Nelson, D. M.. College of Oceanic & Atmospheric Sciences, nelsonda@ucs.orst.edu
Brzezinski, M. M.. Marine Science Instititute, brzezins@lifesci.ucsb.edu
Sigmon, D. E.. College of Oceanic & Atmospheric Sciences, dsigmon@oce.orst.edu
Franck, V. M.. Marine Science Institute,

 
SILICON LIMITATION IN THE POLAR FRONTAL ZONE OF THE SOUTHERN OCEAN DURING AUSTRAL SPRING AND SUMMER, 1997-1998
 
We conducted Silicon-32 kinetic experiments to assess Si limitation in and around the Antarctic Polar Front at 170 degrees W from November, 1997 through March, 1998. During that period a diatom bloom developed and propagated southward, depleting silicic acid concentrations from > 40 uM to < 5 uM. Silicic acid concentrations often limited Si uptake rates to < 30% of their maximum potential rate in the Si-depleted waters north of the bloom. Si limitation thus appears to have played a major role in limiting diatom productivity north of the bloom, and may have limited the bloom's northward extent, causing it to propagate southward with time. Half-saturation constants (Ks) for Si uptake were 0.5 - 5.0 uM, the same general range observed for diatoms in temperate regions. In the Si-rich waters south of the bloom Si limitation was weak, but was frequently detectable. When Si limitation was detectable Ks was usually 15 - 25 uM, which is extraordinarily high. Thus while Si limitation was much less important south of the bloom it cannot be discounted entirely. This unexpected result was caused by surprisingly low affinity (high Ks) for Si uptake by some diatom assemblages south of the Polar Front.
 
Day: Thursday, Feb. 4
Time: 04:30 - 04:45pm
Location: Sweeney Center
 
Code: SS31TH0430S