The Paleoproterozoic and Neoproterozoic Carbon Cycle Promoted the Evolution of a Habitable Earth

The carbon cycle is an important process that regulates Earth's evolution.We compare two typical periods,in the Paleoproterozoic and Neoproterozoic,in which many geological events occurred.It remains an open question when modern plate tectonics started on Earth and how it has influenced the carbon cycle through time.In the Paleoproterozoic,intense weathering in a highly CO_(2)and CH_(4)rich atmosphere caused more nutritional elements to be carried into the ocean.Terrestrial input boosted high biological productivity,deposition of sediments and the formation of an altered oceanic crust,which may have promoted an increase in the oxygen content.Sediment lubrication and a decrease in mantle potential temperature made cold and deep subduction possible,which carried more carbon into the deep mantle.Carbon can be stored in the mantle as diamond and carbonated mantle rocks,being released by arc and mid-ocean ridge outgassing at widely different times.From the Paleoproterozoic through the Neoproterozoic to the Phanerozoic,the carbon cycle has promoted the evolution of a habitable Earth.

δ^(13)C_(org) perturbations preserved by the interglacial Datangpo Formation in South China with implications for stratigraphic correlation and carbon cycle

Palaeoclimatic and palaeoenvironmental reconstructions of the Cryogenian Period have attracted attention in relation to the debated“Snowball Earth”hypothesis and the early evolution of metazoan life.The carbon cycle and redox conditions of the Sturtian-Marinoan non-glacial interval have been subjected to much controversy in the past decades because of the lack of a high-resolution stratigraphic correlation scheme.As one of the typical Sturtian-Marinoan interglacial deposits,the Datangpo Formation was widely distributed in South China with shales continuously deposited.The previous zircon dating data of the Datangpo Formation provide important ages for global constrain of the Sturtian-Marinoan non-glacial interval.Here we present a high-resolution straitigraphic study of the organic carbon isotopes of the Datangpo Formation from a drill core section in northern Guizhou Province.Based on measured episodicδ^(13)C_(org) perturbations,three positive shifts and three negative excursions are identified.Aδ^(13)C_(org)-based chemostratigraphic correlation scheme is proposed herein that works well for the Datangpo Formation regionally.Meanwhile,theδ^(13)C_(org) vertical gradients changed dynamically throughout the formation.This discovery implies that a significant ocean circulation overturn might have occurred in the upper Datangpo Formation,coinciding with the potential oxygenation.

SOME FEATURES OF CARBON CYCLES IN KARST SYSTEM AND THE IMPLICATION FOR EPIKARSTIFICATION —An Example of Yaji Karst Experimental Site in Guilin,China

The carbon pools of biomass,littering,and SOC wre studied with regards to carbon cycles in epikarst zone,taking an example of Yaji Karst Experiemnt Site in Guilin.This study was focused on SOC and its lability,SOC decomposition rate,CO 2 regime in the soils. 13 ctracing was used to persua the relation of bicarbonate in karst water to soil carbon.The results indicated sufficient carbon pool in SOC for the driveing CO 2 in the karst system.It was revealed that about 60percent of carbon in epi-karst springs resulted from SOC during spring and summer.Thus,the CO 2,driving the karstification,was not simply due to adsorption of atmospheric CO 2 but due to carbon transfer through the pathway of air-plant-soil-water.The driving force should not be overlooked for the epi-karst formation by soil as an interface of carbon environmental geochemistry.

Air–water CO2 flux in an algae bloom year for Lake Hongfeng,Southwest China:implications for the carbon cycle of global inland waters

