scholarly journals Evaluation of carbonyl sulfide biosphere exchange in the Simple Biosphere Model (SiB4)

2021 ◽  
Author(s):  
Linda M. J. Kooijmans ◽  
Ara Cho ◽  
Jin Ma ◽  
Aleya Kaushik ◽  
Katherine D. Haynes ◽  
...  
Keyword(s):  
Mole Fraction ◽  
Mechanistic Model ◽  
Carbonyl Sulfide ◽  
Global Scale ◽  
Terrestrial Plants ◽  
Large Variability ◽  
High Productivity ◽  
Crop Fields ◽  
Soil Component ◽  
Biosphere Model

Abstract. The uptake of carbonyl sulfide (COS) by terrestrial plants is linked to photosynthetic uptake of CO2 by a shared diffusion pathway. Applying COS as a photosynthesis tracer in models requires an accurate representation of biosphere COS fluxes, but these models have not been extensively evaluated against field observations of COS fluxes. In this paper, the COS flux as simulated by the Simple Biosphere Model, version 4 (SiB4) is updated with the latest mechanistic insights and evaluated with site observations from different biomes: one evergreen needleleaf forest, two deciduous broadleaf forests, three grasslands, and two crop fields spread over Europe and North America. To account for the effect of atmospheric COS mole fractions on COS biosphere uptake, we replaced the fixed COS mole fraction originally used in SiB4 with spatially and temporally varying COS mole fraction fields. The lower COS mole fractions in the late growing season reduces COS uptake rates in agreement with observations. We also replaced the empirical soil COS uptake model in SiB4 with a mechanistic model that represents both uptake and production of COS in soils, which improves the match with observations over agricultural fields and fertilized grassland soils. SiB4 was capable of simulating the diurnal and seasonal variation of COS fluxes in the boreal, temperate and Mediterranean region. The daytime vegetation COS flux is on average 8 ± 27 % underestimated, albeit with large variability across sites. On a global scale, our model modifications caused a drop in the COS biosphere sink from 922 Gg S yr−1 in the original SiB4 model to 753 Gg S yr−1 in the updated version. The largest drop in fluxes was driven by lower atmospheric COS mole fractions over regions with high productivity, which highlights the importance of accounting for variations in atmospheric COS mole fractions. The change to a different soil model, on the other hand, had a relatively small effect on the global biosphere COS sink. The small role of the modeled soil component in the COS budget supports the use of COS as a global photosynthesis tracer.

scholarly journals Evaluation of carbonyl sulfide biosphere exchange in the Simple Biosphere Model (SiB4)

2021 ◽  
Vol 18 (24) ◽  
pp. 6547-6565
Author(s):  
Linda M. J. Kooijmans ◽  
Ara Cho ◽  
Jin Ma ◽  
Aleya Kaushik ◽  
Katherine D. Haynes ◽  
...  
Keyword(s):  
Mole Fraction ◽  
Mechanistic Model ◽  
Carbonyl Sulfide ◽  
Growing Season ◽  
Global Scale ◽  
Terrestrial Plants ◽  
Large Variability ◽  
Accurate Representation ◽  
High Productivity ◽  
Biosphere Model

