Faroe-Shetland Channel Research Articles

Effects of Superdispersant-25 on the sorption dynamics of naphthalene and phenanthrene in marine sediments

The present study evaluated the effects of Superdispersant-25 (SD25), a commercial dispersant stockpiled in the UK for oil spill response, on the sorption dynamics of two polyaromatic hydrocarbons, naphthalene (NAP) and phenanthrene (PHE), in sediment-seawater systems using three sediments near hydrocarbon exploration areas in the Faroe-Shetland Channel and North Sea. Batch experiments were conducted to evaluate the effects of SD25 on the solubility (analysed by gas chromatography), distribution coefficients and desorption hysteresis of NAP and PHE separately as well as SD25 in the three sediments (analysed by UV-vis spectroscopy and surface tension measurements, respectively). The results revealed that SD25 readily adsorbed to all sediment types but did not desorb from silty loam. SD25 application increased the solubility in seawater of PHE but not of NAP. Adsorbed SD25 increased the distribution coefficients of both polyaromatic hydrocarbons in sand but not silty loam and the solubilising effect of SD25 appeared to drive increased adsorption of PHE rather than sediment-adsorbed SD25 concentration. The findings highlight the influence of SD25 application on the sorption dynamics of NAP and PHE in marine sediments from areas near hydrocarbon exploration and production regions. An understanding of these interactions may aid responders in the decision-making process of dispersant application in the event of a spill as seabed characteristics affect oil-dispersant-sediment interactions.

Hydrocarbon-degrading bacteria in deep-water subarctic sediments (Faroe-Shetland Channel).

AimsThe aim of this study was the baseline description of oil‐degrading sediment bacteria along a depth transect in the Faroe‐Shetland Channel (FSC) and the identification of biomarker taxa for the detection of oil contamination in FSC sediments.Methods and ResultsOil‐degrading sediment bacteria from 135, 500 and 1000 m were enriched in cultures with crude oil as the sole carbon source (at 12, 5 and 0°C respectively). The enriched communities were studied using culture‐dependent and culture‐independent (clone libraries) techniques. Isolated bacterial strains were tested for hydrocarbon degradation capability. Bacterial isolates included well‐known oil‐degrading taxa and several that are reported in that capacity for the first time (Sulfitobacter, Ahrensia, Belliella, Chryseobacterium). The orders Oceanospirillales and Alteromonadales dominated clone libraries in all stations but significant differences occurred at genus level particularly between the shallow and the deep, cold‐water stations. Alcanivorax constituted 64% of clones at FSC135 but was absent at deeper stations. Pseudoalteromonas and Oleispira dominated the bacterial community at 500 and 1000 m.ConclusionsThe genus Oleispira emerged as a major player in the early stages of crude oil degradation in deep‐sea sediments of the FSC particularly at subzero temperatures. This finding is offering a direction for future research into biomonitoring tools for the detection of low levels of crude oil contamination in the deep FSC, and possibly high latitude cold waters in general.Significance and Impact of the StudyOil and gas exploration in the FSC occurs at depths >1000 m but baseline environmental data necessary for the assessment of ecosystem recovery to prespill conditions in the event of an oil spill are lacking. This study will contribute to our ability to assess the impact of oil release in the FSC and guide the direction of bioremediation strategies tailored to the area.

Bacterial Community Response in Deep Faroe-Shetland Channel Sediments Following Hydrocarbon Entrainment With and Without Dispersant Addition

The authors acknowledge Dr. Alan McCue for assistance with GC-FID, the MRV Scotia scientists and crew for assistance with sample collection and Cruikshank Analytical Lab for Carbon content analysis. Amy Bode and Val Johnston are thanked for their assistance with experimental setup and sampling. Dr. Sophie Shaw (CGEBM) is acknowledged for her advice and guidance with molecular analysis. Funding LJP and hydrocarbon analytics were funded through MarCRF funds for a Ph.D. project designed by UW, JA, and AG and awarded to LJP. LDP and microbiological investigations were funded through NERC award no NE/L00982X/1 to UW, JA, and EG. CG-R is funded by a University Research Fellowship.

