Autonomous Lander Instrument Packages for Oceanographic Research

Summary: A high pressure tank was designed to carry out tests with commercially available oxygen sensors under in situ deep-sea conditions, e.g. seawater, high pressure and low temperature. The general characteristics of the pressure tank are: - internal size: 170 mm (diameter) x 585 mm (height) - volume: about 13 litres - pressure range: 0 - 650 bar - temperature range: 0 - 25 C (at 650 bar) - stirrer device included - connectors for up to 4 sensors For calibration, Winkler titrations were carried out before and immediately after the test runs. Artificial seawater was prepared with de-ionized water to minimize oxygen consumption due to bacterial processes in the pressure tank. The long-term stability of a total of seven commercially available oxygen sensors for deep-sea research was tested within this pressure tank (and also in a hyperbaric pressure tank at IFREMER/France) at varying temperatures and pressures. Results of the test trials are summarized in a report available for purchase

Summary: For the control of motors, switches and events a new programmable electronic circuit board was developed and built. It addresses the following requirements: Universal PCB design, CPU and driver electronics can be split into 2 separate circuit boards. printed circuit boards can be connected with flat-ribbon cable and integrated in a variety of different housings (e.g. pressure housings for deep-sea applications). expandable interface for updating chamber with further I/O. Built-in data memory to ensure working or restart even if short interrupts of power supply occur. Serial interface via RS-232/485 to an external terminal, PC or Laptop. Simple programming techniques without expensive programming and erasing hardware. Fully software-guided user interface for pre-deployment programming. Automated self test of all motors before deployment. Source text in a high level language like C/C++ to ensure portable code. The first programmable deep-sea version was tested on the in December 1997 with three deep-sea motors connected. Both hard- & software and the user interface worked perfectly.

Summary: At present our understanding of the fluid flow dynamics in areas with active venting activity is still in its infancy. Single short-term measurements of a few minutes to a few hours cannot be used to estimate fluid flows accurately, especially in settings where variations of venting are known to occur. In order to assess the role of the control mechanism of steady venting and periodic eruptive events (e.g. tides, microseismicities) it is necessary to monitor selected sites for longer periods than at present possible. To achieve this, a concept to disconnect a lander system from the ship's coaxial cable after its video-guided deployment by a launcher on a selected vent site has been realized. The lander is equipped with an semi-enclosed benthic chamber with a large opening at the bottom and a small exhaust port at the top to obtain both direct water flow and samples expelled from active vent sites. After deployment of the chamber the internal volume is initially flooded with ambient seawater and is then slowly replaced by vented fluids. Sequentially timed water samples are collected from inside the chamber. Changes in the concentration of dissolved components within this time series are used to calculate flux rates. A flowmeter is mounted in the exhaust port of the chamber to record the in situ fluid flow rate. The lander is designed as an instrument carrier for a variety of different measurements which can be integrated as modules within this system. The lander can stay on the seafloor for several days up to a month recording the different parameters (e.g. temperature, salinity, methane concentration, fluid flow) and takes samples prior to the recovery of the instrument by acoustic release of the ballast. Several successful tests on a prototype have been conducted in the Baltic and the Arabian Sea.

Summary: Marine biogenic cycles play a key role in controlling atmospheric concentrations of climatic relevant gases. It is necessary to determine the rates at which they are cycled by the ocean. The benthic boundary layer (BBL) is a site of intensive biogeochemical fluxes with gradients from the sediment/water interface in both directions. In order to determine the specific processes and the relative magnitude of fluxes in different BBL-subzones a Nepheloid Layer Chamber (NLC) has been developed capable of carrying out flux measurements in individual compartments of the BBL. The instrument consists of a device to concentrate organisms and particles which are then enclosed in an incubation chamber for the measurement of oxygen consumption rates and other material fluxes. Water samples for such analyses are taken from the incubation chamber by a water sampler/ injection module system in discrete time intervals. The NLC can either be incorporated in a lander system or in a mooring. The enclosing frame of the NLC, built of stainless-free steel, has an area of (30 cm x 30 cm) and a height of app. 150 cm. The inner part is mostly built of Delrin and represents an autonomous module with its own control unit and power supply, rechargeable NiCd-battery packs (7.2 - 12 V, 10 Ah). The system consists of two different chambers. A concentration chamber, which works like a one piston cylinder. Its cylinder is several times opened and closed while the piston is only driven when the enclosed water column is to be transferred into the second incubation chamber. Both the cylinder (diameter is about 20 cm and a volume of 5000 cm3) and the piston are motor driven. A control unit steers the chamber motors and the water sampler/ injection module. The hardware interface is a RS-232 compatible data-link. The incubation chamber (volume 5000 cm3) Is equipped with an oxygen sensor and a stirring device. During the concentration process a 0.2µm filter prevents the escape of bacteria and small particles. All maintenance-free drive units are standard DC motors in stainless steel pressure housings which guarantee a stable low power consumption. The shaft is sealed by specially developed double O-ring construction.

