This file was created by the TYPO3 extension publications --- Timezone: CEST Creation date: 2026-05-26 Creation time: 01:47:21 --- Number of references 16 article DiChiara2025 Article 2025 10.1029/2024GC011933 Geochemistry, Geophysics, Geosystems 26 4 https://www.scopus.com/inward/record.uri?eid=2-s2.0-105003796792&doi=10.1029%2f2024GC011933&partnerID=40&md5=79caf199a19445573b871198a6306444 Cited by: 0; All Open Access, Gold Open Access, Green Open Access Anita Di Chiara Vassil Karloukovski Barbara A. Maher Maarten Van Daele Thijs Meeren Dirk Verschuren article DiChiara2024 Article 2024 10.1029/2023GC011092 Geochemistry, Geophysics, Geosystems 25 3 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85186867348&doi=10.1029%2f2023GC011092&partnerID=40&md5=5bac85ec99c54f68fcbaad10376cabeb Cited by: 1; All Open Access, Gold Open Access, Green Open Access A. Di Chiara M.W. Hounslow B.A. Maher V. Karloukovski M. Van Daele M. Blaauw D. Verschuren article Baxter2024 Branched glycerol monoalkyl glycerol tetraethers (brGMGTs), a relatively understudied group of bacterial membrane lipids structurally similar to branched glycerol dialkyl glycerol tetraethers (brGDGTs), appear to be strongly influenced by temperature in terrestrial settings. In surficial bottom sediments of East African lakes, the abundance of brGMGTs relative to the sum of brGMGTs and brGDGTs (%brGMGT) and brGMGT distribution are strongly related to local mean annual air temperature (MAAT), stimulating development of new paleothermometers. However, applications of these methods to lake-sediment records are currently lacking. Here we investigate brGMGT concentrations and distributions in 916 samples throughout the 250,000-year (250-kyr) sediment sequence from Lake Chala, a presently fresh and permanently stratified (meromictic) tropical crater lake. All seven previously identified brGMGTs occur abundantly, reflected in a relatively high average %brGMGT of 19%. BrGMGTs and brGDGTs concentrations throughout the sequence are strongly correlated (R = 0.83, p < 0.001), suggesting that their producers and/or associated ecological niches substantially overlap. Clear distinction can be made between brGMGTs produced predominantly in the bottom sediments (H1034a and H1034c) versus the anoxic lower water column (H1020a-c and H1034b). Although a 17-month monitoring study of Lake Chala suggested brGMGTs are primarily produced in the sediments, down-core data assign greater importance to aquatic production than previously estimated. Instead of reflecting temperature, %brGMGT variations showed greatest similarity to GDGT proxies reflecting lake depth and/or mixing regime. BrGMGT-based temperature models produce ambiguous reconstructions, showing little similarity to known global temperature trends or the brGDGT-based mean summer temperature (MST) reconstruction from the same sediments. © 2024 The Authors Article 2024 10.1016/j.orggeochem.2024.104812 Organic Geochemistry 195 Elsevier Ltd East Africa; Glycerol; Lipids; Surficial sediments; Branched glycerol dialkyl glycerol tetraether; Branched glycerol monoalkyl glycerol tetraether; DeepCHALLA; East Africa; H-shaped; H-shaped GDGT; ICDP; Lake chala; Lake sediments; Paleoclimates; Tetraethers; air temperature; crater lake; lipid; paleoclimate; relative abundance; sediment transport; water column; Lakes https://www.scopus.com/inward/record.uri?eid=2-s2.0-85199247952&doi=10.1016%2fj.orggeochem.2024.104812&partnerID=40&md5=423a1277759f8f5e3b327d9ec44cbffb Cited by: 0; All Open Access, Hybrid Gold Open Access A.J. Baxter F. Peterse D. Verschuren J.S. Sinninghe Damsté article Baxter20242877 High-resolution paleoclimate records from tropical continental settings are greatly needed to advance understanding of global climate dynamics. The International Continental Scientific Drilling Program (ICDP) project DeepCHALLA recovered a 214.8 m long sediment sequence from Lake Chala, a deep and permanently stratified (meromictic) crater lake