Detecting seasonal shifts in phytoplankton taxa and primary production in the Southern Ocean

The Southern Ocean is the only ocean without continental constraints, moving in an uninterrupted flow around Antarctica [1]. This distance from major land masses results in a reduction in the aeolian nutrient input, including iron, a trace metal essential for the metabolic function of phytoplankton [1, 2, 3]. Therefore, most of this Southern Ocean is seen to be iron limited, and characterised by High Nutrient, Low Chlorophyll (HNLC) waters. There is a seasonal cycle in surface phytoplankton growth. Generally, the austral winter is dominated with strong wind mixing events (light limiting), while the summer sees a strongly stratified surface layer (nutrient limited). Both these growth conditions are associated with a dominance of small eukaryotic nanoflagellates. The most productive time in the Southern Ocean's annual cycle, is the spring, where a phytoplankton bloom of diatoms is observed. These blooms are followed by a significant increase in the export of particulate organic carbon (POC), increasing the Southern Ocean's ability to remove carbon from the atmosphere, transporting it to depth [4].