Biological and environmental rhythms in (dark) deep-sea hydrothermal ecosystems

During 2011, two deep-sea observatories focusing on hydrothermal vent ecology were up and running in the Atlantic (Eiffel Tower, Lucky Strike vent field) and the Northeast Pacific Ocean (NEP) (Grotto, Main Endeavour Field). Both ecological modules recorded imagery and environmental variables jointly for a time span of 23 days (7–30 October 2011) and environmental variables for up to 9 months (October 2011–June 2012). Community dynamics were assessed based on imagery analysis and rhythms in temporal variation for both fauna and environment were revealed. Tidal rhythms were found to be at play in the two settings and were most visible in temperature and tubeworm appearances (at NEP). A  ∼  6 h lag in tidal rhythm occurrence was observed between Pacific and Atlantic hydrothermal vents, which corresponds to the geographical distance and time delay between the two sites.info:eu-repo/semantics/publishedVersio

Distribution and redox speciation of dissolved iron on the European continental margin

To investigate the biogeochemistry of iron in the waters of the European continental margin, we determined the dissolved iron distribution and redox speciation in filtered (<0.2 μm) open-ocean and shelf waters. Depth profiles were sampled over the shelf slope southeast of the Chapelle Bank area (47.61°N, 4.24°W to 46.00°N, 8.01°W) and a horizontal surface-water transect over the shelf and through the English Channel (la Manche) and the southern North Sea (46°N, 8°W to 52°N, 4°E). An abrupt trace-metal front was found near the shelf slope, indicated by a horizontal gradient of dissolved iron (DFe) and aluminium (DAl), which correlated with changing salinities (r2 = 0.572 and 0.528, respectively, n = 92). Labile Fe(II) concentrations varied from <12 pmol L-1 in North Atlantic surface waters to >200 pmol L-1 in the near bottom waters of the shelf break. Labile Fe(II) accounted for ∼5 of the dissolved iron species in surface shelf waters (mean 5.0 ± 2.7), whereas higher Fe(II) fractions (i.e., >8) were observed near the sea bottom on the shelf break and during a midday solar maximum in surface waters in the vicinity of the Scheldt river plume. Benthic processes (resuspension and diagenesis) constituted important sources of Fe(II) and DFe in this region, and photoreduction of Fe(III) species in shelf waters caused enhanced labile Fe(II) concentrations. These processes increased the lability of iron and its potential availability to marine organisms in the shelf ecosystem. © 2007, by the American Society of Limnology and Oceanography, Inc

Toward a Harmonization for Using in situ Nutrient Sensors in the Marine Environment

Improvedcomparabilityofnutrientconcentrationsinseawaterisrequiredtoenhancethe quality and utility of measurements reported to global databases. Significant progress has been made over recent decades in improving the analysis and data quality for traditional laboratory measurements of nutrients. Similar efforts are required to establish high-quality data outputs from in situ nutrient sensors, which are rapidly becoming integral components of ocean observing systems. This paper suggests using the good practices routine established for laboratory reference methods to propose a harmonized setofdeploymentprotocolsandofqualitycontrolproceduresfornutrientmeasurements obtained from in situ sensors. These procedures are intended to establish a framework to standardize the technical and analytical controls carried out on the three main types of in situ nutrient sensors currently available (wet chemical analyzers, ultraviolet optical sensors, electrochemical sensors) for their deployments on all kinds of platform. The routine reference controls that can be applied to the sensors are listed for each step of sensor use: initial qualification under controlled conditions in the laboratory, preparation of the sensor before deployment, field deployment and finally the sensor recovery. The fundamental principles applied to the laboratory reference method are then reviewed in termsofthecalibrationprotocol,instrumentalinterferences,environmentalinterferences, external controls, and method performance assessment. Data corrections (linearity, sensitivity, drifts, interferences and outliers) are finally identified along with the concepts and calculations for qualification for both real time and time delayed data. This paper emphasizes the necessity of future collaborations between research groups, referenceaccredited laboratories, and technology developers, to maintain comparability of the concentrationsreportedforthevariousnutrientparametersmeasuredbyinsitusensors

Metal partitioning after in situ filtration at deep-sea vents of the Lucky Strike hydrothermal field (EMSO-Azores, Mid-Atlantic Ridge, 37°N)

Metal partitioning between the dissolved and particulate phases is still poorly constrained within the early mixing of hydrothermal fluids and deep seawater. In this study, in situ filtration has been used to collect early buoyant plume fluids. This has provided the unique opportunity to reassess precisely metal partitioning along the mixing gradient by limiting chemical exchange processes between the dissolved (0.45 μm) phases during sampling. We report on the partitioning of three major metals (Fe, Cu, Zn) in the early buoyant plume of six black and clear smokers from the Lucky Strike hydrothermal field (37°N, MAR; EMSO-Azores deep sea observatory). We show that chemical changes are limited in the warmest part of the plume [50–150°C, dMn > 40 μM; dilution factor (DF) of ~1–10 by NADW] as metal partitioning displays a chemical signature similar to the end-member one. However, as the dilution ratio between the hydrothermal fluid and North-Atlantic Deep-water (NADW) increases (4–50°C, dMn < 40 μM; DF of 10–100 by NADW), metal partitioning is affected by different precipitation and oxidation processes. Molar ratios normalized to Fe in the particles highlight the onset of Fe oxides formation, the precipitation of barite and the decreasing contribution of sulfide minerals (mainly Cu–Fe sulfides and sphalerite/wurtzite) along with fluid dilution

