This supporting information document provides ancillary methodological detail pertaining to (1) the carbon content of the diatom species identified using Light Microscopy, (2) the identification of phytoplankton groups using flow cytometry and (3) estimates of urea uptake for the purposes of computing total nitrogen consumption relative to net primary production (NPP). It additionally includes two supplemental figures and two supplemental tables. Supporting Text S1. Carbon content of the

more »

... ied Antarctic diatom species Light Microscopy was used for the identification of the diatom cells to the lowest taxonomic classification possible. Due to unforeseen circumstances, we were unable to the measure the size and carbon content of the individual diatom species. We therefore used the average size (μm) and carbon content (pg C cell -1 ) for the diatom species identified in the study as determined by Leblanc et al. (2012) for high latitude locations (50 -70°S) (Table S1 ). S2. Flow cytometric identification of phytoplankton populations Flow cytometry was used to identify the various phytoplankton populations at all stations sampled. The size-class of each cell was determined based on forward scatter area (FSC-A) relative to the FSC-A of 2.8 µm and 20 µm beads ( Figure S1a ). Once categorised as picoplankton (<2.8 µm), nanoplankton (2.8-20 µm) or microplankton (>20 µm), the cells were further subdivided into six populations based on their Phycoerythrin (PE) fluorescence relative to their chlorophyll-a fluorescence ( Figure S1b ).