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Salt marshes are crucial eco-geomorphic features of tidal environments as they provide important ecological functions and deliver a wide range of ecosystem services. Being controlled by the interplay between hydrodynamics, geomorphology, and vegetation, the contribution of both organic matter (OM) and inorganic sediments drives salt marsh vertical accretion. This allows marshes to keep pace with relative sea level rise and likewise capture and store carbon, making them valuable allies in climate mitigation strategies. Thus, soil organic matter (SOM), i.e. the organic component of the soil, plays a key role within salt marsh environments, directly contributing to soil formation and supporting carbon storage. This study aims at inspecting spatial patterns of OM in surface salt marsh soils (top 20 cm), providing further insights into the physical and biological factors driving OM dynamics that affect salt marsh survival and carbon sink potential. Our results reveal two scales of variations in SOM content in marsh environments. At the marsh scale, OM variability is influenced by the interplay between surface elevation and changes in sediment supply linked with the distance from the marsh edge. At the system scale, OM content distribution is dominated by the gradient generated by marine and fluvial influence. The observed variations in SOM are explained by the combination of inorganic and organic input, preservation conditions, and sediment grain size. Our results highlight the importance of marshes as carbon sink environments, further emphasising that environmental conditions within a tidal system may generate strongly variable and site-specific carbon accumulation patterns, enhancing blue carbon assessment complexity. [ABSTRACT FROM AUTHOR]

Achieving climate targets requires mitigation against climate change but also understanding of the response of land and ocean carbon systems. In this context, global soil carbon stocks and their response to environmental changes are key. This paper quantifies the global soil carbon feedbacks due to changes in atmospheric CO 2 , and the associated climate changes, for Earth system models (ESMs) in CMIP6. A standard approach is used to calculate carbon cycle feedbacks, defined here as soil carbon-concentration (βs) and carbon-climate (γs) feedback parameters, which are also broken down into processes which drive soil carbon change. The sensitivity to CO 2 is shown to dominate soil carbon changes at least up to a doubling of atmospheric CO 2. However, the sensitivity of soil carbon to climate change is found to become an increasingly important source of uncertainty under higher atmospheric CO 2 concentrations. [ABSTRACT FROM AUTHOR]

Riverine dissolved organic carbon (DOC) plays a vital role in regional and global carbon cycles. However, the processes of DOC conversion from soil organic carbon (SOC) and leaching into rivers are insufficiently understood, inconsistently represented, and poorly parameterized, particularly in land surface and earth system models. As a first attempt to fill this gap, we propose a generic formula that directly connects SOC concentration with DOC concentration in headwater streams, where a single parameter, the transformation rate from SOC in the soil to DOC leaching flux, Pr , accounts for the overall processes governing SOC conversion to DOC and leaching from soils (along with runoff) into headwater streams. We then derive a high-resolution Pr map over the contiguous U.S. (CONUS) in five major steps: 1) selecting 2595 headwater catchments where observed riverine DOC data are available with reasonable quality; 2) estimating catchment-average SOC for the 2595 catchments based on high-resolution SOC data; 3) estimating the Pr values for these catchments based on the generic formula and catchment-average SOC; 4) developing a predictive model of Pr with machine learning (ML) techniques and catchment-scale climate, hydrology, geology, and other attributes; and 5) deriving a national map of Pr , based on the ML model. For evaluation, we compare the DOC concentration derived using the Pr map and the observed DOC concentration values at another 3210 headwater gauges. The resulting mean absolute scaled error and coefficient of determination are 0.73 and 0.47, respectively, suggesting the effectiveness of the overall methodology. Efforts to constrain uncertainty and evaluate the sensitivity of Pr to different factors are discussed. To illustrate the use of such a map, we derive a riverine DOC concentration reanalysis dataset for more than two million small catchments over CONUS. The map, robustly derived and empirically validated, lays a critical cornerstone for better simulating the terrestrial carbon cycle in land surface and earth system models. Our findings not only set a foundation for improving our predictive understanding of the terrestrial carbon cycle at the regional and global scales but also hold promises for informing policy decisions related to decarbonization and climate change mitigation. [ABSTRACT FROM AUTHOR]

Continental shelf sediments contain some of the largest stocks of organic carbon (OC) on Earth and play a vital role in influencing the global carbon cycle. Quantifying how much OC is stored in shelf sediments and determining its residence time is key to assessing how human activities can accelerate the process of OC remineralization into carbon dioxide. Spatial variations in terrestrial carbon stocks are well studied and mapped at high resolution, but our knowledge of the distribution of marine OC in different seafloor settings is still very limited, particularly in the highly dynamic and spatially variable shelf environments. The lack of knowledge reduces our ability to understand and predict how much and for how long oceans sequester CO2. In this study, we use high-resolution multibeam echosounder (MBES) data from the Eastern Shore Islands offshore Nova Scotia (Canada), combined with OC measurements from discrete samples, to assess the distribution of OC content in seafloor sediments. We derive three different spatial estimates of organic carbon: i) assuming a homogenous seafloor the carbon stock estimates were scaled to the entire study region; ii) using a high-resolution substrate map, the estimates were scaled to the areas of soft substrate only, and, finally, iii) using Empirical Bayesian Regression Kriging (EBRK) regression prediction within the area of soft substrate, carbon stock estimates in areas of soft substrate were refined to account for spatial variability in the concentration of OC. These three distinct spatial models yielded dramatically different estimates of average standing stock of OC in our study area, 1275, 259 and 203 Mt of OC respectively. Our study demonstrates that high-resolution mapping is critically important for improved estimates of OC stocks on continental shelves, and to the identification of carbon hotspots that need to be considered in seabed management and climate mitigation strategies. [ABSTRACT FROM AUTHOR]

Salt marshes are crucial eco-geomorphic features of tidal environments as they provide numerous important ecological functions and deliver a wide range of ecosystem services that contribute to human well-being. Being controlled by the interplay between hydrodynamics, geomorphology and vegetation, the deposition of both organic matter (OM) and inorganic sediments drives salt-marsh vertical accretion. This allows marshes to keep pace with relative sea-level rise, and likewise capture and store carbon, making them valuable allies in climate mitigation strategies. Thus, Soil Organic Matter (SOM), i.e. the organic component of the soil, plays a key role within salt-marsh environments, directly contributing to soil formation and supporting carbon storage. This study aims at inspecting spatial patterns of OM in surface salt-marsh soils, providing further insights into the physical and biological factors driving OM dynamics, affecting salt-marsh survival and carbon sink potential. Our results reveal two scales of variations in sedimentary OM content in salt-marsh soils. At the marsh scale OM variability is influenced by the interplay between surface elevation and changes in sediment supply linked with the distance from tidal channels. At the system scale, OM content distribution is dominated by the gradient generated by marine and fluvial influence. Variations in inorganic and organic inputs, both autochthonous and allochthonous, sediment grain size, and preservation conditions may explain the observed variations in SOM. Our results highlight marsh importance as carbon sink environments, furthermore emphasizing that environmental conditions within a tidal system may generate strongly variable and site-specific carbon accumulation patterns, enhancing blue carbon assessment complexity. [ABSTRACT FROM AUTHOR]

