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The Southern Hemisphere Westerlies (SHW) play a major role in the global climate system. The winds drive ocean circulation and affect the Southern Oceans’ ability to take up atmospheric CO2. Recently, the SHW core belt has strengthened and shifted south, but there is an insufficient understanding of its long-term behaviour. Palaeoclimatic records are key for capturing long-term variability through the SHW’s effect on surface temperature and moisture availability. However, terrestrial records are sparse in the Southern Hemisphere. We use a palynological record from Lake Diamond on sub-Antarctic South Georgia to provide reconstructions of vegetation and climate for the last ~10,000 years. Influx of long-distance transported pollen is used as a measure of surface wind strength. Changes in relative pollen abundance of native taxa occupying either upland (cold) or lowland (warm) environments indicate local climatic variability. On South Georgia, we find long-distance transported pollen from South American taxa, mainly Nothofagus and Ephedra. They show a general increase in abundance throughout the Holocene, with peak influxes between 5700–5400, 2800–1500 and 1000–500 cal yr BP. These intervals coincide with colder periods inferred from the palynological record, suggesting that SHW variation and temperature on South Georgia are highly connected. Agreement with palaeoecological records from eastern Patagonia show that climatic changes have been regionally consistent. The record from Lake Diamond further illustrates the importance of remote islands in contributing to a deeper understanding of atmospheric circulation and climatic variability in the sub-Antarctic.

Using observational data, satellite altimeters, and reanalysis model products, we have investigated eddy-induced seawater anomalies and heat and salt transport in the northeastern tropical Pacific Ocean. An eddy detection algorithm (EDA) was used to identify eddy formation at the Mexican Tehuantepec Gulf (TT) in July 2018 during an unusually strong summer wind event. The eddy separated from the coast with a mean translation velocity of 11 cm s−1 and a mean radius of 115 km and traveled 2050–2400 km westwards off the Central American coast, where it was followed at approx 114∘ W and 11∘ N for oceanographic observation between April and May 2019. The in situ observations show that the major eddy impacts are restricted to the upper 300 m of the water column and are traceable down to 1500 m water depth. In the eddy core at 92 m water depth an extreme positive temperature anomaly of 8.2 ∘C, a negative salinity anomaly of −0.78 psu, a positive fluorescence anomaly of +0.8 mg m−3, and a positive dissolved oxygen concentration anomaly of 137 µmol kg−1 are observed. Compared with annual climatological averages in 2018, the water trapped within the eddy is estimated to transport an average positive westward zonal heat anomaly of 85×1012 W and an average westward negative salt anomaly of -2.1×106 kg s−1. The heat transport is the equivalent of 1 % of the total annual zonal eddy-induced heat transport at this latitude in the Pacific Ocean. Understanding the dynamics of long-lived mesoscale eddies that may reach the seafloor in this region of the Pacific Ocean is especially important in light of potential deep-sea mining activities that are being targeted on this area.

The purpose of the study was to measure in situ the background suspended particulate matter concentration (SPMC) in the DISCOL area (SE Pacific) and its increase due to mechanical mobilization of the seabed. The disturbance experiment imitated future manganese nodule exploitations and was designed to measure the sediment plume generated by such activities. In the direct vicinity of the disturbance, landers equipped with acoustic and optical sensors measured the current velocities and the SPMC. The SPMC at the disturbance was easily up to 10 mg/L and thus about 200 times higher than the background concentration. The downstream sediment plume, measured by the lander, had a SPMC of about 1 mg/L. After tide reversal, the sediment plume was recorded a second time. A sediment transport model reproduced the plume dispersion. After rapid settling of the coarser fraction, a plume of hardly settling fine particles remained in suspension (and no deposition–resuspension cycles). The transport was controlled by the tides and by the vertical velocity component that resulted from bathymetrical differences. The plume may continue to disperse up to 100+ days (up to hundreds of km) depending on the particle size and until background concentration is reached.

Predictability of the dispersion of sediment plumes induced by potential deep-sea mining activities is still very limited due to operational limitations on in-situ observations required for a thorough validation and calibration of numerical models. Here we report on a plume dispersion experiment carried out in the German license area for the exploration of polymetallic nodules in the northeastern tropical Pacific Ocean in 4,200 m water depth. The dispersion of a sediment plume induced by a small-scale dredge experiment in April 2019 was investigated numerically by employing a sediment transport module coupled to a high-resolution hydrodynamic regional ocean model. Various aspects including sediment characteristics and ocean hydrodynamics were examined to obtain the best statistical agreement between sensor-based observations and model results. Results show that the model is capable of reproducing suspended sediment concentration and redeposition patterns observed during the dredge experiment. Due to a strong southward current during the dredging, the model predicts no sediment deposition and plume dispersion north of the dredging tracks. The sediment redeposition thickness reaches up to 9 mm directly next to the dredging tracks and 0.07 mm in about 320 m away from the dredging center. The model results suggest that seabed topography and variable sediment release heights above the seafloor cause significant changes especially for the low sedimentation pattern in the far-field area. Near-bottom mixing is expected to strongly influence vertical transport of suspended sediment.

Prediction of the dispersion of sediment plumes induced by potential mining activities is still very limited due to operational limitations on in-situ observations required for a thorough validation and calibration of numerical models. Here we report on a plume dispersion experiment carried out in the German License Area for the exploration of polymetallic nodules in the northeastern tropical Pacific Ocean. The dispersion of a sediment plume induced by a dredging experiment in April 2019 was investigated by employing a hydrodynamic high-resolution regional ocean model coupled to a sediment transport module.Various aspects including sediment characteristics and ocean hydrodynamics are examined to obtain the best statistical agreement between observation and model results. Results show that the model is capable to reproduce suspended sediment concentration and re-deposition patterns observed in the dredging experiment. Due to a strong southward current during the experiment, the model predicts no sediment deposition and plume dispersion north of the dredging tracks. The sediment re-deposition thickness reaches up to 9 mm at the dredging tracks and 0.01 mm at far-field at a distance of about 500 m from the dredging tracks.The model results suggest that seabed topography and variable sediment release heights above the seafloor cause significant changes especially for the low sedimentation pattern in the far-field region due to different current regimes. The termination of seawater stratification can rise sediment plume above the seafloor and spread it in a larger vertical distances up to 10 m from the seafloor.

Temporal variations of rare earth elements (REE) and their fractionation patterns, major elements, Pb and Hg were determined in two multicores collected at 445 and 2100 m water depth (mwd) in the Cascais submarine canyon (CSC). The PAAS-normalized REE patterns suggest mixing of Tagus estuarine and marine sediments, marked by MREE (Nd‐Dy series) enrichment and by positive Eu-anomaly, with marine sediments. The positive Eu/Eu* implies incorporation of detrital feldspar minerals derived from the estuary. Ce/Ce*, (La/Yb)PAAS and (Nd/Yb)PAAS show differences between the two cores. Core 252-35 from the shallower site is enriched in HREE (Ho‐Lu series) over LREE (La‐Pr series), a pattern also found in the Tagus estuary in the vicinity of an abandoned chemical complex, where the environment is affected by the legacy of massive-sulfide ores processing. There seems to be only limited down-canyon sediment transport to the deeper reaches where core 252-32 was collected. This deeper site shows Ce/Ce* peaks coinciding with low (La/Yb)PAAS values suggesting preferential diagenetic remobilization of LREE relative to HREE. Upcore Pb/Al and Hg/Corg trends observed in both cores indicate dispersion of the anthropogenic component from the estuary through the CSC, which is less obvious from the ∑REE/Al trends particularly in the deeper site. This may suggest the influence of diagenetic processes in the REE signal, associated with relatively low sediment accumulation rates.

