A suspended-particle rosette multi-sampler for discrete biogeochemical sampling in low-particle-density waters

To enable detailed investigations of early stage hydrothermal plume formation and abiotic and biotic plume processes we developed a new oceanographic tool. The Suspended Particulate Rosette sampling system has been designed to collect geochemical and microbial samples from the rising portion of deep-sea hydrothermal plumes. It can be deployed on a remotely operated vehicle for sampling rising plumes, on a wire-deployed water rosette for spatially discrete sampling of non-buoyant hydrothermal plumes, or on a fixed mooring in a hydrothermal vent field for time series sampling. It has performed successfully during both its first mooring deployment at the East Pacific Rise and its first remotely-operated vehicle deployments along the Mid-Atlantic Ridge. It is currently capable of rapidly filtering 24 discrete large-water-volume samples (30–100 L per sample) for suspended particles during a single deployment (e.g. >90 L per sample at 4–7 L per minute through 1 μm pore diameter polycarbonate filters). The Suspended Particulate Rosette sampler has been designed with a long-term goal of seafloor observatory deployments, where it can be used to collect samples in response to tectonic or other events. It is compatible with in situ optical sensors, such as laser Raman or visible reflectance spectroscopy systems, enabling in situ particle analysis immediately after sample collection and before the particles alter or degrade.     

Acoustic propagation analysis with a sound speed feature model in the front area of Kuroshio Extension

This paper aims to analyse acoustic-propagation character in the front area of Kuroshio Extension (KE). By analysing Argo data and the Sea surface height (SSH) data in this KEF area, a two-dimensional (2D) sound-speed feature model (SSPFM) characterising the KEF is proposed. The SSPFM has a transition zone with a width about 100 km and the sound channel changes from 1000 m south of KEF to 300 m north of KEF, resulting in a sharp gradient about 7 m/km. Along with the meandering character of the KEF axis, the sharp gradient results in a rather complicated acoustic environment in the KEF area. With reanalysis data from the hybrid coordinate ocean model, a three-dimensional (3D) sound-speed environment is established. The acoustic propagation character in the KEF area is then analysed with the 2D SSPFM and the 3D acoustic environment. Results show that the KEF affects acoustic propagation mainly by modifying the sound channel depth. Given that acoustic propagation in the KEF area is influenced mainly by the meandering KEF, with the near-real-time SSH data to locate the KEF, the 2D SSPFM is able to provide a near-real-time estimate of the underwater 3D acoustic environment.     

A large volume particulate and water multi-sampler with in situ preservation for microbial and biogeochemical studies

A new tool was developed for large volume sampling to facilitate marine microbiology and biogeochemical studies. It was developed for remotely operated vehicle and hydrocast deployments, and allows for rapid collection of multiple sample types from the water column and dynamic, variable environments such as rising hydrothermal plumes. It was used successfully during a cruise to the hydrothermal vent systems of the Mid-Cayman Rise. The Suspended Particulate Rosette V2 large volume multi-sampling system allows for the collection of 14 sample sets per deployment. Each sample set can include filtered material, whole (unfiltered) water, and filtrate. Suspended particulate can be collected on filters up to 142 mm in diameter and pore sizes down to 0.2 μm. Filtration is typically at flowrates of 2 L min⁻¹. For particulate material, filtered volume is constrained only by sampling time and filter capacity, with all sample volumes recorded by digital flowmeter. The suspended particulate filter holders can be filled with preservative and sealed immediately after sample collection. Up to 2 L of whole water, filtrate, or a combination of the two, can be collected as part of each sample set. The system is constructed of plastics with titanium fasteners and nickel alloy spring loaded seals. There are no ferrous alloys in the sampling system. Individual sample lines are prefilled with filtered, deionized water prior to deployment and remain sealed unless a sample is actively being collected. This system is intended to facilitate studies concerning the relationship between marine microbiology and ocean biogeochemistry.     

