Müller Jens Daniel

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Last Name
Müller
First Name
Jens Daniel
ORCID
0000-0003-3137-0883

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  • Article
    Assessment of global ocean biogeochemistry models for ocean carbon sink estimates in RECCAP2 and recommendations for future studies
    (American Geophysical Union, 2024-03-14) Terhaar, Jens ; Goris, Nadine ; Muller, Jens D. ; DeVries, Tim ; Gruber, Nicolas ; Hauck, Judith ; Perez, Fiz F. ; Seferian, Roland
    The ocean is a major carbon sink and takes up 25%–30% of the anthropogenically emitted CO2. A state-of-the-art method to quantify this sink are global ocean biogeochemistry models (GOBMs), but their simulated CO2 uptake differs between models and is systematically lower than estimates based on statistical methods using surface ocean pCO2 and interior ocean measurements. Here, we provide an in-depth evaluation of ocean carbon sink estimates from 1980 to 2018 from a GOBM ensemble. As sources of inter-model differences and ensemble-mean biases our study identifies (a) the model setup, such as the length of the spin-up, the starting date of the simulation, and carbon fluxes from rivers and into sediments, (b) the simulated ocean circulation, such as Atlantic Meridional Overturning Circulation and Southern Ocean mode and intermediate water formation, and (c) the simulated oceanic buffer capacity. Our analysis suggests that a late starting date and biases in the ocean circulation cause a too low anthropogenic CO2 uptake across the GOBM ensemble. Surface ocean biogeochemistry biases might also cause simulated anthropogenic fluxes to be too low, but the current setup prevents a robust assessment. For simulations of the ocean carbon sink, we recommend in the short-term to (a) start simulations at a common date before the industrialization and the associated atmospheric CO2 increase, (b) conduct a sufficiently long spin-up such that the GOBMs reach steady-state, and (c) provide key metrics for circulation, biogeochemistry, and the land-ocean interface. In the long-term, we recommend improving the representation of these metrics in the GOBMs.
  • 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.