Aluminium and Manganese in the West Atlantic Ocean - a model study

The cycling of aluminium and manganese in the ocean are modelled. Respective models are implemented in the bio-geochemical model PISCES. Modelled distributions are compared to high-quality measurements taken along the west-Atlantic GEOTRACES section.
The main source of aluminium to the ocean is deposition by dust, and the main removal mechanisms is sinking of aluminium adsorped to the silicium frustules of diatoms, whcih are then buried in the sediment. However, observations show an enhanced Al concentration near the bottom, and which probably comes from resuspension and resolution of sediment Al. A model describing these processes is developed and implemented. The correspondence of modelled and observed Al is significantly improved.
Manganese shows a more complicated behaviour. Unlike aluminium it is essential for life, playing an active role in photolysis. It is incorporated in phytoplankton and subsequently into other forms of life. Dissolved in water, it has a complicated chemistry with two different oxidation states. Together, this makes its modelling much more complicated than that of aluminium. The results of the model show that the basic observed distribution of manganese can be reproduced, but that importatn processes are still missing.