in eastern equatorial Africa, covering the past ca. 250 000 years (250 kyr) of continuous lacustrine deposition since the earliest phase of lake-basin development. Lipid biomarker analyses on the sediments of Lake Chala can provide quantitative records of past variation in temperature and moisture balance from this poorly documented region. However, the degree to which climate proxies derived from aquatically produced biomarkers are affected by aspects of lake developmental history is rarely considered, even though it may critically influence their ability to consistently register a particular climate variable through time. Modern-system studies of Lake Chala revealed crucial information about the mechanisms underpinning relationships between proxies based on isoprenoid (iso-) and branched (br-) glycerol dialkyl glycerol tetraethers (GDGTs) and the targeted climate variables, but the persistence of these relationships in the past remains unclear. Here we assess the reliability of long-term climate signals registered in the sediments of Lake Chala by comparing downcore variations in GDGT distributions with major phases in lake-system evolution as reflected by independent proxies of lake depth, mixing regime and nutrient dynamics: seismic reflection data, lithology and fossil diatom assemblages. Together, these records suggest that during early lake history (before ca. 180-200 ka) the distinct mixing-related depth zones with which specific GDGT producers are associated in the modern-day lake were not yet formed, likely due to more open lake hydrology and absence of chemical water-column stratification. Consequently absolute GDGT concentrations dating to this period are relatively low, proxies sensitive to water-column stratification (e.g., branched versus isoprenoid tetraether (BIT) index) display highly irregular temporal variability, and correlations between proxies are dissimilar to expectations based on modern-system understanding. A sequence of lake-system changes between ca. 180-200 and ca. 80 ka first established and then strengthened the chemical density gradient, promoting meromictic conditions despite the overall decrease in lake depth due to the basin gradually being filled up with sediments. From ca. 180 ka onward some GDGTs and derived proxies (e.g., crenarchaeol concentration, BIT index and IR6Me) display strong ∼ 23 kyr periodicity, likely reflecting the predominantly precession-driven insolation forcing of Quaternary climate variability in low-latitude regions. Our results suggest that GDGT-based temperature and moisture-balance proxies in Lake Chala sediments reflect the climate history of eastern equatorial Africa from at least ca. 160 ka onwards, i.e., covering the complete last glacial-interglacial cycle and the penultimate glacial maximum. This work confirms the potential of lacustrine GDGTs for elucidating the climate history of tropical regions at Quaternary timescales, provided they are applied to suitably high-quality sediment archives. Additionally, their interpretation should incorporate a broader understanding of the extent to which lake-system evolution limits the extrapolation back in time of proxy-climate relationships established in the modern system. © 2024 Copernicus Publications. All rights reserved. Article 2024 10.5194/bg-21-2877-2024 Biogeosciences 21 Copernicus Publications 2877 – 2908 11 Arequipa [Peru]; Chala; Peru; biomarker; climate variation; crater lake; ether; glacial-interglacial cycle; lacustrine deposit; paleoclimate; proxy climate record; seismic reflection; stratification https://www.scopus.com/inward/record.uri?eid=2-s2.0-85196263552&doi=10.5194%2fbg-21-2877-2024&partnerID=40&md5=17a3af88d40ef461463988be3c6b5d5a Cited by: 1 Allix J. Baxter Francien Peterse Dirk Verschuren Aihemaiti Maitituerdi Nicolas Waldmann Jaap S. Sinninghe Damsté article Martin-Jones2024 Regional tephrostratigraphic frameworks connect palaeoclimate, archaeological and volcanological records