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The Late Neogene to Quaternary periods include several climate and tectonic events that brought the surface ocean circulation system into its modern configuration. Characterizing how surface conditions, namely temperature and salinity gradients, behaved in response to cooling and warming events has implications for understanding past atmospheric and biotic processes and how the Earth system may respond to increased anthropogenic warming. One region that lacks long-term geochemical records is the Tasman Sea, southwest Pacific Ocean. This region is characterized by a major western boundary current and its extensional flow, which creates large temperature gradients within the basin. Prior geochemical analyses indicate this region warmed and cooled in response to tectonic gateway closures. To build on these geochemical data sets and create a transect across the northern Tasman Sea, we use δ18O and δ13C measurements from the mixed-layer planktic foraminifera species Trilobatus sacculifer to reconstruct surface ocean conditions from the Middle Miocene to early Pleistocene (12–2.3 Ma) at International Ocean Discovery Program Site U1506. We find that surface ocean conditions at the site oscillated through time, with some major stepped changes in the isotopic values through the Miocene. Additional geochemical time series developed in the future from more central and southern Tasman Sea sites will aid in understanding the development and behavior of such frontal boundary systems through the Neogene.