Can seasonal and interannual variation in landscape CO&lt;sub&gt;2&lt;/sub&gt; fluxes be detected by atmospheric observations of CO&lt;sub&gt;2&lt;/sub&gt; concentrations made at a tall tower?

Abstract. The coupled numerical weather model WRF-SPA (Weather Research and Forecasting model and Soil-Plant-Atmosphere model) has been used to investigate a 3 yr time series of observed atmospheric CO2 concentrations from a tall tower in Scotland, UK. Ecosystem-specific tracers of net CO2 uptake and net CO2 release were used to investigate the contributions to the tower signal of key land covers within its footprint, and how contributions varied at seasonal and interannual timescales. In addition, WRF-SPA simulated atmospheric CO2 concentrations were compared with two coarse global inversion models, CarbonTrackerEurope and the National Oceanic and Atmospheric Administration's CarbonTracker (CTE-CT). WRF-SPA realistically modelled both seasonal (except post harvest) and daily cycles seen in observed atmospheric CO2 at the tall tower (R2 = 0.67, rmse = 3.5 ppm, bias = 0.58 ppm). Atmospheric CO2 concentrations from the tall tower were well simulated by CTE-CT, but the inverse model showed a poorer representation of diurnal variation and simulated a larger bias from observations (up to 1.9 ppm) at seasonal timescales, compared to the forward modelling of WRF-SPA. However, we have highlighted a consistent post-harvest increase in the seasonal bias between WRF-SPA and observations. Ecosystem-specific tracers of CO2 exchange indicate that the increased bias is potentially due to the representation of agricultural processes within SPA and/or biases in land cover maps. The ecosystem-specific tracers also indicate that the majority of seasonal variation in CO2 uptake for Scotland's dominant ecosystems (forests, cropland and managed grassland) is detectable in observations within the footprint of the tall tower; however, the amount of variation explained varies between years. The between years variation in detectability of Scotland's ecosystems is potentially due to seasonal and interannual variation in the simulated prevailing wind direction. This result highlights the importance of accurately representing atmospheric transport used within atmospheric inversion models used to estimate terrestrial source/sink distribution and magnitude.

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Can seasonal and interannual variation in landscape CO2 fluxes be detected by atmospheric observations of CO2 concentrations made at a tall tower?

Biogeosciences Discussions ◽

10.5194/bgd-10-14301-2013 ◽

2013 ◽

Vol 10 (8) ◽

pp. 14301-14331

Author(s):

T. L. Smallman ◽

M. Williams ◽

J. B. Moncrieff

Keyword(s):

Interannual Variation ◽

Co2 Exchange ◽

Atmospheric Co2 ◽

Co2 Uptake ◽

Post Harvest ◽

Terrestrial Ecosystem Model ◽

Co2 Concentrations ◽

Atmospheric Co2 Concentrations ◽

Source Sink ◽

Tall Tower

Abstract. The Weather Research and Forecasting (WRF) meteorological model has been coupled to the Soil Plant Atmosphere (SPA) terrestrial ecosystem model, hereafter known as WRF-SPA. SPA generates realistic land-atmosphere exchanges through fully coupled hydrological, carbon and energy cycles. Here we have used WRF-SPA to investigate regional scale observations of atmospheric CO2 concentrations made over a multi-annual period from a tall tower in Scotland. WRF-SPA realistically models both seasonal and daily cycles, predicting CO2 at the tall tower (R2 = 0.67, RMSE = 3.5 ppm, bias = 0.58 ppm), indicating realistic transport, and appropriate source sink distribution and magnitude of CO2 exchange. We have highlighted a consistent post harvest increase in model-observation residuals in atmospheric CO2 concentrations. This increase in model-observation residuals post harvest is likely related to a lack of an appropriate representation of uncultivated components (~ 36% of agricultural holding in Scotland) of agricultural land (e.g., hedgerows and forest patches) which continue to photosynthesise after the crop has been harvested. Through the use of ecosystem specific CO2 tracers we have shown that tall tower observations here do not detect a representative fraction of Scotland's ecosystem CO2 uptake. Cropland CO2 uptake is the dominant ecosystem signal detected at the tall tower, consistent with the dominance of cropland in the area surrounding the tower. However cropland is over-represented in the atmospheric CO2 concentrations simulated to be at the tall tower, relative to the simulated surface cropland CO2 uptake. Observations made at the tall tower were able to detect seasonal variation in ecosystem CO2 uptake, however a majority of variation was only detected for croplands. We have found evidence that interannual variation in weather has a greater impact than interannual variation of the simulated land surface CO2 exchange on tall tower observations for the simulated years. This highlights the importance of accurately representing atmospheric transport used within atmospheric inversion models used to estimate terrestrial source/sink distribution and magnitude.