The carbon cycle of global inland waters is quantitatively comparable to other components in the global carbon budget. Among inland waters, a significant part is man-made lakes formed by damming rivers. Manmade lakes are undergoing a rapid increase in number and size. Human impacts and frequent algae blooms lead to it necessary to make a better constraint on their carbon cycles. Here, we make a primary estimation on the air–water CO_2 transfer flux through an algae bloom year for a subtropical man-made lake—Hongfeng Lake, Southwest China. To do this a new type of glass bottles was designed for content and isotopic analysis of DIC and other environmental parameters. At the early stage of algae bloom,CO_2 was transferred from the atmosphere to the lake with a net flux of 1.770 g·C·m^(-2). Later, the partial pressure(pCO_2) of the aqueous CO_2 increased rapidly and the lake outgassed to the atmosphere with a net flux of 95.727 g·C·m^(-2). In the remaining days, the lake again took up CO_2 from the atmosphere with a net flux of 14.804 g·C·m^(-2). As a whole, Lake Hongfeng released 4527 t C to the atmosphere, accounting for one-third of the atmosphere/soil CO_2 sequestered by chemical weathering in the whole drainage. With an empirical mode decomposition method, we found air temperature plays a major role in controlling water temperature, aqueous pCO_2 and hence CO_2 flux. This work indicates a necessity to make detailed and comprehensive carbon budgets in man-made lakes.

A model study on carbon cycle and phytoplankton dynamical processes in the Bohai Sea

The carbon cycle of lower trophic level in the Bohai Sea is studied with a three-dimensional biological and physical coupled model. The influences of the processes (including horizontal advection, river nutrient load, active transport etc. ) on the phytoplankton biomass and its evolution are estimated. The Bohai Sea is a weak sink of the CO2 in the atmosphere. During the cycle, 13.7% of the gross production of the phytoplankton enter the higher trophic level and 76.8 % of it are consumed by the respiration itself. The nutrient reproduction comes mainly from the internal biogeochemical loop and the rem-ineralization is an important mechanism of the nutrient transfer from organic form to inorganic. Horizontal advection decreases the total biomass and the eutrophication in some sea areas. Change in the nutrient load of a river can only adjust the local system near its estuary. Controlling the input of the nutrient, which limits the alga growth, can be very useful in lessening the phytoplankton biomass.

Simulation of terrestrial carbon cycle balance model in Tibet

Based on climate material, the simplified terrestrial carbon cycle balance (TCCB) model was established, which is semi-mechanism and semi-statistics. Through TCCB model, our estimate indicates that the southeastern part of the Tibetan Plateau has much higher carbon content, and we have calculated the litter carbon pool, NPP, carbon fluxes and described their spatial characteristics in this region. Based on the TCCB model simulation, NPP in Tibet is 1.73×10 8 tC/a, soil organic input rate is 0.66×10 8 tC/a, litter mineralization rate is 1.07×10 8 tC/a, vegetation litterfall rate is 1.73×10 8 tC/a, the litter carbon pool is 7.26×10 8 tC, and soil decomposition rate is 309.54×10 8 tC/a. The carbon budget was also analyzed based on the estimates of carbon pool and fluxes. The spatial distributions of carbon pools and carbon fluxes in different compartments of terrestrial ecosystem were depicted with map respectively in Tibet. The distribution of NPP, vegetation litterfall rate, litter, litter mineralization rate, soil organic input rate and the soil decomposition rate were abstracted with temperature, precipitation, fractional vegetation and land feature.

Effects of elevated pO_3 on carbon cycle between above andbelowground organs of trees

Translocation of carbohydrate from leaves to roots via phloem and reallocation from roots to leaves via xylem regulate the allocation of carbon （C） between above and belowground organs of trees. To quantitatively analyze effects of elevated ozone concentrations pO3 on the internal cycle of C, juvenile beech and spruce were grown in phytotrons and exposed to ambient and elevated pO3 （i.e. twice-ambient O3 levels, restricted to 〈 150 ppb） for two growing seasons. The translocation of C in the phloem and xylem was quantitatively studied by investigating the phloem/xylem-loading of sugars, the differentiation of stem conductive tissue and the hourly water flow through the stem. Results in the present study shown, elevated pO3 significantly decreased C translocation from shoot to roots in beech by reducing both sugar concentration in the phloem and conductive phloem area. Elevated pO3 also significantly decreased C reallocation from the roots to the shoot in beech by reducing both of sugar concentration in the xylem and transpiration rate. The adverse effects of elevated pO3 on C translocation in the phloem and xylem, however, were small in spruce. Contrasting to beech, spruce is less sensitive to elevated pO3, regarding to phloem differentiation and sugar concentrations in the phloem and xylem.

