A comprehensive quantification of global nitrous oxide sources and sinks

Nitrous oxide (N2O), like carbon dioxide, is a long-lived greenhouse gas that accumulates in the atmosphere. Over the past 150 years, increasing atmospheric N2O concentrations have contributed to stratospheric ozone depletion1 and climate change2, with the current rate of increase estimated at 2 per cent per decade. Existing national inventories do not provide a full picture of N2O emissions, owing to their omission of natural sources and limitations in methodology for attributing anthropogenic sources. Here we present a global N2O inventory that incorporates both natural and anthropogenic sources and accounts for the interaction between nitrogen additions and the biochemical processes that control N2O emissions. We use bottom-up (inventory, statistical extrapolation of flux measurements, process-based land and ocean modelling) and top-down (atmospheric inversion) approaches to provide a comprehensive quantification of global N2O sources and sinks resulting from 21 natural and human sectors between 1980 and 2016. Global N2O emissions were 17.0 (minimum–maximum estimates: 12.2–23.5) teragrams of nitrogen per year (bottom-up) and 16.9 (15.9–17.7) teragrams of nitrogen per year (top-down) between 2007 and 2016. Global human-induced emissions, which are dominated by nitrogen additions to croplands, increased by 30% over the past four decades to 7.3 (4.2–11.4) teragrams of nitrogen per year. This increase was mainly responsible for the growth in the atmospheric burden. Our findings point to growing N2O emissions in emerging economies—particularly Brazil, China and India. Analysis of process-based model estimates reveals an emerging N2O–climate feedback resulting from interactions between nitrogen additions and climate change. The recent growth in N2O emissions exceeds some of the highest projected emission scenarios3,4, underscoring the urgency to mitigate N2O emissions

Probabilistic assessments of the marine biogeochemical cycles of calcium carbonate, nitrous oxide, and oxygen

The current anthropogenic perturbation to the carbon cycle and resulting climate change is expected to have profound implications for biogeochemical cycling, ecosystem dynamics, and human livelihood. Quantification of biogeochemical cycles and their feedbacks to climate are usually hampered by sparse observational datasets, such that biogeochemical flux estimates usually come with large uncertainties. In this thesis, marine biogeochemical studies on calcium carbonate (CaCO3), nitrous oxide (N2O), and oxygen (O2) are presented relying on Bayesian, probabilistic ensemble approaches with the Bern3D Earth System Model of Intermediate Complexity (EMIC). Export and dissolution fluxes of CaCO3, and emissions of N2O including their uncertainties are estimated for modern ocean conditions. In addition, the long-term evolution of different Earth system variables are investigated with a focus on ocean deoxygenation. Given the long residence time of anthropogenic CO2 in the atmosphere, and long equilibration timescale of the ocean overturning circulation, such multi-millennial, ensemble perspectives are required when dealing with Earth system feedbacks and climate-related ocean hazards (Chapter 1). The Bern3D EMIC used in this thesis is a cost-efficient, three-dimensional, dynamic ocean model coupled to a two-dimensional energy and moisture balance model of the atmosphere, and to a marine biogeochemistry module. It is designed for ensemble simulations recognizing parameter uncertainty, and for long-term, multi-millennial projections of Earth system variables. The probabilistic approach judges model versions with small deviations from available observations more probable than models with large deviations from the observations (Chapter 2). CaCO3 cycling in the ocean is an important element of the global carbon cycle as it co-governs the distribution of carbon and alkalinity in the water column. Chapter 3, published in Biogeosciences, presents a probabilistic, quantitative assessment of the cycling of CaCO3 and constrains CaCO3 export fluxes out of the surface ocean, dissolution within the water column, and the flux to the ocean floor with observations. In this assessment, different observational data, the influence of ocean-sediment interactions, and ocean transport uncertainties are considered. Three main findings emerged. First, observation-constrained CaCO3 export is large in the Southern Ocean, the tropical Indo-Pacific, the northern Pacific and relatively small in the Atlantic. Second, dissolution within the 200 to 1500 m depth range is substantially lower than inferred in previous studies. These earlier estimates rest on a widely used method that neglects physical tracer transport. As such, their estimates are likely biased high. Third, parameters and mechanisms governing water column dissolution are hardly constrained by currently 4 available observational datasets. Consequently, simple saturation-independent dissolution rate parameterization may be applied in Earth system models to minimize computational costs. N2O is an atmospheric greenhouse gas, and variations in its atmospheric concentration are informative of nitrogen and carbon cycle processes in terrestrial and marine systems. In recognition of recent observational evidence, a new parameterization for marine N2O pathways from nitrification and denitrification is developed in Chapter 4. A range of observational data is used in a Bayesian, probabilistic framework to constrain modern net N2O production based on a 1,000-member ensemble of the Bern3D model. To our knowledge, it is the first time that N2O fluxes from explicit denitrification and nitrification are included in a 3D ocean model. The observation-constrained results narrow the range in N2O emissions considerably compared to the most recent assessment by IPCC. Results are consistent with the global N2O budget and estimates of total denitrification. Probabilistic projections over the 21st century and the next 8,000 years reveal intricate, transient interactions between the marine carbon cycle, N2O, oxygen, and climate. For example, O2 minimum zones are projected to expand in volume, and the oceanic O2 inventory is projected to decrease by approximately a factor of two within the next 2,000 years, with surprisingly small impacts on marine N2O emissions and related N2O-climate feedbacks. As an ongoing follow-up study, marine emissions of N2O have been investigated for the Last Glacial Maximum climate state and past climate changes. New high-resolution ice core reconstructions of atmospheric N2O and its isotopes are available for model evaluation. Understanding of atmospheric N2O variations offers an additional constraint on glacial-interglacial change. The hazard of decreasing marine oxygen and changes in metabolic viability due to anthropogenic climate change are further analyzed in Chapter 5. The Bern3D simulations reveal that the long-term fate of oceanic oxygen is characterized by an initial decline followed by a recovery phase, with the peak decline occurring long after the end of the 21st century. For business as usual scenarios, the ocean oxygen content is projected to decrease by 40% over the next thousand years. This would likely have severe consequences for marine life. Global warming and oxygen loss are linked and meeting the warming target of the Paris climate agreement effectively limits related marine hazards. Marine hazards from warming and deoxygenation add to the list of long-term Earth system commitments including acidification and sea-level rise. A large number of physical and biogeochemical tracers can be investigated in probabilistic applications with the Bern3D model on multi-millennial timescales. Simulations and reconstructions of past climate change can be used for process understanding and model evaluation, and to put anthropogenic climate change into perspective. Many international model intercomparison projects exist which should be used in future studies to evaluate model robustness (Chapter 6)

