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Carbonyl sulfide (COS) is an atmospheric trace gas of interest for C cycle research because COS uptake by continental vegetation is strongly related to terrestrial gross primary productivity (GPP), the largest and most uncertain flux in atmospheric CO2 budgets. However, to use atmospheric COS budgets as an additional tracer of GPP, an accurate quantification of COS exchange by soils is also needed. At present, the atmospheric COS budget is unbalanced globally, with total COS flux estimates from oxic and anoxic soils that vary between −409 and −104 GgS yr−1. This uncertainty hampers the use of atmospheric COS concentrations to constrain GPP estimates through atmospheric transport inversions. In this study we implemented a mechanistic soil COS model in the ORCHIDEE land surface model to simulate COS fluxes in oxic and anoxic soils. Evaluation of the model against flux measurements at 7 sites yields a mean root mean square deviation of 1.6 pmol m−2 s−1, instead of 2 pmol m−2 s−1 when using a previous empirical approach that links soil COS uptake to soil heterotrophic respiration. The new model predicts that, globally and over the 2009–2016 period, oxic soils act as a net uptake of −126 GgS yr−1, and anoxic soils are a source of +96 GgS yr−1, leading to a global net soil sink of only −30 GgS yr−1, i.e., much smaller than previous estimates. The small magnitude of the soil fluxes suggests that the error in the COS budget is dominated by the much larger fluxes from plants, oceans, and industrial activities. The predicted spatial distribution of soil COS fluxes, with large emissions in the tropics from oxic (up to 68.2 pmol COS m−2 s−1) and anoxic (up to 36.8 pmol COS m−2 s−1) soils, marginally improves the latitudinal gradient of atmospheric COS concentrations, after transport by the LMDZ atmospheric transport model. The impact of different soil COS flux representations on the latitudinal gradient of the atmospheric COS concentrations is strongest in the northern hemisphere. We also implemented spatio-temporal variations of near-ground atmospheric COS concentrations in the modelling of biospheric COS fluxes, which helped reduce the imbalance of the atmospheric COS budget by lowering COS uptake by soils and vegetation globally (−10 % for soil, and −8 % for vegetation with a revised mean estimate of −576 GgS y−r1 over 2009–2016). Sensitivity analyses highlighted the different parameters to which each soil COS flux model is the most responsive, selected in a parameter optimization framework. Having both vegetation and soil COS fluxes modelled within ORCHIDEE opens the way for using observed ecosystem COS fluxes and larger scale atmospheric COS mixing ratios to improve the simulated GPP, through data assimilation techniques.

<p>Atmospheric Carbonyl Sulfide (COS) is a useful tracer for assessing gross primary production (GPP). COS is also an important contributor to stratospheric sulfate aerosols (SSA) which cool the climate. However, the global budget of COS remains unresolved due to insufficient observations. We implemented a linear inversion framework within the TM5-4DVAR global chemistry transport model constrained by NOAA surface network to investigate the sources and sinks of COS (Ma et al., 2020). To close the gap between sources and sinks, we focused on inversions that optimize what is thought to be a “missing” source amounting to 432 GgS a<sup>-1</sup>. We found that a tropical missing source was likely, which could either be an indication of an underestimated ocean source, or overestimated biosphere uptake. Additionally, we found the biosphere uptake to be underestimated at higher latitudes of the Northern Hemisphere. Inversions were validated with HIPPO aircraft data, NOAA airborne profiles and satellite data (MIPAS, TES and ACE-FTS), indicating an underestimation of COS in troposphere. We further implemented a first-order dependency of COS biosphere flux on COS mole fractions in the atmosphere boundary layer, which renders the inversions nonlinear. As expected based on the known drawdown of COS by biosphere uptake, it is found that the dependence of the biosphere flux on COS mole fractions reduced the budget gap by 137 GgS a<sup>-1</sup>. We further optimized COS fluxes separately over ocean and land, accounting for the first-order dependency of biosphere uptake on COS mole fractions. These results suggest that the missing COS sources may originate from the ocean (207 GgS a<sup>-1</sup>), despite recent work in which the ocean is explicitly studied suggesting otherwise.  Understanding this apparent discrepancy will be an important topic to elucidate. In the future, we plan to take the advantage of available satellite data products to better constrain the COS flux budget in the tropics. COS products from the MIPAS and TES satellites are good candidates for data assimilation in the current model.</p>

