Basing a remaining carbon budget on warming targets is subject to uncertainty due to uncertainty in the relationship between carbon emissions and warming. Framing emissions targets using a warming target therefore may not prevent dangerous change throughout the entire Earth system. Here, we use a climate emulator to constrain a remaining carbon budget that is more representative of the entire Earth system by using a combination of both warming and ocean acidification targets. The warming targets considered are the Paris Agreement targets of 1.5 and 2 °C; the acidification targets are −0.17 and −0.21 pH units, informed by aragonite saturation states where coral growth begins to be compromised. The aim of the dual targets is to prevent not only damage associated with warming, but damage to corals associated with atmospheric carbon and ocean acidification. We find that considering acidification targets in conjunction with warming targets narrows the uncertainty in the remaining carbon budget, especially in situations where the acidification target is more stringent than, or of similar stringency to, the warming target. Considering a strict combination of the two more stringent targets (both targets of 1.5 °C warming and −0.17 acidification must be met), the carbon budget ranges from −74.0 to 129.8PgC. This reduces uncertainty in the carbon budget from by 29% (from 286.2PgC to 203.8PgC). This reduction comes from reducing the high-end estimate of the remaining carbon budget derived from just a warming target. Assuming an emissions rate held constant since 2021 (which is a conservative assumption), the budget towards both targets was either spent by 2019 or will be spent by 2026.
Continue reading ‘Assessing the remaining carbon budget through the lens of policy-driven acidification and temperature targets’Posts Tagged 'modeling'
Assessing the remaining carbon budget through the lens of policy-driven acidification and temperature targets
Published 18 September 2023 Science Leave a CommentTags: chemistry, globalmodeling, modeling, policy
Seasonal variability of the surface ocean carbon cycle: a synthesis
Published 4 September 2023 Science ClosedTags: chemistry, globalmodeling, modeling, review
Abstract
The seasonal cycle is the dominant mode of variability in the air-sea CO2 flux in most regions of the global ocean, yet discrepancies between different seasonality estimates are rather large. As part of the Regional Carbon Cycle Assessment and Processes phase 2 project (RECCAP2), we synthesize surface ocean pCO2 and air-sea CO2 flux seasonality from models and observation-based estimates, focusing on both a present-day climatology and decadal changes between the 1980s and 2010s. Four main findings emerge: First, global ocean biogeochemistry models (GOBMs) and observation-based estimates (pCO2 products) of surface pCO2 seasonality disagree in amplitude and phase, primarily due to discrepancies in the seasonal variability in surface DIC. Second, the seasonal cycle in pCO2 has increased in amplitude over the last three decades in both pCO2 products and GOBMs. Third, decadal increases in pCO2 seasonal cycle amplitudes in subtropical biomes for both pCO2 products and GOBMs are driven by increasing DIC concentrations stemming from the uptake of anthropogenic CO2 (Cant). In subpolar and Southern Ocean biomes, however, the seasonality change for GOBMs is dominated by Cant invasion, whereas for pCO2 products an indeterminate combination of Cant invasion and climate change modulates the changes. Fourth, biome-aggregated decadal changes in the amplitude of pCO2 seasonal variability are largely detectable against both mapping uncertainty (reducible) and natural variability uncertainty (irreducible), but not at the gridpoint scale over much of the northern subpolar oceans and over the Southern Ocean, underscoring the importance of sustained high-quality seasonally-resolved measurements over these regions.
Key Points
- pCO2 seasonal cycle amplitude changes over 1985-2018 are detectable against both mapping uncertainty and natural variability uncertainty
- The dominant driver of pCO2 amplitude increases over decadal timescales is attributed to the direct effect of Cant invasion
- A discrepancy is found with surface DIC seasonality being systematically less in GOBMs than in surface DIC observation-based products
Drivers of surface ocean acidity extremes in an Earth system model
Published 23 August 2023 Science ClosedTags: chemistry, globalmodeling, modeling
Abstract
Oceanic uptake of anthropogenic carbon causes acidification, a process that describes the increase in hydrogen ion concentrations ([H+]) and decrease in calcium carbonate mineral saturation states (Ω). Of particular concern are ocean acidity extreme (OAX) events, which pose a significant threat to many calcifying marine organisms. However, the mechanisms driving such extreme events are not well understood. Here, we use high-frequency output from a fully-coupled Earth system model of all processes that influence the surface ocean temperature and carbon budgets and ultimately [H+] and Ω anomalies to quantify the driving mechanisms of the onset and decline of high [H+] and low Ω extreme events. We show that enhanced temperature plays a crucial role in driving [H+] extremes, with increased net ocean heat uptake being the dominant driver of the event onset in the subtropics. In the mid-to-high latitudes, decreased downward vertical diffusion and mixing of warm surface waters during summer, and increased vertical mixing with warm and carbon-rich subsurface waters during winter are the main drivers of high [H+] extreme event onset. In the tropics, increases in vertical advection of carbon-rich subsurface waters are the primary driver of the onset of high [H+] extremes. In contrast, low Ω extremes are driven in most regions by increases in surface carbon concentration due to increased vertical mixing with carbon-rich subsurface waters. Our study highlights the complex interplay between heat and carbon anomalies driving OAX events and provides a first foundation for more accurate prediction of their future evolution.
