1,721,003 research outputs found
RRS James Cook Cruise 44, 25 Mar - 22 Apr 2010, Trinidad to Jamaica. Hydrothermal activity and deep-ocean biology of the Mid-Cayman Rise
No full textJC044 was a NERC funded research cruise aboard the UK Research Vessel the RRS James Cook the aim of the cruise was to explore the ultra-slow spreading Mid-Cayman Rise (MCR) in the Caribbean for hydrothermal activity. The MCR is the deepest spreading centre on the Earth and is isolated from the contiguous Mid-Atlantic Ridge, the closest mid-ocean spreading centre. The discovery of hydrothermal activity in this area would help us address the scientific questions related to the biogeography of hydrothermal vent organisms, the effect of high pressures on the chemistry of hydrothermal vents and the geological settings of any vents located.We successfully identified 2 active hydrothermal systems with associated chemosynthetic communities. One site named Beebe, after William Beebe, the first man to observe deep-sea marine organisms in situ. The Beebe vent field is at a depth of around 5000m and is the deepest hydrothermal site ever discovered. The second vent site is on top of an ocean core complex, it exhibits unusual chemical properties and we have named this site the Von Damm vent field after the recently deceased Karen Von Damm, a groundbreaking hydrothermal geochemist. After extensive work in the southern area of the ridge we found no evidence of hydrothermal activity, earlier reported evidence (German et al., 2010) may be re-suspended sediment material.<br/
Total dissolvable manganese anomalies over the Knipovich Ridge: evidence for hydrothermal activity (abstract of paper presented at ASLO/AGU Ocean Sciences Meeting, Honolulu, HI, 11-15 Feb 2002)
No full textRRS James Cook Cruise 77, 02 -28 Sep 2012. Investigating carbon capture and storage at the Sleipner Field
No full textThe NOC lead cruise, JC077 represents the main cruise activity as part of the UK’s input to the EC funded ECO2 project. The project aims to develop a “Best environmental practice” for the carbon capture and storage (CCS) industry. CCS has been proposed as a means of mitigating climate change by storing CO2 in geological reservoirs. The UK has identified sub-seabed storage as the most likely CCS process to be used. Other countries such as the US and Germany are pursuing land based CCS geological storage. Two types of reservoirs have been identified, saline aquifers such as Slepiner or depleted hydrocarbon reservoirs (oil and gas fields). The storage process require a monitoring strategy to ensure that any storage site is effectively monitored to ensure no leakage, or if there is leakage, to detect and monitor the effect of that leakage on the marine environment.The Sleipner site in the Norwegian sector of the North Sea is one of the longest operated CCS sites in Europe. It uses CO2 that has been separated from the natural gas from the Sleipner West Field and injects it into a saline aquifer in a permeable sand body called the Utsira sand. The aquifer is capped by a seal of shale and is thought to be impermeable. The depth of the aquifer is 900 m below the seafloor with 80m of water. This storage site has been in operation since 1996 and contains more than 14 million m3 of CO2 with more being continually added. The site has been monitored mainly though the use of seismic on regular intervals to produce “4D” maps of the distribution of the CO2 though the reservoir. These models show a migration of the plume of CO2 to the north west.JC077 takes a multidisciplinary approach to assess the Sleipner area for signs of leakage from the existing CCS reservoir. We will use a combination of AUV technology with a suite of sensors to determine if leakage is already occurring from the Sleipner field and if so to examine the effects of such leakage. The use of the AUV Autosub allows us to survey areas of the seabed at a resolution that is simply not possible by other means over a comparable time frame. The newly developed pH, pCO2 and Eh sensors attached to Autosub allow us to detect sites of leakage if it is occurring. Chirp and sidescan sonar mounted on Autosub would also allow the identification of sub-seabed and seabed features of interest. In conjunction with this we will use ship based multibeam and EK60 to look for leakage sites, and use water and sediment sampling systems to examine the state of the environment at present, and examine any areas of leakage detected
Hot springs in a cold ocean: evidence for abundant hydrothermal venting on the ultra-slow spreading Gakkel Ridge (abstract of paper presented at AGU Fall Meeting, San Francisco, CA, 10-14 Dec 2001)
No full textSensors and technologies for in situ dissolved methane measurements and their evaluation using Technology Readiness Levels
No full textDissolved methane measurements rely on the time-consuming collection of discrete water samples followed by gas-chromatography analysis. To date, this approach has proved useful for broad interpretation of environmental processes. However, it limits comprehension of environmental processes that are highly variable in space and or time. This has led to increased interest in in situ dissolved methane sensors to augment data from point sampling.So far, three sensing strategies have been explored using:1) gas-phase measurements after gas extraction through semi-permeable silicon membranes;2) measurements using biosensors; and,3) optical measurements (e.g., surface-plasmon resonance and surface-enhanced Raman spectroscopy).Optical measurements may represent the future for in situ dissolved methane sensing.We review and evaluate different in situ methane sensors and technologies using Technology Readiness Levels
Seasonal changes in speciation of dissolved chromium in the surface Sargasso Sea