preserved in soils or lake sediments via shared volcanic ash (tephra) layers. In eastern Africa, tracing of tephra isochrons between geoarchaeological sequences is an established chronostratigraphic approach. However, to date, few long tephra records exist from sites with continuous depositional sequences, such as lake sediments, which offer the potential to connect local and discontinuous sequences at the regional scale. Long lake sediment sequences may also capture more complete eruptive histories of understudied volcanic centres. Here, we present and date the tephrostratigraphic record of a >250,000-year (>250-kyr) continuous sediment sequence extracted from Lake Chala, a crater lake on the Kenya-Tanzania border near Mt Kilimanjaro. Single-grain glass major and minor element analyses of visible and six cryptotephra layers reveal compositions ranging from mafic foidites and basanites to more evolved tephri-phonolites, phonolites, trachytes and a single rhyolite. Of these, nine are correlated to scoria cone eruptions of neighbouring Mt Kilimanjaro or the Chyulu volcanic field ∼60 km to the north; seven are correlated to phonolitic eruptions of Mt Meru, ∼100 km to the west; and four to voluminous trachytic eruptions of Central Kenyan Rift (CKR) volcanoes located ∼350 km to the north. The only rhyolitic tephra layer, a cryptotephra, correlates to the 73.7-ka BP (before present, taken as 1950 CE) Younger Toba Tuff (YTT) from Sumatra. Two of the CKR tephra layers provide direct ties with terrestrial sequences relevant to Middle Stone Age archaeology of the eastern Lake Victoria basin in Kenya. Absolute age estimates obtained by direct 40Ar/39Ar dating of 10 tephra layers are combined with six 210Pb and 162 14C dates covering the last 25-kyr and the well-constrained known age of the YTT to build a first absolute chronology for the full Lake Chala sediment sequence. The uninterrupted >250-kyr Lake Chala sedimentary archive represents a unique tephrostratotype sequence for eastern Africa, optimising the chronological value of tephra correlations in regional palaeoenvironmental, archaeological and volcanological research. Further study of cryptotephra in the Lake Chala sequence and additional geochemical characterisation and dating of ancient volcanic eruptions from nearby and further afield may eventually produce a regionally connected and detailed tephrostratigraphic framework for eastern equatorial Africa. © 2024 The Authors Article 2024 10.1016/j.quascirev.2023.108476 Quaternary Science Reviews 326 Elsevier Ltd Africa; East African Lakes; Lake Victoria; Argon; Geochemistry; Geochronology; Sediments; Volcanoes; Africa; Argon dating; East African Rift; East african rift system; Holocenes; Lake chala; Lake sediments; Palaeoclimate; Pleistocene; Rift systems; Tephrochronology; archaeology; chronology; crater lake; geochemistry; geochronology; Holocene; lacustrine deposit; Mesolithic; paleoclimate; tephrochronology; volcanic ash; Lakes https://www.scopus.com/inward/record.uri?eid=2-s2.0-85182891635&doi=10.1016%2fj.quascirev.2023.108476&partnerID=40&md5=7a433adf9112ece8ad25f1b4ba150a53 Cited by: 0; All Open Access, Hybrid Gold Open Access Catherine Martin-Jones Christine S. Lane Maarten Blaauw Darren F. Mark Dirk Verschuren Thijs Meeren Maarten Van Daele Hannah Wynton Nick Blegen Mary Kisaka Melanie J. Leng Philip Barker article Baxter2023336 Article 2023 10.1038/s41586-023-06272-5 Nature 620 336 – 343 7973 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85167528794&doi=10.1038%2fs41586-023-06272-5&partnerID=40&md5=8e53516a7526b366c7607694baf832b6 Cited by: 35; All Open Access, Green Open Access, Hybrid Gold Open Access A.J. Baxter D. Verschuren F. Peterse D.G. Miralles C.M. Martin-Jones A. Maitituerdi T. Meeren M. Van Daele C.S. Lane G.H. Haug D.O. Olago J.S. Sinninghe Damsté article Maitituerdi2022 Sediments deposited in Lake Chala (Kenya/Tanzania) constitute a high-resolution archive of past climate and environmental