seamounts are crucial prerequisites to identifying vulnerable seamounts and will aid toward understanding the dynamics of these i...
This study seeks to quantify the influence of South Georgia's orography on regional surface winds... more This study seeks to quantify the influence of South Georgia's orography on regional surface winds. A typical case study characterised by large-scale westerly winds is analysed using a high-resolution setup (3.3 km) of the WRF regional model. The simulation produces significant fine-scale spatial variability which is in agreement with satellite derived winds. The model simulation indicates that these orography-driven wind disturbances are responsible for strong wind stress curl and enhanced heat flux over the shelf waters surrounding South Georgia. Such surface forcing is entirely absent from the reanalysis, highlighting the need to use high-resolution forcing in regional ocean model simulations.
Benthic trawling has a recognised impact on sediment whole organism communities, yet little is kn... more Benthic trawling has a recognised impact on sediment whole organism communities, yet little is known about its impact on sediment biogeochemistry. On 2 cruises in October 2001 and July 2002, we measured sediment characteristics (particle size distribution, porosity and organic matter [OM]) and sediment metabolism (oxygen uptake, denitrification, sulphate reduction and sedimentwater nutrient exchange) along gradients of trawling activity at 14 sites in 2 regions of the southern North Sea: one with low tidal disturbance but high trawling disturbance (Outer Silver Pit, OSP), the other with high tidal disturbance but lower trawling disturbance (Thames). There was no measurable impact of trawling activity on oxygen uptake, denitrification or nutrient exchange in either region. In contrast, at the high trawling disturbance sites in the OSP only, there was both a shift in particle size distribution (towards fines) and a greater rate of sulphate reduction (volume specific rates 0.83 and 0.49 nmol SO 4 2cm-3 h-1 at high and low impact sites, respectively), but not in the Thames. In addition, areal rates of sulphate reduction were positively correlated with both silt content (i.e. associated with organics) and long-term trawling in the OSP but not in the Thames. Biogeochemical processes in the upper layers of sediment, both oxic and suboxic, seemed unaffected by trawling in the longterm. In deeper anoxic sediment, however, mineralisation via sulphate reduction may be stimulated by the extra disturbance, at least in areas where tidal energy is slight.
In the Southern Ocean, the at-sea distributions of most predators of Antarctic krill are poorly k... more In the Southern Ocean, the at-sea distributions of most predators of Antarctic krill are poorly known, primarily because tracking studies have only been undertaken on a restricted set of species, and then only at a limited number of sites. For chinstrap penguins, one of the most abundant krill predators breeding across the Antarctic Peninsula, we show that habitat models developed utilizing the distance from the colony and the bearing to the shelf-edge, adjusting for the at-sea density of Pygoscelis penguins from other colonies, can be used to predict, with a high level of confidence, the at-sea distribution of chinstrap penguins from untracked colonies during the breeding season. Comparison of predicted penguin distributions with outputs from a high-resolution oceanographic model shows that chinstrap penguins prefer nearshore habitats, over shallow bathymetry, with slow-flowing waters, but that they sometimes also travel to areas beyond the edge of the continental shelf where the faster-flowing waters of the Coastal Current or the fronts of the Antarctic Circumpolar Current occur. In the slow-moving shelf waters, large penguin colonies may lead to krill depletion during incubation and chick-rearing periods when penguins are acting as central place foragers. The habitats used by chinstrap penguins are also locations preferentially used by the commercial krill fishery, one of the last under-developed marine capture fisheries anywhere on the planet. As it develops, this fishery has the potential to compete with chinstrap penguins and other natural krill predators. Scaling our habitat models by chinstrap penguin population data demonstrates where overlap with the fishery is likely to be most important. Our results suggest that a better understanding of krill retention and krill depletion in areas used by natural predators and by the krill fishery are needed, and that risk management strategies for the fishery should include assessment of how krill movement can satisfy the demands of both natural predators and the fishery across a range of spatial and temporal scales. Such information will help regional management authorities better understand how plausible ecosystem-based management frameworks could be developed to ensure sustainable co-existence of the fishery and competing natural predators.
The ecosystem approach to management of the Antarctic krill fishery - the ‘devils are in the detail’ at small spatial and temporal scales
Journal of Marine Systems, 2021
Abstract Fishery demand for Antarctic krill is increasing, and projected to continue increasing i... more Abstract Fishery demand for Antarctic krill is increasing, and projected to continue increasing into the future. Krill has the potential to contribute approximately 10% to all future marine landings, adding significantly to global food security. However, the fishery is effectively data-limited so is currently managed using precautionary assessments that relate to large spatial and temporal scales that preclude the need for fine-scale ecological data. To respond to recent changes in fishery operation and to mitigate possible ecological impacts, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) plans to revise its management strategy so that it takes into account ecosystem operation at smaller spatial and temporal scales, such as those relevant to krill-dependent predators. Here, we consider how catches in coastal areas potentially present challenges for these predators, where cumulative catches over the fishing season can sometimes be greater than local consumption by predators, and sometimes greater than the standing stock of krill within an area because of krill transport and replenishment by ocean currents. Protecting feeding areas used by land-based predators such as penguins and seals, whilst also offering a high level of protection for pelagic predators such as some species of fish and recovering populations of cetaceans, will require innovative solutions. We highlight critical ecological research needed to reduce management uncertainty. This is important as we demonstrate that krill consumption by predators in near-shore coastal habitats relies absolutely upon krill movement and oceanographic transport. We also highlight the need to improve understanding about krill behaviour, especially in relation to observed seasonal changes in krill biomass. Finally, we highlight that without up-to-date data about changes in krill, krill-dependent predator populations and their oceanographic environment, management will remain challenging in the context of increasing fishing pressure, recovering populations of marine mammals and a changing climate.
In the marine environment, understanding the biophysical mechanisms that drive variability in lar... more In the marine environment, understanding the biophysical mechanisms that drive variability in larval dispersal and population connectivity is essential for estimating the potential impacts of climate change on the resilience and genetic structure of populations. Species whose populations are small, isolated and discontinuous in distribution will differ fundamentally in their response and resilience to environmental stress, compared with species that are broadly distributed, abundant and frequently exchange conspecifics. Here, we use an individual-based modelling approach, combined with a population genetics projection model, to consider the impacts of a warming climate on the population connectivity of two contrasting Antarctic fish species, and . Focussing on the Scotia Sea region, sea surface temperatures are predicted to increase significantly by the end of the 21st century, resulting in reduced planktonic duration and increased egg and larval mortality. With shorter planktonic d...
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