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Glacial deep ocean deoxygenation driven by biologically mediated air–sea disequilibrium

Abstract.

"Deep ocean deoxygenation inferred from proxies has been used to support the hypothesis that a lower atmospheric carbon dioxide during glacial times was due to an increase in the strength of the ocean’s biological pump. This relies on the assumption that surface ocean oxygen (O2) is equilibrated with the atmosphere such that any O2 deficiency observed in deep waters is a result of organic matter respiration, which consumes O2 and produces dissolved inorganic carbon. However, this assumption has been shown to be imperfect because of disequilibrium. Here we used an Earth system[...]"

 

Source: Nature Geoscience 
Authors: Ellen Cliff et al.
DOI: https://doi.org/10.1038/s41561-020-00667-z

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The role of environmental factors in the long-term evolution of the marine biological pump

Abstract.

"The biological pump—the transfer of atmospheric carbon dioxide to the ocean interior and marine sediments as organic carbon—plays a critical role in regulating the long-term carbon cycle, atmospheric composition and climate. Despite its centrality in the Earth system, the response of the biological pump to biotic innovation and climatic fluctuations through most stages of Earth’s history has been largely conjectural. Here we use a mechanistic model of the biological carbon pump to revisit the factors controlling the transfer efficiency of carbon from surface waters to the ocean interior and marine sediments[...]".

 

Source: Nature Geoscience 
Authours: Mojtaba Fakhraee et al.
DOI: https://doi.org/10.1038/s41561-020-00660-6

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Glacial heterogeneity in Southern Ocean carbon storage abated by fast South Indian deglacial carbon release

Abstract.

"Past changes in ocean 14C disequilibria have been suggested to reflect the Southern Ocean control on global exogenic carbon cycling. Yet, the volumetric extent of the glacial carbon pool and the deglacial mechanisms contributing to release remineralized carbon, particularly from regions with enhanced mixing today, remain insufficiently constrained. Here, we reconstruct the deglacial ventilation history of the South Indian upwelling hotspot near Kerguelen Island, using high-resolution 14C-dating of smaller-than-conventional foraminiferal samples and multi-proxy deep-ocean oxygen[...]"

 

Source: Nature Communications 
Authors: Julia Gottschalk et al.
DOI: https://doi.org/10.1038/s41467-020-20034-1

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Permian–Triassic mass extinction pulses driven by major marine carbon cycle perturbations

Abstract.

"The Permian/Triassic boundary approximately 251.9 million years ago marked the most severe environmental crisis identified in the geological record, which dictated the onwards course for the evolution of life. Magmatism from Siberian Traps is thought to have played an important role, but the causational trigger and its feedbacks are yet to be fully understood. Here we present a new boron-isotope-derived seawater pH record from fossil brachiopod shells deposited on the Tethys shelf that demonstrates a substantial decline in seawater pH coeval with the onset of the mass extinction in the latest Permian. Combined with carbon isotope data, our results are integrated in a geochemical model that resolves the carbon cycle dynamics as well as the ocean redox conditions[...]"

Source: Nature Geoscience
Authors: Hana Jurikova et al.
DOI: https://doi.org/10.1038/s41561-020-00646-4

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Heat and carbon coupling reveals ocean warming due to circulation changes

Abstract.

Anthropogenic global surface warming is proportional to cumulative carbon emissions1,2,3; this relationship is partly determined by the uptake and storage of heat and carbon by the ocean4. The rates and patterns of ocean heat and carbon storage are influenced by ocean transport, such as mixing and large-scale circulation5,6,7,8,9,10. However, existing climate models do not accurately capture the observed patterns of ocean warming, with a large spread in their projections of ocean circulation and ocean heat uptake8,11. Additionally, assessing the influence of ocean circulation changes (specifically, the redistribution of heat by resolved advection) on patterns[...]"

Source: Nature
Authors: Ben Bronselaer et al.
DOI: https://doi.org/10.1038/s41586-020-2573-5

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An ice–climate oscillatory framework for Dansgaard–Oeschger cycles

Abstract.

"Intermediate glacial states were characterized by large temperature changes in Greenland and the North Atlantic, referred to as Dansgaard–Oeschger (D–O) variability, with some transitions occurring over a few decades. D–O variability included changes in the strength of the Atlantic meridional overturning circulation (AMOC), temperature changes of opposite sign and asynchronous timing in each hemisphere, shifts in the mean position of the Intertropical Convergence Zone and variations in atmospheric CO2[...]"

 

Source: Nature Reviews Earth and Environment
Authors: Laurie C. Menviel et al.
DOI: https://doi.org/10.1038/s43017-020-00106-y

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Organic Carbon Export and Loss Rates in the Red Sea

Abstract.

"The export and fate of organic carbon in the mesopelagic zone are still poorly understood and quantified due to lack of observations. We exploited data from a biogeochemical‐Argo float that was deployed in the Red Sea to study how a warm and hypoxic environment can affect the fate of the organic carbon in the ocean's interior. We observed that only 10% of the particulate organic carbon (POC) exported survived at depth due to remineralization processes[...]"

 

Source: Global Biogeochemical Cycles
Authors: Malika Kheireddine et al.
DOI: https://doi.org/10.1029/2020GB006650

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The role of calcium in regulating marine phosphorus burial and atmospheric oxygen

Abstract.

"The marine phosphorus cycle plays a critical role in controlling the extent of global primary productivity and thus atmospheric pO2 on geologic time scales. However, previous attempts to model carbon–phosphorus-oxygen feedbacks have neglected key parameters that could shape the global P cycle. Here we present new diagenetic models to fully parameterize marine P burial. We have also coupled this diagenetic framework to a global carbon cycle model. We find that seawater calcium concentration, by strongly influencing carbonate fluorapatite (CFA) formation, is a key factor controlling global phosphorus cycling, and therefore plays[...]"

 

Source: Nature Communications 
Authors: Mingyu Zhao et al.
DOI: https://doi.org/10.1038/s41467-020-15673-3

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Ocean Carbon Uptake Under Aggressive Emission Mitigation

Abstract.

"Nearly every nation has signed the UNFCC Paris Agreement, committing to mitigate global anthropogenic carbon (Cant) emissions and limit global mean temperature increase to 1.5 °C. A consequence of emission mitigation is reduced efficiency of ocean Cant uptake, which is driven by mechanisms that have not been studied in detail. The historical pattern of continual increase in atmospheric CO2 has resulted in a proportional increase in Cant uptake. [...]"

Source: Biogeosciences
Authors: Sean Ridge and Galen McKinley
DOI: 10.5194/bg-2020-254

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Autotrophic Carbon Fixation Pathways Along the Redox Gradient in Oxygen‐Depleted Oceanic Waters

Abstract.

"Anoxic marine zones (AMZs), also known as ‘oxygen‐deficient zones’, contribute to the loss of fixed nitrogen from the ocean by anaerobic microbial processes. While these microbial processes associated with the nitrogen cycle have been extensively studied, those linked to the carbon cycle in AMZs have received much less attention, particularly the autotrophic carbon fixation —a crucial component of the carbon cycle. [...]"

Source: Environmental Microbiology Reports
Authors: Paula Ruiz‐Fernández et al.
DOI: 10.1111/1758-2229.12837

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