scholarly journals Carbon cycle uncertainty in the Alaskan Arctic

2014 ◽  
Vol 11 (15) ◽  
pp. 4271-4288 ◽  
Author(s):  
J. B. Fisher ◽  
M. Sikka ◽  
W. C. Oechel ◽  
D. N. Huntzinger ◽  
J. R. Melton ◽  
...  
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Primary Production ◽  
Net Primary Production ◽  
Carbon Sink ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
The Arctic ◽  
Regional Patterns ◽  
Alaskan Arctic

Abstract. Climate change is leading to a disproportionately large warming in the high northern latitudes, but the magnitude and sign of the future carbon balance of the Arctic are highly uncertain. Using 40 terrestrial biosphere models for the Alaskan Arctic from four recent model intercomparison projects – NACP (North American Carbon Program) site and regional syntheses, TRENDY (Trends in net land atmosphere carbon exchanges), and WETCHIMP (Wetland and Wetland CH4 Inter-comparison of Models Project) – we provide a baseline of terrestrial carbon cycle uncertainty, defined as the multi-model standard deviation (σ) for each quantity that follows. Mean annual absolute uncertainty was largest for soil carbon (14.0 ± 9.2 kg C m−2), then gross primary production (GPP) (0.22 ± 0.50 kg C m−2 yr−1), ecosystem respiration (Re) (0.23 ± 0.38 kg C m−2 yr−1), net primary production (NPP) (0.14 ± 0.33 kg C m−2 yr−1), autotrophic respiration (Ra) (0.09 ± 0.20 kg C m−2 yr−1), heterotrophic respiration (Rh) (0.14 ± 0.20 kg C m−2 yr−1), net ecosystem exchange (NEE) (−0.01 ± 0.19 kg C m−2 yr−1), and CH4 flux (2.52 ± 4.02 g CH4 m−2 yr−1). There were no consistent spatial patterns in the larger Alaskan Arctic and boreal regional carbon stocks and fluxes, with some models showing NEE for Alaska as a strong carbon sink, others as a strong carbon source, while still others as carbon neutral. Finally, AmeriFlux data are used at two sites in the Alaskan Arctic to evaluate the regional patterns; observed seasonal NEE was captured within multi-model uncertainty. This assessment of carbon cycle uncertainties may be used as a baseline for the improvement of experimental and modeling activities, as well as a reference for future trajectories in carbon cycling with climate change in the Alaskan Arctic and larger boreal region.

scholarly journals Carbon cycle uncertainty in the Alaskan Arctic

2014 ◽  
Vol 11 (2) ◽  
pp. 2887-2932 ◽  
Author(s):  
J. B. Fisher ◽  
M. Sikka ◽  
W. C. Oechel ◽  
D. N. Huntzinger ◽  
J. R. Melton ◽  
...  
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Primary Production ◽  
Net Primary Production ◽  
Carbon Sink ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
The Arctic ◽  
Regional Patterns ◽  
Alaskan Arctic

Abstract. Climate change is leading to a disproportionately large warming in the high northern latitudes, but the magnitude and sign of the future carbon balance of the Arctic are highly uncertain. Using 40 terrestrial biosphere models for Alaska, we provide a baseline of terrestrial carbon cycle structural and parametric uncertainty, defined as the multi-model standard deviation (σ) against the mean (x) for each quantity. Mean annual uncertainty (σ/x) was largest for net ecosystem exchange (NEE) (−0.01± 0.19 kg C m−2 yr−1), then net primary production (NPP) (0.14 ± 0.33 kg C m−2 yr−1), autotrophic respiration (Ra) (0.09 ± 0.20 kg C m−2 yr−1), gross primary production (GPP) (0.22 ± 0.50 kg C m−2 yr−1), ecosystem respiration (Re) (0.23 ± 0.38 kg C m−2 yr−1), CH4 flux (2.52 ± 4.02 g CH4 m−2 yr−1), heterotrophic respiration (Rh) (0.14 ± 0.20 kg C m−2 yr−1), and soil carbon (14.0± 9.2 kg C m−2). The spatial patterns in regional carbon stocks and fluxes varied widely with some models showing NEE for Alaska as a strong carbon sink, others as a strong carbon source, while still others as carbon neutral. Additionally, a feedback (i.e., sensitivity) analysis was conducted of 20th century NEE to CO2 fertilization (β) and climate (γ), which showed that uncertainty in γ was 2x larger than that of β, with neither indicating that the Alaskan Arctic is shifting towards a certain net carbon sink or source. Finally, AmeriFlux data are used at two sites in the Alaskan Arctic to evaluate the regional patterns; observed seasonal NEE was captured within multi-model uncertainty. This assessment of carbon cycle uncertainties may be used as a baseline for the improvement of experimental and modeling activities, as well as a reference for future trajectories in carbon cycling with climate change in the Alaskan Arctic.

