Correlation of Early Pliocene diatomite to low amplitude Milankovitch cycles in the ANDRILL AND-1B drill core

In the austral summer of 2006/7 the ANDRILL MIS (ANtarctic geological DRILLing-McMurdo Ice Shelf) project recovered a 1285 m sediment core from beneath the Ross Ice Shelf near Ross Island, Antarctica in a flexural moat associated with volcanic loading. The upper ~ 600 m of this core contain sediments recording 38 glacial/interglacial cycles of Early Pliocene to Pleistocene time, including 13 discrete diatomite units (DUs). The longest of these, DU XI, is ~ 76 m-thick, and has been assigned an Early to Mid-Pliocene age (5–3 Ma). A detailed record of the siliceous microfossil assemblages in DU XI is used in conjunction with geochemical and sedimentological data to subdivide DU XI into four discrete subunits of continuous sedimentation. Within each subunit, changes in diatom assemblages have been correlated with the δ18O record, providing a temporal resolution up to 600 yr, and allowing for the construction of a detailed age model and calculation of associated sediment accumulation rates within DU XI. Results indicate a productivity-dominated sedimentary record with greater proportions of hemipelagic mud accumulating during relatively cool periods. This implies that even during periods of substantial warmth, Milankovitch-paced changes in Antarctic ice volume can be linked to ecological changes recorded in diatom assemblages.