A set of observing system simulation experiments was performed. This assessed the impact on global ocean biogeochemical reanalyses of assimilating chlorophyll from remotely sensed ocean colour and in situ observations of chlorophyll, nitrate, oxygen, and pH from a proposed array of Biogeochemical-Argo (BGC-Argo) floats. Two potential BGC-Argo array distributions were tested: one for which biogeochemical sensors are placed on all current Argo floats and one for which biogeochemical sensors are placed on a quarter of current Argo floats. Assimilating BGC-Argo data greatly improved model results throughout the water column. This included surface partial pressure of carbon dioxide (pCO2), which is an important output of reanalyses. In terms of surface chlorophyll, assimilating ocean colour effectively constrained the model, with BGC-Argo providing no added benefit at the global scale. The vertical distribution of chlorophyll was improved by assimilating BGC-Argo data. Both BGC-Argo array distributions gave benefits, with greater improvements seen with more observations. From the point of view of ocean reanalysis, it is recommended to proceed with development of BGC-Argo as a priority. The proposed array of 1000 floats will lead to clear improvements in reanalyses, with a larger array likely to bring further benefits. The ocean colour satellite observing system should also be maintained, as ocean colour and BGC-Argo will provide complementary benefits.
Continue reading ‘Assimilating synthetic Biogeochemical-Argo and ocean colour observations into a global ocean model to inform observing system design’Posts Tagged 'globalmodeling'
Assimilating synthetic Biogeochemical-Argo and ocean colour observations into a global ocean model to inform observing system design
Published 27 January 2021 Media coverage , Science ClosedTags: biogeochemistry, globalmodeling, methods, modeling
Chapter: Amplifying factors leading to the collapse of primary producers during the Chicxulub impact and Deccan Traps eruptions
Published 21 December 2020 Science ClosedTags: biological response, chemistry, community composition, globalmodeling, modeling, otherprocess, paleo
The latest Cretaceous (Maastrichtian) through earliest Paleogene (Danian) interval was a time marked by one of the five major mass extinctions in Earth’s history. The synthesis of published data permits the temporal correlation of the Cretaceous-Paleogene boundary crisis with two major geological events: (1) the Chicxulub impact, discovered in the Yucatan Peninsula (Mexico), and (2) eruption of the Deccan Traps large igneous province, located on the west-central Indian plateau. In this study, environmental and biological consequences from the Chicxulub impact and emplacement of the Deccan continental flood basalts were explored using a climate-carbon-biodiversity coupled model called the ECO-GEOCLIM model. The novelty of this study was investigation into the ways in which abiotic factors (temperature, pH, and calcite saturation state) acted on various marine organisms to determine the primary productivity and biodiversity changes in response to a drastic environmental change. Results showed that the combination of Deccan volcanism with a 10-km-diameter impactor would lead to global warming (3.5 degrees C) caused by rising carbon dioxide (CO 2) concentration (+470 ppmv), interrupted by a succession of short-term cooling events, provided by a “shielding effect” due to the formation of sulfate aerosols. The consequences related to these climate changes were the decrease of the surface ocean pH by 0.2 (from 8.0 to 7.8), while the deep ocean pH dropped by 0.4 (from 7.8 to 7.4). Without requiring any additional perturbations, these environmental disturbances led to a drastic decrease of the biomass of calcifying species and their biodiversity by similar to 80%, while the biodiversity of noncalcifying species was reduced by similar to 60%. We also suggest that the short-lived acidification caused by the Chicxulub impact, when combined with eruption of the Deccan Traps, may explain the severity of the extinction among pelagic calcifying species.
Continue reading ‘Chapter: Amplifying factors leading to the collapse of primary producers during the Chicxulub impact and Deccan Traps eruptions’Hysteresis of the Earth system under positive and negative CO2 emissions
Published 18 December 2020 Science ClosedTags: chemistry, globalmodeling, mitigation, modeling
Carbon dioxide removal (CDR) from the atmosphere is part of all emission scenarios of the IPCC that limit global warming to below 1.5 degrees C. Here, we investigate hysteresis characteristics in 4x pre-industrial atmospheric CO2 concentration scenarios with exponentially increasing and decreasing CO2 using the Bern3D-LPX Earth system model of intermediate complexity. The equilibrium climate sensitivity (ECS) and the rate of CDR are systematically varied. Hysteresis is quantified as the difference in a variable between the up and down pathway at identical cumulative carbon emissions. Typically, hysteresis increases non-linearly with increasing ECS, while its dependency on the CDR rate varies across variables. Large hysteresis is found for global surface air temperature (Delta SAT), upper ocean heat content, ocean deoxygenation, and acidification. We find distinct spatial patterns of hysteresis: Delta SAT exhibits strong polar amplification, hysteresis in O-2 is both positive and negative depending on the interplay between changes in remineralization of organic matter and ventilation. Due to hysteresis, sustained negative emissions are required to return to and keep a CO2 and warming target, particularly for high climate sensitivities and the large overshoot scenario considered here. Our results suggest, that not emitting carbon in the first place is preferable over carbon dioxide removal, even if technologies would exist to efficiently remove CO2 from the atmosphere and store it away safely.