Mismatch between the optimal ages for ecosystem productivity and net CO2 sequestration in Norway spruce forests

2021 ◽  
Author(s):  
Junbin Zhao ◽  
Holger Lange ◽  
Helge Meissner
Keyword(s):  
Climate Change ◽  
Primary Production ◽  
Norway Spruce ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Economic Benefits ◽  
Sink Strength ◽  
Climate Change Scenarios ◽  
Ecosystem Productivity ◽  
Spruce Forests

<p>Forests have climate change mitigation potential since they sequester carbon. However, their carbon sink strength might depend on management. As a result of the balance between CO<sub>2</sub> uptake and emission, forest net ecosystem exchange (NEE) reaches optimal values (maximum sink strength) at young stand ages, followed by a gradual NEE decline over many years. Traditionally, this peak of NEE is believed to be concurrent with the peak of primary production (e.g., gross primary production, GPP); however, in theory, this concurrence may potentially vary depending on tree species, site conditions and the patterns of ecosystem respiration (R<sub>eco</sub>). In this study, we used eddy-covariance (EC)-based CO<sub>2</sub> flux measurements from 8 forest sites that are dominated by Norway spruce (Picea abies L.) and built machine learning models to find the optimal age of ecosystem productivity and that of CO<sub>2</sub> sequestration. We found that the net CO<sub>2</sub> uptake of Norway spruce forests peaked at ages of 30-40 yrs. Surprisingly, this NEE peak did not overlap with the peak of GPP, which appeared later at ages of 60-90 yrs. The mismatch between NEE and GPP was a result of the R<sub>eco</sub> increase that lagged behind the GPP increase associated with the tree growth at early age. Moreover, we also found that newly planted Norway spruce stands had a high probability (up to 90%) of being a C source in the first year, while, at an age as young as 5 yrs, they were likely to be a sink already. Further, using common climate change scenarios, our model results suggest that net CO<sub>2</sub> uptake of Norway spruce forests will increase under the future climate with young stands in the high latitude areas being more beneficial. Overall, the results suggest that forest management practices should consider NEE and forest productivity separately and harvests should be performed only after the optimal ages of both the CO<sub>2</sub> sequestration and productivity to gain full ecological and economic benefits.</p>

Energy and nutrients

2019 ◽  
pp. 161-176
Author(s):  
Richard T. Corlett
Keyword(s):  
Primary Production ◽  
Forest Ecology ◽  
Net Primary Production ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Nitrogen And Phosphorus ◽  
New Information ◽  
Tropical Forest Ecology ◽  
Toxic Concentrations

This chapter deals with the ecology of Tropical East Asia from the perspective of water, energy, and matter flows through ecosystems, particularly forests. Data from the network of eddy flux covariance towers is revealing general patterns in gross primary production, ecosystem respiration, and net ecosystem production, and exchange. There is also new information on the patterns of net primary production and biomass within the region. In contrast, our understanding of the role of soil nutrients in tropical forest ecology still relies mostly on work done in the Neotropics, with just enough data from Asia to suggest that the major patterns may be pantropical. Nitrogen and phosphorus have received most attention regionally, followed by calcium, potassium, and magnesium, and there has been very little study of the role of micronutrients and potentially toxic concentrations of aluminium, manganese, and hydrogen ions. Animal nutrition has also been neglected.

scholarly journals Nitrogen Fixation in a Changing Arctic Ocean: An Overlooked Source of Nitrogen?