Background and aimsPartitioning the measured net ecosystem carbon dioxide (CO2) exchange into gross primary productivity (GPP) and ecosystem respiration remains a challenge, which scientists try to tackle by using the properties of the trace gas carbonyl sulfide (COS). Its similar pathway into and within the leaf makes it a potential photosynthesis proxy. The application of COS as an effective proxy depends, among other things, on a robust inventory of potential COS sinks and sources within ecosystems. While the soil received some attention during the last couple of years, the role of plant roots is mostly unknown. In our study, we investigated the effects of live roots on the soil COS exchange.MethodsAn experimental setup was devised to measure the soil and the belowground plant parts of young beech trees observed over the course of 9 months.ResultsDuring the growing season, COS emissions were significantly lower when roots were present compared to chambers only containing soil, while prior to the growing season, with photosynthetically inactive trees, the presence of roots increased COS emissions. The difference in the COS flux between root-influenced and uninfluenced soil was fairly constant within each month, with diurnal variations in the COS flux driven primarily by soil temperature changes rather than the presence or absence of roots.ConclusionWhile the mechanisms by which roots influence the COS exchange are largely unknown, their contribution to the overall ground surface COS exchange should not be neglected when quantifying the soil COS exchange.

<strong class="journal-contentHeaderColor">Abstract.</strong> Carbonyl Sulfide (COS) is a useful tracer to estimate Gross Primary Production (GPP) because it shares part of the uptake pathway with CO₂. COS is taken up in plants through hydrolysis, catalyzed by the enzyme carbonic anhydrase (CA), but is not released. The Simple Biosphere model version 4 (SiB4) simulates COS leaf uptake using a conductance approach. SiB4 applies the temperature response of the RuBisCo enzyme (used for photosynthesis) to simulate the COS leaf uptake, but the CA enzyme might respond differently. We introduce a new temperature response function for CA in SiB4, based on enzyme kinetics with an optimum temperature. Moreover, we determine Ball-Berry model parameters for stomatal conductance (<em>g_s</em>) using observation-based estimates of COS flux, GPP, and <em>g_s</em> along with meteorological measurements in an evergreen needleleaf forest (ENF) and deciduous broadleaf forest (DBF). We find that CA has optimum temperatures of 22 &deg;C (ENF) and 38 &deg;C (DBF) with CA&rsquo;s activation energy as 40 kJ mol^-1, which is lower than that of RuBisCo (45 &deg;C), suggesting that air temperature changes can critically affect CA&rsquo;s catalyzation activity. Optimized values for the Ball-Berry offset parameter <em>b₀</em> (ENF: 0.013, DBF: 0.007 mol m^-2 s^-1) are higher (lower) than the original value (0.010 mol m^-2 s^-1) in the ENF (DBF), and optimized values for the Ball-Berry slope parameter <em>b₁</em> (ENF: 16.36, DBF: 11.43) are higher than the original value (9.0) at both sites. We apply the optimized <em>g_CA</em> and <em>g_s</em> parameters in SiB4 site simulations, thereby improving the timing and peak of COS assimilation. In addition, we show that SiB4 underestimates the leaf humidity stress under conditions where high VPD should limit <em>g_s</em> in the afternoon, thereby overestimating <em>g_s</em>. Furthermore, we simulate global COS biosphere fluxes, which show smaller COS uptake in the tropics and larger COS uptake at higher latitudes, corresponding with the updates made to the CA temperature response. This SiB4 update helps resolve gaps in the COS budget identified in earlier studies. Using our optimization and additional observations of COS uptake over various climate and plant types, we expect further improvements in global COS biosphere flux estimates.