The subalpine forests in the Qinghai-Tibet Plateau (QTP) act as carbon sinks in the context of climate change and ecosystem dynamics. In this study, we investigated the carbon sequestration function using the in-situ observations from an eddy covariance system for the subalpine forests. With two-year contiguous observations, the factors driving the seasonal variations in carbon sequestration potential were quantified. We first revealed the seasonal characteristics of carbon dynamics in the subalpine forests during the growing and dormant seasons, respectively. The diurnal carbon exchange exhibited significant fluctuations, as high as 10.78 μmol CO2 s-1 m-2 (12:30, autumn). The period from summer to autumn was identified as the peak in carbon sequestration rate in the subalpine forests. Subsequently, we explored the climatic factors influencing the carbon sequestration function. Photosynthetically active radiation (PAR) was found to be a major climatic factor driving the net ecosystem exchange (NEE) within the same season, significantly influencing forest growth and carbon absorption. Increasing altitude negatively impacts carbon absorption at the regional scale and the rising annual temperature significantly enhances carbon uptake, while the average annual precipitation shows a minor effect on NEE. At the annual scale, the observations at the subalpine forests demonstrated a strong carbon sequestration capability, with an average NEE of 389.03 g C m-2. Furthermore, we roughly assessed the carbon sequestration status of subalpine forests in the QTP. Despite challenges caused by climate change, these forests possess enormous carbon sequestration potential. Currently, they represent the most robust carbon sequestration ecosystem in the QTP. We conclude that enhancing the protection and management of subalpine forests under future climate change scenarios will positively impact global carbon cycling and contribute to climate change mitigation. Moreover, this study provides essential insights for understanding the carbon cycling mechanism in plateau ecosystems and global carbon balance. [ABSTRACT FROM AUTHOR]

Achieving climate targets requires mitigation against climate change, but also understanding of the response of land and ocean carbon systems. In this context, global soil carbon stocks and its response to environmental changes is key. This paper quantifies the global soil carbon feedback to changes in atmospheric CO2, and associated climate changes, for Earth system models (ESMs) in CMIP6. A standard approach is used to calculate carbon cycle feedbacks, defined here as soil specific carbon-concentration (βs) and carbon-climate (γs) feedback parameters. The sensitivity to CO2 is shown to dominate soil carbon changes at least up to a doubling of atmospheric CO2. However, the sensitivity of soil carbon to climate change is found to become an increasingly important source of uncertainty under higher atmospheric CO2 concentrations. [ABSTRACT FROM AUTHOR]

Afforestation and reduction of fossil fuel emissions are two major components of climate mitigation policies. However, their effects on the Earth's climate are different because a reduction of fossil fuel emissions directly alters the biogeochemical cycle of the climate system and modifies the physics of the atmosphere via its impact on radiation and the energy budget, while afforestation causes biophysical changes in addition to changes in the biogeochemical cycle. In this paper, we compare the climate and carbon cycle consequences of carbon removal by afforestation and an equivalent fossil fuel emission reduction using simulations from an intermediate complexity Earth system model. We performed two major sets of idealized simulations in which fossil fuel emissions follow extended Shared Socioeconomic Pathway (SSP) scenarios (SSP2-4.5, 3-7.0, and 5-8.5), and equal amounts of carbon are removed by afforestation in one set and by a reduction in fossil fuel emissions in another set. Our simulations show that the climate is cooler by 0.36, 0.47, and 0.42 ∘C in the long term (2471–2500) in the case of reduced fossil fuel emissions compared to the case with afforestation when the emissions follow the SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios, respectively. The global mean surface temperature is cooler in the reduced fossil fuel emissions case compared to the afforestation case because the net biophysical effect of warming from afforestation partly offsets the biogeochemical cooling effect of afforestation. Thus, in terms of climate benefits, reducing fossil fuel emissions could be relatively more beneficial than afforestation for the same amount of carbon removed from the atmosphere. However, a robust understanding of the processes that govern the biophysical effects of afforestation should be improved before considering our results for climate policy. [ABSTRACT FROM AUTHOR]

Accurate quantification of regional terrestrial fluxes is essential for improving our knowledge of the carbon sequestration potential of ecosystems, ecosystem functioning, and emission reduction demand in the context of climate change mitigation. However, the quantification is challenging owing to methodological and observational constraints, especially for regions with severe gaps in the ground-based observational network, like India. This study examines the potential of recent satellite missions, such as TROPOMI and OCO-2 providing retrievals of Solar-Induced chlorophyll Fluorescence (SIF) to improve terrestrial biosphere CO2 flux estimates over India. Here, we present high-resolution estimates of Gross Primary Productivity (GPP) and Net Ecosystem Exchange (NEE) over India on a 0.1°×0.1° grid at a temporal resolution of 1 hour from 2012 to 2020. These products can be used for various applications such as those related to carbon cycle (e.g., inverse modelling of CO2), benchmarking terrestrial biosphere models over the region, and understanding ecosystem responses to climate change. We follow a satellite-based diagnostic data-driven approach using a biosphere model, namely the Vegetation Photosynthesis and Respiration Model (VPRM) simulating both GPP and NEE, based on light use efficiency and satellite observations of the near-infrared radiance of vegetation (NIRv). We calibrate the standard VPRM GPP estimates using SIF-GPP relationship and investigate the model performance by comparing the simulations with eddy-covariance flux tower measurements. Our best model predictions are with a mean bias error (MBE) = 2.4 µmol m-2 s-1, root mean squared error (RMSE) = 3.8 µmol m-2 s-1 and squared correlation coefficient (R²) = 0.56 when evaluating with observations at a monthly scale over the period from 2012 to 2018. The observed seasonal anomalies in NEE and GPP range from -4.9 to 8.0 µmol m-2 s-1 and -7.0 to 17.0 µmol m-2 s-1, respectively, and are well captured by our model. The model simulations are highly correlated with observations during 2018, the only common year when both EC and SIF observations are available, with R² values of 0.68 and 0.74 for NEE and GPP, respectively. Incorporating the SIF signals in the vegetation model improves model performance in capturing the seasonality and magnitudes of GPP, thereby improving the estimates of NEE. We show the influence of soil temperature and soil moisture on ecosystem respiration and refined the VPRM's ecosystem respiration calculation to better constrain the fluxes, resulting in simulations closer to the observations. Ecosystem respiration fluxes are less well constrained than ecosystem productivity fluxes due to the limited observations. Based on satellite observations and the refined model, the annual NEE and GPP estimates range from -0.38 Pg C yr-1 to -0.53 Pg C yr-1 (land C sink) and 3.39 Pg C yr-1 to 3.88 Pg C yr-1, respectively over India for the years from 2012 to 2020. The biospheric flux distribution over the region is found to be associated with ecosystem heterogeneity, and variations in precipitation, and soil characteristics at a regional scale. Overall, our results show that the satellite-based SIF data products can potentially inform the ecosystem-scale vegetation responses across biomes over India. Future improvements in the terrestrial biosphere CO2 flux estimates over India can be attained through the carbon cycle data assimilation with the availability of both flux and mixing ratio observations of CO2. [ABSTRACT FROM AUTHOR]