Autonomous Microbial Sampler (AMS), a device for the uncontaminated collection of multiple microbial samples from submarine hydrothermal vents and other aquatic environments

An Autonomous Microbial Sampler (AMS) is described that will obtain uncontaminated and exogenous DNA-free microbial samples from most marine, freshwater and hydrothermal ecosystems. Sampling with the AMS may be conducted using manned submersibles, remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs), or when tethered to a hydrowire during hydrocast operations on research vessels. The modular device consists of a titanium nozzle for sampling in potentially hot environments (>350 °C) and fluid-handling components for the collection of six independent filtered or unfiltered samples. An onboard microcomputer permits sampling to be controlled by the investigator, by external devices (e.g., AUV computer), or by internal programming. Temperature, volume pumped and other parameters are recorded during sampling. Complete protection of samples from microbial contamination was observed in tests simulating deployment of the AMS in coastal seawater, where the sampling nozzle was exposed to seawater containing 1×10⁶ cells ml⁻¹ of a red pigmented tracer organism, Serratia marinorubra. Field testing of the AMS at a hydrothermal vent field was successfully undertaken in 2000. Results of DNA destruction studies have revealed that exposure of samples of the Eukaryote Euglena and the bacterium S. marinorubra to 0.5 N sulfuric acid at 23 °C for 1 h was sufficient to remove polymerase chain reaction (PCR) amplifiable DNA. Studies assessing the suitability of hydrogen peroxide as a sterilizing and DNA-destroying agent showed that 20% or 30% hydrogen peroxide sterilized samples of Serratia in 1 h and destroyed the DNA of Serratia in 3 h, but not 1 or 2 h. DNA AWAY™ killed Serratia and destroyed the DNA of both Serratia and the vent microbe (GB-D) of the genus Pyrococcus in 1 h.     

Lifetime Prolonging Algorithms for Underwater Sensor Networks

1.IntroductionRecent advances in acoustic communication,sensor networks and ad hoc networks have motivatedthe development of UASNs which are generallyformed by a surface station,autonomous underwater ve-hicles(AUVs)and sensor nodes that possess sensing,si…     

Automated high resolution determination of the trace elements iron and aluminium in the surface ocean using a towed Fish coupled to flow injection analysis

A towed surface sampling device coupled to two automated flow injection analysis (FIA) systems is described. The towed system permits uncontaminated sampling of seawater from research vessels while underway at full speed. Coupling the sampler to the FIA systems permits automatic determination of Al and Fe in surface waters at natural levels at 5 min intervals, equivalent to ∼1.5 km spacing at a ship speed of 10 knots (5 m s⁻¹). Results from the tropical Atlantic indicate significant (50%) variation in concentrations of both Al and Fe on space scales of less than 90 km. The combined system facilitates surface mapping of large regions of the ocean for dissolved Al and Fe, thus identifying the sites and magnitude of eolian deposition to the surface ocean. In combination with the determination of nutrients and other biological parameters this permits the investigation of the role that eolian deposition plays in modifying surface water biogeochemical cycles.     

Discovery of a new hydrothermal vent based on an underwater,high-resolution geophysical survey

A new hydrothermal vent site in the Southern Mariana Trough has been discovered using acoustic and magnetic surveys conducted by the Japan Agency for Marine-Earth Science and Technology's (JAMSTEC) autonomous underwater vehicle (AUV), Urashima. The high-resolution magnetic survey, part of a near-bottom geophysical mapping around a previously known hydrothermal vent site, the Pika site, during the YK09-08 cruise in June–July 2009, found that a clear magnetization low extends ∼500 m north from the Pika site. Acoustic signals, suggesting hydrothermal plumes, and 10 m-scale chimney-like topographic highs were detected within this low magnetization zone by a 120 kHz side-scan sonar and a 400 kHz multibeam echo sounder. In order to confirm the seafloor sources of the geophysical signals, seafloor observations were carried out using the deep-sea manned submersible Shinkai 6500 during the YK 10-10 cruise in August 2010. This discovered a new hydrothermal vent site (12°55.30′N, 143°38.89′E; at a depth of 2922 m), which we have named the Urashima site. This hydrothermal vent site covers an area of approximately 300 m×300 m and consists of black and clear smoker chimneys, brownish-colored shimmering chimneys, and inactive chimneys. All of the fluids sampled from the Urashima and Pika sites have chlorinity greater than local ambient seawater, suggesting subseafloor phase separation or leaching from rocks in the hydrothermal reaction zone. End-member compositions of the Urashima and Pika fluids suggest that fluids from two different sources feed the two sites, even though they are located on the same knoll and separated by only ∼500 m. We demonstrate that investigations on hydrothermal vent sites located in close proximity to one another can provide important insights into subseafloor hydrothermal fluid flow, and also that, while such hydrothermal sites are difficult to detect by conventional plume survey methods, high-resolution underwater geophysical surveys provide an effective means.     