Abstract. The uptake of carbonyl sulfide (COS) by terrestrial plants is linked to photosynthetic uptake of CO2 as these gases partly share the same uptake pathway. Applying COS as a photosynthesis tracer in models requires an accurate representation of biosphere COS fluxes, but these models have not been extensively evaluated against field observations of COS fluxes. In this paper, the COS flux as simulated by the Simple Biosphere Model, version 4 (SiB4), is updated with the latest mechanistic insights and evaluated with site observations from different biomes: one evergreen needleleaf forest, two deciduous broadleaf forests, three grasslands, and two crop fields spread over Europe and North America. We improved SiB4 in several ways to improve its representation of COS. To account for the effect of atmospheric COS mole fractions on COS biosphere uptake, we replaced the fixed atmospheric COS mole fraction boundary condition originally used in SiB4 with spatially and temporally varying COS mole fraction fields. Seasonal amplitudes of COS mole fractions are ∼50–200 ppt at the investigated sites with a minimum mole fraction in the late growing season. Incorporating seasonal variability into the model reduces COS uptake rates in the late growing season, allowing better agreement with observations. We also replaced the empirical soil COS uptake model in SiB4 with a mechanistic model that represents both uptake and production of COS in soils, which improves the match with observations over agricultural fields and fertilized grassland soils. The improved version of SiB4 was capable of simulating the diurnal and seasonal variation in COS fluxes in the boreal, temperate, and Mediterranean region. Nonetheless, the daytime vegetation COS flux is underestimated on average by 8±27 %, albeit with large variability across sites. On a global scale, our model modifications decreased the modeled COS terrestrial biosphere sink from 922 Gg S yr−1 in the original SiB4 to 753 Gg S yr−1 in the updated version. The largest decrease in fluxes was driven by lower atmospheric COS mole fractions over regions with high productivity, which highlights the importance of accounting for variations in atmospheric COS mole fractions. The change to a different soil model, on the other hand, had a relatively small effect on the global biosphere COS sink. The secondary role of the modeled soil component in the global COS budget supports the use of COS as a global photosynthesis tracer. A more accurate representation of COS uptake in SiB4 should allow for improved application of atmospheric COS as a tracer of local- to global-scale terrestrial photosynthesis.

scholarly journals A new mechanistic framework to predict OCS fluxes from soils

2016 ◽  
Vol 13 (8) ◽  
pp. 2221-2240 ◽  
Author(s):  
Jérôme Ogée ◽  
Joana Sauze ◽  
Jürgen Kesselmeier ◽  
Bernard Genty ◽  
Heidi Van Diest ◽  
...  
Keyword(s):  
Large Scale ◽  
Soil Microorganisms ◽  
Soil Moisture Content ◽  
Mechanistic Model ◽  
Carbonyl Sulfide ◽  
Reaction Diffusion ◽  
Global Scale ◽  
First Order ◽  
Uptake Rates ◽  
Hydrolysis Of

Abstract. Estimates of photosynthetic and respiratory fluxes at large scales are needed to improve our predictions of the current and future global CO2 cycle. Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere and has been proposed as a new tracer of photosynthetic gross primary productivity (GPP), as the uptake of OCS from the atmosphere is dominated by the activity of carbonic anhydrase (CA), an enzyme abundant in leaves that also catalyses CO2 hydration during photosynthesis. However soils also exchange OCS with the atmosphere, which complicates the retrieval of GPP from atmospheric budgets. Indeed soils can take up large amounts of OCS from the atmosphere as soil microorganisms also contain CA, and OCS emissions from soils have been reported in agricultural fields or anoxic soils. To date no mechanistic framework exists to describe this exchange of OCS between soils and the atmosphere, but empirical results, once upscaled to the global scale, indicate that OCS consumption by soils dominates OCS emission and its contribution to the atmospheric budget is large, at about one third of the OCS uptake by vegetation, also with a large uncertainty. Here, we propose a new mechanistic model of the exchange of OCS between soils and the atmosphere that builds on our knowledge of soil CA activity from CO2 oxygen isotopes. In this model the OCS soil budget is described by a first-order reaction–diffusion–production equation, assuming that the hydrolysis of OCS by CA is total and irreversible. Using this model we are able to explain the observed presence of an optimum temperature for soil OCS uptake and show how this optimum can shift to cooler temperatures in the presence of soil OCS emission. Our model can also explain the observed optimum with soil moisture content previously described in the literature as a result of diffusional constraints on OCS hydrolysis. These diffusional constraints are also responsible for the response of OCS uptake to soil weight and depth observed previously. In order to simulate the exact OCS uptake rates and patterns observed on several soils collected from a range of biomes, different CA activities had to be invoked in each soil type, coherent with expected physiological levels of CA in soil microbes and with CA activities derived from CO2 isotope exchange measurements, given the differences in affinity of CA for both trace gases. Our model can be used to help upscale laboratory measurements to the plot or the region. Several suggestions are given for future experiments in order to test the model further and allow a better constraint on the large-scale OCS fluxes from both oxic and anoxic soils.