Climate warming is accelerating the changes in the global terrestrial ecosystems and particularly those in the northern high latitudes (NHLs; poleward of 50 ∘ N) and rendering the land–atmosphere carbon exchange highly uncertain. The Coupled Model Intercomparison Project Phase 6 (CMIP6) employs the most updated climate models to estimate terrestrial ecosystem carbon dynamics driven by a new set of socioeconomic and climate change pathways. By analyzing the future (2015–2100) carbon fluxes estimated by 10 CMIP6 models, we quantitatively evaluated the projected magnitudes, trends, and uncertainties in the global and NHL carbon fluxes under four scenarios plus the role of NHLs in the global terrestrial ecosystem carbon dynamics. Overall, the models suggest that the global and NHL terrestrial ecosystems will be consistent carbon sinks in the future, and the magnitude of the carbon sinks is projected to be larger under scenarios with higher radiative forcing. By the end of this century, the models on average estimate the NHL net ecosystem productivity (NEP) as 0.54 ± 0.77, 1.01 ± 0.98, 0.97 ± 1.62, and 1.05 ± 1.83 Pg C yr -1 under SSP126, SSP245, SSP370, and SSP585, respectively. The uncertainties are not substantially reduced compared with earlier results, e.g., the Coupled Climate–Carbon Cycle Model Intercomparison Project (C4MIP). Although NHLs contribute a small fraction of the global carbon sink (∼ 13 %), the relative uncertainties in NHL NEP are much larger than the global level. Our results provide insights into future carbon flux evolutions under future scenarios and highlight the urgent need to constrain the large uncertainties associated with model projections for making better climate mitigation strategies. [ABSTRACT FROM AUTHOR]

Afforestation and reduction of fossil fuel emissions are two major components of climate mitigation policies. However, their effects on the earth's climate are different because reduction of fossil fuel emissions directly alters the biogeochemical cycle of the climate system, while afforestation causes biophysical changes in addition to changes in the biogeochemical cycle. In this paper, we compare the climate and carbon cycle consequences 15 of carbon removal by afforestation and an equivalent fossil fuel emission reduction using simulations from an intermediate complexity Earth system model. Our simulations show that the climate is cooler by 0.36°C, 0.47°C, and 0.42°C in the long term (2471-2500) in the case of reduced fossil fuel emissions compared to the case with afforestation when the emissions follow the SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios, respectively. Though afforestation results in a lower atmospheric CO2, the cooling from the reduced atmospheric CO2 is partly offset by the warming from surface albedo decrease associated with the regrowth of forests. Since this warming effect from surface albedo decrease is nearly absent in the reduced fossil fuel emission case, the climate is relatively cooler, even though the atmospheric CO2 levels are similar to the afforestation case. Thus, in terms of climate benefits, reducing fossil fuel emissions is relatively more beneficial than afforestation for the same amount of carbon removed from the atmosphere. Nevertheless, fossil fuel emission reduction and afforestation efforts should be pursued simultaneously as both lead to a decrease in global mean warming and reduced ocean acidification. [ABSTRACT FROM AUTHOR]

Despite an increasing attention on the role of land in meeting countries' climate pledges under the Paris Agreement, the range of estimates of carbon fluxes from land use, land-use change, and forestry (LULUCF) in available databases is very large. A good understanding of the LULUCF data reported by countries under the United Nations Framework Convention on Climate Change (UNFCCC) – and of the differences with other datasets based on country-reported data – is crucial to increase confidence in land-based climate change mitigation efforts. Here we present a new data compilation of LULUCF fluxes of carbon dioxide (CO 2) on managed land, aiming at providing a consolidated view on the subject. Our database builds on a detailed analysis of data from national greenhouse gas inventories (NGHGIs) communicated via a range of country reports to the UNFCCC, which report anthropogenic emissions and removals based on the IPCC (Intergovernmental Panel on Climate Change) methodology. Specifically, for Annex I countries, data are sourced from annual GHG inventories. For non-Annex I countries, we compiled the most recent and complete information from different sources, including national communications, biennial update reports, submissions to the REDD + (reducing emissions from deforestation and forest degradation) framework, and nationally determined contributions. The data are disaggregated into fluxes from forest land, deforestation, organic soils, and other sources (including non-forest land uses). The CO 2 flux database is complemented by information on managed and unmanaged forest area as available in NGHGIs. To ensure completeness of time series, we filled the gaps without altering the levels and trends of the country reported data. Expert judgement was applied in a few cases when data inconsistencies existed. Results indicate a mean net global sink of -1.6 Gt CO 2 yr -1 over the period 2000–2020, largely determined by a sink on forest land (-6.4 Gt CO 2 yr -1), followed by source from deforestation (+4.4 Gt CO 2 yr -1), with smaller fluxes from organic soils (+0.9 Gt CO 2 yr -1) and other land uses (-0.6 Gt CO 2 yr -1). Furthermore, we compare our NGHGI database with two other sets of country-based data: those included in the UNFCCC GHG data interface, and those based on forest resources data reported by countries to the Food and Agriculture Organization of the United Nations (FAO) and used as inputs into estimates of GHG emissions in FAOSTAT. The first dataset, once gap filled as in our study, results in a net global LULUCF sink of -5.4 Gt CO 2 yr -1. The difference with the NGHGI database is in this case mostly explained by more updated and comprehensive data in our compilation for non-Annex I countries. The FAOSTAT GHG dataset instead estimates a net global LULUCF source of +1.1 Gt CO 2 yr -1. In this case, most of the difference to our results is due to a much greater forest sink for non-Annex I countries in the NGHGI database than in FAOSTAT. The difference between these datasets can be mostly explained by a more complete coverage in the NGHGI database, including for non-biomass carbon pools and non-forest land uses, and by different underlying data on forest land. The latter reflects the different scopes of the country reporting to FAO, which focuses on area and biomass, and to UNFCCC, which explicitly focuses on carbon fluxes. Bearing in mind the respective strengths and weaknesses, both our NGHGI database and FAO offer a fundamental, yet incomplete, source of information on carbon-related variables for the scientific and policy communities, including under the Global stocktake. Overall, while the quality and quantity of the LULUCF data submitted by countries to the UNFCCC significantly improved in recent years, important gaps still remain. Most developing countries still do not explicitly separate managed vs. unmanaged forest land, a few report implausibly high forest sinks, and several report incomplete estimates. With these limits in mind, the NGHGI database presented here represents the most up-to-date and complete compilation of LULUCF data based on country submissions to UNFCCC. Data from this study are openly available via the Zenodo portal (Grassi et al., 2022), at 10.5281/zenodo.7190601. [ABSTRACT FROM AUTHOR]