Deep-sea mining for polymetallic nodules is expected to have severe environmental impacts because not only nodules but also benthic fauna and the upper reactive sediment layer are removed through the mining operation and blanketed by resettling material from the suspended sediment plume. This study aims to provide a holistic assessment of the biogeochemical recovery after a disturbance event by applying prognostic simulations based on an updated diagenetic background model and validated against novel data on microbiological processes. It was found that the recovery strongly depends on the impact type; complete removal of the reactive surface sediment reduces benthic release of nutrients over centuries, while geochemical processes after resuspension and mixing of the surface sediment are near the pre-impact state 1 year after the disturbance. Furthermore, the geochemical impact in the DISturbance and reCOLonization (DISCOL) experiment area would be mitigated to some degree by a clay-bound Fe(II)-reaction layer, impeding the downward diffusion of oxygen, thus stabilizing the redox zonation of the sediment during transient post-impact recovery. The interdisciplinary (geochemical, numerical and biological) approach highlights the closely linked nature of benthic ecosystem functions, e.g. through bioturbation, microbial biomass and nutrient fluxes, which is also of great importance for the system recovery. It is, however, important to note that the nodule ecosystem may never recover to the pre-impact state without the essential hard substrate and will instead be dominated by different faunal communities, functions and services.

Throughout the world’s oceans, water layers with increased suspended particulate matter concentrations, so called nepheloid layers, play an important role in the lateral transport of sediment, organic matter and pollutants. Nepheloid layers are persistent features in submarine canyons, where they are formed under influence of energetic hydrodynamics. To evaluate their importance it is crucial to properly quantify the amount and type of material that is transported. However, interpretation of turbidity data is not straightforward, since the detected signal is not only dependent on the concentration of particles, but also on the physical characteristics. Therefore we investigated how turbidity fluctuations induced by internal tides in the Whittard Canyon (northern Bay of Biscay, NE Atlantic Ocean) are reflected in time series data, recorded by different types of commonly used optical and acoustic sensors. Results show that in the surface water the transmitted light signal is strongly affected by the chlorophyll-bearing phytoplankton, whilst only a modest response is found in backscattered light. If left unaccounted for, this would result in an overestimation of the suspended particulate matter concentration in this layer. At the bottom of the canyon optical and acoustic sensors responded differently during one tidal cycle, interpreted as cyclic resuspension, whereby different phases of disaggregation, reaggregation and settling of particulate matter were observed. The differences in the records have important implications on the estimation of mass fluxes of suspended particulate matter, which are vital for understanding for instance carbon transport processes in the bottom boundary layer.

Concerns about future access to strategic raw materials for the high-tech industry have led to a renewed interest in mining of mineral resources from the deep-sea as a potential alternative for land-based mining. Polymetallic nodules, especially abundant in the eastern equatorial Pacific Ocean in water depths of 4000-6000 m, are a likely target of future deep-sea mining. However, many questions exist about the environmental sustainability of deep-sea mining, as it would involve the removal of hard substrate, disturbance of the surface sediment layer and dispersion of mobilised sediment over large areas of seabed adjacent to the mining sites. Anticipating on full-scale industrial mining tests, which are likely to start in the near future in the deep Pacific Ocean, we tried approaches for environmental monitoring of mining activities during two industry field tests in relatively shallow water offshore southern Spain, carried out in the framework of the European Blue Nodules project. The aim of these field tests was to assess technical and environmental performance of a scaled polymetallic nodule mining vehicle developed by the Dutch shipbuilder and maritime technology provider Royal IHC. Although the tests were performed in only 300 m water depth, much less than the depth where future deep-sea mining will take place, the weakly stratified bottom water, tide-dominated near-bed currents with mean magnitude around 5-10 cm s-1, and gently sloping seabed covered with fine muddy sediment are fairly comparable to operational conditions in the deep-sea. The plume of suspended sediment mobilised by the mining vehicle, considered to represent a major environmental pressure which may extend far beyond the actual mining area, was monitored with turbidity sensors deployed with ship-operated ROV and CTD, as well as in a static array of moored sensors. It was found that the generated sediment plume extended not more than 2 m above the seabed close to the disturbance (< 100 m), but increased in height with distance away from the disturbance site. Turbidity decreased rapidly with increasing distance from the source, but a distinct signal could still be distinguished above background turbidity at 350 m away from the source. In this near-coast setting, plume monitoring suffered significant interference by bottom trawling activities in neighbouring areas. The monitoring setup proved to be well designed and the findings on the plume size and dispersion can be significantly extrapolated to account for a more realistic mining situation. Seabed surveys with ROV-based video and scanning sonar showed that the tracks of the test vehicle, exerting an average pressure of 3 kPa on the seabed, left impressions of 4±0.8 cm deep in the surface sediment. In sediment cores collected from the path of the vehicle, geotechnical testing showed an increase in undrained shear strength and bearing capacity, as compared to undisturbed sites, indicating compaction of the surface sediment. Surveys revealed ubiquitous signs of bottom trawling, including furrows of approximately 10 cm deep produced by trawl doors.

Continental shelves in arid tropical settings present particular challenges to 210Pb-based analysis of sedimentation rates and surface mixing owing to the combination of coarse sediment, deep and year-round bioturbation, and lower atmospheric flux of 210Pb. The modern continental shelf at the northern terminus of the hyper-arid Gulf of Eilat/Aqaba (GOE) receives flood-runoff of siliciclastics, producing a mixed seabed with ~20% carbonate that is dominated by larger benthic foraminifera and mollusks. Focusing analysis on only the fine-fraction of deep-penetrating cores (≥70 cm) from 15 to 40 m water depths yields reliable 210Pb profiles, in contrast to analysis of bulk sediment (graphical abstract). Sedimentation rates increase offshore five-fold, from 0.01–0.04 cm/y in 15 m water depth to 0.21–0.27 cm/y in 30–40 m depths, reflecting offshore redistribution of flood-delivered siliciclastic sediments away from the wadi mouth, a result also supported by an offshore increase in the inventory of excess 210Pb. In contrast, the thickness of the surface mixed layer (SML) decreases from >30 cm to ~20 cm with proximity to anthropogenic stressors (channelized flood runoff, historic release of sewage and operation of fish cages), which we attribute to the suppression of macrobenthic burrowers. The rate of sedimentation on the Gulf shelf –away from dynamic bypassing in the 15 m shoreface – is comparable to other tropical carbonate shelves rich in large benthic foraminifera, and is higher than rates documented on the adjacent slope, increasing confidence in this approach to 210Pb analysis using only the fine fraction. Analysis of the fine fraction rather than bulk sediment would be a useful adjustment to 210Pb methodology in any area with scarce fine-grained sediment.