scholarly journals Inverse modelling of carbonyl sulfide: implementation, evaluation and implications for the global budget

2021 ◽  
Vol 21 (5) ◽  
pp. 3507-3529
Author(s):  
Jin Ma ◽  
Linda M. J. Kooijmans ◽  
Ara Cho ◽  
Stephen A. Montzka ◽  
Norbert Glatthor ◽  
...  
Keyword(s):  
Mole Fraction ◽  
Satellite Data ◽  
Dimethyl Sulfide ◽  
Transport Model ◽  
Carbonyl Sulfide ◽  
Stratospheric Aerosol ◽  
Inverse Modelling ◽  
Model Framework ◽  
Tropical Ocean ◽  
Biosphere Model

Abstract. Carbonyl sulfide (COS) has the potential to be used as a climate diagnostic due to its close coupling to the biospheric uptake of CO2 and its role in the formation of stratospheric aerosol. The current understanding of the COS budget, however, lacks COS sources, which have previously been allocated to the tropical ocean. This paper presents a first attempt at global inverse modelling of COS within the 4-dimensional variational data-assimilation system of the TM5 chemistry transport model (TM5-4DVAR) and a comparison of the results with various COS observations. We focus on the global COS budget, including COS production from its precursors carbon disulfide (CS2) and dimethyl sulfide (DMS). To this end, we implemented COS uptake by soil and vegetation from an updated biosphere model (Simple Biosphere Model – SiB4). In the calculation of these fluxes, a fixed atmospheric mole fraction of 500 pmol mol−1 was assumed. We also used new inventories for anthropogenic and biomass burning emissions. The model framework is capable of closing the COS budget by optimizing for missing emissions using NOAA observations in the period 2000–2012. The addition of 432 Gg a−1 (as S equivalents) of COS is required to obtain a good fit with NOAA observations. This missing source shows few year-to-year variations but considerable seasonal variations. We found that the missing sources are likely located in the tropical regions, and an overestimated biospheric sink in the tropics cannot be ruled out due to missing observations in the tropical continental boundary layer. Moreover, high latitudes in the Northern Hemisphere require extra COS uptake or reduced emissions. HIPPO (HIAPER Pole-to-Pole Observations) aircraft observations, NOAA airborne profiles from an ongoing monitoring programme and several satellite data sources are used to evaluate the optimized model results. This evaluation indicates that COS mole fractions in the free troposphere remain underestimated after optimization. Assimilation of HIPPO observations slightly improves this model bias, which implies that additional observations are urgently required to constrain sources and sinks of COS. We finally find that the biosphere flux dependency on the surface COS mole fraction (which was not accounted for in this study) may substantially lower the fluxes of the SiB4 biosphere model over strong-uptake regions. Using COS mole fractions from our inversion, the prior biosphere flux reduces from 1053 to 851 Gg a−1, which is closer to 738 Gg a−1 as was found by Berry et al. (2013). In planned further studies we will implement this biosphere dependency and additionally assimilate satellite data with the aim of better separating the role of the oceans and the biosphere in the global COS budget.

Warming effects on biomass allocation are jointly regulated by precipitation and mycorrhizal association in terrestrial plants

2021 ◽  
Author(s):  
Xuhui Zhou ◽  
Lingyan Zhou ◽  
Yanghui He ◽  
Yuling Fu ◽  
Zhenggang Du ◽  
...  
Keyword(s):  
Biomass Allocation ◽  
Mycorrhizal Fungi ◽  
Global Scale ◽  
Mean Annual Precipitation ◽  
Shoot Biomass ◽  
Terrestrial Plants ◽  
Terrestrial Carbon ◽  
Shoot Ratio ◽  
Root Shoot Ratio ◽  
Mycorrhizal Association

