Paleomagnetism and biostratigraphy of sediments from Southern Ocean ODP Site 744 (southern Kerguelen Plateau): Implications for early-to-middle Miocene climate in Antarctica

New paleomagnetic results from lower-to-middle Miocene samples from Ocean Drilling Program (ODP) Holes 744A and 744B, cored during ODP Leg 119 on the southern Kerguelen Plateau (Indian Ocean sector; Southern Ocean), provide a chronostratigraphic framework for an existing and under-utilized paleoclimate archive during a key period of Antarctic climate and ice sheet evolution. Site 744 is strategically positioned for high-latitude paleoceanographic and paleoclimatic studies because it lies within the southern domain of the Antarctic Circumpolar Current (ACC) and in proximity to the large and active Lambert Glacier-Amery Ice Shelf drainage system of the East Antarctic Ice Sheet. Magnetostratigraphic results were reported previously for this site, but technical difficulties and limited sampling prevented confident correlation of the magnetic polarity record with the geomagnetic polarity timescale. Our results, which are constrained by new semi-quantitative analyses of diatom assemblages and radiolarian first and last appearance events that are evaluated within a regional Southern Ocean biostratigraphic dataset through Constrained Optimization (CONOP) model runs, permit significant refinement of previous age models for the lower-to-middle Miocene sequence recovered at Site 744 (spanning the interval from ~ 21 to 13.7 Ma). An extended record of sediment accumulation, with average sedimentation rates of ~ 0.7–0.9 cm/kyr, is interrupted by a series of hiatuses in the middle Miocene. These disruptions in sediment supply, or erosional events, could mark a local response of north–south fluctuations in the location and/or strength of the Antarctic Circumpolar Current during transient glacial events within the Mid-Miocene Climate Optimum (MMCO; ~ 17 to 14.45 Ma). With the enhanced age control provided by this study, combined with a refined chronostratigraphy for the underlying upper Eocene to Oligocene strata, Site 744 becomes a good candidate for future high-resolution stable isotope and microfossil paleoecological work, which will further elucidate the late Paleogene and early Neogene paleoenvironmental history of the Southern Ocean