Continue reading ‘Hysteresis of the Earth system under positive and negative CO2 emissions’Assessing coral reef condition indicators for local and global stressors using Bayesian networks
Published 23 November 2020 Science ClosedTags: biological response, communitymodeling, corals, globalmodeling, modeling
Coral reefs are highly valued ecosystems currently threatened by both local and global stressors. Given the importance of coral reef ecosystems, a Bayesian network approach can benefit an evaluation of threats to reef condition. To this end, we used data to evaluate the overlap between local stressors (overfishing and destructive fishing, watershed‐based pollution, marine‐based pollution, and coastal development threats), global stressors (acidification and thermal stress) and management effectiveness with indicators of coral reef health (live coral index, live coral cover, population bleaching, colony bleaching and recently killed corals). Each of the coral health indicators had Bayesian networks constructed globally and for Pacific, Atlantic, Australia, Middle East, Indian Ocean, and Southeast Asia coral reef locations. Sensitivity analysis helped evaluate the strength of the relationships between different stressors and reef condition indicators. The relationships between indicators and stressors were also evaluated with conditional analyses of linear and nonlinear interactions. In this process, a standardized direct effects analysis was emphasized with a target mean analysis to predict changes in the mean value of the reef indicator from individual changes to the distribution of the predictor variables. The standardized direct effects analysis identified higher risks in the Middle East for watershed‐based pollution with population bleaching and Australia for overfishing and destructive fishing with living coral. For thermal stress, colony bleaching and recently killed coral in the Indian Ocean were found to have the strongest direct associations. For acidification threat, Australia had a relatively strong association with colony bleaching and the Middle East had the strongest overall association with recently killed coral although extrapolated spatial data were used for the acidification estimates. The Bayesian network approach helped to explore the relationships among existing databases used for policy development in coral reef management by examining the sensitivity of multiple indicators of reef condition to spatially‐distributed stress.
Continue reading ‘Assessing coral reef condition indicators for local and global stressors using Bayesian networks’Global trends of ocean CO2 sink and ocean acidification: an observation-based reconstruction of surface ocean inorganic carbon variables
Published 20 November 2020 Science ClosedTags: chemistry, globalmodeling, modeling
Ocean acidification is likely to impact marine ecosystems and human societies adversely and is a carbon cycle issue of great concern. Projecting the degree of ocean acidification and the carbon-climate feedback will require understanding the current status, variability, and trends of ocean inorganic carbon system variables and the ocean carbon sink. With this goal in mind, we reconstructed total alkalinity (TA), dissolved inorganic carbon (DIC), CO2 partial pressure (pCO2sea), sea–air CO2 flux, pH, and aragonite saturation state (Ωarg) for the global ocean based on measurements of pCO2sea and TA. We used a multiple linear regression approach to derive relationships to explain TA and DIC and obtained monthly 1° × 1° gridded values of TA and DIC for the period 1993–2018. These data were converted to pCO2sea, pH, and Ωarg, and monthly sea-air CO2 fluxes were obtained in combination with atmospheric CO2. Mean annual sea–air CO2 flux and its rate of change were estimated to be − 2.0 ± 0.5 PgC year−1 and − 0.3 (PgC year−1) decade−1, respectively. Our analysis revealed that oceanic CO2 uptake decreased during the 1990s and has been increasing since 2000. Our estimate of the globally averaged rate of pH change, − 0.0181 ± 0.0001 decade−1, was consistent with that expected from the trend of atmospheric CO2 growth. However, rates of decline of pH were relatively slow in the Southern Ocean (− 0.0165 ± 0.0001·decade−1) and in the western equatorial Pacific (− 0.0148 ± 0.0002·decade−1). Our estimate of the globally averaged rate of pH change can be used to verify Indicator 14.3.1 of Sustainable Development Goals.
