Recovering long-term sampling equipment
November 15, 2012
When the ROV came up on Wednesday night, it brought back sea cucumbers found in a large aggregation, sediment cores for molecular barcoding, and a sponge for an on-board study. Jake Ellena and Crissy Huffard prepared water samples for later oxygen measurements while Henry Ruhl sectioned and sieved sediment cores and Amanda Kahn identified and prepared the sponge for experiments. Meanwhile, the rest of the science crew wrapped up preparations for an early morning deployment of the Rover.
The deployment went smoothly, with the Rover returning to the water under the rays of the rising sun.
Following the deployment of the Rover, the sediment event sensor (SES) was recalled to the surface using an acoustic signal and brought onto the ship, where over 3,000 images were downloaded from its 5-month deployment at Station M. The SES looks similar to the other sediment traps deployed at Station M, with a collection funnel covered by a baffle at the top, but it does not trap sediments in bottles like a standard sediment trap would. Instead, material that falls into the trap settles onto a microscope slide, which over time accumulates a fine film of detritus. At set intervals, the slide is photographed using wavelengths of light that activate the fluorescence of chlorophyll and phosphorescence, which provide information about the type and quality of food reaching the deep seafloor. This cruise marked the first long-time series deployment of the SES at Station M, and all indicators so far look like it was successful.
In the afternoon, the final piece of equipment for the day was recovered: the camera tripod with sequencing sediment traps. This setup has been deployed since the beginning of work at Station M. The sediment traps capture sinking marine snow and other particulates that make up the food supply to the deep sea. Meanwhile, the camera tripod at the seafloor takes photos once an hour, thus logging animal activity sedimentation events on the seafloor. The tripod has witnessed activity such as the erratic paths of the heart urchin Echinocrepis rostrata, movements and appearances of fish and sea cucumbers, excretion by enteropneusts (worm-like animals), and food pulse events such as when large detrital aggregates sink from surface waters.
Each recovery took at least a few hours, between the time the acoustic signal was sent and the equipment was safely secured on the deck. After an instrument receives the acoustic signal a ballast weight is released, it then ascends to the surface, which from this depth can take a few hours. Then a spar buoy with a flag signals that the instrument is at the surface. Beneath the spar buoy are a series of floats that are buoyant in the water, but in air they are quite heavy and require teamwork to get them safely on board. Once each float has been removed one after another, the equipment is recovered and then moved to the back deck where it is serviced for another deployment.