Synergism between elevated p CO 2 and temperature on the Antarctic sea ice diatom Nitzschia lecointei

• Published in: Biogeosciences
• Main Authors: A. Torstensson, M. Hedblom, J. Andersson, M. X. Andersson, A. Wulff
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2013
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Antarctic; The Antarctic; Antarc*; Ocean acidification; Sea ice
• Online Access: https://doi.org/10.5194/bg-10-6391-2013; https://doaj.org/article/41f7d88908d844e79699979bb6b90303

Polar oceans are particularly susceptible to ocean acidification and warming. Diatoms play a significant role in sea ice biogeochemistry and provide an important food source to grazers in ice-covered oceans, especially during early spring. However, the ecophysiology of ice-living organisms has received little attention in terms of ocean acidification. In this study, the synergism between temperature and partial pressure of CO 2 ( p CO 2 ) was investigated in relationship to the optimal growth temperature of the Antarctic sea ice diatom Nitzschia lecointei . Diatoms were kept in cultures at controlled levels of p CO 2 (∼390 and ∼960 μatm) and temperature (−1.8 and 2.5 °C) for 14 days. Synergism between temperature and p CO 2 was detected in growth rate and acyl lipid fatty acid (FA) content. Optimal growth rate was observed around 5 °C in a separate experiment. Carbon enrichment only promoted (6%) growth rate closer to the optimal growth, but not at the control temperature (−1.8 °C). At −1.8 °C and at ∼960 μatm p CO 2 , the total FA content was reduced relative to the ∼390 μatm treatment, although no difference between p CO 2 treatments was observed at 2.5 °C. A large proportion (97%) of the total FAs comprised on average of polyunsaturated fatty acids (PUFA) at −1.8 °C. Cellular PUFA content was reduced at ∼960 relative to ∼390 μatm p CO 2 . Effects of carbon enrichment may be different depending on ocean warming scenario or season, e.g. reduced cellular FA content in response to elevated CO 2 at low temperatures only, reflected as reduced food quality for higher trophic levels. Synergy between warming and acidification may be particularly important in polar areas since a narrow thermal window generally limits cold-water organisms.