News from the Night Watch

The night watch stays up from 6pm to 6am in the morning studying the oceanography of the water column. We deploy several pieces of gear all from the starboard side sampling station of the ship, better known as the hydrodeck. Although we only deploy one instrument or sampler at a time, all the gear is stored on the deck so things are a bit crowded.

Hydrodeck

Hydro deck at dawn as the night watch ends with the Bongos (white), v-fin VPR (yellow), 3000m CTD (steel), and the MOCNESS (black).

To study the physical oceanography — the temperature, salinity (saltiness) and oxygen concentrations in the ocean — we use instruments called CTDs (Conductivity, Temperature and Depth). We have one CTD that can go to 500 meters depth and a second one that can go over 3000 meters deep. The CTDs send real time data up the wire and then those data are graphed on a computer screen, watched by a scientist, and recorded by a computer on the ship. On this cruise we use these physical data to help us determine where to sample for plankton.

To take pictures of the plankton we use a v-finVPR (Video Plankton Recorder) which takes black and white images of an area of water 2.5cm x 3.0cm, 20 times a second. This means we collect about 7 gigs of image data per hour. We then have the computers on the ship review each image and save only ones with an in-focus plankton image. So far we have seen copepods, krill, salps, and some jellyfish.

washing down bongonets

Desray Reeb, Bureau of Ocean Energy Management, washing down the bongo nets. (Photo credit: NOAA/NEFSC Danielle Cholelwiak)

To capture smaller plankton we use a 61cm Bongo with two nets that sample the whole water column and a 1 meter MOCNESS (Multiple Opening Closing Net Environmental Sensing System) with nine nets that sample at discrete depths. The MOCNESS also has a VPR that takes color images and a strobe system designed to prevent larger plankton and small fish from swimming away from the nets.

hatchet fish

3cm long deep water hatchet fish caught in the MOCNESS.

Lastly to capture larger plankton, like shrimp and krill, and small fish, especially deepwater fish, we use an IKMT (Issac Kidd Midwater Trawl). This can be towed at faster speeds than the two plankton nets, so it is better at catching faster animals.

juvenile fish

Deep water (darker fish) and juvenile fish caught in the IKMT. The round jar lid is 9cm in diameter.

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