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The COVID-19 pandemic has obliged Governments all around the world to implement confinement and social distancing measures. Leisure and business activities on beaches and in ports have restricted direct and indirect contamination from, for example, plastics, hydrocarbon spillage, microbiological loads, and noise levels. This has led to temporarily improved environmental conditions, and the beaches having conditions closer to Marine Protected Areas. Here we report some impacts that have been studied using local surveys and qualitative observations in Ecuador at the popular beaches and ports of Salinas, Manta, and Galapagos. Satellite data support this information. Online surveys were carried out at critical moments of the pandemic: May (15th) and just after when measures were relaxed a little, but within lockdown in July (21st) 2020. Respondents were asked to compare conditions before and during the pandemic lockdown. Most (97–99%) suggested that beaches had significantly improved from visual observations during confinement. On a scale from 1 (worst) to 5 (best), the beaches of Salinas and Manta respectively were rated 2.2 and 2.8 (less than acceptable) before quarantine, and 4.5 and 4.3 after; results from the second survey (after 18 weeks of restrictions) were much the same. Replies from Galapagos showed a similar trend but with less marked differences. In addition to the beaches having less plastic and garbage, more fish, and large marine organisms, including humpback whales (Megaptera novaeangliae), dolphin (bottlenose, Tursiops truncatus), and manta ray (Manta sp.) were observed near to shore. At Galapagos beaches, turtles, sea lions, and sharks were observed many more times than pre COVID. Quantitative satellite data on Chlorophyl and attenuation coefficient (Kd, 490 nm) support the qualitative survey data that there is an improvement in coastal environment quality. Here we recommend that this unique opportunity resulting from the COVID-19 pandemic is used locally, regionally and globally to construct baseline data sets that include information on physical, chemical, biological, and microbiological factors in coastal zones. These parameters can then help establish an effective Coastal Zone Management Plan based on beach description and quality (water standards, noise pollution), as well as the human dimension (tourist load, cultural heritage, and economic value indices). This data and information gathering ideally should be done before the beaches become more heavily used again as the pandemic recedes.

The major advances in knowledge of the concentrations and distributions of trace metals in the seas and oceans have occurred since the mid 1970s. This progress reflects major breakthroughs in procedures for essentially contamination-free (clean) sampling, the adoption of clean methodologies for handling and analysis of samples, and improvements in the analytical methods themselves. The extent of progress by the early 1980s was demonstrated by the major collection of papers edited by Wong et al. 1 Overviews of the subject have been given by Burton and Statham 2 and Bruland. 3 With the improved knowledge of the true variations in the concentrations of metals within the ocean, many systematic features in their distributions have become apparent. It has been possible to classify their marine geochemical behaviors and to interpret these in terms of the interactions of the dissolved chemical species with particulate material, which reflect the fundamental bonding properties of the elements. 4

Whilst Sediment Profile Imaging (SPI) is a very widely used technique in the regulatory assessment of seabed environmental health, and in the study of seafloor sediment-biology interactions, the potential for SPI images to be used in a geochemical context has not been rigorously assessed. Here we have examined relationships between colour and geochemistry in a sediment core collected from the Celtic Sea, North West European Shelf, that was digitally imaged and on which detailed geochemical analyses were also performed. Average oxygen penetration depth was 4.08 ± 0.72 mm, (n = 5), whilst the apparent redox potential discontinuity (aRPD) as determined by sediment colour change was at 78 mm. As iron (oxyhydr)oxides decreased with depth, black sulfide phases increased, and the aRPD most closely correlated with this geochemical change rather than the oxygen penetration depth. Colour analysis of the image showed a clear correlation of brightness with black FeS (acid volatile sulfide). There was a general correlation of iron oxide phases with orange colour in the upper part of the sediment profile, whilst.in the lower part of the core the orange oxide phases appeared to be obscured by the black FeS present. The sulfide-brightness relationship indicates colour analysis can provide an estimate of FeS, and potentially the carrying capacity for toxic metals such as cadmium, zinc and copper as sulfides in this type of sediment. Additionally, detailed geochemical analyses of SPI cores may provide new insights into the activity and impacts of infauna and the link with sediment biogeochemical cycles of carbon and nutrients.

We present the first evidence of Fe(II) complexation by natural organic ligands in estuarine waters. Across five diverse river/estuary systems we find evidence of terrestrially derived ligands with binding constants (log KFe(II)L) mainly in the range 6–8. These Fe(II) ligands were stable over short time periods (1–2 days), generally equivalent to, or in excess of, ambient freshwater Fe(II) concentrations (which ranged from 12 to 3600 nM) and had similar binding constants to ligands that were leached by water from vegetation and detritus (log KFe(II)L 7–8). A class of terrestrially derived ligands may therefore be important in stabilising Fe(II) concentrations in freshwater systems. However, in coastal seawater the impact of these ligands upon Fe(II) speciation is likely to be diminished due to a combination of dilution, loss of humic material during flocculation and increased ionic strength. The temperate and sub-tropical river systems studied included the Beaulieu (England), Itchen (England), Cape Fear (North Carolina, USA), Winyah Bay (South Carolina, USA) and Loch Etive (Scotland). Freshwaters in each system possessed a broad range of dissolved organic carbon (DOC, 200–1300 μM), labile dissolved Fe (LDFe, Fe 10% of freshwater input, ligand binding constants were elevated (up to log KFe(II)L 11) and the expected decrease in LDFe with increasing salinity along the estuary was not observed (LDFe and DOC both peaked at a salinity of 7) due to effluent inputs.

Recent work has shown that glaciers are a globally significant source of the micronutrient Fe to the ocean. Polar regions are particularly susceptible to climate change and have been subject to pronounced warming in the past few decades. In response to this warming, the volume of glacial meltwater runoff from Greenland has increased. This meltwater has a relatively high particulate and dissolved Fe content. Seasonal Fe limitation of marine ecosystems has been found in parts of the North Atlantic, so it has been proposed that increasing fluxes of Fe rich meltwater from Greenland to the North Atlantic could alleviate this Fe limitation and thereby increase marine primary production. However, here we use a synthesis of biogeochemical and physical oceanography studies to suggest that the physical circulation around Greenland does not favour direct export of dissolved or particulate Fe from inshore to offshore waters. The Fe budget in surface waters of the North Atlantic may therefore be insensitive to increasing meltwater fluxes from Greenland.

Reduced iron, Fe(II), accounts for a significant fraction of dissolved Fe across many natural surface waters despite its rapid oxidation under oxic conditions. Here we investigate the temporal and spatial variation in dissolved Fe redox state in a high dissolved organic matter (DOM) estuarine system, the River Beaulieu. We couple manual sample collection with the deployment of an autonomous in situ analyser, designed to simultaneously measure dissolved Fe(II) and total dissolved Fe, in order to investigate processes operating on the diurnal timescale and to evaluate the performance of the analyser in a high DOM environment. Concentrations of dissolved Fe available to the ligand ferrozine are elevated throughout the estuary (up to 21 μM in freshwater) and notably higher than those previously reported likely due to seasonal variation. Fe(II) is observed to account for a large, varying fraction of the dissolved Fe available to ferrozine (25.5 ± 12.5%) and this fraction decreases with increasing salinity. We demonstrate that the very high DOM concentration in this environment and association of this DOM with dissolved Fe, prevents the accurate measurement of dissolved Fe concentrations in situ using a sensor reliant on rapid competitive ligand exchange.