Rapid swing and spin of [deep] taut-wire-moored instruments

Rapid ‘swing’, compass variations O(10°) in O(10 s), and ‘spin’, complete rotations around the vertical axis within a few minutes, are a concern of acoustic current meters moored in-line. Observations are used from fast sampling, at once per 1 and 30 s, instrumentation on deep-ocean moorings mainly outside surface wave and bottom boundary influences. Such instruments do not require a vane common to some historic mechanical current meters and they are often moored in a much easier to handle sub-surface buoy or mounting rack, without vanes. In their mountings they are nearly symmetric, so that they can spin freely in (turbulent; shear) flows. A comparison is made between noise levels of such free spinning instrumentation with those of instruments mounted in a fixed bottom-frame and with those of instruments equipped with a vane to one side. Typical spinning has a single rotation varying between 40 and 200 s. Spinning is shown to be highly binary: on or off. Its effects are found negligible on estimates of ocean currents, provided compass updates are adequate as in existing instrumentation. Acoustic noise is O(10) times larger than noise due to spinning. Some effects of spinning are noticed in the acoustic echo amplitude showing higher noise at frequencies >100 cpd, cycles per day. The character of this noise changes dramatically due to spinning. However, it is mainly in the ocean turbulence range and does not affect measurements of internal waves or periodic zooplankton motions.     

High and very high resolution deep-towed seismic system: Performance and examples from deep water Geohazard studies

We present the technological development and initial results from the deep-towed seismic acquisition device SYstème SIsmique Fond de mer (SYSIF) recently built by Ifremer. The two configurations of the SYSIF are presented (high resolution (HR): 250–1000 Hz and very high resolution (VHR): 650–2000 Hz), and results are compared to conventional seismic acquisition systems such as multi-channel HR or single-channel VHR (hull-mounted sub-bottom profiler). The ability of SYSIF to achieve higher resolution imagery is due to both the technology employed (low-frequency Janus–Helmoltz piezoelectric transducer) and the deep-towed operating mode (reduction in the Fresnel zone). Sea trials have been conducted in various geological environments and in water depths as deep as 2500 m. The new technique improved imaging of deep seafloor and sub-surface features such as pockmarks, carbonate mounds, sub-marine slides and sub-surface faulting. SYSIF, therefore, is a well-suited tool to investigate deep water geological features, especially those related to geohazard for scientific and industrial purposes.     

Aggregation of the Arctic copepod Calanus hyperboreus over the ocean floor of the Greenland Sea

According to combined observations from vertical plankton tows, dredging with epibenthic nets 1 m above the ocean floor, video recordings and acoustic data from a scanning sonar obtained during descent and during deployment on the ocean floor, the calanoid copepod Calanus hyperboreus was aggregated in high concentrations near the ocean floor of the Greenland Sea between 2300 and 2500 m during late July and August. Concentrations were highest very close to the ocean floor and decreased rapidly further upward. These nearly mono-specific aggregations were apparently drifting in cloud-like formations with a horizontal extension of ca. 270 m with the near-bottom currents. Maximum abundances observed were up to 2 orders of magnitude higher than in the water column. The biomass in the bottom 20 m layer was around 18% of the biomass in the rest of the water column. Stage composition, reduced metabolic rates and insensibility to mechanical stimuli indicate that these C. hyperboreus were representing the resting population. The fact that high concentrations were observed during deployments lasting >1 d and in 3 years suggests that aggregation near the ocean floor is a regular, rather than an extraordinary, pattern in the life history of C. hyperboreus in the Greenland Sea, but there is need for comparison with other seas and eventually other Calanus species.     

