Diatoms in Antarctic ice cores: Some implications for the glacial history of Antarctica

The presence of reworked Pliocene and older marine microfossils in glacial tills of the Sirius Group suggests that these sediments were emplaced during the Pliocene or later by glaciers riding up the eastern (East Antarctic) slope of the Transantarctic Mountains. This interpretation implies that there was considerable fluctuation in the size of the East Antarctic ice sheet as recently as ca. 3 Ma. Here we test an alternate scenario (eolian emplacement of the Pliocene microfossils) by comparing diatoms in the Sirius Group with diatoms in Holocene and last glacial maximum ice from the Dome C core from the central Antarctic Plateau. Since the diatoms in Dome C ice are known to be eolian in origin, we hypothesize that if the Sirius diatoms are also eolian, then the two Antarctic sites (Dome C and the Sirius Group), equally remote from the Southern Ocean, will have the same exotic flora (i.e., windblown diatoms from either a fresh-water or marine source). However, whereas the Dome C diatoms are predominantly fresh water, those of the Sirius are predominantly marine. We conclude from these data that the Sirius and Dome C diatoms each reflect a different mode of emplacement and that the diatoms in the Sirius till were not emplaced via wind transport. This conclusion does not prove that the Pliocene diatoms in the Sirius till record a deglaciation and Pliocene reglaciation of East Antarctica but, rather, it removes an alternate mechanism (eolian transport) raised by those who oppose this scenario.