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Environmental variability in northern Tanzania from c. AD 1000 to 1800, as inferred from diatoms and pollen in Lake Duluti
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Fossil pollen and diatoms have been analysed in a sediment sequence from a topographically closed crater lake in northern Tanzania(Lake Duluti), with the aim to reconstruct past changes in lake level and vegetation dynamics. The results contribute with a new paleoenvironmental record from equatorial Africacovering the period c. AD 1000 to AD 1800. Overall, the pollen and diatom records generate comparative stories of dry and wet periods. Dry conditions are inferred at c. AD 1040–1470, c. AD 1510–1640 and c. AD 1650–1670 with the lowest lake levels at c. AD 1260–1290 and AD 1600–1640. Wetter conditions occurred c. AD 1640–1650 and c. AD 1670–1790. The chronology is based on combined analyses of 210Pb activity and AMS 14C on bulk sediment, and a Bayesian model was applied to establish the age-depth relationship. The hydroclimatic record fromLakeDuluti shows good correlation with several East African lakes although precise comparison is hampered by dating uncertainties.

Keyword [en]
Diatoms, Pollen, Crater lake, Tanzania, Palaeolimnology
National Category
Physical Geography
Research subject
Physical Geography; Quarternary Geology
Identifiers
URN: urn:nbn:se:su:diva-65548OAI: oai:DiVA.org:su-65548DiVA: diva2:464121
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2011-12-13Bibliographically approved
In thesis
1. Diatoms in Lake Duluti: Tracking Environmental Variability in Northern Tanzania during the Past 1000 Years
Open this publication in new window or tab >>Diatoms in Lake Duluti: Tracking Environmental Variability in Northern Tanzania during the Past 1000 Years
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The tropics are the regions which are least understood climatically and new data on past climate variability is necessary for reliable future modeling of climate change. This thesis contributes with new paleoenvironmental information from a small crater lake in northern Tanzania and provides an additional link between the integrated history of climate, environment and socioeconomic variability in tropical Africa. Pollen and diatom records from three short sediment cores and one piston core have been used to infer variations in past climate and environmental conditions. The chronological framework has been established by 210Pb and 137Cs activity profiles combined with AMS 14C dates on bulk sediment and Bayesian statistics have been used to construct the age-models. Together, the four cores cover approximately the last 1000 years. Modern limnological conditions (temperature, dissolved oxygen, pH and conductivity) and diatom assemblages from plankton, vegetation, stone scrape and near shore sediments have been surveyed to facilitate the paleoenvironmental interpretation. A detailed morphological analysis of Discostella species in Lake Duluti is presented. Frustule morphology of Discostella species have been examined using light microscope (LM) and scanning electron microscope (SEM) and led to the identification of a new variety; Discostella woltereckii v. minor Öberg, Risberg & Stabell. The multi-proxy record from the piston core infers dry conditions c. AD 1040–1470. Between c. AD 1470 and 1510 there are moist conditions with a lake high-stand centered on c. AD 1490. The period c. AD 1510–1640 is dry and between c. AD 1640 and 1790 there are indications of a continuously increase in moisture and higher lake levels, with a brief reversals in the 1660s. The results from the short cores indicate dry conditions from the late 19th century followed by a rapid rise in lake level sometime in the early 20th century. The observed trends show a good correlation with other paleoenvironmental data from East Africa. The results support the general hypothesis of regionally-wide dry conditions in the beginning of the last millennium and an inverse humidity pattern between western equatorial and eastern equatorial sites during the last centuries.

Place, publisher, year, edition, pages
Stockholm: Department of Physical Geography and Quaternary Geology, Stockholm University, 2011. 42 p.
Series
Dissertations from the Department of Physical Geography and Quaternary Geology, ISSN 1653-7211 ; 29
Keyword
Paleolimnology, Tanzania, Diatoms, Climate change, Crater lake
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:su:diva-65552 (URN)978-91-7447-419-0 (ISBN)
Public defence
2012-02-03, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Accepted. Paper 3: Manuscript.Available from: 2012-01-12 Created: 2011-12-12 Last updated: 2011-12-13Bibliographically approved

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