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It is frequently assumed that taking samples of soft marine sediments using surface-based gravity coring equipment causes minimal disruption to their sedimentological, biogeochemical, and biological condition. This assumption was evaluated by examining the potential disturbances caused when obtaining soft-sediment samples either by SCUBA or Craib-coring, comparing sediment oxygen microprofiles, benthic oxygen flux rates and sediment solid phase analyses (chlorophyll a (Chl a), organic carbon, and porosity) between both methods and against reference values measured in situ by benthic lander. The two sampling methodologies were tested in shallow coastal environments on the west coast of Scotland and generally the results obtained from cores collected using SCUBA exhibited values closest to those observed in situ. Oxygen penetration depth was significantly shallower in cores obtained by Craib-corer compared with the SCUBA cores. Craib cores also produced higher oxygen uptake rates which could be caused by greater levels of sediment disturbance during sampling. In addition, more homogenous levels of Chl a in the top 1 cm of the Craib cores, compared with the SCUBA samples, may indicate either resuspension or compression during gravity coring. Using SCUBA for shallow-water soft-sediment sampling permits steady and controlled core-tube insertion and extraction, and more measured retrieval of the cores to the surface; this probably accounts for the observed differences. Whereas benthic lander-based in situ measurement would be the preferred method for analyzing sediment parameters in detail in this type of environment, SCUBA-based sampling offers a more accurate alternative to surface-based gravity coring.

We investigated the seasonal dynamics of in-stream metabolism at the reach scale (∼ 150 m) of headwaters across contrasting geological sub-catchments: clay, Greensand, and Chalk of the upper River Avon (UK). Benthic metabolic activity was quantified by aquatic eddy co-variance while water column activity was assessed by bottle incubations. Seasonal dynamics across reaches were specific for the three types of geologies. During the spring, all reaches were net autotrophic, with rates of up to 290 mmol C m-2 d-1 in the clay reach. During the remaining seasons, the clay and Greensand reaches were net heterotrophic, with peak oxygen consumption of 206 mmol m-2 d-1 during the autumn, while the Chalk reach was net heterotrophic only in winter. Overall, the water column alone still contributed to ∼ 25% of the annual respiration and primary production in all reaches. Net ecosystem metabolism (NEM) across seasons and reaches followed a general linear relationship with increasing stream light availability. Sub-catchment specific NEM proved to be linearly related to the local hydrological connectivity, quantified as the ratio between base flow and stream discharge, and expressed on a timescale of 9 d on average. This timescale apparently represents the average period of hydrological imprint for carbon turnover within the reaches. Combining a general light response and sub-catchment specific base flow ratio provided a robust functional relationship for predicting NEM at the reach scale. The novel approach proposed in this study can help facilitate spatial and temporal upscaling of riverine metabolism that may be applicable to a broader spectrum of catchments.

This case study demonstrates that Alloy 601 (UNS N06601) is susceptible to strain-age cracking. The observation illustrates the potential importance of post weld heat treatment to the successful utilization of this alloy in certain applications.

The CO2 controlled release experiment “Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbon Storage” (QICS) assessed the impacts of potential CO2 leakage from sub-seabed carbon capture and storage reservoirs to the marine environment. During QICS, CO2 gas was released into shallow sediment in Ardmucknish Bay, Scotland, in the spring and summer of 2012. As part of this project, we investigated the effects of CO2 leakage on sedimentary phosphorus (P), an essential nutrient for marine productivity. We found no statistically significant effects during QICS, as the solid-phase P content in the sediment was constant before, during, and after exposure to CO2. However, laboratory experiments using marine sediment standard materials as well as QICS sediment revealed substantial differences among these different sediment types in their potential for P release during CO2 exposure. Employing the SEDEX sequential extraction technique to determine the sizes of the major P pools in the sediments, we showed that calcium-bound P can be easily released by CO2 exposure, whereas iron-bound P is a major sink of released P. The overall impacts of CO2 leakage on sediment P behavior appear to be low compared to natural variability.

Whilst sub-seabed Carbon Capture and Storage (CCS) has the potential to remove a significant proportion of anthropogenic CO2 emissions at source, research is necessary to constrain the environmental impacts of potential future gas leaks from storage reservoirs. The QICS project (Quantifying and Monitoring Potential Ecosystem Impacts of Geological Carbons Storage) was established to improve our understanding of these potential impacts and to develop tools and best practice for monitoring sub-seabed CCS reservoirs. Exposure to increased environmental CO2 has been shown to raise the tissue pCO2 of many marine invertebrate species, leading to tissue acidosis and perturbations in both ion transport and bicarbonate buffering. These disturbances can cause downstream effects, seen as metabolic depression in susceptible organisms, compromising the role of particular species within an ecosystem and even causing the local extinction of species groups. To monitor the potential impact to surficial benthic megafauna, cages of bivalves (the common mussel Mytilus edulis Linnaeus, 1758 and the king scallop Pecten maximus (Linnaeus, 1758)) were deployed at the gas release site and at a reference site—both within Ardmucknish Bay, Oban, Scotland. Replicate individuals were sampled at six time points over a 125-day period, which spanned both the 37-day injection and recovery phases of the experiment, in order to establish impacts to molecular physiology. Samples of bivalves were also simultaneously sampled from a reference site within the bay in order to contrast changes in physiology induced by the gas release with naturally variability in the physiological performance of both species. We present data on changes in the transcription of genes coding for key ionic and carbon dioxide regulatory proteins. There was no evidence of gene regulation of either selected carbonic anhydrases (CAx genes) or the alpha subunit of sodium potassium ATPAses (ATP1A genes) in individual bivalves collected from the CO2 gas release site, in either species. In the common mussel M. edulis there was only evidence for changes with time in the expression of genes coding for different classes of carbonic anhydrase. It was therefore concluded that the effects of the plume of elevated pCO2 on ion-regulatory gene transcription were negligible in both species. Whilst the analysed data from this current study do not constitute an impediment to the continued development of sub-seabed CCS as a climate mitigation strategy, further modelling is necessary to predict the consequences of larger or longer term leaks. Further analysis is also required in order to constrain the potential physiological impacts of gas leaks to benthic infaunal species and understand the mechanism of possible avoidance behaviour recorded in burrowing heart urchins Echinocardium cordatum (Pennant, 1777).

Highlights • Sub-seabed release of CO2 reduced macrofaunal diversity, abundance and biomass. • Impacts were only detectable in the area of active CO2 leakage, primarily where bubbling was observed. • Community recovery was rapid once leakage had stopped. • Natural seasonal variability was seen in reference areas with additional evidence of natural disturbances (storms). Abstract A sub-seabed release of carbon dioxide (CO2) was conducted to assess the potential impacts of leakage from sub-seabed geological CO2 Capture and Storage CCS) on benthic macrofauna. CO2 gas was released 12 m below the seabed for 37 days, causing significant disruption to sediment carbonate chemistry. Regular macrofauna samples were collected from within the area of active CO2 leakage (Zone 1) and in three additional reference areas, 25 m, 75 m and 450 m from the centre of the leakage (Zones 2, 3 and 4 respectively). Macrofaunal community structure changed significantly in all zones during the study period. However, only the changes in Zone 1 were driven by the CO2 leakage with the changes in reference zones appearing to reflect natural seasonal succession and stochastic weather events. The impacts in Zone 1 occurred rapidly (within a few days), increased in severity through the duration of the leak, and continued to worsen after the leak had stopped. Considerable macrofaunal recovery was seen 18 days after the CO2 gas injection had stopped. In summary, small short-term CCS leakage events are likely to cause highly localised impacts on macrofaunal communities and there is the potential for rapid recovery to occur, depending on the characteristics of the communities and habitats impacted.

The response of the benthic microbial community to a controlled sub-seabed CO2 leak was assessed using quantitative PCR measurements of benthic bacterial, archaeal and cyanobacteria/chloroplast 16S rRNA genes. Samples were taken from four zones (epicentre; 25 m distant, 75 m distant and 450 m distant) during 6 time points (7 days before CO2 exposure, after 14 and 36 days of CO2 release, and 6, 20 and 90 days after the CO2 release had ended). Changes to the active community of microphytobenthos and bacteria were also assessed before, during and after CO2 release. Increases in the abundance of microbial 16S rRNA were detected after 14 days of CO2 release and at a distance of 25 m from the epicentre. CO2 related changes to the relative abundance of both major and minor bacterial taxa were detected: most notably an increase in the relative abundance of the Planctomycetacia after 14 days of CO2 release. Also evident was a decrease in the abundance of microbial 16S rRNA genes at the leak epicentre during the initial recovery phase: this coincided with the highest measurements of DIC within the sediment, but may be related to the release of potentially toxic metals at this time point.