Rainbow Ridge, a 1,950 m deep upthrusted ultramafic block along the axis of the Mid-Atlantic Ridge has an active hydrothermal vent system at 2,400 m on its western slope. However, within one kilometer from the vent excessive temperatures are barely measurable, probably due to strong turbulent mixing. This mixing is studied here using a 400-m long high-resolution temperature sensor array moored with a 600-m ranging 75 kHz acoustic Doppler current profiler. Rich internal wave turbulence was recorded, characterized by 100-200 m upshoots and >200 m large overturning in particular near the end of the warming phase of the up and down moving tide. These highly nonlinear internal waves of tides interacting with buoyancy frequency waves extend up to 400 m above the sloping bottom of the ridge. Whilst a turbulent ‘bottom boundary layer’ could barely be defined, the more intense turbulence higher up in the water column is suggested to lead to the strong dispersion of the hydrothermal plume.

In order to assess the impact of recent industrialization and land-use changes in the Can Gio Mangrove Forest, a Biosphere Reserve in Southern Vietnam, we analyzed heavy metal (HM), total organic carbon (TOC) and total nitrogen (TN) concentrations in a 210Pb-dated sediment core, allowing for the environmental reconstruction of the last three decades. C/N ratios were very high (>20) until ~1990, reflecting highly refractory organic matter. Sediment Quality Guidelines (SQG's) violations were observed particularly after the establishment of industries in the area in the late-1990s. Chromium (Cr) and copper (Cu) exceeded the threshold effect levels (TEL); whereas nickel (Ni) was above the probable effects level (PEL), identifying the risk of potential adverse biological effects. Moderate contamination, mainly from cobalt (Co) and lead (Pb), was detected by the contamination factor (CF) index, with Pb levels likely originating from mainly anthropogenic sources, particularly after ~1992, as indicated by elevated enrichment factor (EF) values. A high positive correlation was found between Pb, Cr, Cu and Ni (r ≥ 0.8), while Co, cadmium (Cd) and TOC were highly positive correlated (r = 0.9). We identified evidence of point sources, atmospheric pollution and erosion as the main contributors to enhanced HM levels. However, negative values of the Geo-accumulation index (I-geo) indicated uncontaminated sediments. This discrepancy in pollution indices was likely due to the use of shale averages instead of regional levels as background values, as well as the influence of multiple stressors.

Deep-sea mining for polymetallic nodules is expected to have severe environmental impacts because in addition to the nodules, benthic fauna as well as the upper reactive sediment layer is removed through the mining operation, and blanketed by resettling material from the suspended sediment plume. This study aims to provide a holistic assessment of the biogeochemical recovery after a disturbance event by applying prognostic simulations based on an updated diagenetic background model and validated with novel (micro)-biological data. It was found that the recovery strongly depends on the impact type; complete removal of the reactive surface sediment reduces seafloor nutrient fluxes over centuries, while geochemical processes after resuspension and mixing of the surface sediment are near pre-impact state one year after the disturbance. Furthermore, the geochemical impact in the DISCOL area would be mitigated to some degree by a clay-bound Fe(II)-reaction layer, impeding the downward diffusion of oxygen, thus stabilizing the redox zonation of the sediment during transient post-impact recovery. The interdisciplinary (geochemical, numerical and biological) approach highlights the closely linked nature of benthic ecosystem functions, e.g. through bioturbation, microbial biomass and nutrient fluxes, which is also of great importance for the system recovery.

Hydrothermal vent fields found at mid-ocean ridges emit hydrothermal fluids which disperse as neutrally buoyant plumes. From these fluids seafloor massive sulfides (SMS) deposits are formed which are being explored as possible new mining sites for (trace) metals and rare earth elements (REE). It has been suggested that during mining activities large amounts of suspended matter will appear in the water column due to excavation processes, and due to discharge of mining waste from the surface vessel. Understanding how natural hydrothermal plumes evolve as they spread away from their source and how they affect their surrounding environment may provide some analogies for the behaviour of the dilute distal part of chemically enriched mining plumes. This study on the extensive Rainbow hydrothermal plume, observed up to 25 km downstream from the vent site, enabled us to investigate how microbial communities change in the presence of a natural plume. The (trace) metal and REE content of suspended particulate matter (SPM) was determined using HR-ICP mass spectrometry and the microbial communities of the neutrally buoyant plume, above plume-, below plume-, and near-bottom water and sediment were characterised by using 16S rRNA amplicon sequencing methods. Both vertically in the water column and horizontally along the neutrally buoyant plume, geochemical and biological changes were evident as the neutrally buoyant plume stood out by its enrichments in (trace) metals and REEs, of which the concentrations changed as the plume aged. This was also reflected in the background pelagic system as Epsilonproteobacteria started to dominate and the biodiversity appeared to reduce with distance away from the Rainbow hydrothermal vent field. The Rainbow hydrothermal plume provides a geochemically enriched natural environment, which is a heterogeneous, dynamic habitat that is conducive to ecological changes in a short time span.

Takahe seep, located on the Opouawe Bank, Hikurangi Margin, is characterized by a well-defined subsurface seismic chimney structure ca. 80,500 m2 in area. Sub-seafloor geophysical data based on acoustic anomaly layers indicated the presence of gas hydrate and free gas layers within the chimney structure. Reaction-transport modeling was applied to porewater data from 11 gravity cores to constrain methane turnover rates and benthic methane fluxes in the upper 10 m. Model results show that methane dynamics were highly variable due to transport and dissolution of ascending gas. The dissolution of gas (up to 3761 mmol m−2 yr−1) dwarfed the rate of methanogenesis within the simulated sediment column (2.6 mmol m−2 yr−1). Dissolved methane is mainly consumed by anaerobic oxidation of methane (AOM) at the base of the sulfate reduction zone and trapped by methane hydrate formation below it, with maximum rates in the central part of the chimney (946 and 2420 mmol m−2 yr−1, respectively). A seep-wide methane budget was constrained by combining the biogeochemical model results with geophysical data and led to estimates of AOM rates, gas hydrate formation and benthic dissolved methane fluxes of 3.68 × 104 mol yr−1, 73.85 × 104 mol yr−1and 1.19 × 104 mol yr−1, respectively. A much larger flux of methane probably escapes in gaseous form through focused bubble vents. The approach of linking geochemical model results with spatial geophysical data put forward here can be applied elsewhere to improve benthic methane turnover rates from limited single spot measurements to larger spatial scales.

