Neutral Tropical African CO2 Exchange Estimated From Aircraft and Satellite Observations

Authors

Benjamin Gaubert, National Center for Atmospheric Research
Britton B. Stephens, National Center for Atmospheric Research
David F. Baker, Colorado State University
Sourish Basu, NASA Goddard Space Flight Center
Michael Bertolacci, University of Wollongong
Kevin W. Bowman, California Institute of Technology
Rebecca Buchholz, National Center for Atmospheric Research
Abhishek Chatterjee, California Institute of Technology
Frédéric Chevallier, Commissariat a l'Energie Atomique et aux Energies Alternatives
Róisín Commane, Lamont-Doherty Earth Observatory
Noel Cressie, University of Wollongong
Feng Deng, University of Toronto
Nicole Jacobs, Colorado State University
Matthew S. Johnson, NASA Ames Research Center
Shamil S. Maksyutov, National Institute for Environmental Studies of Japan
Kathryn McKain, University of Colorado Boulder
Junjie Liu, California Institute of Technology
Zhiqiang Liu, Institute of Atmospheric Physics Chinese Academy of Sciences
Eric Morgan, Scripps Institution of Oceanography
Chris O’Dell, Colorado State University
Sajeev Philip, Indian Institute of Technology Delhi
Eric Ray, National Oceanic and Atmospheric Administration
David Schimel, California Institute of Technology
Andrew Schuh, Colorado State University
Thomas E. Taylor, Colorado State University
Brad Weir, Universities Space Research Association
Dave van Wees, BeZero Carbon Ltd
Steven C. Wofsy, Harvard John A. Paulson School of Engineering and Applied Sciences
Andrew Zammit-Mangion, University of Wollongong

Publication Name

Global Biogeochemical Cycles

Abstract

Tropical lands play an important role in the global carbon cycle yet their contribution remains uncertain owing to sparse observations. Satellite observations of atmospheric carbon dioxide (CO2) have greatly increased spatial coverage over tropical regions, providing the potential for improved estimates of terrestrial fluxes. Despite this advancement, the spread among satellite-based and in-situ atmospheric CO2 flux inversions over northern tropical Africa (NTA), spanning 0–24°N, remains large. Satellite-based estimates of an annual source of 0.8–1.45 PgC yr−1 challenge our understanding of tropical and global carbon cycling. Here, we compare posterior mole fractions from the suite of inversions participating in the Orbiting Carbon Observatory 2 (OCO-2) Version 10 Model Intercomparison Project (v10 MIP) with independent in-situ airborne observations made over the tropical Atlantic Ocean by the National Aeronautics and Space Administration (NASA) Atmospheric Tomography (ATom) mission during four seasons. We develop emergent constraints on tropical African CO2 fluxes using flux-concentration relationships defined by the model suite. We find an annual flux of 0.14 ± 0.39 PgC yr−1 (mean and standard deviation) for NTA, 2016–2018. The satellite-based flux bias suggests a potential positive concentration bias in OCO-2 B10 and earlier version retrievals over land in NTA during the dry season. Nevertheless, the OCO-2 observations provide improved flux estimates relative to the in situ observing network at other times of year, indicating stronger uptake in NTA during the wet season than the in-situ inversion estimates.

Open Access Status

This publication is not available as open access

Volume

37

Issue

12

Article Number

e2023GB007804

Funding Number

80NSSC18K1132

Funding Sponsor

National Science Foundation