This paper explores the social dimensions of an experimental release of carbon dioxide (CO2) carried out in Ardmucknish Bay, Argyll, United Kingdom. The experiment, which aimed to understand detectability and potential effects on the marine environment should there be any leakage from a CO2 storage site, provided a rare opportunity to study the social aspects of a carbon dioxide capture and storage-related event taking place in a lived-in environment. Qualitative research was carried out in the form of observation at public information events about the release, in-depth interviews with key project staff and local stakeholders/community members, and a review of online media coverage of the experiment. Focusing mainly on the observation and interview data, we discuss three key findings: the role of experience and analogues in learning about unfamiliar concepts like CO2 storage; the challenge of addressing questions of uncertainty in public engagement; and the issue of when to commence engagement and how to frame the discussion. We conclude that whilst there are clearly slippages between a small-scale experiment and full-scale CCS, the social research carried out for this project demonstrates that issues of public and stakeholder perception are as relevant for offshore CO2 storage as they are for onshore. (C) 2014 Elsevier Ltd. All rights reserved.

The impact of a sub-seabed CO2 leak from geological sequestration on the microbial process of ammonia oxidation was investigated in the field. Sediment samples were taken before, during and after a controlled sub-seabed CO2 leak at four zones differing in proximity to the CO2 source (epicentre, and 25 m, 75 m, and 450 m distant). The impact of CO2 release on benthic microbial ATP levels was compared to ammonia oxidation rates and the abundance of bacterial and archaeal ammonia amoA genes and transcripts, and also to the abundance of nitrite oxidizer (nirS) and anammox hydrazine oxidoreductase (hzo) genes and transcripts. The major factor influencing measurements was seasonal: only minor differences were detected at the zones impacted by CO2 (epicentre and 25 m distant). This included a small increase to ammonia oxidation after 37 days of CO2 release which was linked to an increase in ammonia availability as a result of mineral dissolution. A CO2 leak on the scale used within this study (

Marine ecosystems are exposed to a range of human-induced climate stressors, in particular changing carbonate chemistry and elevated sea surface temperatures as a consequence of climate change. More research effort is needed to reduce uncertainties about the effects of global-scale warming and acidification for benthic microbial communities, which drive sedimentary biogeochemical cycles. In this research, mesocosm experiments were set up using muddy and sandy coastal sediments to investigate the independent and interactive effects of elevated carbon dioxide concentrations (750 ppm CO2) and elevated temperature (ambient +4°C) on the abundance of taxonomic and functional microbial genes. Specific quantitative PCR primers were used to target archaeal, bacterial, and cyanobacterial/chloroplast 16S rRNA in both sediment types. Nitrogen cycling genes archaeal and bacterial ammonia monooxygenase (amoA) and bacterial nitrite reductase (nirS) were specifically targeted to identify changes in microbial gene abundance and potential impacts on nitrogen cycling. In muddy sediment, microbial gene abundance, including amoA and nirS genes, increased under elevated temperature and reduced under elevated CO2 after 28 days, accompanied by shifts in community composition. In contrast, the combined stressor treatment showed a non-additive effect with lower microbial gene abundance throughout the experiment. The response of microbial communities in the sandy sediment was less pronounced, with the most noticeable response seen in the archaeal gene abundances in response to environmental stressors over time. 16S rRNA genes (amoA and nirS) were lower in abundance in the combined stressor treatments in sandy sediments. Our results indicated that marine benthic microorganisms, especially in muddy sediments, are susceptible to changes in ocean carbonate chemistry and seawater temperature, which ultimately may have an impact upon key benthic biogeochemical cycles.

Este artículo contiene 16 páginas, 10 figuras, 1 tabla., Global concern over increasing CO2 emissions, and the resultant CO2 driven temperature rises and changes in seawater chemistry, necessitates the advancement of understanding into how these changes will affect marine life now and in the future. Here we report on an experimental investigation into the effects of increased CO2 concentration and elevated temperature on sedimentary meiofaunal communities. Cohesive (muddy) and noncohesive (sandy) sediments were collected from the Eden Estuary in St. Andrews, Scotland, UK, placed within a flume setup and exposed to 2 levels of CO2 concentration (380 and 750 ppmv, current at the time of the experiment, and predicted CO2 concentration by 2100, respectively) and 2 temperature levels (12 °C and 16 °C, current in-situ and predicted temperature by 2100, respectively). We investigated the metazoan meiofauna and nematode communities before and after 28 days of exposure under these experimental conditions. The most determinative factor for abundance, diversity and community structure of meiofauna and nematodes was sediment type: on all levels, communities were significantly different between sand and mud sediments which agrees with what is generally known about the influence of sediment structure on meiofaunal organisms. Few CO2 and temperature effects were observed, suggesting that meiofauna and nematodes are generally much less responsive than, for instance, microbial communities and macrofauna to these environmental changes in estuarine environments, where organisms are naturally exposed to a fluctuating environment. This was corroborated by the observed effects related to the different seasons in which the samples were taken from the field to run the experiment. After 28 days, meiofauna and nematode communities in muddy sediments showed a greater response to increased CO2 concentration and temperature rise than in sandy sediments. However, further study is needed to investigate the underlying mechanisms and meiofauna species-specific resilience and responses to ocean acidification and warming, and their interactions with other biota, to understand what such changes may mean for meiofauna communities and the ecosystem processes and functions they contribute to., Authors acknowledge support through the NERC OA programme. PJS acknowledges support from the UK Natural Environment Research Council through National Capability funding and, with the Department for Environment, Food and Rural Affairs, through the Marine Ecosystems Research Programme (grant number NE/L003279/1). JI was supported by a Plymouth Marine Laboratory Post-doctoral Research Fellowship in collaboration with University of Exeter and a Marie Curie Intra-European Fellowship within the 7th European Commission Framework Programme (Grant Agreement FP7-PEOPLE- 2011-IEF no. 00879).

We investigated the seasonal dynamics of in‐stream metabolism at the reach scale (∼ 150 m) of headwaters across contrasting geological sub‐catchments: clay, Greensand, and Chalk of the upper River Avon (UK). Benthic metabolic activity was quantified by aquatic eddy co‐variance while water column activity was assessed by bottle incubations. Seasonal dynamics across reaches were specific for the three types of geologies. During the spring, all reaches were net autotrophic, with rates of up to 290 mmol C m−2 d−1 in the clay reach. During the remaining seasons, the clay and Greensand reaches were net heterotrophic, with peak oxygen consumption of 206 mmol m−2 d−1 during the autumn, while the Chalk reach was net heterotrophic only in winter. Overall, the water column alone still contributed to ∼ 25% of the annual respiration and primary production in all reaches. Net ecosystem metabolism (NEM) across seasons and reaches followed a general linear relationship with increasing stream light availability. Sub‐catchment specific NEM proved to be linearly related to the local hydrological connectivity, quantified as the ratio between base flow and stream discharge, and expressed on a timescale of 9 d on average. This timescale apparently represents the average period of hydrological imprint for carbon turnover within the reaches. Combining a general light response and sub‐catchment specific base flow ratio provided a robust functional relationship for predicting NEM at the reach scale. The novel approach proposed in this study can help facilitate spatial and temporal upscaling of riverine metabolism that may be applicable to a broader spectrum of catchments.

A new sandwich sensor, consisting of an O 2 planar optode overlain by a thin (90 μm) DGT layer is present ed. This sensor can simultaneously resolve 2-D O 2 dynamics and trace metal fluxes in benthic substrates at a high spatial resolution. The DGT layer accumulates metals on a small particle size (0.2 μm) chelating resin and records the locally induced trace metal flux during the deployment, whereas the planar optode resolves the O 2 dynamic in near real time at the same location in the sediment. Despite its ultrathin composition, the DGT layer has high carrying capacity for trace metals with no saturation problems during application to typical coastal- or contaminated sediments. Combined with laser ablation, accumulated metal fluxes could be resolved at a resolution of ~200 μm, whereas the O 2 images had a resolution of ~100 μm. A 2-D diffusion-reaction model showed that the enhanced smearing and reduced response time of the O 2 signal associated with the additional DGT layer were marginal. To test sensor performance at realistic conditions, it was applied to an artificial bur row system consisting of permeable dialysis tubing flushed with oxygenated seawater. The measurements demonstrated localized mobilization of Ni, Cu, and Pb close to the burrow wall, where O 2 was elevated. The lat ter was also confirmed for Cu and Pb in natural sediments irrigated by the polychaete Hediste diversicolor . The sandwich sensor has great potential for investigating interrelations between O 2 dynamics and metal mobiliza tion in complex benthic systems such as burrows, rhizospheres, permeable sands, and microbial mats.

