Berthet Sarah

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Berthet
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Sarah
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  • Article
    Decadal trends in the ocean carbon sink
    (National Academy of Sciences, 2019-05-28) DeVries, Timothy ; Le Quere, Corinne ; Andrews, Oliver D. ; Berthet, Sarah ; Hauck, Judith ; Ilyina, Tatiana ; Landschützer, Peter ; Lenton, Andrew ; Lima, Ivan D. ; Nowicki, Michael ; Schwinger, Jorg ; Séférian, Roland
    Measurements show large decadal variability in the rate of CO2 accumulation in the atmosphere that is not driven by CO2 emissions. The decade of the 1990s experienced enhanced carbon accumulation in the atmosphere relative to emissions, while in the 2000s, the atmospheric growth rate slowed, even though emissions grew rapidly. These variations are driven by natural sources and sinks of CO2 due to the ocean and the terrestrial biosphere. In this study, we compare three independent methods for estimating oceanic CO2 uptake and find that the ocean carbon sink could be responsible for up to 40% of the observed decadal variability in atmospheric CO2 accumulation. Data-based estimates of the ocean carbon sink from pCO2 mapping methods and decadal ocean inverse models generally agree on the magnitude and sign of decadal variability in the ocean CO2 sink at both global and regional scales. Simulations with ocean biogeochemical models confirm that climate variability drove the observed decadal trends in ocean CO2 uptake, but also demonstrate that the sensitivity of ocean CO2 uptake to climate variability may be too weak in models. Furthermore, all estimates point toward coherent decadal variability in the oceanic and terrestrial CO2 sinks, and this variability is not well-matched by current global vegetation models. Reconciling these differences will help to constrain the sensitivity of oceanic and terrestrial CO2 uptake to climate variability and lead to improved climate projections and decadal climate predictions.
  • Article
    A synthesis of global coastal ocean greenhouse gas fluxes
    (American Geophysical Union, 2024-01-20) Resplandy, Laure ; Hogikyan, Allison ; Muller, Jens Daniel ; Najjar, Raymond G. ; Bange, Hermann W. ; Bianchi, Daniele ; Weber, Thomas ; Cai, Wei-Jun ; Doney, Scott C. ; Fennel, Katja ; Gehlen, Marion ; Hauck, Judith ; Lacroix, Fabrice ; Landschutzer, Peter ; Le Quere, Corinne ; Roobaert, Alizee ; Schwinger, Jorg ; Berthet, Sarah ; Bopp, Laurent ; Chau, Thi Tuyet Trang ; Dai, Minhan ; Gruber, Nicolas ; Ilyina, Tatiana ; Kock, Annette ; Manizza, Manfredi ; Lachkar, Zouhair ; Laruelle, Goulven G. ; Liao, Enhui ; Lima, Ivan D. ; Nissen, Cara ; Rodenbeck, Christian ; Seferian, Roland ; Toyama, Katsuya ; Tsujino, Hiroyuki ; Regnier, Pierre
    The coastal ocean contributes to regulating atmospheric greenhouse gas concentrations by taking up carbon dioxide (CO2) and releasing nitrous oxide (N2O) and methane (CH4). In this second phase of the Regional Carbon Cycle Assessment and Processes (RECCAP2), we quantify global coastal ocean fluxes of CO2, N2O and CH4 using an ensemble of global gap-filled observation-based products and ocean biogeochemical models. The global coastal ocean is a net sink of CO2 in both observational products and models, but the magnitude of the median net global coastal uptake is ∼60% larger in models (−0.72 vs. −0.44 PgC year−1, 1998–2018, coastal ocean extending to 300 km offshore or 1,000 m isobath with area of 77 million km2). We attribute most of this model-product difference to the seasonality in sea surface CO2 partial pressure at mid- and high-latitudes, where models simulate stronger winter CO2 uptake. The coastal ocean CO2 sink has increased in the past decades but the available time-resolving observation-based products and models show large discrepancies in the magnitude of this increase. The global coastal ocean is a major source of N2O (+0.70 PgCO2-e year−1 in observational product and +0.54 PgCO2-e year−1 in model median) and CH4 (+0.21 PgCO2-e year−1 in observational product), which offsets a substantial proportion of the coastal CO2 uptake in the net radiative balance (30%–60% in CO2-equivalents), highlighting the importance of considering the three greenhouse gases when examining the influence of the coastal ocean on climate.