Pyrite and chalcopyrite are the two most abundant sulphides observed in seafloor hydrothermal systems. The alteration of sulphides is primarily controlled by reactions on the mineral surfaces and Fe(II)-oxidizing bacteria closely related to Marinobacter aquaeolei are thought to play a major role in iron oxidation under circumneutral conditions. We assessed the influence of M. aquaeolei on the electroactivity of FeS2 and CuFeS2 minerals under circumneutral conditions. Samples for the experiments were obtained from the Trans-Atlantic Geotraverse (TAG) hydrothermal mound (field), 26 °N on the Mid-Atlantic Ridge and Ireland (CuFeS2)]. The experimental approach relied on voltammetry and scanning electrochemical microscopy (SECM). The tip-substrate voltammetry mode of SECM was found to be particularly suitable to probe the major redox processes of those minerals and permitted an assessment of the microorganisms influence on these processes. M. aquaeolei was found to enhance FeS2 and CuFeS2 oxidation, particular...

Supply of Fe to high nitrate low chlorophyll (HNLC) waters, such as the Southern Ocean, is the principle limiting factor for primary production and the associated carbon uptake. Glacial meltwaters have recently been shown to provide a globally substantial input of Fe to both Antarctic and Arctic polar waters. The particulate Fe flux in glacial runoff is several orders of magnitude greater than the dissolved Fe flux and yet little is known, to date, about the potential bioavailability of this particulate Fe. A fraction of particulate Fe may be bioavailable to organisms and thus have a significant impact on biota in HNLC zones. Here, we describe in detail the composition and speciation of Fe released from four different glacial flours. We show that the fraction of labile Fe varies markedly between different flours and is not proportional to total Fe. Furthermore a small fraction of the particulate Fe is available to the Fe(II) selective ligand ferrozine, which indicates active redox cycling on the surface of the flour.

A phytoplankton bloom shown to be naturally iron (Fe) induced occurs north of the Crozet Islands (Southern Ocean) every year, providing an ideal opportunity to study dissolved trace metal distributions within an island system located in a high nutrient low chlorophyll (HNLC) region. We present water column profiles of dissolved nickel (Ni), zinc (Zn), cobalt (Co), cadmium (Cd), lead (Pb), aluminium (Al), and manganese (Mn) obtained as part of the NERC CROZEX program during austral summer (2004–2005). Two stations (M3 and M1) were sampled downstream (north) of Crozet in the bloom area and near the islands, along with a control station (M2) in the HNLC zone upstream (south) of the islands. The general range found was for Ni, 4.64–6.31 nM; Zn, 1.59–7.75 nM; Co, 24–49 pM; Cd, 135–673 pM; Pb, 6–22 pM; Al, 0.13–2.15 nM; and Mn, 0.07–0.64 nM. Vertical profiles indicate little island influence to the south with values in the range of other trace metal deprived regions of the Southern Ocean. Significant removal of Ni and Cd was observed in the bloom and Zn was moderately correlated with reactive silicate (Si) indicating diatom control over the internal cycling of this metal. Higher concentrations of Zn and Cd were observed near the islands. Pb, Al, and Mn distributions also suggest small but significant atmospheric dust supply particularly in the northern region.

Continental shelf sediments are globally important for biogeochemical activity. Quantification of shelf-scale stocks and fluxes of carbon and nutrients requires the extrapolation of observations made at limited points in space and time. The procedure for selecting exemplar sites to form the basis of this up-scaling is discussed in relation to a UK-funded research programme investigating biogeochemistry in shelf seas. A three-step selection process is proposed in which (1) a target area representative of UK shelf sediment heterogeneity is selected, (2) the target area is assessed for spatial heterogeneity in sediment and habitat type, bed and water column structure and hydrodynamic forcing, and (3) study sites are selected within this target area encompassing the range of spatial heterogeneity required to address key scientific questions regarding shelf scale biogeochemistry, and minimise confounding variables. This led to the selection of four sites within the Celtic Sea that are significantly different in terms of their sediment, bed structure, and macrofaunal, meiofaunal and microbial community structures and diversity, but have minimal variations in water depth, tidal and wave magnitudes and directions, temperature and salinity. They form the basis of a research cruise programme of observation, sampling and experimentation encompassing the spring bloom cycle. Typical variation in key biogeochemical, sediment, biological and hydrodynamic parameters over a pre to post bloom period are presented, with a discussion of anthropogenic influences in the region. This methodology ensures the best likelihood of site-specific work being useful for up-scaling activities, increasing our understanding of benthic biogeochemistry at the UK-shelf scale. Electronic supplementary material The online version of this article (doi:10.1007/s10533-017-0366-1) contains supplementary material, which is available to authorized users.

Pore-fluid Fe isotopes may be a unique tracer of sediment respiration by dissimilatory Fe-reducing bacteria, but to date, pore-fluid Fe isotope measurements have been restricted to continental shelf settings. Here, we present δ56Fe values of pore fluids from two distinct sedimentary settings: (1) a riverine-dominated site on the northern California margin (Eel River shelf; 120 m water depth) and (2) biogenic opal-rich volcaniclastic deep-sea sediments from the Southern Ocean (north and south of the Crozet Plateau; 3000-4000 m water depth). The Fe isotope compositions of Crozet region pore fluids are significantly less fractionated (δ56Fe = +0.12‰ to -0.01‰) than the Eel River shelf (δ56Fe = -0.65‰ to -3.40‰) and previous studies of pore-fluid Fe isotopes, relative to average igneous rocks. Our data represent the first measurements of Fe isotope compositions in pore fluids from deep-sea sediments. A comparison of pore-fluid δ56Fe with the relative abundance of highly labile Fe in the reactive sedimentary Fe pool demonstrates that the composition of Fe isotopes in the pore fluids refl ects the different extent of sedimentary Fe redox recycling between these sites. © 2009 Geological Society of America.

Whilst there is increasing evidence for the presence of stabilized FeII associated with organic matter in aquatic environments, the absence of a reliable method for determining FeII speciation in solution has inhibited the study of this aspect of Fe biogeochemistry. A technique is described here for the determination of FeII organic complexation in natural waters that is based on competitive ligand reverse titration and a model fit to experimental results, from which ligand concentration and a conditional stability constant can be obtained. Spectrophotometry was used to detect the Ferrozine (FZ) complex with reactive FeII, which in combination with a liquid waveguide capillary cell (LWCC) enabled high sensitivity and precision measurements of FeII to be made. A series of samples was collected in the Itchen River in Southampton, UK to test the method at a wide range of salinities including river water. Levels of FeII and total dissolved Fe were within previously reported values for this system. FeII was found to occur organically complexed with values for log K ′ Fe II L (conditional stability constant for FeII-natural ligand complexes) of ≈8 at salinities between 0 and 21, whilst no measurable complexation was detected at a salinity of 31. This work demonstrates that spectrophotometry can be used in combination with ligand competition to investigate metal speciation in natural waters.