Abstract Biomass allocation in plants is fundamental for understanding and predicting terrestrial carbon storage. Recent studies suggest that climate warming can differentially affect root and shoot biomass, and subsequently alter root: shoot ratio. However, warming effects on root: shoot ratio and their underlying drivers at a global scale remain unclear. Using a global synthesis of >300 studies, we here show that warming significantly increases biomass allocation to roots (by 13.1%), and two factors drive this response: mean annual precipitation of the site, and the type of mycorrhizal fungi associated with a plant. Warming-induced allocation to roots is greater in relatively drier habitats compared to shoots (by 15.1%), but lower in wetter sites (by 4.9%), especially for plants associated with arbuscular mycorrhizal fungi compared to ectomycorrhizal fungi. Root-biomass responses to warming predominantly determine the biomass allocation in terrestrial plants suggesting that warming can reinforce the importance of belowground resource uptake. Our study highlights that the wetness or dryness of a site and plants’ mycorrhizal associations strongly regulate terrestrial carbon cycle by altering biomass allocation strategies in a warmer world.

scholarly journals Towards a representation of priming on soil carbon decomposition in the global land biosphere model ORCHIDEE (version 1.9.5.2)

2016 ◽  
Vol 9 (2) ◽  
pp. 841-855 ◽  
Author(s):  
Bertrand Guenet ◽  
Fernando Esteban Moyano ◽  
Philippe Peylin ◽  
Philippe Ciais ◽  
Ivan A Janssens
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Soil Carbon ◽  
Global Scale ◽  
Soil Incubation ◽  
First Order ◽  
Carbon Decomposition ◽  
Litter Manipulation ◽  
Global Land ◽  
Biosphere Model

Abstract. Priming of soil carbon decomposition encompasses different processes through which the decomposition of native (already present) soil organic matter is amplified through the addition of new organic matter, with new inputs typically being more labile than the native soil organic matter. Evidence for priming comes from laboratory and field experiments, but to date there is no estimate of its impact at global scale and under the current anthropogenic perturbation of the carbon cycle. Current soil carbon decomposition models do not include priming mechanisms, thereby introducing uncertainty when extrapolating short-term local observations to ecosystem and regional to global scale. In this study we present a simple conceptual model of decomposition priming, called PRIM, able to reproduce laboratory (incubation) and field (litter manipulation) priming experiments. Parameters for this model were first optimized against data from 20 soil incubation experiments using a Bayesian framework. The optimized parameter values were evaluated against another set of soil incubation data independent from the ones used for calibration and the PRIM model reproduced the soil incubations data better than the original, CENTURY-type soil decomposition model, whose decomposition equations are based only on first-order kinetics. We then compared the PRIM model and the standard first-order decay model incorporated into the global land biosphere model ORCHIDEE (Organising Carbon and Hydrology In Dynamic Ecosystems). A test of both models was performed at ecosystem scale using litter manipulation experiments from five sites. Although both versions were equally able to reproduce observed decay rates of litter, only ORCHIDEE–PRIM could simulate the observed priming (R2  =  0.54) in cases where litter was added or removed. This result suggests that a conceptually simple and numerically tractable representation of priming adapted to global models is able to capture the sign and magnitude of the priming of litter and soil organic matter.

Carbonyl sulfide reflections of leaf and ecosystem processes in a tropical rainforest under controlled drought

2020 ◽  
Author(s):  
Laura Meredith ◽  
Róisín Commane ◽  
Ian Baker ◽  
Juliana Gil-Loaiza ◽  
Joost van Haren ◽  
...  
Keyword(s):  
Tropical Rainforest ◽  
Carbonyl Sulfide ◽  
Ecosystem Processes ◽  
Isotopic Tracers ◽  
Biosphere 2 ◽  
Experimental Systems ◽  
Water Cycling ◽  
Need To Evaluate ◽  
Leaf Level ◽  
Biosphere Model