Continue reading ‘Global trends of ocean CO2 sink and ocean acidification: an observation-based reconstruction of surface ocean inorganic carbon variables’OceanSODA-ETHZ: A global gridded data set of the surface ocean carbonate system for seasonal to decadal studies of ocean acidification
Published 23 October 2020 Science ClosedTags: chemistry, globalmodeling, modeling
Ocean acidification has altered the ocean’s carbonate chemistry profoundly since preindustrial times, with potentially serious consequences for marine life. Yet, no long-term global observation-based data set exists that permits to study changes in ocean acidification for all carbonate system parameters over the last few decades. Here, we fill this gap and present a methodologically consistent global data set of all relevant surface ocean parameters, i.e., dissolved inorganic carbon (DIC), total alkalinity (TA), partial pressure of CO2 (pCO2), pH, and the saturation state with respect to mineral CaCO3 (Ω) at monthly resolution over the period 1985 through 2018 at a spatial resolution of 1 × 1°. This data set, named OceanSODA-ETHZ, was created by extrapolating in time and space the surface ocean observations of pCO2 (from the Surface Ocean CO2 ATlas (SOCAT)) and total alkalinity (TA, from the Global Ocean Data Analysis Project (GLODAP)) using the newly developed Geospatial Random Cluster Ensemble Regression (GRaCER) method. This method is based on a two-step (cluster-regression) approach, but extends it by considering an ensemble of such cluster-regressions, leading to higher robustness. Surface ocean DIC, pH, and Ω were then computed from the globally mapped pCO2 and TA using the thermodynamic equations of the carbonate system. For the open ocean, the cluster regression method estimates pCO2 and TA with global near-zero biases and root mean squared errors of 12 µatm and 13 µmol kg−1, respectively. Taking into account also the measurement and representation errors, the total error increases to 14 µatm and 21 µmol kg−1, respectively. We assess the fidelity of the computed parameters by comparing them to direct observations from GLODAP, finding surface ocean pH and DIC global biases of near zero, and root mean squared errors of 0.023 and 16 µmol kg−1, respectively. These errors are very comparable to those expected by propagating the total errors from pCO2 and TA through the thermodynamic computations, indicating a robust and conservative assessment of the errors. We illustrate the potential of this new dataset by analyzing the climatological mean seasonal cycles of the different parameters of the surface ocean carbonate system, highlighting their commonalities and differences. The OceanSODA-ETHZ data can be downloaded from https://doi.org/10.25921/m5wx-ja34 (Gregor and Gruber, 2020).
Projected expansion of Trichodesmium’s geographical distribution and increase in growth potential in response to climate change
Published 15 October 2020 Science ClosedTags: biological response, chemistry, communitymodeling, globalmodeling, growth, modeling, nitrogen fixation, otherprocess, paleo, prokaryotes
Estimates of marine N2 fixation range from 52 to 73 Tg N/year, of which we calculate up to 84% is from Trichodesmium based on previous measurements of nifH gene abundance and our new model of Trichodesmium growth. Here, we assess the likely effects of four major climate change‐related abiotic factors on the spatiotemporal distribution and growth potential of Trichodesmium for the last glacial maximum (LGM), the present (2006–2015) and the end of this century (2100) by mapping our model of Trichodesmium growth onto inferred global surface ocean fields of pCO2, temperature, light and Fe. We conclude that growth rate was severely limited by low pCO2 at the LGM, that current pCO2 levels do not significantly limit Trichodesmium growth and thus, the potential for enhanced growth from future increases in CO2 is small. We also found that the area of the ocean where sea surface temperatures (SST) are within Trichodesmium‘s thermal niche increased by 32% from the LGM to present, but further increases in SST due to continued global warming will reduce this area by 9%. However, the range reduction at the equator is likely to be offset by enhanced growth associated with expansion of regions with optimal or near optimal Fe and light availability. Between now and 2100, the ocean area of optimal SST and irradiance is projected to increase by 7%, and the ocean area of optimal SST, irradiance and iron is projected to increase by 173%. Given the major contribution of this keystone species to annual N2 fixation and thus pelagic ecology, biogeochemistry and CO2 sequestration, the projected increase in the geographical range for optimal growth could provide a negative feedback to increasing atmospheric CO2 concentrations.
