Covariation of Airborne Biogenic Tracers (CO2, COS, and CO) Supports Stronger Than Expected Growing Season Photosynthetic Uptake in the Southeastern US. Issue 10 (29th September 2021)

• Record Type: Journal Article
• Authors: Parazoo, Nicholas C.; Bowman, Kevin W.; Baier, Bianca C.; Liu, Junjie; Lee, Meemong; Kuai, Le; Shiga, Yoichi; Baker, Ian; Whelan, Mary E.; Feng, Sha; Krol, Maarten; Sweeney, Colm; Runkle, Benjamin R.; Tajfar, Elahe; Davis, Kenneth J.
• Is Part Of: Global biogeochemical cycles. Volume 35:Issue 10(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-29
• Subjects: carbon cycle -- carbonyl sulfide -- carbon monoxide -- ecosystem -- OCO2 -- act‐America; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2021GB006956
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: The Atmospheric Carbon Transport (ACT)‐America Earth Venture mission conducted five airborne campaigns across four seasons from 2016 to 2019, to study the transport and fluxes of Greenhouse gases across the eastern United States. Unprecedented spatial sampling of atmospheric tracers (CO2, carbon monoxide [CO], carbonyl sulfide [COS]) related to biospheric processes offers opportunities to improve our qualitative and quantitative understanding of seasonal and spatial patterns of biospheric carbon uptake. Here, we examine co‐variation of boundary layer enhancements of CO2, CO, and COS across three diverse regions: the crop‐dominated Midwest, evergreen‐dominated South, and deciduous broadleaf‐dominated Northeast. To understand the biogeochemical processes controlling these tracers, we compare the observed co‐variation to simulated co‐variation resulting from model‐ and satellite‐ constrained surface carbon fluxes. We found indication of a common terrestrial biogenic sink of CO2 and COS and secondary production of CO from biogenic sources in summer throughout the eastern US, driven by stomatal conductance. Upper Midwest crops drive Δ CO2 and Δ COS depletion from early to late summer. Northeastern temperate forests drive Δ CO2 and Δ COS depletion in late summer. The unprecedented ACT‐America flask samples uncovered evidence that southern humid temperate forests photosynthesize and absorb CO2 and COS, and emit CO precursors, deep into the growing season. Satellite‐ constrained carbon fluxes capture much of the observed seasonal and spatial variability, but underestimate the magnitude of net CO2 and COS depletion in the South, indicating a stronger than expected net sink of CO2 in late summer. Additional sampling of the South will more accurately constrain underlying biological processes and climate sensitivities governing southern carbon dynamics. Plain Language Summary: The Atmospheric Carbon Transport (ACT)‐America airborne mission provided unprecedented sampling of atmospheric greenhouse gas concentrations throughout the eastern United States from 2016 to 2019. A subset of these gases, namely carbon dioxide (CO2 ), carbonyl sulfide (COS), and carbon monoxide (CO), are strongly influenced by photosynthetic activity in plants. Unlike other sources of carbon such as fossil fuels and biomass burning, photosynthetic influences on CO2, COS, and CO are correlated in time and space. As such, the covariation of boundary layer enhancements of CO2, COS, and CO can provide clues about the seasonal and spatial distribution of plant carbon uptake. By examining this covariation across diverse regions in the eastern US, we uncovered evidence that humid temperate forests in the previously poorly constrained southern US continue to photosynthesize and absorb CO2 and COS (and emit CO through biogenic volatile organic compound precursor emissions) deeper into the growing season than expected by models and satellite‐constrained estimates. Our results imply that southern US forests have stronger climate sensitivities than currently accounted for in models. Key Points: Atmospheric Carbon Transport‐America airborne flask observations of CO2, carbonyl sulfide, and carbon monoxide (CO) contains information about photosynthetic carbon uptake Boundary layer enhancements of CO2 and CO show significant anti‐correlation in summer across eastern US Comparison to model and data constrained simulations suggest higher than expected photosynthetic carbon uptake in southern evergreen forests