BIOTA: Ocean BIOgeochemistry response To refined Atmospheric iron inputs in present and future climate

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The deposition of dust and other terrestrial aerosols represents an external supply of nutrients to the ocean surface. This supply helps sustain marine primary production and enhances atmospheric carbon sequestration by sinking biological carbon into the deep ocean. Amongst the nutrients supplied by aerosols, soluble iron deposition has been recognized as a key input for marine productivity in one-third of the ocean waters. Yet, its impact on the carbon cycle is one of the least well-quantified climate feedbacks. This uncertainty partly arises from the interdisciplinary nature and the complexity of the processes at each side of the ocean-atmosphere interface. Consequently, the influence of soluble iron deposition on the marine carbon cycle is still roughly represented in most Earth System Models (ESM), including CMIP6 models. The climate projections delivered by the CMIP6 suite of models and used to inform policy-makers lack a complex yet essential element of the Climate machinery. An element that might gain relevance in a future planet with a more stratified ocean, hence more receptive to nutrients supply from above. 

The project we present here, Ocean BIOgeochemistry response To refined Atmospheric iron inputs in the present and future climate (BIOTA), seeks to evaluate the role of atmospheric iron deposition on the marine carbon cycle now and in the future. BIOTA’s most important innovation is the use of observations from EMIT, a new spaceborne spectrometer that provides soil mineralogy information at unprecedented resolution. EMIT’s wealth of data will inform the EC-Earth-Iron model, an ESM developed by BSC researchers and international collaborators, to simulate the atmospheric iron cycle accurately. EC-Earth3-Iron will also be improved to produce land-use and climate change sensitive projections of iron emissions in the future, which will allow considering both the direct and indirect consequences of human activities on atmospheric iron. Lastly, a state-of-the-art ocean biogeochemical model (PISCES) will be upgraded to include the three pathways linking aerosol deposition with carbon export: fertilisation, changes in the phytoplankton community and the ballast effect caused by the aggregation of organic matter around lithogenic particles. The latter has never been incorporated in an ESM. 

BIOTA’s complete set of modelling experiments will include the new iron fields based on EMIT, improved representation of the anthropogenic sources of dust and biomass burning aerosols (which recently have been shown to play an essential role in phytoplankton fertilisation), and an advanced diagnosis of future changes in land cover, and the subsequent changes in aerosol emissions, under different climate change scenarios. All these atmospheric processes will feed the iron and nutrients aeolian supply in a second set of PISCES simulations. Some of these simulations will include future ocean scenarios to assess the potential changes in ocean receptivity to aerosol deposition.