Three approaches, Eddy Correlation (EC), Turbulent Kinetic Energy (TKE), and Inertial Dissipation (ID) methods, were compared to evaluate their potential for estimation of friction velocity in a Scottish sea loch. As an independent assessment parameter, we used simultaneous O2 recordings of the diffusive boundary layer (DBL) that were compared with theoretical distribution as derived from the respective friction velocity estimates. Friction velocities were calculated based on the three approaches using continuously measured turbulent properties, and values estimated by the TKE method were significantly higher than values of the two other approaches.Time series of calculated friction velocity were subsequently employed as input parameters for nonsteadycalculations of the O2 distribution within the DBL. The friction velocity is a controlling factor for the eddy diffusivity distribution immediately above the sediment surface and for the DBL thickness, and friction velocity values of the TKE method derived significantly higher theoretical O2 concentration while the EC and the ID approach provided results that were not significantly different. Overall differences from measured O2 concentration in the DBL were 0.2% for the EC method, 9.8% for the TKE method, and 0.7% for the ID method. The results reveal that the EC method appear to be the best approach for estimating friction velocities though not significantly different from the ID method, whereas the TKE method was unreliable at the ~70 m deep, relatively calm study site. This information is important for future research in similar sounds, fjords, and sea-lochs.

We present and compare small sediment-water fluxes of O2 determined with the eddy correlation technique, with in situ chambers, and from vertical sediment microprofiles at a 1450 m deep-ocean site in Sagami Bay, Japan. The average O2 uptake for the three approaches, respectively, was 1.62 ± 0.23 (SE, n = 7), 1.65 ± 0.33 (n = 2), and 1.43 ± 0.15 (n = 25) mmol m−2 d−1. The very good agreement between the eddy correlation flux and the chamber flux serves as a new, important validation of the eddy correlation technique. It demonstrates that the eddy correlation instrumentation available today is precise and can resolve accurately even very small benthic O2 fluxes. The correlated fluctuations in vertical velocity and O2 concentration that give the eddy flux had average values of 0.074 cm s−1 and 0.049 µM. The latter represents only 0.08% of the 59 µM mean O2 concentration of the bottom water. Note that these specific fluctuations are average values, and that even smaller variations were recorded and contributed to the eddy flux. Our findings demonstrate that the eddy correlation technique is a highly attractive alternative to traditional flux methods for measuring even very small benthic O2 fluxes.

A transecting microprofiler documented a pronounced small-scale variation in the benthic O-2 concentration at 1450-m water depth (Sagami Bay, Japan). Data obtained during a single deployment revealed that within a sediment area of 190 cm(2) the O-2 penetration depth varied from 2.6 mm to 17.8 mm (average; 6.6 +/- 2.5 mm) and the diffusive O-2 uptake, calculated from the vertical concentration gradient within the diffusive boundary layer, ranged from 0.6 mmol m(-2) d(-1) to 3.9 mmol m(-2) d(-1) (average; 1.8 +/- 0.7 mmol m(-2) d(-1), n = 129). However, correction for microtopography and horizontal diffusion increased the average diffusive O-2 uptake by a factor of 1.26 +/- 0.06. Detailed 2D calculations on the volume-specific O-2 consumption exhibited high variability. The oxic zone was characterized by a mosaic of sediment parcels with markedly different activity levels. Millimeter- to centimeter-sized "hot spots" with O-2 consumption rates up to 10 pmol cm(-3) s(-1) were separated by parcels of low or insignificant O-2 consumption. The variation in aerobic activity must reflect an inhomogeneous distribution of electron donors and suggests that the turnover of material within the oxic zone to a large extent was confined to hot spots. The in situ benthic O-2 uptakes, measured during four cruises, reflected a seasonal signal overlying the observed small-scale variability. The annual benthic mineralization balanced similar to 50% of the estimated pelagic production. However, the central bay is characterized by a significant downslope sediment transport, and mass balance estimates indicate 90% retention of the total organic material reaching the bottom of the central bay. A transecting microprofiler documented a pronounced small‐scale variation in the benthic O2 concentration at 1450‐m water depth (Sagami Bay, Japan). Data obtained during a single deployment revealed that within a sediment area of 190 cm2 the O2 penetration depth varied from 2.6 mm to 17.8 mm (average; 6.6 ± 2.5 mm) and the diffusive O2 uptake, calculated from the vertical concentration gradient within the diffusive boundary layer, ranged from 0.6 mmol m−2 d−1 to 3.9 mmol m−2 d−1 (average; 1.8 ± 0.7 mmol m−2 d−1, n = 129). However, correction for microtopography and horizontal diffusion increased the average diffusive O2 uptake by a factor of 1.26 ± 0.06. Detailed 2D calculations on the volume‐specific O2 consumption exhibited high variability. The oxic zone was characterized by a mosaic of sediment parcels with markedly different activity levels. Millimeter‐ to centimeter‐sized ‚‚hot spots’’ with O2 consumption rates up to 10 pmol cm−3 s−1 were separated by parcels of low or insignificant O2 consumption. The variation in aerobic activity must reflect an inhomogeneous distribution of electron donors and suggests that the turnover of material within the oxic zone to a large extent was confined to hot spots. The in situ benthic O2 uptakes, measured during four cruises, reflected a seasonal signal overlying the observed small‐scale variability. The annual benthic mineralization balanced ~50% of the estimated pelagic production. However, the central bay is characterized by a significant downslope sediment transport, and mass balance estimates indicate 90% retention of the total organic material reaching the bottom of the central bay.

Denitrification and oxygen dynamics were investigated in the sea ice of Franklin Bay (70 degrees N), Canada. These investigations were complemented with measurements of denitrification rates in sea ice from different parts of the Arctic (69 degrees N-85 degrees N). Potential for bacterial denitrification activity (5-194 mu mol N m(-2) day(-1)) and anammox activity (3-5 mu mol N m(-2) day(-1)) in melt water from both first-year and multi-year sea ice was found. These values correspond to 27 and 7%, respectively, of the benthic denitrification and anammox activities in Arctic sediments. Although we report only potential denitrification and anammox rates, we present several indications that active denitrification in sea ice may occur in Franklin Bay (and elsewhere): (1) despite sea ice-algal primary production in the lower sea ice layers, heterotrophic activity resulted in net oxygen consumption in the sea ice of 1-3 mu mol l(-1) sea ice per day at in situ light conditions, suggesting that O-2 depletion may Occur prior to the spring bloom. (2) The ample organic carbon (DOC) and NO3- present in sea ice may support an active denitrification population. (3) Measurements of O-2 conditions in melted sea ice cores showed very low bulk concentrations, and in some cases anoxic conditions prevailed. (4) Laboratory studies using planar optodes for measuring the high-resolution two-dimensional O-2 distributions in sea ice confirmed the very dynamic and heterogeneous O-2 distribution in sea ice, displaying a mosaic of microsites of high and low O-2 concentrations. Brine enclosures and channels were strongly O-2 depleted in actively melting sea ice, and anoxic conditions in parts of the brine system would favour anaerobic processes.

