Attribution of Space‐Time Variability in Global‐Ocean Dissolved Inorganic Carbon

Carroll, Dustin; Menemenlis, Dimitris; Dutkiewicz, Stephanie; Lauderdale, Jonathan Maitland; Adkins, Jess F.; Bowman, K. W.; Brix, Holger; Fenty, Ian; Gierach, M. M.; Hill, Chris; Jahn, O.; Landschützer, Peter; Manizza, Manfredi; Mazloff, Matthew R.; Miller, Charles E.; Schimel, David; Verdy, Ariane; Zhang, Hong

doi:10.1029/2021gb007162

Cited by 33 publications

(25 citation statements)

References 119 publications

(191 reference statements)

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“…Further study to determine these uptake efficiencies, at a finer location sample resolution and ideally with model ensembles, are needed for optimal placement of OAE deployments. While our results give an overall picture and are indicative of the complexity, more sophisticated biogeochemistry models (e.g, Carroll et al, 2022) and higher-resolution regional coupled biogeophysical models (e.g., Sein et al, 2015;Wang et al, 2022) will be essential for simulation and deployment of real-world OAE projects.…”

Section: Discussionmentioning

confidence: 80%

Limits and CO2 equilibration of near-coast alkalinity enhancement

He¹

2022

Preprint

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Abstract. Ocean Alkalinity Enhancement (OAE) has recently gained attention as a potential method for negative emissions at gigatonne scale, with near-coast OAE operations being economically favorable due to proximity to mineral and energy sources. In this paper we study critical questions which determine the scale and viability of OAE: Which coastal locations are able to sustain a large flux of alkalinity at minimal pH and ΩArag (aragonite saturation) changes? What is the interference distance between adjacent OAE projects? How much CO2 is absorbed per unit of alkalinity added? How quickly does the induced CO2 deficiency equilibrate with the atmosphere? Using the LLC270 (0.3deg) ECCO global circulation model we find that the steady-state OAE rate varies over 1–2 orders of magnitude between different coasts and exhibits complex patterns and non-local dependencies which vary from region to region. In general, OAE in areas of strong coastal currents allow the largest fluxes and depending on the direction of coastal currents, neighboring OAE sites can exhibit dependencies as far as 400 km or more. We found that within relatively conservative constraints set on ∆pH or ∆Omega, most regional stretches of coastline are able to accommodate on the order of tens to hundreds of megatonnes of negative emissions within 300 km of the coast. We conclude that near-coastal OAE has the potential to scale globally to several GtCO2/yr of drawdown with conservative pH constraints, if the effort is spread over the majority of available coastlines. Depending on the location, we find a diverse set of equilibration kinetics, determined by the interplay of gas exchange and surface residence time. Most locations reach an uptake-efficiency plateau of 0.6–0.8mol CO2 per mol of alkalinity after 3–4 years, after which there is little further CO2 uptake. The most ideal locations, reaching an uptake of around 0.8 include north Madagascar, San Francisco, Brazil, Peru and locations close to the southern ocean such as Tasmania, Kerguelen and Patagonia, where the gas exchange appears to occur faster than the surface residence time. Some locations (e.g. Hawaii) take significantly longer to equilibrate (up to 8–10 years), though can still eventually achieve high uptake. If the alkalinity released advects into regions of significant downwelling (e.g. around Iceland) up to half of the OAE potential can be lost to bottom waters.

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Section: Discussionmentioning

confidence: 80%

Limits and CO2 equilibration of near-coast alkalinity enhancement

He¹

2022

Preprint

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“…The other assimilation model used here is the ECCO-Darwin model (Carroll et al, 2020(Carroll et al, , 2022. This model features an ocean biogeochemistry and ecology model (Darwin) (Dutkiewicz et al, 2015) coupled to the ECCO data-assimilated physical circulation model (Forget et al, 2015;Zhang et al, 2018).…”

Section: Data Assimilation Modelsmentioning

confidence: 99%

Magnitude, Trends, and Variability of the Global Ocean Carbon Sink From 1985 to 2018

