FePhyrus_Iron limitation and viral lysis, phytoplankton caught between a rock and a hard place

The growth of oceanic phytoplankton that form the base of the marine food web depends on the availability of sunlight and nutrients, typically nitrogen and phosphorus (and silicate for diatoms). The Southern Ocean, however, is an area where iron (Fe) affects the amount of atmospheric CO2 sequestered in deep ocean waters and ocean sediments via the biological pump, with far reaching implications for global climate and the local ecosystem.

Iron not the only driver for atmospheric CO2

Yet, it is becoming increasingly clear that the situation is more complex, and controlled by factors beyond just the scarcity of Fe. New insights highlight the importance of other trace-metals, co-limitation by two or more nutrients and variability in nutrient requirements between species and environmental conditions. Notably for Fe, its solubility and probably also its availability depends strongly on the Fe-binding dissolved organic ligands. In turn, the microbial community composition as well as microbial and viral interactions impact the ligand production and the cycling of metals and metal-binding ligands.

Key issues

Our study addresses three key questions:

(i) What is the relative contribution of the different sources of iron and the bio-essential metals along transects from the Antarctic Peninsula towards the open ocean?

(ii) Is viral lysis affected by the natural iron concentrations along gradients of iron and does viral lysis affect the ligand production and nature of organic ligands?

(ii) What is the effect of increasing temperature on metal quotas for phytoplankton, viral lysis and ligand production?

The proposed research will combine the analysis of multiple trace metal concentrations, isotopes of oxygen, uranium and Fe, Fe-binding ligands and the assessment of the microbial community in both the field as well as bio-assays.