Marine Biomass Regeneration: Simple Modelling of Large-Scale Ocean Carbon Dioxide Removal

Effective and large-scale atmospheric carbon capture is essential in limiting global warming to within 1.5 degrees Celsius as outlined by the Paris Agreement. The oceans make up two thirds of the Earth’s surface and already absorb approximately a quarter of anthropogenic emissions annually, therefore it is imperative to maximise their carbon sequestration ability through large-scale Carbon Dioxide Removal (CDR). One technique that aims to improve the efficiency of oceanic carbon uptake is Marine Biomass Regeneration (MBR), otherwise known as Ocean Iron Fertilisation (OIF). MBR is grounded on evidence that the introduction of certain key nutrients to nutrient depleted areas of the ocean can enhance primary productivity and regenerate ocean biomass, which then acts as a carbon sink. The ocean’s ability to circulate nutrients has been hindered by the over-exploitation of whales, which naturally regulate oceanic nutrient levels by feeding at a depth of 150-200m and defecating at the ocean surface through the whale cycle. Their faeces are rich in nutrients such as nitrates, phosphates and iron, and act as a natural fertiliser. It will take decades to restore the whale population to pre-whaling numbers, therefore, to catalyse the biomass regeneration of oceans, it is proposed that artificial whale faeces are deployed to mimic the whale cycle.

 

A two-dimensional carbon and heat cycling box model with meridional overturning circulation is extended, to include biological processes and nutrient cycling. This model has previously been used to carry out climate projections, by investigating the ocean’s carbon and thermal response to annual anthropogenic emissions, but there has been no investigation on how the changing meridional overturning circulation impacts the biological carbon pump. A simple nutrient-phytoplankton-zooplankton (NPZ) biological model is introduced to model the impact of macronutrient concentrations on phytoplankton and zooplankton growth. Further to this, some basic parameterisations for iron cycling will be added, based off the iron box models of Parekh et al. (2004) and Lefèvre and Watson (1999).  Using the extended model, it will be possible to undertake MBR experiments with different nutrient ratios and concentrations, mimicking the whale cycle, and investigate the impact these parameters have on the oceanic carbon and heat uptake and distribution from anthropogenic carbon emissions. The model also accounts for slower meridional overturning with increased ocean warming, which allows for the investigation of the effect of slower circulation on the biological carbon pump, primary productivity and nutrient distribution.