Key Points
- The physical and biogeochemical drivers of surface ocean acidity extremes are analysed using high-frequency output of an Earth system model
- Higher temperatures due to enhanced ocean heat uptake drive the onset of high [H+] extremes in the subtropics
- In contrast, higher carbon concentrations due to increased vertical mixing and advection cause low Ω extremes in most regions
Rising snow line: Ocean acidification and the submergence of seafloor geomorphic features beneath a rising carbonate compensation depth
Published 22 August 2023 Science ClosedTags: Antarctic, Arctic, chemistry, Indian, modeling, North Atlantic, North Pacific, regionalmodeling, review, South Atlantic, South Pacific
Highlights
- Ocean acidification has caused the carbonate compensation depth (CCD) to rise by ~98 m.
- Seafloor area below the CCD has increased by 3.6% in the last 200 years.
- Risk of impact of rising CCD is greatest in the western equatorial Atlantic Ocean.
- Different geomorphic features impacted by rising CCD in different ocean areas.
Abstract
Due to burning of fossil fuels, carbon dioxide is being absorbed by the ocean where its chemical conversion to carbonic acid has already caused the surface ocean to become more acidic than it has been for at least the last 2 million years. Global ocean modeling suggests that the carbonate compensation depth (CCD) has already risen by nearly 100 m on average since pre-industrial times and will likely rise further by several hundred meters more this century. Potentially millions of square kilometres of ocean floor will undergo a rapid transition in terms of the overlying water chemistry whereby calcareous sediment will become unstable causing the carbonate “snow line” to rise.We carried out a spatial analysis of seafloor geomorphology to assess the area newly submerged below the rising CCD. We found that shoaling of the CCD since the industrial revolution has submerged 12,432,096 km2 of ocean floor (3.60% of total ocean area) below the CCD. Further hypothetical shoaling of the CCD by 100 m increments illustrated that the surface area of seafloor submerged below the CCD has risen by 14% with 300 m of shoaling, such that 51% of the ocean area will be below the CCD. All categories of geomorphic feature mapped in one global database intersect the lysocline and will be (or already are) submerged below the CCD with much regional variation since the rise in CCD depth during the last 150 years varies significantly between different ocean regions. For seamounts, the highest percentages of increase in area submerged below the CCD occurred in the Southern Indian Ocean and the South West Atlantic regions (6.3% and 5.9%, respectively). For submarine canyons we found the South West Atlantic increased from 3.9% in pre-industrial times to 8.0% at the present time, the highest percentage of canyons found below the CCD in any ocean region.We also carried out a relative risk assessment for future submergence of ocean floor below the CCD in 17 ocean regions. In our assessment we assumed that the change in CCD from pre-industrial times to the present is an indicator of the likelihood and the change in percentage of seafloor submerged below the CCD due to a hypothetical 300 m rise in the CCD is an indicator of the consequences. We found that the western equatorial Atlantic is at high risk and 9 other Ocean Regions are at moderate risk. Overall, geomorphic features in the Atlantic Ocean and southern Indian Ocean are at greater risk of impact from a rising CCD than Pacific and other Indian Ocean regions.A separate analysis of the Arctic Ocean points to the possible submergence of glacial troughs incised on the continental shelf within a mid-depth (400–800 m) acidified water mass. We also found that the area of national Exclusive Economic Zones submerged below the rising CCD exhibits extreme variability; with 300 m of CCD shoaling we found a > 12% increase in area submerged below the CCD for 23 national EEZs, whereas there was virtually no change for other countries.
Continue reading ‘Rising snow line: Ocean acidification and the submergence of seafloor geomorphic features beneath a rising carbonate compensation depth’Future physical and biogeochemical ocean conditions under climate change along the British Columbia continental margin
Published 17 August 2023 Science ClosedTags: chemistry, modeling, North Pacific, regionalmodeling
Climate change impacts coastal ecosystems through large scale changes in temperature, stratification, circulation and ocean acidification. Here, the potential response of the British Columbia continental margin to climate change is investigated using a regional ocean circulation-biogeochemical model to downscale climate change projections from the Canadian regional and global climate models (CanRCM4/CanESM2) under two Intergovernmental Panel on Climate Change emission scenarios (RCP 4.5 and RCP 8.5). Projections of future physical and biogeochemical conditions for the 2041–2070 period are compared to the recent past (1981–2010). We found an overall annual average warming of >1.6°C in sea surface temperature, increase in stratification in the upper layer, and decrease in surface pH of as much as 0.21. Increasing stratification and changing winds have a limited impact on nitrate availability, phytoplankton biomass and primary production, whilst ocean warming increases primary production by up to 30% in most of the model domain. Increased atmospheric CO2 contributes to acidification over the model domain with a decrease in pH and aragonite saturation (Ωarag) at all depths resulting in an increase of 20 to 32% of the volume of Ωarag ≤1 in the upper 100 m of the continental shelf depending on the climate scenario. Our projected results, therefore, show that future climate change may alter the amount of food available for higher trophic levels and the habitat of benthic species, since bottom waters on the shelf will be undersaturated with respect to aragonite for 2–3 months in mid-summer. Both climate change scenarios results in a similar pattern of changes but projected changes were stronger and more extensive under RCP 8.5 showing the benefit of mitigation efforts in reducing the effect of climate change on marine ecosystem stressors.
