Francois William Primeau

· ProfessorVerified

University of California, Irvine · Earth System Science

Active 1994–2026

h-index48

Citations9.8k

Papers19452 last 5y

Funding$2.0M

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About

Professor Francois William Primeau is a researcher at the University of California, Irvine, leading the Primeau Research Group. His work focuses on the complex circulation of the ocean, which involves eddies at various scales and large overturning cells that connect different ocean basins. His research aims to understand how these circulation processes transport heat, carbon, nutrients, and oxygen, which are vital for sustaining marine life and regulating Earth's climate. Primeau's group combines satellite, ship, and drifter observations with numerical ocean models, applying Bayesian methods to estimate the joint physical and biogeochemical state of the ocean. His team develops and applies advanced numerical models, diagnostic methods, and computational techniques to improve the representation of ocean circulation and biogeochemical cycles. Notable contributions include the development of global biogeochemical inverse models for the nitrogen cycle, biological carbon pump, and organic matter ratios, as well as innovations in tracer transport operators and inverse modeling techniques to accelerate model spin-up and improve data constraints.

Research topics

Environmental science
Geology
Chemistry
Climatology
Atmospheric sciences
Oceanography
Ecology
Biology
Geography
Meteorology

Selected publications

Enhanced ocean transport despite reduced radiocarbon ventilation at the Last Glacial Maximum: were the models right all along?
2026-03-14
articleOpen accessSenior author
Globally distributed data from the Last Glacial Maximum (LGM) indicate a significant depletion of radiocarbon in the ocean, equivalent to ~800 14Cyrs. Some interpretations of these data have emphasized a slow-down of the North Atlantic overturning, as well as a reduction or even ‘reversal’ of overturning in the North Pacific. While many model simulations have been able to produce a shoaled and weakened circulation in the Atlantic under glacial conditions, many others (and many of the same) produce a stronger overturning overall and in the Pacific. If the glacial ocean circulation was indeed stronger, despite reduced radiocarbon ventilation, it would constrain the balance of contributions from marine ‘respired’ and ‘disequilibrium’ carbon pools to glacial atmospheric CO2 drawdown. Here we show that global marine radiocarbon fields from the LGM and deglaciation are not consistent with the modern transport when taking into account past air-sea equilibration changes at the sea surface. Rather, they imply a reduced and/or shoaled transport in the North Atlantic (consistent with most interpretations to date), and an enhanced transport throughout the Pacific. Although the latter conflicts with some previous interpretations of LGM North Pacific radiocarbon data, it coheres with several key model simulations in suggesting an overall ‘faster’ glacial mass turnover despite weaker exchange of CO2 between the ocean and atmosphere. This would emphasize the role of the disequilibrium carbon pool (and therefore ocean-atmosphere gas-exchange, influenced by upper ocean mixing, sea ice etc.) in determining the overall ocean’s overall sequestered carbon inventory during the last glacial period.
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Decoupled timescales of organic carbon and phosphorus recycling in the global ocean
Proceedings of the National Academy of Sciences · 2026-02-17 · 1 citations
articleOpen access
The ocean’s biological carbon pump exports atmospheric CO 2 to the deep ocean, where it can remain sequestered for decades to centuries, and attempts to artificially enhance this natural carbon sink by fertilizing portions of the open ocean could help mitigate the impacts of excessive anthropogenic CO 2 emissions. However, differences in the cycling rates of carbon and other nutrients may impact the long-term response to ocean fertilization. In this study, we use a steady-state global biogeochemical inverse model, optimized to match hydrographic observations, to examine how differential production, remineralization, and circulation-driven re-exposure timescales of organic carbon and phosphorus affect long-term carbon sequestration. We partition global organic matter production based on the time required for regenerated carbon and phosphorus to return to the ocean surface. We find that less than 15% of total organic carbon and 31% of total organic phosphorus production remains sequestered in the ocean interior for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>≥</mml:mo> </mml:math> 1 y, with only 3.3% (1.8 Pg C y −1 ) and 8.3% (0.046 Pg P y −1 ), respectively, remaining for a century or longer. The C:P ratio of the sequestration flux declines with increasing residence time, from 255:1 for total production to 98:1 for material sequestered for 100+ years, indicating that carbon is recycled to the surface more rapidly than phosphorus. This decoupling between carbon and phosphorus sequestration timescales could result in a “productivity hangover,” where the slow recovery of surface phosphate leads to a long-term suppression of global productivity, reducing the net removal of atmospheric CO 2 .