change in equatorial East Africa spanning two glacial-interglacial cycles. To correctly interpret the proxy records it contains, it is crucial to understand the evolution of lacustrine sedimentation in this volcanic crater basin. Building on previous seismic stratigraphic analysis by Moernaut et al. (2010) of a dense grid of 37 km high-resolution seismic reflection profiles with up to 270 ms two-way travel time (ca. 210 m depth) of sub-bottom penetration, this study presents a seismic-based reconstruction of the complete depositional history of Lake Chala as well as a first-order age model for the major documented stages in lake evolution. The seismic stratigraphic sequence comprises 16 distinct and finely-stratified units (U1-U16, youngest to oldest), grouped into five major depositional stages. Stage I (U16, ca. 249-212 ka) marks the initiation of sedimentation in an originally ring-shaped depositional area surrounding two central tuff cones emerging from the basin floor. Stage II (U15-U12, ca. 212-114 ka) represents the onset of basinwide sedimentation above the tuff cones, implying a gradual rise in lake depth and shift to more strictly hemipelagic sedimentation. Stage III (U11-U8, ca. 114-97 ka) represents the development of a relatively flat lake floor during a period of significantly reduced lake depth. Stage IV (U7-U4, ca. 97–20.5 ka) is again characterized by largely undisturbed hemipelagic sedimentation under mostly high lake-depth conditions. Stage V (U3-U1, 20.5 ka BP to Present) represents the establishment of the present-day, very broad and flat basin floor under fluctuating lake level. Reassessing the Moernaut et al. (2010) suggestion of a minor disconformity at ca. 100 m sub-bottom depth, we here interpret this seismic feature as a thick turbidite related to a mass wasting event. Consequently we can affirm continuity of lacustrine sedimentation in the depocenter of Lake Chala throughout the past ca. 250,000 years. © 2022 Elsevier Ltd 2022 English 1464343X 10.1016/j.jafrearsci.2022.104499 Journal of African Earth Sciences 189 Elsevier Ltd Dr. Moses Strauss Department of Marine Geosciences, Leon H. Charney School of Marine Sciences, University of Haifa, Mount Carmel3498838, Israel; Renard Centre of Marine Geology (RCMG), Department of Geology, Ghent University, Krijgslaan 281/S8, Gent, B-9000, Belgium; Limnology Unit, Department of Biology, Ghent University, K. L. Ledeganckstraat 35, Gent, B-9000, Belgium deposition; environmental change; glacial-interglacial cycle; lacustrine deposit; lake; mass wasting; reconstruction; sediment; seismic stratigraphy, Kilimanjaro [Kilimanjaro (RGA)]; Kilimanjaro [Tanzania]; Tanzania https://www.scopus.com/inward/record.uri?eid=2-s2.0-85126588424&doi=10.1016%2fj.jafrearsci.2022.104499&partnerID=40&md5=8bfdaf5994bedbea5a3dbd3e36d2e5d1 cited By 3 A. Maitituerdi M. Van Daele D. Verschuren M. De Batist N. Waldmann article Martin-Jones2020245 Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria-cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250-ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non-visible (crypto-) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first-order age estimates for seven previously unknown eruptions. Long and well-resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd 2020 English 02678179 10.1002/jqs.3140 Journal of Quaternary Science 35 John Wiley and Sons Ltd 245-255 Department of Geography, University of Cambridge, Cambridge, United Kingdom; Limnology Unit, Department of Biology, Ghent University, Gent, Belgium; Renard Centre of Marine Geology, Department of Geology, Ghent University, Gent, Belgium; Lancaster Environment Centre, University of Lancaster, Lancaster, United Kingdom; Department of Geology, Trinity College Dublin, Dublin, Ireland 1-2 geochemistry; historical perspective; lacustrine deposit; tephra; tephrochronology; volcanic eruption; volcanic glass; volcanism, East African Rift; East African Rift; Kenya; Kenya