Contaminated sediment from a marine harbour was maintained for 16 months in two flumes that continuously re-circulated the overlying water, sustaining a smooth flow at the sediment surface. The sediment was placed in one flume intact, while for the other it was pre-homogenised. The concentrations of trace metals in the porewaters were measured at a vertical resolution of 2 mm using the technique of diffusive equilibration in thin-films (DET) and microelectrodes were used to measure concentration profiles of oxygen and pH. Separate experiments showed good agreement between metals measured by DET and those measured in porewaters extracted by centrifugation and filtration. Local mobilisation of metals was measured in 2-dimensional arrays by deploying DGT (diffusive gradients in thin-films) probes. There were high concentrations of Fe in the porewaters, which limited the concentration of sulphide to less than 0.3 μM. With both DET and DGT measurements, there were sharply defined maxima of Cu and Cd within 2 mm of the sediment water interface, consistent with their release from organic material as it is oxidised. There was a Co maximum about 5–8 mm lower than the Cu and Cd maxima, apparently coincidental with Mn mobilisation. While there were clear Ni maxima, their location appeared to vary from being coincident with Co to a few mm above the Co maxima. The remobilisation of metals could not be explained by the pH gradients in the near-surface sediments. As sulphate reduction rates were appreciable, the apparent lack of metal mobilisation at depth was attributed to the formation of metal sulphides. The DGT measurements in the same probe were well replicated horizontally. This, the replication of the same features between flumes and the reasonable correspondence between DGT and DET, showed that the localised mobilisation of metals was associated with recent diagenetic processes, rather than the depositional history. There were substantial fluxes of Cu and Cd to the overlying water. Even though there were steep gradients of Fe, Mn, Ni and Co within 1 cm of the sediment–water interface, there was no clear evidence for any substantial metal fluxes across the interface. Adsorption of Mn to Fe oxides, rather than oxidation, may be responsible for its removal from solution at the same depth as Fe.

We report measurements of pore-water dissolved organic carbon (DOC), dissolved organic nitrogen, total dissolved carbohydrates, dissolved free monosaccharides, and ammonium in recovered deep-sea sediments from the Porcupine Abyssal Plain (PAP), Northeast Atlantic. There were distinct maxima close to the sediment-water interface of these constituents at all times of the year. The very high diffusive effluxes calculated from these porewater distributions were not compatible with simultaneous sediment trap measurements of particulate organic carbon, nitrogen, and carbohydrate fluxes toward the seafloor. Effluxes calculated from pore-water DOC distributions in recovered cores from another Atlantic deep-sea site, showing almost identical maxima as those at PAP, were more than an order of magnitude greater than simultaneous in situ chamber DOC flux measurements. We suggest that the dissolved organic matter maxima are predominantly artifacts induced by lysis of, or leakage from, mainly bacterial biomass resulting from decompression and/or warming during recovery of the sediment cores from the abyssal seafloor. Temperature elevation during core recovery from the abyss gives a N2 saturation of about 150%, and the combined effect of warming and decompression results in a CO2 saturation of about 135%, which together plausibly are associated with bubble formation creating cell bursting. Previous estimates of microbial biomass in abyssal sediments may be underestimates because of the difficulty of counting lysed bacterial cells. Since exoenzymes are inducible, previous measurements of their activities in recovered abyssal sediments may be overestimates.

Coralline algal (maerl) beds are widespread, slow-growing, structurally complex perennial habitats that support high biodiversity, yet are significantly understudied compared to seagrass beds or kelp forests. We present the first eddy covariance (EC) study on a live maerl bed, assessing the community benthic gross primary productivity (GPP), respiration (R), and net ecosystem metabolism (NEM) derived from diel EC time series collected during 5 seasonal measurement campaigns in temperate Loch Sween, Scotland. Measurements were also carried out at an adjacent (similar to 20 m distant) permeable sandy habitat. The O-2 exchange rate was highly dynamic, driven by light availability and the ambient tidally-driven flow velocity. Linear relationships between the EC O-2 fluxes and available light indicate that the benthic phototrophic communities were light limited. Compensation irradiance (E-c) varied seasonally and was typically similar to 1.8-fold lower at the maerl bed compared to the sand. Substantial GPP was evident at both sites; however, the maerl bed and the sand habitat were net heterotrophic during each sampling campaign. Additional inputs of similar to 4 and similar to 7 mol m(-2) yr(-1) of carbon at the maerl bed and sand site, respectively, were required to sustain the benthic O-2 demand. Thus, the 2 benthic habitats efficiently entrap organic carbon and are sinks of organic material in the coastal zone. Parallel deployment of 0.1 m(2) benthic chambers during nighttime revealed O-2 uptake rates that varied by up to similar to 8-fold between replicate chambers (from -0.4 to -3.0 mmol O-2 m(-2) h(-1); n = 4). However, despite extensive O-2 flux variability on meter horizontal scales, mean rates of O-2 uptake as resolved in parallel by chambers and EC were typically within 20% of one another.

Highlights • Field-scale sub-seabed release experiment to simulate leakage from CO2 reservoir. • CO2 induces pronounced changes in pore water geochemistry. • Dissolution of minerals as a result of increased dissolved CO2 concentrations. • Changes in pore water geochemistry are transient and spatially restricted. • Levels of released metals are low and likely to have minor impact on benthic ecosystems. Abstract The potential for leakage of CO2 from a storage reservoir into the overlying marine sediments and into the water column and the impacts on benthic ecosystems are major challenges associated with carbon capture and storage (CCS) in subseafloor reservoirs. We have conducted a field-scale controlled CO2 release experiment in shallow, unconsolidated marine sediments, and documented the changes to the chemical composition of the sediments, their pore waters and overlying water column before, during and up to 1 year after the 37-day long CO2 release. Increased levels of dissolved inorganic carbon (DIC) were detected in the pore waters close to the sediment-seawater interface in sediments sampled closest to the subsurface injection point within 5 weeks of the start of the CO2 release. Highest DIC concentrations (28.8 mmol L−1, compared to background levels of 2.4 mmol L−1) were observed 6 days after the injection had stopped. The high DIC pore waters have high total alkalinity, and low δ13CDIC values (−20‰, compared to a background value of −2‰), due to the dissolution of the injected CO2 (δ13C = −26.6‰). The high DIC pore waters have enhanced concentrations of metals (including Ca, Fe, Mn) and dissolved silicon, relative to non-DIC enriched pore waters, indicating that dissolution of injected CO2 promotes dissolution of carbonate and silicate minerals. However, in this experiment, the pore water metal concentrations did not exceed levels considered to be harmful to the environment. The spatial extent of the impact of the injected CO2 in the sediments and pore waters was restricted to an area within 25 m of the injection point, and no impact was observed in the overlying water column. Concentrations of all pore water constituents returned to background values within 18 days after the CO2 injection was stopped.

Highlights • Development of a marine monitoring system suitable for operational CCS is achievable. • Monitoring should be hierarchical, starting with anomaly detection. • Comprehensive baselines are required to support monitoring. Abstract The QICS controlled release experiment demonstrates that leaks of carbon dioxide (CO2) gas can be detected by monitoring acoustic, geochemical and biological parameters within a given marine system. However the natural complexity and variability of marine system responses to (artificial) leakage strongly suggests that there are no absolute indicators of leakage or impact that can unequivocally and universally be used for all potential future storage sites. We suggest a multivariate, hierarchical approach to monitoring, escalating from anomaly detection to attribution, quantification and then impact assessment, as required. Given the spatial heterogeneity of many marine ecosystems it is essential that environmental monitoring programmes are supported by a temporally (tidal, seasonal and annual) and spatially resolved baseline of data from which changes can be accurately identified. In this paper we outline and discuss the options for monitoring methodologies and identify the components of an appropriate baseline survey.

A possible effect of a carbon dioxide leak from an industrial sub-sea floor storage facility, utilised for Carbon Capture and Storage, is that escaping carbon dioxide gas will dissolve in sediment pore waters and reduce their pH. To quantify the scale and duration of such an impact, a novel, field scale experiment was conducted, whereby carbon dioxide gas was injected into unconsolidated sub-sea floor sediments for a sustained period of 37 days. During this time pore water pH in shallow sediment (5mm depth) above the leak dropped >0.8unit, relative to a reference zone that was unaffected by the carbon dioxide. After the gas release was stopped, the pore water pH returned to normal background values within a three-week recovery period. Further, the total mass of carbon dioxide dissolved within the sediment pore fluids above the release zone was modelled by the difference in DIC between the reference and release zones. Results showed that between 14 and 63% of the carbon dioxide released during the experiment could remain in the dissolved phase within the sediment pore water.

This work is focused on results from a recent controlled sub-seabed in situ carbon dioxide (CO2) release experiment carried out during May–October 2012 in Ardmucknish Bay on the Scottish west coast. Three types of pCO2 sensors (fluorescence, NDIR and ISFET-based technologies) were used in combination with multiparameter instruments measuring oxygen, temperature, salinity and currents in the water column at the epicentre of release and further away. It was shown that distribution of seafloor CO2 emissions features high spatial and temporal heterogeneity. The highest pCO2 values (?1250 ?atm) were detected at low tide around a bubble stream and within centimetres distance from the seafloor. Further up in the water column, 30–100 cm above the seabed, the gradients decreased, but continued to indicate elevated pCO2 at the epicentre of release throughout the injection campaign with the peak values between 400 and 740 ?atm. High-frequency parallel measurements from two instruments placed within 1 m from each other, relocation of one of the instruments at the release site and 2D horizontal mapping of the release and control sites confirmed a localized impact from CO2 emissions. Observed effects on the water column were temporary and post-injection recovery took A multivariate statistical approach was used to recognize the periods when the system was dominated by natural forcing with strong correlation between variation in pCO2 and O2, and when it was influenced by purposefully released CO2.Use of a hydrodynamic circulation model, calibrated with in situ data, was crucial to establishing background conditions in this complex and dynamic shallow water system.

