Landers transport instruments up and down
The development of benthic landers was pioneered during the late seventies due to increasing concerns on recovery artefacts when sampling at great depth. Over time, the instruments have become more sophisticated, but basically autonomous benthic landers consist of three components: a scientific payload, a flotation unit and a ballast- release system.
During operations, the instrument is released from the ship and sinks to the sea bed where it performs a preprogrammed scientific program, followed by ballast release and instrument ascent.
The advantages of autonomy over tethered operation include independence from expensive research vessels with specialized winches and positioning systems for operating instruments at great depths. Furthermore, autonomous operations enable the ship to move while more instruments are operating at depth. The risks of autonomy have been minimized through the development of multiple ballast release systems and instrument tracking systems.
Within HADES, we have developed two fully autonomous benthic lander systems for hadal explorations.
Four lander systems will be deployed. In addition, a new lander system under development at NIWA might be included for hadal testing (if time allows). The lander systems are described below.
The Transecting Profiling Lander (P- Lander)
This will be provided and run by SDU/MPI and will enable the measurements of numerous benthic O2 , NO3- and resistivity microprofiles across the sediment-water interphase at each site. The exact configuration during deployments will be decided from site to site. the instrument will be 3.1 m in height and the square base has a side length of 1.5 m. The total weight in air will be in the order of 1.3 tonne (weight in water about 50 kg) and the outer configuration will resemble Figure 2.
|Figure 2: The basic structure and deployment configuration of the P & S Landers (the internal instrument package on the two landers will differ from what is depicted), B, Alternative configuration of the floatation to reduce instrument weight during deployment.|
The Sediment Lander (S-Lander)
This will be provided and run by SDU/MPI and the outer configurations resembles the P-Lander depicted in Figure 2. The instrument will enable i) in situ fixation of sediment for microbial analysis, ii) measurements of in situ nitrification rates by injection of 15NH4+ and iii) if other sediment recovery system fails (see below, be used for simple recovery of sediment cores. It is anticipated that the system will operated with 6 sediment core liners with inner diameter of 10 cm and a coring depth of approximately 25 cm. The lander will be equipped with a single baited trap for amphipod sampling.
The Long-Term Camera Lander system (LTC-Lander)
This will be provided by Newcastle University. It is rated to 6000 m. The lander comprises one acoustic release, one lead acid battery, two HD video/stills cameras in which each have two slaved LED banks. The camera will take digital still images and short videos at a pre-determined time lapse interval through the deployment (probably every 2 hours). The instrument will be deployed at the first abyssal site (site 7) and recovered at the end of the voyage. The Lander will jettison ballast (80 Kg) via acoustic command and return to the surface whereupon data are downloaded. The basic design is shown in Figure 3. The frame is 1 x 1 x 0.6 m in size, it is surfaced by virtue of 6 single 17” glass spheres, coupled off line to a short mooring line. In deployment the lander should weigh approximately 180 kg.
|Figur 3: The basic design of the Long-Term Camera Lander (1x1x0.6 m), rated to 6000 m. The system is floated by 6 17” glass spheres. The blue line represents the field of view on the seafloor.|
Two Short-Term Camera Landers (STC-Landers)
These will be provided and run by NU (Figure 4). They will be used as a rapid reconnaissance of the seafloor prior to other benthic operations. The system comprises 4 x 17” glass spheres, a camera and release unit (weighing 180 kg on deck including ballast). To survey the seafloor, or perform transects over a topographical feature, the STC-Landers will be deployed in quick succession whereupon they will descend quickly. HD video will be timed to start recording within 15 min of the seafloor to record the sediment surface prior to impact. The vertical ballast bar will have a scale painting along its length for the camera to record penetration depth that can later be used to aid in characterizing the seafloor. Hi-resolution digital still will commence with the video at 30 s intervals. The lander will be timed to jettison the ballast bar after 25 min on the seafloor to ensure a good series of images is obtained from the bottom. The STC-Landers will need a crane for deployment and a crane and winch for recovery.
6000 m-rated CTD bottle rosette (CTD): The instrument will be provided and run by NIWA personnel. It will be used to collect standard CTD profiles (including O2-concentrations, fluorescence and turbidity) and sample water at predefined depths down to 6000 m. The rosette contains up to 24 bottles with a volume of 10 L.
Hadal-rated bottle rosette (HR)
The instrument will be provided by SDU/MPI and has been tested in the Mariana Trench. It contains 6 Niskin bottles (8 or 12 L) mounted in a circular rack with an outer diameter of 90 cm and a weight in air of 25 kg. The depths at which the respective bottles are to be released are preprogrammed and can be released at predefined depths either during ascend or descend. The instrument does NOT measure CT or O2 in the present configuration. The sampling systems also allow in situ injection of fixatives to maintain cell integrity during recovery and it can take separate 50 ml fixed samples for community analyses. The HR system can potentially be operated in tandem mounted below with the NIWA CTD rosette.
|Figure 4: The hadal water-sampling-system for clarity, only 2 of the 6 bottles mounted.|
The instrument will be provided and run by NIWA personnel and along with a new winch system this will enable recovery of up to 8 sediment corers (internal diameter 10 cm) per deployment. However, we anticipate that the system will be operated with only 4 sediment cores to improve recovery success. We foresee 1-3 deployments per site. In case of failure a box-core will be onboard to use as back-up.
Multi-beam and single-beam eco sounders
The multi-beam will be provided and run by NIWA personnel and will enable high resolution bathymetry down to a maximum depth of 7000 m (reference sites and depth transects for Reivers). A single-beam system will determine the depth at sites >7000 m.