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Physiology and iron modulate diverse responses of diatoms to a warming Southern Ocean


Climate change-mediated alteration of Southern Ocean primary productivity is projected to have biogeochemical ramifications regionally, and globally due to altered northward nutrient supply1,2. Laboratory manipulation studies that investigated the influence of the main drivers (CO2, light, nutrients, temperature and iron) on Southern Ocean diatoms revealed that temperature and iron exert major controls on growth under year 2100 conditions3,4. However, detailed physiological studies, targeting temperature and iron, are required to improve our mechanistic understanding of future diatom responses. Here, I show that thermal performance curves of bloom-forming polar species are more diverse than previously shown5, with the optimum temperature for growth (Topt) ranging from 5–16 °C (the annual temperature range is −1–8 °C). Furthermore, iron deficiency probably decreases polar diatom Topt and Tmax (the upper bound for growth), as recently revealed for macronutrients and temperate phytoplankton6. Together, this diversity of thermal performance curves and the physiological interplay between iron and temperature may alter the diatom community composition. Topt will be exceeded during 2100 summer low iron/warmer conditions, tipping some species close or beyond Tmax, but giving others a distinct physiological advantage. Future polar conditions will enhance primary productivity2,3,4, but will also probably cause floristic shifts, such that the biogeochemical roles and elemental stoichiometry of dominant diatom species will alter the polar biogeochemistry and northwards nutrient supply.

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Fig. 1: Individual TPCs under iron-replete conditions for five polar species used in this study.
Fig. 2: TPCs obtained under iron-replete and iron-deplete conditions.
Fig. 3: Thermal performance curves overlaid with Southern Ocean temperature observations and projections.

Data availability

Data on the species and strain identification, collection and maintenance are detailed in Supplementary Table 1. Following publication, these data will be made available (that is, open access) through the IMAS and UTAS (see All data collected by IMAS researchers are archived, curated and managed by IMAS, and often supported by related organizations such as the Integrated Marine Observing System, Australian Ocean Data Network and Tasmanian Partnership for Advanced Computing. Our guiding framework is that all data that are not commercial-in-confidence or restricted by legislation should be shared with researchers for analysis and interpretation. IMAS also operates facilities and hosts datasets of national and global interest and for the benefit of the community.


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I am grateful to K. Karsh (CSIRO, Australia) for conducting the phytoplankton laboratory culture assays and maintaining the cultures, R. Corkery (TIA, UTAS, Australia) for curve fitting the TPCs, the laboratory of A. McMinn (IMAS, UTAS, Australia) for isolating the polar species, I. Lima (WHOI, USA) and S. Doney (VIMS, USA) for providing the temperature range from NCAR Community Earth System Model 2, J. Llort and P. Strutton (IMAS) for providing the time-series of temperature and chlorophyll a from the profiling bio-floats, and M. Ellwood (ANU, Australia) for sharing unpublished data on C. neglectus. This work was primarily funded by the Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Australia, and by the Australian Research Council through a Laureate awarded to PWB (FL160100131).

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Correspondence to Philip W. Boyd.

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Boyd, P.W. Physiology and iron modulate diverse responses of diatoms to a warming Southern Ocean. Nature Clim Change 9, 148–152 (2019).

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