Benthic-pelagic exchange processes are recognised as important nutrient sources in coastal areas, however, the relative impact of diffusion, resuspension and other processes such as bioturbation and bioirrigation are still relatively poorly understood. Experimental ship-based data are presented showing the effects of diffusion and resuspension on cohesive sediments at a temperate shelf location in the North Sea. Measurements of diffusive fluxes in both spring (1.76, 0.51, −0.91, 17.6 μmol/m2/h) and late summer (8.53, −0.03, −1.12, 35.0 μmol/m2/h) for nitrate, nitrite, phosphate and dissolved silicon respectively, provided comparisons for measured resuspension fluxes. Increases in diffusive fluxes of nitrate and dissolved silicon to the water column in late summer coincided with decreases in bottom water oxygen concentrations and increases in temperature. Resuspension experiments using a ship board annular flume and intact box core allowed simultaneous measurement of suspended particulate matter, water velocity and sampling of nutrients in the water column during a step wise increase in bed shear velocity. The resuspension of benthic fluff led to small but significant releases of phosphate and nitrate to the water column with chamber concentration increasing from 0.70–0.76 and 1.84–2.22 μmol/L respectively. Resuspension of the sediment bed increased water column concentrations of dissolved silicon by as much as 125% (7.10–15.9 μmol/L) and nitrate and phosphate concentrations by up to 67% (1.84–3.08 μmol/L) and 66% (0.70–1.15 μmol/L) respectively. Mass balance calculations indicate that processes such as microbial activity or adsorption/desorption other than simple release of pore water nutrients must occur during resuspension to account for the increase. This study shows that resuspension is potentially an important pathway for resupplying the water column with nutrients before and during phytoplankton blooms and should therefore be considered along with diffusive fluxes in future ecosystem models.

The investigation of the distribution of trace elements between the dissolved, colloidal and particulate phases within a hydrothermal plume is key to understanding plume processes. Particulate and colloidal size fractions of four trace elements (iron, manganese, copper and phosphorus) along with the dissolved size fraction of iron, manganese and copper have been determined in the hydrothermal plume overlying the Edmond vent-site in the Central Indian Ocean. Dissolved iron and manganese are the most heavily enriched metals in hydrothermal fluids emerging from vents and iron plays a significant role in subsequent dissolved-particulate interactions within hydrothermal plumes. Copper and phosphorus are each representative members of discrete groups of tracers (chalcophile elements and oxyanions, respectively) that are known to exhibit distinct patterns of behaviour, relative to iron, within hydrothermal plumes. Here we show that iron is present in all three hydrothermal plume fractions (dissolved, colloidal and particulate), being least abundant in dissolved form. Manganese resides predominantly in the dissolved fraction, copper resides primarily in the particulate phase and phosphorus is abundant in both the colloidal and coarser particulate phases, but not the dissolved fraction. The correlation of phosphorus to iron in the Edmond hydrothermal plume is both (i) constant across the colloidal and coarser particulate phases and (ii) matches well to broader inter-ocean trends reported previously from the Atlantic and Pacific Oceans. These results demonstrate a mechanism whereby plume-height P:Fe ratios are established during the very earliest stages of dissolved Fe(II) oxidation, followed by aggregation into coarser hydrothermal plume particles. This provides a strong argument for the study of P:Fe ratios in hydrothermal sediments as potential paleotracers of deep-water dissolved phosphate distributions and, hence, past deep-ocean circulation patterns.

article i nfo Article history: Iron(Fe)isanessentialmicronutrientforphytoplankton,andisscarceinmanyregionsincludingtheopenSouth- ern Ocean. The western Antarctic Peninsula (WAP), an important source region of Fe to the wider Southern Ocean, is also the fastest warming region of the Southern Hemisphere. The relative importance of glacial versus marine Fe sources is currently poorly constrained, hindering projections of how changing oceanic circulation, productivity, and glacial dynamics may affect the balance of Fe sources in this region. Dissolved and total dissolvable Fe concentrations were measured throughout the summer bloom period at a coastalsiteontheWAP.Ironinputstothesurfacemixedlayerinearlysummerwerestronglycorrelatedwithme- teoric meltwaterfrom glaciers and precipitation. A significant sourceof Fe fromunderlying waters wasalso iden- tified, with dissolved Fe concentrations of up to 9.5 nM at 200 m depth. These two primary Fe sources act on different timescales, with glacial sources supplying Fe during the warm summer growing period, and deep water replenishing Fe over annual periods via deep winter mixing. Iron supply from deep water is sufficient to meet biological demand relative to macronutrient supply, making Fe limitation unlikely in this area even without additional summer Fe inputs from glacial sources. Both glacial and deep-water Fe sources may increase with continued climate warming, potentially enhancing the role of the WAP as an Fe source to offshore waters. © 2015 Published by Elsevier B.V.

Volcanogenic sediments are typically rich in Fe and Mn-bearing minerals that undergo substantial alteration during early marine diagenesis, however their impact on the global biogeochemical cycling of Fe and Mn has not been widely addressed. This study compares the near surface (0-20cm below sea floor [cmbsf]) aqueous (5cmbsf and largely controlled by the oxidation of organic matter. Dissolved Fe and Mn distributions in Montserrat pore waters were lowest in the surface oxic-layer (0.3μM Fe; 32μM Mn), with maxima (20μM Fe; 200μM Mn) in the upper 1-15cmbsf. Unlike Montserrat, Fe and Mn in Crozet pore waters were ubiquitously partitioned between 0.2μm and 0.02μm filtrations, indicating that the pore water distributions of Fe and Mn in the (traditionally termed) 'dissolved' size fraction are dominated by colloids, with respective mean abundances of 80% and 61%. Plausible mechanisms for the origin and composition of pore water colloids are discussed, and include prolonged exposure of Crozet surface sediments to early diagenesis compared to Montserrat, favouring nano-particulate goethite formation, and the elevated dissolved Si concentrations, which are shown to encourage fine-grained smectite formation. In addition, organic matter may stabilise authigenic Fe and Mn in the Crozet pore waters. We conclude that volcanogenic sediment diagenesis leads to a flux of colloidal material to the overlying bottom water, which may impact significantly on deep ocean biogeochemistry. Diffusive flux estimates from Montserrat suggest that diagenesis within tephra deposits of active island volcanism may also be an important source of dissolved Mn to the bottom waters, and therefore a source for the widespread hydrogenous MnO x deposits found in the Caribbean region. © 2011 Elsevier Ltd.

The in situ annular flume, Voyager II, was deployed at three sites in the North Sea in order to investigate resuspension events, to determine the physical characteristics of the seabed, to determine the threshold of resuspension of the bed and to quantify erosion rates and erosion depths. These are the first controlled, in situ flume experiments to study resuspension in the North Sea, and were combined with long-term measurements of waves and currents. Resuspension experiments were undertaken at two muddy, and one sandy site: north of the Dogger Bank (DG: water depths ∼80 m, very fine, poorly sorted, very fine-skewed sediment experiencing seasonal thermal stratification of the water column along with oxygen depletion); the Oyster Grounds (OG: ∼40 m, similar bed properties, year round water column thermal stratification, Atlantic forcing); and in the Sean Gas Field (SGF: ∼20 m, moderately sorted, very coarse-skewed sand, and well mixed water column). The erosion thresholds of the bed were found to be 0.66–1.04 Pa (DG) and 0.91–1.27 Pa (OG), with corresponding erosion depths of 0.1–0.15 mm and 0.02–0.06 mm throughout the experiments. Evaluation of a year of current velocities from 2007 indicated that at OG, resuspension of the consolidated bed was limited to on average ∼8% of the time as a result of tidal forcing alone for short ( Resuspension of bed material and erosion rates were closely related to applied bed shear stresses, and eroded depths were significantly correlated with the physical properties of the bed. Therefore, while complex variations in biogeophysical factors affected the critical threshold of erosion, once exceeded, erosion rates were related to the nature of the sediment.

