Iron manganese co-limitation – a potential driver of Southern Ocean phytoplankton ecology?

Primary production by phytoplankton is governed by several factors such as light and nutrient availability in different parts of the world oceans. Phytoplankton concentrations in the Southern Ocean are low despite high concentrations of macronutrients like nitrate and phosphate. This could be explained by low sea surface concentrations of the trace metals iron and manganese, which are essential for optimal growth of phytoplankton cells. So far, many studies focused on the influence of iron limitation on microalgae and looked at its effects on parameters like growth rate, photophysiology and elemental composition. However, there are only a few studies examining the effects of manganese limitation even though manganese is an important component of the photosynthesis apparatus and is required as central ion for the enzyme superoxide dismutase which acts as an antioxidant by catalyzing the detoxification of reactive oxygen species produced during photosynthesis. Diatoms co-limited by iron and manganese exhibit changes in the production of ROS and in the amount of manganese-containing superoxide dismutase.

In the experiments for my master thesis I will look at the physiological responses of two Antarctic phytoplankton species to different concentrations of iron and manganese. Therefore, the diatom species Chaetoceros debilis and the haptophyte Phaeocystis antarctica will be incubated for two weeks in four different treatments in presence/absence of both iron and manganese additions.

Gaining more inside into the effects of iron and manganese limitation on the physiology of Antarctic phytoplankton is valuable to understand the requirements for optimal phytoplankton growth in the Southern Ocean and will help to improve predictions of future ocean primary production under a changing climate.