Nearshore Macroalgae Cultivation for Carbon Sequestration by Biomass
Harvesting: Evaluating Potential and Impacts with An Earth System Model
Abstract
This study introduces an ocean-based carbon dioxide removal (CDR)
approach: Nearshore Macroalgae Aquaculture for Carbon Sequestration
(N-MACS). By cultivating macroalgae in nearshore ocean surface areas,
N-MACS aims to sequester CO2 with subsequent carbon storage. Utilizing
an Earth System Model with intermediate complexity (EMIC), we explore
the CDR potential of N-MACS alongside its impacts on the global carbon
cycle, marine biogeochemistry and marine ecosystems. Our investigations
unveil that coastal N-MACS could potentially sequester 0.7 to 1.1 GtC
yr-1. However, it also significantly suppresses marine phytoplankton net
primary productivity because of nutrient removal and canopy shading,
counteracting approximately 30% of the N-MACS CDR capacity. This
suppression of surface NPP, in turn, reduces carbon export out of the
euphotic zone to the ocean interior, leading to elevated dissolved
oxygen levels and diminished denitrification in present-day oxygen
minimum zones. Effects due to harvesting-induced phosphorus removal
continue for centuries even beyond the cessation of N-MACS.