Abstract
Anthropogenic climate change is induced by, among other causes, the release of heat-trapping CO2 into the atmosphere from fossil fuel burning. According to the Intergovernmental Panel on Climate Change, in order to meet the target set by the Paris Agreement, emission reduction must be complemented by Carbon Dioxide Removal technologies aiming to sequester CO2 from the atmosphere and store it in natural reservoirs. One of such methods is Ocean Alkalinity Enhancement (OAE), which aims to lower ocean CO2 partial pressure (pCO2) and accelerate the natural CO2 uptake through chemical weathering. As seasonality is a fundamental component of the ocean net annual CO2 uptake, this study aims to bridge the knowledge gap on the impacts of OAE on the seasonal cycle of CO2 flux and ocean pCO2.
An analysis was conducted on two Earth System Model outputs simulating alkalinity addition along the European coastline (with the exception of the Baltic and the Mediterranean seas), for both a low and a high emission scenario (SSP1-2.6 and SSP3-7.0, respectively). It was found that: the CO2 seasonal flux is amplified with alkalinity addition, especially in winter, likely as a consequence of a larger imbalance at the air-sea interface; the ocean pCO2 seasonal cycle is dampened, especially in summer, due to its decreased sensitivity to CO2 fluctuations in an alkalinised ocean; both effects are magnified under SSP3-7.0. This suggests that OAE induces asymmetrical impacts on CO2 seasonality, with potentially significant alterations to the net annual cycle.