7-10-09 Last Bongo Tow

7-10-09

As we continue to head south we are following the 70 meter isobath, a fancy way of saying that the ship is being navigated to stay at a constant depth of 70 meters. The purpose of this is to observe the hydrography (physical characteristics like temperature, salinity, and density) along a constant depth. These types of physical trends in the water column during the summer are set up by the ice cover of the preceding winter and spring. “Everyone (all the organisms in the system) has to play by the rules set by the ice for the entire summer” as it was put by Chief Scientist on board, Ray Sambrotto. This past spring a large mass of ice detached from its original sheet and headed much further south than expected. An observation mooring was moved miles from its original location by a southward iceberg, and had to be recovered and tagged with a GPS unit for later repair.

I looked at the schedule board for the time of our last bongo net tow. For each station we have the time and, which sampling activities will be taking place. From the board I could see that we were arriving at our station, 70m29, at 1:30 AM and that the bongo net was the fourth sampling procedure of the station. As we set up the nets everyone was a little quiet at first. We were anxious to get our last catch of krill and finish up, but sad that our duties on deck were coming to on end. As we waited the MOC-NESS was being received and the operators were looking to see what they had collected. The MOC-NESS (Multiple Opening/Closing Net and Environmental Sampling System) is a series of nets that can be opened and closed at different depths so that one can collect many samples from specific depths. While they did collect some jellyfish, including one huge one held up by Dr. Tracy Shaw in the picture, they also had healthy collection of krill from about 10 to 20 meters.

It was reassuring to know we would at least get some krill during our last tow, and to spice things up a few jellyfish as well. While the bongo was in the water I did my best to will the jellyfish away from the openings of the nets. Each time I would see a jellyfish approach the nets looking like it was heading dead center into the opening, it would just slide past the edge above or below the net. It looked like we might avoid a lot of the stingy tentacles that could damage our sampled krill. When we emptied the cod ends into the cooler we had plenty of krill and only one small jellyfish. We decided to do a second bongo tow for grad student, Jared Weems (also studying krill). Once again our good fortune held up. Lots of krill and only one small jellyfish. After plenty of ups and downs, we got a final taste of favorable catch. It’s probably best that we end now before our luck runs out.














-Eli