No full textThe concentrations of Cr (III) and Cr (VI) were determined in the upper 500 m of the Sargasso Sea at different times of the year. Total Cr concentrations ranged between 2.5 and 4.5 nM, and the predominant species of Cr was the thermodynamically favoured Cr (VI). Cr (III) concentrations were greatest during periods of high biological activity, as indicated by strong correlations between the ratio of Cr (III):Cr (VI) and both bacterial biomass and primary productivity. Whilst the oxidation state varied substantially over the seasonal cycle, the upper water column inventory of Cr was relatively constant. The long residence time of Cr in the surface Sargasso Sea estimated with respect to atmospheric inputs (1410–2240 years) is indicative of the largely conservative behaviour of this element. Deep particle fluxes of Cr are similar or somewhat greater than atmospheric inputs, and this downward flux of Cr is well correlated with organic carbon fluxes from the upper Sargasso Sea. The long residence time coupled with the seasonal changes in oxidation state of Cr implies rapid seasonal recycling of Cr between redox states, with only slow removal via particles to the deep ocean at this site. <br/
Iron (II) distribution and oxidation kinetics in hydrothermal plumes at the Kairei and Edmond vent sites, Indian Ocean
No full textDeep-sea hydrothermal activity cycles the entire volume of the global ocean through deep-sea hydrothermal plumes at least every 4–8 × 103 a, a rapid timescale that is comparable to global deep-ocean mixing. An important process within hydrothermal plumes is the oxidation of dissolved iron discharged with vent fluids, leading to the co-precipitation of many other vent-sourced metals, thus, modifying gross hydrothermal fluxes to the deep ocean, and acting as a net sink in the ocean chemical budgets of certain key tracers. Here, we report direct measurements of dissolved Fe(II) oxidation rates from two recently discovered Indian Ocean vent sites that are intermediate between Pacific and Atlantic values, thus demonstrating that the rate of iron oxidation and formation of scavenging Fe(III) solid phases, in hydrothermal plumes varies systematically along the global deep-ocean “conveyor.? The average pseudo first-order rate constant for the oxidation reaction is 0.303 h?1 and the corresponding half-life 2.31 h. The rate plots show some curvature, however, indicating additional processes, possibly interactions with organic matter, may also influence the net oxidation/removal rate. Different rates of oxidation of iron in hydrothermal plumes in different ocean basins have important implications for the dispersion of produced oxide phases, which in turn may impact on uptake of other metals from seawater and deposition into underlying ridge-crest and ridge flank sediments
Increased fluid flow activity in shallow sediments at the 3 km Long Hugin Fracture in the central North Sea
No full textThe North Sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species, such as methane, from the Earth's interior to its exterior. Here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered, 3-km long Hugin Fracture in the Central North Sea. Although venting of gas bubbles was not observed, concentrations of dissolved methane were significantly elevated (up to six-times background values) in the water column at various locations above the fracture, and microbial mats that form in the presence of methane were observed at the seafloor. Seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane. Sediment porewaters recovered in close proximity to the Hugin Fracture indicate the presence of fluids from two different shallow (<500m) sources: (i) a reduced fluid characterized by elevated methane concentrations and/or high levels of dissolved sulfide (up to 6 mmol L−1), and (ii) a low-chlorinity fluid (Cl ∼305 mmol L−1) that has low levels of dissolved methane and/or sulfide. The area of the seafloor affected by the presence of methane-enriched fluids is similar to the footprint of seepage from other morphological features in the North Sea
Size fractionation of trace metals in the Edmond hydrothermal plume, Central Indian Ocean
No full textThe investigation of the distribution of trace elements between the dissolved, colloidal and particulate phases within a hydrothermal plume is key to understanding plume processes. Particulate and colloidal size fractions of four trace elements (iron, manganese, copper and phosphorus) along with the dissolved size fraction of iron, manganese and copper have been determined in the hydrothermal plume overlying the Edmond vent-site in the Central Indian Ocean. Dissolved iron and manganese are the most heavily enriched metals in hydrothermal fluids emerging from vents and iron plays a significant role in subsequent dissolved-particulate interactions within hydrothermal plumes. Copper and phosphorus are each representative members of discrete groups of tracers (chalcophile elements and oxyanions, respectively) that are known to exhibit distinct patterns of behaviour, relative to iron, within hydrothermal plumes. Here we show that iron is present in all three hydrothermal plume fractions (dissolved, colloidal and particulate), being least abundant in dissolved form. Manganese resides predominantly in the dissolved fraction, copper resides primarily in the particulate phase and phosphorus is abundant in both the colloidal and coarser particulate phases, but not the dissolved fraction. The correlation of phosphorus to iron in the Edmond hydrothermal plume is both (i) constant across the colloidal and coarser particulate phases and (ii) matches well to broader inter-ocean trends reported previously from the Atlantic and Pacific Oceans. These results demonstrate a mechanism whereby plume-height P:Fe ratios are established during the very earliest stages of dissolved Fe(II) oxidation, followed by aggregation into coarser hydrothermal plume particles. This provides a strong argument for the study of P:Fe ratios in hydrothermal sediments as potential paleotracers of deep-water dissolved phosphate distributions and, hence, past deep-ocean circulation patterns
- …
