Physics and Earth Sciences

The trophic state of benthic deep-sea ecosystems can greatly influence key ecological processes (e.g. biomass production and nutrient cycling). Thus, assessing the trophic state of the sediment at different spatial and temporal scales is crucial for a better understanding of deep-sea ecosystem functioning. Here, using a biomimetic ap-5 15 when higher primary production processes occur in surface waters, than in summer and autumn. In both continental margins, bioavailable organic C concentrations did not vary or increase with increasing water depth. Differences in the benthic trophic state of canyons against open slopes were more evident in the Portuguese than in the Catalan margin. Overall our findings indicate that deep-sea sediments are characterized by 20 relatively high amounts of bioavailable organic matter. We suggest that the interactions between biological-related processes in surface waters and particle transport and deposition dynamics can play a crucial role in shaping the quantity and distribution of bioavailable organic detritus and its nutritional value along deep continental margins.

Cold-water coral reefs occur in many regions of the world's oceans. Fundamental questions regarding their functioning remain unanswered. These include the biogeochemical influence of reefs on their environment ("reef effects") and the influence of hydrodynamic processes on reef nutrition. In a succession of field campaigns in 2007 and 2008, these questions were addressed at the Tisler cold-water coral reef, which is centered on a sill peak in the Norwegian Skagerrak. A variety of methodological approaches were used. These consisted of the collection of CTD and chlorophyll profiles, current measurements, sampling of particulate organic matter (POM) in the benthic boundary layer (BBL) across the reef with subsequent chemical analyses, and the chemical analysis of freshly released Lophelia pertusa mucus. CTD and chlorophyll profiles indicated that downstream of the sill crest, downwelling delivered warmer, fresher and chlorophyll richer water masses down to the BBL. Both sides of the reef received downwelling nutrition delivery, as flow direction over the reef reversed periodically. Several chemical composition indicators revealed that suspended POM was significantly fresher on the downstream side of the reef than on the upstream side. L. pertusa mucus from the Tisler Reef was labile in composition, as indicated by a low C/N ratio and a high amino acid degradation index (DI) value. Particulate organic carbon (POC) content in the BBL was significantly depleted across the reef. Lateral depositional fluxes were calculated to be 18-1485 mg POC m −2 d −1 , with a mean of 459 mg POC m −2 d −1 . We propose that the combination of fresh, downwelling POM with mucus released from the reef was the cause of the greater lability of the downstream POM. Our data on POC depletion across the reef suggest that cold-water coral reefs could play an important role in carbon cycling along continental margins.

Sinking of aggregated phytoplankton cells is a crucial mechanism for transporting carbon to the seafloor and benthic ecosystem, with such aggregates often scavenging particulate material from the water column as they sink. In the vicinity of drilling rigs used by the oil and gas industry, the concentration of particulate matter in the water column may at times be enriched as a result of the discharge of 'drill cuttings' -drilling waste material. This investigation exposed laboratory produced phytoplankton aggregates to drill cuttings of various composition (those containing no hydrocarbons from reservoir rocks and those with a <1% hydrocarbon content) and assessed the change in aggregate size, settling rate and resuspension behavior of these using resuspension chambers and settling cylinders. Results indicate that both settling velocity and seabed stress required to resuspend the aggregates are greater in aggregates exposed to drill cuttings, with these increases most significant in aggregates exposed to hydrocarbon containing drill cuttings.

ESONET is a proposed sub sea component of the European GMES (Global Monitoring for Environment and Security) to provide strategic long term monitoring capability in geophysics, geotechnics, chemistry, biochemistry, oceanography, biology and fisheries. To provide representative sampling around Europe 10 nodes are proposed in contrasting oceanographic regions: 1-Arctic, 2-Norwegian margin, 3-Nordic Seas, 4-Porcupine/Celtic, 5-Azores, 6-Iberian, 7-Ligurian, 8-East Sicily, 9-Hellenic, 10-Black Sea. In addition, a mobile response observatory will be available for rapid deployment in areas of anthropogenic or natural disasters to provide data for environment management and government agencies.

