Physical Drivers of Phytoplankton Bloom Initiation in the Southern Ocean's Scotia Sea

Prend, C. J., S. T. Gille, L. D. Talley, B. G. Mitchell, I. Rosso, and M. R. Mazloff, 2019: Physical Drivers of Phytoplankton Bloom Initiation in the Southern Ocean’s Scotia Sea. Journal of Geophysical Research: Oceans124, 5811-5826,

Explanation: The largest regional pilot array of biogeochemical (BGC) Argo floats was deployed in the Antarctic by the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) project. In addition to temperature and salinity, these floats measure oxygen, nitrate, pH, fluorescence, and backscatter. These data have been used to estimate air-sea exchange of carbon dioxide (Gray et al., 2018) and oxygen (Bushinsky et al., 2017), as well as annual net community production (Johnson et al., 2017) and phytoplankton biomass (Haëntjens et al., 2017). One valuable aspect of the BGC Argo data is its ability to relate changes in biogeochemical properties directly to their physical drivers. For example, a recent study used data from these floats to investigate the upper ocean conditions that support the earliest and largest offshore spring phytoplankton bloom in the Southern Ocean (Prend et al., 2019). Float data revealed a close link between biological productivity and seafloor topography. Observations of upper ocean chlorophyll concentration, a proxy for phytoplankton biomass, (right panel) show that the highest values were recorded when the floats were trapped in a recirculating eddy that formed over a seamount (portion of trajectories colored green and enclosed by a red box in the left panel). This is because flow-topography interactions lead to enhanced mixing, which delivers nutrients to the sunlit upper ocean where phytoplankton can grow. Determining the physical processes that regulate biogeochemical cycles, through studies like this, is necessary to improve climate models. Furthermore, given the key role of the ocean in absorbing atmospheric carbon dioxide, increasing the number of ocean biogeochemical measurements through a global BGC Argo array would allow us to better constrain future climate projections.

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