Summary: Until today it has not been possible to obtain high resolution porewater profiles of important solutes such as nitrate (nitrification affects the oxygen uptake and is an important process in the nitrogen cycle), alkalinity (alkalinity profiles can be used to estimate calcium carbonate dissolution which often contributes significantly to the total carbonate (CT) flux from the sediment) and calcium from deep-sea sediments. By casting a polyacrylamide gel (consisting of 96% water) in the groove of a machined Polycarbonate tube gel peepers are manufactured. During bottom deployment on a lander the peepers are gently (autonomously) inserted into the sediment where they are left for approximately 24 hours. During this time the water in the gel will fully equilibrate with all solutes in the sediment pore water by diffusion. After equilibration the peepers are retrieved into protective rubber membranes, which prevents the gel to back-equilibrate with seawater during storage and transport to the surface. In the ship's lab the gel is extracted and cut into desired pieces, depending on the wanted resolution (1 mm possible), and back-equilibrated in a proper medium (Milli-Q water or 0.7 M NaCl). Gel peepers were used in situ, to our knowledge for the first time in the deep-sea (4800 m), on the Göteborg lander during a scientific cruise in September 1998 to the Porcupine Abyssal Plain, NE Atlantic. Preliminary results of calcium profiles from the expedition look promising and compare well, however, with a better vertical resolution with Ca profiles obtained using conventional methods

Summary: The sediment profile imagery (SPI) system works like an optical corer, permitting almost undisturbed images (15 x 23 cm) to be taken of the seafloor sediment-water interface down to depths of 5500 m. Once on the seafloor, up to 100 digital images can be rapidly taken by 'hopping' the wire-deployed machine about the bottom using an attached acoustic pinger to indicate when the machine is on the bottom. These images are quickly downloaded to computer and are available for immediate viewing upon retrieval of the system aboard. A modular design facilitates easy maintenance. Images provide a rapid means of assessing sediment "health".

Summary: An in situ universal benthic chamber, the "deep-sea microcosm" has been realized which can measure interfacial solute fluxes under controllable bed-flow conditions over a period up to 3 days and to full ocean depths. The chamber uses previously patented methods and laboratory designs to produce a calibrated and user-selectable bottom stress over the sediment-surface interface. This is achieved by stirring the water column with a disk whilst withdrawing water up the rotating axis and re-circulating it to the top of the chamber. With such a well controlled hydrodynamic regime inside the chamber it is possible to measure solute fluxes under very high bottom stress conditions (at friction velocities up to 2.0 cm/s) whilst avoiding the detrimental effect on fluxes that can exist in chambers with uncontrolled hydrodynamic regimes. The device realized here is designed to measure solute fluxes, particularly oxygen, but could also be used for various studies of biological, biogeochemical and sedimentological responses of cohesive and other sediments, including those involving super-critical flow. The device is one of two deep-sea versions of an existing laboratory chamber adapted for deep-sea use.

Summary: The Aberdeen University Deep Ocean Submersible (AUDOS) is a sub-sea mooring that lands on the sea-floor (Lander) and carries out fish tracking and environmental monitoring of sea-floor processes at depths between 1000 to 6000 m. AUDOS comprises: - Tubular aluminium (HE30) frame. - Camera & flash unit. - 77kHz short base-line sonar & Code Activated Transponder tracking system. - Environmental monitoring (water current, lander orientation, temperature, salinity, depth & sound speed). - Twin acoustic releases - Syntactic foam buoyancy. AUDOS is used for the in-situ scientific study of deep-sea fish and population density estimates for certain commercial species.

Summary: Autonomous landers represent an important technology for in situ deep-sea oceanographic studies. The tripod system (2.0 m x 1.8 m), which can be totally dismantled, supports commercially available standard acoustic releases and glass spheres (floats). Its open construction can support a universal experimental platform carrying e.g. benthic chamber modules, micro-electrode profiling systems or a wide range of experimental designs. As a long-term observation system it can carry camera systems, ADCPs, and a variety of other deep-sea registration and observation units. The system has been successfully deployed to 4900 m water depth (30x). The lander system offers a transportable and relatively cheap system for in situ environmental, ecological and experimental studies in the deep-sea.