Deep dissolved iron profiles in the eastern North Atlantic in relation to water masses

Concentrations of dissolved iron (DFe, 0.2?m) were determined at two stations in the Biscay Abyssal Plain (North East Atlantic) in March 2002. DFe concentrations in the surface layer (0.23–0.34 nM) were typical of winter conditions in this area. At 1000 m, DFe concentrations increased to 0.62–0.86 nM. This feature is consistent with the production of DFe by remineralization of the biogenic material. However, at this depth, Mediterranean Outflow Water (MOW) could be an additional source of DFe. Below 2500 m, DFe concentrations were constant (0.75 ± 0.04 nM). An interesting feature of the profiles was the intermediate maximum of DFe (1.19–1.12 nM) around 2000 m, associated with the Labrador Sea Water (LSW). We suggest that the iron enrichment of LSW occurred when this water mass reached the continental margin, likely in the vicinity of the Goban plateau. Vertical distributions were highly dependent on water masses encountered

On the early fate of hydrothermal iron at deep-sea vents: A reassessment after in situ filtration

Deep-sea hydrothermal venting is now recognized as a major source of iron (Fe), an essential trace element that controls marine productivity. However, the reactions occurring during dispersal from buoyant plumes to neutrally buoyant hydrothermal plumes are still poorly constrained. Here we report for the first time on the dissolved-particulate partition of Fe after in situ filtration at the early stage of mixing at different hydrothermal discharges, i.e., Lucky Strike (37 degrees N), TAG (26 degrees N), and Snakepit (23 degrees N) on the Mid-Atlantic Ridge. We found that hydrothermal iron is almost completely preserved (>90%) in the dissolved fraction, arguing for low iron-bearing sulfide precipitation of iron in basalt-hosted systems with low Fe:H2S ratios. This result can only be explained by a kinetically limited formation of pyrite. The small part of Fe being precipitated as sulfides in the mixing gradient (<10%) is restricted to the inclusion of Fe in minerals of high Cu and Zn content. We also show that secondary venting is a source of Fe-depleted hydrothermal solutions. These results provide new constrains on Fe fluxes from hydrothermal venting

Integrating Multidisciplinary Observations in Vent Environments (IMOVE): Decadal Progress in Deep-Sea Observatories at Hydrothermal Vents

The unique ecosystems and biodiversity associated with mid-ocean ridge (MOR) hydrothermal vent systems contrast sharply with surrounding deep-sea habitats, however both may be increasingly threatened by anthropogenic activity (e.g., mining activities at massive sulphide deposits). Climate change can alter the deep-sea through increased bottom temperatures, loss of oxygen, and modifications to deep water circulation. Despite the potential of these profound impacts, the mechanisms enabling these systems and their ecosystems to persist, function and respond to oceanic, crustal, and anthropogenic forces remain poorly understood. This is due primarily to technological challenges and difficulties in accessing, observing and monitoring the deep-sea. In this context, the development of deep-sea observatories in the 2000s focused on understanding the coupling between sub-surface flow and oceanic and crustal conditions, and how they influence biological processes. Deep-sea observatories provide long-term, multidisciplinary time-series data comprising repeated observations and sampling at temporal resolutions from seconds to decades, through a combination of cabled, wireless, remotely controlled, and autonomous measurement systems. The three existing vent observatories are located on the Juan de Fuca and Mid-Atlantic Ridges (Ocean Observing Initiative, Ocean Networks Canada and the European Multidisciplinary Seafloor and water column Observatory). These observatories promote stewardship by defining effective environmental monitoring including characterizing biological and environmental baseline states, discriminating changes from natural variations versus those from anthropogenic activities, and assessing degradation, resilience and recovery after disturbance. This highlights the potential of observatories as valuable tools for environmental impact assessment (EIA) in the context of climate change and other anthropogenic activities, primarily ocean mining. This paper provides a synthesis on scientific advancements enabled by the three observatories this last decade, and recommendations to support future studies through international collaboration and coordination. The proposed recommendations include: i) establishing common global scientific questions and identification of Essential Ocean Variables (EOVs) specific to MORs, ii) guidance towards the effective use of observatories to support and inform policies that can impact society, iii) strategies for observatory infrastructure development that will help standardize sensors, data formats and capabilities, and iv) future technology needs and common sampling approaches to answer today’s most urgent and timely questions