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Seasonality in Marine Organic Carbon Export and Sequestration Pathways
Global Biogeochemical Cycles · 2026-01-31
articleOpen accessSenior author
Abstract The ocean's biological carbon pump transports organic carbon from the surface to depth via three main pathways: the gravitational sinking of particles, active transport by vertically migrating zooplankton, and mixing and advection of suspended and dissolved organic carbon. Here, we use a global data‐assimilated ocean biogeochemical model to diagnose the seasonal variability of carbon export and sequestration by these gravitational, migrant, and mixing pumps. The total carbon export and sequestration are 10.2 ± 0.8 PgC yr −1 and 1,339 ± 17 PgC, respectively, similar to previous estimates that did not consider seasonality. However, the seasonality of the export and sequestration pathways is highly variable, especially in the high latitudes. In subpolar regions, the seasonal amplitude of the pumps is ∼40%–60% of the annual mean: export and sequestration by the gravitational and migrant pumps peak in the summer, while the mixing pump strongly opposes this seasonality, reaching a maximum during the winter. The sequestration time of exported carbon is generally higher during winter than summer in the subpolar regions, helping to augment carbon sequestration during the less productive winter months. The gravitational “e‐ratio,” or ratio of gravitational carbon export to net primary production, has a seasonal variability of ∼0.1 at high latitudes, with higher values in the summer compared to winter. Resolving seasonality reduces the inferred geographic variability of the e‐ratio compared with annual‐mean models, demonstrating the importance of seasonal observations and models to understand and quantify the processes regulating carbon export and sequestration.
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Thank You to Our 2025 Peer Reviewers
AGU Advances · 2026-04-01
articleOpen access
Key Points The editors thank the 2025 peer reviewers!
Publisher DOI
Optimizing Global Ocean Circulation with Transient Ocean Tracers
2026-03-14
articleOpen access
We present a data assimilative multi-tracer circulation optimization framework to refine the Ocean Circulation Inverse Model (OCIM) by jointly assimilating radiocarbon, CFCs (chlorofluorocarbons), and SF6 (sulfur hexafluoride). The framework uses a newly compiled global radiocarbon data set that combines dissolved inorganic carbon measurements with coral and mollusk shell records, together with CFC and SF6 observations from GLODAPv2. These tracers provide complementary constraints on ocean ventilation from centennial to decadal timescales. In a steady-state OCIM formulation, mixing and advection parameters are optimized by minimizing a global tracer misfit cost function using gradient information and Bayesian inverse techniques. Joint optimization combines tracers with different temporal sensitivities and improves constraints on large-scale transport pathways and diapycnal mixing compared to single-tracer approaches. The optimized steady-state circulation provides an observationally constrained baseline for studies of ocean heat uptake, carbon storage, and marine biogeochemistry, and offers a flexible framework for multi-tracer data assimilation in climate-relevant ocean modeling.
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Surface Recycling vs Deep Export: Resolving Uncertainties in Biological Carbon Pump Estimates Using Ocean Tracers
2025-03-07
preprintOpen access
The biological carbon pump (BCP) transfers CO₂ from the surface ocean to deep waters and has historically regulated atmospheric CO₂ levels, accounting for around one-third of glacial-interglacial CO₂ fluctuations. Current satellite-based methods for estimating BCP strength rely on empirical relationships between net primary production (NPP) and carbon export ratio. However, these methods contain a critical flaw: they cannot distinguish between organic matter that is quickly recycled near the surface and organic matter that reaches the deep ocean. Using an inverse biogeochemical model, we demonstrate that ~60% of satellite-measured NPP is rapidly recycled in the euphotic zone and never influences deep ocean tracer distributions. This finding has two important implications. First, the true strength of the BCP is better constrained by deep ocean tracer distributions than by satellite measurements - our model shows consistent export rates regardless of which satellite NPP product is used. Second, while deep tracers robustly constrain the mean state of the BCP, they are less useful for capturing temporal variability. We show that combining satellite observations with inverse modeling could help detect interannual variations in BCP strength, though longer observational records of both satellite and hydrographic data will be needed to make these temporal signals statistically significant.