Summary: This Deep Ocean Tripod Lander is designed to place a downward-looking video camera at varying heights, from 0.3-1.5 m, above the sea floor. The design ensures viewing of an undisturbed area of sea- bed and can be deployed at depths down to 6000 m depending on the type of buoyancy and release mechanisms used. Features are: 1. Mounting for twin acoustic releases (MORS) for reliable recovery' 2. Ballast retaining toggle. 3. Telescopic legs allowing adjustment of height above the sea floor. 4. Light-weight sea water resistant tubular aluminium frame. 5. Payload capacity of 250 kg depending on buoyancy.

Summary: Chamber for measuring sediment community oxygen consumption and solute fluxes. Marine biogenic cycles play a key role in controlling atmospheric concentrations of climatically relevant gases. It is necessary to determine the rates at which they are recycled by the ocean. Measurements of in situ benthic fluxes represent an important component to calculate and model material fluxes on different temporal and spatial scales. The sediment metabolism chamber of 20 x 20 cm is guided by a stainless-steel frame that can be incorporated in benthic lander systems. It is built of Delrin and represents an autonomous module with its own control unit and power supply with rechargeable NiCd-battery packs (6 V, 10 Ah). The chamber is driven into the sediment by a motor (motor 1). After implementation of the chamber a top lid supporting a stirrer and an oxygen electrode is closed. At the end of each incubation a shutter is closed by a second motor in order to retrieve the sediment. Once the shutter is closed the chamber is slowly driven out of the sediment by the first motor. All maintenance-free drive units are standard DC motors in stainless steel pressure housings which guarantee a stable low power consumption. The shaft is sealed by a especially developed double O-ring construction. The chambers have been successfully (50x) used on benthic lander systems at water depths down to 4900 m. The chamber represents a valuable device for in situ environmental, ecological and experimental studies in the deep-sea.

Summary: During an international intercalibration (in April 1996) the hydrodynamics of 16 different chamber designs were evaluated and compared. Based on the results from this intercalibration a Sediment Interface Chamber (SIC) was constructed. The aim was to obtain a chamber that better simulates in situ hydrodynamic conditions inside an enclosed chamber. The constructed chamber, denominated the Mississippi type chamber, was evaluated during a second intercalibration (in November 1997). The final results from this work is still being evaluated. Four replicates of the "Mississippi chamber" has been constructed, adapted and used to obtain in situ solute fluxes between the sediment and the overlying water on the Göteborg 2 lander during three BENGAL and ALIPOR cruises in 1998 to Porcupine Abyssal Plain (PAP, North Eastern Atlantic, depth 4800 m).

Summary: The Acoustic Release Command And Display Equipment (ARCADE) is a system for controlling the operation of underwater acoustic releases. Many commercial acoustic releases are available on the market which (under command from the surface) release ballast weights from a sub-surface mooring to enable recovery. However, each manufacturer requires a unique ship based system (deck unit) to command the acoustic release. Furthermore, confirmation of correct operation is often in the form of a digital display of range from the ship to the sub-surface release which is derived from a single acoustic return from the release. In poor acoustic conditions, these acoustic returns are often not detected by the deck unit and the user can not be certain that the acoustic release has released the ballast. Therefore, ship-time can be lost due to this uncertainty. The ARCADE system overcomes these problems in two ways: 1) The ARCADE is a software based system, and acoustic commands used to control releases are generated under software control. Potentially, any acoustic release command can be generated for any current or future commercial acoustic release. Therefore, only one deck unit is required for sub-sea moorings using different manufacturers' acoustic releases. Potential uses for such a system are with oceanographic / commercial research vessels which operate more then one type of acoustic release. 2) By commanding the sub-surface acoustic release to generate short acoustic pulses at regular intervals (a ping), the ARCADE increases the signal to noise ratio of the ping by using a standard pulse-to-pulse correlation technique. The acoustic pings are displayed on a waterfall (X axis - range; Y axis - time; Z axis - signal intensity) display which is sweeping across the display at a rate which is synchronized to the sub-surface acoustic ping repetition rate. Therefore, the pinger appears as a straight vertical line on the display when the range from the ship to the sub-surface acoustic release is constant. When the range is reducing the line slants to the left, and when the range is increasing the line slants to the right. Confirmation that ballast has been released under command from the surface and that the mooring is rising to the surface, can be determined visually by the change in slant of the acoustic pinger trace on the ARCADE display. This technique proves useful when operating acoustic releases from ships of opportunity which may be acoustically noisy, and when sea surface conditions generate excessive acoustic noise levels. The ARCADE system was also central in determining the precise location of a lost sub-sea mooring, which was eventually successfully dragged for in 2500m water depth. The ARCADE has been used at sea and successfully operated commercial acoustic releases deployed at depths of 4800m.

