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Changing carbon-to-nitrogen ratios of organic-matter export under ocean acidification

Abstract.

"Ocean acidification (OA) will affect marine biotas from the organism to the ecosystem level. Yet, the consequences for the biological carbon pump and thereby the oceanic sink for atmospheric CO2 are still unclear. Here we show that OA considerably alters the C/N ratio of organic-matter export (C/Nexport), a key factor determining efficiency of the biological pump. By synthesizing sediment-trap data from in situ mesocosm studies in different marine biomes[...]

 

Source: Nature Climate Change 
Authors: Jan Taucher et al.
DOI:https://doi.org/10.1038/s41558-020-00915-5

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Calibration of temperature-dependent ocean microbial processes in the cGENIE.muffin (v0.9.13) Earth system model

Abstract.

"Temperature is a master parameter in the marine carbon cycle, exerting a critical control on the rate of biological transformation of a variety of solid and dissolved reactants and substrates. Although in the construction of numerical models of marine carbon cycling, temperature has been long recognised as a key parameter in the production and export of organic matter at the ocean surface, its role in the ocean interior is much less frequently accounted for. There, bacteria (primarily) transform sinking particulate organic matter (POM) into its dissolved constituents and consume dissolved oxygen (and/or other electron acceptors such as sulfate). The nutrients and carbon[...]"

 

Source: EGU- European Geosciences Union 
Authors: Katherine A. Crichton
DOI: https://doi.org/10.5194/gmd-14-125-2021

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Triple Oxygen Isotopes in Silica–Water and Carbonate–Water Systems

Abstract.

"The field of stable isotope geochemistry began with the recognition that the oxygen isotope composition of ancient carbonates could be used as a paleothermometer (Urey 1947; Urey et al. 1951). As stated by Urey (1947), “Accurate determinations of the Ol8 content of carbonate rocks could be used to determine the temperature at which they were formed”. This concept was based on the temperature dependence for the oxygen isotope fractionation between calcite and water. Urey realized that if a mass spectrometer with sufficient precision could be built, a method of reproducibly extracting oxygen from[...]"

 

Source: Reviews in Mineralogy and Geochemistry
Authors: Jordan A.G. Wostbrock et al.
DOI: https://doi.org/10.2138/rmg.2021.86.11

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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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