Diatom traits regulate Southern Ocean silica leakage

Ocean circulation is a remarkable interconnecting conduit, such that biological processes occurring in the remote Southern Ocean can influence the regulation of productivity in Northern Hemisphere waters. Marine phytoplankton, despite their small size, play a disproportionately important role in setting the stoichiometric relationship between elements such as nitrogen, phosphorus, carbon and silicon in the global ocean (1, 2). In turn this ecological stoichiometry helps to set the ultimate limiting nutrient(s) for primary productivity (2, 3). To date, investigation of stoichiometric effects has mainly been centered on low latitude waters (3, 4). However, the Southern Ocean plays a fundamental role in setting the productivity of distant waters, such as the Equatorial Pacific (5), by controlling the leakage of waters with high Silicic acid:Nitrate ratios—the so-called silicic acid leakage hypothesis (SALH) (6, 7). In PNAS, Assmy et al. (8) provide unprecedented detail of how the ecological traits of different polar diatom species contribute to the regulation of ocean nutrient stoichiometry. Thus, diatom floristics help to control the leakage of silicic acid, relative to that of nitrate, into the global ocean, which sets the magnitude of Northern Hemisphere diatom productivity, export, and hence carbon sequestration. Assmy et al. (8) are able to reveal the potent linkages between Southern Ocean ecology and regional biogeochemistry because they conducted a transdisciplinary 35-d study [European Iron Fertilization Experiment (EIFEX)] on a scale of 100 km. Such mesoscale iron enrichments represent some of the largest ecological manipulation experiments globally (9). Thus, they are of sufficient scale, scope, and longevity to provide a holistic view of how environmental manipulations drive a diverse range of biological responses. Such responses consequently transform many ecological processes, each with characteristic biogeochemical signatures. When these ecological responses are placed in a wider biogeochemical context, and animated by ocean circulation, the …