Photosynthesis–irradiance responses in the Ross Sea, Antarctica: a meta-analysis

Abstract. A meta-analysis of photosynthesis–irradiance measurements was completed using data from the Ross Sea, Antarctica, using a total of 417 independent measurements. P_m^B, the maximum, chlorophyll-specific, irradiance-saturated rate of photosynthesis, averaged 1.1 ± 0.06 μg C (μg Chl)⁻¹ h⁻¹. Light-limited, chlorophyll-specific photosynthetic rates (α_B) averaged 0.030 ± 0.023 μg C (μg Chl)⁻¹ h⁻¹ (μmol quanta m⁻² s⁻¹)⁻¹. Significant variations in P_m^B and α^B were found as a function of season, with spring maximum photosynthetic rates being 60% greater than those in summer. Similarly, α values were 48% greater in spring. There was no detectable effect of sampling location on the photo-synthetic parameters, and temperature and macronutrient (NO₃) concentrations also did not have an influence. However, irradiance and carbon dioxide concentrations, when altered under controlled conditions, exerted significant influences on photosynthetic parameters. Specifically, reduced irradiance resulted in significantly decreased P_m^B and increased α^B values, and increased CO₂ concentrations resulted in significantly increased P_m^B and α^B values. Comparison of photosynthetic parameters derived at stations where iron concentrations were above and below 0.1 nM indicated that reduced iron levels were associated with significantly increased P_m^B values, confirming the importance of iron within the photosynthetic process. No significant difference was detected between stations dominated by diatoms and those dominated by the haptophyte Phaeocystis antarctica. The meta-analysis confirms the photosynthetic rates predicted from global analyses that are based solely on temperature and irradiance availability, but suggests that, for more accurate predictions of productivity in polar systems, a more detailed model that includes temporal effects of photosynthetic parameters will be required.