This PhD project will assess the factors that control the fluxes of silica from sediment as well as the relationship between silica concentrations and other environmental conditions in the Baltic Sea waters.

Background

Silicon is a macronutrient that plays important ecological roles. In aquatic systems, dissolved silicon concentrations control the composition of the phytoplankton communities. Silicon limitations hinder the production of diatoms which require silicon for their growth. On the contrary, the population of other algal communities that do not require silicon increase when silicon concentrations are limited. These algal communities include the blue-green algae and dinoflagellates which are toxic for fish. As diatoms have high nutritional value for zooplankton and herbivorous fish, silicon limitations can result in massive fish kills. In marine waters Si concentration may control the biological “carbon pump”, i.e. the uptake of atmospheric CO2 by phytoplankton followed by its transport and sequestration in sediment. Diatoms are the major contributors to this biological carbon pump as they account for around 20% of the global photosynthetic fixation of CO2, that is more than the contribution of all world’s tropical rainforest. Silica concentrations relative to other nutrients such as phosphorus and nitrogen have decreased in the Baltic Sea during the last century. Larger areas of the Baltic Sea may become silica limited. The mechanisms controlling silica concentrations in the sea water are not fully understood. How changing environmental conditions such as temperature, acidity, oxygen concentrations affect silica concentrations in the water mass and what factors control the release of silica from the sediments are the key questions I am trying to answer.

What will you do at Askö?

Sampling sediment and bottom water from oxic, hypoxic and anoxic bottom areas. Pre-incubation of 24 sediment cores (2 days). Project with Askö grant.