Continue reading ‘Projected expansion of Trichodesmium’s geographical distribution and increase in growth potential in response to climate change’Increase in ocean acidity variability and extremes under increasing atmospheric CO2
Published 28 September 2020 Science ClosedTags: chemistry, globalmodeling, modeling
Ocean acidity extreme events are short-term periods of relatively high [H+] concentrations. The uptake of anthropogenic CO2 emissions by the ocean is expected to lead to more frequent and intense ocean acidity extreme events, not only due to changes in the long-term mean but also due to changes in short-term variability. Here, we use daily mean output from a five-member ensemble simulation of a comprehensive Earth system model under low- and high-CO2-emission scenarios to quantify historical and future changes in ocean acidity extreme events. When defining extremes relative to a fixed preindustrial baseline, the projected increase in mean [H+] causes the entire surface ocean to reach a near-permanent acidity extreme state by 2030 under both the low- and high-CO2-emission scenarios. When defining extremes relative to a shifting baseline (i.e., neglecting the changes in mean [H+]), ocean acidity extremes are also projected to increase because of the simulated increase in [H+] variability; e.g., the number of days with extremely high surface [H+] conditions is projected to increase by a factor of 14 by the end of the 21st century under the high-CO2-emission scenario relative to preindustrial levels. Furthermore, the duration of individual extreme events is projected to triple, and the maximal intensity and the volume extent in the upper 200 m are projected to quintuple. Similar changes are projected in the thermocline. Under the low-emission scenario, the increases in ocean acidity extreme-event characteristics are substantially reduced. At the surface, the increases in [H+] variability are mainly driven by increases in [H+] seasonality, whereas changes in thermocline [H+] variability are more influenced by interannual variability. Increases in [H+] variability arise predominantly from increases in the sensitivity of [H+] to variations in its drivers (i.e., carbon, alkalinity, and temperature) due to the increase in oceanic anthropogenic carbon. The projected increase in [H+] variability and extremes may enhance the risk of detrimental impacts on marine organisms, especially for those that are adapted to a more stable environment.
Twenty-first century ocean warming, acidification, deoxygenation, and upper-ocean nutrient and primary production decline from CMIP6 model projections
Published 10 July 2020 Science ClosedTags: globalmodeling, modeling
Anthropogenic climate change is projected to lead to ocean warming, acidification, deoxygenation, reductions in near-surface nutrients, and changes to primary production, all of which are expected to affect marine ecosystems. Here we assess projections of these drivers of environmental change over the twenty-first century from Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) that were forced under the CMIP6 Shared Socioeconomic Pathways (SSPs). Projections are compared to those from the previous generation (CMIP5) forced under the Representative Concentration Pathways (RCPs). A total of 10 CMIP5 and 13 CMIP6 models are used in the two multi-model ensembles. Under the high-emission scenario SSP5-8.5, the multi-model global mean change (2080–2099 mean values relative to 1870–1899) ± the inter-model SD in sea surface temperature, surface pH, subsurface (100–600 m) oxygen concentration, euphotic (0–100 m) nitrate concentration, and depth-integrated primary production is +3.47±0.78 ∘C, −0.44±0.005, −13.27±5.28, −1.06±0.45 mmol m−3 and −2.99±9.11 %, respectively. Under the low-emission, high-mitigation scenario SSP1-2.6, the corresponding global changes are +1.42±0.32 ∘C, −0.16±0.002, −6.36±2.92, −0.52±0.23 mmol m−3, and −0.56±4.12 %. Projected exposure of the marine ecosystem to these drivers of ocean change depends largely on the extent of future emissions, consistent with previous studies. The ESMs in CMIP6 generally project greater warming, acidification, deoxygenation, and nitrate reductions but lesser primary production declines than those from CMIP5 under comparable radiative forcing. The increased projected ocean warming results from a general increase in the climate sensitivity of CMIP6 models relative to those of CMIP5. This enhanced warming increases upper-ocean stratification in CMIP6 projections, which contributes to greater reductions in upper-ocean nitrate and subsurface oxygen ventilation. The greater surface acidification in CMIP6 is primarily a consequence of the SSPs having higher associated atmospheric CO2 concentrations than their RCP analogues for the same radiative forcing. We find no consistent reduction in inter-model uncertainties, and even an increase in net primary production inter-model uncertainties in CMIP6, as compared to CMIP5.
Using the Health Belief Model to explore the impact of environmental empathy on behavioral intentions to protect ocean health
Published 26 June 2020 Science ClosedTags: globalmodeling, modeling, socio-economy
We examine psychological mediating mechanisms to promote ocean health among the U.S. public. Ocean acidification (OA) was chosen as the focus, as experts consider it as important as climate change with the same cause of humanity’s excessive carbon dioxide (CO2) emissions, but it is lesser known. Empathy is a multi-dimensional concept that includes cognitive and emotional aspects. Previous literature argues that environmental empathy can facilitate positive behaviors. We tested the hypothesis that empathy affects beliefs and behavioral intentions regarding ocean health using the Health Belief Model. We found that higher empathy toward ocean health led to higher perceived susceptibility and severity from OA, greater perceived benefits of CO2 emissions reduction, greater perceived barriers, and keener attention to the media. Beliefs and media attention positively influenced behavioral intentions (e.g., willingness to buy a fuel efficient car). Theoretical and practical implications regarding audience targeting and intervention design are discussed.