Highlights • A unique and novel CO2 release experiment in the marine environment. • Field-scale simulated leak of CO2 gas from a carbon capture and storage facility. • Experimental design and set-up for the QICS experiment, conducted during the summer of 2012. Abstract Carbon capture and storage is a mitigation strategy that can be used to aid the reduction of anthropogenic CO2 emissions. This process aims to capture CO2 from large point-source emitters and transport it to a long-term storage site. For much of Europe, these deep storage sites are anticipated to be sited below the sea bed on continental shelves. A key operational requirement is an understanding of best practice of monitoring for potential leakage and of the environmental impact that could result from a diffusive leak from a storage complex. Here we describe a controlled CO2 release experiment beneath the seabed, which overcomes the limitations of laboratory simulations and natural analogues. The complex processes involved in setting up the experimental facility and ensuring its successful operation are discussed, including site selection, permissions, communications and facility construction. The experimental design and observational strategy are reviewed with respect to scientific outcomes along with lessons learnt in order to facilitate any similar future.

The community respiration of 2 tidally dominated cold-water coral (CWC) sites was estimated using the non-invasive eddy correlation (EC) technique. The first site, Mingulay Reef Complex, was a rock ridge located in the Sea of Hebrides off Scotland at a depth of 128 m and the second site, Stjernsund, was a channel-like sound in Northern Norway at a depth of 220 m. Both sites were characterized by the presence of live mounds of the reef framework-forming scleractinian Lophelia pertusa and reef-associated fauna such as sponges, crustaceans and other corals. The measured O-2 uptake at the 2 sites varied between 5 and 46 mmol m(-2) d(-1), mainly depending on the ambient flow characteristics. The average uptake rate estimated from the similar to 24 h long deployments amounted to 27.8 +/- 2.3 mmol m(-2) d(-1) at Mingulay and 24.8 +/- 2.6 mmol m(-2) d(-1) at Stjernsund (mean +/- SE). These rates are 4 to 5 times higher than the global mean for soft sediment communities at comparable depths. The measurements document the importance of CWC communities for local and regional carbon cycling and demonstrate that the EC technique is a valuable tool for assessing rates of benthic O2 uptake in such complex and dynamic settings.

Highlights • pH profiling methods often fall short of marine OA and CCS experimental needs. • A new optical sensor application (MOPP) helps to meet these needs. • MOPP identified distinct impact and recovery patterns in different sediment types. • Patterns depend on sediment characteristics, i.e. buffering capacity and permeability. • CCS and OA impact assessment thus require consideration of these differences. Abstract Available methods for measuring the impact of ocean acidification (OA) and leakage from carbon capture and storage (CCS) on marine sedimentary pH profiles are unsuitable for replicated experimental setups. To overcome this issue, a novel optical sensor application is presented, using off-the-shelf optode technology (MOPP). The application is validated using microprofiling, during a CCS leakage experiment, where the impact and recovery from a high CO2 plume was investigated in two types of natural marine sediment. MOPP offered user-friendliness, speed of data acquisition, robustness to sediment type, and large sediment depth range. This ensemble of characteristics overcomes many of the challenges found with other pH measuring methods, in OA and CCS research. The impact varied greatly between sediment types, depending on baseline pH variability and sediment permeability. Sedimentary pH profile recovery was quick, with profiles close to control conditions 24 h after the cessation of the leak. However, variability of pH within the finer sediment was still apparent 4 days into the recovery phase. Habitat characteristics need therefore to be considered, to truly disentangle high CO2 perturbation impacts on benthic systems. Impacts on natural communities depend not only on the pH gradient caused by perturbation, but also on other processes that outlive the perturbation, adding complexity to recovery.

A laboratory-based optical pH sensor for 2-dimensional pH imaging at benthic interfaces is presented. The sensor consists of a single-layer hydrogel matrix embedding the fluorescent pH indicator 2′, 7′-dihexyl-5(6)-Noctadecyl-carboxamidofluorescein ethyl ester (DHFAE) and the phosphorescent ruthenium(II)-Tris-4,7-diphenyl1,10-phenanthroline incorporated in nanoparticles, serving as an inert reference standard. The measuring principle is based on time domain dual-lifetime referencing (t-DLR). The fluorophore/phosphor couple is simultaneously excited by a green LED (λ max 530 nm) pulsed in the microsecond range, and the sensor emission is recorded by a fast-gateable CCD camera. For each pH image, intensity images in 2 time windows (1 during and 1 after the excitation phase) are taken. The ratio of these 2 images is proportional to the pH of the sample and not affected by the overall signal intensity. The sensor has a dynamic range suitable for marine conditions (pH 7.3 to 9.3) with an apparent pK a of 8.3. The sensor was long-term stable (months) when kept in darkness and had a response time of < 200 s when going from pH 8.3 to 7.6. Light proved to have a negative effect on the sensor performance due to photobleaching of the pH indicator, resulting in a negative drift in the signal ratio at higher pH after prolonged light exposure. The spatial resolution (83 by 83 μm/pixel) of the sensor was capable of resolving smallscale spatial variability in the pH at a heterogeneous sediment-water interface, and time series of calibrated pH images also expressed a marked temporal variability in the pH distribution across this interface. Hotspots with intensified microbial activity were observed, and pH minima along burrow walls of polychaetes indicated elevated diagenetic activity in these zones. Individually extracted profiles from the pH images agreed well with independently measured pH microelectrode profiles, confirming the robustness of the approach.

Rates of transformation, recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP), NE Atlantic during eight cruises from 1996 to 2000. Benthic fluxes of ammonium (NH4) and nitrate (NO3) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were calculated from pore water profiles of DON and NO3, respectively. Burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with 14C-based sediment accumulation rates and dry bulk density. Average NH4 and NO3-effluxes were 7.4 ± 19 [mu]mol m-2 d-1 (n = 7) and 52 ± 30 [mu]mol m-2 d-1 (n = 14), respectively, during the period 1996-2000. During the same period, the DON-flux was 11 ± 5.6 [mu]mol m-2 d-1 (n = 5) and the denitrification rate was 5.1 ± 3.0 [mu]mol m-2 d-1 (n = 22). Temporal and spatial variations were only found in the benthic NO3 fluxes. The average burial rate was 4.6 ± 0.9 [mu]mol m-2 d-1. On average over the sampling period, the recycling efficiency of the PON input to the sediment was ~94% and the burial efficiency hence ~6%. The DON flux constituted ~14% of the nitrogen recycled, and it was of similar magnitude as the sum of burial and denitrification. By assuming the PAP is representative of all deep-sea areas, rates of denitrification, burial and DON efflux were extrapolated to the total area of the deep-sea floor (>2000 m) and integrated values of denitrification and burial of 8 ± 5 and 7 ± 1 Tg N year-1, respectively, were obtained. This value of total deep-sea sediment denitrification corresponds to 3-12% of the global ocean benthic denitrification. Burial in deep-sea sediments makes up at least 25% of the global ocean nitrogen burial. The integrated DON flux from the deep-sea floor is comparable in magnitude to a reported global riverine input of DON suggesting that deep-sea sediments constitute an important source of DON to the world ocean.