On the spatial scale needed for benthos community monitoring in the coastal North Sea

In community monitoring an attempt is made to identify long-term trends by regular sampling of selected sites. Since the benthos is reputed to be fairly sedentary, the spatial resolution is often reduced to single sites. However, members of many benthic invertebrate species have been found drifting across sedimentary seabeds in shallow waters. Transportation by currents may result in changes of their spatial pattern in the sediment, thereby changing local community composition. The quantitative importance of drifting was tested by repeated sampling of a 2-km² shallow (10 m) offshore area west of the island of Sylt (North Sea). Within the fortnight period between two samplings the benthic community composition had changed dramatically. Despite fairly calm weather, translocation of organisms by currents exceeded 1 km. In about half of the species, the spatial changes in abundance within these two weeks roughly equalled the average variation between consecutive years. This example suggests that community monitoring needs a wide spatial scale to discriminate long-term temporal changes from short-term variability. Extending the sampling area from 2 to 180 km² strongly reduced the variability of abundance estimates. However, only in a few species was the spatial distribution over the sampling sites found on one sampling date a suitable estimator for the spatial pattern found one or two months later, at the same sites. Instead the spatial patterns of the fauna changed strongly during a single month with a spatial scale of re-distribution exceeding several km in some species. At the same time the granulometric sediment composition changed, indicating changes of habitat quality. Hence, sampling of a large area, with random selection of the sampling sites on each sampling date, is suggested to yield the most reliable estimates of population development in the coastal North Sea. However, in view of the expected spatial scale of re-distribution during storm tides and the spatial variability of recruitment, even a 180-km² sampling area may be too small.     

Dynamic response of cylindrical shell structures subjected to underwater explosion

This study investigated the linear and nonlinear dynamic responses of three cylindrical shell structures subjected to underwater small charge explosions in a 4 m×4 m×4 m water tank. The dimensions of the cylindrical shell structures were 90 cm×30 cm×1 mm (length×diameter×thickness). Both ends of the cylindrical shell were mounted with thick plates to provide support and create an enclosed space. The three cylindrical shell structures were un-stiffened, internally stiffened and externally stiffened, respectively. The experiments involving the dynamic response of cylinders subjected to underwater explosion (UNDEX) were performed under different standoff distances, varying from 210 to 35 cm. A small quantity of explosives was used to generate the shock loading. The plastic deformation of the cylindrical shell was observed at a standoff distance of less than 50 cm. Other conditions were tested to examine cylinder linear response. Dynamic analyses were performed for the experimental model using FEM and compared with the test results. The accelerations and dynamic strains of cylindrical shells obtained from the experiment were compared with those obtained by FE analysis. Finally, problems related to small-scale UNDEX experiments performed in small water tanks were analyzed.     

Bioluminescence in the deep sea: Free-fall lander observations in the Atlantic Ocean off Cape Verde

A novel autonomous free-fall lander vehicle, with a capability down to 6000 m, was deployed off Cape Verde for studies on bioluminescence in the deep sea. The system was equipped with a high-sensitivity Intensified Silicon Intensified Target (ISIT) video camera, a programmable control-recording unit and an acoustic current meter with depth and temperature sensors. The ISIT lander was used in three modes: (1) free falling at 34 m min⁻¹, with the camera looking downwards at a mesh screen, recording impacts of luminescent organisms to obtain a vertical profile down to the abyssal sea floor, sampling at >100 l s⁻¹; (2) rotating, with the lander on the sea floor and the camera orienting to the bottom current using a servo-controlled turntable, impacts of luminescent organisms carried by the bottom current onto a mesh screen mounted 0.5 m in front of the camera were recorded to estimate abundance in the benthic boundary layer; (3) baited, with the camera focused on a bait placed on the sea floor.Profiles recorded abundance of luminescent organisms as 26.7 m⁻³ at 500–999 m depth, decreasing to 1.6 m⁻³ at 2000–2499 m and 0.5 m⁻³ between 2500 m and the sea floor at 4046 m, with no further detectable significant change with depth. Rotator measurements at a 0.5 m height above the sea floor gave a mean abundance of 0.47 m⁻³ in the benthic boundary layer at 4046 m and of 2.04 m⁻³ at 3200 m. Thirty five minutes after the bait was placed on the sea floor at 3200 m, bioluminescent fauna apparently arrived at the bait and produced luminescent displays at a rate of 2 min⁻¹. Moving, flashing light sources were observed and luminescent material was released into the bottom current.     

