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Climatic and hydrological instability in semi-arid equatorial eastern Africa during the late Glacial to Holocene transition:  a multiproxy reconstruction of aquatic ecosystem response in northern Tanzania
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
2007 (English)In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, Vol. 248, no 3-4, 440-458 p.Article in journal (Refereed) Published
Abstract [en]

This paper reports new multi-proxy palaeoenvironmental data on the late Glacial-Holocene transition (c. 14.8–9.3 ka) in equatorial East Africa, in the form of microfossil assemblages (chironomids, diatoms and ostracods) recovered from the sediment record of Lake Emakat, Empakaai Crater, northern Tanzania. In the context of available palaeoclimatic and palaeoecological information from the region and previously published fossil pollen and carbon and nitrogen isotopic data for the same sediment sequence, we here reconstruct local lake-system response to regional climatic and hydrological instability during the period of post-glacial warming. The aquatic biological proxy indicators suggest that the water level and chemistry of Lake Emakat evolved, first from a shallow freshwater body at 14.8 ka to a deeper freshwater phase between c.14.4 and 10.3 ka and then to a markedly shallower, alkaline-saline environment after c.10.3 ka. The lake appears to have been deepest between 13.2 and 12.0 ka, at a time of climatic drying when moist montane forest vegetation within the lake's crater catchment was being replaced by open wood-and scrubland. Some palaeohydrological changes reconstructed for Lake Emakat are in phase with lake evolution elsewhere in the region and thus apparently track broad-scale climate changes, but some are not. Collectively these multi-proxy paleolimnological data indicate a complex adjustment of the local aquatic ecosystem to temporal variations both in total annual effective precipitation and its seasonal distribution. The lake's hydrological response was further conditioned by local factors, notably its geological and topographic setting.

Place, publisher, year, edition, pages
Elsevier B.V , 2007. Vol. 248, no 3-4, 440-458 p.
Keyword [en]
Climate change; Crater lake; Chironomids; Diatoms; East Africa; Empakaai; Multi-proxy reconstruction; Ostracods
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:su:diva-24291DOI: 10.1016/j.palaeo.2006.12.014ISI: 000247250200009OAI: diva2:197164
Part of urn:nbn:se:su:diva-6835Available from: 2007-05-10 Created: 2007-05-10 Last updated: 2010-12-21Bibliographically approved
In thesis
1. Past environmental and climate changes in northern Tanzania: Vegetation and lake level variability in Empakaai Crater
Open this publication in new window or tab >>Past environmental and climate changes in northern Tanzania: Vegetation and lake level variability in Empakaai Crater
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents palaeoenvironmental data from equatorial Africa covering two important time intervals; i) the warming period forming the Pleistocene/Holocene transition and ii) the last millennium. The Empakaai Crater, in northern Tanzania contains a lake from where sediment cores, spanning two time-slices 14.8-9.3 ka and 800-2000 AD, have been studied. Palaeoecological and palaeohydrological reconstruction is based on a multitude of proxies from the sediments, representing both catchment environment and the lakes aquatic ecosystem response. Between 14.8 and 10 ka the catchment vegetation and lake hydrology responded to both regional climate changes and local environment, but with different amplitude and frequency, reflecting temporal and spatial lags between the two systems. However, at c 10 ka both lake conditions and catchment vegetation showed drastic changes towards drier conditions. The record covering the last millennium reveals environmental changes related to climate and human activities. The catchment’s vegetation was affected by frequent fires, most probably human induced, while near shore vegetation responded to lake level fluctuation associated with rainfall variability. About 15 km from Empakaai Crater is an extensive abandoned irrigation system, the Engaruka complex, which was in active use between c 1400 AD and 1840 AD. By comparing a number of social and environmental factors potentially influencing the societal development at Engaruka it is shown that wet climate conditions have had positive effects on the societal development but also that dry climate conditions were not always disastrous to the society. The resemblance of the pollen taxa present is strong between the two time slices and pollen representing catchment conditions respond in similar manner in both records. The lake conditions are however very different between the two periods Thus the lake responds to both long and short term changes of variable amplitude, while the catchment vegetation seems to responds to high amplitude, low frequency changes.

Place, publisher, year, edition, pages
Stockholm: Institutionen för naturgeografi och kvartärgeologi, 2007. 102 p.
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 5
palaeoecology, palaeolimnology, physical and societal factors, Holocene, Tanzania, Lake Emakat, Engaruka
National Category
Earth and Related Environmental Sciences
Research subject
Physical Geography
urn:nbn:se:su:diva-6835 (URN)978-91-7155-455-0 (ISBN)
Public defence
2007-06-01, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 8 A, Stockholm, 13:00
Available from: 2007-05-10 Created: 2007-05-10 Last updated: 2010-10-07Bibliographically approved

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