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 all of the instruments.
A porpoise swims around while we wait for a seismometer to show up at the horizon. Photo by Vera Schlindwein
Each seismometer is attached with a hook to an iron frame that keeps them on the sea-bottom over the 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 leave the instrument free to float up. When one instrument is released we are all out at the bridge looking for it to show up at the horizon.
Przemek, Sunil and Stefan enjoy the calm sea while waiting for the instrument to appear at the surface
When the OBS is at the surface one of the crew fishes it out and grabs it with the crane or pick it up in the dingy.
To the left Jan throws the hook to fish the OBS so the crane can grab it. To the right, Stormer and Peter goes to pick an OBS that appeared farther away from the ship
Usually it takes about half an hour for one OBS to raise through 1200 m. 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 7 instruments.
An OBS is taken from the sea back to the ship with the crane
Text and pictures by Andreia Plaza-Faverola