Silicon isotope records from diatoms can be used as a proxy for the relative consumption of dissolved silicic acid (DSi) in surface waters. Silicon isotopes in sponges provide information on the concentration of DSi within the ambient seawater in which the sponges reside. Here we provide deglacial silicon isotope records from both diatoms (d30Si_diat) and sponges (d30Si_sponge) collected in three piston cores from the Southern Ocean. Isolated diatom samples were produced from bulk sediment by mechanical separation and chemical cleaning. Pure diatom samples were digested in 0.1 M NaOH before removal of matrix via cation exchange chromatography. The samples were analysed by MC-ICP-MS at the University of Edinburgh. Sponge spicules were individually picked from sediment and underwent the same analytical procedure as decribed above. We relate the d30Si_diat records to changes in the deep upwelling DSi supply and diatom demand for DSi in the Southern Ocean surface across the deglaciation. We suggest that during the late deglaciation, the supply increased dramatically, leading to a decline in the d30Si_diat in all records. The d30Si_sponge data were used in conjunction with older previously published data to elucidate how a restructing of the deep ocean - which supplies DSi to the Southern Ocean - during the deglaciation, could explain the apparent increase in DSi supply that is recorded in the d30Si_diat data.