Text and photos: Andrea Plaza-Faverola, researcher CAGE; project leader SEAMSTRESS.
Seven ocean bottom seismometers (OBS) have been recording earthquakes for about a year at more than 1000 m water depth offshore the west-Svalbard margin. In a calm sea, surrounded by whales and dolphins we fished out one by one. We managed to retrieve all of the instruments.
Each seismometer is attached with a hook to an iron frame that keeps them on the sea-bottom for the desired recording period. To bring them back to the surface they are released from their weight using an acoustic device that sends a signal from the ship through the water, and basically tells the hook to rotate to free the instrument so that it can float up. When one instrument is released, we are all out on the bridge looking for it to show up in the horizon.
When the OBS is at the surface one of the crew fishes it out and grabs it with the crane or picks it up using the dingy.
Usually it takes about half an hour for one OBS to raise through 1200 meters of water. There is always a latent fear of not getting the instruments back to the surface. But once again the operation was successful, and we retrieved the seven instruments.