Continue reading ‘Using the Health Belief Model to explore the impact of environmental empathy on behavioral intentions to protect ocean health’Irreversibility of marine climate change impacts under carbon dioxide removal
Published 25 May 2020 Science ClosedTags: globalmodeling, mitigation, modeling
Artificial carbon dioxide removal (CDR) from the atmosphere has been proposed as a measure for mitigating climate change and restoring the climate system to a target state after exceedance (“overshoot”). This research investigates to what extent overshoot and subsequent recovery of a given cumulative CO2 emissions level by CDR leaves a legacy in the marine environment using an Earth system model. We use RCP2.6 and its extension to year 2300 as the reference scenario and design a set of cumulative emissions and temperature overshoot scenarios based on other RCPs. Our results suggest that the overshoot and subsequent return to a reference cumulative emissions level would leave substantial impacts on the marine environment. Although the changes in sea surface temperature, pH and dissolved oxygen are largely reversible, global mean values and spatial patterns of these variables differ significantly from those in the reference scenario when the reference cumulative emissions are attained.
Continue reading ‘Irreversibility of marine climate change impacts under carbon dioxide removal’Towards an understanding of the Ca isotopic signal related to ocean acidification and alkalinity overshoots in the rock record
Published 21 May 2020 Science ClosedTags: chemistry, globalmodeling, modeling, paleo
In this contribution, we explore the idea that the Ca isotope proxy has utility as an indicator of carbonate authigenesis (i.e., post-depositional precipitation of CaCO3 within the sedimentary package). Given the strong contrast in isotopic fractionation factor between the formational and diagenetic environments, Ca isotopes have the potential to fingerprint carbonate authigenesis when it occurs close to the seawater-sediment interface. We demonstrate that Ca isotopes are particularly applicable to exploring ocean acidification events, and potentially ocean anoxic events, and focus our attention on ocean acidification related to the Paleocene-Eocene Thermal Maximum (PETM). We present three scenarios that vary in magnitude and duration of carbon fluxes simulated using an Earth System model of intermediate complexity (cGENIE) and use the cGENIE output to constrain the upper boundary conditions of 1-D reactive transport models of authigenesis and recrystallization in the sedimentary section. Along with simple mixing calculations, the models inform our exploration of the hypothesis that authigenic carbonate induced by a saturation state overshoot during the PETM explains recently published Ca isotope records, and perhaps bulk carbonate records over Ocean Anoxic Event (OAE) 2. Our simulations suggest that fractionation factor variability does not explain the PETM δ44Ca records, and we propose a δ44Ca-CaCO3 space framework to assist with the elucidation of authigenic additions over time scales that are short relative to the residence time of Ca in the ocean (~1 Ma). Ultimately, we find that the ‘authigenic zone’ generated in the sedimentary column may be influenced by alkalinity overshoots or redox state; the CaCO3 produced in this zone can overprint temporal signals with depth-dependent signals that reflect lithology and sedimentation rate and need not be spatially uniform, even when driven by a global event. Ultimately, we demonstrate the utility of Ca isotopes for exploring short time scale climatic events and a quantitative framework to guide interpretations.