Gross primary production (GPP) by boreal forests is highly sensitive to environmental changes. However, GPP simulated by land surface models (LSMs) remains highly uncertain due to the lack of direct photosynthesis observations at large scales. Carbonyl sulfide (COS) has emerged as a promising proxy to improve the representation of GPP in LSMs. Because COS is absorbed by vegetation following the same diffusion pathway as CO2 during photosynthesis and not emitted back to the atmosphere, incorporating a mechanistic representation of vegetation COS uptake in LSMs allows using COS observations to refine GPP representation. Here, we perform ecosystem COS flux and GPP data assimilations to constrain the COS‐ and GPP‐related parameters in the ORCHIDEE LSM for boreal evergreen needleleaf forests (BorENF). Assimilating ecosystem COS fluxes at Hyytiälä forest increases the simulated net ecosystem COS uptake by 14%. This increase largely results from changes in the internal conductance to COS, highlighting the need to improve the representation of COS internal diffusion and consumption. Moreover, joint assimilation of ecosystem COS flux and GPP at Hyytiälä improves the simulated latent heat flux, contrary to the GPP‐only data assimilation, which fails to do so. Finally, we scaled this assimilation framework up to the boreal region and find that the joint assimilation of COS at Hyytiälä and GPP fluxes at 10 BorENF sites increases the modeled vegetation COS uptake up to 18%, but not GPP. Therefore, this study encourages the use of COS flux observations to inform GPP and latent heat flux representations in LSMs.

<strong class="journal-contentHeaderColor">Abstract.</strong> The seasonality and interannual variability of terrestrial carbonyl sulfide (COS) fluxes are poorly constrained. We present the first easy-to-use parameterization for the net COS forest sink based on the longest existing eddy covariance record from a boreal pine forest, covering 32 months over 5 years. Fluxes from hourly to yearly scales are reported, with the aim of revealing controlling factors and the level of interannual variability. The parameterization is based on the photosynthetically active radiation, vapor pressure deficit, air temperature, and leaf area index. Wavelet analysis of the ecosystem fluxes confirmed earlier findings from branch-level fluxes at the same site and revealed a 3 h lag between COS uptake and air temperature maxima at the daily scale, whereas no lag between radiation and COS flux was found. The spring recovery of the flux after the winter dormancy period was mostly governed by air temperature, and the onset of the uptake varied by 2 weeks. For the first time, we report a significant reduction in ecosystem-scale COS uptake under a large water vapor pressure deficit in summer. The maximum monthly and weekly median COS uptake varied by 26 % and 20 % between years, respectively. The timing of the latter varied by 6 weeks. The fraction of the nocturnal uptake remained below 21 % of the total COS uptake. We observed the growing season (April–August) average net flux of COS totaling <span class="inline-formula">−58.0</span> <span class="inline-formula">g S ha^−1</span> with 37 % interannual variability. The long-term flux observations were scaled up to evergreen needleleaf forests (ENFs) in the whole boreal region using the Simple Biosphere Model Version 4 (SiB4). The observations were closely simulated using SiB4 meteorological drivers and phenology. The total COS uptake by boreal ENFs was in line with a missing COS sink at high latitudes pointed out in earlier studies.