The increasing rates of CO 2 due to anthropogenic activities are causing important potential climate threats for the Mediterranean Sea: ocean acidification and warming. In this region, two seagrass species, Posidonia oceanica and Cymodocea nodosa, can play a crucial role in climate change mitigation. Seagrasses can act as carbon sinks, buffer lowering pH values during the day and storing carbon in the sediment underneath their meadows. However, available data documenting these processes are scattered and collected using different methodologies, which makes its interpretation and generalization very challenging. In this study, we analyzed published and unpublished data (collected for this study) on seagrass community metabolism to compare two methodologies, benthic chambers and multiparametric sensors, and evaluate trends through time for these two species. Furthermore, we analyzed seasonal trends of both seagrass species' metabolic rates and their variation between the eastern and western Mediterranean basins. Most evaluated meadows, 80.9 %, were autotrophic. Calculated metabolic rates differ between methodologies, with multiparametric sensors estimating rates almost an order of magnitude higher, 143.22±28.21 (SE) mmol O 2 m -2 d -1 for net community production (NCP) compared to an average of 18.75±3.80 (SE) mmol O 2 m -2 d -1 for measurements with benthic chambers. However, sensors are not able to differentiate between habitats and only useful to assess seagrass metabolism at a broader community level, whereas benthic chambers are capable of evaluating rates at the species level and confirm that P. oceanica is more productive compared to C. nodosa. We found similar metabolic rates in the eastern and western Mediterranean regions for P. oceanica with the benthic-chamber technique and higher NCP in the west based on sensor measurements. [ABSTRACT FROM AUTHOR]

Climate warming is accelerating the changes in the global terrestrial ecosystems and particularly those in the northern high latitudes (NHL), and rendering the land-atmosphere carbon exchange highly uncertain. The Coupled Model Intercomparison Project Phase 6 (CMIP6) employs the most updated climate models to estimate terrestrial ecosystem carbon dynamics driven by a new set of socioeconomic and climate change pathways. By analyzing the future (2015-2100) carbon fluxes estimated by ten CMIP6 models, we quantitatively evaluated the projected magnitudes, trends and uncertainties of global and NHL carbon fluxes under four scenarios plus the role of NHL in the global terrestrial ecosystem carbon dynamics. Overall, the models suggest that the global and NHL terrestrial ecosystems will be consistent carbon sinks in the future, and the extent of the carbon sinks is projected to be larger under scenarios with higher radiative forcing. By the end of this century, the models by average estimate the NHL net ecosystem productivity (NEP) as 0.54±0.77, 1.01±0 .98, 0.97±1.62, and 1.05±1.83 PgC/yr under SSP126, SSP245, SSP370 and SSP585, respectively. The uncertainties are not substantially reduced compared with earlier results, e.g., the Coupled Climate Carbon Cycle Model Intercomparison Project (C4MIP). Although NHL contributes a small fraction of the global carbon sink (~13%), the relative uncertainties of NHL NEP are much larger than the global level. Our results provide insights into future carbon flux evolutions under future scenarios and highlight the urgent need to constrain the large uncertainties associated with model projections for making better climate mitigation strategies. [ABSTRACT FROM AUTHOR]

Along with habitat transformation, climate change has profound impacts on biodiversity and may alter ecosystem services on which human welfare depends. Many studies of the carbon cycle have focused on lowland tropical forests; however, upland forests have been less explored despite their pivotal role in carbon sequestration. Here, I synthesized the state of knowledge on the allocation of carbon in its different stocks (aboveground, belowground, and soil) as well as in its main fluxes (plant decomposition, respiration, and litterfall) in tropical upland ecosystems of the planet. In November 2020, a systematic review was carried out to identify references published from 2000 to 2020 through a combination of key terms in Google Scholar and Scopus databases, thus analysing bibliographic, geographical, methodological, and carbon cycling information of the global upland tropics (between 23.5 ∘ N–23.5 ∘ S). After analysing a total of 1967 references according to inclusion–exclusion criteria, 135 references published in the last 20 years were selected. Most of the studies were conducted in the tropical and subtropical moist broadleaf forest of South America. The main factors studied were elevation and forest type. Forest structure and soil variables were largely associated when studying carbon cycling in these ecosystems. Estimations of carbon stocks comprised three-fourths of the total studies, while the remaining fraction focused on carbon fluxes. Aboveground biomass and carbon in soils were highly investigated, while plant decomposition and respiration were the components that received the least attention. Even though in the last 20 years there was a slight increase in the number of studies on carbon cycle in tropical upland forests, I found bias associated with the biomes and ecoregions studied (especially in the Andes). Elevation was the main factor examined but other essential aspects such as the successional gradient, landscape management, diversity–productivity relationship, faunal and microbial effect, trophic cascades, and Gadgil effect require more attention. The inclusion of different litter species and origins (i.e. roots and stems) and theoretical frameworks including home-field advantage, substrate–matrix interaction, and phenology–substrate match may provide explanatory mechanisms to better understand litter decomposition over these forests. Despite respiration being a paramount link that is closely tied to above- and belowground compartment, this flux constitutes one of the important gaps to fulfil in future research. For a comprehensive understanding of the carbon cycle in upland forests, it is necessary to obtain information on its main fluxes and integrate them into climate change mitigation plans. [ABSTRACT FROM AUTHOR]

