Monitoring, Reporting, and Verification for Ocean Alkalinity Enhancement

Abstract

Abstract. Monitoring, Reporting, and Verification (MRV) refers to the multistep process of monitoring the amount of greenhouse gas removed by a Carbon Dioxide Removal (CDR) activity and reporting the results of the monitoring to a third party. The third party then verifies the reporting so the results. While MRV is usually conducted in pursuit of certification in a voluntary or regulated CDR market, this chapter focuses on key recommendations for MRV relevant to ocean alkalinity enhancement (OAE) research. Early-stage MRV for OAE research may become the foundation on which markets are built. Therefore, we argue that such research carries a special obligation toward comprehensiveness, reproducibility, and transparency. Observational approaches during field trials should aim to quantify the delivery of alkalinity to seawater and monitor for secondary precipitation, biotic calcification, and other ecosystem changes that can feed back on sources or sinks of greenhouse gases where alkalinity is measurably elevated. Observations of resultant shifts in ocean pCO2 and pH can help determine the efficacy of OAE and are amenable to autonomous monitoring. However, because the ocean is turbulent and energetic and CO2 equilibration between the ocean and atmosphere can take several months or longer, added alkalinity will be diluted to perturbation levels undetectable above background variability on timescales relevant for MRV. Therefore, comprehensive quantification of carbon removal via OAE will be impossible through observational methods alone and numerical simulations will be required. The development of fit-for-purpose models, carefully validated against observational data, will be a critical part of MRV research.

Biological response of eelgrass epifauna, Taylor’s sea hare (Phyllaplysia taylori) and eelgrass isopod (Idotea resecata), to elevated ocean alkalinity

“…In practice, the maximum pH resulting from an OAE intervention will be observed at the outfall or point of dispersal. The pH will decrease rapidly with distance through the mixing zone until the alkaline plume has diluted enough to where it will be indistinguishable from natural variation in the open environment (Ho et al, 2023;Wang et al, 2023). If the species are mobile over an area larger than the mixing zone radius, they will only experience the mixing zone maximum pH for some period of time.…”

Quantifying Regional Efficiency of Marine Carbon Dioxide Removal (mCDR) via Alkalinity Enhancement using the ECCO-Darwin Ocean Biogeochemistry State Estimate and an Idealized Vertical 1-D Model

“…As the efficiency of OAE-based mCDR varies across different spatial and temporal scales, field deployments must be carefully planned to achieve maximum efficiency while minimizing cost and logistical risk. While a number of field methods, technical approaches, and experiment designs have been proposed (Eisaman et al, 2023), the use of numerical ocean models to simulate and quantify OAE impacts before expensive field trials occur, and provide much-needed MRV quantification (Ho et al, 2023), still remains in its infancy.…”

A comprehensive assessment of electrochemical ocean alkalinity enhancement in seawater: kinetics, efficiency, and precipitation thresholds

“…Dilution will spread the impacts over a broad area, to an extent that it is unlikely that the impacts on the DIC distribution can be quantified using only direct measurements, given current instrument resolution and the typical dynamic range of natural variability (Wang et al, 2023). In general, options for measurement, reporting, and verification (MRV) of OAE will therefore rely on (Ho et al, 2023) characteristics of alkalinity addition into seawater; monitoring the seawater carbonate and environmental chemistry in the immediate vicinity of the outfall via sensors and sampling (Cyronak et al, 2023;Schulz et al, 2023); and ocean modeling to estimate CDR beyond the range of direct detection (Fennel et al, 2023).…”