The long-term variability of chlorophyll a (Chl-a) was analyzed during a 12-year period (2002–2014) in the Bransfield Strait, Antarctica, to assess the interannual variability of the Chl-a and its main regulating environmental variables. We found that Chl-a was significantly correlated with the El Niño Southern Oscillation (ENSO) phase (r = -0.65), sea surface temperature (SST) (r = 0.70), and wind speed (r = 0.72), and changes in these factors preceded the Chl-a change by 0–4 months. High phytoplankton blooms (indicated by Chl-a levels) tended to coincide with higher SSTs, and lagged with wind speed variation during La Niña periods. This suggests that atmospheric teleconnections with ENSO-related processes, SST, and wind speed could have a direct impact on phytoplankton biomass in the Bransfield Strait in short-term (<4 months) scales. Furthermore, our simple multivariable regression analysis showed the prominent possibility of using the three variables to predict Chl-a in the Bransfield Strait region. Overall, this study will help us to understand how atmospheric and oceanic fluctuations could affect phytoplankton dynamics in the Southern Ocean.