2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 40-36
Presentation Time: 9:00 AM-5:30 PM


BENSON, Josephine, Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, IVORY, Sarah, Department of Geosciences, University of Arizona, Department of Geosciences, University of Arizona, Tucson, AZ 85705 and RUSSELL, James M., Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, josephine_benson@brown.edu

Lowland vegetation in tropical Africa, such as forests and deciduous woodlands, house high levels of biodiversity and many unique endemic species. Climatic and land-use changes are shrinking these areas, threatening many species of plants and animals. Pollen records from lacustrine sediment cores can be used to understand past vegetation change in these forests and possibly understand how they will continue to change in the future.

In equatorial East Africa, previous studies have shown a gradual trend towards aridity from the mid-Holocene to today. This drying trend has had a marked influence on ecosystems in the region. However, there is also evidence of human occupation and the possibility that land-use change may also have played an important role in the development of the modern landscape. In this study we did pollen analysis of a 6000 yr sediment core record from Lake Edward, Uganda, and compared with paleoclimate data from the same basin. Preliminary results show dramatic changes in forests present in the basin, consistent with increasing aridification of the region towards modern day. Before ~5000yrs BP, we observe large proportions of rainforest trees, such as Celtis africana and Olea spp. This is in agreement with sedimentological analysis showing higher lake levels and wetter conditions in the basin from ~9000 to 5200 yrs BP. There is a distinct opening of the vegetation as we move towards modern day with, younger samples contain more grasses, sedges, and Euphorbia. This relates to a noted drying beginning ~5200 yrs BP and continuing through modern day, with the lake lowstand at ~2000 yrs BP, as evidenced by calcite precipitation. Our work suggests that large scale vegetation changes are related to regional drying, but comparing palynological records of vegetation and isotopic records of regional hydrology may indicate human alterations to the landscape over this period.