Abundant and well-preserved marine macrofossils on Seymour Island, Antarctica, provide a valuable resource to establish paleoenvironmental conditions at high southern latitudes during the warm Paleogene. Stable isotope, minor element, and 87Sr/86Sr compositions have been measured for the aragonite bivalve Cucullaea from the Eocene La Meseta Formation. The 87Sr/86Sr stratigraphy suggests an early to late Eocene age for the La Meseta Formation. Sea surface temperature estimates based on δ18O values range from 14.5¿ to 15.5¿C in the early and middle Eocene to 10.5¿C in the late Eocene. High-resolution sampling along growth structures provides estimates of seasonality in temperature, which decrease considerably up section. To address the relative contribution of temperature and ice volume or salinity to the δ18O record, Sr/Ca was measured and evaluated as a potential independent paleothermometer for Cucullaea.