Ocean Carbon Dioxide Research Articles

Spatiotemporal weighted neural network reveals surface seawater pCO2 distributions and underlying environmental mechanisms in the North Pacific Ocean

The North Pacific Ocean plays a pivotal role as a carbon sink within the global carbon cycle. However, a comprehensive understanding of the spatiotemporal dynamics of carbon dioxide concentration and its determinants in this domain remains elusive due to its vast dimensions and the intricacies of influencing factors, with previous research on carbon dioxide partial pressure in the North Pacific Ocean also being relatively scarce. While prevalent machine learning methodologies have been extensively applied to predict the partial pressure of ocean carbon dioxide (pCO2), their limited interpretability has impeded substantial progress in elucidating the underlying mechanisms. This study introduces a gridded spatiotemporal neural network weighted regression (GSTNNWR) model to illuminate temporal and spatial relationships among relevant environmental variables and pCO2. The GSTNNWR model achieves high-precision and high-resolution forecasts of surface pCO2 in the North Pacific Ocean, demonstrating commendable performance (R2 = 0.863 and RMSE=15.123 µatm). Simultaneously, we obtain a quantitative characterization of how various environmental factors influence pCO2 across different temporal and spatial scales. Results show a dominant positive effect of temperature on the pCO2, with an averaged normalized coefficient of 0.28, and variability in the effects of chlorophyll and salinity on the pCO2 at different spatial and temporal locations and temperatures, whose average normalized coefficients are −0.10 and −0.04.The findings of our study will provide insights into the mechanisms and interactions within the North Pacific carbon cycle, contributing to a better understanding of ocean carbon sink formation and the dynamic regulation of the North Pacific carbon cycle.

Alkaline earth metal ions affect the dissolution of kaolinite-bearing olivine and its carbon storage effects

Olivine dissolution applications in coastal environments hold great promise for both ocean alkalinity enhancement and carbon dioxide storage. Yet the dissolution mechanism of olivine and the influence of metal ions, such as Mg2+ and Ca2+, remain unclear. Moreover, the weathering products, such as clay minerals are usually mixed with olivine, and the influence of the associated minerals on the dissolution also unexplored. In this study, an 80-day dissolution experiment was performed in Ca2+-free artificial seawater (ASW-Ca) and ASW lacking both Ca2+ and Mg2+ (ASW-CaMg), to elucidate the mechanism of olivine dissolution and the impact of Ca2+ and Mg2+ on the presence of an associated clay mineral, kaolinite. To evaluate the mineral properties before and after dissolution, X-ray diffraction spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy analyses were used. Etch pits were observed on olivine's surface as well as its reduced crystallinity. The atomic ratio of Mg/Si in olivine decreased from 1.49 ± 0.56 in the raw samples to 1.29 ± 0.53 in the samples obtained from ASW-CaMg after undergoing the 80-day dissolution, whereas it was much higher, at 1.85 ± 0.32, in the samples from ASW-Ca. The increasing Mg/Si was attributed to the Mg2+ adsorption on the surface of olivine, which inhibited the release of structural Mg2+. Hence, Mg2+ was a key environmental factor influencing the process of olivine dissolution, and estuaries, which have low Mg2+ content and low pH may be the promising areas for the olivine application. Moreover, in ASW-CaMg, the total alkalinity (TA), dissolved inorganic carbon (DIC) concentration, and charge concentration of alkaline earth metal ions increased by 3392 ± 28, 2922 ± 3, and 3740 ± 91 μmol kg−1, respectively, compared to the data from the blank experiment. Notably, TA and DIC had strong linear relationships with the alkaline earth metal ions (Mg2+ and Ca2+). The release of free alkaline earth metal cations during olivine dissolution was a controlling factor for long-term carbon dioxide storage in ASW-CaMg. Finally, during the 80-day dissolution experiment, no dissolution of the associated kaolinite was observed, however, kaolinite may influence the olivine dissolution by adsorbing the released Si.

