Active chlorophyll-a fluorescence was measured during five summer research cruises (2008 – 2016), spanning the Atlantic sector of the Southern Ocean. This unique data set provides information for assessing zonal, inter-annual and intra-seasonal variability (early versus late summer) of photosynthetic efficiency (F_v/F_m). The zonal variability of F_v/F_m showed a typical latitudinal decline from a maximum in the Polar Frontal Zone (PFZ) (0.24±0.03) to a minimum in the Southern Antarctic Circumpolar Current Zone (SACCZ) (0.18±0.07). The inter-annual variability in F_v/F_m (between each cruise) was the highest in the SACCZ, while the Antarctic Zone (AZ) exhibited low inter-annual variability. Intra-seasonal variability between the zones was limited to a significantly higher mean F_v/F_m in the PFZ and AZ in early summer compared to late summer. Intra-seasonal variability between the cruises was, however, inconsistent as higher mean F_v/F_m in early summer were seen during some years as opposed to others. Ancillary physical and biogeochemical parameters were also assessed to investigate potential direct and indirect drivers of co-variability with F_v/F_m through a series of statistical t-tests, where significant differences in F_v/F_m were used as focus points to interrogate the plausibility of co-variance. Inter-zonal variability of surface seawater temperature (SST) and Silicate:Phosphate (Si:P) ratios were highlighted as co-varying with F_v/F_m in all zones, whilst community structure played an indirect role in some instances. Similarly, inter-annual variability in F_v/F_m co-varied with SST, Nitrate:Phosphate (N:P) and Si:P ratios in the PFZ, AZ and SACCZ, while community structure influenced inter-annual variability in the PFZ and SACCZ. Intra-seasonal variability in F_v/F_m was linked to all the ancillary parameters, except community structure in the AZ, whilst different ancillary parameters dominated differences during each of the cruises. These results were further scrutinized with a Principal Component Analysis for a subset of co-located data points, where N:P and Si:P ratios emerged as the principal indirect drivers of F_v/F_m variability. This study highlights the scope for using F_v/F_m to reflect the net response of phytoplankton photophysiology to environmental adjustments and accentuates the complex interplay of different physical and biogeochemical parameters that act simultaneously and oftentimes antagonistically, influencing inter-zonal, inter-annual and intra-seasonal variability of F_v/F_m.