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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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Southern Ocean carbon export efficiency in relation to temperature and primary productivity

Abstract.

"Satellite remote sensing and numerical models are widely used to estimate large-scale variations in ocean carbon export, but the relationship between export efficiency (e-ratio) of sinking organic carbon out of the surface ocean and its drivers remains poorly understood, especially in the Southern Ocean. Here, we assess the effects of temperature and primary productivity on e-ratio by combining particulate organic carbon export flux from in situ measurements during 1997–2013, environmental parameters from satellite products, and outputs from ocean biogeochemical models in the Southern Ocean. Results show that “High Productivity Low E-ratio” (HPLE) is a common phenomenon in the Subantarctic Zone and the Polar Frontal Zone, but not the Antarctic Zone[...]"

 

Source: Nature Scientific Reports
Authors: Gaojing Fan et al.
DOI: https://doi.org/10.1038/s41598-020-70417-z 

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Early deglacial CO2 release from the Sub-Antarctic Atlantic and Pacific oceans

Abstract.

"Over the last deglaciation there were two transient intervals of pronounced atmospheric CO2 rise; Heinrich Stadial 1 (17.5-15 kyr) and the Younger Dryas (12.9-11.5 kyr). Leading hypotheses accounting for the increased accumulation of CO2 in the atmosphere at these times invoke deep ocean carbon being released from the Southern Ocean and an associated decline in the global efficiency of the biological carbon pump. Here we present new deglacial surface seawater pH and CO2sw records from the Sub-Antarctic regions of the Atlantic [...]"

 

Source: Science Direct
Autors: R. Shuttleworth et al.
DOI: https://doi.org/10.1016/j.epsl.2020.116649

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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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Source partitioning of oxygen-consuming organic matter in the hypoxic zone of the Chesapeake Bay

Abstract.

"We surveyed the carbonate system along the main channel of the Chesapeake Bay in June 2016 to elucidate carbonate dynamics and the associated sources of oxygen‐consuming organic matter. Using a two endmember mixing calculation, chemical proxies, and stoichiometry, we demonstrated that in early summer, dissolved inorganic carbon (DIC) dynamics were controlled by aerobic respiration in the water column (43%), sulfate reduction in the sediment (39%), atmospheric CO2 invasion (13%), and CaCO3 dissolution (5%). A mass balance of the DIC concentration and its stable isotope suggested that the apparent δ13C of oxygen‐consuming[...]"

 

Source: Association for the Sciences of Limnology and Oceanography
Authors: Jianzhong Su et al.
DOI: https://doi.org/10.1002/lno.11419

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Biogeochemical Controls on the Redox Evolution of Earth`s Oceans and Atmosphere

Abstract.

"The redox state of Earth’s atmosphere has undergone a dramatic shift over geologic time from reducing to strongly oxidizing, and this shift has been coupled with changes in ocean redox structure and the size and activity of Earth’s biosphere. Delineating this evolutionary trajectory remains a major problem in Earth system science. Significant insights have emerged through the application of redox-sensitive geochemical systems. Existing and emerging biogeochemical modeling tools are pushing the limits of the quantitative constraints on ocean–atmosphere[...]"


Source: Elements
Authors: Christopher T. Reinhard et al.
DOI: https://doi.org/10.2138/gselements.16.3.191

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The Northeast Atlantic is running out of excess carbonate in the horizon of cold-water corals communities

Abstract.

"The oceanic uptake of atmospheric carbon dioxide (CO2) emitted by human activities alters the seawater carbonate system. Here, the chemical status of the Northeast Atlantic is examined by means of a high-quality database of carbon variables based on the GO-SHIP A25 section (1997–2018). The increase of atmospheric CO2 leads to an increase in ocean anthropogenic carbon (Cant) and a decrease in carbonate that is unequivocal in the upper and mid-layers (0–2,500 m depth). In the mid-layer, the carbonate content in the Northeast Atlantic is maintained by the interplay between the northward spreading of recently conveyed Mediterranean Water with excess of carbonate and the arrival of subpolar-origin waters close to carbonate[...]".

Source: Nature Reviews Earth & Environment
Authors: Marcos Fontela et al.
DOI: https://doi.org/10.1038/s41598-020-71793-2

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Decadal acidification in Atlantic and Mediterranean water masses exchanging at the Strait of Gibraltar

Abstract.

"Seawater pH is undergoing a decreasing trend due to the absorption of atmospheric CO2, a phenomenon known as ocean acidification (OA). Biogeochemical processes occurring naturally in the ocean also change pH and hence, for an accurate assessment of OA, the contribution of the natural component to the total pH variation must be quantified. [...]"

Source: Scientific Reports
Authors: Susana Flecha et al.
DOI: 10.1038/s41598-019-52084-x

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Air–sea fluxes of greenhouse gases and oxygen in the northern Benguela Current region during upwelling events

Abstract.

"Ground-based atmospheric observations of CO2δ(O2∕N2), N2O, and CH4 were used to make estimates of the air–sea fluxes of these species from the Lüderitz and Walvis Bay upwelling cells in the northern Benguela region, during upwelling events. Average flux densities (±1σ) were 0.65±0.4 µmol m−2 s−1 for CO2, −5.1±2.5 µmol m−2 s−1 for O2 (as APO), 0.61±0.5 nmol m−2 s−1 for N2O, and 4.8±6.3 nmol m−2 s−1 for CH4. A comparison of our top-down (i.e., inferred from atmospheric anomalies) flux estimates with shipboard-based measurements showed that the two approaches agreed within ±55 % on average, though the degree of agreement varied by species and was best for CO2. [...]"

Source: Biogeosciences
Authors: Eric J. Morgan et al.
DOI: 10.5194/bg-16-4065-2019

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The IPCC oceans report is a wake-up call for policymakers

"The importance of the ocean in climate regulation is enormous—yet undervalued. The ocean is estimated to have absorbed 93 percent of the excess heat generated by human activities since the 1970s, acting as a buffer against the global warming we've seen to date. The majority of the global carbon cycle circulates through the ocean, through marine food-webs and other processes, and carbon is locked-away in coastal and marine habitats and deep in ocean sediments. Coastal ecosystems alone sequester more carbon than terrestrial forest per unit area. [...]"

Source: Phys.org

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