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Sources and Sinks of Atmospheric CO2

Australian Journal of Botany ◽

10.1071/bt9920407 ◽

1992 ◽

Vol 40 (5) ◽

pp. 407 ◽

Cited By ~ 101

Author(s):

JA Taylor ◽

J Lloyd

Keyword(s):

Climate Change ◽

Biomass Burning ◽

Transport Model ◽

Atmospheric Co2 ◽

Tropical Rainforests ◽

Co2 Uptake ◽

Tracer Transport ◽

Intergovernmental Panel ◽

Co2 Concentrations ◽

Atmospheric Co2 Concentrations

The biosphere plays an important role in determining the sources, sinks, levels and rates of change of atmospheric CO2 concentrations. Significant uncertainties remain in estimates of the fluxes of CO2 from biomass burning and deforestation, and uptake and storage of CO2 by the biosphere arising from increased atmospheric CO2 concentrations. Calculation of probable rates of carbon sequestration for the major ecosystem complexes and global 3-D tracer transport model runs indicate the possibility that a significant net CO2 uptake (> 1 Pg C yr-1), a CO2 'fertilisation effect', may be occurring in tropical rainforests, effectively accounting for much of the 'missing sink'. This sink may currently balance much of the CO2 added to the atmosphere from deforestation and biomass burning. Interestingly, CO2 released from biomass burning may itself be playing an important role in enhanced carbon storage by tropical rainforests. This has important implications for predicting future CO2 concentrations. If tropical rainforest destruction continues then much of the CO2 stored as a result of the CO2 'fertilisation effect' will be rereleased to the atmosphere and much of the 'missing sink' will disappear. These effects have not been considered in the IPCC (Intergovernmental Panel on Climate Change) projections of future atmospheric CO2 concentrations. Predictions which take account of the combined effects of deforestation, the return of carbon previously stored through the CO2 'fertilisation effect' and the loss of a large proportion of the 'missing sink' as a result of deforestation, would result in much higher predicted concentrations and rates of increase of atmospheric CO2 and, as a consequence, accelerated rates of climate change.

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The ocean carbon sink – impacts, vulnerabilities, and challenges

Earth System Dynamics Discussions ◽

10.5194/esdd-5-1607-2014 ◽

2014 ◽

Vol 5 (2) ◽

pp. 1607-1672

Author(s):

C. Heinze ◽

S. Meyer ◽

N. Goris ◽

L. Anderson ◽

R. Steinfeldt ◽

...

Keyword(s):

Carbon Sink ◽

Mitigation Strategies ◽

Atmospheric Co2 ◽

Co2 Uptake ◽

Spatial And Temporal Scales ◽

The Past ◽

Research Fields ◽

Co2 Concentrations ◽

Ocean Carbon ◽

Atmospheric Co2 Concentrations

Abstract. Carbon dioxide (CO2) is, next to water vapour, considered to be the most important natural greenhouse gas on Earth. Rapidly rising atmospheric CO2 concentrations caused by human actions such as fossil-fuel burning, land-use change or cement production over the past 250 years have given cause for concern that changes in Earth's climate system may progress at a much faster pace and larger extent than during the past 20 000 years. Investigating global carbon cycle pathways and finding suitable mitigation strategies has, therefore, become of major concern in many research fields. The oceans have a key role in regulating atmospheric CO2 concentrations and currently take up about 25% of annual anthropogenic carbon emissions to the atmosphere. Questions that yet need to be answered are what the carbon uptake kinetics of the oceans will be in the future and how the increase in oceanic carbon load will affect its ecosystems and their services. This requires comprehensive investigations, including high-quality ocean carbon measurements on different spatial and temporal scales, the management of data in sophisticated data bases, the application of state-of-the-art Earth system models to provide future projections for given emission scenarios as well as a global synthesis and outreach to policy makers. In this paper, the current understanding of the ocean as an important carbon sink is reviewed with respect to these topics. Emphasis is placed on the complex interplay of different physical, chemical, and biological processes that yield both positive and negative air–sea flux values for natural and anthropogenic CO2 as well as on increased CO2 (uptake) as the regulating force of the radiative warming of the atmosphere and the gradual acidification of the oceans. Major future ocean carbon challenges in the fields of ocean observations, modelling, and process research as well as the relevance of other biogeochemical cycles and greenhouse gases are discussed.