DeVries,

Yamamoto,

Wanninkhof

et al. 2023

Global Biogeochemical Cycles

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This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985‐2018, using a combination of models and observation‐based products. The mean sea‐air CO2 flux from 1985‐2018 is ‐1.6±0.2 PgC yr‐1 based on an ensemble of reconstructions of the history of sea surface pCO2 (pCO2 products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO2, which is estimated at ‐2.1±0.3 PgC yr‐1 by an ensemble of ocean biogeochemical models, and ‐2.4±0.1 PgC yr‐1 by two ocean circulation inverse models. The ocean also degasses about 0.65±0.3 PgC yr‐1 of terrestrially‐derived CO2, but this process is not fully resolved by any of the models used here. From 2001‐2018, the pCO2 products reconstruct a trend in the ocean carbon sink of ‐0.61±0.12 PgC yr‐1 decade‐1, while biogeochemical models and inverse models diagnose an anthropogenic CO2‐driven trend of ‐0.34±0.06 and ‐0.41±0.03 PgC yr‐1 decade‐1, respectively. This implies a climate‐forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate‐driven variability exceeding the CO2‐forced variability by 2‐3 times. These results suggest that anthropogenic CO2 dominates the ocean CO2 sink, while climate‐driven variability is potentially large but highly uncertain and not consistently captured across different methods.

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“…Still, two recent papers found that the advective flux of DIC plays an important role in the carbon budget of the region (Carroll et al, 2022;Rosso et al, 2017). For example, Carroll et al (2022) find that the DIC tendency and interannual variability in their SIZ biome is dominated by net advection, although they do not show the contribution from the different advective components. Rosso et al (2017) do separate the advection into vertical, geostrophic and ageostrophic components, however, they compute their budget down to 650 m, which implicitly reduces the relative importance of Ekman transport (which only occurs in the top ∼80 m).…”

Section: Discussionmentioning

confidence: 97%

“…Comparison to model-based DIC budgets is also difficult since they are typically computed over fixed depths, and many models have seasonal variations in air-sea carbon fluxes that are inconsistent with observations (Mongwe et al, 2018). Still, two recent papers found that the advective flux of DIC plays an important role in the carbon budget of the region (Carroll et al, 2022;Rosso et al, 2017). For example, Carroll et al (2022) find that the DIC tendency and interannual variability in their SIZ biome is dominated by net advection, although they do not show the contribution from the different advective components.…”

Section: Discussionmentioning

confidence: 99%

Carbon Outgassing in the Antarctic Circumpolar Current Is Supported by Ekman Transport From the Sea Ice Zone in an Observation‐Based Seasonal Mixed‐Layer Budget

Sauvé,

Gray,

Prend

et al. 2023

JGR Oceans

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Despite its importance for the global cycling of carbon, there are still large gaps in our understanding of the processes driving annual and seasonal carbon fluxes in the high‐latitude Southern Ocean. This is due in part to a historical paucity of observations in this remote, turbulent, and seasonally ice‐covered region. Here, we use autonomous biogeochemical float data spanning 6 full seasonal cycles and with circumpolar coverage of the Southern Ocean, complemented by atmospheric reanalysis, to construct a monthly climatology of the mixed layer budget of dissolved inorganic carbon (DIC). We investigate the processes that determine the annual mean and seasonal cycle of DIC fluxes in two different zones of the Southern Ocean—the Sea Ice Zone (SIZ) and Antarctic Southern Zone (ASZ). We find that, annually, mixing with carbon‐rich waters at the base of the mixed layer supplies DIC which is, in the ASZ, either used for net biological production or outgassed to the atmosphere. In contrast, in the SIZ, where carbon outgassing and the biological pump are weaker, the surplus of DIC is instead advected northward to the ASZ. In other words, carbon outgassing in the southern Antarctic Circumpolar Current (ACC), which has been attributed to remineralized carbon from deep water upwelled in the ACC, is also due to the wind‐driven transport of DIC from the SIZ. These results stem from the first observation‐based carbon budget of the circumpolar Southern Ocean and thus provide a useful benchmark to evaluate climate models, which have significant biases in this region.

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Attribution of Space‐Time Variability in Global‐Ocean Dissolved Inorganic Carbon

Cited by 33 publications

References 119 publications

Limits and CO2 equilibration of near-coast alkalinity enhancement

Limits and CO2 equilibration of near-coast alkalinity enhancement

Magnitude, Trends, and Variability of the Global Ocean Carbon Sink From 1985 to 2018

Carbon Outgassing in the Antarctic Circumpolar Current Is Supported by Ekman Transport From the Sea Ice Zone in an Observation‐Based Seasonal Mixed‐Layer Budget

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