Abstract
In 2019, one of Indonesia’s most devastating bushfires burned about 3.1 million hectares of forests and peatlands, releasing approximately 708 million tonnes of CO2. The fires were driven by an extreme positive Indian Ocean Dipole (pIOD), which strengthened easterly winds and brought cooler and drier air to the region, creating severe drought conditions. These conditions triggered widespread forest fires across Indonesia. Simultaneously, the same easterly winds displaced warm, nutrient-poor surface waters westward in the eastern equatorial Indian Ocean (EEIO), enhancing upwelling of nutrient-rich deep waters. This process fueled a massive phytoplankton bloom extending over 1000 km. In addition, nutrient deposition from aerosols emitted by the Indonesian fires further enriched the bloom. Together, oceanic upwelling and atmospheric deposition boosted the biomass of large phytoplankton. Satellite estimates suggest that the bloom sequestered approximately 40.19 Tg of carbon, equivalent to 10.1% of the CO2 released by the Indonesian fires, into the deeper ocean. In contrast, air-sea CO2 flux anomalies indicate negligible net atmospheric CO2 uptake, with only 0.05% (0.33 Tg CO2) of the emissions reabsorbed, due to the upwelling-driven dissolved inorganic carbon (DIC)-rich waters. Together, these results highlight a coupled but asymmetric response to climate extremes. The pIOD can simultaneously intensify terrestrial carbon losses through fires, while upwelling enhances the biological pump through blooms. However, the strength of the sequestration was offset by the DIC-rich waters from the upwelling. Understanding this dual impact is crucial for modelling future climate scenarios and assessing the long-term impacts of climate variability on global carbon cycles.
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Data availability
The datasets analysed during the current study are available at the following repositories. https://data.marine.copernicus.eu/product/OCEANCOLOUR_GLO_BGC_L4_MY_009_104/description, https://stateoftheocean.osmc.noaa.gov/sur/ind/dmi.php, https://sites.science.oregonstate.edu/ocean.productivity/carbon2.model.php. The datasets generated and/or analyzed during the current study are not publicly available at the time of submission because they are under temporary embargo pending publication of this article. They are available from the corresponding author on reasonable request and will be deposited in a public repository upon publication.
Code availability
All data analyses were conducted using Python, whereas statistically analysis were performed in R version 4.5.152. Any codes used in the manuscript are available upon request from the corresponding author.
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Acknowledgements
This research was funded by the Higher Institution Centre of Excellence (HICoE) Fund, Ministry of Higher Education Malaysia, Universiti Malaya RU Grant (RU003-2025A), and FIO-UM Joint Center of Marine and Technology Research Fund. Z.Y.K. gratefully acknowledges the HICoE fund for supporting his master’s studies. T.C. would like to acknowledge the support from Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) (No. SML2024SP020). BGC-Argo data were collected and made freely available by the International Argo Program and the national programs that contribute to it (https://argo.ucsd.edu, https://www.ocean-ops.org). The Argo Program is part of the Global Ocean Observing System. The authors would like to thank the following agencies: Copernicus Marine Service (CMEMS), National Aeronautics and Space Administration (NASA), National Oceanic and Atmospheric Administration (NOAA), European Centre for Medium-Range Weather Forecasts (ECMWF), Japan Meteorological Agency (JMA), and Oregon State University (OSU) for making the data freely available.
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W.C. designed research; Z.Y.K. analyzed data; Z.Y.K. and W.C. wrote the paper; J.I., E.S., J. P. K., T.V.S.U.B., Y.F., B. L., T.C., M.F.F.M.N., and A.A.S. contributed data and analysis; all authors reviewed and edited the paper; A.A.S. and W.C. provided primary funding for the research.
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Kang, Z.Y., Cheah, W., Ishizaka, J. et al. Asymmetric carbon response to the 2019 extreme positive Indian Ocean Dipole.
npj Clim Atmos Sci (2026). https://doi.org/10.1038/s41612-026-01402-y
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DOI: https://doi.org/10.1038/s41612-026-01402-y
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