Influence of Deep-Sea Carbonate Sediments on the Durability of Carbon Storage from Ocean Alkalinity Enhancement

[Geoengineering News]

https://essopenarchive.org/doi/full/10.22541/essoar.15001952/v1

Authors: Sina Acksen, Dr. Wolfgang Koeve, Dr. Markus Pahlow, Dr. Christopher J. Somes, and Prof. Andreas Oschlies 

13 April 2026

Primary Abstract

Ocean Alkalinity Enhancement (OAE) is a marine carbon dioxide removal strategy with a theoretical sequestration potential of 3–30 Gt CO2 yr-1. The durability of OAE-induced carbon storage depends on the persistence of the added alkalinity in the ocean, which is influenced by sedimentary processes, terrestrial weathering, and biological and physical feedbacks. Using the UVic v2.10 Earth System Model of intermediate complexity, we investigated the millennial-scale durability of OAE-induced carbon storage and the role of deep-sea calcium carbonate sediments. We conducted 10,000-year simulations for four emissions scenarios, each combined with a global alkalinity addition experiment (0.135 Pmol yr-1 for 50 years) with and without interactive carbonate sediments. Neither the added alkalinity nor the associated oceanic carbon storage remained fully stable on millennial timescales compared to a baseline simulation. By year 10,000, 35–59 % of the initial alkalinity increase through OAE is lost due to CaCO3 dynamics in deep-sea sediments. CO2 outgassing progressively reduces OAE-induced carbon storage, with losses of 0–5 % by year 2100, 0–26 % after 300 years, and 18–55 % by year 10,000, depending on the emissions scenario. 44–55 % of the stored carbon by OAE is lost by year 10,000 including sedimentary processes and 18–41 % is lost without sedimentary processes. Episodic Southern Ocean deep convection events further contributed to variability in Earth system responses during global cooling.

Source: ESS Open Archive