Carbon Dioxide Removal via Macroalgae Open-ocean Mariculture and Sinking: An Earth System Modeling Study

In this study we investigate open-ocean macroalgae mariculture and sinking (MOS) as ocean-based carbon dioxide removal (CDR) method. Embedding a macroalgae model into an Earth system model, we simulate macroalgae mariculture in the open-ocean surface layer followed by fast sinking of the carbon-rich macroalgal biomass to the deep seafloor (depth > 3,000 m). We also test the combination of MOS with artificial upwelling (AU), which fertilizes the macroalgae by pumping nutrient-rich deeper water to the surface. The simulations are done under RCP4.5 a moderate emission pathway. When deployed globally between years 2020 and 2100, the simulated CDR potential of MOS is 270 PgC, which is further boosted by AU to 447 PgC. More than half of MOS-sequestered carbon retains in the ocean after cessation at year 2100 until year 3000. The major side effect of MOS on pelagic ecosystems is the reduction of phytoplankton net primary production (PNPP) due to the nutrient competition and canopy shading by macroalgae. MOS shrinks the mid layer oxygen minimum zones (OMZs) by reducing the organic matter export to, and remineralization in, subsurface and intermediate waters, while it creates new OMZs on the seafloor by oxygen consumption from remineralization of sunken biomass. MOS also impacts the global carbon cycle, reduces the atmospheric and terrestrial carbon reservoir when enhancing the ocean carbon reservoir. MOS also enriches the dissolved inorganic carbon in the deep ocean. Effects are mostly reversible after cessation of MOS, though recovery is not complete by year 3000. In a sensitivity experiment without remineralization of sunk MOS biomass, the entire MOS-captured carbon is permanently stored in the ocean, but the lack of remineralized nutrients causes a long-term nutrient decline in the surface layers and thus reduces PNPP. Our results suggest that MOS has a considerable potential as an ocean-based CDR method. However, MOS has inherent side effects on marine ecosystems and biogeochemistry, which will require a careful evaluation beyond this first idealized modeling study.

Carbon cycle perturbation and mercury anomalies in terrestrial Oceanic Anoxic Event 1b from Jiuquan Basin, NW China

The Oceanic Anoxic Event (OAE) 1b is well documented in western Tethys, however, records in Eurasia are still lacking. Here, we carried out high-resolution organic carbon isotope (δ13Corg), total organic carbon (TOC) contents and mercury (Hg) concentrations analysis of the lacustrine sediments from the Xiagou and Zhonggou formations in the Hanxiagou section, Jiuquan Basin, northwestern China. The lacustrine δ13Corg curve presents three stages of negative excursions above the basalt layer dated at 112.4 ± 0.3 Ma in the lowermost Zhonggou Formation. The three negative δ13Corg excursions, well corresponded with the three subevents (Kilian, Paquier, and Leenhardt) of the OAE1b in Poggio le Guaine (central Italy), Vocontian Basin (SE France) and St Rosa Canyon (NE Mexico) sections, supporting the record of the terrestrial OAE 1b in the Jiuquan Basin. Five mercury enrichment (ME) intervals in Hg/TOC ratios were recognized, indicating that the pulsed volcanism from the southern Kerguelen Plateau likely triggered the OAE 1b. However, the decoupling between NIE shifts and mercury enrichments signifying other carbon reservoir (with no link to mercury) probably contributed to the global carbon cycle perturbation during the OAE 1b period. Our results provide direct evidence to link the OAE 1b and terrestrial ecosystem in the Eurasia.

An explosive component in a December 2020 Milan earthquake suggests outgassing of deeply recycled carbon

Carbon dragged at sub-arc depths and sequestered in the asthenospheric upper mantle during cold subduction is potentially released after millions of years during the breakup of continental plates. However, it is unclear whether these deep-carbon reservoirs can be locally remobilized on shorter-term timescales. Here we reveal the fate of carbon released during cold subduction by analyzing an anomalously deep earthquake in December 2020 in the lithospheric mantle beneath Milan (Italy), above a deep-carbon reservoir previously imaged in the mantle wedge by geophysical methods. We show that the earthquake source moment tensor includes a major explosive component that we ascribe to carbon-rich melt/fluid migration along upper-mantle shear zones and rapid release of about 17,000 tons of carbon dioxide when ascending melts exit the carbonate stability field. Our results underline the importance of carbon-rich melts at active continental margins for emission budgets and suggest their potential episodic contributions to atmospheric carbon dioxide.