Continue reading ‘Towards an understanding of the Ca isotopic signal related to ocean acidification and alkalinity overshoots in the rock record’Dissolved inorganic carbon pump in methane-charged shallow marine sediments: state of the art and new model perspectives
Published 5 May 2020 Science ClosedTags: biogeochemistry, chemistry, globalmodeling, modeling
Methane transport from subsurface reservoirs to shallow marine sediment is characterized by unique biogeochemical interactions significant for ocean chemistry. Sulfate-Methane Transition Zone (SMTZ) is an important diagenetic front in the sediment column that quantitatively consumes the diffusive methane fluxes from deep methanogenic sources toward shallow marine sediments via sulfate-driven anaerobic oxidation of methane (AOM). Recent global compilation from diffusion-controlled marine settings suggests methane from below and sulfate from above fluxing into the SMTZ at an estimated rate of 3.8 and 5.3 Tmol year–1, respectively, and wider estimate for methane flux ranges from 1 to 19 Tmol year–1. AOM converts the methane carbon to dissolved inorganic carbon (DIC) at the SMTZ. Organoclastic sulfate reduction (OSR) and deep-DIC fluxes from methanogenic zones contribute additional DIC to the shallow sediments. Here, we provide a quantification of 8.7 Tmol year–1 DIC entering the methane-charged shallow sediments due to AOM, OSR, and the deep-DIC flux (range 6.4–10.2 Tmol year–1). Of this total DIC pool, an estimated 6.5 Tmol year–1 flows toward the water column (range: 3.2–9.2 Tmol year–1), and 1.7 Tmol year–1 enters the authigenic carbonate phases (range: 0.6–3.6 Tmol year–1). This summary highlights that carbonate authigenesis in settings dominated by diffusive methane fluxes is a significant component of marine carbon burial, comparable to ∼15% of carbonate accumulation on continental shelves and in the abyssal ocean, respectively. Further, the DIC outflux through the SMTZ is comparable to ∼20% of global riverine DIC flux to oceans. This DIC outflux will contribute alkalinity or CO2 in different proportions to the water column, depending on the rates of authigenic carbonate precipitation and sulfide oxidation and will significantly impact ocean chemistry and potentially atmospheric CO2. Settings with substantial carbonate precipitation and sulfide oxidation at present are contributing CO2 and thus to ocean acidification. Our synthesis emphasizes the importance of SMTZ as not only a methane sink but also an important diagenetic front for global DIC cycling. We further underscore the need to incorporate a DIC pump in methane-charged shallow marine sediments to models for coastal and geologic carbon cycling.
Potential predictability of marine ecosystem drivers
Published 17 April 2020 Science ClosedTags: globalmodeling, modeling
Climate variations can have profound impacts on marine ecosystems and the socioeconomic systems that may depend upon them. Temperature, pH, oxygen (O2) and net primary production (NPP) are commonly considered to be important marine ecosystem drivers, but the potential predictability of these drivers is largely unknown. Here, we use a comprehensive Earth system model within a perfect modeling framework to show that all four ecosystem drivers are potentially predictable on global scales and at the surface up to 3 years in advance. However, there are distinct regional differences in the potential predictability of these drivers. Maximum potential predictability (>10 years) is found at the surface for temperature and O2 in the Southern Ocean and for temperature, O2 and pH in the North Atlantic. This is tied to ocean overturning structures with “memory” or inertia with enhanced predictability in winter. Additionally, these four drivers are highly potentially predictable in the Arctic Ocean at the surface. In contrast, minimum predictability is simulated for NPP (<1 years) in the Southern Ocean. Potential predictability for temperature, O2 and pH increases with depth below the thermocline to more than 10 years, except in the tropical Pacific and Indian oceans, where predictability is also 3 to 5 years in the thermocline. This study indicating multi-year (at surface) and decadal (subsurface) potential predictability for multiple ecosystem drivers is intended as a foundation to foster broader community efforts in developing new predictions of marine ecosystem drivers.
Continue reading ‘Potential predictability of marine ecosystem drivers’
Meeting climate targets by direct CO2 injections: what price would the ocean have to pay? (update)
Published 6 April 2020 Science ClosedTags: biogeochemistry, globalmodeling, modeling
We investigate the climate mitigation potential and collateral effects of direct injections of captured CO2 into the deep ocean as a possible means to close the gap between an intermediate CO2 emissions scenario and a specific temperature target, such as the 1.5 ∘C target aimed for by the Paris Agreement. For that purpose, a suite of approaches for controlling the amount of direct CO2 injections at 3000 m water depth are implemented in an Earth system model of intermediate complexity.
Following the representative concentration pathway RCP4.5, which is a medium mitigation CO2 emissions scenario, cumulative CO2 injections required to meet the 1.5 ∘C climate goal are found to be 390 Gt C by the year 2100 and 1562 Gt C at the end of simulations, by the year 3020. The latter includes a cumulative leakage of 602 Gt C that needs to be reinjected in order to sustain the targeted global mean temperature.
CaCO3 sediment and weathering feedbacks reduce the required CO2 injections that comply with the 1.5 ∘C target by about 13 % in 2100 and by about 11 % at the end of the simulation.