Environmental awareness and technological advances has spurred development of new monitoring solutions for the petroleum industry. This paper presents experience from a monitoring program off Norway. To maintain operation within the limits of the government regulations Statoil tested a new monitoring concept. Multisensory data were cabled to surface buoys and transmitted to land via wireless communication. The system collected information about distribution of the drilling wastes and the welfare of the corals in relation to threshold values.

1 of 24 contributions over space and time. In contrast to precipitates of high-temperature fluids which mainly scavenge their REE contents from seawater the crusts of this study show 143 Nd/ 144 Nd of up to 0.512817 (eNd = +3.5). This is close to the signature of the nearby island arc rocks and far above the expected local seawater ratio of $0.51209 (eNd = À10.7). These crusts also show high 176 Hf/ 177 Hf (up to 0.283102), low 87 Sr/ 86 Sr (up to 0.7069), and low 187 Os/ 188 Os (up to 0.16) compared with local seawater, as expected from hydrothermal, island-arc-derived metal contributions. In contrast, the Pb isotope signatures of the crusts cannot be explained by mixing between seawater and hydrothermal sources. It is suggested that Pb was either removed from the ascending fluids within the sediment column before they reached seawater or the temperatures were too low to leach significant amounts of Pb from the rocks or sediments. External sources such as Saharan dust, particulate inputs from the Orinoco River, or even incongruent release of Pb isotopes from the island arc rock-derived particles must have contributed to the observed Pb isotope variability. Our results suggest that submarine hydrothermalism originating from intraoceanic island arc volcanism creates distinct geochemical environments for the dispersion of hydrothermal fluids and may be an important mechanism to supply metals of hydrothermal origin to seawater.

Depending on the geological setting, the interaction of submarine hydrothermal fluids with the host rock leads to distinct energy and mass transfers between the lithosphere and the hydrosphere. The Nibelungen hydrothermal field is located at 8°18′S, about 9 km off-axis of the Mid-Atlantic Ridge (MAR). At 3000 m water depth, 372°C hot, acidic fluids emanate directly from the bottom, without visible sulfide chimney formation. Hydrothermal fluids obtained in 2009 are characterized by low H 2 S concentrations (1.1 mM), a depletion of B (192 μM) relative to seawater, lower Si (13.7 mM) and Li (391 μM) concentrations relative to basaltic-hosted hydrothermal systems and a large positive Eu anomaly, and display a distinct stable isotope signature of hydrogen (Δ 2 H H2O = 7.6-8.7‰) and of oxygen (Δ 18 O H2O = 2.2-2.4‰). The heavy hydrogen isotopic signature of the Nibelungen fluids is a specific feature of ultramafic-hosted hydrothermal systems and is mainly controlled by the formation of OH-bearing alteration minerals like serpentine, brucite, and tremolite during pervasive serpentinization. New isotopic data obtained for the ultramafic-hosted Logatchev I field at 14°45′N, MAR (Δ 2 H H2O = 3.8-4.2‰) display a similar trend, being clearly distinguished from other, mafic-hosted hydrothermal systems at the MAR. The fluid geochemistry at Nibelungen kept stable since the first sampling campaign in 2006 and is evident for a hybrid alteration of mafic and ultramafic rocks in the subseafloor. Whereas the ultramafic-fingerprint parameters Si, Li, B, Eu anomaly and Δ 2 H H2O distinguish the Nibelungen field from other hydrothermal systems venting in basaltic settings at similar physico-chemical conditions and are related to the interaction with mantle rocks, the relatively high concentrations of trace alkali elements, Pb, and Tl can only be attributed to the alteration of melt-derived gabbroic rocks. The elemental and isotopic composition of the fluid suggest a multi-step alteration sequence: (1) low-to medium-temperature alteration of gabbroic rocks, (2) pervasive serpentinization at moderate to high temperatures, and (3) limited high-temperature interaction with basaltic rocks during final ascent of the fluid. The integrated water/rock ratio for the Nibelungen hydrothermal system is about 0.5. The fluid compositional fingerprint at Nibelungen is similar to the ultramafic-hosted Logatchev I fluids with respect to key parameters. Some compositional differences can be ascribed to different alteration temperatures and other fluid pathways involving a variety of source rocks, higher water/rock ratios, and sulfide precipitation in the sub-seafloor at Logatchev I.