Continue reading ‘Future physical and biogeochemical ocean conditions under climate change along the British Columbia continental margin’Using meta-analysis to explore the roles of global upwelling exposure and experimental design in bivalve responses to low pH
Published 16 August 2023 Science ClosedTags: biological response, individualmodeling, modeling, mollusks, physiology, respiration, review
Highlights
- Meta-analysis was used to assess bivalve responses to low pH.
- Strong upwelling regions may yield bivalves that are less sensitive to low pH.
- Upwelling explains up to 49 % variability of bivalve metabolic responses to low pH.
- Larger carbonate chemistry deltas in experiments yield stronger responses.
Abstract
Low pH conditions, associated with ocean acidification, represent threats to many commercially and ecologically important organisms, including bivalves. However, there are knowledge gaps regarding factors explaining observed differences in biological responses to low pH in laboratory experiments. Specific sources of local adaptation such as upwelling exposure and the role of experimental design, such as carbonate chemistry parameter changes, should be considered. Linking upwelling exposure, as an individual oceanographic phenomenon, to responses measured in laboratory experiments may further our understanding of local adaptation to global change. Here, meta-analysis is used to test the hypotheses that upwelling exposure and experimental design affect outcomes of individual, laboratory-based studies that assess bivalve metabolic (clearance and respiration rate) responses to low pH. Results show that while bivalves generally decrease metabolic activity in response to low pH, upwelling exposure and experimental design can significantly impact outcomes. Bivalves from downwelling or weak upwelling areas decrease metabolic activity in response to low pH, but bivalves from strong upwelling areas increase or do not change metabolic activity in response to low pH. Furthermore, experimental temperature, exposure time and magnitude of the change in carbonate chemistry parameters all significantly affect outcomes. These results suggest that bivalves from strong upwelling areas may be less sensitive to low pH. This furthers our understanding of local adaptation to global change by demonstrating that upwelling alone can explain up to 49 % of the variability associated with bivalve metabolic responses to low pH. Furthermore, when interpreting outcomes of individual, laboratory experiments, scientists should be aware that higher temperatures, shorter exposure times and larger changes in carbonate chemistry parameters may increase the chance of suppressed metabolic activity.
Continue reading ‘Using meta-analysis to explore the roles of global upwelling exposure and experimental design in bivalve responses to low pH’Upwelling intensity and source water properties drive high interannual variability of corrosive events in the California Current
Published 16 August 2023 Science ClosedTags: chemistry, modeling, North Pacific, regionalmodeling
Ocean acidification is progressing rapidly in the California Current System (CCS), a region already susceptible to reduced aragonite saturation state due to seasonal coastal upwelling. Results from a high-resolution (~ 3 km), coupled physical-biogeochemical model highlight that the intensity, duration, and severity of undersaturation events exhibit high interannual variability along the central CCS shelfbreak. Variability in dissolved inorganic carbon (DIC) along the bottom of the 100-m isobath explains 70–90% of event severity variance over the range of latitudes where most severe conditions occur. An empirical orthogonal function (EOF) analysis further reveals that interannual event variability is explained by a combination coastal upwelling intensity and DIC content in upwelled source waters. Simulated regional DIC exhibits low frequency temporal variability resembling that of the Pacific Decadal Oscillation, and is explained by changes to water mass composition in the CCS. While regional DIC concentrations and upwelling intensity individually explain 9 and 43% of year-to-year variability in undersaturation event severity, their combined influence accounts for 66% of the variance. The mechanistic description of exposure to undersaturated conditions presented here provides important context for monitoring the progression of ocean acidification in the CCS and identifies conditions leading to increased vulnerability for ecologically and commercially important species.
