Synergism between elevated <i>p</i>CO₂ and temperature on the Antarctic sea ice diatom <i>Nitzschia lecointei</i>

• Main Authors: A. Torstensson, M. Hedblom, J. Andersson, M. X. Andersson, A. Wulff
• Format: Article
• Language: English
• Published: Copernicus Publications 2013-10-01
• Series: Biogeosciences
• Online Access: http://www.biogeosciences.net/10/6391/2013/bg-10-6391-2013.pdf

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 CO₂ (<i>p</i>CO₂) was investigated in relationship to the optimal growth temperature of the Antarctic sea ice diatom <i>Nitzschia lecointei</i>. Diatoms were kept in cultures at controlled levels of <i>p</i>CO₂ (&sim;390 and &sim;960 μatm) and temperature (−1.8 and 2.5 °C) for 14 days. Synergism between temperature and <i>p</i>CO₂ 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 &sim;960 μatm <i>p</i>CO₂, the total FA content was reduced relative to the &sim;390 μatm treatment, although no difference between <i>p</i>CO₂ 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 &sim;960 relative to &sim;390 μatm <i>p</i>CO₂. Effects of carbon enrichment may be different depending on ocean warming scenario or season, e.g. reduced cellular FA content in response to elevated CO₂ 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.