2020 ◽  
Vol 11 ◽  
Author(s):  
Lisa W. von Friesen ◽  
Lasse Riemann
Keyword(s):  
Climate Change ◽  
Nitrogen Fixation ◽  
Primary Production ◽  
Arctic Ocean ◽  
Current Knowledge ◽  
Carbon Sink ◽  
Spatial Scales ◽  
The Arctic ◽  
Future Research ◽  
The Arctic Ocean

The Arctic Ocean is the smallest ocean on Earth, yet estimated to play a substantial role as a global carbon sink. As climate change is rapidly changing fundamental components of the Arctic, it is of local and global importance to understand and predict consequences for its carbon dynamics. Primary production in the Arctic Ocean is often nitrogen-limited, and this is predicted to increase in some regions. It is therefore of critical interest that biological nitrogen fixation, a process where some bacteria and archaea termed diazotrophs convert nitrogen gas to bioavailable ammonia, has now been detected in the Arctic Ocean. Several studies report diverse and active diazotrophs on various temporal and spatial scales across the Arctic Ocean. Their ecology and biogeochemical impact remain poorly known, and nitrogen fixation is so far absent from models of primary production in the Arctic Ocean. The composition of the diazotroph community appears distinct from other oceans – challenging paradigms of function and regulation of nitrogen fixation. There is evidence of both symbiotic cyanobacterial nitrogen fixation and heterotrophic diazotrophy, but large regions are not yet sampled, and the sparse quantitative data hamper conclusive insights. Hence, it remains to be determined to what extent nitrogen fixation represents a hitherto overlooked source of new nitrogen to consider when predicting future productivity of the Arctic Ocean. Here, we discuss current knowledge on diazotroph distribution, composition, and activity in pelagic and sea ice-associated environments of the Arctic Ocean. Based on this, we identify gaps and outline pertinent research questions in the context of a climate change-influenced Arctic Ocean – with the aim of guiding and encouraging future research on nitrogen fixation in this region.

scholarly journals Carbon Balance in Salt Marsh and Mangrove Ecosystems: A Global Synthesis

2020 ◽  
Vol 8 (10) ◽  
pp. 767 ◽  
Author(s):  
Daniel M. Alongi
Keyword(s):  
Organic Carbon ◽  
Primary Production ◽  
Salt Marshes ◽  
Dissolved Inorganic Carbon ◽  
Net Primary Production ◽  
Ecosystem Respiration ◽  
Soil Depth ◽  
Gross Primary Production ◽  
Coastal Ocean ◽  
Microbial Decomposition

Mangroves and salt marshes are among the most productive ecosystems in the global coastal ocean. Mangroves store more carbon (739 Mg CORG ha−1) than salt marshes (334 Mg CORG ha−1), but the latter sequester proportionally more (24%) net primary production (NPP) than mangroves (12%). Mangroves exhibit greater rates of gross primary production (GPP), aboveground net primary production (AGNPP) and plant respiration (RC), with higher PGPP/RC ratios, but salt marshes exhibit greater rates of below-ground NPP (BGNPP). Mangroves have greater rates of subsurface DIC production and, unlike salt marshes, exhibit active microbial decomposition to a soil depth of 1 m. Salt marshes release more CH4 from soil and creek waters and export more dissolved CH4, but mangroves release more CO2 from tidal waters and export greater amounts of particulate organic carbon (POC), dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC), to adjacent waters. Both ecosystems contribute only a small proportion of GPP, RE (ecosystem respiration) and NEP (net ecosystem production) to the global coastal ocean due to their small global area, but contribute 72% of air–sea CO2 exchange of the world’s wetlands and estuaries and contribute 34% of DIC export and 17% of DOC + POC export to the world’s coastal ocean. Thus, both wetland ecosystems contribute disproportionately to carbon flow of the global coastal ocean.

scholarly journals Eddy covariance carbon flux in a scrub in the Mexican highland

2020 ◽  
Author(s):  
Aurelio Guevara-Escobar ◽  
Enrique González-Sosa ◽  
Mónica Cervantes-Jiménez ◽  
Humberto Suzán-Azpiri ◽  
Mónica Elisa Queijeiro-Bolaños ◽  
...  
Keyword(s):  
Primary Production ◽  
Eddy Covariance ◽  
Vegetation Index ◽  
Carbon Sink ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Net Ecosystem Exchange ◽  
R Package ◽  
Dark Cycle ◽  
Remote Sensors