Monitoring of Polycyclic Aromatic Hydrocarbons (PAHs) in Scottish Deepwater environments

Polycyclic aromatic hydrocarbons (PAHs) were measured in environmental samples (sponges, fish and sediment) collected in 2014 and 2016 from the Faroe-Shetland Channel and Rosemary Bank Seamount. These data could be used to provide a baseline against which any changes can be assessed in the event of an oil spill and contribute to any environmental impact assessment. Concentrations in all samples were low, often below the detection limits, and were typical of reference sites. Sponges can be used as an alternative indicator species to mussels for monitoring PAHs in the marine environment as they can accumulate PAHs from both the dissolved and particulate phase. PAH concentrations in marine sponges from Scottish waters have not previously been reported. Concentrations were low, but contained a higher proportion of heavier 4- to 6-ring PAHs compared to the fish samples.

Glacially influenced morphodynamic features – examples from the north Faroe margin

High resolution reflection seismic data, subbottom profiler and side scan sonar information, together with results from sediment core studies, have been used to study various glacially influenced morphodynamic features on the northern Faroese continental margin. On the shelf and upper slope a thick, buried turbate complex has been found, which we estimate to have been formed between ca 470,000 and 120,000yearsBP. We interpret this turbate to be the result of episodic, extensive iceberg grounding during extreme glaciation within the period MIS 12–MIS 6 (Elster-Saale complex). Late MIS 6 is found to be the most likely age of the last episode of turbate formation as suggested by age/depth correlation with dated sediment cores from the nearby area. The origin of the iceberg turbate may be attributed to deglacial drift of deep-draft icebergs from icestream sources in the Arctic, East Greenland and/or northern Iceland. At the base of slope and adjacent deep-water area a complex of mud diapir features has been observed. Our data show that activation of these features are the result of density inversion processes caused by fine-grained, unconsolidated hemipelagic deposits being overlain by dense, glacigenic North Sea Fan (NSF) deposits. Due to sudden and fast accumulation of the fan sediments, a normal and regular compaction and dewatering of the underlying hemipelagic sediments could not occur; instead, sub-seabed sediment mobilisation took place resulting in enhanced diapir formation. A general intensification of the diapiric processes is likely related to the MIS 6 (Saalian) glacial period, as NSF-derived glacigenic debris flows reached the northern outlet of the Faroe-Shetland Channel. The most recent diapir activity is concluded to have occurred during the last (Weichselian) glaciation.

Continued warming, salinification and oxygenation of the Greenland Sea gyre

The Greenland Sea gyre is one of the few areas where the water column is ventilated through open ocean convection. This process brings both anthropogenic carbon and oxygen from the atmosphere and surface ocean into the deep ocean, and also makes the Greenland Sea gyre interesting in a global perspective. In this study, a combination of ship- and float-based observations during the period 1986–2016 are analysed. Previous studies have shown warming and salinification of the upper 2000 m until 2011. The extended data record used here shows that this is continuing until 2016. In addition, oxygen concentrations are increasing over the entire period. The changes in temperature, salinity, and especially oxygen have been more pronounced since the turn of the century. This period has also been characterised by deeper wintertime mixed-layer depths, linking the warming, salinification and oxygenation to strengthened ventilation in the Greenland Sea gyre after 2000. The results also demonstrate that the strengthened ventilation can be tied to advection of warmer and more saline surface water from the North Atlantic through the Faroe-Shetland Channel. This advection has led to more saline surface waters in the Greenland Sea gyre, which is contributing to the deeper wintertime mixed layers.

