12 April 2004
Monday, 12 April 2004
Rolling with the punches
We had to leave the South Biophysical Mooring station before breakfast. The plan had been to conduct a deep CTD cast, and recover the mooring, but 50-knot winds and 6–8-metre swell prevented this. At sunrise the ship headed north to Chatham Rise. This resulted in the ship taking big rolls, hampering almost all activities, including sleeping. The rough sea did not however prevent deploying the second French Carioca Buoy in the area. This will drift around the Southern Ocean and measuring CO2 dissolved in the water, and daily transmit the data back to its home institution in Paris.
Although other research activities were halted, biologists were not stopped by the heavy seas, but continued with several experiments. During this cruise the biological signal from the iron enrichment had been minor in terms of biomass growth. The main reasons for the lack of biomass accumulation in the patch were attributed to the physics and biology. The biological control is grazing by microheterotrophs (top down control), and the physical control dispersal. The ratio of these controls remains to be seen. For the present stage of species succession, the plankton community is dominated by small heterotrophs and autorophs and carbon production is rapidly consumed by predators. During this cruise light levels have also been very low which may explain some of the minimal phytoplankton growth and the low biomass signal. Additional experiments were thus set to test the light-limitation hypothesis. Despite the minor biomass signal of iron enrichment, growth enhancement may still be significant, but we do not carry instruments on board to directly measure autotrophic and heterotrophic growth (primary and bacterial production).The biologists are hoping to find clear signals of enrichment from these rate measurements when the samples arrive in Hamilton for liquid scintillation counting.
I am working with Julie Hall’s group of biologists. We are studying the pelagic food web from bacteria to mesozooplankton including autotrophic, heterotrophic and mixotrophic organisms. My personal contribution to the microbial food-web studies are measurement of bacterioplankton production (with tritiated thymidine incorporation technique), staining of flagellates with primulin for fluorescence microscopy, and preservation of samples for further microscopy of microzooplankton. These basic measurements have been carried out every day from the patch station and from stations outside the patch.
For the bacterial production measurement, I am doing basic methodological work determining carbon conversion factors and saturation levels for thymidine incorporation from inside and outside the patch. Moreover, I am measuring bacterial carbon conversion efficiency, the growth efficiency of bacteria from predator-free seawater cultures. I have prepared bacteria seawater cultures from both inside and outside the fertilized patch, and collected samples from these cultures for measurements of particulate organic carbon (POC), bacteria cell counts and cell size, thymidine incorporation and oxygen uptake during incubation. Dave Katz has done precise Winkler titrations from bacteria seawater cultures and the results suggest very slow growth rates, a few micromolar of oxygen taken up during 4 days of incubation. The slow bacterial growth outside the patch station suggests carbon limitation and challenges the methodology of BOD (biological oxygen demand) determination.
The biology group has also focused on micronutrient control of the growth and made experimental studies with iron, cobolt and other trace elements. The experiments with Michael Ellwood, Julie Hall, Karl Safi and Jill Peloquin are revealing new perspectives in trace element controls of the community at this stage of seasonal succession. Julie Hall is making measurements with flow cytometry of the samples coming from the experiments and from the water column. This flow cytometry technique allows rapid biomass observations from autotrophs, picocyanobacteria and bacteria and is thus a vital tool in tuning the experiments and the experiental design. During this cruise the flow has showed its potential in tuning our experiments and new findings. My contribution in the experiments has been bacterioplankton production measurements to assess carbon and trace element controls.
Jorma Kuparinen (University of Helsinki, Finland)