Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Diatoms in Lake Duluti: Tracking Environmental Variability in Northern Tanzania during the Past 1000 Years
Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
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 [en]
Paleolimnology, Tanzania, Diatoms, Climate change, Crater lake
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
URN: urn:nbn:se:su:diva-65552ISBN: 978-91-7447-419-0 (print)OAI: oai:DiVA.org:su-65552DiVA: diva2:464164
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
List of papers
1. Climate Change in Southern and East Africa during the Past Millennium and its Implications for Societal Development.
Open this publication in new window or tab >>Climate Change in Southern and East Africa during the Past Millennium and its Implications for Societal Development.
2007 (English)In: The World System and the Earth System: global socioenvironmental change and sustainability since the Neolithic / [ed] Alf Hornborg & Carole Crumley, Walnut Creek, Calif: Left Coast Press Inc., 2007, 121-131 p.Chapter in book (Refereed)
Place, publisher, year, edition, pages
Walnut Creek, Calif: Left Coast Press Inc., 2007
National Category
Natural Sciences
Identifiers
urn:nbn:se:su:diva-16615 (URN)1-59874-100-4 (ISBN)
Available from: 2007-10-07 Created: 2007-10-07 Last updated: 2011-12-13Bibliographically approved
2. Morphology, valve ultrastructure and stratigraphical variability of Discostella taxa in a tropical crater lake, northern Tanzania
Open this publication in new window or tab >>Morphology, valve ultrastructure and stratigraphical variability of Discostella taxa in a tropical crater lake, northern Tanzania
2009 (English)In: Diatom Research, ISSN 0269-249X, Vol. 24, no 2, 341-356 p.Article in journal (Refereed) Published
Abstract [en]

Morphological and ultrastructural variability of Discostella Houk et Klee (Bacillariophyceae) valves from a small crater lake in northern Tanzania have been examined under scanning electron microscope (SEM) and light microscope (LM). Three types of Discostella are described; Discostella woltereckii, as well as a small variety of D. woltereckii denoted Discostella woltereckii var. minor Öberg, Risberg et Stabell and an unidentified species, Discostella sp. The diatom record during the last ~100 years is dominated by D. woltereckii and D. woltereckii var. minor. The lithology and diatom stratigraphy of a 36 cm sediment surface core show a period of low lake level with extensive aquatic vegetation from around AD 1600. Sometime around AD 1900 there is a substantial rise in the lake water level indicated by an increase in euplanktonic Aulacoseira ambigua and facultative planktonic Discostella spp.

Place, publisher, year, edition, pages
Bristol: Biopress Ltd, 2009
Keyword
Discostella, Valve ultrastructure, Tanzania, Lake Duluti, paleolimnology
National Category
Physical Geography
Research subject
Plant Morphology; Physical Geography
Identifiers
urn:nbn:se:su:diva-31885 (URN)000271296500006 ()
Available from: 2009-11-30 Created: 2009-11-30 Last updated: 2011-12-13Bibliographically approved
3. A diatom record of recent environmental change in Lake Duluti, northern Tanzania
Open this publication in new window or tab >>A diatom record of recent environmental change in Lake Duluti, northern Tanzania
Show others...
2012 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 48, no 2, 401-416 p.Article in journal (Refereed) Published
Abstract [en]

Lake Duluti is a small, topographically closed crater lake located on the flanks of Mt Meru, northern Tanzania. Analyses of diatoms in three short sediment cores and four modern samples from Lake Duluti were used to infer past environmental changes. 210Pb and 137Cs activity profiles combined with AMS 14C dates provide the chronological framework. Weak agreement between the 210Pb and 14C records, together with dating uncertainty, precludes construction of precise age models. The modern diatom flora, from plankton and three periphytic habitats, is dominated by Aulacoseira ambigua (Grunow) Simonsen, Gomphonema parvulum (Kützing) Grunow and Nitzschia amphibia Grunow. All three cores display similar stratigraphic succession, but the relative ratio of habitats represented by the diatoms varies substantially between cores. Diatoms indicate that the oldest part of the record is characterized by relatively low lake level and swampy vegetation. In the late nineteenth or early twentieth century there was a rapid lake level rise and the swamp turned into an open-water lake. High lake levels have prevailed since that time.

Keyword
Diatoms, Crater Lake, Tanzania, Lake level change, 210Pb
National Category
Physical Geography
Research subject
Physical Geography; Quaternary Geology
Identifiers
urn:nbn:se:su:diva-65545 (URN)10.1007/s10933-012-9615-4 (DOI)000305959000009 ()
Funder
Sida - Swedish International Development Cooperation Agency, SWE-2005-341
Available from: 2013-01-05 Created: 2011-12-12 Last updated: 2017-09-11Bibliographically approved
4. Environmental variability in northern Tanzania from c. AD 1000 to 1800, as inferred from diatoms and pollen in Lake Duluti
Open this publication in new window or tab >>Environmental variability in northern Tanzania from c. AD 1000 to 1800, as inferred from diatoms and pollen in Lake Duluti
Show others...
(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
Diatoms, Pollen, Crater lake, Tanzania, Palaeolimnology
National Category
Physical Geography
Research subject
Physical Geography; Quarternary Geology
Identifiers
urn:nbn:se:su:diva-65548 (URN)
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2011-12-13Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Öberg, Helena
By organisation
Department of Physical Geography and Quaternary Geology
Physical Geography

Search outside of DiVA

GoogleGoogle Scholar

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 420 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf