The use of trace metal-rich Greenlandic glacial rock flour for ocean enrichment experiments

In order to keep global warming below 2ºC, it is imperative not only to reduce future carbon dioxide (CO2) emissions but also to adopt negative emissions technologies (NETs) to remove approximately 600 Gt of CO2 from the atmosphere by the end of the twenty-first century. Among NETs, ocean alkalinity enhancement and ocean enrichment emerge as promising strategies for Carbon Dioxide Removal (CDR), leveraging the immense carbon-absorbing capacity of oceans. Glacial rock flour (GRF), an ultra fine-grained silicate mineral originating beneath the Greenland Ice Sheet, holds potential as a contributor to large-scale marine CO2 removal (mCDR). As it is transported into coastal waters, the dissolution of GRF in seawater naturally releases mineral components into the ocean. As a silicate-rich substance with micronutrients like iron and manganese, GRF has the dual capacity to enhance alkalinity and promote phytoplankton growth, presenting a viable avenue for mCDR. In a field study from the Kangerlussuaq fjord and glacier near the Greenland Ice Sheet (summer 2023) we observed that melt- and seawater contained an array of trace metals in high concentrations, including iron, manganese, zinc, copper, and cobalt, and the concentrations increased towards the fjord and away from the source. We explore the response to varying treatments with GRF, iron, manganese and zinc using laboratory incubation experiments with an Arctic phytoplankton diatom species (Coscinodiscus radiatus). We identify the relative mobilization rate of these trace metals in the GRF that can support phytoplankton growth and hypothesise that GRF can alleviate the co-limitation of iron and manganese on phytoplankton growth.