Posts Tagged 'globalmodeling'

The potential impact of nuclear conflict on ocean acidification

We demonstrate that the global cooling resulting from a range of nuclear conflict scenarios would temporarily increase the pH in the surface ocean by up to 0.06 units over a 5‐year period, briefly alleviating the decline in pH associated with ocean acidification. Conversely, the global cooling dissolves atmospheric carbon into the upper ocean, driving a 0.1 to 0.3 unit decrease in the aragonite saturation state (Ωarag) that persists for ~10 years. The peak anomaly in pH occurs 2 years post‐conflict, while the Ωarag anomaly peaks 4‐5 years post‐conflict. The decrease in Ωarag would exacerbate a primary threat of ocean acidification: the inability of marine calcifying organisms to maintain their shells/skeletons in a corrosive environment. Our results are based on sensitivity simulations conducted with a state‐of‐the‐art Earth system model integrated under various black carbon (soot) external forcings. Our findings suggest that regional nuclear conflict may have ramifications for global ocean acidification.

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Potential predictability of marine ecosystem drivers

Climate variations can have profound impacts on marine ecosystems and the socio-economic 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 modelling 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 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 to more than 10 years below the thermocline, except in the tropical Pacific and Indian Ocean, where predictability is also three to five 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.

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The magnitude of surface ocean acidification and carbon release during Eocene Thermal Maximum 2 (ETM‐2) and the Paleocene–Eocene Thermal Maximum (PETM)

Eocene Thermal Maximum 2 (ETM‐2; 54.1 Ma) was the second largest Eocene hyperthermal. Like the Paleocene–Eocene Thermal Maximum (PETM), ETM‐2 was characterized by massive carbon emissions and several degrees of global warming, thus can serve as a case study for assessing the impacts of rapid CO2 emissions on ocean carbonate chemistry, biota and climate. Marine carbonate records of ETM‐2 are better preserved than those of the PETM due to more subdued carbonate dissolution. As yet, however, the magnitude of this carbon cycle perturbation has not been well constrained. Here, we present the first records of surface ocean acidification for ETM‐2, based on stable boron isotope records in mixed‐layer planktic foraminifera from two mid‐latitude ODP Sites (1210 in the N. Pacific and 1265 in the S.E. Atlantic), which indicate conservative minimum global sea surface acidification of –0.20 +0.12/–0.13 pH units. Using these estimates of pH and temperature as constraints on carbon cycle model simulations, we conclude that the total mass of C, released over a period of 15 to 25 kyr during ETM‐2, likely ranged from 2,600 to 3,800 Gt C, which is greater than previously estimated on the basis of other observations (i.e., stable carbon isotopes and carbonate compensation depth) alone.

Continue reading ‘The magnitude of surface ocean acidification and carbon release during Eocene Thermal Maximum 2 (ETM‐2) and the Paleocene–Eocene Thermal Maximum (PETM)’

Reduced CaCO3 flux to the seafloor and weaker bottom current speeds curtail benthic CaCO3 dissolution over the 21st century

Results from a range of Earth System and climate models of various resolution run under high‐CO2 emission scenarios challenge the paradigm that seafloor CaCO3 dissolution will grow in extent and intensify as ocean acidification develops over the next century. Under the “business as usual,” RCP8.5 scenario, CaCO3 dissolution increases in some areas of the deep ocean, such as the eastern central Pacific Ocean, but is projected to decrease in the Northern Pacific and abyssal Atlantic Ocean by the year 2100. The flux of CaCO3 to the seafloor and bottom‐current speeds, both of which are expected to decrease globally through the 21st century, govern changes in benthic CaCO3 dissolution rates over 53% and 31% of the dissolving seafloor, respectively. Below the calcite compensation depth, a reduced CaCO3 flux to the CaCO3‐free seabed modulates the amount of CaCO3 material dissolved at the sediment‐water interface. Slower bottom‐water circulation leads to thicker diffusive boundary layers above the sediment bed and a consequent stronger transport barrier to CaCO3 dissolution. While all investigated models predict a weakening of bottom current speeds over most of the seafloor by the end of the 21st century, strong discrepancies exist in the magnitude of the predicted speeds. Overall, the poor performance of most models in reproducing modern bottom‐water velocities and CaCO3 rain rates coupled with the existence of large disparities in predicted bottom‐water chemistry across models hampers our ability to robustly estimate the magnitude and temporal evolution of anthropogenic CaCO3 dissolution rates and the associated anthropogenic CO2 neutralization.