Characterizing the stable oxygen isotopic composition of the southeast Indian Ocean

New seawater stable oxygen isotope (δ18O) samples were collected from the southeast Indian Ocean as part of the Coring to Reconstruct Ocean Circulation and Carbon dioxide Across 2 Seas (CROCCA-2S) expedition in November – December of 2018. These data fill a gap in the δ18O sampling coverage of the southern Indian basin, providing new insights into the hydrologic and oceanographic processes influencing the δ18O distribution of the region and its relationship to salinity in the upper ocean. Our surface ocean data (<100 m)—in combination with decades of observations from the broader south Indian Ocean—show distinct δ18O – salinity characteristics on either side of ∼85°E. The balance between evaporation and precipitation yields a strong, robust δ18O – salinity relationship west of 85°E (δ18O = 0.50(±0.01) * S – 17.2(±0.22)). However, within the mesoscale eddy field initiated by the Leeuwin Current further east (∼85–120°E), our observations fall along a mixing line between the southwest Indian Ocean and data collected from the Australian coastal margin, illustrating for the first time how the unique eastern boundary system of the south Indian Ocean drives regional-scale variability in the δ18O – salinity relationship of the surface ocean. A comparison between our observations in the shallow subsurface (100–1000 m) and those from neighboring surveys reinforces this upper ocean connection across the Indo-Australian basin. Antarctic Intermediate Water from the Indian Ocean can be isotopically distinguished from the more regional Tasman Intermediate Water occupying the South Australian Bight, suggesting exchange between the two regions is most prevalent at surface and mode water depths. In deeper waters (> ∼1500 m), we observe a notable 0.87‰ spread in δ18O. This variability may represent interactions between distinct deep water masses in the region, although additional data are needed to confirm. Overall, our data provide a new look at the hydrography and isotopic chemistry of the southeast Indian Ocean, emphasizing the impact of the region's mesoscale eddy field and its interconnectivity with neighboring basins.

The annual update GLODAPv2.2023: the global interior ocean biogeochemical data product

Abstract. The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface to bottom ocean biogeochemical bottle data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of seawater samples. GLODAPv2.2023 is an update of the previous version, GLODAPv2.2022 (Lauvset et al., 2022). The major changes are as follows: data from 23 new cruises were added. In addition, a number of changes were made to the data included in GLODAPv2.2022. GLODAPv2.2023 includes measurements from more than 1.4 million water samples from the global oceans collected on 1108 cruises. The data for the now 13 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, chlorofluorocarbon-11 (CFC-11), CFC-12, CFC-113, CCl4, and SF6) have undergone extensive quality control with a focus on the systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but converted to World Ocean Circulation Experiment (WOCE) exchange format and (ii) as a merged data product with adjustments applied to minimize bias. For the present annual update, adjustments for the 23 new cruises were derived by comparing those data with the data from the 1085 quality-controlled cruises in the GLODAPv2.2022 data product using crossover analysis. SF6 data from all cruises were evaluated by comparison with CFC-12 data measured on the same cruises. For nutrients and ocean carbon dioxide (CO2), chemistry comparisons to estimates based on empirical algorithms provided additional context for adjustment decisions. The adjustments that we applied are intended to remove potential biases from errors related to measurement, calibration, and data-handling practices without removing known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 µmol kg−1 in dissolved inorganic carbon, 4 µmol kg−1 in total alkalinity, 0.01–0.02 in pH (depending on region), and 5 % in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete CO2 fugacity (fCO2), were not subjected to bias comparison or adjustments. The original data, their documentation, and DOI codes are available at the Ocean Carbon and Acidification Data System of NOAA National Centers for Environmental Information (NCEI), which also provides access to the merged data product. This is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/zyrq-ht66 (Lauvset et al., 2023). These bias-adjusted product files also include significant ancillary and approximated data, which were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2023 methods and provides a broad overview of the secondary quality control procedures and results.

Accuracy of Ocean CO2 Uptake Estimates at a Risk by a Reduction in the Data Collection

AbstractObservation‐based quantification of ocean carbon dioxide (CO2) uptake relies on synthesis data sets such as the Surface Ocean CO2 ATlas (SOCAT). However, the data collection effort has dramatically declined and the number of annual data sets in SOCATv2023 decreased by ∼35% from 2017 to 2021. This decline has led to a 65% increase (from 0.15 to 0.25 Pg C yr−1) in the standard deviation of seven SOCAT‐based air‐sea CO2 flux estimates. Reducing the availability of the annual data to that in the year 2000 creates substantial bias (50%) in the long‐term flux trend. The annual mean CO2 flux is insensitive to the seasonal skew of the SOCAT data and to the addition of the lower accuracy data set available in SOCAT. Our study highlights the need for sustained data collection and synthesis, to inform the Global Carbon Budget assessment, the UN‐led climate negotiations, and measurement, reporting, and verification of ocean‐based CO2 removal projects.