&amp;lt;p&amp;gt;In search for a constraint on the gross primary productivity (GPP) on ecosystem level, the sulfur containing gas carbonyl sulfide (COS) shows great promise. COS takes a very similar route into the leaf as carbon dioxide (CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;), that is through the leaf boundary layer, the stomata and the mesophyll until COS is fully catalyzed in a one-way reaction by the enzyme carbonic anhydrase (CA), whereas CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; reaches its endpoint at RuBisCO within the chloroplast stroma. For the calculation of the GPP based on COS fluxes, a beforehand knowledge about the ratio of the deposition velocities of COS to CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, also called leaf relative uptake (LRU), is needed. Differences in the LRU between plants and under different environmental conditions might hinder a straightforward usage of this approach.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;To investigate the LRU and its dependencies on the involved conductances, we conducted eddy covariance measurements of COS, CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and H&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O at an agricultural field in Ariis, Italy. At this field, 2 different varieties of soybean were planted in adjacent plots. One was the commercial variety Eiko, to which we will refer to as the green &amp;amp;#8220;wild type&amp;amp;#8221; (WT). The other was a chlorophyll deficient golden/yellow variety called MinnGold (MG). Due to a lack of rain, all plots were irrigated 2 and 3 weeks into our 4 week campaign.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;br&amp;gt;Despite having a reduced chlorophyll content, MG was able to match and even exceeded the rate of photosynthesis of the WT during our observation period. While the GPP was similar for both varieties during the first week, we observed a higher decline for WT in week 2 due to a naturally occurring drought. Even after the irrigation of both plots, the GPP of MG recovered faster. We also observed considerably higher COS uptake by MG during the whole campaign. The resulting LRU under high light conditions was also consequently higher for MG (1.41) than for WT (0.97).&amp;lt;br&amp;gt;We calculated the aerodynamic, boundary layer, stomatal and internal conductance for both varieties and grouped the values into 4 phases: pre-drought, drought, rewetting and recovery. Based on these values and a linear perturbation analysis, we identified the internal conductance as the largest driver for the different LRUs between the two varieties.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Our results indicate that the stomatal conductance is not the only controlling factor for the LRU and that the mesophyll conductance can&amp;amp;#8217;t be neglected. We also show, the LRU response to drought differs between plants, even at the level of varieties.&amp;amp;#160;&amp;lt;/p&amp;gt;

©2014. American Geophysical Union. All Rights Reserved. Carbonyl sulfide (COS) was measured in Antarctic ice core samples from the Byrd, Siple Dome, Taylor Dome, and West Antarctic Ice Sheet Divide sites covering the last 8000 years of the Holocene. COS levels decrease downcore in most of these ice cores. The magnitude of the downcore trends varies among the different ice cores and is related to the thermal histories of the ice sheet at each site. We hypothesize that this is due to the temperature-dependent hydrolysis of COS that occurs in situ. We use a one-dimensional ice flow and heat flux model to infer temperature histories for the ice core samples from different sites and empirically determine the kinetic parameters for COS hydrolysis. We estimate e-folding lifetimes for COS hydrolysis ranging from 102 years to 106 years over a temperature range of 0°C to -50°C. The reaction kinetics are used to estimate and correct for the in situ COS loss, allowing us to reconstruct paleoatmospheric COS trends during the mid-to-late Holocene. The results suggest a slow, long-term increase in atmospheric COS that may have started as early as 5000 years ago. Given that the largest term in the COS budget is uptake by terrestrial plants, this could indicate a decline in terrestrial productivity during the late Holocene.

The uptake rates of carbonyl sulfide (COS) by soils in subtropical forests with different successional stages were measured using static chambers in Dinghushan Biosphere Reserve (DBR) in south China from July 2004 to March 2005. The three typical tropical forests studied included monsoon evergreen broad‐leaf forest (BF), pine and broad‐leaf mixed forest (MF) and pine forest (PF), representing forests with different succession stages in the region. COS exchange rates were also compared between the plots with litter‐fall remaining (plots L) and those with litter‐fall removed (plots S) in each forest. Results showed that these forest soils all acted as sinks for COS with exchange rates of −1.22 to −11.82 pmol m−2 s−1. The MF in the midsuccessional stage had significantly higher uptake rates, and the mean exchange rates in the BF, MF, and PF were −3.90, −4.77, and −3.65 pmol m−2 s−1, respectively. COS uptake rates at plots L were higher than those at plots S. Mean COS fluxes were significantly higher in March (−6.06 pmol m−2 s−1) than those in July (−3.60 pmol m−2 s−1), August (−3.82 pmol m−2 s−1), September (−3.45 pmol m−2 s−1), and October (−3.54 pmol m−2 s−1). Significant correlation was observed between the COS uptake rates and soil respiration rates or microbial biomass, indicating that microbial activity was an important factor controlling the soil uptake of COS. Significant correlations between COS fluxes and initial COS mixing ratios were only observed in the BF and MF. COS fluxes showed no correlation with soil temperature or water content alone in any of the three forests, but do correlate well with soil temperature and water content together in polynomial forms with an order of 2.