Atlantic water flow through the Faroese Channels

Abstract. Through the Faroese Channels – the collective name for a system of channels linking the Faroe–Shetland Channel, Wyville Thomson Basin, and Faroe Bank Channel – there is a deep flow of cold waters from Arctic regions that exit the system as overflow through the Faroe Bank Channel and across the Wyville Thomson Ridge. The upper layers, in contrast, are dominated by warm, saline water masses from the southwest, termed Atlantic water. In spite of intensive research over more than a century, there are still open questions on the passage of these waters through the system with conflicting views in recent literature. Of special note is the suggestion that there is a flow of Atlantic water from the Faroe–Shetland Channel through the Faroe Bank Channel, which circles the Faroes over the slope region in a clockwise direction. Here, we combine the observational evidence from ship-borne hydrography, moored current measurements, surface drifter tracks, and satellite altimetry to address these questions and propose a general scheme for the Atlantic water flow through this channel system. We find no evidence for a continuous flow of Atlantic water from the Faroe–Shetland Channel to the Faroe Bank Channel over the Faroese slope. Rather, the southwestward-flowing water over the Faroese slope of the Faroe–Shetland Channel is totally recirculated within the combined area of the Faroe–Shetland Channel and Wyville Thomson Basin, except possibly for a small release in the form of eddies. This does not exclude a possible westward flow over the southern tip of the Faroe Shelf, but even including that, we estimate that the average volume transport of a Circum-Faroe Current does not exceed 0.5 Sv (1 Sv = 106 m3 s−1). Also, there seems to be a persistent flow of Atlantic water from the western part of the Faroe Bank Channel into the Faroe–Shetland Channel that joins the Slope Current over the Scottish slope. These conclusions will affect potential impacts from offshore activities in the region and they imply that recently published observational estimates of the transport of warm water towards the Arctic obtained by different methods are incompatible.

Ocean-ice sheet interaction along the SE Nordic Seas margin from 35 to 15 ka BP

Sediment cores from the south-eastern Nordic Seas simultaneously archive the variability of the Fennoscandian Ice Sheet (FIS), the British-Irish Ice Sheet (BIIS) and the regional oceanic conditions. This study aims to contribute to our understanding of the marine-based section of the FIS and the BIIS between 35,000 and 15,000years BP, by using cores MD99-2283, MD99-2284 and MD99-2289, retrieved along the upper continental slope between the Faroe-Shetland Channel and the Vøring Plateau. For this, we present a revised, radiocarbon based, Bayesian modelled chronological framework and a compilation of new and published sedimentological, geochemical and micro-paleontological datasets. Our results show a possibly first Weichselian FIS/BIIS confluence at ca. 25,500years BP in the central North Sea, which buttressed the BIIS to the East, potentially leading to a northwards BIIS deflection via the Shetlands. The Norwegian Channel Ice Stream (NCIS) most likely only reached the shelf edge after 23,300±500years BP, possibly for the first time during the Weichselian. The NCIS onset directly preceded a pronounced influx of warm Atlantic water to the northern North Sea margin possibly implying forcing through ocean melt. We find a highly variable NCIS, with three ~1400 yearlong episodes of increased ice rafted debris flux interrupted by ~600 yearlong minima. When compared to other sides of the European Ice Sheet, these episodes appear to correlate well, suggesting a common forcing mechanism. In conclusion, our data supports recent suggestions that the last glacial stage of the BIIS was more extensive in the central North Sea and the confluence later than previously thought.

The Variable Influence of Dispersant on Degradation of Oil Hydrocarbons in Subarctic Deep-Sea Sediments at Low Temperatures (0\u20135\u2009\xb0C)

The microbial degradation of petroleum hydrocarbons at low temperatures was investigated in subarctic deep-sea sediments in the Faroe Shetland Channel (FSC). The effect of the marine oil dispersant, Superdispersant 25 on hydrocarbon degradation was also examined. Sediments collected at 500 and 1000 m depth were spiked with a model oil containing 20 hydrocarbons and incubated at ambient temperature (5 and 0 °C, respectively) with and without marine dispersant. Treatment of sediments with hydrocarbons resulted in the enrichment of Gammaproteobacteria, and specifically the genera Pseudoalteromonas, Pseudomonas, Halomonas, and Cobetia. Hydrocarbon degradation was faster at 5 °C (500 m) with 65–89% of each component degraded after 50 days compared to 0–47% degradation at 0 °C (1000 m), where the aromatic hydrocarbons fluoranthene, anthracene, and Dibenzothiophene showed no degradation. Dispersant significantly increased the rate of degradation at 1000 m, but had no effect at 500 m. There was no statistically significant effect of Superdispersant 25 on the bacterial community structure at either station. These results show that the indigenous bacterial community in the FSC has the capacity to mitigate some of the effects of a potential oil spill, however, the effect of dispersant is ambiguous and further research is needed to understand the implications of its use.

