Iron and light are two important abiotic factors that influence diatom growth and distribution in the Southern Ocean (SO). Through a combination of physiological and transcriptomic approaches, I have explored the molecular underpinnings of nine SO diatoms that allow for adaptation and/or acclimation to low iron and light conditions. SO diatoms used in this study ranged across five orders of magnitude in size and displayed various degrees of resistance to iron and light limitation. Specifically, we investigated the presence or absence of 22 key genes involved in iron acquisition and homeostasis, photosynthesis, and nitrogen assimilation. SO diatoms have a variety of unique resource utilization strategies coupled with gene repertoires that allow them to take advantage of ecological niches or play important roles in phytoplankton blooms. Certain diatom genes, such as B12-independent methionine synthase (MetE) and flavodoxin, were found to exhibit biogeographical patterns in distribution that favor high-nutrient, low-chlorophyll regions.