Monitoring the integrated deep meridional flow in the tropical North Atlantic: Long-term performance of a geostrophic array

As a component of the meridional overturning variability experiment in the tropical North Atlantic, a four-year-long time series of meridional transport of North Atlantic deep water has been obtained from moored end point measurements of density and bottom pressure. This study presents a quality assessment of the measurement elements. Rigorous pre- and post- deployment in situ calibration of the density sensors and subsequent data processing establish an accuracy of O(1.5 Sv) in internal transport in the 1200–5000 dbar range at subinertial time scales. A similar accuracy is reached in the bottom pressure-derived external transport fluctuations. However, for pressure, variability with periods longer than a deployment's duration (presently about one year) is not measurable. This effect is demonstrated using numerical simulations and a possible solution for detecting long-term external transport changes is presented.     

A wideband connection to sperm whales: A fiber-optic,deep-sea hydrophone array

A 10-element, 950 m long, vertical hydrophone array based on fiber-optic data transmission has been developed primarily for studying the beam pattern from deep diving cetaceans emitting sonar pulses. The array elements have a configurable sampling rate and resolution with a maximum signal bandwidth of 90 kHz and a maximum dynamic range of 133 dB. The array has been deployed from a 14 m ketch with a crew of four. In the course of the development a number of mechanical and electrical problems have been solved.     

Antipodal acoustic thermometry: 1960, 2004

On 21 March 1960, sounds from three 300-lb depth charges deployed at 5.5-min intervals off Perth, Australia were recorded by the SOFAR station at Bermuda. The recorded travel time of these signals, about 13,375 s, is a historical measure of the ocean temperature averaged across several ocean basins. The 1960 travel time measurement has about 3-s precision. High-resolution global ocean state estimates for 2004 from the “Estimating the Circulation and Climate of the Ocean, Phase II” (ECCO2) project were combined with ray tracing to determine the paths followed by the acoustic signals. The acoustic paths are refracted geodesics that are slightly deflected by either small-scale topographic features in the Southern Ocean or the coast of Brazil. The refractive influences of intense, small-scale oceanographic features, such as Agulhas Rings or eddies in the Antarctic Circumpolar Current, greatly reduce the necessary topographic deflection and cause the acoustic paths to meander in time. The ECCO2 ocean state estimates, which are constrained by model dynamics and available data, were used to compute present-day travel times. Measured and computed arrival coda were in good agreement. Based on recent estimates of warming of the upper ocean, the travel-time change over the past half-century was nominally expected to be about −9 s, but little difference between measured (1960) and computed (2004) travel times was found. Taking into account uncertainties in the 1960 measurements, the 2004 ocean state estimates, and other approximations, the ocean temperature averaged along the sound channel axis over the antipodal paths has warmed at a rate less than about 4.6 m °C yr⁻¹ (95% confidence). At this time, the estimated uncertainties are comparable in size to the expected warming signal, however.     

An autonomous instrument for time series analysis of TCO2 from oceanographic moorings