Abstract. Vegetation fixes C in its biomass through photosynthesis or might release it into the atmosphere through respiration. Measurements of these fluxes would help us understand ecosystem functioning. The eddy covariance technique (EC) is widely used to measure the net ecosystem exchange of C (NEE) which is the balance between gross primary production (GPP) and ecosystem respiration (Reco). Orbital satellites such as MODIS can also provide estimates of GPP. In this study, we measured NEE with the EC in a scrub at Bernal in Mexico, and then partitioned into gross primary production (GPP-EC) and Reco using the recent R package Reddyproc. Measurements of GPP-EC were related to the estimates from the MODIS satellite provided in product MOD17A2H, which contains data of the gross primary productivity (GPP-MODIS). The Bernal site was a carbon sink despite it was an overgrazed site, the average NEE during fifteen months of 2017 and 2018 was −0.78 g C m−2 d−1 and the flux was negative in all measured months. The GPP-MODIS underestimated the ground data when representing the relation with a Theil-Sen regression: GPP-EC = 1.866 + 1.861 GPP-MODIS; an ordinary less squares regression had similar coefficients and the R2 was 0.6. Although cacti (CAM), legume shrubs (C3) and herbs (C3) had a similar vegetation index, the nighttime flux was characterized by positive NEE suggesting that the photosynthetic dark-cycle flux of cacti was lower than Reco. The discrepancy among the GPP flux estimates stresses the need to understand the limitations of EC and remote sensors, while incorporating complementary monitoring and modelling schemes of nighttime Reco, particularly in the presence of species with different photosynthetic cycles.

scholarly journals Constraining uncertainty in projected gross primary production with machine learning

2020 ◽  
Author(s):  
Manuel Schlund ◽  
Veronika Eyring ◽  
Gustau Camps-Valls ◽  
Pierre Friedlingstein ◽  
Pierre Gentine ◽  
...  
Keyword(s):  
Machine Learning ◽  
Carbon Cycle ◽  
Primary Production ◽  
Carbon Sink ◽  
Gross Primary Production ◽  
Boosted Regression Trees ◽  
Supervised Machine Learning ◽  
Climate Projections ◽  
Intergovernmental Panel ◽  
The Future

<p>By absorbing about one quarter of the total anthropogenic CO<sub>2</sub> emissions, the terrestrial biosphere is an important carbon sink of Earth’s carbon cycle. A key metric of this process is the terrestrial gross primary production (GPP), which describes the biogeochemical production of energy by photosynthesis. Elevated atmospheric CO<sub>2</sub> concentrations will increase GPP in the future (CO<sub>2</sub> fertilization effect). However, projections from different Earth system models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) show a large spread in carbon cycle related quantities. In this study, we present a new supervised machine learning approach to constrain multi-model climate projections using observation-driven data. Our method based on Gradient Boosted Regression Trees handles multiple predictor variables of the present-day climate and accounts for non-linear dependencies. Applied to GPP in the representative concentration pathway RCP 8.5 at the end of the 21st century (2081–2100), the new approach reduces the “likely” range (as defined by the Intergovernmental Panel on Climate Change) of the CMIP5 multi-model projection of GPP to 161–203 GtC yr<sup>-1</sup>. Compared to the unweighted multi-model mean (148–224 GtC yr<sup>-1</sup>), this is an uncertainty reduction of 45%. Our new method is not limited to projections of the future carbon cycle, but can be applied to any target variable where suitable gridded data is available.</p>

The Carbon Cycle

2019 ◽  
pp. 129-158
Author(s):  
Han Dolman
Keyword(s):  
Carbon Cycle ◽  
Primary Production ◽  
Ocean Circulation ◽  
Net Primary Production ◽  
Gross Primary Production ◽  
Carbon Stocks ◽  
Climate Feedback ◽  
Fossil Fuel Burning ◽  
Thermal Maximum ◽  
Natural Carbon

The chapter first shows carbon dioxide variability over long geological timescales. The current stocks and fluxes of carbon are then given, for the whole planet and for the atmosphere, ocean and land separately. The main flows of carbon in the ocean, through the biological pump (via uptake through photosynthesis) and the physical pump (via involving chemical transformation uptake in water and production of carbonate), and on land, through photosynthesis (Gross Primary Production) and respiration leading to Net Primary Production, Net Ecosystem Production and Net Biome Production and through the storage of carbon in biomass, are described. Next, carbon interactions during the Paleocene–Eocene Thermal Maximum and glacial–interglacial transitions, thought to involve changes in ocean circulation and upwelling, are examined. The key changes from anthropogenic perturbation of the natural carbon cycle are shown to be due to fossil fuel burning and land-use change (deforestation). The effects of the carbon–climate feedback on temperature and carbon stocks are also shown.

scholarly journals Impacts of droughts and extreme temperature events on gross primary production and ecosystem respiration: a systematic assessment across ecosystems and climate zones