Summary: The Water sampler/injection module sampler is a device of to take water samples or inject substances (e.g. tracers) into deep-sea experimental cambers. Both functions are implemented in one carrier frame of about (45 cm x 30 cm x15 cm) which is mainly built of Delrin and PVC. A deep-sea motor is coupled with a cam shaft releases a series of eight 50 ml glass syringes. The force needed to pull the syringe plungers is delivered by a strong rubber band. The release functions are controlled by a control unit. The module works totally autonomously with power supply rechargeable NiCd-battery packs (7.2 - 12 V, 10 Ah). Water sampler/injection module is applicable for use with benthic and nepheloid layer flux chambers.

Summary: Field bus architectures provide oceanographic equipment with a lot of benefits, among them an unmatched flexibility, the possibility of easily integrating existing subsystems, an excellent global reliability and shortened development durations. Although those architectures are today of common use in the industrial world, they are still very rarely implemented in oceanography. This project demonstrated that the CAN (Controller Area Network, a registered trademark from ROBERT BOSCH GmbH) bus, meeting the very specific constraints and requirements related to oceanography, was perfectly suitable in most applications and thus could reveal the potential of field bus architectures in oceanography.

Summary: It is essential to know that benthic chambers used on landers give reliable estimates of solute fluxes at the sea-floor, and that different chambers provide the same (or at least very similar) flux estimates for a specific sediment. These topics were addressed during two benthic chamber intercalibration workshops. Sixteen different designs of chambers were characterized and compared for a range of hydrodynamic (visualization, mixing time, pressure gradients, Diffusive Boundary Layer thickness, current speed and shear stress) and biogeochemical (flux incubations on a homogeneous sediment of: oxygen, silicate, phosphate, nitrate, nitrite and ammonium) parameters. Apart from the actual intercalibrations the work also involved development of new measuring equipment (e.g. a sensitive multi-channel instruments measuring mixing induced absolute pressures 0.2-50 Pa) as well as computer simulations of hydrodynamics using commercially available software (e.g. CFX) and multivariate statistical evaluations. A report characterizing each of the participating chambers in detail has been distributed to all participants. Multivariate statistical evaluations reveal significant differences in measured fluxes between the chambers as well as unexpected coupling between some of the measured solute fluxes. The reasons for these results will be studied in further detail using extended statistical evaluations.

Summary: The deep-sea respirometer lander (RAP 2) is an autonomous vehicle capable of carrying out in situ measurements of solute flux rates at the sediment-water interface at great depths (6000 m). Its novelty lies in the positioning of the large sampling cells (100 ml) within the measurement chambers which prevents volume loss and perturbations due to suction during sub-sampling. Field trials down to 4850 m depth were successful and it is possible to measure with the lander concentration changes of various species during incubations ranging from 24 to 75 hr. The multi-incubation programme permits the measurement of long-term temporal variations of exchanges at the sediment-water interface during the same deployment. The drawer is a device intended to be mounted on deep-sea lander systems (e.g. RAP 2). It provides an automated means to operate an instrument outside the main lander structure in such a way that the measurement is performed on undisturbed sediment. The drawer is so designed that the safety of recovery of the lander is not decreased when it is mounted on it.

Summary: The Code Activated Transponder (CAT) is a miniature ultra-sonic tagging device designed for underwater location and tracking of objects and animals. The CAT is small enough to be attached to, or ingested by fish which can then be followed using a special code interrogation sonar. Special features are: 1. Small size: 16 mm diameter - 60 mm length. 2. Can work to a depth of 6000 m in the deep-sea. 3. High frequency (77kHz) inaudible to most animals. 4. Range 500 m. 5. Battery life 14 days. 6. 32 different ID codes. 7. Delayed response feature avoids problems of reverberation allowing short range tracking close to acoustic reflecting surfaces.

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