Dissolved aluminium and manganese in the polar oceans

PhD ceremony: Mr. R. Middag, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Dissolved aluminium and manganese in the polar oceans

Promotor(s): prof. H.J.W. de Baar

Faculty: Mathematics and Natural Sciences

Trace metals are essential for phytoplankton growth and vitality as they are used as co-factors in many enzymes in vital processes. A co-factor is bound within an enzyme and is required for its biological function. For example, Mn and Fe are co-factors in several enzymes for photosynthesis. Aluminium has no known function within the living cell, but it has been shown Al is build into the siliceous frustules of diatoms. The PhD research of Middag was conducted within the frame work of the International Polar Year (IPY) and of the GEOTRACES program. GEOTRACES aims to assess and better understand the global marine biogeochemical cycles of trace elements. This way the response of these cycles to global change can be predicted, and their impact on the carbon cycle and climate understood. Two of these important trace elements are aluminium (Al) and manganese (Mn).

The concentrations of these two elements have been measured and the current situation has been assessed to be able to detect possible future changes. Moreover, the sources, sinks and internal cycles of Al and Mn have been studied and more insight was gained in the processes that affect these cycles. For Al specifically, there now is a better understanding how the global cycle of Al is partly coupled to the cycle of silicon. It appears Mn is an important nutrient for algal growth in the Southern Ocean and Mn deficiency most likely can limit algal growth in this ocean region.