With respect to the injection-related impacts we find that average pH values in the surface ocean are increased by about 0.13 to 0.18 units, when compared to the control run. In the model, this results in significant increases in potential coral reef habitats, i.e., the volume of the global upper ocean (0 to 130 m depth) with omega aragonite > 3.4 and ocean temperatures between 21 and 28 ∘C, compared to the control run. The potential benefits in the upper ocean come at the expense of strongly acidified water masses at depth, with maximum pH reductions of about −2.37 units, relative to preindustrial levels, in the vicinity of the injection sites. Overall, this study demonstrates that massive amounts of CO2 would need to be injected into the deep ocean in order to reach and maintain the 1.5 ∘C climate target in a medium mitigation scenario on a millennium timescale, and that there is a trade-off between injection-related reductions in atmospheric CO2 levels accompanied by reduced upper-ocean acidification and adverse effects on deep-ocean chemistry, particularly near the injection sites.
A global assessment of the vulnerability of shellfish aquaculture to climate change and ocean acidification
Published 17 March 2020 Science ClosedTags: globalmodeling, modeling, socio-economy
Human‐induced climate change and ocean acidification (CC‐OA) is changing the physical and biological processes occurring within the marine environment, with poorly understood implications for marine life. Within the aquaculture sector, molluskan culture is a relatively benign method of producing a high‐quality, healthy, and sustainable protein source for the expanding human population. We modeled the vulnerability of global bivalve mariculture to impacts of CC‐OA over the period 2020–2100, under RCP8.5. Vulnerability, assessed at the national level, was dependent on CC‐OA‐related exposure, taxon‐specific sensitivity and adaptive capacity in the sector. Exposure risk increased over time from 2020 to 2100, with ten nations predicted to experience very high exposure to CC‐OA in at least one decade during the period 2020–2100. Predicted high sensitivity in developing countries resulted, primarily, from the cultivation of species that have a narrow habitat tolerance, while in some European nations (France, Ireland, Italy, Portugal, and Spain) high sensitivity was attributable to the relatively high economic value of the shellfish production sector. Predicted adaptive capacity was low in developing countries primarily due to governance issues, while in some developed countries (Denmark, Germany, Iceland, Netherlands, Sweden, and the United Kingdom) it was linked to limited species diversity in the sector. Developing and least developed nations (n = 15) were predicted to have the highest overall vulnerability. Across all nations, 2060 was identified as a tipping point where predicted CC‐OA will be associated with the greatest challenge to shellfish production. However, rapid declines in mollusk production are predicted to occur in the next decade for some nations, notably North Korea. Shellfish culture offers human society a low‐impact source of sustainable protein. This research highlights, on a global scale, the likely extent and nature of the CC‐OA‐related threat to shellfish culture and this sector enabling early‐stage adaption and mitigation.
Year of emergence of ocean acidification in the global ocean
Published 24 February 2020 Science 1 CommentTags: globalmodeling, modeling
Year of emergence (YoE) is the year when an environment and the organisms within begin to experience significant different conditions (two times of natural variability) from the pre-industrial conditions (~1770 C.E.). This study calculates the global surface ocean YoEs for pH, partial pressure of CO(CO) and aragonite saturation (Ω) from a recent calculated surface ocean carbonate chemistry data product. The data product is calculated from the Surface Ocean CO Atlas version 6 (SOCATv6) with modeled CO changes in the global surface ocean from the ESM2M model. We find that CO, pH and Ω generally emerged from preindustrial conditions in the open ocean by the year 1950, while these properties have still not yet emerged along many ocean margins. We also find that Ω had a significantly delayed YoE compared to pH and CO. The delayed YoE for Ω is caused by its lasting sensitivity to temperature variability, which increases the natural variability experienced by organisms, and a partial cancellation of the long term acidification trend by the global warming. Together, YoEs presented here highlight that there are hotspots (open ocean) and coldspots (ocean margins that were impacted by boundary currents) for the emergence of anthropogenic signals. Continuous data collection and synthesis are needed to further examine the impact of ocean acidification on ecosystem health.
Continue reading ‘Year of emergence of ocean acidification in the global ocean’
Processes driving global interior ocean pH distribution
Published 7 February 2020 Science ClosedTags: chemistry, globalmodeling, modeling
Ocean acidification evolves on the background of a natural ocean pH gradient that is the result of the interplay between ocean mixing, biological production and remineralization, calcium carbonate cycling, and temperature and pressure changes across the water column. While previous studies have analyzed these processes and their impacts on ocean carbonate chemistry, none have attempted to quantify their impacts on interior ocean pH globally. Here we evaluate how anthropogenic changes and natural processes collectively act on ocean pH, and how these processes set the vulnerability of regions to future changes in ocean acidification. We use the mapped data product from the Global Ocean Data Analysis Project version 2, a novel method to estimate preformed total alkalinity based on a combination of a total matrix intercomparison and locally interpolated regressions, and a comprehensive uncertainty analysis. We find that the largest contribution to the interior ocean pH gradient comes from organic matter remineralization, with CaCO3 cycling being the second most important process. The estimates of the impact of anthropogenic CO2 changes on pH reaffirm the large and well‐understood anthropogenic impact on pH in the surface ocean, and put it in the context of the natural pH gradient in the interior ocean. We also show that in the depth layer 500–1,500 m natural processes enhance ocean acidification by on average 28 ± 15%, but with large regional gradients.