Interannual variability of carbon cycle implied by a 2-D atmospheric transport model

A 2-dimensional atmospheric transport model is deployed in a simplified CO 2 inverse study. Calculated carbon flux distribution for the interval from 1981 to 1997 confirms the existence of a terrestrial carbon sink in mid-high latitude area of North Hemisphere. Strong interannual variability exists in carbon flux patterns, implying a possible link with ENSO and other natural episodes such as Pinatubo volcano eruption in 1991. Mechanism of this possible link was investigated with statistic method. Correlation analysis indicated that in North Hemisphere, climatic factors such as temperature and precipitation, to some extend, could influence the carbon cycle process of land and ocean, thus cause considerable change in carbon flux distribution. In addition, correlation study also demonstrated the possible important role of Asian terrestrial ecosystems in carbon cycle.

Three-step modernization of the ocean:Modeling of carbon cycles and the revolution of ecological systems in the Ediacaran/Cambrian periods

Important ecological changes of the Earth （oxidization of the atmosphere and the ocean） increase in nutrient supply due to the break-up of the super continent （Rodinia） and the appearance of multi-cellular organisms （macroscopic algae and metazoan） took place in the Ediacaran period, priming the Cambrian explosion. The strong perturbations in carbon cycles in the ocean are recorded as excursions in carbonate and organic carbon isotope ratio （δ13Ccarb and δ13Corg） from the Ediacaran through early Cambrian periods. The Ediacaran-early Cambrian sediment records of δ13Ccarb and δ13Corg, obtained from the drill-core samples in Three Gorges in South China, are compared with the results of numerical simulation of a sim- ple one-zone model of the carbon cycle of the ocean, which has two reservoirs （i.e., dissolved organic carbon （DOC） and dissolved inorganic carbon （DIC）. The fluxes from the reservoirs are assumed to be proportional to the mass of the carbon reservoirs. We constructed a model, referred to here as the Best Fit Model （BFM）, which reproduce δ13Ccarb and δ13Corg records in the Ediacaran-early Cambrian period noted above. BFM reveals that the Shuram excursion is related to three major changes in the carbon cycle or the global ecological system of the Earth： （1） an increase in the coefficient of remineralization by a factor of ca. 100, possibly corresponding to a change in the dominant metabolism from anaerobic respiration to aerobic respiration, （2） an increase of carbon fractionation index from 25‰, to 33‰, possibly corresponding to the change in the primary producer from rock-living cyanobacteria to free-living macro algae, and （3） an in- crease in the coefficient of the organic carbon burial by a factor of ca. 100, possibly corresponding to the onset of a biological pump driven by the flourishing metazoan and zooplankton. The former two changes took place at the start of the Shuram excursion, while the third occurred at the end of the Shuram excursion. The other two excursions are explained by the tentative decrease in primary production due to cold periods, which correspond to the Gaskiers （ca. 580 Ma） and Bikonor （ca. 542 Ma） glaciations.

Global Carbon Project (GCP) Beijing Office:a new bridge for understanding regional carbon cycles

It has been widely accepted that human activities, especially burning fossil fuels and land use change, have altered the climate on earth and anthropogenic carbon fluxes have become comparable in magnitude with the natural fluxes in the global carbon cycle. The present and potential threat of adverse consequences has focused the attention of the scientists, policy makers and general public on the interaction among carbon cycle, climate change and human system. Asia is a hot spot from environmental change and sustainable development perspectives. The development pathways and environmental changes in the region have obvious consequences for the regional carbon cycle, even for global carbon budget, and the complex, diverse social, economic and environmental conditions make it highly diffficult to understand and quantify these consequences. The GCP Beijing Office ＂will have a supporting and coordinating role and will provide coordination, leadership and capacity building on carbon cycle sciences in China and to the larger region of Asia＂ and ＂liaise with the two International Project Offices based in Canberra and Tsukuba to coordinate a regional and global strategy consistent with the GCP Science and Implementation Framework＂.