The effect of artificial acidic polysaccharides (PS) and exudates of Phaeodactylum tricornutum on the half-life of Fe(II) in seawater was investigated in laboratory experiments. Strong photochemical hydrogen peroxide (H2O2) production of 5.2 to 10.9 nM (mg C)−1 h−1 was found in the presence of PS and diatom exudates. Furthermore when illuminated with UV light the presence of algal exudates had a net stabilising effect on ferrous iron in seawater (initial value 100 nmol L−1) above that expected from oxidation kinetics. In the dark the PS gum xanthan showed no stabilising effect on Fe(II). The photochemical formation of superoxide (O2−) in the presence of diatom exudates and its reducing effect on Fe(III) appears to result in greater than expected concentrations of Fe(II). A model of the photochemical redox cycle of iron incorporating these processes supported the observed data well. Diatom exudates seem to have the potential to play an important role for the photochemistry of iron in coastal waters.

Fe isotopes are a potential tool for tracing the biogeochemical redox cycle of Fe in the ocean. Specifically, it is hypothesized that Fe isotopes could enable estimation of the contributions from multiple Fe sources to the dissolved Fe budget, an issue that has received much attention in recent years. The first priority however, is to understand any Fe isotope fractionation processes that may occur as Fe enters the ocean, resulting in modification of original source compositions. In this study, we have investigated the Fe inputs from a basalt-hosted, deep-sea hydrothermal system and the fractionation processes that occur as the hot, chemically reduced and acidic vent fluids mix with cold, oxygen-rich seawater. The samples collected were both end-member vent fluids taken from hydrothermal chimneys, and rising buoyant plume samples collected directly above the same vents at 5°S, Mid-Atlantic Ridge. Our analyzes of these samples reveal that, for the particulate Fe species within the buoyant plume, 25% of the Fe is precipitated as Fe-sulfides. The isotope fractionation caused by the formation of these Fe-sulfides is δFe(II)–FeS = +0.60 ± 0.12‰. The source isotope composition for the buoyant plume samples collected above the Red Lion vents is calculated to be −0.29 ± 0.05‰. This is identical to the value measured in end-member vent fluids collected from the underlying “Tannenbaum” chimney. The resulting isotope compositions of the Fe-sulfide and Fe-oxyhydroxide species in this buoyant plume are −0.89 ± 0.11‰ and −0.19 ± 0.09‰, respectively. From mass balance calculations, we have been able to calculate the isotope composition of the dissolved Fe fraction, and hypothesize that the isotope composition of any stabilised dissolved Fe species exported to the surrounding ocean may be heavier than the original vent fluid. Such species would be expected to travel some distance from areas of hydrothermal venting and, hence, contribute to not only the dissolved Fe budget of the deep-ocean but also it’s dissolved Fe isotope signature.

article Natural iron fertilization processes are occurring around the Crozet Islands (46°26'S-52°18'E), thus relieving the water masses from the normally encountered High Nutrients Low Chlorophyll (HNLC) conditions of the Southern Ocean. During austral summers 2004/2005 and 2005/2006, iron and aluminium concentrations were investigated in large particles (N53 µm) collected from just below the mixed layer at stations under the influence of island inputs, and also in adjacent HNLC waters. These large particles are anticipated to sink out of the mixed layer, and to reflect the net effects of input and cycling of these elements in the overlying mixed layer. Labile and refractory fractions were determined by a two-stage leaching technique. Data showed that water masses downstream of the islands were enriched in total iron and aluminium (0.25-2.68 nmol L �1 and 0.34-3.28 nmol L �1 respectively), relative to the southern HNLC control sites (0.15-0.29 nmol L �1 for Fe and 0.12-0.29 nmol L �1 for Al), with only a small fraction (typically b1%) being acid leachable in both environments. Particulate iron predominantly derived from the island system represents a significant fraction of the total water column iron inventory and may complement dissolved Fe inputs that help support the high summer productivity around the Crozet islands.

The release of dissolved iron from artificial aggregates formed from oxic natural coastal water and senescent phytoplankton material was demonstrated under dark conditions. The rate of release was controlled by the amount of reducible Fe(III) available, and appears to be limited by the competing oxidation of Fe(II). Molecular (16S rRNA gene) analyses showed the bacterial community associated with the aggregates, originating from estuarine water, to be dominated by oxic heterorophs. However, it was possible to culture NO3- and Fe (III)-reducing bacteria from the artificial aggregates, and marine particles incubated with Fe(III) under anaerobic conditions contained microorganisms belonging to the genera Desulfovibrio and Marinobacter, bacteria known to reduce Fe(III). Whilst the precise mechanism of reduction is not clear, it is evident that marine aggregates can be a source of Fe(II), and thus ultimately iron in other forms, in coastal waters and most probably other natural water systems.

We present the first extensive dataset for copper (Cu) isotopes in rivers, as well as preliminary data for estuaries and seawater. Rivers exhibit a range in dissolved δ 65 Cu (relative to NIST SRM 976) of + 0.02 to + 1.45 per mil (‰). The discharge-weighted average dissolved δ 65 Cu and Cu concentration for the studied rivers, representing around 25% of the global riverine water discharge, are + 0.68‰ and 18.8 nmol kg − 1 , respectively. Isotopic data for the dissolved phase in two small estuaries in SE England exhibit relatively minor variation through the salinity gradient (+ 0.42 to + 0.94‰) and are close to both the data for the rivers upstream from the estuaries and a measurement of the coastal sea at their mouths. Analyses of the particulate phase in the estuaries reveal a complementary light pool (− 0.24 to − 1.02‰). The isotopic composition of the total Cu inventory is, however, close to that of the crustal source. These data, along with published constraints, suggest that the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of Cu between a light fraction adsorbed to particulates and a heavy dissolved fraction dominated by Cu bound to strong organic complexes. Open ocean seawater samples generally exhibit even heavier dissolved Cu isotopic compositions than the riverine input (δ 65 Cu = + 0.9 to + 1.5‰). The heavy isotopic composition of seawater is inferred to originate from intra-oceanic processes. The small dataset presented here is most consistent with further isotopic partitioning between an isotopically light pool adsorbed to particulates and a heavy dissolved pool strongly bound to organic ligands. Scavenging appears to have greatest impact in the surface ocean and least in both the oxygen minimum zone and the ocean bottom, perhaps reflecting the relative importance of scavenging, and thus the sequestration of light Cu to particulate material, at different depths.

Over much of the world's surface oceans, nitrate and phosphate concentrations are below the limit of detection (LOD) of conventional techniques of analysis. However, these nutrients play a controlling role in primary productivity and carbon sequestration in these waters. In recent years, techniques have been developed to address this challenge, and methods are now available for the shipboard analysis of nanomolar (nM) nitrate and phosphate concentrations with a high sample throughput. This article provides an overview of the methods for nM nitrate and phosphate analysis in seawater. We outline in detail a system comprising liquid waveguide capillary cells connected to a conventional segmented-flow autoanalyser and using miniaturised spectrophotometers. This approach is suitable for routine field measurements of nitrate and phosphate and achieves LODs of 0.8 nM phosphate and 1.5 nM nitrate. © 2008 Elsevier Ltd. All rights reserved.