Different factors influencing recycling and burial rates of organic carbon (OC) were investigated in the continental margin sediments of the Skagerrak (NE North Sea). Two different areas, one in the southern and one in the northeastern part of the Skagerrak were visited shortly after a spring bloom (March 1999) and in late summer (August 2000). Results suggested that: (1) Organic carbon oxidation rates (C ox ) (2.2-18 mmol C m -2 d -1 ) were generally larger than the O 2 uptake rates (1.9-25 mmol m -2 d -1 ). Both rates were measured in situ using a benthic lander. A mean apparent respiration ratio (C ox :O 2coor ) of 1.3 ± 0.5 was found, indicating some long-term burial of reduced inorganic substances in these sediments. Measured O 2 fluxes increased linearly with increasing C ox rates during the late summer cruise but not on the early spring cruise, indicating a temporal uncoupling of anaerobic mineralization and reoxidation of reduced substances. (2) Dissolved organic carbon (DOC) fluxes (0.2-1.0 mmol C m -2 d -1 ) constituted 3-10% of the C ox rates and were positively correlated with the latter, implying that net DOC production rates were proportional to the overall sediment OC remineralization rates. (3) Chlorophyll a (Chl-a) concentrations in the sediment were significantly higher in early spring compared to late summer. The measured C ox rates, but not O 2 fluxes, showed a strong positive correlation with the Chl-a inventories in the top 3 cm of the sediment. (4) Although no relationship was found between the benthic fluxes and the macrofaunal biomass in the chambers, total in situ measured dissolved inorganic carbon (C T ) fluxes were 1-5.4 times higher than diffusive mediated C T fluxes, indicating that macrofauna have a significant impact on benthic exchange rates of OC remineralization products in Skagerrak sediments. (5) OC burial fluxes were generally higher in northeastern Skagerrak than in the southern part. The same pattern was observed for burial efficiencies, with annual means of ∼62% and ∼43% for the two areas respectively. (6) On a basin-wide scale, there was a significant positive linear correlation between the burial efficiencies and sediment accumulation rates. (7) The calculated particulate organic carbon (POC) deposition, from benthic flux and burial measurements, was only 24-78% of the sediment trap measured POC deposition, indicating a strong near-bottom lateral transport and resuspension of POC. (8) A larger fraction of the laterally advected material of lower quality seemed to seetle in the northeastern Skagerrak rather than in the southern Skagerrak. (9) Skagerrak sediments, especially in the northeastern part, act as an efficient net sink for organic carbon, even in a global continental margin context.

Rates of degradation, recycling and burial of organic carbon (OC) and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP) in the Northeast Atlantic Ocean (depth 4800–4850 m) during six cruises in August 1996—April 1999. Benthic fluxes of total dissolved inorganic carbon ( C T ) and alkalinity ( A T ) were measured in situ using benthic chambers of a free-vehicle benthic lander on four of the cruises. To obtain the OC oxidation rate ( C ox ), the C T flux in each chamber was corrected for CaCO 3 dissolution. Burial of OC was determined by using downcore profiles of OC ( n =20) in the solid phase of the sediment and sediment accumulation rates estimated from a model age based on 14 C dating of foraminifera. Results obtained showed that during 1996–1999 C ox rates in PAP sediments varied between deployments from 0.21±0.04 to 0.86±0.23 mmol m −2 d −1 with a total mean of 0.46 mmol m −2 d −1 (SD±0.37, n =31). No statistically significant spatial (between stations) or temporal (seasonal as well as interannual) variation in the C ox rates could be detected during the sampling period. The mean burial rate was determined to be 0.03±0.01 mmol m −2 d −1 . On average over the sampling period, ∼94% of the particulate organic carbon (POC) deposited was recycled as C T to the overlying water and ∼6% was buried. The calculated mean POC demand during 1996–1999 of 0.49±0.37 mmol m −2 d −1 (the sum of corrected C T and burial fluxes) was not significantly different from the annual integrated mean POC supply (1997–1999) of 0.24±0.06 mmol m −2 d −1 estimated from calibrated sediment traps 1800 mab at the same locality.

The hydrodynamic properties and the capability to measure sediment–water solute fluxes, at assumed steady state conditions, were compared for three radically different benthic chamber designs: the “Microcosm”, the “Mississippi” and the “Goteborg” chambers. The hydrodynamic properties were characterized by mounting a PVC bottom in each chamber and measuring mixing time, diffusive boundary layer thickness (DBL thickness) shear velocity (u ∗ ) , and total pressure created by the water mixing. The Microcosm had the most even distribution of DBL thickness and u ∗ , but the highest differential pressure at high water mixing rates. The Mississippi chamber had low differential pressures at high u ∗ . The Goteborg chamber was in between the two others regarding these properties. DBL thickness and u ∗ were found to correlate according to the following empirical formula: DBL=76.18(u ∗ ) −0.933 . Multiple flux incubations with replicates of each of the chamber types were carried out on homogenized, macrofauna-free sediments in four tanks. The degree of homogeneity was determined by calculating solute fluxes (of oxygen, silicate, phosphate and ammonium) from porewater profiles and by sampling for porosity, organic carbon and meiofauna. All these results, except meiofauna, indicated that there were no significant horizontal variations within the sediment in any of the parallel incubation experiments. The statistical evaluations also suggested that the occasional variations in meiofauna abundance did not have any influence on the measured solute fluxes. Forty-three microelectrode profiles of oxygen in the DBL and porewater were evaluated with four different procedures to calculate diffusive fluxes. The procedure presented by Berg, Risgaard-Petersen and Rysgaard, 1989 [Limnol. Oceanogr. 43, 1500] was found to be superior because of its ability to fit measured profiles accurately, and because it takes into consideration vertical zonation with different oxygen consumption rates in the sediment. During the flux incubations, the mixing in the chambers was replicated ranging from slow mixing to just noticeable sediment resuspension. In the “hydrodynamic characterizations” these mixing rates corresponded to average DBL thickness from 120 to 550 μm, to u ∗ from 0.12 to 0.68 cm/s, and to differential pressures from 0–3 Pa. Although not directly transferable, since the incubations were done on a “real” sediment with a rougher surface while in the characterizations a PVC plate simulated the sediments surface, these data give ideas about the prevailing hydrodynamic condition in the chambers during the incubations. The variations in water mixing did not generate statistically significant differences between the chamber types for any of the measured fluxes of oxygen or nutrients. Consequently it can be concluded that, for these non-permeable sediments and so long as appropriate water mixing (within the ranges given above) is maintained, the type of stirring mechanism and chamber design used were not critical for the magnitude of the measured fluxes. The average measured oxygen flux was 11.2 ± 2.7 (from 40 incubations), while the diffusive flux calculated (from 43 profiles using the Berg et al., 1989 [Limnol. Oceanogr. 43, 1500] procedure) was 11.1 ± 3.0 mmol m−2 day−1. This strongly suggests that accurate oxygen flux measurements were obtained with the three types of benthic chambers used and that the oxygen uptake is diffusive.

Fossil fuel power generation and other industrial emissions of carbon dioxide are a threat to global climate, yet many economies will remain reliant on these technologies for several decades. Carbon dioxide capture and storage (CCS) in deep geological formations provides an effective option to remove these emissions from the climate system. In many regions storage reservoirs are located offshore, over a kilometre or more below societally important shelf seas. Therefore, concerns about the possibility of leakage and potential environmental impacts, along with economics, have contributed to delaying development of operational CCS. Here we investigate the detectability and environmental impact of leakage from a controlled sub-seabed release of CO2 . We show that the biological impact and footprint of this small leak analogue (2 d â '1) is confined to a few tens of metres. Migration of CO2 through the shallow seabed is influenced by near-surface sediment structure, and by dissolution and re-precipitation of calcium carbonate naturally present in sediments. Results reported here advance the understanding of environmental sensitivity to leakage and identify appropriate monitoring strategies for full-scale carbon storage operations.

In this paper we provide an overview of new knowledge on oxygen depletion (hypoxia) and related phenomena in aquatic systems resulting from the EU-FP7 project HYPOX ("In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and landlocked water bodies", http://www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and climate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and consequences. Temporal dynamics and spatial patterns of hypoxia were analyzed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia, as well as seasonal changes in bottom-water oxygenation in stratified systems, are discussed. Geologically driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of water-column oxygenation, from basin-scale seasonal patterns to meter-scale sub-micromolar oxygen distributions, were resolved. Existing multidecadal monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions. Organic and inorganic proxies were used to extend investigations on past oxygen conditions to centennial and even longer timescales that cannot be resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic communities that slowly recover upon a reduction in eutrophication in a system where naturally occurring hypoxia overlaps with anthropogenic hypoxia. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on the microbially mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic mineralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Technical issues are therefore also addressed, including the availability of suitable sensor technology to resolve the gradual changes in bottom-water oxygen in marine systems that can be expected as a result of climate change. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards, and how ocean observations can contribute to global earth observation attempts.

This case study demonstrates that Alloy 601 (UNS N06601) is susceptible to strain-age cracking. The observation illustrates the potential importance of post weld heat treatment to the successful utilization of this alloy in certain applications.