<p>A promising tracer for partitioning the global balance of CO<sub>2</sub> is carbonyl sulfide (COS or OCS), a trace gas with leaf-level mechanisms shared with carbon dioxide (CO<sub>2</sub>) and water (H<sub>2</sub>O). COS is therefore used to derive insights into photosynthesis and transpiration at ecosystem to global scales. However, it remains unclear whether COS reflects photosynthesis or stomatal conductance most strongly, as its leaf biochemical and physical processes are not perfectly analogous to either CO<sub>2</sub> or H<sub>2</sub>O. There is therefore a need to evaluate the models that encapsulate our current understanding of leaf and soil COS fluxes and predictions of carbon and water cycling against independent constraints in tractable experimental systems.</p><p>In this study, we measured ecosystem, leaf, and soil fluxes of COS in the model Biosphere 2 (B2) Tropical Rainforest across a controlled whole ecosystem drought manipulation. We simultaneously, measured the stable isotopes of CO<sub>2</sub>, H<sub>2</sub>O, and their isotopes (<sup>13</sup>C-CO<sub>2</sub>, <sup>18</sup>O-CO<sub>2</sub>, <sup>2</sup>H-H<sub>2</sub>O, <sup>18</sup>O-H<sub>2</sub>O) on atmosphere, leaf, and soil measurement streams connected to atmospheric towers, leaf chambers, and soil flux chambers. During the B2 Water, Atmosphere, and Life Dynamics (B2 WALD) campaign, the enclosed ecosystem received no rain for 66 days and was first rewet at depth (2-4 m) at 54 days. Here, we compare COS fluxes to simultaneous and independent measurements of GPP and transpiration from the leaf to ecosystem scales across ecosystem control, drought, and recovery. We further integrate COS measurements with the aforementioned isotopic tracers of carbon and water cycling into the Simple Biosphere Model (SiB3). Our goal is to explore the strengths and limitations of COS as a tracer of ecosystem processes dynamically responding to severe and controlled ecosystem drought.</p>

Methane emissions from coal mines ventilation shafts in Upper Silesia, Poland

2020 ◽  
Author(s):  
Mila Stanisavljevic ◽  
Jaroslaw Nęcki ◽  
Piotr Korbeń ◽  
Hossein Maazallahi ◽  
Malika Menoud ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Mole Fraction ◽  
Coal Mine ◽  
Meteorological Data ◽  
Coal Mines ◽  
Isotope Ratio Mass Spectrometry ◽  
Global Scale ◽  
Methane Emissions ◽  
Atmospheric Methane ◽  
Isotopic Characterization

<p>Atmospheric methane is the second most important anthropogenic greenhouse gas after carbon dioxide. On the global scale, methane emissions are reasonably well constrained but the contributions from individual sources are highly uncertain (Saunois, 2016). According to bottom-up estimates, methane emissions from underground coal mining excavation contribute 11% to all anthropogenic methane sources (Saunois, 2016). However, there is a lack of in situ measurement to verify these estimates. Here we present results from measurements of the methane mole fraction over the Polish part of the Upper Silesian Coal Basin (USCB). Methane mole fraction was measured using vehicles equipped with high precision laser-based instruments (Picarro G2201-i CRDS, Picarro G2301- CRDS). Basic meteorological data (wind speed, wind direction) and GPS location data were collected on the roof of the vehicles. In order to obtain emission estimates, we attempted to cross the plumes from the coal mine shafts using public roads approximately perpendicular to plume downwind from the source. When possible, the plumes were intersected several times at different distances in order to have a closer look at uncertainties. A Gaussian plume model was used to calculate the release rate from the methane single source.</p><p>In addition to methane mole fraction measurements, we collected air samples for isotopic characterization (δ<sup>13</sup>C and δD) using isotope ratio mass spectrometry. We observed significant variation in measured methane isotopic composition over USCB (the results are in a range of -321 to -142 ‰ SMOW for δD and -31 to -58 ‰ VPDB for δ<sup>13</sup>CH<sub>4</sub>). The results indicated a much larger variability of the isotopic composition of methane emitted from coal mines than assumed previously, which may complicate the distinction of methane emissions from different sources by isotopic characterization.</p><p><strong>Keywords</strong>: Methane, Greenhouse Gases, Clime Change, Coal Mine Ventilation Shafts, Methane Isotopic Compositions</p><p>Reference:</p><p>Saunois, M., Bousquet, P., Poulter, B., et al., 2016a. The global methane budget, 2000–2012. Earth Syst. Sci. Data 8, 697–751. https://doi.org/10.5194/essd-8-697-2016. www.earth-syst-sci-data.net/8/697/2016/.</p><p>This work is part of the Marie Sklodowska-Curie Initial Training Network MEMO2 , which enable us to extend these measurements to other European locations</p>

scholarly journals A multi-year record of airborne CO<sub>2</sub> observations in the US Southern Great Plains