Estoque e Mecanismo de Proteção Física do Carbono no Solo em Manejos Agrícolas

O compartimento terrestre é o maior reservatório de carbono no solo e armazena cerca de três vezes mais que o compartimento atmosférico. Porém, a atmosfera tem aumentado suas concentrações, devido as elevadas emissões de gases de efeito estufa, decorrente principalmente do consumo de combustíveis fosseis e queimadas das florestas. O Brasil é um dos maiores emissores, especialmente de dióxido de carbono, pelo qual o setor de mudanças do uso da terra e florestas são responsáveis majoritariamente pelas emissões. O solo em condições naturais tem um equilíbrio entre a entrada e saída de carbono, no entanto quando o solo é cultivado, principalmente com sistemas convencionais, há uma perda significativa dos estoques de carbono do solo. No entanto, quando é adotado manejos conservacionistas ocorre o mecanismo de proteção física do carbono através da formação e estabilização dos agregados, que dificulta o acesso dos microrganismos a decomposição e mantém estocado no solo, o que mitiga a emissão para atmosfera. Diante do exposto, este trabalho teve como objetivo mostrar como os manejos influenciam no estoque de carbono no solo, e como é atuação do mecanismo de proteção física de agregados em sistemas conservacionistas, demostrando como foram os avanços na pesquisa da interação da matéria orgânica com a formação e estabilização de agregados. Stock and Mechanism of Physical Protection of Soil Carbon in Agricultural Managements A B S T R A C TThe terrestrial compartment is the largest carbon reservoir in the soil and stores about three times as much as the atmospheric compartment. However, the atmosphere has increased its concentrations, due to the high emissions of greenhouse gases, mainly due to the consumption of fossil fuels and forest fires. Brazil is one of the largest emitters, especially of carbon dioxide, for which the sector of land use change and forests are responsible for the majority of emissions. Soil under natural conditions has a balance between carbon input and output, however when the soil is cultivated, mainly with conventional systems, there is a significant loss of soil carbon stocks. However, when conservation management is adopted, there is a mechanism for the physical protection of carbon through the formation and stabilization of aggregates, which hinders the access of microorganisms to decomposition and keeps them stored in the soil, which mitigates the emission into the atmosphere. In view of the above, this study aimed to show how the management influences the carbon stock in the soil, and how the mechanism of physical protection of aggregates in conservationist systems works, demonstrating how advances were made in researching the interaction of organic matter with formation and stabilization of aggregates.Key words: aggregates, carbon dioxide, greenhouse effect, crop-livestock-forest integration, organic matter

Comparison of PM10 Sources at Traffic and Urban Background Sites Based on Elemental, Chemical and Isotopic Composition: Case Study from Krakow, Southern Poland