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Evaluation of atmosphere-biosphere exchange estimations with TCCON measurements

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-12759-2012 ◽

2012 ◽

Vol 12 (5) ◽

pp. 12759-12800 ◽

Cited By ~ 7

Author(s):

J. Messerschmidt ◽

N. Parazoo ◽

N. M. Deutscher ◽

C. Roehl ◽

T. Warneke ◽

...

Keyword(s):

Boreal Forest ◽

Large Scale ◽

Growing Season ◽

Atmospheric Co2 ◽

Total Carbon ◽

Co2 Uptake ◽

Co2 Concentrations ◽

Time Period ◽

Atmospheric Co2 Concentrations ◽

Biosphere Model

Abstract. Three estimates of the atmosphere-biosphere exchange are evaluated using Total Carbon Column Observing Network (TCCON) measurements. We investigate the Carnegie-Ames-Stanford Approach (CASA), the Simple Biosphere (SiB) and the GBiome-BGC models transported by the GEOS-Chem model to simulate atmospheric CO2 concentrations for the time period between 2006 and 2010. The CO2 simulations are highly dependent on the choice of the atmosphere-biosphere model and large-scale errors in the estimates are identified through a comparison with TCCON data. Enhancing the CO2 uptake in the boreal forest by 40% and shifting the onset of the growing season significantly improve the simulated seasonal CO2 cycle using CASA estimates. The SiB model gives the best estimate for the atmosphere-biosphere exchange in the comparison with TCCON measurements.

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The ocean carbon sink – impacts, vulnerabilities and challenges

Earth System Dynamics ◽

10.5194/esd-6-327-2015 ◽

2015 ◽

Vol 6 (1) ◽

pp. 327-358 ◽

Cited By ~ 51

Author(s):

C. Heinze ◽

S. Meyer ◽

N. Goris ◽

L. Anderson ◽

R. Steinfeldt ◽

...

Keyword(s):

Carbon Sink ◽

Mitigation Strategies ◽

Atmospheric Co2 ◽

Co2 Uptake ◽

Spatial And Temporal Scales ◽

The Past ◽

Research Fields ◽

Co2 Concentrations ◽

Ocean Carbon ◽

Atmospheric Co2 Concentrations

Abstract. Carbon dioxide (CO2) is, next to water vapour, considered to be the most important natural greenhouse gas on Earth. Rapidly rising atmospheric CO2 concentrations caused by human actions such as fossil fuel burning, land-use change or cement production over the past 250 years have given cause for concern that changes in Earth's climate system may progress at a much faster pace and larger extent than during the past 20 000 years. Investigating global carbon cycle pathways and finding suitable adaptation and mitigation strategies has, therefore, become of major concern in many research fields. The oceans have a key role in regulating atmospheric CO2 concentrations and currently take up about 25% of annual anthropogenic carbon emissions to the atmosphere. Questions that yet need to be answered are what the carbon uptake kinetics of the oceans will be in the future and how the increase in oceanic carbon inventory will affect its ecosystems and their services. This requires comprehensive investigations, including high-quality ocean carbon measurements on different spatial and temporal scales, the management of data in sophisticated databases, the application of Earth system models to provide future projections for given emission scenarios as well as a global synthesis and outreach to policy makers. In this paper, the current understanding of the ocean as an important carbon sink is reviewed with respect to these topics. Emphasis is placed on the complex interplay of different physical, chemical and biological processes that yield both positive and negative air–sea flux values for natural and anthropogenic CO2 as well as on increased CO2 (uptake) as the regulating force of the radiative warming of the atmosphere and the gradual acidification of the oceans. Major future ocean carbon challenges in the fields of ocean observations, modelling and process research as well as the relevance of other biogeochemical cycles and greenhouse gases are discussed.

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