2013 ◽  
Vol 6 (3) ◽  
pp. 751-763 ◽  
Author(s):  
S. C. Biraud ◽  
M. S. Torn ◽  
J. R. Smith ◽  
C. Sweeney ◽  
W. J. Riley ◽  
...  
Keyword(s):  
Mole Fraction ◽  
Great Plains ◽  
Atmospheric Transport ◽  
Meteorological Data ◽  
Carbonyl Sulfide ◽  
Vertical Profiles ◽  
Southern Great Plains ◽  
Airborne Measurements ◽  
Mauna Loa ◽  
The Us

Abstract. We report on 10 yr of airborne measurements of atmospheric CO2 mole fraction from continuous and flask systems, collected between 2002 and 2012 over the Atmospheric Radiation Measurement Program Climate Research Facility in the US Southern Great Plains (SGP). These observations were designed to quantify trends and variability in atmospheric mole fraction of CO2 and other greenhouse gases with the precision and accuracy needed to evaluate ground-based and satellite-based column CO2 estimates, test forward and inverse models, and help with the interpretation of ground-based CO2 mole-fraction measurements. During flights, we measured CO2 and meteorological data continuously and collected flasks for a rich suite of additional gases: CO2, CO, CH4, N2O, 13CO2, carbonyl sulfide (COS), and trace hydrocarbon species. These measurements were collected approximately twice per week by small aircraft (Cessna 172 initially, then Cessna 206) on a series of horizontal legs ranging in altitude from 460 m to 5500 m a.m.s.l. Since the beginning of the program, more than 400 continuous CO2 vertical profiles have been collected (2007–2012), along with about 330 profiles from NOAA/ESRL 12-flask (2006–2012) and 284 from NOAA/ESRL 2-flask (2002–2006) packages for carbon cycle gases and isotopes. Averaged over the entire record, there were no systematic differences between the continuous and flask CO2 observations when they were sampling the same air, i.e., over the one-minute flask-sampling time. Using multiple technologies (a flask sampler and two continuous analyzers), we documented a mean difference of < 0.2 ppm between instruments. However, flask data were not equivalent in all regards; horizontal variability in CO2 mole fraction within the 5–10 min legs sometimes resulted in significant differences between flask and continuous measurement values for those legs, and the information contained in fine-scale variability about atmospheric transport was not captured by flask-based observations. The CO2 mole fraction trend at 3000 m a.m.s.l. was 1.91 ppm yr−1 between 2008 and 2010, very close to the concurrent trend at Mauna Loa of 1.95 ppm yr−1. The seasonal amplitude of CO2 mole fraction in the free troposphere (FT) was half that in the planetary boundary layer (PBL) (~ 15 ppm vs. ~ 30 ppm) and twice that at Mauna Loa (approximately 8 ppm). The CO2 horizontal variability was up to 10 ppm in the PBL and less than 1 ppm at the top of the vertical profiles in the FT.

scholarly journals A global scale mechanistic model of the photosynthetic capacity

2015 ◽  
Vol 8 (8) ◽  
pp. 6217-6266 ◽  
Author(s):  
A. A. Ali ◽  
C. Xu ◽  
A. Rogers ◽  
R. A. Fisher ◽  
S. D. Wullschleger ◽  
...  
Keyword(s):  
Electron Transport ◽  
Environmental Conditions ◽  
Photosynthetic Capacity ◽  
Mechanistic Model ◽  
Global Scale ◽  
Plant Functional Types ◽  
Climate Conditions ◽  
Functional Types ◽  
Light Capture ◽  
Earth System Models

