2019 Volume 35 Pages 18-27
The marine diatom, Thalassiothrix antarctica, has a circum-Antarctic distribution in the modern ocean, whereas T. longissima prefers cold-water regions in the northern hemisphere. This different distribution has been thought to apply to their fossil record as well. An examination of upper Pliocene to lower Pleistocene sediments from the subpolar North Atlantic, however, has revealed abundant specimens of T. antarctica but none of T. longissima. These specimens of T. antarctica are characterized by morphological heteropolarity: a head-pole with two apical spines and a rimoportula at the end of an areolar area; a foot-pole with no spines and a rimoportula on a hyaline foot apex. Additionally, the specimens have a twisted, sigmoidally curved outline in the middle, a specific characteristic of T. antarctica. The late Pliocene to the early Pleistocene was a transitional period that led to the formation of continental ice sheets in northern high latitudes and onset of pronounced glacial-interglacial cycles. Concomitant oceanographic changes at that time may have resulted in the disappearance of T. antarctica in the northern hemisphere.
