Oceanography | Vol. 38, No. 3
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(Gruber et al., 2023; Vivian et al., 2024). While much more
research is needed, a few examples are emerging: recent model-
ing work suggested that using macroalgae as an mCDR approach
had limited potential because of ocean circulation and biologi-
cal feedbacks that resulted in reduced efficacy of carbon seques-
tration (Berger et al., 2023). Other modeling work has shown that
when iron fertilization was considered as an mCDR approach
alongside ongoing climate change, phytoplankton growth result-
ing from the iron addition led to extra climate-induced stress
on the growth of other organisms (consumers), and limited CO2
sequestration (Tagliabue et al., 2023).
In summary, the mCDR approaches discussed here have the
potential to prevent further OA by their very nature, in that they
aim to remove CO2 from the atmosphere. However, atmospheric
equilibrium processes and possible remineralization add uncer-
tainty as to their effectiveness at either reversing OA or allevi-
ating it at global scales, especially as mCDR methods are, by
design, using the ocean to store the extra carbon from the atmo-
sphere. Therefore, the location of the stored carbon and the
stability of the store will ultimately determine whether or not
the problem of OA is alleviated or just transferred to another
part of the ocean.
GOA-ON GOALS AND mCDR RESEARCH
As an established network of international scientists and ocean
professionals, GOA-ON offers a wealth of knowledge to the mCDR
community. Here we explore the three goals of GOA-ON and how
they offer lessons learned by the OA community that are relevant to
mCDR and how each of these goals could support mCDR research.
GOA-ON GOAL 1: IMPROVE UNDERSTANDING OF
GLOBAL OCEAN ACIDIFICATION CONDITIONS
GOA-ON’s first goal is to enhance global monitoring of ocean car-
bonate chemistry, with key observations being pCO2, pH, alkalin-
ity, and DIC (Newton et al., 2015). This monitoring is achieved
by establishing and supporting standardized observation proto-
cols, as well as increasing the spatial and temporal coverage of OA
monitoring efforts through capacity building activities. By improv-
ing our understanding of the spatial and temporal variations in
carbonate chemistry, GOA-ON provides the scientific baseline
necessary for evaluation of any large-scale marine intervention,
including mCDR.
GOAL 1 LESSONS LEARNED RELEVANT FOR mCDR
RESEARCH AND CURRENT STATE OF OBSERVATIONS
Early OA monitoring was mostly carried out in open ocean systems
where variability is relatively low. However, increasingly, observa-
tions show higher variability, especially in coastal areas. Carbonate
chemistry is influenced by a complex interaction between physi-
cal, chemical, and biological processes, sediment-seawater inter-
actions, and proximity to coastal and land-based inputs (e.g., Cai
et al., 2021). Static, long-term observations (such as moorings
or repeat hydrographic transect sections) and underway systems
such as on ships and uncrewed systems that provide broader spa-
tial coverage, including throughout the water column, are funda-
mental for understanding OA. However, there have been chal-
lenges because researchers lack reliable, cost-effective sensors and
readily available reference materials for calibrating measurements,
and OA observations have limited spatial coverage. To address
these challenges, GOA-ON and other networks have supported
capacity development (see later section on GOA-ON’s Network
and Capacity) that has expanded observations across the globe. To
facilitate awareness of existing data and platforms, GOA-ON cre-
ated an online data explorer (Figure 4a) that displays >750 assets
and is a first port of call for anyone trying to understand where car-
bonate chemistry monitoring activities are being conducted and
who is leading those activities.
Ocean carbon data archiving is now being streamlined, with
general consensus among scientists globally that individual
FIGURE 4. Maps show (a) OA-relevant monitoring, taken from the GOA-ON
Data Explorer (correct as of January 2025), and (b) mCDR activities between
2000 and 2025 (numbers in circles indicate number of projects in that area),
taken from the Geoengineering Map (correct as of January 2025).