Within the framework of the EU-funded BENGAL programme, the effects of seasonality on biogenic silica early diagenesis have been studied at the Porcupine Abyssal Plain (PAP), an abyssal locality located in the northeast Atlantic Ocean. Nine cruises were carried out between August 1996 and August 1998. Silicic acid (DSi) increased downward from 46.2 to 213 μM (mean of 27 profiles). Biogenic silica (BSi) decreased from ca. 2% near the sediment–water interface to

Fluxes contributing to the particulate carbonate system in deep-sea sediments were investigated at the BENGAL site in the Porcupine Abyssal Plain (Northeast Atlantic). Deposition fluxes were estimated using sediment traps at a nominal depth of 3000 m and amounted to 0.37±0.1 mmol C m−2 d−1. Dissolution of carbonate was determined using flux of total alkalinity from in situ benthic chambers, is 0.4±0.1 mmol C m−2 d−1. Burial of carbonate was calculated from data on the carbonate content of the sediment and sedimentation rates from a model age based on 14C dating on foraminifera (0.66±0.1 mmol C m−2 d−1). Burial plus dissolution was three times larger than particle deposition flux which indicates that steady-state is not achieved in these sediments. Mass balances for other components (BSi, 210Pb), and calculations of the focusing factor using 230Th, show that lateral inputs play only a minor role in this imbalance. Decadal variations of annual particle fluxes are also within the uncertainty of our average. Long-term change in dissolution may contribute to the imbalance, but can not be the main reason because burial alone is greater than the input flux. The observed imbalance is thus the consequence of a large change of carbonate input flux which has occured in the recent past. A box model is used to check the response time of the solid carbonate system in these sediments and the time to reach a new steady-state is in the order of 3 kyr. Thus it is likely that the system has been perturbed recently and that large dissolution and burial rates reflect the previously larger particulate carbonate deposition rates. We estimate that particulate carbonate fluxes have certainly decreased by a factor of at least 3 and that this change has occurred during the last few centuries.

Pore water profiles were obtained at high resolution (millimeter scale) in marine sediments using a DET (diffusive equilibration in thin films) gel probe. A plastic probe which holds a 1–2 mm thick polyacrylamide gel covered by a 0.45 μm Millipore filter is inserted into the sediment. The gel was prehydrated in water of similar salinity to the in situ sampling conditions. Chloride and sulphate needed 24 and 48 h for complete front and back equilibration, respectively, while 6–8 h (front) and 4–6 h (back) were used for calcium and alkalinity. Ammonia-N and total CO2 were back-equilibrated for 2 h. Probes were sectioned immediately after sampling, stored for up to 1–2 days (NH4+, ∑CO2) or for up to 1–2 weeks (Ca, alkalinity, Cl, SO4, NO3), before they were back-equilibrated into Milli-Q water or 0.7 M NaCl (calcium and alkalinity). The gel retains between 3–7% of the total sulphate. A simple procedure has been developed to correct for this incomplete recovery. Recovery tests using seawater and 50% seawater spiked to concentrations found in nearshore pore waters, showed recoveries of 101.4±0.5% (chloride), 101.4±0.7% (bromide), 100.3±0.2% (nitrate), 96.6±0.7% (sulphate), 99.7±0.8% (ammonia-N), 99.1±1.2% (∑CO2), 96.9±0.8% (calcium) and 96.8±1.4% (alkalinity) (mean±standard error). Pore water profiles obtained simultaneously using gel probes and conventional techniques (box core-anoxic slicing followed by centrifugation) showed excellent comparability at cm resolution though features which required higher resolution which could only be seen in the gel profiles.

ISI Document Delivery No.: 192NG Times Cited: 0 Cited Reference Count: 54 Cited References: Austin WEN, 2002, POLAR RES, V21, P251, DOI 10.1111/j.1751-8369.2002.tb00078.x BOLLINGER MS, 1984, NATURE, V309, P444, DOI 10.1038/309444a0 BROECKER WS, 1967, SCIENCE, V158, P1307, DOI 10.1126/science.158.3806.1307 BROECKER WS, 1973, EARTH PLANET SC LETT, V20, P35, DOI 10.1016/0012-821X(73)90137-4 Charette MA, 2001, LIMNOL OCEANOGR, V46, P465 CHUNG Y, 1980, EARTH PLANET SC LETT, V49, P309, DOI 10.1016/0012-821X(80)90074-6 Cloern JE, 2001, MAR ECOL PROG SER, V210, P223, DOI 10.3354/meps210223 COCHRAN J. K, 1984, THE ESTUARY AS A FIL, P179 COCHRAN JK, 1980, AM J SCI, V280, P849 COHEN AS, 1991, ANAL CHEM, V63, P2705, DOI 10.1021/ac00023a008 EDWARDS A, 1986, NATO ASI SERIES G, VG7, P195 EDWARDS A, 1977, ESTUAR COAST MAR SCI, V5, P575, DOI 10.1016/0302-3524(77)90085-8 EDWARDS A, 1986, SCOTTISH MARINE BIOL Foster DA, 2004, MAR CHEM, V87, P59, DOI 10.1016/j.marchem.2004.02.003 Geibert W, 2008, MAR CHEM, V109, P409, DOI 10.1016/j.marchem.2007.07.005 HAMMOND DE, 1990, J GEOPHYS RES-OCEANS, V95, P3321, DOI 10.1029/JC095iC03p03321 Hancock GJ, 2006, J GEOPHYS RES-OCEANS, V111, DOI 10.1029/2006JC003608 Hancock GJ, 2000, GEOCHIM COSMOCHIM AC, V64, P3685, DOI 10.1016/S0016-7037(00)00469-5 HOWE J. A, 2001, ARGYLL SCOTT J GEOL, V37, P3 Howe JA, 2002, MAR GEOL, V185, P417, DOI 10.1016/S0025-3227(01)00299-7 Howe JA, 2010, GEOL SOC SPEC PUBL, V344, P5, DOI 10.1144/SP344.2 Hsieh YT, 2011, J ANAL ATOM SPECTROM, V26, P1338, DOI 10.1039/c1ja10013k Inall M, 2004, OCEAN DYNAM, V54, P307, DOI 10.1007/s10236-003-0059-2 Inall ME, 2009, GEOPHYS RES LETT, V36, DOI 10.1029/2008GL036849 KADKO D, 1987, GEOCHIM COSMOCHIM AC, V51, P1613, DOI 10.1016/0016-7037(87)90342-5 Karakassis I, 2000, ICES J MAR SCI, V57, P1462, DOI 10.1006/jmsc.2000.0925 KAUFMAN A, 1973, J GEOPHYS RES, V78, P8827, DOI 10.1029/JC078i036p08827 VanderLoeff MMR, 1995, DEEP-SEA RES PT II, V42, P1533 KU TL, 1994, J GEOPHYS RES-OCEANS, V99, P10255, DOI 10.1029/94JC00089 Ku TL, 2008, RADIOACTIV ENVIRONM, V13, P307, DOI 10.1016/S1569-4860(07)00009-5 LI YH, 1979, EARTH PLANET SC LETT, V43, P343, DOI 10.1016/0012-821X(79)90089-X MOORE WS, 1985, J GEOPHYS RES-OCEANS, V90, P6983, DOI 10.1029/JC090iC04p06983 Moore WS, 1998, P INDIAN AS-EARTH, V107, P343 Moore WS, 1996, J GEOPHYS RES-OCEANS, V101, P1321, DOI 10.1029/95JC03139 Moore WS, 2000, J GEOPHYS RES-OCEANS, V105, P22117, DOI 10.1029/1999JC000289 Moore WS, 2000, CONT SHELF RES, V20, P1993, DOI 10.1016/S0278-4343(00)00054-6 Moore WS, 2008, MAR CHEM, V109, P188, DOI 10.1016/j.marchem.2007.06.015 Moore WS, 2008, NAT GEOSCI, V1, P309, DOI 10.1038/ngeo183 Overnell J, 2002, ESTUAR COAST SHELF S, V55, P481, DOI 10.1006/ecss.2001.0919 Porcelli D, 2003, REV MINERAL GEOCHEM, V52, P317, DOI 10.2113/0520317 Rama, 1996, GEOCHIM COSMOCHIM AC, V60, P4645 RIDGWAY IM, 1987, MAR CHEM, V21, P229, DOI 10.1016/0304-4203(87)90061-2 SANTSCHI PH, 1980, EARTH PLANET SC LETT, V51, P248, DOI 10.1016/0012-821X(80)90208-3 SARMIENTO JL, 1976, EARTH PLANET SC LETT, V32, P357, DOI 10.1016/0012-821X(76)90076-5 Scholten JC, 2010, MAR CHEM, V121, P206, DOI 10.1016/j.marchem.2010.04.009 Skogen MD, 2009, AQUACULTURE, V298, P70, DOI 10.1016/j.aquaculture.2009.10.018 STAHL H, 2011, SET UP AND IMPLEMENT Stashchuk N, 2007, J PHYS OCEANOGR, V37, P1793, DOI 10.1175/JPO3087.1 Statham PJ, 2005, ENVIRON SCI TECHNOL, V39, P9440, DOI 10.1021/es050980t Straneo F, 2011, NAT GEOSCI, V4, P322, DOI [10.1038/ngeo1109, 10.1038/NGEO1109] TAMMEMAGI HY, 1976, GEOL MAG, V113, P271 van Beek P, 2008, DEEP-SEA RES PT II, V55, P622, DOI 10.1016/j.dsr2.2007.12.025 WEBSTER IT, 1994, LIMNOL OCEANOGR, V39, P1917 WOOD BJB, 1973, J ECOL, V61, P569, DOI 10.2307/2259045 Hsieh, Yu-Te Geibert, Walter van-Beek, Pieter Stahl, Henrik Aleynik, Dmitry Henderson, Gideon M. British Council 'Alliance' grant [09.014]; Scottish Alliance for Geosciences, Environment and Society (SAGES); EU FP7 project HYPOX [226213]; Swire Educational Trust for Hsieh's scholarship at University College, University of Oxford We thank the crew of R/V Calanus for sampling assistance. Sabine Cockenpot, Tristan Horner, Robyn Tuerena, and Xinyuan Zheng are also acknowledged for their assistance in sample collections. We thank John Howe for providing the bathymetry and sedimentary background of Loch Etive and Mark Inall for discussion of ocean mixing in Loch Etive. Willard Moore and Don Porcelli are also thanked for helpful discussion. Alex Thomas, Andrew Mason, and Steve Wyatt are acknowledged for assistance with mass spectrometry and laboratory support. W.G. and P.vB. were supported by the British Council 'Alliance' grant 09.014. W.G. was supported by the Scottish Alliance for Geosciences, Environment and Society (SAGES). The cabled mooring installation in Loch Etive was supported by EU FP7 project HYPOX (grant 226213). The Swire Educational Trust is thanked for Hsieh's scholarship at University College, University of Oxford. We are grateful to Bo Thamdrup, the associate editor, Michiel Rutgers van der Loeff, and an anonymous referee for very helpful reviews and constructive comments. 0 AMER SOC LIMNOLOGY OCEANOGRAPHY WACO LIMNOL OCEANOGR; The radium (Ra) quartet (Ra-228, Ra-226, Ra-224, and Ra-223) has been investigated in Loch Etive, a Scottish fjord, to provide new constraints on water mixing rates and on the inputs of Ra from sediments. Maximum water transport rates for the inflowing estuarine layer at 5 m depth, determined from the excess Ra-223 (Ra-223(ex)), indicate that this water travels at no more than 2.4 +/- 0.2 cm s(-1) net and that it takes 17 +/- 2 d for waters to travel from the mouth to the head of the loch if no horizontal mixing is taken into account. Alternatively, neglecting advection, the short-lived Ra distribution could be explained by horizontal mixing rates of 6.1 x 10(6) cm(2) s(-1) (Ra-223(ex)) or 9.1 x 10(6) cm(2) s(-1) (Ra-224(ex)). Periodic overturning circulation plays an important role in resetting chemical cycles in the isolated deep basin of the inner loch. Sediment in this deep basin provides the major input of Ra-228 to the isolated deep water, and the accumulation of Ra-228 in deep waters allows an assessment of sedimentary fluxes of Ra-228, a poorly constrained aspect of the Ra-228 input to the global ocean. The calculated sedimentary Ra-228 flux of 2.1 +/- 0.2 (x 10(9)) atoms m(-2) yr(-1) in the inner deep basin is comparable with previous measurements of sedimentary Ra-228 inputs from shelf sediments, supporting existing global Ra-228 budgets, which are used to assess global rates of groundwater discharge to the ocean.