Continue reading ‘Reduced CaCO3 flux to the seafloor and weaker bottom current speeds curtail benthic CaCO3 dissolution over the 21st century’

Attributing ocean acidification to major carbon producers

Recent research has quantified the contributions of CO2 and CH4 emissions traced to the products of major fossil fuel companies and cement manufacturers to global atmospheric CO2, surface temperature, and sea level rise. This work has informed societal considerations of the climate responsibilities of these major industrial carbon producers. Here, we extend this work to historical (1880–2015) and recent (1965–2015) acidification of the world’s ocean. Using an energy balance carbon-cycle model, we find that emissions traced to the 88 largest industrial carbon producers from 1880–2015 and 1965–2015 have contributed ~55% and ~51%, respectively, of the historical 1880–2015 decline in surface ocean pH. As ocean acidification is not spatially uniform, we employ a three-dimensional ocean model and identify five marine regions with large declines in surface water pH and aragonite saturation state over similar historical (average 1850–1859 to average 2000–2009) and recent (average 1960–1969 to average of 2000–2009) time periods. We characterize the biological and socioeconomic systems in these regions facing loss and damage from ocean acidification in the context of climate change and other stressors. Such analysis can inform societal consideration of carbon producer responsibility for current and near-term risks of further loss and damage to human communities dependent on marine ecosystems and fisheries vulnerable to ocean acidification.

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Surface ocean pH and buffer capacity: past, present and future

The ocean’s chemistry is changing due to the uptake of anthropogenic carbon dioxide (CO2). This phenomenon, commonly referred to as “Ocean Acidification”, is endangering coral reefs and the broader marine ecosystems. In this study, we combine a recent observational seawater CO2 data product, i.e., the 6th version of the Surface Ocean CO2 Atlas (1991–2018, ~23 million observations), with temporal trends at individual locations of the global ocean from a robust Earth System Model to provide a high-resolution regionally varying view of global surface ocean pH and the Revelle Factor. The climatology extends from the pre-Industrial era (1750 C.E.) to the end of this century under historical atmospheric CO2 concentrations (pre-2005) and the Representative Concentrations Pathways (post-2005) of the Intergovernmental Panel on Climate Change (IPCC)’s 5th Assessment Report. By linking the modeled pH trends to the observed modern pH distribution, the climatology benefits from recent improvements in both model design and observational data coverage, and is likely to provide improved regional OA trajectories than the model output could alone, therefore, will help guide the regional OA adaptation strategies. We show that air-sea CO2 disequilibrium is the dominant mode of spatial variability for surface pH, and discuss why pH and calcium carbonate mineral saturation states, two important metrics for OA, show contrasting spatial variability.

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Strong time dependence of ocean acidification mitigation by atmospheric carbon dioxide removal

In Paris in 2015, the global community agreed to limit global warming to well below 2 ∘C, aiming at even 1.5 ∘C. It is still uncertain whether these targets are sufficient to preserve marine ecosystems and prevent a severe alteration of marine biogeochemical cycles. Here, we show that stringent mitigation strategies consistent with the 1.5 ∘C scenario could, indeed, provoke a critical difference for the ocean’s carbon cycle and calcium carbonate saturation states. Favorable conditions for calcifying organisms like tropical corals and polar pteropods, both of major importance for large ecosystems, can only be maintained if CO2 emissions fall rapidly between 2025 and 2050, potentially requiring an early deployment of CO2 removal techniques in addition to drastic emissions reduction. Furthermore, this outcome can only be achieved if the terrestrial biosphere remains a carbon sink during the entire 21st century.

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Ocean acidification in the IPCC AR5 WG II

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