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

• Published in: Nature Climate Change
• Main Author: Boyd, PW
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2019
• Subjects: Earth Sciences; Oceanography; Chemical oceanography; Southern Ocean
• Online Access: https://doi.org/10.1038/s41558-018-0389-1; http://ecite.utas.edu.au/151329

Climate change-mediated alteration of Southern Ocean primary productivity is projected to have biogeochemical ramifications regionally, and globally due to altered northward nutrient supply 1 , 2 . Laboratory manipulation studies that investigated the influence of the main drivers (CO 2 , light, nutrients, temperature and iron) on Southern Ocean diatoms revealed that temperature and iron exert major controls on growth under year 2100 conditions 3 , 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 shown 5 , with the optimum temperature for growth ( T opt ) ranging from 516 C (the annual temperature range is −18 C). Furthermore, iron deficiency probably decreases polar diatom T opt and T max (the upper bound for growth), as recently revealed for macronutrients and temperate phytoplankton 6 . Together, this diversity of thermal performance curves and the physiological interplay between iron and temperature may alter the diatom community composition. T opt will be exceeded during 2100 summer low iron/warmer conditions, tipping some species close or beyond T max , but giving others a distinct physiological advantage. Future polar conditions will enhance primary productivity 2 , 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.