In large urban agglomerations, car traffic is one of the main sources of particulate matter. It consists of particulate matter directly generated in the process of incomplete liquid fuel burning in vehicle engine, secondary aerosols formed from exhaust gaseous pollutants (NOx, SO2) as well as products of tires, brake pads and pavement abrasion. Krakow is one of the cities in Europe with the highest concentrations of particulate matter. The article presents the results of combined elemental, chemical and isotopic analyses of particulate matter PM10 at two contrasting urban environments during winter and summer seasons. Daily PM10 samples were collected during the summer and winter seasons of 2018/2019 at two stations belonging to the network monitoring air quality in the city. Mean PM10 concentrations at traffic-dominated stations were equal to 35 ± 7 µg/m3 and 76 ± 28 µg/m3 in summer and winter, respectively, to be compared with 25.6 ± 5.7 µg/m3 and 51 ± 25 µg/m3 in summer and winter, respectively, recorded at the urban background station. The source attribution of analyzed PM10 samples was carried out using two modeling approaches: (i) The Positive Matrix Factorization (PMF) method for elemental and chemical composition (concentrations of elements, ions, as well as organic and elemental carbon in daily PM10 samples), and (ii) Isotope Mass Balance (IMB) for 13C and 14C carbon isotope composition of carbonaceous fraction of PM10. For PMF application, five sources of particulate matter were identified for each station: fossil fuel combustion, secondary inorganic aerosols, traffic exhaust, soil, and the fifth source which included road dust, industry, construction work. The IMB method allowed the partitioning of the total carbon reservoir of PM10 into carbon originating from coal combustion, from biogenic sources (natural emissions and biomass burning) and from traffic. Both apportionment methods were applied together for the first time in the Krakow agglomeration and they gave consistent results.

A largely invariant marine dissolved organic carbon reservoir across Earth's history

Marine dissolved organic carbon (DOC), the largest pool of reduced carbon in the oceans, plays an important role in the global carbon cycle and contributes to the regulation of atmospheric oxygen and carbon dioxide abundances. Despite its importance in global biogeochemical cycles, the long-term history of the marine DOC reservoir is poorly constrained. Nonetheless, significant changes to the size of the oceanic DOC reservoir through Earth’s history have been commonly invoked to explain changes to ocean chemistry, carbon cycling, and marine ecology. Here, we present a revised view of the evolution of marine DOC concentrations using a mechanistic carbon cycle model that can reproduce DOC concentrations in both oxic and anoxic modern environments. We use this model to demonstrate that the overall size of the marine DOC reservoir has likely undergone very little variation through Earth’s history, despite major changes in the redox state of the ocean–atmosphere system and the nature and efficiency of the biological carbon pump. A relatively static marine DOC reservoir across Earth’s history renders it unlikely that major changes in marine DOC concentrations have been responsible for driving massive repartitioning of surface carbon or the large carbon isotope excursions observed in Earth’s stratigraphic record and casts doubt on previously hypothesized links between marine DOC levels and the emergence and radiation of early animals.

Biobased plastic: A plausible solution to carbon neutrality in plastic industry

Biobased plastic combined with plastic recycling could be a plausible solution for achieving carbon neutrality by plastic industry. Herein we use production data, emission factors, and future plastic demands (2021-2060) to build a model, evaluating carbon neutrality under five scenarios. Our simulation indicates that carbon neutrality can be achieved by 2060 when biobased plastics takes 90% of plastic production with near 50% of recycling ratio. The amount of carbon captured through photosynthesis surpasses that of carbon released through plastic life cycle. Recycling reduces virgin plastic production, which is the primary carbon source. A one-fold increase in the use of recycled plastics could lead to a three-fold reduction of virgin plastic production. Existing plastics stored 6.82 giga tons of carbon (GtC) in 2020, serving as an artificial carbon reservoir never recognized before. This carbon reservoir will expand to 23.0 and 27.4 GtC under 22% and 50% recycling scenarios, respectively, by 2060.

Paleocene/Eocene carbon feedbacks triggered by volcanic activity

The Paleocene–Eocene Thermal Maximum (PETM) was a period of geologically-rapid carbon release and global warming ~56 million years ago. Although modelling, outcrop and proxy records suggest volcanic carbon release occurred, it has not yet been possible to identify the PETM trigger, or if multiple reservoirs of carbon were involved. Here we report elevated levels of mercury relative to organic carbon—a proxy for volcanism—directly preceding and within the early PETM from two North Sea sedimentary cores, signifying pulsed volcanism from the North Atlantic Igneous Province likely provided the trigger and subsequently sustained elevated CO2. However, the PETM onset coincides with a mercury low, suggesting at least one other carbon reservoir released significant greenhouse gases in response to initial warming. Our results support the existence of ‘tipping points’ in the Earth system, which can trigger release of additional carbon reservoirs and drive Earth’s climate into a hotter state.