Continue reading ‘Upwelling intensity and source water properties drive high interannual variability of corrosive events in the California Current’An empirical projection of ocean acidification in southwestern Japan over the 21st century
Published 31 July 2023 Science ClosedTags: chemistry, modeling, North Pacific, regionalmodeling
Most of Japan’s coral reefs are distributed in the Ryukyu Islands, in the southwestern part of Japan. Since they support biodiversity in the tropical and subtropical seas and are vulnerable to ocean acidification as well as ocean heat waves and pollution, projecting acidification over multidecadal or longer periods of time is a topic. Currently, the majority of long-term acidification projections are based on Earth System Models (ESMs), and the validation of these projections relies on intercomparisons among ESMs. This study evaluated the multi-decadal trends in total dissolved inorganic carbon (DIC) around the Ryukyu Islands over the past 25 years from 1995 to 2019. Multiple linear regression using temperature, salinity and time parameters as explanatory variables was applied to evaluate the salinity-normalized dissolved inorganic carbon (nDIC) concentrations. The coefficient of time (+1.15 ± 0.03 μmol kg−1 yr−1) was insignificantly different from the growth rate of nDIC that was calculated from the growth rate of atmospheric CO2 concentrations during the same period. Assuming that nDIC in this region will continue to increase at a rate that is consistent with the expected growth rate of atmospheric CO2 concentrations, we projected future trends of pH and aragonite saturation state (ΩA) under scenarios RCP4.5 and RCP8.5. The empirical projection of acidification by the end of the 21st century was generally consistent with projections based on ESMs. At present, global corals are generally distributed in waters with ΩA > 3.0. According to the empirical projection under the RCP8.5 scenario, ΩA around Okinawa Island would fall below 3.0 in winter in the 2030s and throughout the year in the 2060s.
Continue reading ‘An empirical projection of ocean acidification in southwestern Japan over the 21st century’Model development to assess carbon fluxes during shell formation in blue mussels
Published 28 July 2023 Newsletters and reports , Science ClosedTags: biogeochemistry, biological response, calcification, individualmodeling, modeling, morphology
In order to quantify the amount of carbonate, precipitated as calcium-carbonate in the shells of blue mussel (Mytilus edulis) in a temperate climate, an existing Dynamic Energy Budget (DEB) model for the blue mussel was adapted by separating shell growth from soft tissue growth. Hereby, two parameters were added to the original DEB-model, a calcification cost [J/mgCaCO3] and an energy allocation fraction [-], which resulted in the energy allocated for structural growth being divided between shell and meat growth. As values for these new parameters were lacking, they were calibrated by fitting the model to field data. Calibration results showed that an Energy allocation fraction of 0.5 and a calcification cost of 0.9 J/mgCaCO3, resulted in the best fit when fitted on 2017 and 2018 field data separately. These values however, show the best fit for data obtained within the first couple of years of the shellfish life, and do not take later years into account. Also it could be discussed that some parameters vary throughout the lifespan of the species. The results were compared to a regular DEB model, where the shell output was calculated through a simple allometric relationship. It is sometimes assumed that the carbon storage in shell material as calcium carbonate could be regarded as a form of carbon sequestration, with a positive impact on the atmospheric CO2 concentrations. However, studies on the physical-chemical processes related to shell formation have shown that from an oceanographic perspective, shell formation should be regarded as a source of atmospheric CO2 rather than a sink. The removal of carbonates, through the biocalcification process, reduces the buffer capacity (alkalinity) of the water to store CO2. As a result CO2 is released from the water to the atmosphere when shell material is formed. The actual amount of CO2 that escapes from the water to the atmosphere as a result of biocalcification depends strongly on local water characteristics. In this study, the effect of calcification by mussels on the CO2 flux to the atmosphere is studied using an adapted DEB model where energy costs of calcification are modelled explicitly. The model was subsequently run under two future climate scenarios, (RCP 4.5 and RCP 8.3) with elevated temperature and decreased pH, and the total released CO2 as a result of shell formation was calculated with the SeaCarb model. This showed growth of mussels, under future climate conditions to be slower, and with that the cumulative shell mass and carbonate precipitated to CaCO3 to decrease. Yet the amount of CO2 released, due to biocalcification, increased. This is due to the fact that the amount of CO2 released/gr of CaCO3 precipitated will be higher, as a result of the decreased buffering capacity of seawater under future climatic environmental conditions.
In summary the conclusions of the project were:
- Biocalcification (shell formation) of marine organisms, such as bivalves, cannot be regarded as a process resulting in negative CO2 emission to the atmosphere;
- The actual amount of CO2 that, due to biocalcification, is released from the water to the atmosphere depends on the physicochemical characteristics of the water, which are influenced by (future) climate conditions;
- Our first model calculations suggest that at future climate conditions mussel’s grow rate will be somewhat reduced. While the amount of CO2 that due to biocalcification, escapes to the atmosphere during its life-time will slightly increase. Making the ratio of g CO2 release/g CaCO3 precipitated slightly higher;
- Our model calculations should be considered an exercise rather than a definite prediction of how mussels will respond to future climate scenarios. Additional information/experimentation is strongly needed to validate the model settings, and to test the validity of the above mentioned outcome of the model.
