Committee:

R. Michael L. McKay, Advisor Low Fe availability constrains algal primary production in numerous oceanic provinces. Although not numerically abundant, the diatom microplankton (> 20 μm) are important contributors to new production in these regions. To better understand the contributions made to new production by diatoms in Fe-depleted waters, this dissertation work addressed the Fe-specific physiological and biochemical autecology of this group. A field component consisted of two research cruises in 2002 and 2003 along a transect at 29°N spanning the eastern half of the Central North Pacific (CNP) gyre, and focused on the vertically migrating bouyant giant diatom genera Rhizosolenia spp. and Ethmodiscus spp. The lab component examined physiological, biochemical and growth responses of large open-ocean and coastal diatom isolates to perturbations of Fe in the growth medium. Whereas mats of Rhizosolenia showed elevated values (ca. 0.61, n = 88) of Fv/Fm, a measure of photochemical energy conversion efficiency, along the easterly transect from Hawaii to San Diego, a clear decline in this parameter measured at locations west of 165°W provide