Sosik, H. M.. Woods Hole Oceanographic Institution, hsosik@whoi.edu
Olson, R. M.. Woods Hole Oceanographic Institution, rolson@whoi.edu
Chekalyuk, A. M. NASA, (757) 824-1036

 
IRON LIMITATION IN THE SOUTHERN OCEAN: ACTIVE FLUORESCENCE MEASUREMENTS OF PHYTOPLANKTON POPULATIONS AND INDIVIDUAL CELLS
 
Iron limitation in the Southern Ocean was investigated using individual-cell "Pump During Probe" (PDP) and bulk water "Fast Repetition Rate" (FRR) measurements of single turnover chlorophyll fluorescence induction. Samples from depth profiles and on deck enrichment experiments were analyzed. The physiological state of the phytoplankton was poor at most stations; variable fluorescence yield, Fv/Fm, was typically only about 0.3 (which is less than half of the potential maximum value). The highest Fv/Fm values observed in the Ross Sea in Feb-Mar 1997 were at a coastal station in pack ice, while during the Polar Front cruise in Mar 1998, the highest values were at the southernmost station (71.5 S). In two iron enrichment experiments carried out by the Moss Landing group in the Ross Sea, the phytoplankton responded to iron enrichment, with increasing Fv/Fm over several days. Similar results were obtained in 3 of 6 shorter-term experiments carried out during the Polar Front cruise. PDP flow cytometry of anoplankton and PDP microfluorometry of individual cells of the large diatom Corethron and the small flagellate Phaeocystis revealed in each case that iron-enriched cells had higher relative variable fluorescence than control cells. Abundance and size distributions of phytoplankton from conventional flow cytometric analysis of preserved samples will also be discussed.
 
Day: Thursday, Feb. 4
Time: 02:15 - 02:30pm
Location: Sweeney Center
 
Code: SS31TH0215S