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The sequestration efficiency of the deep ocean
2025-05-05
preprintOpen access
Ocean sediments may provide adequate long-term storage for carbon dioxide removal (CDR), with the abyssal ocean providing extra sequestration. The transit of carbon from seafloor release to ocean surface can take up to millennia, as it occurs through many pathways characterized by long-tailed transit-time distributions (TTDs). Here, we introduce an idealized methodological framework for efficiently computing these TTDs from climate-model archives. We apply this framework to one Earth System Model and estimate the deep ocean sequestration efficiency for the 2030s and 2090s ocean circulations. We find the highest sequestration efficiencies on abyssal plains isolated from the deep branches of the conveyor belt, such as the North Pacific Basins, where less than 10% of water makes contact with the surface after 1000 years. The climate-warming induced slowdown of the 2090s deep ocean circulation extends return times by about 30%, which exceeds internal variability (~20%) estimated from the ensemble of simulations.
Publisher OA PDF DOI
Seasonality in Marine Organic Carbon Export and Sequestration Pathways
2025-06-11
preprintOpen accessSenior author
The ocean’s biological carbon pump transports organic carbon from the surface to depth via three main pathways: the gravitational sinking of particles, active transport by vertically migrating zooplankton, and mixing and advection of suspended and dissolved organic carbon. Here, we use a global data-assimilated ocean biogeochemical model to diagnose the seasonal variability of carbon export and sequestration by these gravitational, migrant, and mixing pumps. The total carbon export and sequestration are 9.8±0.8 PgC yr -1 and 1296±21 PgC, respectively, similar to previous estimates that do not consider seasonality. However, the seasonality of the export and sequestration pathways is highly variable. In subtropical regions the seasonal amplitude of carbon export is ~20-30% of the annual mean: gravitational and migrant pump export peak during winter, while mixing pump export peaks during spring and early summer. Contrastingly, in subpolar regions the seasonal amplitude of the pumps is ~40-60% of the annual mean: export and sequestration by the gravitational and migrant pumps peak in the summer, while the mixing pump strongly opposes this seasonality, reaching a maximum during the winter. The gravitational "e-ratio", or ratio of gravitational carbon export to net primary production, shows strong seasonal variability. The seasonal variability of the gravitational e-ratio is ~0.1 at high latitudes, with higher values in the summer compared to winter. Resolving seasonality reduces the inferred geographic variability of the e-ratio compared to annual-mean models, demonstrating the importance of seasonal observations and models to understand the processes regulating carbon export and sequestration.
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Thank You to Our 2024 Reviewers
AGU Advances · 2025-03-08
articleOpen access
Abstract The editorial team of AGU Advances is grateful for the excellent contributions of our peer reviewers. We rely on their expertise to ensure that the manuscripts submitted to the journal undergo a rigorous, fair, and timely review. Remarkably, during 2024, the journal benefitted from the dedication from 273 reviewers, contributing a total of 338 reviews. These reviewers represented 24 countries. These reviewers provided insights of tremendous and generous value, and they assisted our authors in strengthening the rigor, quality, and presentation of their scholarship. Peer reviewing provides a natural way to engage in continuous learning and professional development. The majority of our reviewers are geoscientists, although we also have interdisciplinary contributions as the scope of Advances covers the extended domain of geosciences, intersecting with economics, communication and computational science, and the social sciences at large. Authors benefit greatly from reviewers' comments and suggestions: already more than 10 years ago, a study reported that most authors (90%) believe that peer review improved the last paper they published (Mulligan et al., 2013, https://doi.org/10.1002/asi.22798 ). Although the research and publishing arena is rapidly changing, peer review is considered the optimal standard for evaluating and selecting quality scientific manuscripts for publication, and therefore is highly deserving of our appreciation. We thank all of our peer reviewers for their selfless service and dedication to the scientific community. Your continuing support to the authors and editorial team of AGU Advances is deeply appreciated.
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AIBECS.jl: A tool for exploring global marine biogeochemical cycles
Zenodo (CERN European Organization for Nuclear Research) · 2025-12-19
otherOpen access
AIBECS v0.14.0 Diff since v0.13.6 Breaking changes Remove some unnecessary deps update downloading functions remove broken Kok tests Closed issues: Change license and wording (#101)
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