Hazards of decreasing marine oxygen: the near-term and millennial-scale benefits of meeting the Paris climate targets

Abstract. Ocean deoxygenation is recognized as key ecosystem stressor of the future ocean and associated climate-related ocean risks are relevant for current policy decisions. In particular, benefits of reaching the ambitious 1.5 °C warming target mentioned by the Paris Agreement compared to higher temperature targets are of high interest. Here, we model oceanic oxygen, warming and their compound hazard in terms of metabolic conditions on multi-millennial timescales for a range of equilibrium temperature targets. Scenarios where radiative forcing is stabilized by 2300 are used in ensemble simulations with the Bern3D Earth System Model of Intermediate Complexity. Transiently, the global mean ocean oxygen concentration decreases by a few percent under low forcing and by 40 % under high forcing. Deoxygenation peaks about a thousand years after stabilization of radiative forcing and new steady-state conditions are established after AD 8000 in our model. Hypoxic waters expand over the next millennium and recovery is slow and remains incomplete under high forcing. Largest transient decreases in oxygen are projected for the deep sea. Distinct and near-linear relationships between the equilibrium temperature response and marine O₂ loss emerge. These point to the effectiveness of the Paris climate target in reducing marine hazards and risks. Mitigation measures are projected to reduce peak decreases in oceanic oxygen inventory by 4.4 % °C⁻¹ of avoided equilibrium warming. In the upper ocean, the decline of a metabolic index, quantified by the ratio of O₂ supply to an organism's O₂ demand, is reduced by 6.2 % °C⁻¹ of avoided equilibrium warming. Definitions of peak hypoxia demonstrate strong sensitivity to additional warming. Volumes of water with less than 50 mmol O₂ m⁻³, for instance, increase between 36 % and 76 % °C⁻¹ of equilibrium temperature response. Our results show that millennial-scale responses should be considered in assessments of ocean deoxygenation and associated climate-related ocean risks. Peak hazards occur long after stabilization of radiative forcing and new steady-state conditions establish after AD 8000

Marine N₂O Emissions From Nitrification and Denitrification Constrained by Modern Observations and Projected in Multimillennial Global Warming Simulations

