Potential influence of applying glacial rock flour for stimulating primary production for marine carbon dioxide removal

Potential influence of applying glacial rock flour for stimulating primary production for marine carbon dioxide removal.

 

Jørgen Bendtsen^1,2, Niels Daugbjerg³, Kristina Vallentin Larsen¹

¹Centre for Rock Flour Research, Globe Institute, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark

²ClimateLab, Symbion Science Park, Fruebjergvej 3, DK-2100 Copenhagen Ø, Denmark

³Department of Biology, University of Copenhagen, Universitetsparken 4, DK-2100 Copenhagen Ø, Denmark

 

Glacial rock flour (GRF) is a fine-grained silicate mineral that is transported to the coastal ocean by meltwater rivers and subglacial discharge from the Greenland Ice Sheet. It is formed below glaciers when they abrade the bedrock to a fine powder, and it is available in very large quantities in sedimentary deposits. GRF has typically a median grain-size of ~2-5 µm, and it contains essential nutrients and trace metals for phytoplankton growth. The fine grain size results in residence times of suspended GRF in the surface layer of the order of days or weeks, and furthermore implies a relatively large reactivity due to its large surface area. The long residence time allows phytoplankton and marine microbiomes to exploit nutrients released by silicate hydrolysis or to directly interact and mobilize macro-nutrients (i.e., P, Si) and trace metals (e.g., iron) from the GRF. These characteristics, and the fact that GRF constitute a natural source of elements to the ocean, makes the material potentially relevant for marine carbon dioxide removal (mCDR). Here we analyse the potential impacts of dispersing GRF in the ocean on phytoplankton growth and biogeochemical cycling by implementing critical parameters of mobilisation rates of bioavailable nutrients and trace metals from GRF in a 1-dimensional model of the water column. Previous studies have demonstrated a positive effect of GRF on the growth rates of phytoplankton, however, the actual compounds that stimulates the growth is poorly known. Results from our incubation experiments show that iron, manganese and phosphorus can be mobilized from GRF and support an exponential growth of a subpolar green alga. We also estimate the potential maximum amount of iron that can be extracted from the GRF. These critical parameters are implemented in the model and the potential impact on CO₂-uptake, primary production, biogeochemical cycling, chlorophyll a and light of dispersing GRF in iron-depleted areas are simulated. The dose-response relationship between GRF-dispersal and impact on surface chlorophyll, pCO₂ and oxygen are analysed in relation to monitoring the efficacy of mCDR.