Implementing a coral reef CaCO3 production module in the iLOVECLIM climate model
Published 20 July 2023 Science ClosedTags: biological response, corals, globalmodeling, methods, modeling
Coral reef development is intricately linked to both climate and the concentration of atmospheric CO2, specifically through temperature and carbonate chemistry in the upper ocean. In turn, the calcification of corals modifies the concentration of dissolved inorganic carbon and total alkalinity in the ocean, impacting air-sea gas exchange, atmospheric CO2 concentration, and ultimately the climate. This retroaction between atmospheric conditions and coral biogeochemistry can only be accounted for with a coupled coral-carbon-climate model. Here we present the implementation of a coral reef calcification module into an Earth System model. Simulated coral reef production of the calcium carbonate mineral aragonite depends on photosynthetically active radiation, nutrient concentrations, salinity, temperature and the aragonite saturation state. An ensemble of 210 parameter perturbation simulations was performed to identify carbonate production parameter values that optimise the simulated distribution of coral reefs and associated carbonate production. The tuned model simulates the presence of coral reefs and regional-to-global carbonate production values in good agreement with data-based estimates. The model enables assessment of past and future coral-climate coupling on seasonal to millennial timescales, highlighting how climatic trends and variability may affect reef development and the resulting climate-carbon feedback.
Continue reading ‘Implementing a coral reef CaCO3 production module in the iLOVECLIM climate model’Carbonate pump feedbacks on alkalinity and the carbon cycle in the 21st century and beyond
Published 19 July 2023 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, modeling
Ocean acidification is likely to impact all stages of the ocean carbonate pump, i.e. the production, export, dissolution and burial of biogenic CaCO3. However, the associated feedbacks on anthropogenic carbon uptake and ocean acidification have received little attention. It has previously been shown that Earth system model (ESM) carbonate pump parameterizations can affect and drive biases in the representation of ocean alkalinity, which is critical to the uptake of atmospheric carbon and provides buffering capacity towards associated acidification. In the sixth phase of the Coupled Model Intercomparison Project (CMIP6), we show divergent responses of CaCO3 export at 100 m this century, with anomalies by 2100 ranging from -74 % to +23 % under a high-emissions scenario. The greatest export declines are projected by ESMs that consider pelagic CaCO3 production to depend on the local calcite/aragonite saturation state. Despite the potential effects of other processes on alkalinity, there is a robust negative correlation between anomalies in CaCO3 export and salinity-normalized surface alkalinity across the CMIP6 ensemble. Motivated by this relationship and the uncertainty in CaCO3 export projections across ESMs, we perform idealized simulations with an ocean biogeochemical model and confirm a limited impact of carbonate pump anomalies on twenty-first century ocean carbon uptake and acidification. However between 2100 and 2300, we highlight a potentially abrupt shift in the dissolution of CaCO3 from deep to subsurface waters when the global scale mean calcite saturation state reaches about 1.23 at 500 m (likely when atmospheric CO2 reaches 900 to 1100 ppm). During this shift, upper ocean acidification due to anthropogenic carbon uptake induces deep ocean acidification driven by a substantial reduction in CaCO3 deep dissolution following its decreased export at depth. Although the effect of a diminished carbonate pump on global ocean carbon uptake and surface ocean acidification remains limited until 2300, it can have a large impact on regional air-sea carbon fluxes, particularly in the Southern Ocean.
Continue reading ‘Carbonate pump feedbacks on alkalinity and the carbon cycle in the 21st century and beyond’Feeding in mixoplankton enhances phototrophy increasing bloom-induced pH changes with ocean acidification
Published 14 July 2023 Science ClosedTags: biogeochemistry, BRcommunity, communitymodeling, modeling, phytoplankton, protists, zooplankton
Plankton phototrophy consumes CO2, increasing seawater pH, while heterotrophy does the converse. Elevation of pH (>8.5) during coastal blooms becomes increasingly deleterious for plankton. Mixoplankton, which can be important bloom-formers, engage in both photoautotrophy and phagoheterotrophy; in theory, this activity could create a relatively stable pH environment for plankton growth. Using a systems biology modelling approach, we explored whether different mixoplankton functional groups could modulate the environmental pH compared to the extreme activities of phototrophic phytoplankton and heterotrophic zooplankton. Activities by most mixoplankton groups do not stabilize seawater pH. Through access to additional nutrient streams from internal recycling with phagotrophy, mixoplankton phototrophy is enhanced, elevating pH; this is especially so for constitutive and plastidic specialist non-constitutive mixoplankton. Mixoplankton blooms can exceed the size of phytoplankton blooms; the synergisms of mixoplankton physiology, accessing nutrition via phagotrophy as well as from inorganic sources, enhance or augment primary production rather than depressing it. Ocean acidification will thus enable larger coastal mixoplankton blooms to form before basification becomes detrimental. The dynamics of such bloom developments will depend on whether the mixoplankton are consuming heterotrophs and/or phototrophs and how the plankton community succession evolves.
