Response of Southern Ocean Phytoplankton Communities to Trace Metal (including Iron) and Light Availability

Susanne Fietz1, Alakendra N Roychoudhury1, Sandy Jane Thomalla2, Thato Nicholas Mtshali2, Raissa Philibert3, Natasha Van Horsten1,2, Jean Christian Loock1 and Ryan Cloete1, (1)Stellenbosch University, Earth Sciences, Stellenbosch, South Africa, (2)CSIR, Southern Ocean Carbon and Climate Observatory, South Africa, (3)University of British Columbia, Coastal Ocean Research Institute, Ocean Wise, Vancouver, BC, Canada
Abstract:
Phytoplankton primary productivity depends on macro- and micronutrient availability and in turn plays a key role in the marine biogeochemical cycles. The role of iron in regulating phytoplankton primary production and thus biogeochemical cycles in the Southern Ocean has been widely recognized; however, it also became obvious that iron is not the sole factor limiting primary production in the Southern Ocean and that light, for instance, might aggravate or relief trace nutrient limitation. We conducted a suite of ship-board incubation experiments in austral summer 2013/14, 2014/15 and winter 2015 to shed light on the complex interplay between trace metal and light limitation. We observed a strong difference in acclimation and photophysiological response depending on the environmental conditions of the in-situ communities prior to the experiment. The differences in acclimation and photophysiological responses resulted in different growth and macronutrient uptake rates. Revisited stations did, however, not always show the same responses. At at least one station we will link the incubation experiments to the in-situ vertical profiles of trace metals, macronutrients and primary productivity.