Proxy development: a new facet of morphological diversity in the marine diatom Eucampia antarctica (Castracane) Mangin

The varied aspect ratios observed in the Antarctic marine diatom Eucampia antarctica are described and quantified. Data are compiled from detailed measurements of the gross morphology of winter stage specimens found in samples of modern marine sediments. Surface sediment samples come from a range of oceanographic settings spanning almost 20° of latitude from north of the Polar Front in the SW Atlantic to close to continental Antarctica in the southern Amundsen Sea. Results are compared with previously recorded morphological data ascribed to the polar and sub-polar varieties of E. antarctica (E. antarctica var recta and E. antarctica var antarctica) and reveal that the aspect ratio of both varieties responds independently of symmetry and colony structure. The discussion considers the likely basis of the observed aspect ratio distribution and whether the morphological diversity offers any potential for use as proxy evidence in Antarctic palaeoceanographic reconstructions. Although it requires further study, valve symmetry offers promising potential as a quantitative proxy for austral summer sea surface temperatures.