Fishing gear with enhanced drapability and biodegradability: Artificial, eco-friendly fibers inspired by the mussel byssus

Abandoned, lost, and discarded fishing gear (ALDFG) poses a global challenge for marine ecosystems because it results in the destruction of algal forests, the largest oceanic carbon dioxide sinks. Biodegradable polybutylene succinate (PBS), which has a tensile strength similar to that of nylon, has been suggested as a potential fishing-gear material. However, its slow degradation in the marine environment and limited drapability need to be addressed before it can be used in environmentally friendly fishing gear. Inspired by the mussel byssus, a thread-like holdfast known for its stiff yet extensible mechanical properties, we developed fishing gear using a mussel-byssus-mimetic fiber (artificial byssus fiber, ABf) structure. The ABf was composed of poly(butylene adipate-co-butylene terephthalate) (PBAT) fibers with favorable draping characteristics coated with mechanically resilient and PBS, which demonstrated sufficient toughness and draping properties for use in fishing gear. AB shows promise as a material for fishing-gear capable of mitigating issues related to ALDFG, especially given its marine degradability by microbial strains that degrade PBS and PBAT. Furthermore, it could serve as a substrate for ocean afforestation, given the improved settlement and growth of seaweed spores (Pyropia yezoensis) on AB. Overall, AB-based fishing gear is expected to enhance macroalgal forest conservation and expansion and facilitate marine carbon capture through marine afforestation.

An Assessment of CO2 Storage and Sea‐Air Fluxes for the Atlantic Ocean and Mediterranean Sea Between 1985 and 2018

AbstractAs part of the second phase of the Regional Carbon Cycle Assessment and Processes project (RECCAP2), we present an assessment of the carbon cycle of the Atlantic Ocean, including the Mediterranean Sea, between 1985 and 2018 using global ocean biogeochemical models (GOBMs) and estimates based on surface ocean carbon dioxide (CO2) partial pressure (pCO2 products) and ocean interior dissolved inorganic carbon observations. Estimates of the basin‐wide long‐term mean net annual CO2 uptake based on GOBMs and pCO2 products are in reasonable agreement (−0.47 ± 0.15 PgC yr−1 and −0.36 ± 0.06 PgC yr−1, respectively), with the higher uptake in the GOBM‐based estimates likely being a consequence of a deficit in the representation of natural outgassing of land derived carbon. In the GOBMs, the CO2 uptake increases with time at rates close to what one would expect from the atmospheric CO2 increase, but pCO2 products estimate a rate twice as fast. The largest disagreement in the CO2 flux between GOBMs and pCO2 products is found north of 50°N, coinciding with the largest disagreement in the seasonal cycle and interannual variability. The mean accumulation rate of anthropogenic CO2 (Cant) over 1994–2007 in the Atlantic Ocean is 0.52 ± 0.11 PgC yr−1 according to the GOBMs, 28% ± 20% lower than that derived from observations. Around 70% of this Cant is taken up from the atmosphere, while the remainder is imported from the Southern Ocean through lateral transport.

Machine learning reveals regime shifts in future ocean carbon dioxide fluxes inter-annual variability

The inter-annual variability of global ocean air-sea CO2 fluxes are non-negligible, modulates the global warming signal, and yet it is poorly represented in Earth System Models (ESMs). ESMs are highly sophisticated and computationally demanding, making it challenging to perform dedicated experiments to investigate the key drivers of the CO2 flux variability across spatial and temporal scales. Machine learning methods can objectively and systematically explore large datasets, ensuring physically meaningful results. Here, we show that a kernel ridge regression can reconstruct the present and future CO2 flux variability in five ESMs. Surface concentration of dissolved inorganic carbon (DIC) and alkalinity emerge as the critical drivers, but the former is projected to play a lesser role in the future due to decreasing vertical gradient. Our results demonstrate a new approach to efficiently interpret the massive datasets produced by ESMs, and offer guidance into future model development to better constrain the CO2 flux.