Rift; Kilimanjaro [Tanzania]; Lake Challa; Tanzania https://www.scopus.com/inward/record.uri?eid=2-s2.0-85071268499&doi=10.1002%2fjqs.3140&partnerID=40&md5=9164e0fd515ee4cb72fa21608be7b271 cited By 6 C. Martin-Jones C. Lane M. Van Daele T.V.D. Meeren C. Wolff H. Moorhouse E. Tomlinson D. Verschuren article Meyer2020 Grain-size analysis and end-member modeling of the clastic fraction of the 25-kyr sediment sequence from Lake Chala, a meromictic crater lake on the lower east slope of Mt. Kilimanjaro, reveal crucial aspects of climate-driven environmental change in equatorial East Africa since the Last Glacial Maximum. The finely laminated sediments of Lake Chala contain only up to 40% of clastic components, the rest are mainly diatom frustules and amorphous organic matter. Measured grain-size distributions were split into six statistically meaningful end members, of which four could be linked to a distinct source and transport mechanism of clastic mineral input: fine aeolian dust from distal sources (EM1), fine catchment runoff (EM2), coarser aeolian dust from proximal sources (EM5) and coarse erosive material from the upper crater slopes (EM6). The two other end members (EM3 and EM4) represented frustules of the two most common diatom taxa in Lake Chala, Afrocymbella barkeri and Nitzschia fabiennejansseniana, which had (partly) survived sample pre-treatment. Temporal variation in normalized abundance of the two dust-derived end members are valuable proxies for past changes in monsoon circulation over equatorial East Africa. During Northern Hemisphere cold periods (e.g., Last Glacial Maximum and Younger Dryas) the Inter-Tropical Convergence Zone shifted southward, enhancing northeasterly monsoon winds in the Lake Chala area and increasing advection of fine dust from the dry Horn of Africa region. Simultaneously, more modest continental heating reduced the prevalence of small-scale atmospheric turbulence, and thus the occurrence of dust devils, resulting in reduced influx of coarse dust from drylands nearby. Conversely, abrupt intensification of the southeasterly monsoon at the onset of the Holocene is recorded by an abrupt increase in the amount of coarse dust delivered to Lake Chala. Temporal variation in the end members representing catchment run-off (EM2) and erosion (EM6) mainly reflect changes in lacustrine sedimentation dynamics associated with major lake-level fluctuation, as evidenced by other paleoenvironmental proxies. Overall this study shows that subdivision of the clastic fraction of lacustrine sediments into statistically robust grain-size end members can provide multiple independent and quantitative proxies which help constrain reconstructions of a region's multi-faceted climate history. © 2020 The Authors Article 2020 English 02773791 10.1016/j.quascirev.2020.106574 Quaternary Science Reviews 247 Elsevier Ltd Bourgogne-Franche-Comte; France; Horn of Africa; Jura [Bourgogne-Franche-Comte]; Kilimanjaro [Kilimanjaro (RGA)]; Kilimanjaro [Tanzania]; Lake Chalain; Tanzania; Bacillariophyta; Nitzschia; Atmospheric thermodynamics; Atmospheric turbulence; Catchments; Climate change; Dust; Glacial geology; Grain size and shape; Lakes; Runoff; Size distribution; Amorphous organic matters; Grain size distribution; Intertropical convergence zone; Lacustrine sedimentations; Lacustrine sediments; Lake level fluctuations; Northern Hemispheres; Small-scale atmospheric turbulence; crater lake; diatom; environmental change; eolian deposit; grain size; lacustrine deposit; Last Glacial Maximum; paleoenvironment; proxy climate record; sedimentation; Sediments https://www.scopus.com/inward/record.uri?eid=2-s2.0-85090738058&doi=10.1016%2fj.quascirev.2020.106574&partnerID=40&md5=0d31a2c9e470b8dee6ca5ed473ee06f8 Cited by: 9; All Open Access, Green Open Access, Hybrid Gold Open Access Inka Meyer Maarten Van Daele Niels Tanghe Marc De Batist Dirk Verschuren article Meyer201892 This study presents the merit of visible-spectrum scanning