Global Drivers of Phytoplankton Phenology Trends

Guest, Joe K. ORCID: https://orcid.org/0000-0003-4806-3767, Racault, Marie-Fanny ORCID: https://orcid.org/0000-0002-7584-2515 and Le Quéré, Corinne ORCID: https://orcid.org/0000-0003-2319-0452 (2026) Global Drivers of Phytoplankton Phenology Trends. Global Change Biology, 32 (6). ISSN 1354-1013

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Abstract

Phytoplankton are key contributors to global primary production and serve as sensitive indicators of changes in marine ecosystems. Changes in phytoplankton phenology, and in particular the onset, termination, and duration of their growing period, have important implications for higher trophic levels that feed on them. Several local studies have provided evidence linking phenological shifts to climate change. However, global analyses have so far relied on time-series observations of surface chlorophyll covering less than two decades, making it difficult to separate trends from variability and establish the coherence of underlying drivers at the global level. Here we use the OC-CCIv5 satellite-derived observations harmonised across satellite sensors and the NEMO-PlankTOM12 global ocean biogeochemical model to revisit recent trends in phytoplankton phenology and identify their global drivers during the 1998–2020 period. Using statistical analysis to separate and control for covariance among underlying drivers, we show that SST warming trends are clearly associated with earlier initiation, later termination, and longer duration of the phytoplankton growing season. In contrast, changes in MLD, SST variability, and chlorophyll are associated with shifts in initiation and termination in the same direction, such that both boundaries move in parallel, partly cancelling their effect on duration. The PlankTOM12 model successfully reproduces most of the observed patterns in phenology and their association with the underlying drivers, providing evidence of the mechanistic relationships, and helping to ascertain the global significance of the drivers. Our findings suggest that trends towards earlier initiation, later termination, and longer duration of phytoplankton growing periods are likely associated with climate change, and may therefore persist in the near future under continued global warming.

Item Type:	Article
Additional Information:	Data Availability Statement: All data required to reproduce the analysis as well as the phenologymetrics produced by the data are archived at Zenodo: https:// zenodo.org/ recor ds/ 17368092. This dataset contains all environmental and biological fields used in the study, including processed output from thePlankTOM12.2 global marine biogeochemical model and observation-ally derived products, provided on a consistent 1° × 1° global grid for the period 1998–2020. Model output includes chlorophyll-a concentration(TCHL), sea surface temperature (tos), sea surface salinity (sos), and mixed-layer depth (somxl030). Full model description and equations are provided by Buitenhuis et al. (2023), and further details on the model configuration are available in Guest (2023). Physical driver fields are de-rived from the ARMOR3D global ocean reanalysis product, which com-bines satellite and in situ observations through statistical interpolation. The construction of these fields is described by Guinehut et al. (2012) and Mulet et al. (2012). Preprocessing steps applied in this study are documented within the Zenodo archive. Satellite chlorophyll-a data are based on the ESA Ocean Colour Climate Change Initiative (OC-CCI) v5.0 product. Due to data distribution constraints, the raw OC-CCI data must be downloaded separately from the official repository. A fully reproducible processing workflow, including bias correction, spatial aggregation, gap filling, and temporal smoothing, is provided within the Zenodo archive and at the project repository: https://github.com/joe-kguest/global-phytoplankton-phenology. All derived datasets and processing steps necessary to reproduce the results and figures are included in the Zenodo archive and github repository.
Uncontrolled Keywords:	global and planetary change,environmental chemistry,ecology,general environmental science,sdg 13 - climate action,sdg 14 - life below water ,/dk/atira/pure/subjectarea/asjc/2300/2306
Faculty \ School:	Faculty of Science > School of Environmental Sciences University of East Anglia Research Groups/Centres > Theme - ClimateUEA Faculty of Science > Tyndall Centre for Climate Change Research University of East Anglia Research Groups/Centres > Faculty of Science > Research Centres > Tyndall Centre for Climate Change Research
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences Faculty of Science > Research Centres > Centre for Ecology, Evolution and Conservation
Related URLs:	https://www.scopus.com/pages/publication...
Depositing User:	LivePure Connector
Date Deposited:	06 Aug 2026 10:58
Last Modified:	09 Aug 2026 05:35
URI:	https://ueaeprints.uea.ac.uk/id/eprint/104010
DOI:	10.1111/gcb.70955

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