This special issue describes the findings of the first planned natural iron fertilisation experiment in the Southern Ocean, the CROZet natural iron bloom and EXport experiment (CROZEX), which took place from November 2004 to January 2005. The bloom that occurs annually north of the Crozet Islands and Plateau (Crozet) was surveyed and compared with a high-nutrient low-chlorophyll (HNLC) region south of Crozet. Papers in this volume confirm that iron from Crozet fertilised the bloom and that phytoplankton production rates and most export flux estimates were much larger in the bloom area than in the HNLC control area. This introductory paper summarises the reasons for choosing the Crozet area, and provides an overview of the two cruises that comprised CROZEX and their major findings.

Elevated levels of productivity in the wake of Southern Ocean island systems are common despite the fact that they are encircled by high-nutrient low-chlorophyll (HNLC) waters. In the Crozet Plateau region, it has been hypothesized that iron from island runoff or sediments of the plateau could be fueling the austral summer phytoplankton bloom. Here, we use radium isotopes to quantify the rates of surface-ocean iron supply fueling the bloom in the Crozet Plateau region. A 1D eddy-diffusion-mixing model applied to a 228 Ra profile (t1/2 ¼ 5.75 years) at a station north of the islands suggests fast vertical mixing in the upper 300 m (Kz ¼ 11–100 cm 2 s � 1 ) with slower mixing between 300 and 1000 m (Kz ¼ 1.5 cm 2 s � 1 ). This estimate is discussed in the context of Kz derived from the CTD/LADCP data. In combination with the dissolved Fe profile at this location, we estimated a vertical flux of between 5.6 and 31 nmol Fe m � 2 d � 1 . The cross-plateau gradients in the short-lived radium isotopes, 224 Ra (t1/2 ¼ 3.66 d) and 223 Ra (t1/2 ¼ 11.4 d), yielded horizontal eddy diffusivities (Kh )o f 39 and 6.6 m 2 s � 1 , respectively. If we assume that the islands (surface runoff) alone were supplying dissolved Fe to the bloom region, then the flux estimates range from 2.3 to 14 nmol Fe m � 2 d � 1 . If the plateau sediments are considered a source of Fe, and conveyed to the bloom region through deep winter mixing combined with horizontal transport, then this flux may be as high as 64–390 nmol Fe m � 2 d � 1 . Combined, these Fe sources are sufficient to initiate and maintain the

The annual phytoplankton bloom occurring north of the Crozet Plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high-nutrient low-chlorophyll (HNLC) conditions normally associated with the Southern Ocean. Therefore, during CROZet natural iron bloom and EXport experiment (CROZEX), a large multidisciplinary study performed between November 2004 and January 2005, measurements of total dissolved iron (DFe⩽0.2 μm) were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples. DFe concentrations were determined by flow injection analysis with N,N-dimethyl-p-phenylenediamine dihydrochloride (DPD) catalytic spectrophotometric detection. DFe concentrations varied between 0.086 and 2.48 nM, with low values in surface waters. Enrichment of dissolved iron (>1 nM) at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron. Waters farther north also appear to be affected by this input of coastal and shelf origin, although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of ∼0.07 nM km−1 at the time of sampling. Using lateral and vertical diffusion coefficients derived from Ra isotope profiles and also estimates of atmospheric inputs, it was then possible to estimate a DFe concentration of ∼0.55 nM to the north of the islands prior to the bloom event, which is sufficient to initiate the bloom, the lateral island source being the largest component. A similar situation is observed for other Sub-Antarctic Islands such as Kerguelen, South Georgia, that supply dissolved iron to their surrounding waters, thus enhancing chlorophyll concentrations.

Shelf break systems are highly dynamic environments. However little is known about the influence that benthic interactions and water mass mixing may have on vertical distributions of iron in these systems. Dissolved Fe (< 0.4 μm) concentrations were measured in samples from nine vertical profiles across the upper slope (150–2950 m water depth) at the Atlantic Ocean–Celtic Sea shelf break. Dissolved iron concentrations varied between less than 0.2 and 5.4 nM, and the resulting detailed section showed evidence of a range of processes influencing the Fe distributions. The near sea floor data were interpreted in terms of release and removal processes. The concentrations of dissolved Fe present in near seabed waters were consistent with release of Fe from in situ remineralisation of particulate organic matter at two upper slope stations, and possibly release from pore water upon resuspension on shelf. Lateral transport of dissolved iron was evident from elevated Fe concentrations in an intermediate nepheloid layer and its advection along isopycnals. Surface waters at the shelf break also showed evidence of vertical mixing of deeper iron-rich waters. These waters contained macronutrients that sustained primary productivity in these otherwise nutrient-depleted surface waters. The data also suggest some degree of stabilisation of relatively high concentrations of iron, presumably through ligand association or as colloids. This study supports the view that lateral export of dissolved iron to the interior of the ocean from shelf and coastal zones and may have important implications for the global budget of oceanic iron.

The concentrations of Cr (III) and Cr (VI) were determined in the upper 500 m of the Sargasso Sea at different times of the year. Total Cr concentrations ranged between 2.5 and 4.5 nM, and the predominant species of Cr was the thermodynamically favoured Cr (VI). Cr (III) concentrations were greatest during periods of high biological activity, as indicated by strong correlations between the ratio of Cr (III):Cr (VI) and both bacterial biomass and primary productivity. Whilst the oxidation state varied substantially over the seasonal cycle, the upper water column inventory of Cr was relatively constant. The long residence time of Cr in the surface Sargasso Sea estimated with respect to atmospheric inputs (1410–2240 years) is indicative of the largely conservative behaviour of this element. Deep particle fluxes of Cr are similar or somewhat greater than atmospheric inputs, and this downward flux of Cr is well correlated with organic carbon fluxes from the upper Sargasso Sea. The long residence time coupled with the seasonal changes in oxidation state of Cr implies rapid seasonal recycling of Cr between redox states, with only slow removal via particles to the deep ocean at this site.

A series of shipboard experiments using the radiotracer 109Cd investigated the role of phytoplankton and bacteria in the uptake of dissolved Cd in the English Channel and Celtic Sea. The results demonstrate that Cd uptake is related to rates of primary production and bacterial numbers. Statistical analysis of plankton species abundance infer that Rhizosolenia, Chaetoceros and Pseudonitzschia diatom species are largely responsible for the higher Cd uptake observed in the >5 ?m size fraction during a diatom-dominated spring bloom. Total Cd uptake rates during winter non-bloom conditions were between 0.04 and 0.29 pmol l–1 h–1, and increased to between 0.43 and 1.23 pmol l–1 h–1 during diatom bloom conditions. These uptake rates are consistent with the seasonal surface depletion of Cd reported in the Celtic Sea and attributed to uptake by phytoplankton bloom material. A calculated Cd:C ratio of 3.1 ?mol mol–1 for natural plankton samples of the Celtic Sea agrees well with results of previous culture studies, which have reported ratios between 0.1 and 5.0 ?mol mol–1 for the coastal diatoms Thalassiosira weissflogii and T. pseudonana. Cd uptake was also linearly related to bacterial numbers, which was attributed to surface adsorption of Cd ions onto bacterial particles which have relatively high specific surface areas. These results demonstrate surface adsorption of Cd onto bacterial surfaces, and other biogenic non-living particles, i.e. ‘passive Cd uptake’, which is significantly augmented during a spring diatom bloom.