reflectance spectroscopy (VIS-RS) as a rapid technique for determining the concentration of chlorophyll a (Chl a) and its derivatives in lake sediments. In a 25,000-yr sediment record from Lake Challa, in East Africa, we found that VIS-RS values correlate with Chl a concentrations measured by High Performance/Pressure Liquid Chromatography. Observed variation in sedimentary values of RABD660;670 appears linked to proxies of climatic moisture balance as well as to a seismically-derived lake-level reconstruction over this period, indicating that VIS-RS can be used as a proxy for long-term paleo-hydrological change. Changes in the reflectance of Lake Challa sediments are likely related to differences in the preservation/degradation of algal pigments in response to changes in water-column depth and the stability of stratification. The connecting mechanism may be that during lake lowstands, more frequent injection of oxygen to (near-) bottom waters enhance the breakdown of labile organic compounds before permanent burial. We suggest that fast and inexpensive VIS-RS scanning, although less specific than HPLC in quantifying individual pigments, provides accurate data on down-core variations in the concentration of Chl a and its derivatives in lake sediments, hence allows to reconstruct long-term changes in the hydrology of climate-sensitive lakes. The main prerequisite for its successful application is that temporal variation in lake hydrology over the period of interest has not appreciably affected sedimentation dynamics at the core site, since major changes in sediment texture and organic content are likely to create confounding effects in the VIS-RS signature. © 2017 Association for the Sciences of Limnology and Oceanography 2018 English 15415856 10.1002/lom3.10230 Limnology and Oceanography: Methods 16 Wiley Blackwell 92-105 Renard Centre of Marine Geology (RCMG), Department of Geology, Ghent University, Gent, Belgium; PProGRess/UGCT – Department of Geology, Ghent University, Ghent, Belgium; Protistology and Aquatic Ecology, Department of Biology, Ghent University, Gent, Belgium; Limnology Unit, Department of Biology, Ghent University, Gent, Belgium 2 https://www.scopus.com/inward/record.uri?eid=2-s2.0-85042356651&doi=10.1002%2flom3.10230&partnerID=40&md5=0e7ddf519ff2b045ad5d755d3d364965 cited By 9 I. Meyer M. Van Daele G. Fiers E. Verleyen M. De Batist D. Verschuren article vanBree2016132 We studied the high-resolution and well-dated 25,000 year sedimentary record of Lake Challa, a deep tropical crater lake in equatorial East Africa, to explore new proxies for paleoenvironmental and paleohydrological change. Sedimentary biomarker analysis revealed the presence of des-A-triterpenoids with oleanane, ursane and lupane carbon skeletons, microbial degradation products of angiosperm plant triterpenoids. Their increased influx from 16,000 years ago corresponds with previously documented changes in the terrestrial vegetation of the Lake Challa basin during postglacial warming, in particular the relative increase in C3/C4 plant ratio inferred from the stable carbon isotopic signature (δ13C) of sedimentary n-alkanes derived from plant leaf waxes. In contrast to this n-alkane δ13C signature, the δ13C of des-A-lupane maintains a constant value of −27.4 ± 1.1‰ across the glacial–interglacial transition. Since des-A-lupane is derived from C3 plants, its δ13C signature is here proposed to represent a novel and independent proxy for the time-variable carbon isotopic composition of local terrestrial C3 plants, which can improve estimates of the C3/C4 plant ratio based on two-end member mixing models of n-alkane δ13C values. © 2016 Elsevier Ltd 2016 English 01466380 10.1016/j.orggeochem.2016.09.003 Organic Geochemistry 101 Elsevier Ltd 132-139 NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Microbiology and Biogeochemistry, Utrecht University, PO Box 59, AB Den Burg, 1790, Netherlands; Utrecht University, Faculty of