Sino-Canadian Project on Carbon Cycle Kicks Off

A Sino-Canadian research project titled "Responding to the global warming: Improving China's carbon storage capacity" was officially initiated on August 2.……

Unraveling the Cenozoic carbon cycle by reconstructing carbonate compensation depth(CCD)

The Carbonate Compensation Depth(CCD)refers to the depth within the ocean where the production and dissolution rates of carbonates reach equilibrium,widely likened to the oceanic calcareous‘snowline’.The reconstruction of deep-time CCD has significant implications for understanding ocean circulation,seawater chemical conditions,sediment distribution,and the surface carbon cycle.This paper critically reviews the methods for CCD reconstruction,summarizes the driving mechanisms of the Cenozoic CCD evolution and its association with the carbon cycle,and offers insights into future directions for CCD research.CCD reconstruction has evolved over the past half century from early qualitative to quantitative methods.These methodological improvements have markedly improved the accuracy and resolution of CCD.Existing studies have indicated a general trend of the CCD deepening across major ocean basins since the Cenozoic,interspersed with a minor shallowing phase during the mid-Miocene.The variations in the CCD are primarily influenced by factors such as ocean productivity,weathering,and shelf-basin partitioning.During climate events such as the Paleocene-Eocene Thermal Maximum,the CCD exhibits pulselike fluctuations.Future research should focus on precision and quantification while integrating model simulations to further explore the correlations and response mechanisms between the CCD and the paleoclimate as well as the carbon cycle.

Key processes of carbon cycle and sink enhancement paths in natural wetland ecosystems in China

Wetland ecosystems have become one of the long-term solutions for mitigating global climate change due to their strong carbon sequestration potential.However,the key carbon cycle processes in wetland ecosystems still lack a systematic summary.In the context of wetland protection and restoration,there is still a lack of consensus on the technical pathways to realize carbon sink multiplication in wetland ecosystems.In this paper,the key processes of carbon cycle,such as photosynthetic carbon uptake,microbial carbon decomposition and carbon deposition and burial,are sorted out and summarized in four major wetland types,namely,swamp and peat wetlands,river and riparian wetlands,lake and lakeshore wetlands,and estuarine and coastal wetlands.Based on the key processes of carbon cycle,three technological pathways for carbon sink multiplication are proposed,including,vegetation carbon sequestration and sink enhancement technology,soil carbon emission reduction technology and carbon deposition and burial technology.The key technologies under each pathway are further refined.And the carbon sink effects of the carbon sink technologies in different wetland types are qualitatively described.Also,wetland protection and restoration methods in corresponding regions are given in the light of the regional characteristics of wetlands in China.This will provide a scientific basis for the strategy of doubling the carbon sinks of China′s wetland ecosystems.

Constraint of satellite CO_(2)retrieval on the global carbon cycle from a Chinese atmospheric inversion system

Satellite carbon dioxide(CO_(2))retrievals provide important constraints on surface carbon fluxes in regions that are undersampled by global in situ networks.In this study,we developed an atmospheric inversion system to infer CO_(2)sources and sinks from Orbiting Carbon Observatory-2(OCO-2)column CO_(2)retrievals during 2015–2019,and compared our estimates to five other state-of-the-art inversions.By assimilating satellite CO_(2)retrievals in the inversion,the global net terrestrial carbon sink(net biome productivity,NBP)was found to be 1.03±0.39 petagrams of carbon per year(Pg C yr^(-1));this estimate is lower than the sink estimate of 1.46–2.52 Pg C yr^(-1),obtained using surface-based inversions.We estimated a weak northern uptake of 1.30 Pg C yr-1and weak tropical release of-0.26 Pg C yr^(-1),consistent with previous reports.By contrast,the other inversions showed a strong northern uptake(1.44–2.78 Pg C yr-1),but diverging tropical carbon fluxes,from a sink of 0.77 Pg C yr^(-1) to a source of-1.26 Pg C yr^(-1).During the 2015–2016 El Ni?o event,the tropical land biosphere was mainly responsible for a higher global CO_(2)growth rate.Anomalously high carbon uptake in the northern extratropics,consistent with concurrent extreme Northern Hemisphere greening,partially offset the tropical carbon losses.This anomalously high carbon uptake was not always found in surface-based inversions,resulting in a larger global carbon release in the other inversions.Thus,our satellite constraint refines the current understanding of flux partitioning between northern and tropical terrestrial regions,and suggests that the northern extratropics acted as anomalous high CO_(2)sinks in response to the 2015–2016 El Nino event.

