TREE RINGS AS HIGH LATITUDE PALEOCLIMATE PROXIES

Well-preserved tree rings of mature gymnosperm wood have been found in Late Permian and Middle Triassic peat deposits in the Beardmore Glacier region of Antarctica. This fossil wood is unique in that it represents an environment with no modern analogue, as the trees were growing at polar latitudes during times of global warmth. Tree rings were analyzed using standard dendrochronology and wood anatomy techniques, which provides a more accurate explanation of wood and tree growth than methods utilized in some previous fossil tree ring studies. Ring width averages 1.69-2.3 mm, with maximum thickness of 6.83-9.9 mm, an order of magnitude larger than ring widths produced at high latitudes today. The extensive amount of earlywood and very small amount of latewood in both Permian and Triassic woods (only 1-5 cells) indicates a long growing season with a very rapid transition to seasonal dormancy, probably in response to decreasing light levels. These fossil woods from Antarctica present something of a paradox. Late Permian and Middle Triassic floras from the region vary substantially in floral diversity and these time periods have been reconstructed with different paleoclimates. The wood anatomy, however, does not reflect these differences, and raises important questions about paleoclimatic hypotheses. Tree ring analysis, in conjunction with studies of floral diversity and abundance, is an important potential source of information on climatic conditions in Antarctica at this time.