Scientific Communities Striving for a Common Cause: Innovations in Carbon Cycle Science

Abstract

Where does the carbon released by burning fossil fuels go? Currently, ocean and land systems remove about half of the CO2 emitted by human activities; the remainder stays in the atmosphere. These removal processes are sensitive to feedbacks in the energy, carbon, and water cycles that will change in the future. Observing how much carbon is taken up on land through photosynthesis is complicated because carbon is simultaneously respired by plants, animals, and microbes. Global observations from satellites and air samples suggest that natural ecosystems take up about as much CO2 as they emit. To match the data, our land models generate imaginary Earths where carbon uptake and respiration are roughly balanced, but the absolute quantities of carbon being exchanged vary widely. Getting the magnitude of the flux is essential to make sure our models are capturing the right pattern for the right reasons. Combining two cutting edge tools, carbonyl sulfide (OCS) and solar-induced fluorescence (SIF), will help develop an independent answer of how much carbon is being taken up by global ecosystems. Photosynthesis requires CO2, light, and water. OCS provides a spatially and temporally-integrated picture of the ‘front door’ of photosynthesis, proportional to CO2 uptake and water loss through plant stomata. SIF provides a high-resolution snapshot of the ‘side door’, scaling with the light captured by leaves. These two independent pieces of information help us understand plant water and carbon exchange. A coordinated effort to generate SIF and OCS data through satellite, airborne, and ground observations will improve our process-based models to predict how these cycles will change in the future.

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

“…It is difficult to say whether in situ and laboratory measurements are too sparse and not representative enough of the variability of plants and environmental conditions across the globe to have a reasonable confidence in their derived mean or median LRU values, or whether we can use these LRU values to falsify the modelled COS and/or GPP fluxes. We may also add that LRU values derived from measurements performed in leaf chamber measurements, which are well ventilated and thus associated with large leaf boundary layer conductances, may not be representative of the real-world transfer processes, where the boundary layer conductances vary with wind speed, temporally and within canopy depth (Wohlfahrt et al, 2012).…”

“…Having both the vegetation and soil contributions, we will also be able to assimilate ecosystem COS fluxes to optimise COS-related parameters such as α in the internal conductance formulation from the Berry et al (2013) model for vegetation uptake, and those related to the stomatal conductance (Wehr et al, 2017;Berkelhammer et al, 2020). We will also later look at the complementary constraints on GPP brought by COS and solar-induced fluorescence, another GPP proxy (Bacour et al, 2019;Whelan et al, 2020).…”

Satellite soil moisture data assimilation impacts on modeling weather variables and ozone in the southeastern US – Part 2: Sensitivity to dry deposition parameterizations

“…A variety of data products were utilized in this study to assess the model performance in no-DA and DA cases. Many of these evaluation datasets have been applied and introduced in detail in Huang et al (2021), which are: 1) National Centers for Environmental Prediction Global Surface Observational Weather Data as well as weather data collected onboard the NASA B-200 aircraft during the ACT-America campaign; 2) hourly O3 measurements at the US Environmental Protection above-ground canopy biomass, and was used together with a 10-day average Copernicus Global Land Service GVF product to derive GVF for the focused 13-day period; 2) the daily GPP estimates from the 9 km SMAP level 4 carbon (L4C) product version 6, developed based on the SMAP L4 surface (0-5 cm) and rootzone (0-100 cm) SM together with satellite LULC and vegetation datasets, which was supplemented by two independent GPP proxies (Whelan et al, 2020) of satellite-derived solar-induced chlorophyll fluorescence (SIF) data (Yu et al, 2019) and the Portable Flask Package (Sweeney et al, 2015) carbonyl sulfide (OCS) measurements collected onboard the B-200 and C-130 aircraft during the ACT-America campaign, and other airborne trace gas (e.g., benzene) measurements during this campaign were analyzed together with the OCS data to help distinguish the influences of combustion sources from plant CO2 uptake on the observed OCS distributions; and 3) Vd data from selected CASTNET sites, estimated using a multilayer model (MLM, not supported by CASTNET as of 2017) version 3.0 which has known limitations and biases against eddy covariance flux measurements as well as Vd estimated using other methods (e.g., Finkelstein et al, 2000;Saylor et al, 2014;Wu et al, 2018). The known limitations of MLM and how they may affect our model comparisons with the CASTNET Vd data are discussed.…”

Covariation of Airborne Biogenic Tracers (CO2, COS, and CO) Supports Stronger Than Expected Growing Season Photosynthetic Uptake in the Southeastern US

“…Ecosystem model simulations of GPP show a range of spatial patterns in the eastern US, and only a subset of models are consistent with strong crop uptake in the Midwest inferred from SIF and COS (Guanter et al, 2014;Hilton et al, 2017). Multi-tracer data thus provide important proxies for studying spatial GPP variability, and offer unique benchmarks for improving model formulations of agricultural productivity, light capture by leaves, and CO 2 diffusion by stomatal conductance (Hilton, 2018;Whelan et al, 2020).…”