On the spatial coherence of the Atlantic Water inflow across the Nordic Seas

AbstractThe covariability of the Atlantic Water (AW) branches in the Nordic Seas is investigated over the period 1979–2012 using an eddy permitting model. A noticeable circulation change is found in the mid‐1990s. Prior to the mid‐1990s, the leading mode of variability defines a large‐scale pattern, with concomitant variations in the Atlantic Water (AW) inflow in the Faroe‐Shetland Channel (FSC), the Norwegian Atlantic Slope Current (NwASC), the AW inflow to the Barents Sea, and the West Spitsbergen Current (WSC). After the mid‐1990s, the covariability between the NwASC and the AW inflow in both the FSC and the WSC is lost. Consequently, the northern Barents Sea circulation anomaly pattern, which is present throughout the full period, becomes the leading mode of circulation in the northern Nordic Seas after the mid‐1990s. The circulation change of the mid‐1990s appears to be linked to a weakening of the southwesterly wind anomalies in Norwegian Sea, as the northern center of action of the first mode of sea level pressure weakens. Passive tracer experiments suggest that this circulation change may be accompanied by increased heat transfer from the AW current to the interior Nordic Seas. This in turn may have limited the influence of the recently observed AW warming in the Iceland‐Scotland Passage on the NwASC downstream.

Role of EPS, Dispersant and Nutrients on the Microbial Response and MOS Formation in the Subarctic Northeast Atlantic

In this study we report the formation of marine oil snow (MOS), its associated microbial community, the factors influencing its formation, and the microbial response to crude oil in surface waters of the Faroe-Shetland Channel (FSC). The FSC is a subarctic region that is hydrodynamically complex located in the northeast Atlantic where oil extraction is currently occurring and where exploration is likely to expand into its deeper waters (>500 m). A major oil spill in this region may mirror the aftermath that ensued following the Deepwater Horizon (DWH) blowout in the Gulf of Mexico, where the massive influx of Macondo crude oil triggered the formation of copious quantities of rapidly sinking MOS and successional blooms of opportunistic oil-degrading bacteria. In laboratory experiments, we simulated environmental conditions in sea surface waters of the FSC using water collected from this site during the winter of 2015. We demonstrated that the presence of dispersant triggers the formation of MOS, and that nutrient amendments magnify this. Illumina MiSeq sequencing revealed the enrichment on MOS of associated oil-degrading (Cycloclasticus, Thalassolituus, Marinobacter) and EPS-producing (Halomonas, Pseudoalteromonas, Alteromonas) bacteria, and included major representation by Psychrobacter and Cobetia with putative oil-degrading/EPS-producing qualities. The formation of marine snow, in the absence of crude oil and dispersant, in seawater amended with nutrients alone indicated that the de novo synthesis of bacterial EPS is a key factor in MOS formation, and the glycoprotein composition of the MOS aggregates confirmed that its amorphous biopolymeric matrix was of microbial (likely bacterial) origin. The presence of dispersants and crude oil with/without nutrients resulted in distinct microbial responses marked by intermittent, and in some cases short-lived, blooms of opportunistic heterotrophs, principally obligate hydrocarbonoclastic (Alcanivorax, Cycloclasticus, Thalassolituus, Marinobacter) and EPS-producing (Halomonas, Alteromonas, Pseudoalteromonas) bacteria. Interestingly, members of the Vibrionales (principally the genus Vibrio) were strongly enriched by crude oil (with/without dispersant or nutrients), highlighting a putative importance for these organisms in crude oil biodegradation in the FSC. Our findings mirror those observed at DWH and hence underscore their broad relevance.