Paleoecological assessment is challenging in highly dynamic environments such as estuaries, where sedimentation of material derived from the catchment interferes with marine processes. In this study we analyzed sedimentary heavy metal contents of the last decades to assess the impact of recent industrialization and changes in land use of the Thi Vai Estuary in Southern Vietnam. Two sediment cores (upstream and downstream) were dated using 210Pb, allowing the environmental reconstruction of the last three decades. Considering the recent and fast economic growth of this region these results are suitable for the evaluation of anthropogenic impacts. Mean sedimentation rates (9.2 cm yr−1 upstream, 4.7 cm yr−1downstream) indicate high land erosion likely due to deforestation and dumping of dredged material. Sediment quality guidelines (SQG's) showed that Cr and Cu levels exceed threshold values (TEL) in both cores. Upstream Ni is above the probable effect level (PEL) suggesting risk of potential adverse biological effects. Geo-accumulation (I-geo), enrichment factor (EF) and contamination factor (CF) indices were calculated based on geogenic background values. Most indices show only moderate contamination for different elements, particularly by Cr and Pb. However, considering the historical land use impacts (such as discharge of untreated wastewater, intense agricultural practices, tanning operations, etc.), pollutant concentrations are lower than expected, presumably due to dilution by high sedimentation rates and tidal hydrodynamics. Nonetheless, heavy metal indices and SQG's indicate the ecological condition in the area is of concern, particularly upstream as corroborated by high metal fluxes, highlighting severe impacts in the region.

In this study, we assess the impact of the quantity and quality of the organic matter on the distribution of live benthic foraminifera on a cross-margin transect off the Douro River (western Iberian margin). Surface sediments from five stations ranging from 50 to 2000 m water depth were collected in March 2011 at the end of the period of maximal river runoff, in order to better evaluate the importance of terrestrial input. Living (stained) benthic foraminiferal assemblages (> 150 μm) and environmental parameters (grain size, total organic carbon (TOC), total nitrogen (TN), C/N ratio, δ 13 C TOC , pigments and amino acids) were investigated. Organic matter amounts follow the sediment grain size pattern with higher concentration in fine sediments and seem to control faunal density, except at the shallowest station where TOC is low and faunal density high. At this coastal site, a massive sandy deposit is identified and associated with very low faunal diversity. Labile organic matter is richest at the shelf stations where benthic foraminifera standing stocks are high. This is particularly evident on the Douro mud patch where both density and diversity are high. Foraminiferal faunas living at the shelf stations are dominated by species (e.g., Nonion scaphum , Ammonia beccari , i Bulimina aculeata and Eggerella scabra ) characteristic of the rich trophic conditions, with organic matter of mixed estuarine and marine origin. Very low total standing stocks on the upper slope are associated with coarse sediments, probably resulting from intense bottom currents at this depth resulting in poor trophic conditions. Deeper environments are characterized by species (e.g., Hoeglundina elegans , Uvigerina mediterranea and Reophax scorpiurus ) indicative of fairly abundant but low-quality organic matter. Finally, the faunal differences between the shelf stations may reflect different successional stages: an early stage at 50 m water depth where unstable conditions are observed, with faunas dominated by opportunistic species and a more mature fauna in the mud patch where more stable conditions prevail.

Coccolithophores are calcifying phytoplankton and major contributors to both the organic and inorganic oceanic carbon pumps. Their export fluxes, species composition and seasonal patterns were determined in two sediment trap moorings in the open equatorial North Atlantic (M4 at 12° N 49° W and M2 at 14° N 37° W), which collected settling particles synchronously in successive 16-day intervals from October 2012 to November 2013, at 1200 m water depth. The two trap locations show a similar seasonal pattern in total coccolith export fluxes and a predominantly tropical coccolithophore settling assemblage throughout the monitored year. Species fluxes were yearlong dominated by lower photic zone (LPZ) taxa (Florisphaera profunda, Gladiolithus flabellatus), but also included upper photic zone (UPZ) taxa (Umbellosphaera spp., Rhabdosphaera spp., Umbilicosphaera spp., Helicosphaera spp.). The LPZ flora was most abundant during fall 2012, whereas the UPZ flora was more important during summer. In spite of these similarities, the western part of the study area produced persistently higher fluxes, averaging 241 × 107 coccoliths m−2 d−1 (117 × 107 to 423 × 107 coccoliths m−2 d−1) at station M4, compared to only 66 × 107 coccoliths m−2 d−1 (25 × 107 to 153 × 107 coccoliths m−2 d−1) at station M2. Higher fluxes at M4 were mainly produced by the LPZ species, although most UPZ species also contributed higher fluxes, reflecting enhanced productivity in the western equatorial North Atlantic. In addition, we found two marked flux peaks of the more opportunistic species Gephyrocapsa muellerae and Emiliania huxleyi indicating a fast response to nutrient-enrichment of the UPZ, probably by wind-forced mixing, whereas increased fluxes of G. oceanica and E. huxleyi in October/November 2013 coincided with the occurrence of Amazon River affected surface waters. Since the spring and fall events of 2013 were also accompanied by two dust flux peaks we propose a scenario where atmospheric dust also provided fertilizing nutrients to this area. Enhanced surface buoyancy associated to the river plume indicates that the Amazon acted not only as a nutrient source, but also as a surface density retainer for nutrients supplied from the atmosphere. Still, lower total coccolith fluxes during these events compared to the maxima recorded in November 2012 and July 2013 indicate that transient productivity by opportunistic species was less important than background tropical productivity in the equatorial North Atlantic. This study illustrates how two seemingly similar sites in an open-ocean tropical setting actually differ greatly in ecological and oceanographic terms, and provides valuable insights into the processes governing the ecological dynamics and the downward export of coccolithophores in the tropical North Atlantic.

Cable bacteria induce long-distance electron transport in the seafloor and can exert a powerful control on the elemental cycling in marine sediments by creating extreme excursions in porewater pH. Yet, the natural distribution of cable bacteria is still largely unknown, and so their role in coastal biogeochemical cycling remains poorly quantified. Here we show that cable bacteria can be abundant in the sediments of intertidal bivalve reefs, where they strongly influence the pore water geochemistry, resulting in a potentially beneficial interaction between the sulfur oxidizing microbes and biodepositing fauna. Cable bacteria occurred in sediments accumulating within mussel and oyster reefs in the Wadden Sea (The Netherlands), at cumulative filament densities up to 1038 m cm−2. Additionally, cable bacteria were found at moderately high cumulative filament densities (up to 56 m cm−2) in a heavily bioturbated sandy sediment adjacent to the muddy reefs. Microsensor profiling revealed strong sulfide removal and intense acid generation associated with the electrogenic sulfide oxidation metabolism of the cable bacteria. Strongly elevated concentrations of dissolved calcium (up to 35 mM), manganese (up to 250 μM), and iron (up to 700 μM) were observed in the pore waters, consistent with acidity-driven dissolution of calcium carbonates and iron sulfides. This field study provides substantive evidence that cable bacteria exert a decisive control on the cycling of sulfur and carbonate minerals in cohesive coastal sediments, and identifies that the distribution and influence of cable bacteria covers a greater range of natural habitats than previously believed.

