The Western Antarctic Peninsula is an exceptionally climate-sensitive area and investigations into its environmental response to recent and past climate changes may support our understanding of the complex interactions in the ice-ocean-atmosphere system. Organic geochemical and micropaleontological analyses of a 210Pb-dated sediment core from the Bransfield Strait (located between the Antarctic Peninsula and the South Shetland Islands) reveal highly variable sea ice conditions over the past 200 years and increased phytoplankton productivity since the 1930s. Concentrations of biomarker lipids (highly branched isoprenoids (IPSO25), phytosterols) and diatom-based sea ice estimates are compared to satellite data and further environmental information derived from Antarctic Peninsula ice cores extending back in time beyond instrumental records. Fluctuations in the sedimentary abundance of the sea ice biomarker IPSO25 (Belt et al., 2016) and sea ice-associated diatom assemblages seem to be linked to changes in atmospheric (ENSO, SAM) and oceanic circulation patterns. Interestingly, both IPSO25- and diatom-based sea ice reconstructions for the spring and winter season, respectively, do not reflect the overall warming trend and sea ice decline observed in the study area over past decades (e.g., Stammerjohn et al., 2008). This observation may highlight the need for an improved understanding and more reasoned interpretations of proxy archives.