Continue reading ‘Feeding in mixoplankton enhances phototrophy increasing bloom-induced pH changes with ocean acidification’Forecasting seasonal changes in ocean acidification using a novel Grey Seasonal Model with Grey Wolf Optimization
Published 11 July 2023 Science ClosedTags: chemistry, globalmodeling, methods, modeling
Ocean acidification forecasting has important implications for studying global carbon dioxide emissions reductions. However, due to seasonal and cyclical features, ocean acidification forecasting remains an extremely challenging task. Therefore, this paper proposes a grey wolf optimized fractional-order-accumulation discrete grey seasonal model (GFSM(1,1)). The GFSM(1,1) model improves the prediction of ocean acidification in two ways: The new information priority of seasonal data is improved by the fractional accumulation operator, and the adaptability of the grey model to seasonal data is increased by seasonal item parameters. The above two works have significantly improved the prediction accuracy of the grey prediction model for ocean acidification. The prediction results in practical cases prove that the prediction effect of the GFSM(1,1) model is not only better than the existing grey models (FMGM(1,N). NSGM(1,N), and GM(1,1)) but also better than statistical models (Nonlinear regression and ARIMA), traditional neural network model (LSTM) and deep learning model (SVM). Finally, the GFSM(1,1) model is applied to the prediction of seawater acidification. The forecast results show that the ocean will be acidified at a rate of 0.001863 per year, and the pH of the ocean will decrease by about 0.03% per year compared to the same period in previous years.
Continue reading ‘Forecasting seasonal changes in ocean acidification using a novel Grey Seasonal Model with Grey Wolf Optimization’Methane-derived authigenic carbonates – a case for a globally relevant marine carbonate factory
Published 6 July 2023 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, methods, modeling, paleo, review
Precipitation of methane-derived authigenic carbonates (MDAC) is an integral part of marine methane production and consumption, but MDAC’s relative significance to the global marine carbon cycle is not well understood. Here we provide a synthesis and perspective to highlight MDAC from a global marine carbon biogeochemistry viewpoint. MDAC formation is a result and archive of carbon‑sulfur (C – S) coupling in the shallow sulfatic zone and carbon‑silicon (C – Si) coupling in deeper methanic sediments. MDAC constitute a carbon sequestration of 3.93 Tmol C yr−1 (range 2.34–5.8 Tmol C yr−1) in the modern ocean and are the third-largest carbon burial mechanism in marine sediments. This burial compares to 29% (11–57%) organic carbon and 10% (6–23%) skeletal carbonate carbon burial along continental margins. MDAC formation is also an important sink for benthic alkalinity and, thereby, a potential contributor to bottom water acidification. Our understanding of the impact of MDAC on global biogeochemical cycles has evolved over the past five decades from what was traditionally considered a passive carbon sequestration mechanism in a seep-oasis setting to what is now considered a dynamic carbonate factory expanding from deep sediments to bottom waters—a factory that has been operational since the Precambrian. We present a strong case for the need to improve regional scale quantification of MDAC accumulation rates and associated carbonate biogeochemical parameters, leading to their incorporation in present and paleo‑carbon budgets in the next phase of MDAC exploration.
Continue reading ‘Methane-derived authigenic carbonates – a case for a globally relevant marine carbonate factory’Predicting carbonate chemistry on the Northwest Atlantic shelf using neural networks
Published 4 July 2023 Science ClosedTags: chemistry, methods, modeling, North Atlantic, regionalmodeling
The Northwest Atlantic Shelf (NAS) region has experienced accelerated warming, heatwaves, and is susceptible to ocean acidification, yet also suffers from a paucity of carbonate chemistry observations, particularly at depth. We address this critical data gap by developing three different neural network models to predict dissolved inorganic carbon (DIC) and total alkalinity (TA) in the NAS region from more readily available hydrographic and satellite data. The models predicted DIC with r2 between 0.913 – 0.963 and root mean square errors (RMSE) between 15.4 – 23.7 (µmol kg-1) and TA with r2 between 0.986 – 0.983 and RMSE between 9.0 – 10.4 (µmol kg-1) on an unseen test data set that was not used in training the models. Cross-validation analysis revealed that all models were insensitive to the choice of training data and had good generalization performance on unseen data. Uncertainty in DIC and TA were low (coefficients of variation 0.1-1%). Compared with other predictive models of carbonate system variables in this region, a larger and more diverse dataset with full seasonal coverage and a more sophisticated model architecture resulted in a robust predictive model with higher accuracy and precision across all seasons. We used one of the models to generate a reconstructed seasonal distribution of carbonate chemistry fields based on DIC and TA predictions that shows a clear seasonal progression and large spatial gradients consistent with observations. The distinct models will allow for a range of applications based on the predictor variables available and will be useful to understand and address ocean sustainability challenges.