The distributions of branched glycerol dialkyl glycerol tetraethers (brGDGTs), which are transported from the soils where they are predominantly produced to marine sediments via rivers, have been applied in reconstructing mean annual air temperatures (MAT) and pH of soils. However, paleoclimate reconstructions using sedimentary brGDGTs have proven difficult in arid regions including the Iberian Peninsula. Recently, six novel 6-methyl brGDGTs have been described using new analytical methods (in addition to the nine 5-methyl brGDGTs previously used for climate reconstructions), and so new pH and MAT calibrations have been developed that in a set of global soil samples were shown to improve the accuracy of reconstructions, especially in arid regions. Because of this we decided to apply the new method to separate the 5- and 6-methyl isomers along with the novel calibrations to a sample set that runs in a transect from source to sink along the Tagus River and out to the deep ocean off the Portuguese margin and spans the last 6,000 years in order to determine if it improves paleoclimate reconstructions in this area. We found that although pH reconstructions in the soils were improved using the new calibration, MAT reconstructions were not much better even with the separation of the 5- and 6-methyl brGDGTs. This confirmed the conclusion of previous studies that the amount of aquatically produced brGDGTs is overwhelming the soil derived ones in marine sediments and complicating MAT reconstructions in the region. Additionally, the new separation revealed a strong relationship between the new degree of cyclization (DC’) of the brGDGTs and MAT not seen before that could be making temperature reconstructions in this and other arid regions difficult.

We have assessed the redistribution of a secondary source of sedimentary anthropogenic mercury in the Haifa bay (HB) area (SE Levantine basin), which is the northern sink for Nile-driven sand. A long-term (30 years) ~ 80% decrease of the total sedimentary mercury concentrations (THg) was recorded in the inner bay, while an up to 3-fold increase was recorded in the top sediments of the outer bay. Sedimentary THg depth profiles and their temporal variability were used to model the main re-distribution processes, mainly resuspension associated with winter storm-derived transport. This mechanism transforms a secondary, sandy and well-aerated sink into a tertiary, more silty and hypoxic source at adjacent peripheral areas, affecting mercury bioavailability. We revisited the concept of environmental relaxation, i.e. the rate of return of a polluted environment to an acceptable state, showing that sedimentary transport processes may affect the associated ecological risks, mainly at shallow-water coastal sites.

Recent sediment transport and deposition in the Lisbon–Setubal and Cascais submarine canyons, Portuguese continental margin, were investigated on the basis of water column profiles of suspended particulate matter, records of near-bottom currents and settling fluxes of particulate matter obtained with benthic landers, and analysis of surface sediments. The results show that fine-grained predominantly lithogenic sediment derived from adjacent shelf areas accumulates in the upper reaches of the canyons. Sediment deposited further down in the middle and lower reaches of the canyons is essentially similar to the hemipelagic sediment found on the adjacent continental slope, indicating that down-canyon transport of sediment from the upper to the lower canyon is limited. Tidal currents measured at various depths in the Lisbon–Setubal Canyon appear sufficiently strong to resuspend and transport sediment, but net up-canyon flow of the bottom water may retain shelf-derived lithogenic sediment in the upper canyon. Sediment gravity flows, which in the nearby Nazare Canyon are an effective mechanism for down-canyon sediment transport, appear rare in the Lisbon–Setubal Canyon and probably also in the Cascais Canyon. Turbidity current events recorded in the sedimentary record of the canyons may correspond to seismic events of 1969 and 1755 AD.

The Cascais Canyon delivers contaminated sediments from the shelf to the deep marine environment. Multi-core PE252-32, located at 2100 m water depth in the canyon, records the latest 300 years of sedimentation. It was dated by 210Pb and analyzed texturally and geochemically for major elements and selected trace metals (Cu, Cr, Hg, Li, Ni, Pb and Zn). Cluster analysis performed on the down-core geochemical data identified four groups of variables related by grain-size, geochemical source and composition. Mercury, Pb and Zn were grouped in a cluster representing the anthropogenic component. Cluster analysis was applied again particularly to the latter cluster relatively to depth, in order to constrain the onset and temporal evolution of anthropogenic contamination. A second clustering, made on the basis of Hg, Pb and Zn, grouped samples by age and degree of anthropogenic contamination. One cluster contained relatively uncontaminated samples older than 1900 AD, and another cluster samples younger than 1900 AD with distinct metal enrichment. Maximum enrichments occurred during the early 1980s, followed by a slight recovery from the mid-1980s to the present. Mercury was the element with the highest enrichment factor (EFHg=5). Despite relatively low accumulation rates at this core location, our results show the importance of the Cascais Canyon as a transport route for contaminated sediments from the Tagus prodelta into the deep regions of the Portuguese Margin. El Cañón submarino de Cascais distribuye sedimentos contaminados de la plataforma continental al medio marino profundo. El testigo PE252-32, situado a 2100 metros de profundidad dentro del cañón, registra los últimos 300 años de su sedimentación. Se ha datado con 210Pb y ha sido analizada su granulometría, elementos mayoritarios y traza (cobre, cromo, mercurio, litio, níquel, plomo y zinc). Se ha llevado a cabo un análisis estadístico clúster, inicialmente aplicado a las series de datos geoquímicos en función de la profundidad, identificándose 4 grupos de variables, relacionados por la granulometría, procedencia y composición geoquímica. Los metales mercurio, plomo y zinc aparecen agrupados en un clúster que representa la componente antropogénica. A continuación el mismo análisis estadístico se aplicó específicamente a este grupo, en función de la profundidad, organizando las muestras según la edad de contaminación antropogénica. Como resultado las muestras quedan agrupadas en dos clústers principales, el de las muestras no contaminadas y más antiguas de 1900 AC, y el de las muestras más recientes de 1900 AC, marcando esta fecha el inicio de la contaminación por impacto de la actividad humana. Los máximos enriquecimientos ocurren durante el inicio de la década de los años ochenta, seguidos de un ligero descenso a partir de mediados de la misma década hasta la actualidad. De entre los demás, el mercurio es el elemento con el mayor grado de enriquecimiento (EFHg=5). Aunque la tasa de acumulación de sedimentos en este lugar es relativamente baja, los resultados obtenidos ponen en evidencia la importancia del Cañón submarino de Cascais como vía de transporte de sedimentos contaminados depositados en el pro-delta del Tajo a las regiones profundas del margen de Portugal.

We describe the quantitative and compositional (phytopigment, protein, carbohydrate and lipid) patterns of sedimentary organic matter along bathymetric gradients in seven submarine canyons and adjacent open slopes located at four European regions: one along the NE Atlantic and three along the Mediterranean continental margins. The investigated areas are distributed along a putative longitudinal gradient of decreasing primary production from the Portuguese (northeastern Atlantic Ocean), to the Catalan (western Mediterranean Sea), Southern Adriatic (central Mediterranean Sea) and Southern Cretan (eastern Mediterranean Sea) margins. Sediment concentrations of organic matter differed significantly between the Portuguese margin and the Mediterranean regions and also from one study area to the other within the Mediterranean Sea. Differences in quantity and composition of sediment organic matter between canyons and open slopes were limited and significant only in the eutrophic Portuguese margin, where the differences were as large as those observed between regions (i.e. at the mesoscale). These results suggest that the overall trophic status of deep margin sediments is controlled mostly by the primary productivity of the overlying waters rather than by the local topography. Moreover, we also report that the quantity and nutritional quality of sediment organic matter in canyons and adjacent open slopes do not show any consistent depth-related pattern. Only the Nazare and Cascais canyons in the Portuguese margin, at depths deeper than 500 m, displayed a significant accumulation of labile organic matter. The results of our study underline the need of further investigations of deep margins through sampling strategies accounting for adequate temporal and spatial scales of variability.