Geosciences, Department of Earth Sciences, PO Box 80.115, TC Utrecht, 3508, Netherlands; Department of Botany and Microbiology, Addiriyah Chair for Environmental Studies, College of Science, King Saud University, P.O. Box 2455, Riyadh, 11451, Saudi Arabia; Ghent University, Limnology Unit, K.L. Ledeganckstraat 35, Gent, B-9000, Belgium Biodegradation; Degradation; Isotopes; Lakes; Sedimentology; Vegetation, Carbon isotopic composition; Des-A-lupane; East Africa; Interglacial transitions; Lacustrine sediments; Microbial degradation; Terrestrial vegetation; Triterpenoids, Paraffins, alkane; angiosperm; C3 plant; C4 plant; carbon isotope; isotopic ratio; lacustrine deposit; leaf; microbial activity; paleoenvironment; paleohydrology; Postglacial; reconstruction; stable isotope; terpene; warming; wax, Kilimanjaro [Tanzania]; Lake Challa; Tanzania, Magnoliophyta https://www.scopus.com/inward/record.uri?eid=2-s2.0-84988939092&doi=10.1016%2fj.orggeochem.2016.09.003&partnerID=40&md5=b53a6f65480aba981180fb2bec9c4f50 cited By 11 L.G.J. Bree W.I.C. Rijpstra N.A. Al-Dhabi D. Verschuren J.S. Sinninghe Damsté J.W. Leeuw article https://doi.org/10.4319/lo.2014.59.5.1621 From November 2006 to January 2010, a sediment trap that was cleared monthly was deployed in Lake Challa, a deep stratified freshwater lake on the eastern slope of Mt. Kilimanjaro in southern Kenya. Geochemical data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to characterize the effect of single parameters on productivity and sedimentation processes in the crater basin. During the southern hemisphere summer (November—March), when the water temperature is high and the lake is biologically productive (nondiatom algae), calcite predominated in the sediment trap samples. During the “long rain” season (March—May) a small amount of organic matter and lithogenic material caused by rainfall appeared. This was followed by the cool and windy months of the southern hemisphere winter (June—October) when diatoms were the main component, indicating a diatom bloom initiated by improvement of nutrient availability related to upwelling processes. The sediment trap data support the hypothesis that the light—dark lamination couplets, which are abundant in Lake Challa cores, reflect seasonal delivery to the sediments of diatom-rich particulates during the windy months and diatom-poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Niño—Southern Oscillation (ENSO)-related rainfall and drought cycles, exert a strong influence on the magnitude and geochemical composition of particle export to the hypolimnion of Lake Challa. 2014 https://doi.org/10.4319/lo.2014.59.5.1621 Limnology and Oceanography 59 1621-1636 5 https://aslopubs.onlinelibrary.wiley.com/doi/abs/10.4319/lo.2014.59.5.1621 Christian Wolff Iris Kristen-Jenny Georg Schettler Birgit Plessen Hanno Meyer Peter Dulski Rudolf Naumann Achim Brauer Dirk Verschuren Gerald H. Haug article VanBree201489 We studied the distribution of long-chain alkenes (n-C23 to n-C31) in well-dated sediments from Lake Challa, a deep crater lake near Mt. Kilimanjaro in equatorial East Africa, to reveal signatures of palaeo-environmental and palaeo-climatic changes affecting the production of these compounds during the last 25kyr. The apolar fractions of organic sediment extracts dated to the last 16kyr showed an unusual dominance of δ13C-depleted n-C25:1 and n-C27:1 alk-1-enes. These alkenes were not detected in soil and litter from near the shoreline and from the inner rim of the crater, pointing to an autochthonous, aquatic source. Analysis of suspended particulate matter indicated that the n-alk-1-enes are produced in the well-oxygenated upper 30m of the water column, indicating a phytoplanktonic origin. Sedimenting particles collected monthly from December 2006 to November 2007 showed increased fluxes of n-alk-1-enes following the locally prominent short rain season in November-December. Green algae and/or cyanobacteria were identified as candidate