Spatial variability of iron and light co-limitation in the Southern Ocean during the Austral summer.

The Southern Ocean is considered a high-nutrient low-chlorophyll region, abundant in macro-nutrients but often low in Chlorophyll due to iron limitation of phytoplankton growth. However, the Southern Ocean is also a high-latitude ocean where phytoplankton can be limited by light, particularly in winter or when cells are deeply mixed by upper ocean turbulence. A mechanistic understanding of how phytoplankton are co-limited by iron, light and the environmental conditions that control their respective supply, is critical to better model and predict primary productivity and carbon uptake in the Southern Ocean.

We collected data from a research cruise off East Antarctica during the Austral summer of 2019 and conducted a series of incubation experiments to investigate the effects of iron and light co-limitation on phytoplankton growth. The results from the incubations confirm that iron limitation is exacerbated under high-light conditions, but substantial spatial differences were observed in treatment responses. We use underway and satellite data to explore the differences between stations and how the effects of iron and light co-limitation are impacted by physical properties in the area such as mixed layer depths and frontal boundaries.