Modelling the marine biogeochemical implications of aeolian, sedimentary and riverine iron supply

• Main Author: Nickelsen, Levin
• Format: Thesis
• Language: English
• Published: 2015
• Subjects: Southern Ocean
• Online Access: https://oceanrep.geomar.de/id/eprint/30983/; https://oceanrep.geomar.de/id/eprint/30983/1/diss_lnickelsen.pdf

Iron is an important nutrient for marine phytoplankton and low concentrations of iron limit phytoplankton growth in around 40% of the surface area of the ocean. Due to the low solubility of iron in the sea, the concentrations of iron are largely dependent on external sources such as atmospheric deposition of iron-containing dust derived from arid areas on land. However, also release of iron from the sediment and the supply of iron from rivers are important external sources of iron to the ocean. In this thesis the role of these external sources in influencing marine biogeochemistry is studied. In a first step, an existing ocean biogeochemical model is used to study the sensitivity of oceanic CO2 uptake to dust deposition. The so-called iron hypothesis suggests that enhanced atmospheric dust deposition to the Southern Ocean during the Last Glacial Maximum around 20,000 years decreased atmospheric CO2 concentrations by increasing phytoplankton growth and export of organically bound carbon to the deep ocean. The first part of the thesis shows that the sensitivity of organic matter export and oceanic CO2 uptake to dust deposition is increased significantly if the impact of iron bioavailability on light harvesting capabilities is explicitly considered. These results also indicate that there is still uncertainty in the biogeochemical response to dust deposition. In the second part of the thesis, a model of the oceanic iron cycle is developed and implemented in the University of Victoria Earth System Climate Model (UVic). This implementation allows iron cycling sensitivity studies in the framework of an earth system model of intermediate complexity. The results show that a precise description of the depth of the sedimentary iron release is necessary to simulate the iron supply from the sediment to the euphotic zone. Scaling the sedimentary iron release with temperature leads to a better agreement of simulated iron concentrations with observations, indicating a possible influence of temperature on the sediment release on ...