The stable isotope compositions of Zn and Cu in natural materials are newly available for measurement with the advent of multiple-collector inductively coupled mass spectrometry (MC–ICPMS). Although the oceans are prime scientific targets, no progress has been made as yet because of considerable analytical challenges involving the low concentrations of these elements in seawater. We present a procedure which allows isotopic analysis of Zn and Cu isotope compositions of seawater samples at least 1 L in size by MC ICPMS. The main difficulty in analysing Zn and Cu isotopes from seawater samples is their low concentrations (nM/kg) in a matrix with much higher concentrations of other elements. We have surmounted these problems using a procedure that involves pre-concentration using either a BioRad Chelex®100 column or co-precipitation, followed by further purification and separation of Cu and Zn on an anion column. The major advantage of co-precipitation is that the blank is low and allows the precise isotopic analysis of even the most Zn-depleted surface ocean samples. Zn samples have been analysed using a double spike in order to correct for analytical mass discrimination. This approach has been tested using standard-doped seawater samples that had previously been stripped of their metal contents using the Chelex column. The approach is highly successful and yields δ 66 Zn = − 0.02 ± 0.05‰ ( n = 5) relative to the standard dopant. For multiple analyses of a large sample of the English Channel we obtain a result for δ 66 Zn of 0.35 ± 0.08‰ ( n = 11) for Chelex extraction and 0.31 ± 0.04‰ ( n = 5) for co-precipitation. For both Cu and Zn, correction for instrumental mass discrimination using standard-bracketing requires some care to overcome artefacts-related sample introduction into the mass spectrometer. A depth profile from the NE Pacific is also presented. Measured concentrations are very similar to those reported elsewhere. Cu and Zn isotopes in the upper 400 m of the water column are anti-correlated and may reflect the dominance of scavenging for Cu and biological recycling for Zn.

Tritium (3H) concentrations in tree rings should reflect ambient precipitation. Thus, to improve knowledge of the 3H input to the oceans, we developed a new technique to measure 3H concentrations in annual tree rings. Measurements of 3H were made on cellulose, the primary constituent of wood, as the isotopic signal of its carbon bound hydrogen atoms should be unchanged since biosynthesis. Traditional cellulose extraction techniques from softwoods are slow and were found to not yield reproducibly pure cellulose. Therefore, a new microwave method was developed which reduces extraction times from 3–5 days to approximately 3 h. Potential 3H contamination from the hydroxyl groups of the cellulose molecule was subsequently removed by exchange with 3H-free NaOH, thus avoiding the dangers of working with large amounts of cellulose nitrate. The validity of the technique was tested by presenting a 3H time series from a cedar tree which grew in Tollymore Forest Park, Northern Ireland, for comparison with 3H data from the Valentia weather station. We find that the 3H in the cellulose clearly reflects the 3H in precipitation with no significant smearing of the bomb signal. A simple box model illustrates that the maximum reservoir residence time of source water for the tree is less than 1 yr, suggesting that groundwater is not a major source of water for this tree. In general, however, the groundwater input needs to be quantified for accurate 3H reconstructions to be made. This work demonstrates the potential of using 3H in wood cellulose as a proxy for 3H in precipitation and, thus, opens the door to reconstruction of past 3H inputs to the ocean.

Iron- and zinc-enrichment experiments were carried out at Ocean Station Papa in the subarctic North Pacific. In iron-enriched treatments, phytoplankton chlorophyll a (Chl a) increased 20-fold (9.7 m gL 21 ) above the concentration on day zero. No stimulation of Chl a production or nitrate drawdown was observed on addition of zinc alone compared to the control. In the iron-enriched treatment, bioavailable zinc concentration decreased to 0.2 pmol L 21 lower than that which is known in culture experiments to limit some phytoplankton growth. Theoretical analyses suggest that this zinc concentration would cause diffusion-limited growth of large diatom cells present at the end of the incubation. Direct measurements of zinc-binding ligands indicate that the natural microbial planktonic assemblages have the ability to respond rapidly to conditions of high dissolved zinc concentrations. Rapid ligand production may be a mechanism by which certain phytoplankton reduce zinc toxicity or for maintaining zinc concentrations in the upper water column. Zinc-binding ligands were observed to be both produced and removed on the timescale of 1 d. We suggest that these zinc-binding ligands are produced to assist assimilation, particularly under iron-enriched conditions when concentrations of bioavailable zinc were extremely low, thereby alleviating the effects of zinc limitation.

Deep-sea hydrothermal activity cycles the entire volume of the global ocean through deep-sea hydrothermal plumes at least every 4–8 × 103 a, a rapid timescale that is comparable to global deep-ocean mixing. An important process within hydrothermal plumes is the oxidation of dissolved iron discharged with vent fluids, leading to the co-precipitation of many other vent-sourced metals, thus, modifying gross hydrothermal fluxes to the deep ocean, and acting as a net sink in the ocean chemical budgets of certain key tracers. Here, we report direct measurements of dissolved Fe(II) oxidation rates from two recently discovered Indian Ocean vent sites that are intermediate between Pacific and Atlantic values, thus demonstrating that the rate of iron oxidation and formation of scavenging Fe(III) solid phases, in hydrothermal plumes varies systematically along the global deep-ocean “conveyor.? The average pseudo first-order rate constant for the oxidation reaction is 0.303 h?1 and the corresponding half-life 2.31 h. The rate plots show some curvature, however, indicating additional processes, possibly interactions with organic matter, may also influence the net oxidation/removal rate. Different rates of oxidation of iron in hydrothermal plumes in different ocean basins have important implications for the dispersion of produced oxide phases, which in turn may impact on uptake of other metals from seawater and deposition into underlying ridge-crest and ridge flank sediments.

Dissolved iron (Fe) distributions in the water column of the Cretan Sea show consistent patterns of elevated surface mixed layer concentrations (mean values of 1.44 and 1.95 nmol L 21 in March and September, respectively) that rapidly decrease with depth to low and relatively uniform concentrations in deep waters (circa 0.5 nmol L 21 ). These features are consistent with inputs of dissolved Fe to surface waters and with rapid scavenging to low values in deep waters. The main source of surface dissolved Fe is probably Saharan atmospheric dust, the supply of which is variable depending on sporadic dust storm events and transport to the Cretan Sea. The short residence times estimated for dissolved Fe in the mixed layer (0.7‐2 yr) emphasize the rapid removal of this element from surface waters and are consistent with recent mass balance calculations for Fe in the western Mediterranean Sea, in which rapid removal of Fe to sediments is needed to provide a balance in the budget. The deep-water concentrations are strikingly constant and similar to or slightly lower than those reported for the open ocean. The high surface concentrations we observed would be ample to support substantial primary production, and it is likely that the macronutrients, and phosphorus in particular, limit production in this region. Iron (Fe) is an essential nutrient for phytoplankton, bacteria, and other marine microorganisms, and the role of this metal as a potentially limiting factor for phytoplankton has come under increasing scrutiny since the initial ‘‘iron hypothesis’’ was put forward by Martin et al. (1988) to explain limited productivity in high-nutrient low-chlorophyll (HNLC) oceanic systems. Experiments such as IRONEX and SOIREE have now clearly demonstrated that Fe additions can stimulate phytoplankton growth in HNLC zones (Watson 2001), although many questions still remain about the forms of Fe present, uptake mechanisms, and the impact of Fe on export carbon production. The distributions, sources, and sinks of Fe in seawater have recently been reviewed (De Baar and De Jong 2001). There is a coherent trend in reported data for all regions, with increasing concentrations approaching the continental margins (up to circa 100 nmol L 21 ), while in the open ocean, dissolved Fe has typically low concentrations in surface waters (0.02‐1 nmol L 21 ) and higher (0.4‐2.0 nmol L 21 ) concentrations in deep waters. The rapid removal of dissolved Fe through association with biotic and abiotic particles and its loss from the water column results in Fe having a short residence time (De Baar and De Jong 2001), and upper-ocean concentrations should largely reflect local inputs (e.g., aeolian and shallow benthic sourc1

