Tropical climate is rapidly changing, but the effects of these changes on the geosphere are unknown, despite a likelihood of climatically-induced changes on weathering and erosion. The lack of long, continuous paleo-records prevents an examination of terrestrial responses to climate change with sufficient detail to answer questions about how systems behaved in the past and may alter in the future. We use high-resolution records of pollen, clay mineralogy, and particle size from a drill core from Lake Malawi, southeast Africa, to examine atmosphere-biosphere-geosphere interactions during the last deglaciation (~ 18-9 ka), a period of dramatic temperature and hydrologic changes. The results demonstrate that climatic controls on Lake Malawi vegetation are critically important to weathering processes and erosion patterns during the deglaciation. At 18 ka, afromontane forests dominated but were progressively replaced by tropical seasonal forest, as summer rainfall increased. Despite indication of decreased rainfall, drought-intolerant forest persisted through the Younger Dryas (YD) resulting from a shorter dry season. Following the YD, an intensified summer monsoon and increased rainfall seasonality were coeval with forest decline and expansion of drought-tolerant miombo woodland. Clay minerals closely track the vegetation record, with high ratios of kaolinite to smectite (K/S) indicating heavy leaching when forest predominates, despite variable rainfall. In the early Holocene, when rainfall and temperature increased (effective moisture remained low), open woodlands expansion resulted in decreased K/S, suggesting a reduction in chemical weathering intensity. Terrigenous sediment mass accumulation rates also increased, suggesting critical linkages among open vegetation and erosion during intervals of enhanced summer rainfall. This study shows a strong, direct influence of vegetation composition on weathering intensity in the tropics. As climate change will likely impact this interplay between the biosphere and geosphere, tropical landscape change could lead to deleterious effects on soil and water quality in regions with little infrastructure for mitigation.
Digital Object Identifier (DOI)
Lake Malawi Drilling Project-Earth System History Program (NSF-EAR-0602404) funded field operations, logistics, and some laboratory analysis. NSF Graduate Research Fellowship (2009078688) provided student salary and tuition and some travel support for laboratory analysis. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Ivory, Sarah J.; McGlue, Michael M.; Ellis, Geoffrey S.; Lézine, Anne-Marie; Cohen, Andrew S.; and Vincens, Annie, "Vegetation Controls on Weathering Intensity During the Last Deglacial Transition in Southeast Africa" (2014). Earth and Environmental Sciences Faculty Publications. 3.
Figure 1 (PNG). Geography, vegetation, and geology of the study site.
journal.pone.0112855.g001.ppt (298 kB)
Figure 1 (PPT). Geography, vegetation, and geology of the study site.
journal.pone.0112855.g001.TIF (2028 kB)
Figure 1 (TIFF). Geography, vegetation, and geology of the study site.
journal.pone.0112855.g002.png (6327 kB)
Figure 2 (PNG). Core MAL05-2A lithostratigraphy within the study interval.
journal.pone.0112855.g002.ppt (304 kB)
Figure 2 (PPT). Core MAL05-2A lithostratigraphy within the study interval.
journal.pone.0112855.g002.TIF (5000 kB)
Figure 2 (TIFF). Core MAL05-2A lithostratigraphy within the study interval.
journal.pone.0112855.g003.png (422 kB)
Figure 3 (PNG). Vegetation and weathering indicators from drill core MAL05-2A.YD, Younger Dryas. H1, Heinrich event 1.
journal.pone.0112855.g003.ppt (103 kB)
Figure 3 (PPT). Vegetation and weathering indicators from drill core MAL05-2A.YD, Younger Dryas. H1, Heinrich event 1.
journal.pone.0112855.g003.TIF (994 kB)
Figure 3 (TIFF). Vegetation and weathering indicators from drill core MAL05-2A.YD, Younger Dryas. H1, Heinrich event 1.
Methods_S1.doc (45 kB)
Materials and methods details of particle size and x-ray diffraction analysis.
Table_S1.xlsx (52 kB)
Pollen counts from core MAL05-2A.
Table_S2.xlsx (12 kB)
Particle size and clay mineralogy from core MAL05-2A.