Large-scale forcing of the European Slope Current and associated inflows to the North Sea

Abstract. The European Slope Current provides a shelf-edge conduit for Atlantic Water, a substantial fraction of which is destined for the northern North Sea, with implications for regional hydrography and ecosystems. Drifters drogued at 50 m in the European Slope Current at the Hebridean shelf break follow a wide range of pathways, indicating highly variable Atlantic inflow to the North Sea. Slope Current pathways, timescales and transports over 1988–2007 are further quantified in an eddy-resolving ocean model hindcast. Particle trajectories calculated with model currents indicate that Slope Current water is largely recruited from the eastern subpolar North Atlantic. Observations of absolute dynamic topography and climatological density support theoretical expectations that Slope Current transport is to first order associated with meridional density gradients in the eastern subpolar gyre, which support a geostrophic inflow towards the slope. In the model hindcast, Slope Current transport variability is dominated by abrupt 25–50 % reductions of these density gradients over 1996–1998. Concurrent changes in wind forcing, expressed in terms of density gradients, act in the same sense to reduce Slope Current transport. This indicates that coordinated regional changes of buoyancy and wind forcing acted together to reduce Slope Current transport during the 1990s. Particle trajectories further show that 10–40 % of Slope Current water is destined for the northern North Sea within 6 months of passing to the west of Scotland, with a general decline in this percentage over 1988–2007. Salinities in the Slope Current correspondingly decreased, evidenced in ocean analysis data. Further to the north, in the Atlantic Water conveyed by the Slope Current through the Faroe–Shetland Channel (FSC), salinity is observed to increase over this period while declining in the hindcast. The observed trend may have broadly compensated for a decline in the Atlantic inflow, limiting salinity changes in the northern North Sea during this period. Proxies for both Slope Current transport and Atlantic inflow to the North Sea are sought in sea level height differences across the FSC and between Shetland and the Scottish mainland (Wick). Variability of Slope Current transport on a wide range of timescales, from seasonal to multi-decadal, is implicit in sea level differences between Lerwick (Shetland) and Tórshavn (Faroes), in both tide gauge records from 1957 and a longer model hindcast spanning 1958–2012. Wick–Lerwick sea level differences in tide gauge records from 1965 indicate considerable decadal variability in the Fair Isle Current transport that dominates Atlantic inflow to the northwest North Sea, while sea level differences in the hindcast are dominated by strong seasonal variability. Uncertainties in the Wick tide gauge record limit confidence in this proxy.

Simulating pathways of subsurface oil in the Faroe–Shetland Channel using an ocean general circulation model

Little is known about the fate of subsurface hydrocarbon plumes from deep-sea oil well blowouts and their effects on processes and communities. As deepwater drilling expands in the Faroe–Shetland Channel (FSC), oil well blowouts are a possibility, and the unusual ocean circulation of this region presents challenges to understanding possible subsurface oil pathways in the event of a spill. Here, an ocean general circulation model was used with a particle tracking algorithm to assess temporal variability of the oil-plume distribution from a deep-sea oil well blowout in the FSC. The drift of particles was first tracked for one year following release. Then, ambient model temperatures were used to simulate temperature-mediated biodegradation, truncating the trajectories of particles accordingly. Release depth of the modeled subsurface plumes affected both their direction of transport and distance travelled from their release location, and there was considerable interannual variability in transport.

Review of velocity models in the Faroe–Shetland Channel

Abstract Over the last few decades, a number of wide-angle seismic experiments have been conducted in the Faroe–Shetland Channel area with the objective of mapping the crustal structure. However, the volcanic rocks covering most of the area present a challenge for the imaging of sub-basalt structures. The results of the seismic studies are consistent in describing the Faroe–Shetland Channel as thinned continental crust and in establishing the presence of sub-basalt sediments. However, the various datasets often show differences in depth to crystalline basement and to the Moho. This paper presents a review of the velocity models in the Faroe–Shetland Channel and analyses the differences at line intersections. Down to top basalt the models are fairly consistent, while there are deviations of up to 1 km s −1 in basalt velocities and sub-basalt sediment velocities, 2 km in basalt thickness, 3.2 km in depth to crystalline basement, and 11.7 km in depth to the Moho.

