ANTARCTIC FOSSIL WOOD: PROVIDING UNIQUE DATA TO DETERMINE PERMIAN AND TRIASSIC ANTARCTIC ENVIRONMENTS

Paleoclimate reconstructions indicate that though Antarctica was at polar latitudes during the Permian and Triassic, the climate consisted of cold winters and cool summers (Kiel and Shields, 2005). Since there is no modern analog with similar temperature and light regimes, Antarctic fossil plants represent a unique landscape during a time of global warming. Indirect evidence, leaf mats in varved sediments, suggests a deciduous habit for the plants comprising the Permian Glossopteris and the Triassic corystosperm floras. Additionally, in situ forests in Permian and Triassic deposits provide additional information on wood environmental responses. Initial examination of wood tracheid cells demonstrates a growth pattern similar to those of tropical trees with an extensive amount of earlywood and very little latewood, signifying an equitable environment with occasional disturbances producing a small amount of latewood. Since the light and temperature regimes of equatorial and polar regions are markedly different the cause of the formation of latewood cells remains unknown. Analysis of the wood anatomy to determine whether the trees are deciduous, as suggested by leaf mats, or evergreen, as seen in near-polar regions in the Northern Hemisphere today results in the presence of both habits. While these anatomical studies on fossil wood indicates plant responses not comparable to extant woods, high resolution studies using stable isotopes provides support for these data. Carbon isotope patterns within fossil growth rings are highly comparable to extant growth rings, and provide high-resolution data that cannot be observed in the anatomy. Carbon isotope fractionation in Antarctic wood provides evidence that both the evergreen and deciduous habits were present, similar to the results from tree ring analysis. The similar data provided by anatomical and isotope studies indicate that: (1) geochemical inferences of physiology are supported by anatomical evidence, creating a robust interpretive framework, and (2) further studies on Antarctic fossil wood will provide more detail on plant responses to Permian and Triassic environments.