Nitrous oxide (N₂O) is a potent greenhouse gas (GHG) and ozone destructing agent; yet global estimates of N₂O emissions are uncertain. Marine N₂O stems from nitrification and denitrification processes which depend on organic matter cycling and dissolved oxygen (O₂). We introduce N₂O as an obligate intermediate product of denitrification and as an O₂-dependent by-product from nitrification in the Bern3D ocean model. A large model ensemble is used to probabilistically constrain modern and to project marine N₂O production for a low (Representative Concentration Pathway (RCP)2.6) and high GHG (RCP8.5) scenario extended to A.D. 10,000. Water column N₂O and surface ocean partial pressure N₂O data serve as constraints in this Bayesian framework. The constrained median for modern N₂O production is 4.5 (±1σ range: 3.0 to 6.1) Tg N yr⁻¹, where 4.5% stems from denitrification. Modeled denitrification is 65.1 (40.9 to 91.6) Tg N yr⁻¹, well within current estimates. For high GHG forcing, N2O production decreases by 7.7% over this century due to decreasing organic matter export and remineralization. Thereafter, production increases slowly by 21% due to widespread deoxygenation and high remineralization. Deoxygenation peaks in two millennia, and the global O₂ inventory is reduced by a factor of 2 compared to today. Net denitrification is responsible for 7.8% of the long-term increase in N2O production. On millennial timescales, marine N₂O emissions constitute a small, positive feedback to climate change. Our simulations reveal tight coupling between the marine carbon cycle, O₂, N₂O, and climate

Influence of a specific aquatic adapted physical activity in a child with Autism Spectrum Disorders: A case study

Aquatic environment offers an exciting and motivating place for children and aquatic exercise programs provide an appropriate setting for early educational interventions in individuals with autism spectrum disorders (ASD). The purpose of this study was to examine the effects of a specific Multi-systemic Aquatic Therapy (CI-MAT) on gross motor and adaptive skills in a child with ASD. The study was divided into three phases: baseline, 12-week CI-MAT program and Post-Test. Child was administered a battery of tests incorporating anthropometric measurements, gross motor development test (TGM test), Vineland Adaptive Behavior Scales (VABS) and Psychoeducational Profile (PEP-3) before and after a 12-week CI-MAT program. The child improved locomotor and object control skills after CI-MAT program. Concerning social behaviors, the higher proportion of gains was observed in the sensitivity of other\u2019s presence and eye contact for the contact domain and in the comply turn for the domain relationship. Furthermore, after the CI-MAT program period, the child showed improvements in his social behaviors. The results of this study showed that CI-MAT program was effective for the development of gross-motor and social skills in a child with ASD. Moreover, there is an urge to carry out a whole psychological assessment targeting both motor and adaptive development suitable to provide educational and vocational plans of exercises for people with ASD

Influence of a Specific Aquatic Program on Social and Gross Motor Skills in Adolescents with Autism Spectrum Disorders: Three Case Reports

Swimming pool activities revealed to be efficacious to train psychomotor skills and increase adaptive behaviors in children with Autism Spectrum Disorders (ASD). Therefore, the purpose of this study was to investigate the efficacy of a specific multi-systemic aquatic therapy (CI-MAT) on gross motor and social skills in three adolescents with Autism Spectrum Disorders (ASD). Methods: three adolescents with ASD of which two boys (M1 with a chronological age of 10.3 years and a mental age of 4.7 years; M2 with a chronological age of 14.6 and a mental age inferior to 4 years) and one girl (chronological age of 14.0 and a mental age inferior to 4 years). The study was divided into three phases: baseline, 12-week CI-MAT program and Post-Test. Participants were administered a battery of tests incorporating anthropometric measurements, gross motor development test and a social skills questionnaire before and after a 12-week MAT-CI program. Results: Subjects improved locomotors and object control skills following the CI-MAT program in a different way. Concerning social behaviors, the higher proportion of gains was observed in the sensitivity of other’s presence and eye contact, for the contact domain, and in the comply turn for the relationship domain. Conclusions: The results of this study showed that the CI-MAT program was effective for the development of gross-motor skills and social behaviors in subjects with ASD. Moreover there is an urge to carry out a whole psychological assessment targeting both motor and adaptive development suitable to provide educational and vocational plans of exercises for people with ASD

Low terrestrial carbon storage at the Last Glacial Maximum: constraints from multi-proxy data