To achieve the Paris Agreement requires aggressive mitigation strategies alongside negative emission technologies. Recent studies suggest that increasing tree cover can make a substantial contribution to negative emissions, with the tropics being the most suitable region from a biogeophysical perspective. Yet these studies typically do not account for subsequent carbon cycle and climate responses to large-scale land-use change. Here we quantify the maximum potential temperature and CO 2 benefits from pantropical forest restoration, including the Earth system response, using a fully coupled, emission-driven Earth system model (HadGEM2-ES). We perform an idealised experiment where all land use in the tropics is stopped and vegetation is allowed to recover, on top of an aggressive mitigation scenario (RCP2.6). We find that tropical restoration of 1529 Mha increases carbon stored in live biomass by 130 Pg C by 2100 CE. Whilst avoiding deforestation and tropical restoration in the tropics removes 42 Pg C compared to RCP2.6, the subsequent reduction in extratropical and ocean carbon uptake means that carbon in the atmosphere only reduces by 18 Pg C by 2100. The resulting small CO 2 (9 ppm) benefit does not translate to a detectable reduction in global surface air temperature compared to the control experiment. The greatest carbon benefit is achieved 30–50 years after restoration before the Earth system response adjusts to the new land-use regime and declining fossil fuel use. Comparing our results with previous modelling studies, we identify two model-independent key points: (i) in a world where emission reductions follow the Paris Agreement, restoration is best deployed immediately, and (ii) the global carbon cycle response to reduced emissions limits the efficacy of negative emissions technologies by more than half. We conclude that forest restoration can reduce peak CO 2 mid-century, but it can only modestly contribute to negative emissions. [ABSTRACT FROM AUTHOR]

Quantifying the net carbon flux from land use and land cover changes (fLULCC) is critical for understanding the global carbon cycle and, hence, to support climate change mitigation. However, large-scale fLULCC is not directly measurable and has to be inferred from models instead, such as semi-empirical bookkeeping models and process-based dynamic global vegetation models (DGVMs). By definition, fLULCC estimates are not directly comparable between these two different model types. As an important example, DGVM-based fLULCC in the annual global carbon budgets is estimated under transient environmental forcing and includes the so-called loss of additional sink capacity (LASC). The LASC results from the impact of environmental changes on land carbon storage potential of managed land compared to potential vegetation and accumulates over time, which is not captured in bookkeeping models. The fLULCC from transient DGVM simulations, thus, strongly depends on the timing of land use and land cover changes mainly because LASC accumulation is cut off at the end of the simulated period. To estimate the LASC, the fLULCC from pre-industrial DGVM simulations, which is independent of changing environmental conditions, can be used. Additionally, DGVMs using constant present-day environmental forcing enable an approximation of bookkeeping estimates. Here, we analyse these three DGVM-derived fLULCC estimations (under transient, pre-industrial, and present-day forcing) for 12 models within 18 regions and quantify their differences as well as climate- and CO2 -induced components and compare them to bookkeeping estimates. Averaged across the models, we find a global fLULCC (under transient conditions) of 2.0±0.6 PgC yr -1 for 2009–2018, of which ∼40 % are attributable to the LASC (0.8±0.3 PgC yr -1). From 1850 onward, the fLULCC accumulated to 189±56 PgC with 40±15 PgC from the LASC. Around 1960, the accumulating nature of the LASC causes global transient fLULCC estimates to exceed estimates under present-day conditions, despite generally increased carbon stocks in the latter. Regional hotspots of high cumulative and annual LASC values are found in the USA, China, Brazil, equatorial Africa, and Southeast Asia, mainly due to deforestation for cropland. Distinct negative LASC estimates in Europe (early reforestation) and from 2000 onward in the Ukraine (recultivation of post-Soviet abandoned agricultural land), indicate that fLULCC estimates in these regions are lower in transient DGVM compared to bookkeeping approaches. Our study unravels the strong dependence of fLULCC estimates on the time a certain land use and land cover change event happened to occur and on the chosen time period for the forcing of environmental conditions in the underlying simulations. We argue for an approach that provides an accounting of the fLULCC that is more robust against these choices, for example by estimating a mean DGVM ensemble fLULCC and LASC for a defined reference period and homogeneous environmental changes (CO2 only). [ABSTRACT FROM AUTHOR]

Scenarios avoiding global warming greater than 1.5 or 2 ∘ C, as stipulated in the Paris Agreement, may require the combined mitigation of anthropogenic greenhouse gas emissions alongside enhancing negative emissions through approaches such as afforestation–reforestation (AR) and biomass energy with carbon capture and storage (BECCS). We use the JULES land surface model coupled to an inverted form of the IMOGEN climate emulator to investigate mitigation scenarios that achieve the 1.5 or 2 ∘ C warming targets of the Paris Agreement. Specifically, within this IMOGEN-JULES framework, we focus on and characterise the global and regional effectiveness of land-based (BECCS and/or AR) and anthropogenic methane (CH4) emission mitigation, separately and in combination, on the anthropogenic fossil fuel carbon dioxide (CO2) emission budgets (AFFEBs) to 2100. We use consistent data and socio-economic assumptions from the IMAGE integrated assessment model for the second Shared Socioeconomic Pathway (SSP2). The analysis includes the effects of the methane and carbon–climate feedbacks from wetlands and permafrost thaw, which we have shown previously to be significant constraints on the AFFEBs. Globally, mitigation of anthropogenic CH4 emissions has large impacts on the anthropogenic fossil fuel emission budgets, potentially offsetting (i.e. allowing extra) carbon dioxide emissions of 188–212 Gt C. This is because of (a) the reduction in the direct and indirect radiative forcing of methane in response to the lower emissions and hence atmospheric concentration of methane and (b) carbon-cycle changes leading to increased uptake by the land and ocean by CO2 -based fertilisation. Methane mitigation is beneficial everywhere, particularly for the major CH4 -emitting regions of India, the USA, and China. Land-based mitigation has the potential to offset 51–100 Gt C globally, the large range reflecting assumptions and uncertainties associated with BECCS. The ranges for CH4 reduction and BECCS implementation are valid for both the 1.5 and 2 ∘ C warming targets. That is the mitigation potential of the CH4 and of the land-based scenarios is similar for regardless of which of the final stabilised warming levels society aims for. Further, both the effectiveness and the preferred land management strategy (i.e. AR or BECCS) have strong regional dependencies. Additional analysis shows extensive BECCS could adversely affect water security for several regions. Although the primary requirement remains mitigation of fossil fuel emissions, our results highlight the potential for the mitigation of CH4 emissions to make the Paris climate targets more achievable. [ABSTRACT FROM AUTHOR]