Carbon Sequestration and Climate Change

The long-term storage of carbon dioxide in soils, vegetation, oceans, and geological formations, with the objective of reducing or postponing global warming, is known as carbon sequestration. It reduces the amount of greenhouse gas emitted by various human activities. Scientists estimate that there is a direct correlation between rising global temperatures and atmospheric carbon dioxide levels, with the atmosphere containing 30% more carbon today than it did 150 years ago. One recommended approach to reducing atmospheric carbon dioxide is to increase carbon storage globally through a variety of means. To slow the net rate of increase in atmospheric CO2, carbon sequestration involves storing CO2 in long-lived global pools found in forests, oceans, biomass, and geological strata. This process is crucial for the maintenance of the global carbon cycle. To combat climate change, the global community must lower carbon emissions and increase net carbon sequestration. These methods can reduce the risks associated with climate change, but it is important to weigh the advantages and disadvantages of each suggested carbon sequestration strategy. The present study attempts to discuss various methods of carbon sequestration to reduce global warming.

What factors cause ocean CO2? A panel data analysis.

Over the past three decades, industrial innovations and technological advancements have changed business dynamics, adversely devastating the overall environment. As a result, our oceans have been severely affected due to climate change and global warming. To address this issue, this study investigates the factors that cause ocean CO2 using a sample of 44 countries over 2012-2021 and explores a dynamic and causal relationship between economic growth, ocean carbon dioxide emissions, energy consumption, and control variables relating to the ocean industry. This study finds that increasing economic activity tends to increase ocean carbon emissions. The results support the evidence of the environmental Kuznets curve (EKC) hypothesis suggesting an inverted U-shaped association between ocean emissions and real income for the sample countries. Moreover, this study reports that ocean health index, maritime container transport, trade of fishery and ocean species, aquaculture production and marine species, and employment rate in the fishery processing sector are the significant factors of ocean CO2. Region-wise analyses suggest that real income positively influences ocean emissions and confirm the evidence of the EKC hypothesis in European sample countries but these relationships have an insignificant effect in Asia and the Pacific and the American regions. Furthermore, a short-run unidirectional panel causality flows from the production of aquaculture and other species to RD&D, from OHI and GDP to trade of fishery and other species, and from OHI to employment rate in the fishery sector. Likewise, bidirectional causality runs from energy consumption and maritime transport to ocean CO2 in the long term. Regarding the long-run causal association, the results determine that all of the estimated coefficients of the lagged error correction terms are statistically significant which explains that they are crucial in the adjustment process as they deviate from the long-run equilibrium.

Ocean Carbon Dioxide Uptake in the Tailpipe of Industrialized Continents

AbstractA simplifying assumption in many studies of ocean carbon uptake is that the atmosphere is well‐mixed, such that zonal variations in its carbon dioxide (CO2) content can be neglected in the calculation of air‐sea fluxes. Here, we examine this assumption at various scales to quantify the errors it introduces. For global annual averages, we find that positive and negative errors effectively cancel, so the use of atmospheric zonal‐average CO2 introduces reassuringly small errors in fluxes. However, for millions of square kilometers of the North Pacific and Atlantic that are downwind of the highly industrialized northern hemisphere continents, these biases average to over 6% of the annual ocean uptake and can cause errors of up to 30% on a given day. This work highlights the need to use a high quality, spatially‐resolved atmospheric CO2 product for process studies and for accurate long‐term average maps of ocean carbon uptake.

Physical Mechanisms Driving Enhanced Carbon Sequestration by the Biological Pump Under Climate Warming

AbstractAs ocean Carbon Dioxide Removal techniques are being considered, it is critical that they be evaluated against our scientific understanding of the global biological carbon pump. In a recent paper Nowicki et al. (2022, https://doi.org/10.1029/2021GB007083) provide an innovative and comprehensive breakdown of the different mechanistic pathways of carbon sequestration through the present‐day biological pump but then speculate that “These results suggest that ocean carbon storage will weaken as the oceans stratify and the subtropical gyres expand due to anthropogenic climate change.” Essentially, the authors combine their steady state result that oligotrophic subtropical gyres have lower residence times than other areas with the climate change result of these areas increasing under climate warming and extrapolate—assuming “all else is equal”—that the overall ocean will suffer a reduction in carbon sequestration efficiency. Expressing global changes in carbon sequestered by the ocean's biological pump as the summation of local changes in the sequestered carbon, timescale of return to the surface, and biogeographical area, I discuss how all three terms are tightly coupled, and summarize decades of climate change modeling consistently indicating that the global scale physical sequestration response is an increase ‐ in opposition of what one would infer from changes in subtropical area alone.

