Assessing Sub-Antarctic Zone primary productivity from fast repetition rate fluorometry

In situ primary productivity (PP) in the Sub-Antarctic Zone (SAZ) and the Polar Frontal Zone (PFZ) south of Australia was estimated using fast repetition rate fluorometry (FRRF). FRRF-derived PP at Process station 3 (P3) southeast of Tasmania (46 degrees S, 153 degrees E) were higher than P1 in the southwest of Tasmania (46 degrees S, 140 degrees E) and P2 in the Polar Frontal Zone (54 degrees S, 146 degrees E). The FRRF-derived PP rates were well correlated with C-14-uptake rates from one-hour incubations (r(2)=0.85, slope= 1.23 +/- 0.05, p < 0.01, n=85) but the relationship between both methods differed vertically and spatially. There was a linear relationship between FRRF-based PP and C-14-based PP under light-limited conditions in deeper waters. Under light-saturated conditions near the surface (0-45 m), the relationship was less clear. This was likely associated with the effects of physiological processes such as cyclic electron flow and the Mehler reaction, which are stimulated at high irradiance. Our results indicate that FRRF can be used to estimate photosynthesis rates in the SAZ and PFZ but to derive an accurate estimation of C-fixation requires a detailed understanding of the physiological properties of the cells and their response to oceanographic parameters under different environmental conditions. (C) 2011 Elsevier Ltd. All rights reserved.