Aluminium and manganese in the West Atlantic Ocean: A model study

The objective of this study is to come to a better understanding of the behaviour of the trace metals Al and Mn in the ocean, by means of simulating the dissolved Al and Mn distributions with biogeochemical models that are embedded in a general circulation model. Recently, many measurements have been performed that have been verified versus international reference samples and their consensus values of the SAFe and GEOTRACES programmes. They are compared with the simulated dissolved Al and Mn concentrations. In turn, the results from these simulations can be used for further development of these models to simulate the dissolved Al and Mn distributions more precisely, and/or improve the understanding of the processes.

The main features of the global dissolved Al distribution have been simulated in accordance with available observations. We are especially able to simulate the West Atlantic GEOTRACES observations reasonably well. Specifically, the high below and upstream of dust deposition, the high near the bottom of the North Atlantic Ocean and the low in the polar oceans, were reproduced by the model.

This thesis contains the first published study in which the three-dimensional distributions of and have been modelled. Many of the features of the distribution of are captured by the model. These features include the generally higher concentration of below and upstream of dust deposition areas and the elevated concentrations near hydrothermal vents.

However, there are notable shortcomings as well, most importantly the difficulty to keep sufficient Mn dissolved in the seawater. There appears to be an inconsistency between the basic assumptions on the removal of Mn and the measured dissolved Mn concentrations. For the moment, this is solved by introducing thresholds for oxidation or aggregation in the model.