Calcium isotopic fractionation during aragonite and high-Mg calcite precipitation at methane seeps

The formation of authigenic carbonate in marine environments represents a process that buffers ocean chemistry and atmospheric carbon dioxide levels. The isotopic composition of calcium (δ44/40Ca) in authigenic carbonate can be used to investigate the calcium (Ca) cycle, seawater chemistry, and diagenesis of carbonate rocks, archiving key information on the evolution of the Earth's surface environments. Laboratory experiments have shown that Ca isotopic fractionation during carbonate precipitation – the basis of the δ44/40Ca proxy – is mainly determined by both mineral phase and precipitation rate. However, the precipitation rate of submarine authigenic carbonate is much lower than rates in laboratory experiments. This study investigated the Ca isotopic composition of pore water and carbonate nodules collected from two gravity piston cores and one push core from the Haima seeps in the northern South China Sea. Methane fluxes calculated for the three cores range from 12 to 134 µmol cm−2 yr−1. The core with intermediate methane flux showed evidence of aragonite precipitation, while high-Mg calcite was the dominant mineral phase in the other two cores as indicated by Mg/Ca and Sr/Ca ratios of pore water. Numerical modeling of pore water geochemistry revealed that: (1) precipitation rates of carbonate per unit reactive surface area range from 0.05 to 21 µmol m−2 h−1, which is one to three orders of magnitude lower than rates in precipitation experiments; (2) Ca isotopic fractionation for aragonite precipitation is –1.8 ± 0.3 ‰, close to the reported equilibrium isotopic fractionation in precipitation experiments; and (3) Ca isotopic fractionation for high-Mg calcite precipitation is similar for the two cores (−0.9 ± 0.3 ‰ and −0.8 ± 0.3 ‰), although the modeled precipitation rates differed by two orders of magnitude. These results indicate that mineralogy rather than precipitation rate is the primary control on Ca isotopic fractionation during carbonate precipitation at seeps, resulting in lower δ44/40Ca values of aragonite (0.91±0.06 ‰, N = 4) than of high-Mg calcite (1.41±0.04 ‰, N = 9) reported relative to NIST SRM915a. This study documents distinguishable Ca isotopic fractionation during the formation of methane-derived high-Mg calcite and aragonite, providing fundamental parameters for further exploration of the calcium isotopic composition of marine authigenic carbonates in the geological record.

Seasonal cycles of biogeochemical fluxes in the Scotia Sea, Southern Ocean: a stable isotope approach

Abstract. The biological carbon pump is responsible for much of the decadal variability in the ocean carbon dioxide (CO2) sink, driving the transfer of carbon from the atmosphere to the deep ocean. A mechanistic understanding of the ecological drivers of particulate organic carbon (POC) flux is key both to the assessment of the magnitude of the ocean CO2 sink and for accurate predictions as to how this will change with changing climate. This is particularly important in the Southern Ocean, a key region for the uptake of CO2 and the supply of nutrients to the global thermocline. In this study we examine sediment-trap-derived particle fluxes and stable isotope signatures of carbon (C), nitrogen (N), and biogenic silica (BSi) at a study site in the biologically productive waters of the northern Scotia Sea in the Southern Ocean. Both deep (2000 m) and shallow (400 m) sediment traps exhibited two main peaks in POC, particulate N, and BSi flux: one in austral spring and one in summer, reflecting periods of high surface productivity. Particulate fluxes and isotopic compositions were similar in both deep and shallow sediment traps, highlighting that most remineralisation occurred in the upper 400 m of the water column. Differences in the seasonal cycles of isotopic compositions of C, N, and Si provide insights into the degree of coupling of these key nutrients. We measured increasing isotopic enrichment of POC and BSi in spring, consistent with fractionation during biological uptake. Since we observed isotopically light particulate material in the traps in summer, we suggest physically mediated replenishment of lighter isotopes of key nutrients from depth, enabling the full expression of the isotopic fractionation associated with biological uptake. The change in the nutrient and remineralisation regimes, indicated by the different isotopic compositions of the spring and summer productive periods, suggests a change in the source region of material reaching the traps and associated shifts in phytoplankton community structure. This, combined with the occurrence of advective inputs at certain times of the year, highlights the need to make synchronous measurements of physical processes to improve our ability to track changes in the source regions of sinking particulate material. We also highlight the need to conduct particle-specific (e.g. faecal pellets, phytoplankton detritus, zooplankton moults) isotopic analysis to improve the use of this tool in assessing particle composition of the sinking material and to develop our understanding of the drivers of biogeochemical fluxes.