&amp;lt;p&amp;gt;The atmospheric budget of carbonyl sulfide (COS, lifetime ~2 years) is primarily determined by emissions from anthropogenic and oceanic sources and uptake by the biosphere. Once the budget of COS is adequately understood, COS could be a suitable tracer to estimate Gross Primary Productivity (GPP), since stomatal uptake by plants is basically a one-way process, unlike the assimilation of CO2. However, currently the global budget of COS is not closed. Here, we will report progress on the use of inverse modelling to better constrain the atmospheric COS budget. To that end, we assimilate data from the MIPAS instrument that flew onboard the ENVISAT satellite (2002&amp;amp;#8211;2012). MIPAS is a limb sounder that measures atmospheric emission profiles down to the upper troposphere. Tropospheric COS retrievals are assimilated together with NOAA COS surface observations, and a bias correction scheme is employed to correct for potential calibration differences. Using the 4DVAR-TM5 model, we derive a consistent global COS budget. However, evaluation with independent data reveals that TM5 remains biased low in the free troposphere. We will show that this underestimate may be resolved by accounting for an aqueous-phase oxidation process of the newly discovered HydroPeroxyMethylThioFormate (HPMTF) intermediate in the DMS oxidation chain.&amp;lt;/p&amp;gt;

Emissions of biogenic sulfur gases (hydrogen sulfide (H2S) and carbonyl sulfide (COS)) from Phragmites australis coastal marsh in the Yellow River estuary of China were determined during April to December in 2014 using static chamber-gas chromatography technique with monthly sampling. The results showed that the fluxes of H2S and COS both had distinct seasonal and diurnal variations. The H2S fluxes ranged from 0.09 μg/(m2·h) to 7.65 μg/(m2·h), and the COS fluxes ranged from–1.10 μg/(m2·h) to 3.32 μg/(m2·h). The mean fluxes of H2S and COS from the P. australis coastal marsh were 2.28 μg/(m2·h), and 1.05 μg/(m2·h), respectively. The P. australis coastal marsh was the emission source of both H2S and COS over the whole year. Fluxes of H2S and COS were both higher in plant growing season than in the non-growing season. Temperature had a dramatic effect on the H2S emission flux, while the correlations between COS flux and the environmental factors were not found during sampling periods. More in-depth and comprehensive research on other related factors, such as vegetation, sediment substrates, and tidal action is needed to discover and further understand the key factors and the release mechanism of sulfur gases.

