ALBERT

Description: Microfossil assemblages in Pliocene sediments from DSDP Site 274 (68°59.81'S, 173°2564'E) provide data on the age of the sediments and suggest the presence of Nothofagus (southern beach) in Antarctica during the Pliocene. A suite of 17 samples was collected in an interval from Samples 28-274-6R-1, 83-87 cm to 28-274-11R-4, 73-77 cm (48.33-100.29 mbsf). Biostratigraphic study of the abundant diatom assemblages combined with published radiolarian data indicates that the sample interval ranges in age from 5.0 to 2.2 Ma, with an apparent unconformity between about 3.8 and 3.2 Ma. Nothofagidites (the genus for fossil pollen referable to Nothofagus) occurs throughout the interval, as well as pollen and spores with known stratigraphic ranges that unequivocally indicate reworking from older rocks. Species of Nothofagidites recovered include N. asperus, N. brachyspinulosus, N. flemingii, N. senectus, and N. sp. cf. N. lachlaniae; the latter form is previously known from the Sirius Group in the Transantarctic Mountains. Abundant palynomorphs were recovered in only three of the samples from Site 274 (Samples 28-274-9R-2,15-19 cm; 28-274-9R-2,48-52 cm; and 28-274-9R-2,65-69 cm). Based on the diatom and radiolarian biostratigraphic data, the ages of these samples range from 3.00 to 3.01 Ma. The relative abundance of N. sp. cf. N. lachlaniae in the three samples is an order of magnitude higher than relative abundances for the other species of Nothofagidites in the same samples. The signiticantly higher relative abundance of N. sp. cf. N. luchlaniae suggests that this pollen was derived from trees of Nothofugus that were living in Antarctica during the mid Pliocene. Diatom assemblages from these three samples indicate that sediments in this interval were rapidly deposited as biogenic oozes in an open-ocean setting relatively free of sea ice, thus decreasing the possibility of reworking from a single source bed rich in N. sp. cf. N. lachlaniae. Clearly, more detailed work in additional well-dated cores from around Antarctica is needed before a clear picture of the Neogene history of Antarctic terrestrial vegetation emerges.

Description: Disturbance plays a major role in shaping and maintaining many of the Earth'sterrestrial ecosystems. In fact, many ecosystems depend on fire for theirvery existence. Global Change is expected to result in changed distributionof current ecosystems, changed composition of those ecosystems, and increation of new ecosystems. The International Geosphere Biosphere Program(IGBP), through the Core Projects Biospheric Aspects of the HydrologicalCycle, International Global Atmospheric Chemistry, Global Change andTerrestrial Ecosystems and International Global Atmospheric Chemistry,Biomass Burning Working Group, recognized that disturbances need to beincluded in the modeling efforts of each project. Disturbance from fire, landuse and other factors may be as important as climate change in shaping futurelandscapes (Weber and Flannigan 1998). Three main themes were recognized:impact of disturbance on carbon pools, vegetation change, and feedbacks to theatmosphere. In June 1998, a workshop was held in Potsdam, Germany to developa strategy to introduce disturbance into dynamic global vegetation models.This strategy was based on the fact that vegetation burning influencesatmospheric chemistry, that feedbacks of energy, water and trace gases tothe atmosphere are influenced by vegetation, and that changes in thecomposition of ecosystems have direct impact on the carbon pool, onbiodiversity, and on health and productivity of the land. Disturbanceincludes fire, insect, disease, drought and flooding, land conversion,land use, air pollution, and introduction of exotic species. While it willbe necessary to ultimately include all disturbances, the Potsdam workshoplimited itself to fire. This strategy is based on the fact that there areno process driven models for all disturbances, and that fire has a numberof reliable models with which to begin the process of introducing disturbanceinto dynamic global vegetation models. While this workshop limited itself tofire, a great deal of consideration was given to the fact that the modelshell must be able to include other disturbances in the future. As a result,the strategy was to focus on a hazard function which would lead to effectsof disturbance. The hazard function is basically a probability statement ofrisk of effects. This approach seems equally valid for all forms ofdisturbance.