Extending Residual-Mean Overturning Theory to the Topographically Localized Transport in the Southern Ocean

Abstract The Southern Ocean plays a major role in global air–sea carbon fluxes, with some estimates suggesting it contributes to up to 40% of the oceanic anthropogenic carbon dioxide uptake, despite only comprising about 20% of oceanic surface area. Thus, the Southern Ocean overturning, the circulation that transports tracers between the surface and deep ocean interior, is particularly important for climate. Recent studies show that vertical velocities and tracer transport are largest just downstream of bottom topography; these quantities are related to the overturning, but provide incomplete information about the net Lagrangian transport, usually described with the residual-mean theory in a zonally integrated sense. This study uses an idealized Southern Ocean–like channel model with particle tracking to visualize the thickness-weighted velocities that capture the net overturning transport of a parcel, connecting residual-mean overturning theory to the three-dimensional, localized nature of the overturning. From this, we split the flow into three main drivers of transport: a wind-driven Ekman pumping into or out of a density layer, and standing eddies and transient eddies, both of which are localized near the topography. In this framework, the three-dimensional overturning circulation is not a small residual between the eddy and Eulerian-mean transport. The existence of a ridge weakens the response of the overturning to changes in wind, especially in the lower cell. This local understanding of the overturning framework suggests that careful modeling and sampling of specific regions near topography in the Southern Ocean are vital to understand climate sensitivity, transport, carbon export, and connections with the oceans to the north.

Coccolithophores and diatoms resilient to ocean alkalinity enhancement: A glimpse of hope?

It is increasingly apparent that adequately mitigating anthropogenic climate interference will require ocean carbon dioxide removal (CDR) strategies. Ocean alkalinity enhancement (OAE) is an abiotic ocean CDR approach that aims to increase the ocean's CO2 uptake capacity through the dispersal of pulverized mineral or dissolved alkali into the surface ocean. However, OAE's effect on marine biota is largely unexplored. Here, we investigate the impacts of moderate (~700 μmol kg-1) and high (~2700 μmol kg-1) limestone-inspired alkalinity additions on two biogeochemically and ecologically important phytoplankton functional group representatives: Emiliania huxleyi (calcium carbonate producer) and Chaetoceros sp. (silica producer). The growth rate and elemental ratios of both taxa showed a neutral response to limestone-inspired alkalinization. While our results are encouraging, we also observed abiotic mineral precipitation, which removed nutrients and alkalinity from solution. Our findings offer an evaluation of biogeochemical and physiological responses to OAE and provide evidence supporting the need for continued research into how OAE strategies affect marine ecosystems.

Seawater alkalinity enhancement with magnesium hydroxide and its implication for carbon dioxide removal

For the first time we used lab and wind-wave tank experiments to prove the concept of using Mg(OH)2 for the ocean alkalinity enhancement and carbon dioxide removal approach (OAE-CDR). Experiment results showed up to 370 μmol kg−1 seawater total alkalinity (TA) increase without precipitation, stable enhanced TA, and OAE-CDR efficiency (ΔDIC/ΔTA) consistent with theoretical calculation. Based on the experimental results, we calculated the global Mg(OH)2 OAE-CDR efficiency and CO2 sink from this approach. The efficiency is in favor of lower initial DIC to TA ratio, lower temperature, and higher atmospheric CO2, and therefore is the lowest at the equator (0.7–0.8) and increases with latitude (1.0–1.2 above 70 N/S). However, factoring in the ocean's surface area, low latitude regions can absorb more atmospheric CO2. We conservatively estimate that 44. 4 × 109 ton of CO2 (∼ 3.3 times of current annual CO2 sink in the ocean) could be removed from the atmosphere with 175 μmol kg−1 Mg(OH)2 (equivalent to 350 μmol kg−1 of TA) added to the top 10 m of the ocean.

