Phytoplankton response in growth, photophysiology and community structure to iron and light in the Polar Frontal Zone and Antarctic waters

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Viljoen, JJ, Philibert, R, Van Horsten, Natasha R, Mtshali, Thato N, Roychoudhury, AN, Thomalla, Sandy J, Fietz, S
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2018
• Subjects: Bioassay; GEOTRACES; Iron fertilization; Pigments; CHEMTAX; Antarctic; Southern Ocean; The Antarctic; Antarc*
• Online Access: http://hdl.handle.net/10204/10996; https://doi.org/10.1016/j.dsr.2018.09.006; https://www.sciencedirect.com/science/article/pii/S0967063718301420?via%3Dihub

Copyright: 2018 Elsevier. Due to copyright restrictions, the attached PDF file only contains the abstract version of the full-text item. For access to the full-text item, please consult the publisher's website. The definitive version of the work is published in Deep-Sea Research Part I: Oceanographic Research Papers, Vol 141, pp. 118-129 Availability of dissolved iron and light are both regulating factors for primary productivity in high (macro) nutrient, low chlorophyll regions of the Southern Ocean. Here, using on-board iron/light incubation experiments conducted in 2015 in the Atlantic sector of the Southern Ocean, we show that irradiance limited significant phytoplankton growth (in chlorophyll-a and particulate organic carbon) north of the Polar Front (46 °S 08 °E), while iron addition resulted in growth stimulation even at low light levels in the Antarctic zone (65 °S 0 °E). The phytoplankton community in the Polar Frontal Zone showed a greater functional diversity than the one in the Antarctic Zone. The community structure changed over the course of the incubations in response to increased iron and light. The observed increase in chlorophyll-a under high light in the Polar Frontal Zone was driven predominantly by an increase in pico-(0.2–2 µm) and large (> 5 µm) nanophytoplankton. Pigment fingerprinting indicated an increase in the contribution of diatoms and Phaeocystis over the course of the incubation. In contrast, in the Antarctic Zone, the increase in chlorophyll-a after iron enrichment was predominantly due to an increase in the contribution of diatoms and large nanophytoplankton. The photochemical efficiency (Fv/Fm) was low at both sites at the beginning of the incubations, but increased upon iron fertilization in both water masses, indicating stress relief. However, the acclimation strategies fundamentally differed between the two communities. The ratio of photoprotective versus light-harvesting pigments increased under high light in the Polar Frontal Zone independent of iron enrichment, ...