Atmosphere-Land Surface Fluxes and Continental Boundary Layer Moisture Recycling: Insights from Stable Water Isotope Ratios in Soil, Surface Vapor and Precipitation at a Mid-Latitude Tall-Tower Site

Atmosphere-land surface exchanges represent the largest uncertainties in climate models used to make projections about future hydroclimate. Measurements of stable isotope ratios in water can be exploited to better understand mechanisms controlling land surface-atmosphere water fluxes, as they provide more process-level information than bulk water. This thesis examines mechanistic controls on boundary layer moisture cycling using four years of meteorological and stable isotope ratio measurements of water (&delta;D and &delta;18O) in vapor, precipitation, vegetation and soil from the Boulder Atmospheric Observatory (BAO), a 300-meter tall-tower site in Erie, Colorado. First, near-surface water isotope ratios in vapor, precipitation and soil were used to evaluate the net ecosystem exchange of water at BAO. Stable water vapor isotope ratio profiles coupled with soil water isotope ratio and meteorological measurements constrained surface evaporation models to weight the contributions of rainfall, surface water vapor exchange and sub-surface vapor diffusion to soil water isotope ratios. A multi-year time series allowed for validation of model parameters, such as kinetic fractionation factor, that are not easily measurable. Results show a strong evaporative contribution from sub-surface vapor, and less diffusive control on evaporative exchange than previously thought. Reconciling isotope-derived evapotranspiration partitioning with an isotope-independent method highlighted mechanisms and model parameterizations that are relevant for correct latent heat flux partitioning. Next, boundary layer rain re-evaporation was measured using stable water isotope ratios in precipitation and vapor coupled with disdrometer measurements of raindrop size. Precipitation isotopes represent an integrated condensation history of the water parcel, controlled by air mass source, temperature and continental recycling along the parcel back-trajectory. Vapor isotopes show seasonality, which reflects air mass source and surface evaporative exchange. Results show that temperature equilibration explained 80% of the isotope correlations, however, the correlation for summer rainfall was much lower at 50%. Isotope-enabled models that explicitly used weighted drop size distribution information significantly improved the prediction of rainfall isotope ratios for summer rainfall, which has implications for improving representations of rainfall evaporation in isotope-enabled climate models. These results provide critical observational constraints for further refinement of climate models that will ultimately be used to predict future biogeochemical and hydroclimate changes.</p

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

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 &sim;50&ndash;200&thinsp;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&plusmn;27&thinsp;%, albeit with large variability across sites. On a global scale, our model modifications decreased the modeled COS terrestrial biosphere sink from 922&thinsp;Gg&thinsp;S&thinsp;yr&minus;1 in the original SiB4 to 753&thinsp;Gg&thinsp;S&thinsp;yr&minus;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. Full List of Authors Linda M. J. Kooijmans1, Ara Cho1, Jin Ma2, Aleya Kaushik3,4, Katherine D. Haynes5, Ian Baker5, Ingrid T. Luijkx1, Mathijs Groenink1, Wouter Peters1,6, John B. Miller4, Joseph A. Berry7, Jerome Og&eacute;e8, Laura K. Meredith9, Wu Sun7, Kukka-Maaria Kohonen10, Timo Vesala10,11,12, Ivan Mammarella10, Huilin Chen6, Felix M. Spielmann13, Georg Wohlfahrt13, Max Berkelhammer14, Mary E. Whelan15, Kadmiel Maseyk16, Ulli Seibt17, Roisin Commane18, Richard Wehr19,20, and Maarten Krol1,2 1Meteorology and Air Quality, Wageningen University and Research, Wageningen, the Netherlands 2Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, the Netherlands 3Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO, USA 4NOAA Global Monitoring Laboratory, Boulder, CO, USA 5Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA 6Centre for Isotope Research, University of Groningen, Groningen, the Netherlands 7Department of Global Ecology, Carnegie Institution for Science, Stanford, CA, USA 8INRAE, Bordeaux Sciences Agro, UMR 1391 ISPA, 33140 Villenave-d'Ornon, France 9School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, USA 10Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki, Finland 11Institute for Atmospheric and Earth System Research/Forest Sciences, University of Helsinki, Helsinki, Finland 12Yugra State University, 628012, Khanty-Mansiysk,&nbsp;Russia 13Department of Ecology, University of Innsbruck, Innsbruck, Austria 14Department of Earth and Environmental Sciences, University of Illinois Chicago, Chicago, IL, USA 15Department of Environmental Sciences, Rutgers University, New Brunswick, NJ, USA 16School of Environment, Earth and Ecosystem Sciences, The Open University, Milton Keynes, MK7 6AA, UK 17Department of Atmospheric &amp; Oceanic Sciences, UCLA, Los Angeles, CA, USA 18Department of Earth &amp; Environmental Sciences, Lamont&ndash;Doherty Earth Observatory, Columbia University, Palisades, NY, USA 19Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ, USA 20currently at: Center for Atmospheric and Environmental Chemistry, Aerodyne Research, Inc., Billerica, MA, USA </div