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. Here, we explore how this proportionality will weaken and find significant effects related to changes in the vertical transfer of Cant from the surface to the deep ocean, and also ocean chemistry. We define ocean uptake growth consistent with an exact proportionality to the atmospheric growth rate, i.e. the historical scaling, to be 100% efficient. Using a model hierarchy consisting of a commonly used one-dimensional ocean carbon cycle model and a complex Earth System Model (ESM), we find that declines in the efficiency of ocean uptake are greatest under aggressive emission mitigation. To understand the drivers of efficiency declines, 10 we use the ESM to compare scenarios with aggressive emission mitigation (1.5°C), intermediate emission mitigation (RCP4.5), and no emission mitigation (RCP8.5). Using the one-dimensional ocean carbon cycle model, we demonstrate how growth of ocean Cant uptake is a balance between enhancement due to a positive atmospheric CO2 growth rate, and decreases due to the positive growth rate of dissolved CO2 in the surface ocean. Without emission mitigation (RCP8.5), changes in efficiency are almost entirely the result of changes in the buffer capacity of the ocean, which accelerates the growth rate of dissolved 15 CO2 in the surface ocean. Under the declining CO2 regime of the 1.5° C scenario, the dominant driver of efficiency decline is the carbon gradient effect, wherein Cant in the ocean interior slows the removal of Cant from the surface. Although the carbon gradient effect is an unavoidable consequence of emission mitigation, it can be reduced by hastily pursuing emission mitigation. [ABSTRACT FROM AUTHOR]

Forest ecosystems are already responding to changing environmental conditions that are driven by increased atmospheric CO2 concentrations. These developments affect how societies can utilise and benefit from the woodland areas in the future, be it for example climate change mitigation as carbon sinks, lumber for wood industry, or preserved for nature tourism and recreational activities. We assess the effect and the relative magnitude of different uncertainty sources in ecosystem model simulations from the year 1980 to 2100 for two Finnish boreal forest sites. The models used in this study are the land ecosystem model JSBACH and the forest growth model PREBAS. The considered uncertainty sources for both models are model parameters and four prescribed climates with two RCP (representative concentration pathway) scenarios. Usually, model parameter uncertainty is not included in these types of uncertainty studies. PREBAS simulations also include two forest management scenarios. We assess the effect of these sources of variation at four different points in time on several ecosystem indicators, e.g. gross primary production (GPP), ecosystem respiration, soil moisture, recurrence of drought, length of the vegetation active period (VAP), length of the snow melting period and the stand volume. The uncertainty induced by the climate models remains roughly the same throughout the simulations and is overtaken by the RCP scenario impact halfway through the experiment. The management actions are the most dominant uncertainty factors for Hyytiälä and as important as RCP scenarios at the end of the simulations, but they contribute only half as much for Sodankylä. The parameter uncertainty is the least influential of the examined uncertainty sources, but it is also the most elusive to estimate due to non-linear and adverse effects on the simulated ecosystem indicators. Our analysis underlines the importance of carefully considering the implementation of forest use when simulating future ecosystem conditions, as human impact is evident and even increasing in boreal forested regions. [ABSTRACT FROM AUTHOR]

Forest ecosystems play an important role in the global climate system and are thus intensively discussed in the context of climate change mitigation. Over the past decades temperate forests were a carbon (C) sink to the atmosphere. However, it remains unclear to which degree this C uptake is driven by a recovery from past land use and natural disturbances or ongoing climate change, inducing high uncertainty regarding the future temperate forest C sink. Here our objectives were (i) to investigate legacies within the natural disturbance regime by empirically analyzing two disturbance episodes affecting the same landscape 90 years apart, and (ii) to unravel the effects of past land use and natural disturbances as well as the future climate on 21st century forest C uptake by means of simulation modeling. We collected historical data from archives to reconstruct the vegetation and disturbance history of a forest landscape in the Austrian Alps from 1905 to 2013. The effects of legacies and climate were disentangled by individually controlling for past land use, natural disturbances, and future scenarios of climate change in a factorial simulation study. We found only moderate spatial overlap between two episodes of wind and bark beetle disturbance affecting the landscape in the early 20th and 21st century, respectively. Our simulations revealed a high uncertainty about the relationship between the two disturbance episodes, whereas past land use clearly increased the impact of the second disturbance episode on the landscape. The future forest C sink was strongly driven by the cessation of historic land use, while climate change reduced forest C uptake. Compared to land-use change the two past episodes of natural disturbance had only marginal effects on the future carbon cycle. We conclude that neglecting legacies can substantially bias assessments of future forest dynamics. [ABSTRACT FROM AUTHOR]

Accurate assessment of forest carbon storage and uptake is central to policymaking aimed at mitigating climate change and understanding the role forests play in the global carbon cycle. Disturbances have highly diverse impacts on forest carbon dynamics, making them a challenge to quantify and report. Time since disturbance is a key intermediate determinant that aids the assessment of disturbancedriven carbon emissions and removals legacies. We propose a new methodology of quantifying time since disturbance and carbon flux across forested landscapes in the Pacific Northwest (PNW) at a fine scale (30 m) by combining remote sensing (RS)-based disturbance year, disturbance type, and above-ground biomass with forest inventory data. When a recent disturbance is detected, time since disturbance can be directly determined by combining three RSderived disturbance products, or time since the last stand clearing can be inferred from a RS-derived 30m biomass map and field inventory-derived species-specific biomass accumulation curves. Net ecosystem productivity (NEP) is further mapped based on carbon stock and flux trajectories derived from the Carnegie-Ames-Stanford Approach (CASA) model in our prior work that described how NEP changes with time following harvest, fire, or bark beetle disturbances of varying severity. Uncertainties from biomass map and forest inventory data were propagated by probabilistic sampling to provide a statistical distribution of stand age and NEP for each forest pixel. We mapped mean, standard deviation, and statistical distribution of stand age and NEP at 30m in the PNW region. Our map indicated a net ecosystem productivity of 5.9 Tg C yr-1 for forestlands circa 2010 in the study area, with net uptake in relatively mature (> 24 years old) forests (13.6 Tg C yr-1) overwhelming net negative NEP from tracts that had recent harvests (-6.4 TgC yr-1), fires (-0.5 TgC yr-1), and bark beetle outbreaks (-0.8 TgC yr-1). The approach will be applied to forestlands in other regions of the conterminous US to advance a more comprehensive monitoring, mapping, and reporting of the carbon consequences of forest change across the US. [ABSTRACT FROM AUTHOR]

