Synergism between elevated &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and temperature on the Antarctic sea ice diatom &amp;lt;i&amp;gt;Nitzschia lecointei&amp;lt;/i&amp;gt;

A Torstensson,M X Andersson,M Hedblom,A Wulff,J Andersson

doi:10.5194/bg-10-6391-2013

Abstract

Abstract. 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 (pCO2) 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 pCO2 (∼390 and ∼960 μatm) and temperature (−1.8 and 2.5 °C) for 14 days. Synergism between temperature and pCO2 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 pCO2, the total FA content was reduced relative to the ∼390 μatm treatment, although no difference between pCO2 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 pCO2. 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.

Highlights

High-latitude marine environments are vulnerable to ocean acidification due to the high solubility of CO2 in cold waters (Orr et al, 2005)
3.1 Growth and photosynthesis In Experiment A, an interaction between warming and rising pressure of CO2 (pCO2) was observed for specific growth rate of N. lecointei (p < 0.05; two-factor ANOVA; Fig. 1a)
Growth rate increased (6 %) significantly in ∼ 960 μatm compared to the ∼ 390 μatm pCO2 at 2.5 ◦C (Fig. 1a)

Summary

Introduction

High-latitude marine environments are vulnerable to ocean acidification due to the high solubility of CO2 in cold waters (Orr et al, 2005). The Southern Ocean has a naturally low carbonate saturation state and is believed to be one of the first oceans to become persistently undersaturated with respect to aragonite (Orr et al, 2005; Steinacher et al, 2009). Along with elevated levels of greenhouse gases in the atmosphere, an increase in average sea surface temperature (SST) of 0.74 ◦C has been recorded from year 1906 to 2005 (IPCC, 2007). The extent of sea ice in the Arctic reached a record low as reported in September 2012 (Parkinson and Comiso, 2013)

Methods

Results

Conclusion