ROV Modules & Elevator lander

Ocean Elevator (OCE)

The elevator is a newly designed lander which serves as a carrier system for scientific payloads which are handled by an ROV on the seafloor and increases the efficiency of the ROV deployment at greater depth. The stainless steel frame of the lander is of squared design and has two platforms on which scientific ROV modules can be transported. Two large blocks of syntactic foam are used for buoyancy, additional blocks or cylinders can be added to achieve a total payload of approx. 200 kg. Beneath these blocks 2 drawers can be used for transport of push corers or other scientific samples. The lander is equipped with 2 acoustic releasers and a release line which can be handled by the ROV to drop the anchor weight.

The elevator can be used to deploy up to 2 benthic chambers, 2 eddy correlation modules and a pore water sampler. The lander and the ROV modules are equipped with homer beacons for relocation. After its video-guided deployment with the launcher, the ROV unloads these modules from the elevator and deploys them at distinct sites. After the end of the measurement or sampling, the ROV carries them back to the elevator, secures the modules on the platform by hooks and rubber bands. After recovery of the ROV, the anchor weight of the elevator is released by acoustic command and the lander is picked up by the vessel.

This ROV deployed chamber is carefully inserted into the sediment using the ROV manipulator. After chamber insertion the overlying water body is replaced with ambient sea water in order to establish start conditions which are not affected by solutes that are released from the sea bed during insertion. Similarly to the BIGO Lander, the sediment inside the chamber is retrieved for latter onboard analyses.

The general idea of the eddy correlation technique is that by correlating the vertical velocity fluctuations with the fluctuations of the constituents, the instantaneous exchange flux can be calculated in a straight-forward manner. The advantage of the EC technique over i.e. benthic chambers which exclude the hydrodynamic regime

Using the GEOMAR facilities and technical skills, we have developed the next generation of EC for oxygen measurements. Our system consists of a Nortek ADV coupled with a Clark-type oxygen microsensor. The sensor microamplifiers as well as the ROV deployable light inox steel EC frame were completely designed at GEOMAR.

One of our goals is to extend the existing O₂ Eddy Correlation (EC) systems to include heat flux measurements with a fast (7-12 ms response time) FP07 temperature microsensor system (sensor, amplifier and housing). The coupling of benthic heat and O₂ flux measurements is expected to help determine if, and to which extent, O₂ fluctuations are due to active turbulence or to non-active (fossil) signals. The combined EC system will also help determine temperature dependencies on O₂ fluctuation as well as the extraction O₂ fluxes. By integrating concurrently measured water column turbulence data, it is then possible to more accurately characterize the transport of dissolved gasses and heat within both the water column and at the sediment-water interface.

The PWS has been used for the first time in the North Sea for high-resolution extraction of pore water within a depth range of up to 40 cm below the sediment surface. The advantage of this method is to separate pore water and sediment before sample retrieval, which prevents artefacts by decompression and temperature changes. The device basically consists of a lance with small filtering elements (Rhizones) and a syringe carrier. After penetration of the lance into the seafloor the Rhizones can be moved laterally out into the sediment. Pore water will be ingested by applying a vacuum through pressure-resistant syringes.