Assessment of forest carbon storage and uptake is central to understanding the role forests play in the global carbon cycle and policy-making aimed at mitigating climate change. Current U.S. carbon stocks and fluxes are monitored and reported at fine-scale regionally, or coarse-scale nationally. We proposed a new methodology of quantifying carbon uptake and release across forested landscapes in the Pacific Northwest (PNW) at a fine scale (30 m) by combining remote-sensing based disturbance year, disturbance type, and aboveground biomass with forest inventory data in a carbon modelling framework. Time since disturbance is a key intermediate determinant that aided the assessment of disturbance-driven carbon emissions and removals legacies. When a recent disturbance was detected, time since disturbance can be directly determined by remote sensing-derived disturbance products; and if not, time since last stand-clearing was inferred from remote sensing-derived 30 m biomass map and field inventory-derived species-specific biomass regrowth curves. Net ecosystem productivity (NEP) was further mapped based on carbon stock and flux trajectories that described how NEP changes with time following harvest, fire, or bark beetle disturbances of varying severity. Uncertainties from biomass map and forest inventory data were propagated by probabilistic sampling to provide a probabilistic, statistical distribution of stand age and NEP for each forest pixel. We mapped mean, standard deviation and statistical distribution of stand age and NEP at 30 m in the PNW region. Our map indicated a net ecosystem productivity of 5.2 Tg C y-1 for forestlands circa 2010 in the study area, with net uptake in relatively mature (> 24 year old) forests (13.6 Tg C y-1) overwhelming net negative NEP from tracts that have seen recent harvest (-6.4 Tg C y-1), fires (-0.5 Tg C y-1), and bark beetle outbreaks (-1.4 Tg C y-1). The approach will be applied to forestlands in other regions of the conterminous U.S. to advance a more comprehensive monitoring, mapping and reporting the carbon consequences of forest change across the U.S. [ABSTRACT FROM AUTHOR]

Since 70% of global forests are managed and forests impact the global carbon cycle and the energy exchange with the overlying atmosphere, forest management has the potential to mitigate climate change. Yet, none of the land-surface models used in Earth system models, and therefore none of today's predictions of future climate, accounts for the interactions between climate and forest management. We addressed this gap in modelling capability by developing and parametrising a version of the ORCHIDEE land-surface model to simulate the biogeochemical and biophysical effects of forest management. The most significant changes between the new branch called ORCHIDEE-CAN (SVN r2290) and the trunk version of ORCHIDEE (SVN r2243) are the allometric-based allocation of carbon to leaf, root, wood, fruit and reserve pools; the transmittance, absorbance and reflectance of radiation within the canopy; and the vertical discretisation of the energy budget calculations. In addition, conceptual changes were introduced towards a better process representation for the interaction of radiation with snow, the hydraulic architecture of plants, the representation of forest management and a numerical solution for the photosynthesis formalism of Farquhar, von Caemmerer and Berry. For consistency reasons, these changes were extensively linked throughout the code. Parametrisation was revisited after introducing 12 new parameter sets that represent specific tree species or genera rather than a group of often distantly related or even unrelated species, as is the case in widely used plant functional types. Performance of the new model was compared against the trunk and validated against independent spatially explicit data for basal area, tree height, canopy structure, gross primary production (GPP), albedo and evapotranspiration over Europe. For all tested variables, ORCHIDEE-CAN outperformed the trunk regarding its ability to reproduce large-scale spatial patterns as well as their inter-annual variability over Europe. Depending on the data stream, ORCHIDEE-CAN had a 67 to 92% chance to reproduce the spatial and temporal variability of the validation data. [ABSTRACT FROM AUTHOR]

Natural peatlands are important carbon sinks and sources of methane (CH4). In contrast, drained peatlands turn from a carbon sink to a carbon source and potentially emit nitrous oxide (N2O). Rewetting of peatlands thus potentially implies climate change mitigation. However, data about the time span that is needed for the re-establishment of the carbon sink function by restoration are scarce. We therefore investigated the annual greenhouse gas (GHG) balances of three differently vegetated sites of a bog ecosystem 30 years after rewetting. All three vegetation communities turned out to be sources of carbon dioxide (CO2) ranging between 0.6 ± 1.43 t CO2 ha-2yr-1 (Sphagnum-dominated vegetation) and 3.09 ± 3.86 t CO 2ha-2yr-1 (vegetation dominated by heath). While accounting for the different global warming potential (GWP) of CO2, CH4 and N2O, the annual GHG balance was calculated. Emissions ranged between 25 and 53 t CO2-eq ha-1yr-1 and were dominated by large emissions of CH4 (22-51 t CO2-eq ha-1 yr-1), with highest rates found at purple moor grass (Molinia caerulea) stands. These are to our knowledge the highest CH4 emissions so far reported for bog ecosystems in temperate Europe. As the restored area was subject to large fluctuations in the water table, we assume that the high CH4 emission rates were caused by a combination of both the temporal inundation of the easily decomposable plant litter of purple moor grass and the plant-mediated transport through its tissues. In addition, as a result of the land use history, mixed soil material due to peat extraction and refilling can serve as an explanation. With regards to the long time span passed since rewetting, we note that the initial increase in CH4 emissions due to rewetting as described in the literature is not inevitably limited to a short-term period. [ABSTRACT FROM AUTHOR]

Through 1959-2012, an airborne fraction (AF) of 0.44 of total anthropogenic CO2 emissions remained in the atmosphere, with the rest being taken up by land and ocean CO2 sinks. Understanding of this uptake is critical because it greatly alleviates the emissions reductions required for climate mitigation, and also reduces the risks and damages that adaptation has to embrace. An observable quantity that reflects sink properties more directly than the AF is the CO2 sink rate (kS), the combined land-ocean CO2 sink flux per unit excess atmospheric CO2 above preindustrial levels. Here we show from observations that kS declined over 1959-2012 by a factor of about 1/3, implying that CO2 sinks increased more slowly than excess CO2. Using a carbon-climate model, we attribute the decline in kS to four mechanisms: slower-than-exponential CO2 emissions growth (~ 35 % of the trend), volcanic eruptions (~ 25 %), sink responses to climate change (~ 20 %), and nonlinear responses to increasing CO2, mainly oceanic (~20%). The first of these mechanisms is associated purely with the trajectory of extrinsic forcing, and the last two with intrinsic, feedback responses of sink processes to changes in climate and atmospheric CO2. Our results suggest that the effects of these intrinsic, nonlinear responses are already detectable in the global carbon cycle. Although continuing future decreases in kS will occur under all plausible CO2 emission scenarios, the rate of decline varies between scenarios in non-intuitive ways because extrinsic and intrinsic mechanisms respond in opposite ways to changes in emissions: extrinsic mechanisms cause kS to decline more strongly with increasing mitigation, while intrinsic mechanisms cause kS to decline more strongly under high-emission, low-mitigation scenarios as the carbon-climate system is perturbed further from a near-linear regime. [ABSTRACT FROM AUTHOR]

