Late Paleocene Arctic coastal climate inferred from molluscan stable and radiogenic isotope ratios

Characterizing polar climates during past warm intervals is important for understanding ‘greenhouse’ climate dynamics because high-latitude surface temperatures and precipitation patterns are extremely sensitive to global climatic conditions. Model-data comparisons of high-latitude climates during past warm intervals (Cretaceous–Eocene, Pliocene) are currently at odds. Specifically, simulations of past warm climates produce polar regions characterized by sub-freezing temperatures and significant seasonality, whereas limited fossil proxy data indicate higher mean annual temperatures and low seasonality (i.e. an equable climate). We have constructed a data set to infer northern hemisphere polar marine temperatures during the late Paleocene. Seasonal and mean annual temperature and the oxygen isotopic composition of precipitation are reconstructed for an Arctic coastal setting during the Thanetian (57–58 Ma) using fossil shell stable isotope profiles. We estimate that coastal water temperatures varied between 10 and 15°C during the seasons of growth, presumably spring, summer and fall. These findings support paleontological evidence, implying Northern Hemisphere polar climates were seasonally warm during the late Paleocene. In addition, estuarine fossil oxygen isotope profiles show periodic excursions to low values (as low as −19‰ VPDB), which indicate seasonal pulses of isotopically-depleted freshwater.