Continue reading ‘Processes driving global interior ocean pH distribution’
Increase in ocean acidity variability and extremes under increasing atmospheric CO2
Published 28 January 2020 Science ClosedTags: globalmodeling, modeling
Ocean acidity extreme events are short-term periods of extremely high [H+] concentrations. The uptake of anthropogenic CO2 emissions by the ocean is expected to lead to more frequent and intense ocean acidity extreme events, not only due to mean ocean acidification, but also due to increases in ocean acidity variability. Here, we use daily output from ensemble simulations of a comprehensive Earth system model under a low and high CO2 emission scenario to isolate and quantify the impact of changes in variability on changes in ocean acidity extremes. We show that the number of days with extreme [H+] conditions for surface waters is projected to increase by a factor of 14 by the end of the 21st century under a high CO2 emission scenario relative to preindustrial levels. The duration of individual events is projected to triple, and the maximal intensity and the volume extent in the upper 200 m to quintuple. Similar changes are projected in the thermocline. At surface, the changes are mainly driven by increases in [H+] seasonality, whereas changes in interannual variability are also important in the thermocline. Increases in [H+] variability and extremes arise predominantly from increases in the sensitivity of [H+] to variations in its drivers. In contrast to [H+] extremes, the occurrence of short-term extremes in low aragonite saturation state due to changes in variability is projected to decrease. An increase in [H+] variability and an associated increase in extreme events superimposed onto the long-term ocean acidification trend will enhance the risk of severe and detrimental impacts on marine organisms, especially for those that are adapted to a more stable environment.
Twenty-first century ocean warming, acidification, deoxygenation, and upper ocean nutrient decline from CMIP6 model projections
Published 27 January 2020 Science ClosedTags: globalmodeling, modeling
Anthropogenic climate change leads to ocean warming, acidification, deoxygenation and reductions in near-surface nutrient concentrations, all of which are expected to affect marine ecosystems. Here we assess projections of these drivers of environmental change over the twenty-first century from Earth system models (ESMs) participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6) that were forced under the CMIP6 Shared Socioeconomic Pathways (SSPs). Projections are compared to those from the previous generation (CMIP5) forced under the Representative Concentration Pathways (RCPs). 10 CMIP5 and 13 CMIP6 models are used in the two multi-model ensembles. Under the high-emission scenario SSP5–8.5, the model mean change (2080–2099 mean values relative to 1870–1899) in sea surface temperature, surface pH, subsurface (100–600 m) oxygen concentration and euphotic (0–100 m) nitrate concentration is +3.48 ± 0.78 °C, −0.44 ± 0.005, −13.27 ± 5.28 mmol m−3 and −1.07 ± 0.45 mmol m−3, respectively. Under the low-emission, high-mitigation scenario SSP1–2.6, the corresponding changes are +1.42 ± 0.32 °C, −0.16 ± 0.002, −6.36 ± 2.92 mmol m−3 and −0.53 ± 0.23 mmol m−3. Projected exposure of the marine ecosystem to these drivers of ocean change depends largely on the extent of future emissions, consistent with previous studies. The Earth system models in CMIP6 generally project greater surface warming, acidification, deoxygenation and euphotic nitrate reductions than those from CMIP5 under comparable radiative forcing, with no reduction in inter-model uncertainties. Under the high-emission CMIP5 scenario RCP8.5, the corresponding changes in sea surface temperature, surface pH, subsurface oxygen and euphotic nitrate concentration are +3.04 ± 0.62 °C, −0.38 ± 0.005, −9.51 ± 2.13 mmol m−3 and −0.66 ± 0.49 mmol m−3, respectively. The greater surface acidification in CMIP6 is primarily a consequence of the SSPs having higher associated atmospheric CO2 concentrations than their RCP analogues. The increased projected warming results from a general increase in the climate sensitivity of CMIP6 models relative to those of CMIP5. This enhanced warming results in greater increases in upper ocean stratification in CMIP6 projections, which contributes to greater reductions in euphotic nitrate and subsurface oxygen ventilation.
