07 April 2004
Wednesday, 7 April 2004
A plankton brew
It was a late night. We had our first and probably only opportunity to run Go-flow bottles for trace metal chemistry tonight. I was assisting Mike Elwood with this sampling, which he estimated would take about 3 hours but it ended up taking us around 6 hours. It all went very successfully in the end and we managed to collect samples from a wide range of depths.
Overall today was another busy day with the setup of a microzooplankton (small animal plankton) grazing experiment in the morning and the processing of another microzooplankton grazing experiment through into the afternoon. This was followed by the Go-flows after dinner. The microzooplankton grazing experiments were experiment number 18 and 19 of this type and involve collecting water from the CTD casts and incubated different treatments for 24 hours in on-deck incubators at the back of the ship.
The experiments give us an estimate of how well the small (<200 µm) grazers are controlling the phytoplankton populations within our patch and preventing them from blooming. Unfortunately most of the analysis of these experiments cannot be conducted on board the ship and we will have to wait until we return to port and process the numerous samples we have collected. Fortunately however, Steve Archer, who is working on DMSp, has been taking subsamples from these experiments, and his results have given us some indication of how things have been going. The results indicate that growth rates of phytoplankton in our patch have, as we hoped, increased but that these small grazers (microzooplankton) have also been doing a good job of eating this production and perhaps preventing the phytoplankton bloom we expected.
During the day, while I was in the lab running these grazing experiments, many other activities were going on. Stu was, as usual working throughout the day, keeping an eye on the nutrients. It is essential that we follow the nutrient levels to make sure they are not limiting the growth of the phytoplankton. We are also interested in whether the phytoplankton themselves have been using up the nutrients for growth, but so far Stu has seen little evidence of this. Stu has also been running samples from all the various incubation experiments including my grazing experiments to make sure nutrients levels do not become an issue in our incubations.
The sight of Naiad going over the side in between Go-flows this evening was quite spectacular against the pitch black of night. The weather was also good today which always makes the job out here much easier and there was a great full moon that made it a little more pleasant out on deck despite the bitterly cold wind.
Karl Safi (NIWA)
Stuart Pickmere (NIWA)