@article{StoofLeichsenringJungingerOlakaetal.2011, author = {Stoof-Leichsenring, Kathleen Rosemarie and Junginger, Annett and Olaka, Lydia A. and Tiedemann, Ralph and Trauth, Martin H.}, title = {Environmental variability in Lake Naivasha, Kenya, over the last two centuries}, series = {Journal of paleolimnolog}, volume = {45}, journal = {Journal of paleolimnolog}, number = {3}, publisher = {Springer}, address = {Dordrecht}, issn = {0921-2728}, doi = {10.1007/s10933-011-9502-4}, pages = {353 -- 367}, year = {2011}, abstract = {Lake Naivasha, Kenya, is one of a number of freshwater lakes in the East African Rift System. Since the beginning of the twentieth century, it has experienced greater anthropogenic influence as a result of increasingly intensive farming of coffee, tea, flowers, and other horticultural crops within its catchment. The water-level history of Lake Naivasha over the past 200 years was derived from a combination of instrumental records and sediment data. In this study, we analysed diatoms in a lake sediment core to infer past lacustrine conductivity and total phosphorus concentrations. We also measured total nitrogen and carbon concentrations in the sediments. Core chronology was established by (210)Pb dating and covered a similar to 186-year history of natural (climatic) and human-induced environmental changes. Three stratigraphic zones in the core were identified using diatom assemblages. There was a change from littoral/epiphytic diatoms such as Gomphonema gracile and Cymbella muelleri, which occurred during a prolonged dry period from ca. 1820 to 1896 AD, through a transition period, to the present planktonic Aulacoseira sp. that favors nutrient-rich waters. This marked change in the diatom assemblage was caused by climate change, and later a strong anthropogenic overprint on the lake system. Increases in sediment accumulation rates since 1928, from 0.01 to 0.08 g cm(-2) year(-1) correlate with an increase in diatom-inferred total phosphorus concentrations since the beginning of the twentieth century. The increase in phosphorus accumulation suggests increasing eutrophication of freshwater Lake Naivasha. This study identified two major periods in the lake's history: (1) the period from 1820 to 1950 AD, during which the lake was affected mainly by natural climate variations, and (2) the period since 1950, during which the effects of anthropogenic activity overprinted those of natural climate variation.}, language = {en} } @article{JungingerRollerOlakaetal.2014, author = {Junginger, Annett and Roller, Sybille and Olaka, Lydia A. and Trauth, Martin H.}, title = {The effects of solar irradiation changes on the migration of the Congo Air Boundary and water levels of paleo-Lake Suguta, Northern Kenya Rift, during the African Humid Period (15-5 ka BP)}, series = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, volume = {396}, journal = {Palaeogeography, palaeoclimatology, palaeoecology : an international journal for the geo-sciences}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0031-0182}, doi = {10.1016/j.palaeo.2013.12.007}, pages = {1 -- 16}, year = {2014}, abstract = {The water-level record from the 300 m deep paleo-lake Suguta (Northern Kenya Rift) during the African Humid Period (AHP, 15-5 ka BP) helps to explain decadal to centennial intensity variations in the West African Monsoon (WAM) and the Indian Summer Monsoon (ISM). This water-level record was derived from three different sources: (1) grain size variations in radiocarbon dated and reservoir corrected lacustrine sediments, (2) the altitudes and ages of paleo-shorelines within the basin, and (3) the results of hydro-balance modeling, providing important insights into the character of water level variations (abrupt or gradual) in the amplifier paleo-Lake Suguta. The results of these comprehensive analyses suggest that the AHP highstand in the Suguta Valley was the direct consequence of a northeastwards shift in the Congo Air Boundary (CAB), which was in turn caused by an enhanced atmospheric pressure gradient between East Africa and India during a northern hemisphere insolation maximum. Rapidly decreasing water levels of up to 90 m over less than a hundred years are best explained by changes in solar irradiation either reducing the East African-Indian atmospheric pressure gradient and preventing the CAB from reaching the study area, or reducing the overall humidity in the atmosphere, or a combination of both these effects. In contrast, although not well documented in our record we hypothesize a gradual end of the AHP despite an abrupt change in the source of precipitation when a decreasing pressure gradient between Asia and Africa prevented the CAB from reaching the Suguta Valley. The abruptness was probably buffered by a contemporaneous change in precession producing an insolation maximum at the equator during October. Whether or not this is the case, the water-level record from the Suguta Valley demonstrates the importance of both orbitally-controlled insolation variations and short-term changes in solar irradiation as factors affecting the significant water level variations in East African rift lakes.