Quantifying Northern High Latitude Gross Primary Productivity (GPP) Using Carbonyl Sulfide (OCS)

Abstract

The northern high latitude (NHL, 40°N to 90°N) is where the second peak region of gross primary productivity (GPP) other than the tropics. The summer NHL GPP is about 80% of the tropical peak, but both regions are still highly uncertain (Norton et al. 2019, https://doi.org/10.5194/bg-16-3069-2019). Carbonyl sulfide (OCS) provides an important proxy for photosynthetic carbon uptake. Here we optimize the OCS plant uptake fluxes across the NHL by fitting atmospheric concentration simulation with the GEOS‐CHEM global transport model to the aircraft profiles acquired over Alaska during NASA's Carbon in Arctic Reservoirs Vulnerability Experiment (2012–2015). We use the empirical biome‐specific linear relationship between OCS plant uptake flux and GPP to derive the six plant uptake OCS fluxes from different GPP data. Such GPP‐based fluxes are used to drive the concentration simulations. We evaluate the simulations against the independent observations at two ground sites of Alaska. The optimized OCS fluxes suggest the NHL plant uptake OCS flux of −247 Gg S year−1, about 25% stronger than the ensemble mean of the six GPP‐based OCS fluxes. GPP‐based OCS fluxes systematically underestimate the peak growing season across the NHL, while a subset of models predict early start of season in Alaska, consistent with previous studies of net ecosystem exchange. The OCS optimized GPP of 34 PgC yr−1 for NHL is also about 25% more than the ensembles mean from six GPP data. Further work is needed to fully understand the environmental and biotic drivers and quantify their rate of photosynthetic carbon uptake in Arctic ecosystems.

Carbon and Water Fluxes of the Boreal Evergreen Needleleaf Forest Biome Constrained by Assimilating Ecosystem Carbonyl Sulfide Flux Observations

“…All studies focusing on the BorENF PFT find an increase in vegetation COS uptake after optimization (Figure 9), which is in line with a suspected high‐latitude missing sink of COS proposed in recent inversion studies (Hu et al., 2021; Kuai et al., 2022; Ma et al., 2021; Remaud et al., 2022). Remaud et al.…”

“…All studies focusing on the BorENF PFT find an increase in vegetation COS uptake after optimization (Figure 9), which is in line with a suspected high-latitude missing sink of COS proposed in recent inversion studies (Hu et al, 2021;Kuai et al, 2022;Ma et al, 2021;Remaud et al, 2022). Remaud et al (2022) optimized the COS and CO 2 gross fluxes simulated in ORCHIDEE against atmospheric concentrations from the NOAA/ESRL/GML and provided prior and posterior values for GPP and vegetation COS uptake for each PFT.…”

“…Then, Kuai et al. (2022) also used atmospheric COS observations to optimize the vegetation COS uptake but using aircraft profiles over Alaska (CARVE). The vegetation COS uptake was increased by 25% over the Northern high latitudes (40°–90°N), as well as GPP given that vegetation COS flux and GPP are linked with a linear relationship.…”

“…The optimization performed in Remaud et al (2022) increased the GPP considerably for BorENF (from 5.8 PgC yr −1 to 7.2 PgC yr −1 ), which would disagree with the estimates from the FLUXCOM and FLUX-SAT products (3.94 PgC yr −1 and 4.76 PgC yr −1 respectively over land grid cells that have a fractional coverage of BorENF higher than 40%). Then, Kuai et al (2022) also used atmospheric COS observations to optimize the vegetation COS uptake but using aircraft profiles over Alaska (CARVE). The vegetation COS uptake was increased by 25% over the Northern high latitudes (40°-90°N), as well as GPP given that vegetation COS flux and GPP are linked with a linear relationship.…”

Intercomparison of Atmospheric Carbonyl Sulfide (TransCom‐COS; Part One): Evaluating the Impact of Transport and Emissions on Tropospheric Variability Using Ground‐Based and Aircraft Data

“…COS is taken up in leaves through similar pathways as carbon dioxide, but without significant respiration (Protoschill‐Krebs et al., 1996; Wohlfahrt et al., 2012). For this reason, COS has been proposed as a tracer that can be used to infer Gross Primary Productivity (GPP) at large scale (Campbell et al., 2008; Hu et al., 2021; Le Kuai et al., 2022; Montzka et al., 2007; Remaud et al., 2022).…”