http://journals.cambridge.org Downloaded: 11 Dec 2013 IP address: 174.129.245.72 New Zealand sub-Antarctic phytoliths and their potential for past vegetation reconstruction VANESSA C. THORN Earth Sciences, School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK v.thorn@see.leeds.ac.uk Abstract: Phytoliths in the modern vegetation of sub-Antarctic Campbell Island are compared with those in the soil beneath to assess the accuracy of vegetation reconstructions made from dispersed phytolith assemblages. The soil phytoliths alone suggest the source vegetation is a grassland association for all study sites, which reflects none of the herb, fern or shrub component of the overlying vegetation. It is concluded that at this locality dispersed phytoliths on their own are not reliable indicators of source vegetation and should be used with caution in this context for palaeoecological studies. However, they can provide useful botanical information where all other organic material is absent. With further research, based on the abundance and diversity of Poaceae phytoliths observed in this and other studies, dispersed phytoliths from the fossil record have the potential to contribute significantly to the understanding of grassland ecosystem development in the geological past. Received 4 December 2006, accepted 26 March 2007 Key words: Antarctica, Campbell Island, palaeoecology, phytoliths Introduction The study of southern high latitude vegetation contributes to the search for modern analogues for the sparse Cenozoic palaeobotanical record around the Antarctic margin (e.g. Edwards 1921, Cookson 1947, Askin 2000, Raine & Askin 2001, Thorn 2001, Ashworth & Cantrill 2004, Truswell et al. 2005, MacPhail & Cantrill 2006, Prebble et al. 2006). Understanding these fossil deposits has been an important pursuit for decades, in conjunction with interest in the development of the Antarctic Ice Sheet, its processes and response to global climate change (e.g. Francis 1999). Established ‘nearest modern relative’ or ‘nearest modern equivalent’ techniques compare the composition of the fossil flora with that of similar modern day vegetation associations which, by extrapolation, allow assumptions to be made about the past vegetation stature and environmental conditions of growth. The fern-bush communities of the southern oceanic islands, e.g. the New Zealand sub-Antarctic islands, have been suggested as modern analogues for late Eocene floras (e.g. the Cytadela and Petrified Forest Creek floras of King George Island) (Birkenmajer & Zastawniak 1989, Askin 1992, Birkenmajer 1997). These floras were growing in cool, humid climates in the Antarctic Peninsula region as climate deteriorated before the permanent establishment of a significant East Antarctic Ice Sheet. This investigation contributes to the analogue reference collection of phytoliths from the high southern latitudes first described in Thorn (2004) by studying phytoliths in the modern plants and soil of sub-Antarctic Campbell Island, south of New Zealand. This investigation also provides a case study for a preliminary assessment of the likely accuracy of reconstructing past vegetation using dispersed phytoliths alone. Phytoliths are microscopic particles formed from the solidification of biogenic silica (biosilica) gel within and between the cells of many plants. They have a varied morphology depending upon the plant species and host cell type, can be isolated idioblastic forms or skeletal structures, and are commonly between 5 and 200 lm in size. Due to the multiplicity and redundancy of phytolith forms (Rovner 1971) the taxonomic affinity of individual phytoliths, when separated from their source plant, is complex. However, ongoing studies on phytolith production in modern plants can identify the parent plant to generic and sometimes species level (e.g. Piperno & Pearsall 1998, Carnelli et al. 2004). Due to their siliceous composition, they can survive in oxidizing conditions and commonly provide an in situ record of vegetation composition. Phytoliths therefore have the potential to both complement and supplement plant macrofossil and terrestrial palynology records and are becoming increasingly used in palaeoecological studies. Campbell Island is located c. 600 km SSE of South Island, New Zealand, and comprises the remains of a dissected Pliocene volcanic cone (Fig. 1; Oliver et al. 1950, Beggs 1978, Michaux & Leschen 2005). The majority of the island is covered in vegetation and peat soils (blanket peats average up to four metres thick), which began to accumulate after the last glaciation c. 13 000 BP (Fig. 2; Campbell 1980, McGlone et al. 1997, McGlone 2002). Prevailing winds are from the west to west–north-west and the climate is generally cloudy, moist and cool with minimal sunshine. 21 Antarctic Science 20 (1), 21–32 (2008) & Antarctic Science Ltd 2008 Printed in the UK DOI: 10.1017/S0954102007000727