The design and testing of a robotic analyzer for autonomous TCO₂ measurement from oceanographic moorings is described. The analyzer employs a conductimetric method of TCO₂ measurement wherein CO₂ from an acidified sample diffuses across a semi-permeable membrane into a NaOH solution decreasing the conductivity of the base. The instrument is capable of ～850 analyses over a period of at least six months. It is designed to operate to depths of at least 1000 m. TCO₂ calibration is based on in situ standardization throughout a deployment.We report both laboratory and in situ tests of the analyzer. In the laboratory automated analyses over a period of 38 days at temperatures ranging from 8° to 25 °C yielded a TCO₂ accuracy and precision of ±2.7 μmol/kg. In situ tests were conducted at the WHOI dock with a deployment of 8 weeks at in situ temperatures of 5°–13 °C. The accuracy and precision of TCO₂ analyses over the deployment period, based on in situ calibration, was ±3.6 μmol/kg.Laboratory tests of reagent and standard solution stability are also reported. Standards, based on Certified Reference Material were followed for periods of up to 2 years. In all cases TCO₂ increased. Drift of the standards was the equivalent of ～1 to 3 μmol/kg per 6 months. The conductivity indicator solution was found to be stable for at least 2 months.     

Population ecology and habitat preferences of juvenile flounder Platichthys flesus (Actinopterygii: Pleuronectidae) in a temperate estuary

The European flounder Platichthys flesus is a widely distributed epibenthic species and an important component of demersal fish assemblages in the European Atlantic coastal waters. In Portuguese estuaries, this species reaches high densities, especially in Minho estuary (NW Iberian Peninsula, Europe), potentially playing an important role in the system's ecology. In this context, the population structure, production and the habitat use of juvenile P. flesus were investigated. Sampling took place monthly, from February 2009 until July 2010 along the entire estuarine gradient (5 sampling stations distributed in the first 29 km from the river mouth, with S1 located near the river mouth, S2 inside a salt marsh, S3 in a salinity transition zone, while S4 and S5 were located in the upper estuary). Flounder's density varied significantly among sampling stations and seasons (two-way PERMANOVA: p < 0.001), with the majority of the individuals being found during the spring (30.1%) and in S3 and S4 (72.6%). Males and females presented an even distribution, with a higher proportion of males observed during summer. Fish length also differed among sampling stations and seasons (two-way PERMANOVA: p < 0.001), with larger fishes being found in S1 during the autumn (168.50 ± 59.50 mm) and the smallest in S4 during the spring (33.80 ± 3.12 mm). Size classes associated differently with environmental variables, with larger juveniles being more abundant in the downstream areas of the estuary, whereas smaller juveniles were related to higher water temperatures, suggesting a habitat segregation of P. flesus of different sizes. The fish condition of P. flesus in Minho estuary was higher than in other systems, probably due to the dominance of juveniles on the population. Also, the densities found in this estuary were up to 32 times higher than in other locations, suggesting that Minho estuary is an important nursery area for the species. The estimated secondary production of P. flesus was lower than previous studies acknowledged in the system (0.037 g.WWm^− 2.year^− 1), indicating that the production estimates of this species in estuaries can vary considerably depending on of several factors such as the sampling year and strategy, population and fish size.     

Seasonal variation of diel vertical migration of zooplankton from ADCP backscatter time series data in the Lazarev Sea,Antarctica

Ten-month time series of mean volume backscattering strength (MVBS) and vertical velocity obtained from three moored acoustic Doppler current profilers (ADCPs) deployed from February until December 2005 at 64°S, 66.5°S and 69°S along the Greenwich Meridian were used to analyse the diel vertical zooplankton migration (DVM) and its seasonality and regional variability in the Lazarev Sea. The estimated MVBS exhibited distinct patterns of DVM at all three mooring sites. Between February and October, the timing of the DVM and the residence time of zooplankton at depth were clearly governed by the day–night rhythm. Mean daily cycles of the ADCP-derived vertical velocity were calculated for successive months and showed maximum ascent and descent velocities of 16 and –15 mm s^?1. However, a change of the MVBS pattern occurred in late spring/early austral summer (October/November), when the zooplankton communities ceased their synchronous vertical migration at all three mooring sites. Elevated MVBS values were then concentrated in the uppermost layers (<50 m) at 66.5°S. This period coincided with the decay of sea ice coverage at 64°S and 66.5°S between early November and mid-December. Elevated chlorophyll concentrations, which were measured at the end of the deployment, extended from 67°S to 65°S and indicated a phytoplankton bloom in the upper 50 m. Thus, we propose that the increased food supply associated with an ice edge bloom caused the zooplankton communities to cease their DVM in favour of feeding.