}, language = {en} } @phdthesis{Olaka2011, author = {Olaka, Lydia Atieno}, title = {Hydrology across scales : sensitivity of East African lakes to climate changes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-55029}, school = {Universit{\"a}t Potsdam}, year = {2011}, abstract = {The lakes of the East African Rift System (EARS) have been intensively studied to better understand the influence of climate change on hydrological systems. The exceptional sensitivity of these rift lakes, however, is both a challenge and an opportunity when trying to reconstruct past climate changes from changes in the hydrological budget of lake basins on timescales 100 to 104 years. On one hand, differences in basin geometrics (shape, area, volume, depth), catchment rainfall distributions and varying erosion-deposition rates complicate regional interpretation of paleoclimate information from lacustrine sediment proxies. On the other hand, the sensitivity of rift lakes often provides paleoclimate records of excellent quality characterized by a high signal-to-noise ratio. This study aims at better understanding of the climate-proxy generating process in rift lakes by parameterizing the geomorphological and hydroclimatic conditions of a particular site providing a step towards the establishment of regional calibrations of transfer functions for climate reconstructions. The knowledge of the sensitivity of a lake basin to climate change furthermore is crucial for a better assessment of the probability of catastrophic changes in the future, which bear risks for landscapes, ecosystems, and organisms of all sorts, including humans. Part 1 of this thesis explores the effect of the morphology and the effective moisture of a lake catchment. The availability of digital elevation models (DEM) and gridded climate data sets facilitates the comparison of the morphological and hydroclimatic conditions of rift lakes. I used the hypsometric integral (HI) calculated from Shuttle Radar Topography Mission (SRTM) data to describe the morphology of ten lake basins in Kenya and Ethiopia. The aridity index (AI) describing the difference in the precipitation/evaporation balance within a catchment was used to compare the hydroclimatic of these basins. Correlating HI and AI with published Holocene lake-level variations revealed that lakes responding sensitively to relatively moderate climate change are typically graben shaped and characterized by a HI between 0.23-0.30, and relatively humid conditions with AI >1. These amplifier lakes, a term first introduced but not fully parameterized by Alayne Street-Perrott in the early 80s, are unexceptionally located in the crest of the Kenyan and Ethiopian domes. The non-amplifier lakes in the EARS either have lower HI 0.13-0.22 and higher AI (>1) or higher HI (0.31-0.37) and low AI (<1), reflecting pan-shaped morphologies with more arid hydroclimatic conditions. Part 2 of this work addresses the third important factor to be considered when using lake-level and proxy records to unravel past climate changes in the EARS: interbasin connectivity and groundwater flow through faulted and porous subsurface lithologies in a rift setting. First, I have compiled the available hydrogeological data including lithology, resistivity and water-well data for the adjacent Naivasha and Elmenteita-Nakuru basins in the Central Kenya Rift. Using this subsurface information and established records of lake-level decline at the last wet-dry climate transitions, i.e., the termination of the African Humid Period (AHP, 15 to 5 kyr BP), I used a linear decay model to estimate typical groundwater flow between the two basins. The results suggest a delayed response of the groundwater levels of ca. 5 kyrs if no recharge of groundwater occurs during the wet-dry transition, whereas the lag is 2-2.7 kyrs only using the modern recharge of ca. 0.52 m/yr. The estimated total groundwater flow from higher Lake Naivasha (1,880 m a.s.l. during the AHP) to Nakuru-Elmenteita (1,770 m) was 40 cubic kilometers. The unexpectedly large volume, more than half of the volume of the paleo-Lake Naivasha during the Early Holocene, emphasizes the importance of groundwater in hydrological modeling of paleo-lakes in rifts. Moreover, the subsurface connectivity of rift lakes also causes a significant lag time to the system introducing a nonlinear component to the system that has to be considered while interpreting paleo-lake records. Part 3 of this thesis investigated the modern intraseasonal precipitation variability within eleven lake basins discussed in the first section of the study excluding Lake Victoria and including Lake Tana. Remotely sensed rainfall estimates (RFE) from FEWS NET for 1996-2010, are used for the, March April May (MAM) July August September (JAS), October November (ON) and December January February (DJF). The seasonal precipitation are averaged and correlated with the prevailing regional and local climatic mechanisms. Results show high variability