2017 ◽  
Author(s):  
Jannis von Buttlar ◽  
Jakob Zscheischler ◽  
Anja Rammig ◽  
Sebastian Sippel ◽  
Markus Reichstein ◽  
...  
Keyword(s):  
Heat Stress ◽  
Primary Production ◽  
Extreme Events ◽  
Extreme Event ◽  
Carbon Sink ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Extreme Temperature ◽  
Initial Increase ◽  
Climate Zones

Abstract. Extreme climatic events, such as droughts and heat stress induce anomalies in ecosystem-atmosphere CO2 fluxes, such as gross primary production (GPP) and ecosystem respiration (Reco), and, hence, can change the net ecosystem carbon balance. However, despite our increasing understanding of the underlying mechanisms, the magnitudes of the impacts of different types of extremes on GPP and Reco within and between ecosystems remain poorly predicted. Here we aim to identify the major factors controlling the amplitude of extreme event impacts on GPP, Reco, and the resulting net ecosystem production (NEP). We focus on the impacts of heat and drought and their combination. We identified hydrometeorological extreme events in consistently downscaled water availability and temperature measurements over a 30 year time period. We then used FLUXNET eddy-covariance flux measurements to estimate the CO2 flux anomalies during these extreme events across dominant vegetation types and climate zones. Overall, our results indicate that short-term heat extremes increased respiration more strongly than they down-regulated GPP, resulting in a moderate reduction of the ecosystem’s carbon sink potential. In the absence of heat stress, droughts tended to have smaller and similarly dampening effects on both GPP and Reco, and, hence, often resulted in neutral NEP responses. The combination of drought and heat typically led to a strong decrease in GPP, whereas heat and drought impacts on respiration partially offset each other. Taken together, compound heat and drought events led to the strongest C sink reduction compared to any single-factor extreme. A key insight of this paper, however, is that duration matters most: for heat stress during droughts, the magnitude of impacts systematically increased with duration, whereas under heat stress without drought, the response of Reco over time turned from an initial increase to a down-regulation after about two weeks. This confirms earlier theories that not only the magnitude but also the duration of an extreme event determines its impact. Our study corroborates the results of several local site-level case studies, but as a novelty generalizes these findings at the global scale. Specifically, we find that the different response functions of the two antipodal land-atmosphere fluxes GPP and Reco can also result in increasing NEP during certain extreme conditions. Apparently counterintuitive findings of this kind bear great potential for scrutinizing the mechanisms implemented in state-of-the-art terrestrial biosphere models and provide a benchmark for future model development and testing.

scholarly journals Neglecting plant–microbe symbioses leads to underestimation of modeled climate impacts

2019 ◽  
Vol 16 (2) ◽  
pp. 457-465 ◽  
Author(s):  
Mingjie Shi ◽  
Joshua B. Fisher ◽  
Richard P. Phillips ◽  
Edward R. Brzostek
Keyword(s):  
Climate Change ◽  
Primary Production ◽  
Climate Model ◽  
Net Primary Production ◽  
Carbon Sink ◽  
Climate Impacts ◽  
Nitrogen Acquisition ◽  
Carbon Cost ◽  
Precipitation Regimes ◽  
Microbial Symbionts

Abstract. The extent to which terrestrial ecosystems slow climate change by sequestering carbon hinges in part on nutrient limitation. We used a coupled carbon–climate model that accounts for the carbon cost to plants of supporting nitrogen-acquiring microbial symbionts to explore how nitrogen limitation affects global climate. To do this, we first calculated the reduction in net primary production due to the carbon cost of nitrogen acquisition. We then used a climate model to estimate the impacts of the resulting increase in atmospheric CO2 on temperature and precipitation regimes. The carbon costs of supporting symbiotic nitrogen uptake reduced net primary production by 8.1 Pg C yr−1, with the largest absolute effects occurring in tropical forest biomes and the largest relative changes occurring in boreal and alpine biomes. Globally, our model predicted relatively small changes in climate due to the carbon cost of nitrogen acquisition with temperature increasing by 0.1 ∘C and precipitation decreasing by 6 mm yr−1. However, there were strong regional impacts, with the largest impact occurring in boreal and alpine ecosystems, where such costs were estimated to increase temperature by 1.0 ∘C and precipitation by 9 mm yr−1. As such, our results suggest that carbon expenditures to support nitrogen-acquiring microbial symbionts have critical consequences for Earth's climate, and that carbon–climate models that omit these processes will overpredict the land carbon sink and underpredict climate change.

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