Processes, pathways and fluxes of sediment transport and deposition in the Nazaré submarine canyon, Portuguese continental margin, were investigated by water column profiling of suspended particulate matter, recording of near-bottom currents and suspended particulate matter fluxes with benthic landers, and by analysis of surface sediment cores. The results show that fine-grained suspended sediment from the adjacent shelf is captured in the upper canyon and actively transported through the canyon to the abyssal plain under influence of tidal currents and intermittent sediment gravity flows. Tidal currents are actively resuspending and transporting sediment in the upper to middle canyon, as reflected by high concentration of suspended particles in bottom waters, high horizontal and vertical sediment fluxes in the bottom water layer and high sediment accumulation rate on the seabed. Diminishing strength of tidal currents leads to focussed sediment deposition in the middle canyon. Further transport of sediments toward the lower canyon takes place predominantly by sediment gravity flows occurring on yearly or longer timescale. Turbidity currents strong enough to transport sand-sized material to the lower canyon occur only on centennial or longer timescales. © 2007 Elsevier B.V. All rights reserved.

Favali, Paolo ... et. al.-- OCEANS 2015, 18-21 May 2015, Genova, EMSO (European Multidisciplinary Seafloor and water-column Observatory; http://www.emso-eu.org) is a large-scale European Research Infrastructure (RI) of the ESFRI roadmap composed of fixed-point, seafloor and water-column observatories with the basic scientific objective of near- and realtime, long-term monitoring of environmental processes related to the interaction between the geosphere, biosphere, and hydrosphere. It is geographically distributed in key sites of European waters, spanning from the Arctic, through the Atlantic and Mediterranean Sea to the Black Sea

In this study we describe recent coccolith assemblages from surface sediments of the central Portuguese continental margin. By investigating variation in coccolith concentrations and relative abundances along north–south and onshore–offshore gradients and between submarine canyons and open shelf and slope areas, and by correlation of coccolith distribution with sediment characteristics (sediment bulk composition and particle-size, Corg/Ntot and sediment accumulation rate), we assess to what extent (paleo)ecological information can be distinguished from taphonomical effects (dissolution and mechanical destruction, lateral transport and dilution with terrigenous material). The main finding of this study is that original distribution patterns reported for living coccolithophores from the Portuguese margin surface waters are reflected by patterns in relative abundances of coccoliths in the underlying sediment, despite the vigorous current dynamics and active sediment transport on the shelf and in the canyons. Like in the surface water assemblages, Gephyrocapsa oceanica, Coronosphaera mediterranea, Helicosphaera carteri and Coccolithus pelagicus are more prevalent in sediments of the continental shelf and upper canyon reaches, whereas Gephyrocapsa muellerae, Calcidiscus leptoporus and the group comprising Umbilicosphaera sibogae, Umbellosphaera irregularis and Rhabdosphaera spp. have higher relative abundances in sediments of the open slope. Greater abundance of the coastal assemblage in sediments of the upper Nazare Canyon appears associated with persistent high productivity driven by amplification of coastal upwelling and internal tidal pumping in the canyon head and the shelf area south of it. Enrichment of oceanic species in the upper reaches of both the Nazare and Lisbon–Setubal Canyon, compared with adjacent shelf areas, suggests displacement of oceanic coccolithophores in oceanic surface water masses advected coastwards along the canyon axes. While coccolith relative abundances in the sediment thus seem to reflect original distribution patterns, precluding major post-mortem redistribution of coccoliths, we found a distinct inverse relationship between coccolith concentration and sediment particle size, suggesting that sedimentary processes control the accumulation of coccoliths in the sediment. We propose a taphonomy-driven scenario, in which coccolith preservation is favored by rapid incorporation in the sediment near their area of origin, while coccoliths reworked by currents and transported away from their area of origin are subject to non-selective destructive processes, including dissolution and mechanical abrasion. This scenario would explain the observed apparent paradox of the preservation of the primary ecological signal in an environment known for its dynamic sedimentary processes. This study provides important insights on the processes governing the preservation of the ecological signature in the sedimentary record and testifies on the enormous potential of coccoliths in paleoapplications.

The Whittard Canyon (NE Atlantic) is one of the largest canyon systems on the northern Bay of Biscay margin. It likely receives a high input of organic matter from the productive overlying surface waters, and part of this organic matter may eventually be transferred down the canyon into the Whittard Channel extending from the canyon mouth onto the Biscay Abyssal Plain. To establish if substantial transport of organic matter takes place from the canyon into the deep-sea channel we: (1) deployed a benthic lander in the Whittard Channel for a period of one year to measure near-bottom particulate matter transport and deposition rates; (2) collected surface sediment samples from the Whittard Channel and adjacent areas to assess possible organic matter enrichment in the channel (3) surveyed transects across the channel and adjacent areas with towed video camera to assess distribution of benthic megafauna potentially indicating enhanced flux of fresh organic material. The video surveys revealed massive occurrence of elpidiid holothurians in the proximal Whittard Channel, whilst only low numbers were counted further down the channel and on areas adjacent to the channel. We speculate that these deposit-feeding holothurians were attracted by the elevated content of relatively fresh organic matter in surface sediments of the proximal channel, as indicated by analysis of the surface sediment samples. Yet, whilst we expected that organic matter enrichment in the channel could be attributed to down-canyon transport through the Whittard Canyon, this could not be confirmed by data recorded by the benthic lander. During most of the 1-year deployment period, the net near-bottom currents and suspended particulate matter transport was directed in up-channel direction. During two sediment-gravity flow events recorded in March and July 2011, most likely originating from the Whittard Canyon, substantial deposition of particulate matter did occur in the Whittard Channel. However, the material deposited during those events consisted largely of inorganic sediment and was relatively poor in fresh organic material, and hence could not have substantially contributed to the organic matter enrichment observed in the channel. The highest deposition flux of fresh organic matter, recorded in May 2011, was not associated with any down-channel flow and more likely was derived from local settling of phytodetritus produced during the spring phytoplankton bloom. Based on our observations we infer that the organic enrichment observed in the proximal Whittard Channel is due to redistribution of phytodetritus by bottom currents, and accumulation of this material in the topographic depression formed by the Whittard Channel. The mobility of the elpidiid holothurians allows them to exploit these localised food sources.

X-ray fluorescence (XRF) core scanning provides rapid high-resolution (down to 1 mm) records of chemical composition on split sediment cores. The measurements are non-destructive and require very limited sample preparation. The new Avaatech XRF Core Scanner, operational since 2002, covers the atomic mass range from Al to U. Instrument parameters, especially tube voltage, can be adjusted to provide optimum settings for selected elements or sets thereof. Owing to the nature of the surface of split sediment cores, particularly effects resulting from sample inhomogeneity and surface roughness, results are semiquantitative, yet provide reliable records of the relative variability in elemental composition downcore. Selected case studies from diverse sedimentary settings in the NE Atlantic Ocean illustrate a range of applications of XRF logging data. These include preliminary stratigraphic interpretations (glacial-interglacial cycles), provenance studies of the terrigenous sediment fraction, lithological characterization, early diagenetic processes and distinction between carbonate phases (aragonite v. calcite).