with Biennial to Triennial precipitation patterns. The spatial distribution of precipitation in JAS are linked to the onset and strength of the Congo Air Boundary (CAB) and Indian Summer Monsoon (ISM) dynamics. while in ON they are related to the strength of Positive ENSO and IOD phases This study describes the influence of graben morphologies, extreme climate constrasts within catchments and basins connectivity through faults and porous lithologies on rift lakes. Hence, it shows the importance of a careful characterization of a rift lake by these parameters prior to concluding from lake-level and proxy records to climate changes. Furthermore, this study highlights the exceptional sensitivity of rift lakes to relatively moderate climate change and its consequences for water availability to the biosphere including humans.}, language = {en} } @article{TrauthMaslinDeinoetal.2010, author = {Trauth, Martin H. and Maslin, Mark A. and Deino, Alan L. and Junginger, Annett and Lesoloyia, Moses and Odada, Eric O. and Olago, Daniel O. and Olaka, Lydia A. and Strecker, Manfred and Tiedemann, Ralph}, title = {Human evolution in a variable environment : the amplifier lakes of Eastern Africa}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2010.07.007}, year = {2010}, abstract = {The development of rise Cenozoic East African Rift System (EARS) profoundly re-shaped the landscape and significantly increased the amplitude of short-term environmental response to climate variation. In particular, the development of amplifier lakes in rift basins after three million years ago significantly contributed to this exceptional sensitivity of East Africa to climate change compared to elsewhere on the African continent. Amplifier lakes are characterized by tectonically-formed graben morphologies in combination with an extreme contrast between high precipitation in the elevated parts of the catchment and high evaporation in the lake area. Such amplifier lakes respond rapidly to moderate, precessional-forced climate shifts, and as they do so apply dramatic environmental pressure to the biosphere. Rift basins, when either extremely dry or lake-filled, form important barriers for migration, mixing and competition of different populations of animals and hominins. Amplifier lakes link long-term, high-amplitude tectonic processes and short-term environmental fluctuations. East Africa may have become the place where early humans evolved as a consequence of this strong link between different time scales. (C) 2010 Elsevier Ltd. All rights reserved.}, language = {en} } @misc{GuentherMangelsdorfMitzneretal.2012, author = {G{\"u}nther, Oliver and Mangelsdorf, Birgit and Mitzner, Rolf and Loschelder, Wolfgang and Peter, Andreas and Eckert, Barbara and Mikelskis, Helmut and Klein, Alfred and Kirsch, B{\"a}rbel and Edelstein, Wolfgang and Thomas, Gr{\"u}newald and Thomas, P{\"o}sl and Wagner, Dieter and Winskowski, Friedrich and Schad, Martina and Frey, Anne and Bickenbach, Wulf and Madani, Roya and Olaka, Lydia}, title = {Portal alumni}, series = {Das Ehemaligen-Magazin der Universit{\"a}t Potsdam}, journal = {Das Ehemaligen-Magazin der Universit{\"a}t Potsdam}, number = {9}, organization = {Stabsstelle Studierendenmarketing/Alumniprogramm Im Auftrag der Pr{\"a}sidentin der Universit{\"a}t Potsdam}, issn = {1613-2343}, doi = {10.25932/publishup-44494}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-444943}, pages = {60}, year = {2012}, abstract = {Das zur{\"u}ckliegende Jahr stand an der Universit{\"a}t Potsdam auch im Zeichen des zwanzigj{\"a}hrigen Jubil{\"a}ums der Hochschule. Am 15. Juli 1991, wurde sie gegr{\"u}ndet und w{\"a}hrend einer Festwoche feierten Professorinnen und Professoren, Mitarbeiterinnen, Mitarbeiter und Studierende dieses Jubil{\"a}um geb{\"u}hrend. Seit der Gr{\"u}ndung der gr{\"o}ßten brandenburgischen Hochschule sind wissenschaftliches Renommee, Ansehen und Attraktivit{\"a}t stetig gewachsen. Gerade in den letzten Jahren hat sie ihr Profil gesch{\"a}rft. Vor allem die Kognitions-, die Geo- und Biowissenschaften sind hier zu nennen. Aber auch die Lehrerbildung besitzt einen hohen Stellenwert. International anerkannte Forschungsbereiche, Wissenschaftspreise, eine erfolgreiche Drittmittelbilanz und nicht zuletzt die bauliche Entwicklung an allen drei Standorten sind sichtbare Indikatoren f{\"u}r die erfolgreiche Entwicklung, die die Universit{\"a}t Potsdam in den letzten zwei Jahrzehnten durchlaufen hat. Die drei ehemaligen Pr{\"a}sidenten sowie verschiedene andere Protagonisten werfen in dieser Ausgabe der Portal Alumni einen Blick auf unterschiedliche Aspekte der zur{\"u}ckliegenden Entwicklung der Universit{\"a}t. Vom Erfolg der Universit{\"a}t zeugt auch die wachsende Zahl der Absolventinnen und Absolventen, die die Universit{\"a}t verlassen. Portal Alumni stellt in der vorliegenden Ausgabe deshalb Absolventen und deren universit{\"a}re und berufliche Lebenswege genauer vor und l{\"a}sst damit zugleich kaleidoskopartig 20 Jahre Studium an der Universit{\"a}t Potsdam Revue passieren.}, language = {de} }