Cryoconite holes are near-vertical tubes that form in the surface of glaciers when solar-heated debris melts into the ice. Those that form in the McMurdo Dry Valleys of Antarctica are distinctive, in that they have ice lids and are closed to the atmosphere for periods of years to decades. Photoautotrophs and heterotrophs grow within this closed environment, perturbing the poorly buffered water chemistry, yet maintaining the potential for photosynthesis. Microbial excretion and decomposition of organic matter produces dissolved organic carbon (DOC): dissolved inorganic carbon ratios of ?1 : 2. Much of the dissolved nitrogen pool (80–100%) exists as dissolved organic nitrogen (DON). The DON:DOC ratio is ?1 : 11 (mol/mol), typical of organic particulate material at the Earth’s surface. The combination of photoautotrophy, heterotrophy and weak chemical buffering within these microcosms promotes values of pH, pCO2, O2 saturation and percentage total dissolved nitrogen as DON that reach 10·99, 10?7·6 atm, 160% and 100% respectively, which are a unique combination among the surface waters on Earth. These ice-sealed cryoconite holes could be important analogues of refugia on Snowball Earth and other icy planets.

Near-surface seawater from the northeastern subarctic Pacific was incubated on deck for 8 d, supplemented with (1) control, no additions (2) 1Zn (3) 1Fe (4) 1Zn1Fe. Concentrations of total Zn and Fe at time zero (t0) and in the control remained at ;0.1‐0.2 nmol L 21 . In the control, chlorophyll (,0.3 mg m 23 ), 14 C uptake into POC and PIC, and inorganic nutrients all remained relatively constant. Addition of Zn slightly but significantly increased chlorophyll ( p , 0.05), decreased phosphate ( p , 0.01) and nitrate ( p , 0.05), and in P versus E experiments, increased Pm .10-fold and P 2‐3-fold. The abundance of small diatoms and coccolithophores was higher in the chl m 1Zn treatment compared to the control. The 1Fe and 1Zn1Fe treatments, compared to the control, both showed .10-fold increases in chlorophyll and 14 C uptake into POC and PIC and complete removal of nitrate (#0.2 mmol m 23 ). However, differences were observed in size-fractionated data; the 1Zn1Fe treatment had significantly lower percent chlorophyll in the .20-mm fraction (p , 0.01) and a higher percentage in the 0.2‐5-mm fraction (p , 0.01) than the 1Fe treatment. In P versus E experiments, both 1Fe treatments increased Pm and a around 100-fold and P and a chl by 5‐10-fold compared to the control. The 1Fe treatment showed a slightly higher a chl and slightly chl m lower P than the 1Zn1Fe treatment. Abundance of large diatoms, small diatoms, small flagellates, and coccolchl m ithophores all increased substantially ( ;7‐1,000-fold) in response to Fe addition, whereas dinoflagellate abundance only doubled. The 1Zn1Fe treatment had higher abundances of small diatoms and small flagellates than the 1Fe treatment. We conclude that Zn additions had limited influence on conventional indices of phytoplankton growth compared to Fe, but that there might be subtle influences of Zn that require further attention.

The concentrations of dissolved and particulate manganese and iron and of dissolved oxygen in the water column have been measured as a function of depth in the upper basin of Loch Etive, over a 17 month period. For most of this period the bottom water was isolated, which caused low dissolved oxygen concentrations within the water column and concomitant high levels of manganese. The highest concentrations of manganese were close to the bottom. During the study period an overturn event occurred which caused complete mixing of the water column, and flushing of the low oxygen, high manganese deep water. By using published rate constants for the oxidation of Mn2+ and by assuming steady state, we estimate that the oxidation of dissolved Mn2+ (and by implication the return of solid phase manganese to the sediment) occurred at the rate of 2·2–5·4 mmole m−2 d−1, on an areal basis during the period of isolation. Mn2+ efflux experiments gave values of 0·44 and 0·81 mmole m−2 d−1.

Total dissolved Zn concentrations are reported for winter and summer along the E–W line P transect and for summer along S–N line Z transect extending from Ocean Station Papa (OSP; 50°N 145°W) to the respective shelf waters. Surface-water (10 m) concentrations ranged from 0.04 nM in the open ocean to 0.9 nM at the Canadian shelf station. A clear gradient is evident, with dissolved Zn concentrations decreasing with increasing distance from shore along the E–W transect in both summer and winter. No consistent trend was observed along the S–N transect. Low concentrations of Zn (0.05–0.07 nM) were observed in near-surface water at OSP in winter. The vertical distribution of dissolved Zn is oceanographically consistent, showing a silicon-like vertical profile. Concentrations of silicic acid and dissolved Zn at depth are higher than those at equivalent depths in the Atlantic, as expected from deep-water circulation patterns and build-up in concentration of these elements. Dissolved Zn/Si ratios in the upper 200 m indicate a trend of decreasing with distance from shore, which infers a decoupling between dissolved Zn and silicic acid in the upper ocean. We hypothesise that the silicon-like profile of dissolved Zn is a result of recycling from relatively biologically resistant organic particulate phases, that leads to profiles very similar to those of dissolved silicon. Other than at two stations where there is very high primary production, there is no apparent horizontal relationship between total dissolved Zn and chlorophyll a or production.

The redox sensitive trace metals iron and manganese are two important elements that help shape the biogeochemistry of aquatic systems and thus their measurement is important. Current laboratory methods are expensive, time consuming and cannot provide the spatial and temporal resolution needed to characterize these elements in natural waters. Here we describe the first autonomous analyzer capable of providing vertical profiles as well as routine in-situ determinations of dissolved Fe(II) and Mn in aquatic environments. The spectrophotometric sensor uses microfluidic methods (Lab-on-a-chip technology) and mixes reagents and samples using a novel in-cell diffusion process. Fe(II) and Mn can be measured with a frequency of up to 12 and 6 samples per hour respectively with limits of detection of 27 nM for Fe(II), 2.1% precision (n=20), and 28 nM for Mn, 2.4% precision (n=19). The device combines relatively low cost, low power usage, low reagent consumption, portability, and tolerance to pressures up to at least 170 bars, with high precision and accuracy. We present data from a successful demonstration of the sensor during a cruise to the Gotland and Landsort Deep Basins of the Baltic Sea.