The preservation of C org in various shelf seas from different geological, hydrological and climatological settings is compared. Most of these shelves have been studied extensively over the last two to three decades, often within the framework of large (inter)national research projects. Various factors (physical oceanography, chemical conditions, sedimentation rates) that could influence the preservation of C org are discussed. Not only recent conditions, but also longer time scale fluctuations (glacials versus inter-glacials, sea level variations) are dealt with. Most (>95%) of the C org introduced onto shelves by primary production and imported from the oceans and continents is mineralized in the water column and sediments. It appears that the role of shelves as sinks for C org is sometimes overestimated. Large areas of the continental shelves do not show any accumulation of organic matter under present day conditions. Only locally, where hydrological and sedimentological conditions are favourable for organic matter accumulation considerable amounts of C org are buried. On longer time scales the role of shelves as sinks for C org is limited, even more than under recent conditions. Continental slopes, canyons and deep-sea fans are thought to be the main sinks for C org .

Guerreiro, Catarina ... et al.-- Special issue Submarine Canyons: Complex Deep-Sea Environments Unravelled by Multidisciplinary Research.-- 24 pages, 37 figures, 3 tables, 2 appendix, This paper presents a first attempt to characterize coccolithophore assemblages occurring in the context of an active submarine canyon. Coccolithophores from the upper-middle sections of the Nazaré Canyon (central Portuguese margin) - one of the largest canyons of the European continental margin - were investigated during a late winter period (9-12 March 2010). Species distributions were analyzed in a multiparameter environmental context (temperature, salinity, turbidity, Chl-a and nutrient concentrations). Monthly averaged surface water Chl-a concentrations between 2006 and 2011 assessed from satellite data are also presented, as a framework for interpreting spatial and temporal distribution of phytoplankton in the Nazaré Canyon. The Nazaré Canyon was observed to act as a conduit for advection of relatively nutrient-poor oceanic waters of ENACWst origin into nearshore areas of the continental shelf (less than 10. km off the coast), whilst at the surface a nutrient-rich buoyant plume resulting from intensive coastal runoff prior and during the beginning of the cruise was spreading in oceanward direction. Two distinct coccolithophore assemblages appear representative for the coast to open-ocean gradient: (1) Emiliania huxleyi together with Gephyrocapsa ericsonii and Coronosphaera mediterranea dominated the more productive assemblage present within coastal-neritic surface waters; and (2) Syracosphaera spp. and Ophiaster spp. displayed a higher affinity with open-ocean conditions, and also generally a broader vertical distribution. Local >hotspots> of coccolithophore and phytoplankton biomass potentially associated with perturbations of surface water circulation by the canyon are discussed. © 2013 Elsevier Ltd., This research was supported by the HERMIONE project (EC contract 226354) funded by the European Commission and the Cd Tox-CoN project (FCT-PTDC/MAR/102800/2008) funded by the Portuguese Science Foundation FCT. The first author benefited from an FCT PhD grant( FRH/BD/41330/2007)

Best, M.M.R. et. al.-- Oceans 2014, 14-19 Sept. 2014, St. John's, NL, Canada.-- 7 pages, EMSO (The European Multidisciplinary Seafloor and water-column Observatory, www.emso-eu.org) is forging ahead through the next challenge in Earth-Ocean Science: How to co-ordinate ocean data acquisition, analysis and response across provincial, national, regional, and global scales. The coordination, analysis, and dissemination of ocean data continue to be a challenge across international boundaries. EMSO is a large-scale European Research Distributed Infrastructure (RI) of the ESFRI (European Strategy Forum on Research Infrastructures) roadmap, and is composed of fixed-point, seafloor and water-column observatories with the basic scientific objective of (near)-real-time, long-term monitoring of environmental processes across the geosphere, biosphere, and hydrosphere. It is geographically distributed in key sites of European waters, from the Arctic through the Atlantic and Mediterranean, to the Black Sea. EMSO ended its Preparatory Phase, EU Framework Programme 7 (FP7) funded project in 2012, and is now in the Interim phase transitioning to the formation of the legal entity for managing the distributed infrastructure: the EMSO European Research Infrastructure Consortium (hereinafter EMSO-ERIC). A phased implementation will characterize EMSO site extension, construction and operation. Countries currently participating in EMSO are: Italy, France, Ireland, Spain, Greece, United Kingdom, Portugal, Romania, Norway, Sweden, Turkey, Germany, and the Netherlands. The user community is open to all, and will be coordinated through an association called ESONET-Vi (European Seafloor Observatory NETwork ¿ The Vision), following on the extensive scientific community planning contributions of the ESONET-NoE FP6 project. The most striking characteristic of observatory design is its ability to address interdisciplinary objectives simultaneously across temporal and spatial scales. Data are collected from the surface ocean through the water column, the benthos, and the sub-se- floor. Depending on the application, in situ infrastructures can either be attached to a cable, which provides power and enables data transfer, or operate as independent stand-alone benthic and moored instruments. Data, in both cases, can be transmitted realtime through either fibre optic cables, or through cable and acoustic networks that are connected to satellite-linked buoys. EMSO provides power, communications, sensors, and data infrastructure for continuous, high resolution, (near)-real-time, interactive ocean observations across a truly multi- and interdisciplinary range of research areas including biology, geology, chemistry, physics, engineering, and computer science; from polar to tropical environments, down to the abyss. Such coordinated data allow us to pose multivariate questions in space and time, rather than focusing on single data streams. Continuous data are required to document episodic events, such as earthquakes, submarine slides, tsunamis, benthic storms, biodiversity changes, pollution, and gas hydrate release. Longer term time series are relevant for monitoring global change. EMSO not only brings together countries and disciplines, but allows the pooling of resources and coordination to assemble harmonised data into a comprehensive regional ocean picture which it will then make available to researchers and stakeholders worldwide on an open and interoperable access basis

Continental slopes are presumed key areas for deposition of organic carbon exported from the shelf. Analysis of across-slope differences in diatom and silicoflagellate fluxes recorded in bottom sediments of the Goban Spur margin, a typical North Atlantic slope environment, was carried out to test if they can provide information on the magnitude of advection of material from the shelf into deeper waters. Total diatom and silicoflagellate accumulation rates showed strong across-slope differences. Minimum values are recorded at the shelf break where maximum surface productivity conditions occur while the deeper sampling stations record fluxes as high as 183×106 valves cm–2 ka–1. While high diatom fluxes show a clear correspondence with the activity of a permanent bottom nepheloid layer operating in the region, they do not correlate with productivity patterns observed in the water column. Diatom assemblages are mainly composed of Chaetoceros resting spores and Thalassionema nitzschioides (Grunow) Grunow ex Hustedt, typical indicators of spring bloom conditions in the area. The absence of clear across-slope trends in the diatom assemblages is interpreted as the effect of random mixing driven by the strong hydrodynamic regime provoked by the activity of the bottom nepheloid layer. The dominance of Chaetoceros resting spores across the slope is related to important exportation of shelf-derived production. However, due to the broad ecological tolerances of the main taxa composing the diatom assemblages, they do not allow precise estimations on the magnitude of the primary vertical flux vs. the secondary lateral flux in this slope environment. Use of the tychoplanktonic and benthic diatoms, which are restricted to the neritic realm, allows only the estimation of the minimum amount of shelf-derived diatoms reaching the slope sediments (at least 13% of the total diatom assemblage for the upper slope area of the Goban Spur). This study shows that major limitations exist for the use of diatoms preserved in surface sediments of this area as tracers of shelf-derived production transported to the continental slope.

