Abstract
Extreme temperature events are becoming widespread with global warming, impacting phytoplankton, the foundation of the marine ecosystem. In the Southern Ocean, these impacts are not well understood, despite the key role of phytoplankton in global carbon cycling and climate. Here, we use 26 years of satellite observations and confirm previously identified impacts of marine heatwaves (MHWs) on phytoplankton in the Southern Ocean, while systematically comparing the opposite impacts of marine cold spells (MCSs). MHWs decrease phytoplankton chlorophyll-a (Chl-a) in subtropical regions (−21.11%) but less so in polar regions, with Chl-a even increasing in the Sub-Antarctic Zone ( + 22.26%). MCSs exhibit opposite patterns, enhancing Chl-a in subtropical regions ( + 32.37%) while inhibiting it in southern regions (−21.19%). These regional differences in Chl-a anomalies are mediated by distinct responses in phytoplankton size composition to MHWs and MCSs. As extreme events intensify with global warming, Southern Ocean’s phytoplankton will be disrupted, with implications for global biogeochemical cycles. These findings highlight the importance of simultaneously considering both MHWs and MCSs when assessing the ecological impacts of climate extremes.
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Data availability
The daily SST-CCI (version 3.0) and SIC data are provided by ESA from their website: https://doi.org/10.5285/4a9654136a7148e39b7feb56f8bb02d2. The daily Rrs-CCI and kd (version 6.0) data are provided by ESA from their website: https://rsg.pml.ac.uk/thredds/catalog-cci.html. The PAR data are provided by GlobColour from their website: https://hermes.acri.fr/index.php?class=archive. The nitrate data provided by CMEMS from their website: https://doi.org/10.48670/moi-00019. The MLD (GLORYS12V1) data provided by CMEMS from their website: https://doi.org/10.48670/moi-00021. The HPLC data provided by PANGAEA from their website: https://doi.org/10.1594/PANGAEA.938703. The HPLC data provided by ADON from their website: https://portal.aodn.org.au/search. The data used to generate the figures presented in this study are available via figshare at https://doi.org/10.6084/m9.figshare.3021702187.
Code availability
The analyses were performed using MATLAB and Python; the main code used in this study is available at https://doi.org/10.5281/zenodo.1722329288, with BGC-Argo data processing based on code from https://github.com/NOAA-PMEL/OneArgo-Mat and MHWs/MCSs detection using code from https://github.com/ZijieZhaoMMHW/m_m hw1.0.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (NSFC). Specifically, Z.J. received support from NSFC Grants #42176173 and 42476168, while D.L. was supported by NSFC Grant #42406172. Additional funding was provided by the Guangdong Basic and Applied Basic Research Foundation (Grant # 2023A1515110837) awarded to D.L., and by the Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) (Grants #SML2024SP023 and SML2024SP029), and the Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai) (Grant #311020004), awarded to Z.J. R.J.W.B. is supported by a UKRI Future Leader Fellowship (MR/V022792/1) and the European Space Agency’s project Tipping points and abrupt changes In the Marine Ecosystem (TIME). The author acknowledges the European Space Agency (ESA) for providing daily Sea Surface Temperature (SST), Sea Ice Concentration (SIC), Diffuse Attenuation Coefficient (Kd), and Remote Sensing Reflectance (Rrs) data products through the Ocean Colour Climate Change Initiative (OC-CCI). The author also thanks the Copernicus Marine Environment Monitoring Service (CMEMS) for providing daily model data of Nitrate (NO₃), and Mixed-Layer Depth (MLD). Appreciation is extended to GlobColour for providing Level-3 (L3) daily Photosynthetically Available Radiation (PAR) data. Additionally, the author acknowledges the PANGAEA Data Publisher for Earth & Environmental Science and the Australian Waters Bio-optical Database (AWBD) for providing High-Performance Liquid Chromatography (HPLC) datasets. We further acknowledge the Argo Program, which is part of the Global Ocean Observing System (https://www.seanoe.org/data/00311/42182/), as well as the Southern Ocean Observing System (SOOS) and the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) Project, funded by the National Science Foundation, Division of Polar Programs (NSF PLR-1425989 and OPP-1936222), and supplemented by NASA. The BGC-Argo data were collected and made freely available by the International Argo Program and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org).
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B.Z.M. and D.L. conducted data processing and analysis under Z.J.’s instruction. H.W.B. provided the conceptual framework. H.W.B. and Q. C. contributed data and algorithms. B.Z.M. drafted the initial manuscript, and Z.J. and R.J.W.B. reviewed the paper.
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Bai, Z., Deng, L., Brewin, R.J.W. et al. Extreme temperature events reshuffle the ecological landscape of the Southern Ocean.
Nat Commun (2025). https://doi.org/10.1038/s41467-025-68029-0
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DOI: https://doi.org/10.1038/s41467-025-68029-0
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