Mantle-derived ultramafic rocks commonly occur on the seafloor at slow-spreading axes and are tectonically emplaced along shear zones. Since the early 1990s, a growing number of hydrothermal systems have been detected in ultramafic settings. But chemical data for fluid compositions in active systems are still limited. Besides the Logatchev field at 15°N on the Mid-Atlantic Ridge (MAR), the only other active high-temperature (N 300°C) hydrothermal field known to be strongly influenced by ultramafics is the Rainbow field at 36°N on the MAR. The field at Logatchev consists of six active vent sites at about 3000 m water depth, situated along a NW-SE-trending line with distances of 50-200 m between the individual sites. The vent sites were mapped in detail and re-sampled during two cruises in 2004 and 2005 using a ROV. The geochemical composition of the hydrothermal fluids is characterized by very high concentrations of dissolved methane and hydrogen (up to 3.5 mM and 19 mM, respectively) related to serpentinization processes in the reaction zone. Together with moderate Si concentrations of 9 mM, a depletion in B compared to seawater and Li concentrations lower than in basaltic systems, this fluid composition has been identified as characteristic signature of high-temperature hydrothermal fluids reacting with ultramafic rocks. However, additional alteration of gabbroic intrusions is likely. The fluid composition is very similar at all vent sites, indicating a common source in the reaction zone and little variation during upflow. Spatial differences in fluid composition were observed between smoking craters and the complex chimney system IRINA II, but are restricted to elements with strong temperature-controlled solubility, as Cu and Co. These differences can be related to different exit temperatures (up to 350°C and b 300°C, respectively). Concentrations of rare earth elements, and chondrite-normalized patterns with LREE enrichment and positive Eu anomalies are comparable to those of basaltic-hosted systems, thus indicating minor influence of host-rock composition. A comparison of published fluid composition data from 1996 . The Rainbow vent fluids (36°14'N, MAR): the influence of ultramafic rocks and phase separation on trace metal content in Mid-Atlantic Ridge hydrothermal fluids. Chemical Geology, 184: 37-48.] with our own data indicates that the system remained stable over the past nine years. There is no clear indication of phase separation taking place at Logatchev. chemical composition of the rocks, reaction temperature, and partly sub-seafloor mixing with entraining seawater are supposed to be the main controlling parameters of fluid geochemistry in the Logatchev field.

1] The effect of volcanic activity on submarine hydrothermal systems has been well documented along fast-and intermediate-spreading centers but not from slow-spreading ridges. Indeed, volcanic eruptions are expected to be rare on slow-spreading axes. Here we report the presence of hydrothermal venting associated with extremely fresh lava flows at an elevated, apparently magmatically robust segment center on the slow-spreading southern Mid-Atlantic Ridge near 5°S. Three high-temperature vent fields have been recognized so far over a strike length of less than 2 km with two fields venting phase-separated, vapor-type fluids. Exit temperatures at one of the fields reach up to 407°C, at conditions of the critical point of seawater, the highest temperatures ever recorded from the seafloor. Fluid and vent field characteristics show a large variability between the vent fields, a variation that is not expected within such a limited area. We conclude from mineralogical investigations of hydrothermal precipitates that vent-fluid compositions have evolved recently from relatively oxidizing to more reducing conditions, a shift that could also be related to renewed magmatic activity in the area. Current high exit temperatures, reducing conditions, low silica contents, and high hydrogen contents in the fluids of two vent sites are consistent with a shallow magmatic source, probably related to a young volcanic eruption event nearby, in which basaltic magma is actively crystallizing. This is the first reported evidence for direct magmatic-hydrothermal interaction on a slow-spreading mid-ocean ridge.