Continue reading ‘Predicting carbonate chemistry on the Northwest Atlantic shelf using neural networks’Planktic foraminiferal resilience to environmental change associated with the PETM
Published 28 June 2023 Science ClosedTags: abundance, Arctic, biological response, chemistry, community composition, communitymodeling, modeling, North Pacific, otherprocess, paleo, protists, South Pacific
Carbonate-forming organisms play an integral role in the marine inorganic carbon cycle, yet the links 21 between carbonate production and the environment are insufficiently understood. Carbonate production is driven by the abundance of calcifiers, and the amount of calcite produced by each individual (their size and weight). Here we investigate how foraminiferal carbonate production changes in the Atlantic, Pacific and Southern Ocean in response to a 4-5°C warming and a 0.3 surface ocean pH reduction during the Palaeocene-Eocene Thermal Maximum (PETM). To put these local data into a global context, we apply a trait-based plankton model (ForamEcoGEnIE) to the geologic record for the first time. Our data illustrates negligible change in the assemblage test size and abundance of foraminifers. ForamEcoGEnIE resolves small reductions in size and biomass, but these are short-lived. The response of foraminifersshowsspatial variability linked to a warming-induced poleward migration and suggested differences in nutrient availability between open-ocean and shelf locations. Despite low calcite saturation at high latitudes, we reconstruct stable foraminiferal size-normalised weight. Based on these findings, we postulate that sea surface warming had a greater impact on foraminiferal carbonate production during the PETM than ocean acidification. Changes in the composition of bulk carbonate suggest a higher sensitivity of coccolithophores to environmental change during the PETM than foraminifers.
Continue reading ‘Planktic foraminiferal resilience to environmental change associated with the PETM’FNRCThe roles of carbonate, borate, and bicarbonate ions in affecting zooplankton hatching success under ocean acidification
Published 27 June 2023 Science ClosedTags: biogeochemistry, biological response, individualmodeling, modeling, multiple factors, physiology, reproduction, respiration, review, temperature, zooplankton
Two ocean acidification studies about egg hatching success (HS) in geographically important marine copepods, Calanus finmarchicus and C. helgolandicus, were reanalyzed with improved statistical procedures. The new results at low and moderate levels of seawater acidification showed no HS inhibition at normal habitat temperatures but statistically significant inhibition at warmer and colder temperatures. These HS results were compared with seawater carbonate system and borate concentrations from precise seawater measurements. The temperature dependent differences in HS could not be directly explained by changes in the seawater concentrations of either H+, bicarbonate (HCO3−), or CO2* (CO2* being the sum of unhydrated CO2 and H2CO3). In contrast, HS differences did match trends in seawater carbonate (CO32−) concentrations. A numerical model was developed which evaluates the concentrations of O2 or CO2*, HCO3−, and CO32− at the cellular level across an egg and embryo by considering both gas diffusion with the seawater and respiration by the embryo. Again, temperature-dependent trends in HS could not be explained changes in intracellular CO2* or HCO3− concentrations, but HS did trend with the changes in intracellular CO32− concentrations. Carbonate ions form strong coordination complexes with metals, so acidification-driven decreases in external seawater carbonate concentrations, which are amplified at warmer temperatures, could release injurious metals, thus driving the HS inhibition at warmer temperatures. Increases in cytoplasmic carbonate concentrations at warmer temperatures caused by seawater acidification could complex with biochemically-needed nutrient-type metals within the cells, also causing the increased HS inhibition at warmer temperatures. Furthermore, boron is essential in chemically signaling within and between cells. Seawater borate concentrations were closely correlated with HS inhibition via Michaelis-Menton equations, suggesting that acidification-driven decreases in seawater borate concentrations may also inhibit HS. Finally, the acidification-driven increases in CO2 diffusion into cells dramatically increased intracellular bicarbonate concentrations. At mild levels of seawater acidification, an organism might compensate by exporting bicarbonate from the cells to the haemolymph and then to the seawater. Although the energetic cost, as percentage of ATP production, might be high, increased respiration rates at warmer temperatures might better allow the organism to survive. However, as temperature is lowered, the cellular respiration rate declines more rapidly with respect to temperature than does the gas diffusion coefficient. Consequently, bicarbonate accumulation driven by inward CO2 diffusion might overwhelm the egg’s bicarbonate export capacity at colder temperatures, explaining the colder temperature HS inhibition.