On the reconstruction of ocean circulation and climate based on the “Gardar Drift”

AbstractSediment‐based reconstructions of bottom water velocity at the Gardar Drift are commonly interpreted to reflect changes in the eastern Nordic Seas overflows. Here we investigate the relationship between changes in the water that overflows through the Faroe Shetland Channel and downstream bottom velocity at the location of the Gardar Drift as represented in a 500 year long simulation with the Bergen Climate Model. We identify a region in our simulation proximal to the geographical location of the northern Gardar Drift where 76% of the variance in bottom velocity can be explained by changes in the volume transport and density of the Faroe Shetland Channel overflow. By contrast, Labrador Sea Water changes do not appear to play a significant role in the bottom flow over the Gardar Drift. Our findings support the assumption in the paleo literature that reconstructions of bottom water velocity at the Gardar Drift reflect past changes in the eastern Nordic Seas overflows. However, our results suggest that velocity changes downstream are not a simple metric for the strength of the overflow, rather overflow density plays the largest role.

Glacigenic debris-flows observed in 3D seismic high-resolution seafloor imagery, Faroe–Shetland Channel, NE Atlantic

Glacigenic debris-flows represent successive mass-flow deposits that build out a prograding wedge of sediment beyond the grounding zone of an ice sheet (e.g. Laberg & Vorren 1995; King et al. 1998). A prograding sedimentary depocentre extending from the outer shelf to the upper slope has been observed in geophysical datasets from the West Shetland margin of the Faroe–Shetland Channel, NW of the UK in the NE Atlantic. Overlapping, glacigenic debris-flows comprise the Rona and Foula wedges and provide insight into the extent and stability of the northern sector of the British Ice Sheet during the last full-glacial period (Stoker & Varming 2011). The Rona and Foula sedimentary wedges dominate the West Shetland margin south of 61° N (Fig. 1a) and overlap to form an elongate, outer-shelf to upper-slope depocentre up to 300 m in thickness (Stoker & Varming 2011). Typically elongate and sinuous lobe-like landforms are observed on seafloor imagery (Fig. 1a), and form a stacked association of lobes in seismic-reflection profiles (Fig. 1f). The sedimentary lobes of the Rona Wedge occur in water depths from approximately 400 to 1000 m, partly cover the floor of the Faroe–Shetland Channel and infill part of the Judd Deeps (Fig. 1a). The lobes of …

The decomposition of the Faroe-Shetland Channel water masses using Parametric Optimum Multi-Parameter analysis

The Faroe-Shetland Channel (FSC) is an important conduit for the poleward flow of Atlantic water towards the Nordic Seas and, as such, it plays an integral part in the Atlantic's thermohaline circulation. Mixing processes in the FSC are thought to result in an exchange of properties between the channel's inflow and outflow, with wider implications for this circulation; the nature of this mixing in the FSC is, however, uncertain. To constrain this uncertainty, we used a novel empirical method known as Parametric Optimum Multi-Parameter (POMP) analysis to objectively quantify the distribution of water masses in the channel in May 2013. This was achieved by using a combination of temperature and salinity measurements, as well as recently available nutrient and δ18O measurements. The outcomes of POMP analysis are in good agreement with established literature and demonstrate the benefits of representing all five water masses in the FSC. In particular, our results show the recirculation of Modified North Atlantic Water in the surface layers, and the pathways of Norwegian Sea Arctic Intermediate Water and Norwegian Sea Deep Water from north to south for the first time. In a final step, we apply the mixing fractions from POMP analysis to decompose the volume transport through the FSC by water mass. Despite a number of caveats, our study suggests that improved estimates of the volume transport of Atlantic inflow towards the Arctic and, thus, the associated poleward fluxes of salt and heat are possible. A new prospect to more accurately monitor the strength of the FSC branch of the thermohaline circulation emerges from this study.

