Ice core records of methanesulfonic acid (MSA) from three sites around the WeddellSea are investigated for their potential as sea ice proxies. It is found that the amount ofMSA reaching the ice core sites decreases following years of increased winter sea icein the Weddell Sea; opposite to the expected relationship if MSA is to be used as a sea iceproxy. It is also shown that this negative MSA-sea ice relationship cannot be explained bythe influence that the extensive summer ice pack in the Weddell Sea has on MSAproduction area and transport distance. A historical record of sea ice from the northernWeddell Sea shows that the negative relationship between MSA and winter sea ice existsover interannual (7-year period) and multidecadal (20-year period) timescales.National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR) reanalysis data suggest that this negative relationship is most likely due tovariations in the strength of cold offshore wind anomalies traveling across the WeddellSea, which act to synergistically increase sea ice extent (SIE) while decreasing MSAdelivery to the ice core sites. Hence our findings show that in some locations atmospherictransport strength, rather than sea ice conditions, is the dominant factor that determines theMSA signal preserved in near-coastal ice cores. A cautious approach is thus requiredin using ice core MSA for reconstructing past sea ice conditions, including the need fornetworks of ice core records and multiproxy studies to assess the significance of past MSAchanges at different locations around Antarctica.