The Increasing Impact of Seasonality Biases on Model‐Based Estimates of the Ocean Carbon Sink

Details

• Journal Title:
  Global Biogeochemical Cycles
• Personal Author:
  Arroyo, Mar C. ; Fassbender, Andrea J. ; Rodgers, Keith B.
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; PMEL (Pacific Marine Environmental Laboratory)
• Description:
  Ocean carbon cycle syntheses combine observation-based surface ocean pCO2 products and global ocean biogeochemical models (GOBMs) to estimate air-sea CO2 fluxes. These efforts show that GOBMs underestimate the ocean's anthropogenic CO2 sink compared to observation-based products, though the causes remain uncertain. Observations and models indicate that the seasonal amplitude of surface pCO2 is increasing due to anthropogenic carbon (Cant) accumulation, potentially altering net annual CO2 fluxes. Here, we test the hypothesis that systematic biases in model representations of surface pCO2 seasonality contribute to long-term biases in annual ocean carbon uptake trends. Using simulations from seven GOBMs, we evaluate changes in surface pCO2 seasonal amplitude over 1980–2018, separating contributions from Cant accumulation and climate-state changes. Within each model, seasonal pCO2 amplitude growth is primarily caused by Cant-driven enhancement in pCO2 sensitivity to seasonal thermal and biophysical processes. Across models, differences in Cant-driven pCO2 amplification are closely linked to differences in initial seasonal variability of surface temperature and dissolved inorganic carbon. Models with larger seasonal pCO2 amplitudes in 1980–1984 exhibit proportionally larger Cant-driven growth, widening the across-model disagreement in seasonal pCO2 amplitudes over time. Consequently, growing model disagreement in wintertime sea-air pCO2 disequilibrium causes divergence in cumulative ocean carbon sink estimates. Seasonal wind variability may further modulate CO2 flux differences, but its role could not be directly assessed. These findings demonstrate that systematic seasonal pCO2 biases contribute to diverging annual ocean carbon uptake trends, highlighting the importance of improving seasonal carbon cycle process representations to reduce uncertainty in future climate change projections.
• Source:
  Global Biogeochemical Cycles, 40(3)
• DOI:
  https://doi.org/10.1029/2025GB008713
• ISSN:
  0886-6236 ; 1944-9224
• Format:
  PDF
• Publisher:
  American Geophysical Union (AGU)
• Document Type:
  Journal Article
• License:
  https://creativecommons.org/licenses/by/4.0/
• Rights Information:
  CC BY
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha-512:db636667f90a550c0bf3dcf8544f6be27adc7327d7eadd62aeb7de62151dd4f8b4df4df6ecff857b25f0ca084d43ce68ebc9d5d3576ceea4b1d6d86a2408639f
• Download URL:
  https://repository.library.noaa.gov/view/noaa/73532/noaa_73532_DS1.pdf
• File Type:
  [PDF - 4.75 MB ]