Carbonyl Sulphide (COS), a trace gas showing striking similarity to CO2 in terms of biochemical diffusion pathway into leaves, has been recognized as a promising indicator of the plant gross primary production (GPP), the amount of carbon dioxide that is absorbed through photosynthesis by terrestrial ecosystems. However, large uncertainties about the other components of its atmospheric budget prevent us from directly relating the atmospheric COS measurements to GPP. The largest uncertainty comes from the closure of its atmospheric budget, with a source component missing. Here, we explore the benefit of assimilating both COS and CO2 measurements into the LMDz atmospheric transport model to obtain consistent information on GPP, plant respiration and COS budget. To this end, we develop an analytical inverse system that optimizes biospheric fluxes for the 15 plant functional types (PFTs) defined in the ORCHIDEE global land surface model. Plant uptake of COS is parameterized as a linear function of GPP of the leaf relative uptake (LRU), which is the ratio of COS to CO2 deposition velocities in plants. A possible scenario for the period 2008–2019 leads to a global biospheric sink of 800 GgS.yr−1, with higher absorption in the high latitudes and higher oceanic emissions between 400 and 600 GgS.yr−1 most of which is located in the tropics. As for the CO2 budget, the inverse system increases GPP in the high latitudes by a few GtC.yr−1 without modifying the respiration compared to the ORCHIDEE fluxes used as a prior. In contrast, in the tropics the system tends to weaken both respiration and GPP. The optimized components of the COS and CO2 have been evaluated against independent measurements over Northern America, the Pacific Ocean, at three sites in Japan and at one site in France. Overall, the posterior COS concentrations are in better agreement with the COS retrievals at 250 hPa from the MIPAS satellite and with airborne measurements made over North America and the Pacific Ocean. The system seems to have rightly corrected the underestimated GPP over the high latitudes. However, the change in seasonality of GPP in the tropics disagrees with Solar Induced Fluorescence (SIF) data. The decline in biospheric sink in the Amazon driven by the inversion also disagrees with MIPAS COS retrievals at 250 hPa, highlighting the lack of observational constraints in this region. Moreover, the comparison with the surface measurements in Japan and France suggests misplaced sources in the prior anthropogenic inventory, emphasizing the need for an improved inventory to better partition oceanic and continental sources in Asia and Europe.

In the Arctic and Boreal region (ABR) where warming is especially pronounced, the increase of gross primary production (GPP) has been suggested as an important driver for the increase of the atmospheric CO2 seasonal cycle amplitude (SCA). However, the role of GPP relative to changes in ecosystem respiration (ER) remains unclear, largely due to our inability to quantify these gross fluxes on regional scales. Here, we use atmospheric carbonyl sulfide (COS) measurements to provide observation-based estimates of GPP over the North American ABR. Our annual GPP estimate is 3.6 (2.4 to 5.5) PgC · y-1 between 2009 and 2013, the uncertainty of which is smaller than the range of GPP estimated from terrestrial ecosystem models (1.5 to 9.8 PgC · y-1). Our COS-derived monthly GPP shows significant correlations in space and time with satellite-based GPP proxies, solar-induced chlorophyll fluorescence, and near-infrared reflectance of vegetation. Furthermore, the derived monthly GPP displays two different linear relationships with soil temperature in spring versus autumn, whereas the relationship between monthly ER and soil temperature is best described by a single quadratic relationship throughout the year. In spring to midsummer, when GPP is most strongly correlated with soil temperature, our results suggest the warming-induced increases of GPP likely exceeded the increases of ER over the past four decades. In autumn, however, increases of ER were likely greater than GPP due to light limitations on GPP, thereby enhancing autumn net carbon emissions. Both effects have likely contributed to the atmospheric CO2 SCA amplification observed in the ABR.

Understanding plant biophysical and biochemical responses to drought is essential for predicting ecosystem carbon–water exchange and gross primary productivity (GPP) under a changing climate. Here, we investigate stomatal and non-stomatal responses to natural drought events by integrating carbonyl sulfide (COS) fluxes as a novel observational constraint into the Soil–Canopy Observation of Photosynthesis and Energy fluxes (SCOPE) model. Because plants take up COS in parallel with CO2 via practically similar pathways but do not re-emit COS, it can be used as promising proxy for GPP and stomatal conductance. SCOPE is a physically based land-surface model that links plant processes to spectrally resolved within-canopy radiative transfer; adding COS provides an independent constraint on canopy conductance and carbon uptake. We leverage multiple years of concurrent COS and CO2 flux as well as hyperspectral reflectance measurements from a Scots pine dominated montane forest in Austria, including naturally occurring drought periods, to refine model representations of stomatal regulation, internal conductance, and water-stress responses at the ecosystem scale. This model–data integration framework improves detection and prediction of drought impacts on canopy function and enhances constraints on ecosystem carbon–water dynamics.

Modeling carbonyl sulfide and carbon dioxide fluxes in a northern boreal coniferous forest using memory-based deep learning