Purpose:Diagenetic modelling, the mathematical simulation of the breakdown of sedimentary organic matter and subsequent fate of associated nutrients, has progressed to a point where complex, non-steady state environments can be accurately modelled. A genetic algorithm has never been used in conjunction with an early diagenetic model, and so we aim to discover whether this method is viable to determining a set of realistic model parameters, which itself is often a difficult task.Materials and methods:A range of sensitivity analyses were conducted to establish the parameters for which the model was most sensitive before a micro-genetic algorithm (?GA) was used to fit an output from a previously published diagenetic model (OMEXDIA) to observational data, taken at the North Dogger site from a series of cruises in the North Sea. Profiles of carbon, oxygen, nitrate and ammonia were considered. The method allows a set of parameters to be determined in a manner analogous to natural selection. Each iteration of the genetic algorithm within each experiment decreases the variance between the observed profiles and those calculated by OMEXDIA.Results and discussion:Despite some of the observed profiles, particularly for carbon, showing unusual patterns, the genetic algorithm was able to generate a set of parameters which was able to fit the observations. The genetic algorithm can therefore help to determine the values of other parameters used in the model, for which observational values are difficult to measure (e.g. the flux of organic matter to the sediment from the overlying water column and the rates of degradation of organic matter). We also show that the values of the parameters determined by the ?GA technique are able to be used in a potentially temporally predictive manner.Conclusions:The ?GA used is a viable method to fit carbon and nutrient sedimentary profiles observed in complex, dynamic shelf sea systems, despite OMEXDIA originally being designed for a different sedimentary environment. The results therefore show that this novel use of a genetic algorithm is a suitable method for both model calibration and validation and that the technique may help in explaining processes which are poorly understood.

The concentrations of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were measured in several soft-tissue types of the Antarctic soft-shelled clam, Laternula elliptica, which had been collected from Rothera Research Station, Adelaide Island, Antarctic Peninsula. Concentrations of Mn, Ni, Cr and Pb were significantly higher in the kidney than in any other soft tissue and highest concentrations of Cu were observed in the digestive gland. In general, the total tissue concentrations of heavy metals in L. elliptica were considered to be at baseline levels, except for Cu in organisms near the end of the runway. Copper concentrations were an order of magnitude greater (357 µg/g dry weight) than baseline levels, suggesting anthropogenic contamination or an unidentified natural source. However, there was no indication of anthropogenic metal contamination occurring close to the sewage outfall at Rothera, which is a significant metal source. The results indicate that L. elliptica is a useful long-term biomonitor of heavy metal contamination in Antarctic coastal waters.

We have identified first evidence for the presence of submarine hydrothermal activity along the East Scotia Ridge an isolated back-arc spreading centre located at 55–60°S in the Atlantic sector of the Southern Ocean. Using a combination of in situ optical light-scattering sensor data, and total dissolvable Mn concentrations, we demonstrate the existence of hydrothermal plumes overlying two segments of this ∼500 km ridge-crest; both segments exhibit anomalous topography and at least one segment is also underlain by an axial magma chamber seismic reflector. Future investigation of the fauna that inhabit these remote hydrothermal environments may provide an important ‘missing link’ between the distinct biogeographical provinces delimited from previous investigation of northern Atlantic versus eastern Pacific vent-sites.

Measurements of dissolved Mn and Fe and total particulate Mn, Fe and Al were made on seawater samples collected in the Northern Adriatic Sea in different seasons (May 1994, June–July 1994, September 1994 and February 1995), and in the Central Adriatic Sea in June–July 1994. Porewaters were also analysed for dissolved Mn and Fe in February 1994, June 1994, September 1994 and February 1995. Seasonal observations of dissolved Mn and Fe and particulate excess Mn and Fe in the Northern Adriatic Sea have demonstrated pronounced temporal and spatial variability of their distribution. This variability was mainly due to: (a) storm events which broke down stratification of the water column and enhanced resuspension and advective transport of particulate forms, and (b) fluctuations of oxygen concentrations in the water column and sediment–water interface, related to the biodegradation of the organic matter produced during bloom periods. Large inputs of dissolved Mn and Fe were attributed to reductive solubilization and diffusion from the sediment–water interface. Particulate excess Mn and Fe concentrations were also increased by oxidation in the presence of oxygen of dissolved Mn and Fe, which had diffused from the sediment–water interface.

A first order mass balance of six different trace metals (Mn, Fe, Pb, Zn, Cu, Ni) was presented for a 1-year period for the different compartments of the Adriatic Sea: compartment 1 (northern Adriatic Sea), compartment 2 (central Adriatic Sea and surface layer of the southern Adriatic Sea) and compartment 3 (deep water of the southern Adriatic Sea). The Adriatic Sea appeared to be a source of dissolved Cu, Mn and Fe for the Mediterranean Sea through the Strait of Otranto whereas for dissolved Zn and Pb the Adriatic Sea appeared to be a net sink. For dissolved Ni, inputs and outputs through the Strait of Otranto balanced each other. The residence times of all metals in compartment 1 were significantly shorter than that of water indicating significant removal. In compartments 2 and 3, residence times of Mn and Fe were relatively short suggesting removal from the water column whereas for the other metals their residence times were similar to that of water. Calculations of turnover times of metals with respect to different processes showed that in compartments 1 and 2, sedimentation was the main process that affected the content of the reservoirs whereas in compartment 3, the water flux exchanges played an important role for Zn, Cu and Ni. Most of the metals clearly undergo a very dynamic cycle of sedimentation/remobilization particularly in the Northern Adriatic Sea. In the northern Adriatic Sea, most of the Mn and Fe in deposited sediment were remobilized. This was related to diagenetic processes involving the utilisation and solubilisation of Mn and Fe oxides, which occur in the surface of the sediment in the northern Adriatic Sea. In the central Adriatic Sea, remobilization of Mn and Fe was less than in the northern Adriatic Sea, suggesting that diagenesis processes appear deeper in the sediment. Advective transport of sediment was a major source of metals for the deep basin. As much as 80% of the sediments in the South Adriatic Pit might be advected from the shelf. Remobilization fluxes in the South Adriatic Pit were significantly less than in the Northern and Central Adriatic Sea reflecting hemi-pelagic sediments.

Concentrations of total dissolved Cd, Cu, Mn and Ni were measured at the shelf edge in the Celtic and Hebridean Seas during the Ocean Margin Exchange (OMEX) and the Land Ocean Interaction Study (LOIS) programmes, respectively, in order to assess the relative importance of the processes which control the distributions of these elements. These processes include those related to hydrographic features specific to the shelf edge such as fronts, slope currents and cascading, as well as the more ubiquitous processes such as particle exchange, atmospheric and benthic inputs, remineralisation and mixing between water masses. In near-surface waters at both study sites, mixing between shelf and oceanic waters was the predominant process influencing the distributions of Cu, Ni and Mn. The concentrations of Mn decreased from shelf to oceanic waters, but a chemical front could not be characterised at the study sites. Comparison between atmospheric inputs and concentrations in surface waters of the Celtic Sea suggests that the atmosphere may be a source of Mn near the shelf edge. The distributions of Cd were little affected by lateral mixing. Cd concentrations were controlled by inputs from deep water masses, biological uptake and regeneration. The influence of biological activity and possibly of wet atmospheric inputs may explain the differences in concentrations of Cu and Cd observed at different seasons. At depth, off the shelf, the effect of mixing with shelf water decreased and processes, such as mixing between deep water masses and remineralisation, were dominant.