Ocean alkalinity enhancement in an open-ocean ecosystem: biogeochemical responses and carbon storage durability

作者：A. J. Paul, Mathias Haunost, Silvan Urs Goldenberg, Jens Hartmann, Nicolás Sánchez, Julieta Schneider, Niels Suitner, Ulf Riebesell · 发表于：Biogeosciences · 年份：2025 · DOI：10.5194/bg-22-2749-2025 · 被引用次数：10 · 研究领域：Ocean Acidification Effects and Responses、Methane Hydrates and Related Phenomena、Coral and Marine Ecosystems Studies

Abstract. Ocean alkalinity enhancement (OAE) is considered for the long-term removal of gigatonnes of carbon dioxide (CO2) from the atmosphere to achieve our climate goals. Little is known, however, about the ecosystem-level changes in biogeochemical functioning that may result from the chemical sequestration of CO2 in seawater and how stable the sequestration is. We studied these two aspects in natural plankton communities under carbonate-based, CO2-equilibrated OAE of up to a doubling of ambient alkalinity (+2400 µeq kg−1, Ωaragonite∼10) in the nutrient-poor North Atlantic. During our month-long mesocosm experiment, the majority of biogeochemical pools, including inorganic nutrients, particulate organic carbon and phosphorus, and biogenic silica, remained unaltered across all OAE levels. Noticeable exceptions were a minor decrease in particulate organic nitrogen and an increase in the carbon-to-nitrogen ratio (C:N) of particulate organic matter in response to OAE. Thus, in our nitrogen-limited system, nitrogen turnover processes appear more susceptible than those of other elements, which could lead to decreased food quality and increased organic carbon storage. However, alkalinity and chemical CO2 sequestration were not stable at all levels of OAE. Two weeks after alkalinity addition, we measured a loss of added alkalinity and of the initially stored CO2 in the mesocosm where alkalinity was highest. The loss rate in this mesocosm accelerated over time and amounted to ∼10 % ...