Comparison of the carbon cycle and climate response to artificial ocean alkalinization and solar radiation modification

Carbon dioxide removal and solar radiation modification(SRM)are two classes of proposed climate intervention methods.A thorough understanding of climate system response to these methods calls for a good understanding of the carbon cycle response.In this study,we used an Earth system model to examine the response of global climate and carbon cycle to artificial ocean alkalinization(AOA),a method of CO_(2)removal,and reduction in solar irradiance that represents the overall effect of solar radiation modification.In our simulations,AOA is applied uniformly over the global ice-free ocean under the RCP8.5 scenario to bring down atmospheric CO_(2)to the level of RCP4.5,and SRM is applied uniformly over the globe under the RCP8.5 scenario to bring down global mean surface temperature to the level of RCP4.5.Our simulations show that with the same goal of temperature stabilization,AOA and SRM cause fundamentally different perturbations of the ocean and land carbon cycle.By the end of the 21st century,relative to the simulation of RCP8.5,AOA-induced changes in ocean carbonate chemistry enhances global oceanic CO_(2)uptake by 983 PgC and increases global mean surface ocean pH by 0.42.Meanwhile,AOA reduces land CO_(2)uptake by 79 PgC and reduces atmospheric CO_(2)concentration by 426×10^(−6).By contrast,relative to the simulation of RCP8.5,SRM has a minor effect on the oceanic CO_(2)uptake and ocean acidification.SRM-induced cooling enhances land CO_(2)uptake by 140 PgC and reduces atmospheric CO_(2)concentration by 63×10^(−6).A sudden termination of SRM causes a rate of temperature change that is much larger than that of RCP8.5.A sudden termination of AOA causes a rate of temperature change that is comparable to that of RCP8.5 and a rate of ocean acidification that is much larger than that of RCP8.5.

Why are East Asian ecosystems important for carbon cycle research?

The global carbon cycle is one of the most important biogeochemical cycles. Through photosynthesis, green plants absorb CO2 from the atmosphere to produce organic matters,

The spatio-temporal responses of the carbon cycle to climate and land use/land cover changes between 1981-2000 in China

This paper represents the first national effort of its kind to systematically investigate the impact of changes in climate and land use and land cover （LULC） on the carbon cycle with high-resolution dynamic LULC data at the decadal scale （1990s and 2000s）. Based on simulations using well calibrated and validated Carbon Exchanges in the Vegetation-Soil-Atmosphere （CEVSA） model, tem- poral and spatial variations in carbon storage and fluxes in China may be generated empower us to relate these variations to climate variability and LULC with respect to net primary productivity （NPP）, heterotrophic respiration （HR）, net ecosystem productivity （NEP）, storage and soil carbon （SOC）, and vegetation carbon （VEGC） individually or collectively. Overall, the increases in NPP were greater than HR in most cases due to the effect of global warming with more precipitation in China from 1981 to 2000. With this trend, the NEP remained positive during that period, resulting in a net increase of total amount of carbon being stored by about 0.296 PgC within a 20-year time frame. Because the climate effect was much greater than that of changes of LULC, the total carbon storage in China actually increased by about 0.17 PgC within the 20-year time period. Such findings will contribute to the generation of carbon emissions control policies under global climate change impacts.