Climatic Variability of the North Atlantic Oscillation Index and the Associated Fluctuations of Temperature and Water Mass Transport in the Upper Layer of the North Atlantic

Processes of formation of the North Atlantic Oscillation index (NAO) during different phases of the current (1868–2010) quasi-centurial variability of solar activity (the Wolf number) are considered. It is found that during the lowest solar activity of a quasi-centurial cycle, the NAO index tends to the value higher than those observed during maximum of solar activity. During the even cycles the NAO index tends to be a few times higher than those during the odd ones. The conceptual scheme is proposed assuming that at anomalously high NAO taking place mainly during even cycles, the western disturbance in the troposphere over the North Atlantic groves that intensifi es circulation in the upper layer of the subtropical gyre, leading to decrease of the amount of the Atlantic water mass infl owing to high latitudes. At anomalously low NAO observed mainly during the odd cycles, circulation in the subtropical gyre weakens that results in increase of the amount of the Atlantic water mass infl owing to high latitudes through the Faeroe–Shetland channel to the Norwegian and Barents seas. The range of the NAO variability is found (±0.5), at which average multi-year (climatic) regime of hydrometeorological characteristics is realized in the North Atlantic. Validity of the proposed conceptual scheme is confi rmed by the materials on water mass transport through the Faeroe–Shetland channel, formation of temperature anomalies in the North Atlantic upper layer and the Barents sea ice cover at NAO = ±0.5; NAO ≥ 1 and NAO ≤ –1.

Advective loss of overwintering Calanus finmarchicus from the Faroe–Shetland Channel

The flow of deep water from the Norwegian Sea to the North Atlantic via the Faroe–Shetland Channel is one of the critical bottlenecks in the meridional overturn circulation. It is also a flow that potentially carries with it a large number of the overwintering copepod, Calanus finmarchicus, a regionally important secondary producer. Using a high resolution hydrodynamic model, MIKE 3 FM, we simulate the overflow of deep water and estimate the associated loss rate of C. finmarchicus as a function of the water depth strata within which they reside. We estimate a net advective loss from the Norwegian Sea population of 80±10kt carbon bound in lipids of C. finmarchicus biomass per year, a number that constitutes about 50% of the total overwintering population. Estimates of water mass characteristics and particle tracking suggest that the fate of individuals transported in the overflowing water is to be entrained into warmer waters of the North Atlantic Basin, a habitat that appears to be unsuitable for successful overwintering.

Benthic biomass size spectra in shelf and deep-sea sediments

Abstract. The biomass distributions of marine benthic metazoans (meio- to macro-fauna, 1 μg–32 mg wet weight) across three contrasting sites were investigated to test the hypothesis that allometry can consistently explain observed trends in biomass spectra. Biomass (and abundance) size spectra were determined from observations made at the Faroe–Shetland Channel (FSC) in the Northeast Atlantic (water depth 1600 m), the Fladen Ground (FG) in the North Sea (150 m), and the hypoxic Oman Margin (OM) in the Arabian Sea (500 m). Observed biomass increased with body size as a power law at FG (scaling exponent, b = 0.16) and FSC (b = 0.32), but less convincingly at OM (b = 0.12 but not significantly different from 0). A simple model was constructed to represent the same 16 metazoan size classes used for the observed spectra, all reliant on a common detrital food pool, and allowing the three key processes of ingestion, respiration and mortality to scale with body size. A micro-genetic algorithm was used to fit the model to observations at the sites. The model accurately reproduces the observed scaling without needing to include the effects of local influences such as hypoxia. Our results suggest that the size-scaling of mortality and ingestion are dominant factors determining the distribution of biomass across the meio- to macrofaunal size range in contrasting marine sediment communities. Both the observations and the model results are broadly in agreement with the "metabolic theory of ecology" in predicting a quarter power scaling of biomass across geometric body size classes.