FIGURE 1. The three main components of a marine carbon dioxide removal (mCDR) monitor-
ing system are the tools to be used, field implementation, and reporting and verification. These
would interact, and thus progressively improve, prior to and during the long-term mCDR deploy-
ment. The development of tools would be accelerated by the urgency created by the mCDR
deployments. Connections between the three objectives of the monitoring system (i.e., detection,
attribution, and determination of side effects) and the monitored variables are described under
“Monitoring mCDR Deployments” in the text. OSSE = Observation System Simulation Experiment.
TRL = Technological Readiness Level. Licensed under CC BY-SA 4.0 by Thomas Boniface
(M) as described in this study, reporting (R) of the result-
ing data to a certified authority, and verification (V) by this
authority, using data and models, that any deployment is
successful at increasing CO2 influx from the atmosphere
and enhancing its sequestration in the ocean. Successful
verification of removal and sequestration will result in cer-
tification of the mCDR. The last two MRV components are
mentioned in the last section of the study.
Our study for this “Frontiers in Ocean Observing” sup-
plement of Oceanography focuses on the observational
aspects of the monitoring of open- ocean mCDR deploy-
ments, with less emphasis on the corresponding, essential
modeling components. We nevertheless briefly describe
the latter where necessary.
OBJECTIVES OF AN mCDR MONITORING SYSTEM
Monitoring is essential in order to quantify the effective-
ness (removal) and durability (sequestration) of carbon
storage resulting from open- ocean mCDR deployments
and to identify environmental impacts (NASEM, 2022).
Here, we examine three objectives of a future open- ocean
mCDR monitoring system. Our definitions of detection and
attribution are consistent with those in the Glossary of the
Intergovernmental Panel on Climate Change (IPCC, 2021).
Detection. To quantify the amount of carbon sequestered
as DIC. This will require quantification of metrics that docu-
ment both the amount of carbon removed, based on mod-
els that assimilate accurate in situ measurements of carbon
system variables, and the durability of its removal (i.e., long-
term [decadal] estimates of air- sea CO2 exchanges).
Attribution. To assign the detected carbon sequestra-
tion solely to a particular mCDR deployment. Attribution
requires an understanding of the processes that jointly
determine the success or failure of the given mCDR
deployment and must thus address the influence of com-
plex drivers in the carbon cycle to demonstrate additional-
ity (see next section). Attribution addresses the proportion
of carbon sequestration that can be attributed to an mCDR
deployment, even if there are contributions by other
drivers within the carbon cycle. This will involve advanced
modeling capabilities that simulate the state of the cou-
pled physical and biogeochemical ocean and its modifica-
tion by the mCDR deployment.
Determination of Side Effects. To identify and quantify
ecological impacts of the mCDR and ensure that they do
not exceed the impacts expected from the pilot studies.