Urban carbon footprint and carbon cycle pressure： The case study of Nanjing

Urban carbon footprint reflects the impact and pressure of human activities on ur- ban environment. Based on city level, this paper estimated carbon emissions and carbon footprint of Nanjing city, analyzed urban carbon footprint intensity and carbon cycle pressure and discussed the influencing factors of carbon footprint through LMDI decomposition model. The main conclusions are as follows： （1） The total carbon emissions of Nanjing increased rapidly since 2000, in which the carbon emission from the use of fossil energy was the largest Meanwhile, carbon sinks of Nanjing presented a declining trend since 2000, which caused the decrease of carbon compensation rate and the increase of urban carbon cycle pressure. （2） The total carbon footprint of Nanjing increased rapidly since 2000, and the carbon deficit was more than ten times of total land areas of Nanjing in 2009, which means Nanjing confronted high carbon cycle pressure. （3） Generally, carbon footprint intensity of Nanjing was on de- crease and the carbon footprint productivity was on increase. This indicated that energy utilization rate and carbon efficiency of Nanjing was improved since 2000, and the policy for energy conservation and emission reduction taken by Nanjing＇s government received better effects. （4） Economic development, population and industrial structure are promoting factors for the increase of carbon footprint of Nanjing, while the industrial carbon footprint intensity was inhibitory factor. （5） Several countermeasures should be taken to decrease urban carbon footprint and alleviate carbon cycle pressure, such as： improvement of the energy efficiency, industrial structure reconstruction, afforestation and environmental protection and land use control. Generally, transition to low-carbon economy is essential for Chinese cities to realize sustainable development in the future.

Summary of Recent Climate Change Studies on the Carbon and Nitrogen Cycles in the Terrestrial Ecosystem and Ocean in China

This article reviews recent advances over the past and their relationship to climate change in China. The was 0.19-0.26 Pg C yr-1 for the 1980s and 1990s. 4 years in the study of the carbon-nitrogen cycling net carbon sink in the Chinese terrestrial ecosystem Both natural wetlands and the rice-paddy regions emitted 1.76 Tg and 6.62 Tg of CH4 per year for the periods 1995 2004 and 2005 2009, respectively. China emitted -1.1 Tg N20-N yr-1 to the atmosphere in 2004. Land soil contained -8.3 Pg N. The excess nitrogen stored in farmland of the Yangtze River basin reached 1.51 Tg N and 2.67 Tg N in 1980 and 1990, respectively. The outer Yangtze Estuary served as a moderate or significant sink of atmospheric CO2 except in autumn. Phytoplankton could take up carbon at a rate of 6.4 ×1011 kg yr-1 in the China Sea. The global ocean absorbed anthropogenic CO2 at the rates of 1.64 and 1.73 Pg C yr-1 for two sinmlations in the 1990s. Land net ecosystem production in China would increase until the mid-21st century then would decrease gradually under future climate change scenarios. This research should be strengthened in the future, including collection of more observation data, measurement of the soil organic carbon （SOC） loss and sequestration, evaluation of changes in SOC in deep soil layers, and the impacts of grassland management, carbon-nitrogen coupled effects, and development and improvement of various component models and of the coupled carbon cycle-climate model.

Terrestrial carbon cycle model-data fusion:Progress and challenges

The terrestrial carbon cycle is an important component of global biogeochemical cycling and is closely related to human well-being and sustainable development.However,large uncertainties exist in carbon cycle simulations and observations.Model-data fusion is a powerful technique that combines models and observational data to minimize the uncertainties in terrestrial carbon cycle estimation.In this paper,we comprehensively overview the sources and characteristics of the uncertainties in terrestrial carbon cycle models and observations.We present the mathematical principles of two model-data fusion methods,i.e.,data assimilation and parameter estimation,both of which essentially achieve the optimal fusion of a model with observational data while considering the respective errors in the model and in the observations.Based upon reviewing the progress in carbon cycle models and observation techniques in recent years,we have highlighted the major challenges in terrestrial carbon cycle model-data fusion research,such as the“equifinality”of models,the identifiability of model parameters,the estimation of representativeness errors in surface fluxes and remote sensing observations,the potential role of the posterior probability distribution of parameters obtained from sensitivity analysis in determining the error covariance matrixes of the models,and opportunities that emerge by assimilating new remote sensing observations,such as solar-induced chlorophyll fluorescence.It is also noted that the synthesis of multisource observations into a coherent carbon data assimilation system is by no means an easy task,yet a breakthrough in this bottleneck is a prerequisite for the development of a new generation of global carbon data assimilation systems.This article also highlights the importance of carbon cycle data assimilation systems to generate reliable and physically consistent terrestrial carbon cycle reanalysis data products with high spatial resolution and longterm time series.These products are critical to the accurate estimation of carbon cycles at the global and regional scales and will help future carbon management strategies meet the goals of carbon neutrality.