International audienceAbstract. Past changes in the inventory of carbon stored in vegetation and soils remain uncertain. Earlier studies inferred the increase in the land carbon inventory (Δland) between the Last Glacial Maximum (LGM) and the preindustrial period (PI) based on marine and atmospheric stable carbon isotope reconstructions, with recent estimates yielding 300–400 GtC. Surprisingly, however, earlier studies considered a mass balance for the ocean–atmosphere–land biosphere system only. Notably, these studies neglect carbon exchange with marine sediments, weathering–burial flux imbalances, and the influence of the transient deglacial reorganization on the isotopic budgets. We show this simplification to significantly reduce Δland in simulations using the Bern3D Earth System Model of Intermediate Complexity v.2.0s. We constrain Δland to ∼850 GtC (median estimate; 450 to 1250 GtC ±1SD) by using reconstructed changes in atmospheric δ13C, marine δ13C, deep Pacific carbonate ion concentration, and atmospheric CO2 as observational targets in a Monte Carlo ensemble with half a million members. It is highly unlikely that the land carbon inventory was larger at LGM than PI. Sensitivities of the target variables to changes in individual deglacial carbon cycle processes are established from transient factorial simulations with the Bern3D model. These are used in the Monte Carlo ensemble and provide forcing–response relationships for future model–model and model–data comparisons. Our study demonstrates the importance of ocean–sediment interactions and burial as well as weathering fluxes involving marine organic matter to explain deglacial change and suggests a major upward revision of earlier isotope-based estimates of Δland

Marine N₂O emissions during a Younger Dryas-like event: the role of meridional overturning, tropical thermocline ventilation, and biological productivity

Past variations in atmospheric nitrous oxide (N₂O) allow important insight into abrupt climate events. Here, we investigate marine N₂O emissions by forcing the Bern3D Earth System Model of Intermediate Complexity with freshwater into the North Atlantic. The model simulates a decrease in marine N₂O emissions of about 0.8 TgN yr⁻¹ followed by a recovery, in reasonable agreement regarding timing and magnitude with isotope-based reconstructions of marine emissions for the Younger Dryas Northern Hemisphere cold event. In the model the freshwater forcing causes a transient near-collapse of the Atlantic Meridional Overturning Circulation (AMOC)leading to a fast adjustment in thermocline ventilation and an increase in O₂ in tropical eastern boundary systems and in the tropical Indian Ocean. In turn, net production by nitrification and denitrification and N₂O emissions decrease in these regions. The decrease in organic matter export, mainly in the North Atlantic where ventilation and nutrient supply is suppressed, explains the remaining emission reduction. Modeled global marine N₂O production and emission changes are delayed, initially by up to 300 years, relative to the AMOC decrease, but by less than 50 years at peak decline. The N₂O perturbation is recovering only slowly and the lag between the recovery in AMOC and the recovery in N₂O emissions and atmospheric concentrations exceeds 400 years. Thus, our results suggest a century-scale lag between ocean circulation and marine N₂O emissions, and a tight coupling between changes in AMOC and tropical thermocline ventilation

Low terrestrial carbon storage at the Last Glacial Maximum: constraints from multi-proxy data

Past changes in the inventory of carbon stored in vegetation and soils remain uncertain. Earlier studies inferred the increase in the land carbon inventory (Δland) between the Last Glacial Maximum (LGM) and the preindustrial period (PI) based on marine and atmospheric stable carbon isotope reconstructions, with recent estimates yielding 300–400 GtC. Surprisingly, however, earlier studies considered a mass balance for the ocean–atmosphere–land biosphere system only. Notably, these studies neglect carbon exchange with marine sediments, weathering–burial flux imbalances, and the influence of the transient deglacial reorganization on the isotopic budgets. We show this simplification to significantly reduce Δland in simulations using the Bern3D Earth System Model of Intermediate Complexity v.2.0s. We constrain Δland to ∼850 GtC (median estimate; 450 to 1250 GtC ±1SD) by using reconstructed changes in atmospheric δ13C, marine δ13C, deep Pacific carbonate ion concentration, and atmospheric CO2 as observational targets in a Monte Carlo ensemble with half a million members. It is highly unlikely that the land carbon inventory was larger at LGM than PI. Sensitivities of the target variables to changes in individual deglacial carbon cycle processes are established from transient factorial simulations with the Bern3D model. These are used in the Monte Carlo ensemble and provide forcing–response relationships for future model–model and model–data comparisons. Our study demonstrates the importance of ocean–sediment interactions and burial as well as weathering fluxes involving marine organic matter to explain deglacial change and suggests a major upward revision of earlier isotope-based estimates of Δland