This study reports on measurements of organic carbon (Corg) and total nitrogen (Ntot) in surface sediments originating from 6 transects along the northwest European continental margin. After elimination of carbonates by an acidification technique using sulphurous acid, both elements were analysed in the same sediment sample using an elemental analyser. Corg and Ntot in the sample were comparatively low, ranging between 1 and 10 mg C and 0.2 to 1 mg N g−1 dry sediment. In a second analysis, the samples were analysed without acid addition, resulting in Ntot concentrations of 0–50% higher compared to their acidified counterparts. As a consequence, molar C/N ratios derived from the analysis of Corg and Ntot in the acidified sample ranged between 6 to 11, while the Ntot separate analysis reduced C/N ratios to 6 to 8. It is suggested that the addition of sulphurous acid to eliminate inorganic carbon volatilises nitrogenous organic matter.

Stable Pb isotope ratios ((206)Pb/(207)Pb, (208)Pb/(206)Pb), (210)Pb, Pb, Al, Ca, Fe, Mn and Si concentrations were measured in 7 sediment cores from the west coast of the Iberian Peninsula to assess the Pb contamination throughout the last 200 years. Independently of their locations, all cores are characterized by increasing Pb/Al rends not related to grain-size changes. Conversely, decreasing trends of (206)Pb/(207)Pb were found towards the present. This tendency suggest a change in Pb sources reflecting an increased proportion derived from anthropogenic activities. The highest anthropogenic Pb inventories for sediments younger than 1950s were found in the two shallowest cores of Cascais and Lisboa submarine canyons, reflecting the proximity of the Tagus estuary. Lead isotope signatures also help demonstrate that sediments contaminated with Pb are not constrained to estuarine-coastal areas and upper parts of submarine canyons, but are also to transferred to a lesser extent to deeper parts of the Portuguese Margin.

Three short marine sediment cores from the Cascais Submarine Canyon (CSC; cores 252-32 and 252-35) and the Estremadura Spur (core 252-16) on the central Portuguese Margin were analysed for Hg, Pb, Al, and Mn concentrations, and both Pb and Hg stable isotope compositions, in order to reconstruct trends in Hg and Pb sources and accumulation. Sediment ages were determined based on Pb-210 measurements. The studied cores reveal increasing Hg and Pb concentration, independent of grain-size variations, since the middle of the 19th century towards the Present. Concomitantly, a decreasing trend of Pb-206/Pb-207 to less radiogenic values towards the surface was found, indicating increasing anthropogenic inputs. The lowest values of delta Hg-202 were generally observed in the older sediments characterized by low Hg and Pb concentrations, suggesting a low input of anthropogenic metals. Odd mass number (Hg-199 and Hg-201) Hg isotopes in sediment samples from core 252-16 were characterized by positive mass independent fractionation (MIF), while recent sediments from cores 252-32 and 252-35 did not reveal significant MIF, probably reflecting both the proximity to the source of anthropogenic Hg contamination (Tagus Estuary) and the importance of the CSC as a particle carrier. The multi-tracer approach, based on both stable Hg and Pb isotopic signatures, confirms anthropogenic Hg and Pb enrichment in recent marine sediments and also allows us to distinguish between areas dominated by detrital (e.g. CSC) versus hemipelagic (Estremadura Spur) sedimentation.

Guerreiro, Catarina ... et al.-- 19 pages, 13 figures, 3 tables, 2 apendix, Coccolithophore communities collected during late winter (9-19 March of 2010) over the central Portuguese margin showed a major change in species abundance and composition within a few days' time, closely related to the highly transient meteorological and oceanographic conditions.Particularly favourable conditions for coccolithophore growth resulted from late winter continental runoff combined with northerly winds prevailing over the shelf, under clear sky conditions. A nutrient-rich Buoyant Plume (BP) resulting from intense river water runoff prior to and during the start of the cruise, was observed to spread out over the denser winter mixed layer water beneath, and extend equatorwards and offshore under influence of Ekman superficial dynamics. Stabilization of buoyancy, settling of suspended sediment from the BP and the prevailing clear sky conditions in the transition to the 2nd leg of the cruise resulted in optimum conditions for coccolithophores to develop, at the expense of nutrient availability in the superficial sunlit layer. Within a few days, coccolithophore cell densities and associated phytoplankton biomass more than tripled, reaching maximum values of 145,000. cells/l and ~13. μg/l Chl-a, respectively.Often considered as a uniform functional group of calcifying phytoplankton thriving in low-turbulence, low-nutrients and high-light environments, results presented in this study clearly show that coccolithophore life strategies are much more diverse than expected. The increase of cell densities was mainly due to the bloom of Emiliania huxleyi and Gephyrocapsa oceanica in the coastal region west off Cape Carvoeiro, together with other opportunistic phytoplankton genera (Chaetoceros s.l., Thalassiosira s.l and Skeletonema s.l.). This confirms their role as early succession r-selected taxa, capable of rapid growth within nutrient-rich environments. On the contrary, Syracosphaera spp. and Ophiaster spp. displayed the characteristics of K-selected species, being consistently more abundant in more oceanic and less eutrophic waters, away from the influence of the BP, during both low- and high-productive periods.A general description of coccolithophore communities as well as the environmental conditions during this period is presented in this study (i.e. hydrography and nutrient availability). Multivariate analysis was used to investigate the impact of short-term environmental changes on the productivity and ecology of this group. In view of the observed dominance of coccolithophores off Portugal during winter, this transitional period appears particularly favourable for coccolithophores to develop. The results highlight the importance of taking short-term hydrographic and meteorological variability into account when interpreting the ecological preferences of coccolithophores from coastal-neritic-oceanic transitional settings. © 2013 Elsevier Ltd., This research was supported by the HERMIONE project (EC contract 226354) funded by the European Commission and the Cd Tox-CoN project (FCT-PTDC/MAR/102800/2008) funded by the Portuguese Science Foundation FCT. The first author benefits from an FCT PhD grant (FRH/BD/41330/2007)

We present a conceptual model which explains benthic foraminiferal microhabitat preferences in terms of differences in the downward organic flux. We argue that under oligotrophic conditions the microhabitat depth is controlled by the availability of metabolizable food particles in the sediment. Under more eutrophic conditions, the ecosystem is no longer food-controlled, but instead, a critical oxygen level determines down to what depth we find a living fauna. Under food-limited conditions, anaerobic degradation of organic matter may provide an additional food source around the redox front, which could explain deep infaunal maxima reported in the literature. In a sample transect through the Adriatic Sea, both microhabitat controls (food-limited and oxygen-limited) are present. On the shelf and the upper part of the slope, the rather shallow depth of the microhabitat is controlled by a critical oxygen level. In the 1250 m deep southern basin and on the lower part of the slope, on the contrary, the availability of metabolizable organic matter, and not a critical oxygen level, determines down to what depth living foraminifera are found.