The significance of freshwaters as key players in the global budget of both carbon dioxide and methane has recently been highlighted. In particular, rivers clearly do not act simply as inert conduits merely piping carbon from catchment to coast, but, on the whole, their metabolic activity transforms a considerable fraction of the carbon that they convey. In addition, nitrogen is cycled, sometimes in tight unison with carbon, with appreciable amounts being ‘denitrified’ between catchment and coast. However, shortfalls in our knowledge about the significance of exchange and interaction between rivers and their catchments, particularly the significance of interactions mediated through hyporheic sediments, are still apparent. From humble beginnings of quantifying the consumption of oxygen by small samples of gravel, to an integrated measurement of reach scale transformations of carbon and nitrogen, our understanding of the cycling of these two macro elements in rivers has improved markedly in the past few decades. However, recent discoveries of novel metabolic pathways in both the nitrogen and carbon cycle across a spectrum of aquatic ecosystems, highlights the need for new directions and a truly multidisciplinary approach to quantifying the flux of carbon and nitrogen through rivers.

We present and compare small sediment‐water fluxes of O2 determined with the eddy correlation technique, with in situ chambers, and from vertical sediment microprofiles at a 1450 m deep‐ocean site in Sagami Bay, Japan. The average O2 uptake for the three approaches, respectively, was 1.62 ± 0.23 (SE, n = 7), 1.65 ± 0.33 (n = 2), and 1.43 ± 0.15 (n = 25) mmol m−2 d−1. The very good agreement between the eddy correlation flux and the chamber flux serves as a new, important validation of the eddy correlation technique. It demonstrates that the eddy correlation instrumentation available today is precise and can resolve accurately even very small benthic O2 fluxes. The correlated fluctuations in vertical velocity and O2 concentration that give the eddy flux had average values of 0.074 cm s−1 and 0.049 µM. The latter represents only 0.08% of the 59 µM mean O2 concentration of the bottom water. Note that these specific fluctuations are average values, and that even smaller variations were recorded and contributed to the eddy flux. Our findings demonstrate that the eddy correlation technique is a highly attractive alternative to traditional flux methods for measuring even very small benthic O2 fluxes.

On the basis of in situ NO3−1 microprofiles and chamber incubations complemented by laboratory‐based assessments of anammox and denitrification we evaluate the nitrogen turnover of an ocean margin sediment at 1450‐m water depth. In situ NO3−1 profiles horizontally separated by 12 mm reflected highly variable NO3−1 penetration depths, NO3−1 consumption rates, and nitrification. On average the turnover time of the pore‐water NO3−1 pool was ~0.2 d. Net release of NH4+ during mineralization (0.95 mmol m−2 d−1) sustained a net efflux of ammonia (53%), nitrification (24%), and anammox activity (23%). The sediment had a relatively high in situ net influx of NO3−1 (1.44 mmol m−2 d−1) that balanced the N2 production as assessed by onboard tracer experiments. N2 production was attributed to prokaryotic denitrification (59%), anammox (37%), and foraminifera‐based denitrification (4%). Anammox thereby represented an important nutrient sink, but the N2 production was dominated by denitrification. Despite the fact that NO3−1 stored inside foraminifera represented ~80% of the total benthic NO3−1 pool, the slow intracellular NO3−1 turnover that, on average, sustained foraminifera metabolism for 12‐52 d, contributed only to a minor extent to the overall N2 production. The microbial activity in the surface sediment is a net nutrient sink of ~1.1 mmol N m−2 d−1, which aligns with many studies performed in coastal and shelf environments. Continental margin areas can act as significant N sinks and play an important role in regional N budgets.

The first long time monitoring of O2 dynamics at sediment-water interface (SWI) was conducted using with a newly developed planar O2 optode system for in situ measurement. The monitoring was carried out connecting the optode system with Hatsushima permanent station with a 100 meter-long extension cable under supporting by the operation of ROV Hyper-dolphin. The monitoring was successfully carried out for 113.3 hours. During the experiment, 3,141 two dimensional O2 profiles and the corresponding pseudo-grayscale images across SWI were obtained, respectively. From the results, further understanding of new insights on dynamic interactions between fauna activities and environmental changes are expected.

Editor: Scottish Association for Marine Science, Scotland, U.K.