Phytoplankton and iron limitation of photosynthetic efficiency in the Southern Ocean during late summer

Abstract

As part of two USJGOFS cruises, we investigated spatial variability in phytoplankton properties across the strong environmental gradient associated with the Antarctic Polar Frontal Zone during late austral summers of 1997 and 1998. Cell properties, including size and an index of pigment content as well as photosynthetic efficiency (as indicated by relative variable fluorescence), changed dramatically across this frontal region. A general trend toward reduced photosynthetic efficiency south of the Polar Front was correlated with low dissolved iron concentration and is consistent with physiological iron limitation in the phytoplankton. We detected no significant differences in photosynthetic efficiency among different size classes of the dominant pico-to nanophytoplankton, despite a systematic community level shift toward larger sized cells south of the Polar Front. In contrast to other cells, those classified as cryptophyte algae showed relatively high photosynthetic efficiency in low iron waters; however, this group was never found in high abundance. One group, all cells p2 mm, showed an unexpected increase in intracellular pigment content (based on single cell chlorophyll fluorescence measurements) south of the Polar Front where dissolved iron concentration and the cells' relative abundance were low. Overall, these results suggest that group-or size-specific differences in physiological status were not directly regulating community structure in the pico-to nanophytoplankton during the late summer season; other processes, such as differential grazing or sinking losses, must be important.

Bio-optical modelling of primary production in the SW Finnish coastal zone, Baltic Sea: fast repetition rate fluorometry in Case 2 waters

“…The water layer affected by the RLE in our study was the upper 2 to 3 m. In an oceanic environment, the thickness of the RLE layer has been observed to vary from 5 to 10 m (Suggett et al 2001, Sosik & Olson 2002. High K d (685) values from 0.62 to 0.72 m -1 explain the shallower RLE layer in our study.…”

Comparison of different filter types on chlorophyll-a retention and nutrient measurements

“…Hence the chlorophyll(-a) content in algae is influenced by many abiotic factors like light, temperature and nutrients (Van Leeuwe and Stefels, 1998;Marañón et al, 2000;Barlow et al, 2002;Lalli and Parsons, 2002;Malinsky-Rushansky et al, 2002;Sosik and Olson, 2002), we recommend not to increase the probability of a wrong measurement by using an unsuitable filter. We were able to show how various the results of different filter types with same pore sizes can be.…”

Interpretation of fast repetition rate (FRR) fluorescence: signatures of phytoplankton community structure versus physiological state

“…One of the fundamental applications of FRR fluorometry has been to examine the nutrient status of phytoplankton communities , Behrenfeld et al 1996, Olson et al 2000, Boyd & Abraham 2001, Sosik & Olson 2002, Moore et al 2006a, 2008. The majority of these studies have focused on low-Fe, high-nutrient, low-chlorophyll a (HNLC) ocean regions.…”

“…Until the development of FRR, active fluorometry typically only measured F v /F m and so had to rely on independent measurements of light absorption to calculate PET rates in absolute terms (Kromkamp & Forster 2003, Johnsen & Sakshaug 2007. The measurements of σ PSII also proved to be an additional advancement for active fluorometry, since this variable also appears to characterise an (eco-) physiological response to changes in environmental conditions (Greene et al 1994, Behrenfeld et al 1996, Behrenfeld & Kolber 1999, Sosik & Olson 2002, Moore et al 2006a,b, 2007, Six et al 2008.…”