Abstract. Although plant photosynthetic capacity as determined by the maximum carboxylation rate (i.e., Vc, max25) and the maximum electron transport rate (i.e., Jmax25) at a reference temperature (generally 25 °C) is known to vary substantially in space and time in response to environmental conditions, it is typically parameterized in Earth system models (ESMs) with tabulated values associated to plant functional types. In this study, we developed a mechanistic model of leaf utilization of nitrogen for assimilation (LUNA V1.0) to predict the photosynthetic capacity at the global scale under different environmental conditions, based on the optimization of nitrogen allocated among light capture, electron transport, carboxylation, and respiration. The LUNA model was able to reasonably well capture the observed patterns of photosynthetic capacity in view that it explained approximately 55 % of the variation in observed Vc, max25 and 65 % of the variation in observed Jmax25 across the globe. Our model simulations under current and future climate conditions indicated that Vc, max25 could be most affected in high-latitude regions under a warming climate and that ESMs using a fixed Vc, max25 or Jmax25 by plant functional types were likely to substantially overestimate future global photosynthesis.

scholarly journals Carbonyl sulfide: comparing a mechanistic representation of the vegetation uptake in a land surface model and the leaf relative uptake approach

2021 ◽  
Vol 18 (9) ◽  
pp. 2917-2955
Author(s):  
Fabienne Maignan ◽  
Camille Abadie ◽  
Marine Remaud ◽  
Linda M. J. Kooijmans ◽  
Kukka-Maaria Kohonen ◽  
...  
Keyword(s):  
Land Surface ◽  
Carbonyl Sulfide ◽  
Land Surface Model ◽  
Global Scale ◽  
C3 Plants ◽  
Surface Model ◽  
High Temporal Resolution ◽  
Co2 Uptake ◽  
Mechanistic Approach ◽  
Relative Uptake

Abstract. Land surface modellers need measurable proxies to constrain the quantity of carbon dioxide (CO2) assimilated by continental plants through photosynthesis, known as gross primary production (GPP). Carbonyl sulfide (COS), which is taken up by leaves through their stomates and then hydrolysed by photosynthetic enzymes, is a candidate GPP proxy. A former study with the ORCHIDEE land surface model used a fixed ratio of COS uptake to CO2 uptake normalised to respective ambient concentrations for each vegetation type (leaf relative uptake, LRU) to compute vegetation COS fluxes from GPP. The LRU approach is known to have limited accuracy since the LRU ratio changes with variables such as photosynthetically active radiation (PAR): while CO2 uptake slows under low light, COS uptake is not light limited. However, the LRU approach has been popular for COS–GPP proxy studies because of its ease of application and apparent low contribution to uncertainty for regional-scale applications. In this study we refined the COS–GPP relationship and implemented in ORCHIDEE a mechanistic model that describes COS uptake by continental vegetation. We compared the simulated COS fluxes against measured hourly COS fluxes at two sites and studied the model behaviour and links with environmental drivers. We performed simulations at a global scale, and we estimated the global COS uptake by vegetation to be −756 Gg S yr−1, in the middle range of former studies (−490 to −1335 Gg S yr−1). Based on monthly mean fluxes simulated by the mechanistic approach in ORCHIDEE, we derived new LRU values for the different vegetation types, ranging between 0.92 and 1.72, close to recently published averages for observed values of 1.21 for C4 and 1.68 for C3 plants. We transported the COS using the monthly vegetation COS fluxes derived from both the mechanistic and the LRU approaches, and we evaluated the simulated COS concentrations at NOAA sites. Although the mechanistic approach was more appropriate when comparing to high-temporal-resolution COS flux measurements, both approaches gave similar results when transporting with monthly COS fluxes and evaluating COS concentrations at stations. In our study, uncertainties between these two approaches are of secondary importance compared to the uncertainties in the COS global budget, which are currently a limiting factor to the potential of COS concentrations to constrain GPP simulated by land surface models on the global scale.

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