Ocean alkalinity enhancement (OAE) has been proposed as a marine carbon dioxide removal strategy, but uncertainties remain concerning its scalability and potential side effects. Side effects are challenging to evaluate under environmentally relevant conditions without running extensive field trials, yet such trials often face strong social opposition. A potential solution to this challenge is to use natural analogues of OAE to gain insight into biogeochemical mechanisms. Glacier fjords have been proposed as a natural analogue for mineral-based OAE because glaciers generate large quantities of fine glacial rock flour which is dispersed into seawater, where it may release alkalinity and silica. Here, we combine field observations from Disko Bay (Greenland) and west Spitsbergen (Svalbard) with incubation experiments using glacial rock flour to assess whether glacier fjords can inform our understanding of the environmental impacts of mineral-based OAE.
Across both regions, total alkalinity (TA) was diluted at low salinity, with extrapolated freshwater endmembers of 60 µmol kg⁻¹ in Disko Bay and 590 µmol kg⁻¹ in west Spitsbergen. Incubations of glacial rock flour in seawater demonstrated a slow release of TA and dissolved silica, with TA release rates up to a maximum of 32 µmol g⁻¹ day⁻¹. Weathering rates at in situ temperatures are too slow for this flux to be discernible in glacier estuaries. Whilst glaciers do strongly affect the carbonate system, they typically drive low TA, low pCO₂, and low aragonite saturation states (Ω_aragonite) in seawater. At steady-state, glaciers would promote OAE on millennial timescales. However, in the modern-day context of negative ice sheet mass balance, glacier meltwater is diluting marine TA on annual timescales. Whilst glacier-induced perturbations to the carbonate system are not directly analogous to OAE, glacier fjords nevertheless function as valuable natural laboratories for assessing mineral-based environmental side effects, including particle dispersion, turbidity, ecological exposure to high mineral loads, and potential benthic weathering or reverse-weathering feedbacks.