Canada's marine carbon sink: an early career perspective on the state of research and existing knowledge gaps

Improving our understanding of how the ocean absorbs carbon dioxide is critical to climate change mitigation efforts. We, a group of early career ocean professionals working in Canada, summarize current research and identify steps forward to improve our understanding of the marine carbon sink in Canadian national and offshore waters. We have compiled an extensive collection of reported surface ocean air–sea carbon dioxide exchange values within each of Canada's three adjacent ocean basins. We review the current understanding of air–sea carbon fluxes and identify major challenges limiting our understanding in the Pacific, the Arctic, and the Atlantic Ocean. We focus on ways of reducing uncertainty to inform Canada's carbon stocktake, establish baselines for marine carbon dioxide removal projects, and support efforts to mitigate and adapt to ocean acidification. Future directions recommended by this group include investing in maturing and building capacity in the use of marine carbon sensors, improving ocean biogeochemical models fit-for-purpose in regional and ocean carbon dioxide removal applications, creating transparent and robust monitoring, verification, and reporting protocols for marine carbon dioxide removal, tailoring community-specific approaches to co-generate knowledge with First Nations, and advancing training opportunities for early career ocean professionals in marine carbon science and technology.

Acidification of the Global Surface Ocean: What We Have Learned from Observations

The chemistry of the global ocean is rapidly changing due to the uptake of anthropogenic carbon dioxide (CO2). This process, commonly referred to as ocean acidification (OA), is negatively impacting many marine species and ecosystems. In this study, we combine observations in the global surface ocean collected by NOAA Pacific Marine Environmental Laboratory and Atlantic Oceanographic and Meteorological Laboratory scientists and their national and international colleagues over the past four decades, along with model outputs, to provide a high-resolution, regionally varying view of global surface ocean carbon dioxide fugacity, carbonate ion content, total hydrogen ion content, pH on total scale, and aragonite and calcite saturation states on selected time intervals from 1961 to 2020. We discuss the major roles played by air-sea anthropogenic CO2 uptake, warming, local upwelling processes, and declining buffer capacity in controlling the spatial and temporal variability of these parameters. These changes are occurring rapidly in regions that would normally be considered OA refugia, thus threatening the protection that these regions provide for stocks of sensitive species and increasing the potential for expanding biological impacts.

GLODAPv2.2022: the latest version of the global interior ocean biogeochemical data product

Abstract. The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface-to-bottom ocean biogeochemical bottle data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of seawater samples. GLODAPv2.2022 is an update of the previous version, GLODAPv2.2021 (Lauvset et al., 2021). The major changes are as follows: data from 96 new cruises were added, data coverage was extended until 2021, and for the first time we performed secondary quality control on all sulfur hexafluoride (SF6) data. In addition, a number of changes were made to data included in GLODAPv2.2021. These changes affect specifically the SF6 data, which are now subjected to secondary quality control, and carbon data measured on board the RV Knorr in the Indian Ocean in 1994–1995 which are now adjusted using certified reference material (CRM) measurements made at the time. GLODAPv2.2022 includes measurements from almost 1.4 million water samples from the global oceans collected on 1085 cruises. The data for the now 13 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, chlorofluorocarbon-11 (CFC-11), CFC-12, CFC-113, CCl4, and SF6) have undergone extensive quality control with a focus on systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but converted to World Ocean Circulation Experiment (WOCE) exchange format and (ii) as a merged data product with adjustments applied to minimize bias. For the present annual update, adjustments for the 96 new cruises were derived by comparing those data with the data from the 989 quality-controlled cruises in the GLODAPv2.2021 data product using crossover analysis. SF6 data from all cruises were evaluated by comparison with CFC-12 data measured on the same cruises. For nutrients and ocean carbon dioxide (CO2) chemistry comparisons to estimates based on empirical algorithms provided additional context for adjustment decisions. The adjustments that we applied are intended to remove potential biases from errors related to measurement, calibration, and data handling practices without removing known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent to better than 0.005 in salinity, 1 % in oxygen, 2 % in nitrate, 2 % in silicate, 2 % in phosphate, 4 µmol kg−1 in dissolved inorganic carbon, 4 µmol kg−1 in total alkalinity, 0.01–0.02 in pH (depending on region), and 5 % in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete CO2 fugacity (fCO2), were not subjected to bias comparison or adjustments. The original data, their documentation, and DOI codes are available at the Ocean Carbon and Acidification Data System of NOAA NCEI (https://www.ncei.noaa.gov/access/ocean-carbon-acidification-data-system/oceans/GLODAPv2_2022/, last access: 15 August 2022). This site also provides access to the merged data product, which is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/1f4w-0t92 (Lauvset et al., 2022). These bias-adjusted product files also include significant ancillary and approximated data, which were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2022 methods and provides a broad overview of the secondary quality control procedures and results.