Becker et al. (2013) argue that an afforestation of 0.73 109 ha with Jatropha curcas plants would generate an additional terrestrial carbon sink of 4.3 PgC yr-1, enough to stabilise the atmospheric mixing ratio of carbon dioxide (CO2) at current levels. However, this is not consistent with the dynamics of the global carbon cycle. Using a well established global carbon cycle model, the effect of adding such a hypothetical sink leads to a reduction of atmospheric CO2 levels in the year 2030 by 25 ppm compared to a reference scenario. However, the stabilisation of the atmospheric CO2 concentration requires a much larger additional sink or corresponding reduction of anthropogenic emissions. [ABSTRACT FROM AUTHOR]

Earth system models are an important basis to develop adaptation and mitigation strategies for climate change. Fire impacts the carbon cycle and climate on global scale and therefore is an important component in Earth system models. We here review the literature over the recent years with respect to advances in understanding and quantification of the impacts of fire on the carbon cycle and climate with the aim to identify potential for model improvement and research needs to adequately represent fire in Earth system models.The quantification of peatland carbon and pyrogenic carbon ages provides important constraints for models. Both components are mostly not included in global models. Peatlands accumulated carbon for the holocene. Climate change and human activities increase the vulnerability of this old carbon pools, that will likely not recover their pre-fire state. Charcoal is a byproduct of incomplete combustion. This pyrogenic carbon is accumulated in soils and ocean sediments for hundreds and thousands of years. Although it is a small fraction, the huge reservoirs show that it is an important component of the carbon cycle. The reservoirs are big in comparison to expected losses from the terrestrial carbon stocks and therefore might indicate that fires are a net sink. Human climate mitigation strategies plan to use biochar as a measure of negative emissions. This will lead to a large perturbation of the pyrogenic carbon cycle, a better understanding of it is therefore important. The effects of fire impacts on vegetation not only influence the carbon cycle but also the effect on climate. The ability of ecosystems to recover after fire determines the duration of the impacts. The strong impacts of humans on fire regimes strongly influences global patterns. The relationship between humans and fire is however not sufficiently well understood.Improvements in global models for peatland burning, pyrogenic carbon and the effects of vegetation types and traits are possible based on the recent advances and will help to improve Earth system model to provide the necessary information on the future fate of carbon storage and climate. [ABSTRACT FROM AUTHOR]

In 2016, 175 parties agreed to ambitious greenhouse gas reductions under the UNFCCC Paris agreement, yet estimates of greenhouse gas emissions and uptake by sinks remain uncertain. The capability to verify emissions reductions at sub-national to national scale and guide carbon mitigation policy is urgently needed to support climate mitigation. Atmospheric greenhouse gas measurements have a key role to play. The amount of greenhouse gases stored in the atmosphere is the by far the most well-known component of greenhouse gas budgets due to precise, accurate greenhouse gas records from a global network that comprises more than 400 stations, supported by over 80 nations. These measurements have been crucial to a range of scientific studies, but we have only begun to explore their potential to inform carbon mitigation policy. We will present results form a case study in New Zealand, which suggests that NZ's land biosphere absorbs much more carbon than expected from the National Inventory Report (NIR) and previous synthesis reports. The NIR is the official national reporting of our greenhouse gas emissions and removals that follows international protocols and must be submitted annually to meet our UNFCCC obligations. The atmospheric data suggests that much of this missing carbon sink occurs in Fiordland, a high rainfall region dominated by indigenous forests. In addition to the results of our pilot study will present plans to expand this effort through the newly funded CarbonWatch-NZ project. This five year programme will expand our national observing network to 11 permanent and 2 temporary stations, introduce urban and regional forest scale studies, leverage measurements of isotopes and carbonyl sulphide to understand source and sink processes, and integrate flux tower observations to understand the role of pastures. In addition to addressing the scientific findings of this study, we will discuss the process used to engage New Zealand's NIR and environmental policy communities, starting from the development phase of the project. This will include the strategies used to resolve differences between components of the carbon budget counted in the NIR and those detected by the inversion, communicate uncertainties, and plan research activities that meet policy needs. [ABSTRACT FROM AUTHOR]

The global carbon cycle is currently being perturbed by the large-scale burning of fossil fuels, leading to rising global temperatures and related stress and damage to life on Earth. At the same time, we lack a detailed understanding of the various reservoirs and fluxes of the coastal and marine carbon cycle. Quantification of marine organic carbon stocks and their vulnerability to climate change and human activities is crucial for effective climate change mitigation and other management strategies. Recently, research has focussed on the ability of salt marshes, mangroves, seagrasses and macroalgae, so-called Blue Carbon ecosystems, to remove carbon dioxide from the atmosphere and store it as organic carbon. Likewise, fjords have been identified as locations of rapid burial of organic carbon. Less attention has, however, been directed to continental shelf sediments, presumably due to low carbon densities found in such sediments. Despite this, there are indications that organic carbon stocks of surficial shelf sediments are important: It was estimated that the upper 10 cm of the north-west European continental shelf sea sediments store between 230 and 882 teragrams (Tg) of organic carbon. A recent study found that organic carbon stocks of continental shelf sediments by far exceed those of salt marshes and seagrasses in the United Kingdom. Additionally, it was reported that marine sediment organic carbon stocks might be of similar magnitude as terrestrial soil stocks in some maritime nations.Here we report on initial results of a pilot study, which aims to spatially predict organic carbon stocks and burial rates of surface sediments in the Norwegian Trough and North Sea. This pilot study attempts to establish suitable methodologies for making such spatial predictions based on a comprehensive set of existing data on organic carbon concentrations, sediment properties and sedimentation rates. It is hoped that a complete assessment of stocks and burial rates on the Norwegian continental shelf will subsequently be conducted under the auspices of the MAREANO seafloor mapping programme. Initial results indicate that the Norwegian Trough stores approximately 67 Tg of organic carbon in the upper 10 cm of the sediment column alone. By comparison, the sediments of the Norwegian part of the North Sea, which have organic carbon densities typical for the north-west European continental shelf, contain approximately 36 Tg of organic carbon in an area that is 25% larger than the Norwegian Trough. These results indicate that the Norwegian Trough is an important regional store for organic carbon. Subsequent analysis will attempt to shed light on burial rates and the residence time of organic carbon within the zone of active degradation. [ABSTRACT FROM AUTHOR]