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

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 obser- vations 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 similar to 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.Peer reviewe

Harnessing the NEON data revolution to advance open environmental science with a diverse and data-capable community

It is a critical time to reflect on the National Ecological Observatory Network (NEON) science to date as well as envision what research can be done right now with NEON (and other) data and what training is needed to enable a diverse user community. NEON became fully operational in May 2019 and has pivoted from planning and construction to operation and maintenance. In this overview, the history of and foundational thinking around NEON are discussed. A framework of open science is described with a discussion of how NEON can be situated as part of a larger data constellation—across existing networks and different suites of ecological measurements and sensors. Next, a synthesis of early NEON science, based on >100 existing publications, funded proposal efforts, and emergent science at the very first NEON Science Summit (hosted by Earth Lab at the University of Colorado Boulder in October 2019) is provided. Key questions that the ecology community will address with NEON data in the next 10 yr are outlined, from understanding drivers of biodiversity across spatial and temporal scales to defining complex feedback mechanisms in human–environmental systems. Last, the essential elements needed to engage and support a diverse and inclusive NEON user community are highlighted: training resources and tools that are openly available, funding for broad community engagement initiatives, and a mechanism to share and advertise those opportunities. NEON users require both the skills to work with NEON data and the ecological or environmental science domain knowledge to understand and interpret them. This paper synthesizes early directions in the community’s use of NEON data, and opportunities for the next 10 yr of NEON operations in emergent science themes, open science best practices, education and training, and community building

Comment on “An approach to sulfate geoengineering with surface emissions of carbonyl sulfide” by Quaglia et al. (2022)

Solar radiation management through artificially increasing the amount of stratospheric sulfate aerosol is being considered as a possible climate engineering method. To overcome the challenge of transporting the necessary amount of sulfur to the stratosphere, Quaglia and co-workers suggest deliberate emissions of carbonyl sulfide (OCS), a long-lived precursor of atmospheric sulfate. In their paper, published in Atmospheric Chemistry and Physics in 2022, they outline two scenarios with OCS emissions either at the Earth's surface or in the tropical upper troposphere and calculate the expected radiative forcing using a climate model. In our opinion, the study (i) neglects a significantly higher surface uptake that will inevitably be induced by the elevated atmospheric OCS concentrations and (ii) overestimates the net cooling effect of this OCS geoengineering approach due to some questionable parameterizations and assumptions in the radiative forcing calculations. In this commentary, we use state-of-the-art models to show that at the mean atmospheric OCS mixing ratios of the two emissions scenarios, the terrestrial biosphere and the oceans are expected to take up more OCS than is being released to reach these levels. Using chemistry climate models with a long-standing record for estimating the climate forcing of OCS and stratospheric aerosols, we also show that the net radiative forcing of the emission scenarios suggested by Quaglia and co-workers is smaller than suggested and insufficient to offset any significant portion of anthropogenically induced climate change. Our conclusion is that a geoengineering approach using OCS will not work under any circumstances and should not be considered further

COS-derived GPP relationships with temperature and light help explain high-latitude atmospheric CO2 seasonal cycle amplification

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 CO 2 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 CO 2 SCA amplification observed in the ABR

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

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 GgSyr-1 in the original SiB4 to 753 GgSyr-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