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Global-scale evaluation of coastal ocean alkalinity enhancement in a fully-coupled Earth system model
  • Julien Palmiéri,
  • Andrew Yool
Julien Palmiéri
National Oceanography Centre, Southampton
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Andrew Yool
National Oceanography Centre, Southampton

Corresponding Author:axy@noc.ac.uk

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The Paris Climate Accords plan for “net-zero” carbon dioxide (CO2) by 2050. However, reducing emissions from some sectors is challenging, and “net-zero” permits carbon dioxide removal (CDR) activities. One CDR scheme is ocean alkalinity enhancement (OAE), which proposes to dissolve basic minerals into seawater to increase its total alkalinity (TA) and buffering capacity for CO2. While modelling studies have often investigated OAE by adding TA to the ocean’s surface at basin or global scale, some proposals focus on readily-accessible coastal shelves, with TA added through the dissolution of olivine sands. Critically, by settling and dissolving sands on shallow seafloors, this retains the added TA in near-surface waters in direct contact with atmospheric CO2. To investigate this, we add dissolved TA to the global shelves (<100m) of an Earth system model (UKESM1) running a high emissions scenario. As UKESM1 is fully-coupled, wider effects of OAE-mediated increase in ocean CO2 uptake –e.g. atmospheric xCO2, air temperature and marine pH– are fully-quantified. Applying OAE from 2020-2100 decreases atmospheric xCO2 ~10 ppm, and increases air-to-sea CO2 uptake ~8%. Due to advection of added TA, ~50% of this uptake occurs remotely from OAE operations. In-line with other studies, CO2 uptake per unit of TA added occurs at a rate of ~0.8~mol~C~(mol~TA)$^{-1}$, though this is elevated in enclosed regions. Meanwhile, changes in air temperature and marine pH are indistinguishable from natural variability. While practical uncertainties and model representation caveats remain, this analysis estimates the effectiveness of this specific OAE scheme to assist with net-zero planning.
09 Aug 2023Submitted to ESS Open Archive
12 Aug 2023Published in ESS Open Archive