Continue reading ‘FNRCThe roles of carbonate, borate, and bicarbonate ions in affecting zooplankton hatching success under ocean acidification’A glimpse into the climate, seasonality, hydrological cycle, carbonate chemistry and marine ecosystem shift of the pre-Petm and the Petm using Ncar Cesm1.2
Published 22 June 2023 Science ClosedTags: biological response, BRcommunity, chemistry, community composition, modeling, North Atlantic, paleo, phytoplankton, regionalmodeling, South Atlantic
The Paleocene-Eocene Thermal Maximum (PETM, ~56 my ago, 170,000y event) is characterized by a negative δ13C excursion into the atmosphere. This event caused global temperature to increase by about 5-6 °C, followed by climate responses such as marine acidification, ocean stratification, shoaling of calcite compensation depth (CCD), stronger hydrological cycle, and significant changes in marine ecosystems. It is one of the very few analogies of today’s global warming climate and thus is valuable to study. It still holds much potential for research, including using the state-of-the-art model CESM1.2. Proxy records are limited due to the nature of geological preservation and tectonic evolution. Modeling and simulations can provide insights to supplement the limited proxy records research. Here, we explore the seasonality, hydrological cycles, and controlling factors of their changes from pre-PETM to the PETM in the first paper; the ability of CESM1.2 to simulate carbonate chemistry, changes in lysocline and CCD in the Atlantic Ocean in the second paper; and the shift of phytoplankton functional groups, using the same preferendum to capture first-hand reactions to environmental changes, from pre-industrial pCO2 to pre-PETM in the third paper. All papers use CESM1.2 simulation results with or without BEC. Our results show that from pre-PETM to PETM, seasonality increases in mid-latitude continental interiors and decreases in high and low latitudes, along with globally enhanced moisture transfer in hydrological cycles. The main controlling factors of these areas are snow-albedo effect, soil moisture, and precipitation. CESM1.2 and ocean Biogeochemical (BGC) Elemental Cycling (BEC) can simulate the changes of carbonate chemistry of the Atlantic Ocean, with certain modifications in the code base and without the need of extra models. There are noticeable and significant changes in chlorophyll, nutrient and NPP from PETM in pre-industrial pCO2 and pre-PETM, but distinct variations from pre-industrial and PETM in pre-industrial pCO2 simulations. Proxy record scarcity is the main limitation of the studies on PETM and should be used with care. In the meantime, machine learning is encouraged for multi-disciplinary research of complicated topics such as carbon chemistry and phytoplankton functional group preferendum and ecosystem dynamics.
Continue reading ‘A glimpse into the climate, seasonality, hydrological cycle, carbonate chemistry and marine ecosystem shift of the pre-Petm and the Petm using Ncar Cesm1.2’Increased biogenic calcification and burial under elevated pCO2 during the Miocene: a model-data comparison
Published 15 June 2023 Science ClosedTags: biogeochemistry, chemistry, modeling, North Pacific, paleo, regionalmodeling, review, South Pacific
Abstract
Ocean acidification due to anthropogenic CO2 emission reduces ocean pH and carbonate saturation, with the projection that marine calcifiers and associated ecosystems will be negatively affected in the future. On longer time scale, however, recent studies of deep-sea carbonate sediments suggest significantly increased carbonate production and burial in the open ocean during the warm Middle Miocene. Here, we present new model simulations in comparison to published Miocene carbonate accumulation rates to show that global biogenic carbonate production in the pelagic environment was approximately doubled relative to present-day values when elevated atmospheric pCO2 led to substantial global warming ∼13–15 million years ago. Our analysis also finds that although high carbonate production was associated with high dissolution in the deep-sea, net pelagic carbonate burial was approximately 30%–45% higher than modern. At the steady state of the long-term carbon cycle, this requires an equivalent increase in riverine carbonate alkalinity influx during the Middle Miocene, attributable to enhanced chemical weathering under a warmer climate. Elevated biogenic carbonate production resulted in a Miocene ocean that had carbon (dissolved inorganic carbon) and alkalinity (total alkalinity) inventories similar to modern values but was poorly buffered and less saturated in both the surface and the deep ocean relative to modern.
Key Points
- Pelagic carbonate production during the warm Middle Miocene was approximately doubled relative to present-day values
- Net pelagic carbonate burial of the Middle Miocene was likely ∼30%–45% higher than modern values
- The decreases in [
]sw and carbonate production toward the present kept Neogene dissolved inorganic carbon and total alkalinity nearly constant despite a global pCO2 decrease
Severe 21st-century ocean acidification demands continuance and expansion of Antarctic Marine Protected Areas
Published 14 June 2023 Science ClosedTags: Antarctic, chemistry, mitigation, modeling, regionalmodeling
Antarctic coastal waters are home to several established or proposed Marine Protected Areas (MPAs) supporting exceptional biodiversity, which is threatened by anthropogenic climate change. Despite a particular sensitivity to ocean acidification (OA), little is known about the future carbonate chemistry of high-latitude Southern Ocean waters. Here, we use a high resolution ocean–sea ice–biogeochemistry model with realistic ice-shelf geometry to investigate 21st-century OA in Antarctic MPAs under four emission scenarios. By 2100, we project surface pH declines of up to 0.42 (total scale), corresponding to a 161% increase in hydrogen ion concentration relative to the 1990s. End-of-century aragonite undersaturation is ubiquitous across MPAs under the three highest emission scenarios. Vigorous vertical mixing of anthropogenic carbon on the continental shelves produces severe OA within the Weddell Sea, East Antarctic, and Ross Sea MPAs. Our findings call for continuity and expansion of Antarctic MPAs to reduce pressures on ecosystem integrity.
Continue reading ‘Severe 21st-century ocean acidification demands continuance and expansion of Antarctic Marine Protected Areas’