sources of these alkenes. Production of the n-C25:1 and n-C27:1 alkenes in Lake Challa was much reduced during the Last Glacial Maximum and early late-glacial period, suggesting a temperature or CO2 effect on habitat suitability. We explored the potential of n-alk-1-ene accumulation rates, and of a derived Alkene Index [n-C27:1]/([n-C25:1]+[n-C27:1]), to record longer-term climatic changes. The Alkene Index record of Lake Challa over the past 25kyr shows clear periodicity with a dominant frequency of ~2.3kyr, potentially indicative of monsoon variability directly or indirectly forced by variation in solar radiation. © 2014 Elsevier Ltd. 2014 English 00167037 10.1016/j.gca.2014.08.035 Geochimica et Cosmochimica Acta 145 Elsevier Ltd 89-102 NIOZ Royal Netherlands Institute for Sea Research, Department of Marine Organic Biogeochemistry, P.O. Box 59, AB Den Burg, 1790, Netherlands; Utrecht University, Faculty of Geosciences, Department of Earth Sciences, P.O. Box 80.021, TA Utrecht, 3508, Netherlands; National Botanic Garden of Belgium, Domein van Bouchout, Meise, B-1860, Belgium; Ghent University, Limnology Unit, K.L. Ledeganckstraat 35, Gent, B-9000, Belgium; Department of Botany and Microbiology, Addiriyah Chair for Environmental Studies, College of Science, King Saud University, P.O. Box 245511451 Riyadh, Saudi Arabia accumulation rate; alkene; climate variation; cyanobacterium; geological record; green alga; lacustrine deposit; Last Glacial Maximum; monsoon; paleoclimate; paleoenvironment; solar radiation; suspended particulate matter, Kilimanjaro [Kilimanjaro (RGA)]; Kilimanjaro [Tanzania]; Lake Challa; Tanzania https://www.scopus.com/inward/record.uri?eid=2-s2.0-84908192035&doi=10.1016%2fj.gca.2014.08.035&partnerID=40&md5=5d5efd353a206eaf2f9c8c7ce625f06f cited By 16 L.G.J. Van Bree W.I.C. Rijpstra C. Cocquyt N.A. Al-Dhabi D. Verschuren J.S. Sinninghe Damsté J.W. Leeuw article Buckles2014106 The MBT/CBT palaeotemperature proxy uses the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs), membrane lipids that are supposed to derive from soil bacteria, to reconstruct mean annual air temperature (MAAT). Applied successfully in coastal marine sediments, its extension to lake-sediment records with potentially high time resolution would greatly expand its utility. Over the last years, however, studies have indicated the presence of additional sources of brGDGTs within lake systems. To constrain the factors influencing the MBT/CBT palaeotemperature proxy in lakes, detailed investigation of brGDGT fluxes in a modern lake system is necessary to identify their potential sources. This study concentrates on Lake Challa, a permanently stratified crater lake in equatorial East Africa with limited catchment area. An almost 3-year time series of approximately monthly samples of settling particles, supplemented with a depth profile of suspended particulate matter (SPM) and sets of profundal surface-sediment and catchment soil samples, were analysed for both the 'living' intact polar lipids (IPLs) and 'fossil' core lipids (CLs) of GDGTs. We found that brGDGTs are produced in oxic, suboxic and anoxic zones of the water column, and in substantial amounts compared to influxes from catchment soils. Additional in situ production within the lake sediments is most probable, but cannot be definitely confirmed at this time. These lacustrine brGDGTs display a different response to temperature variation than soil-derived brGDGTs, signifying either a different physiological adaptation to changing conditions within the water column and/or a different composition of the respective bacterial communities. Using this specific relationship with temperature, a local calibration based on brGDGT distributions in SPM generates relatively accurate water temperature estimates from settling particles but fails for surface sediments. © 2014 Elsevier Ltd. Article 2014 English 00167037 10.1016/j.gca.2014.04.042 Geochimica et Cosmochimica Acta 140 Elsevier Ltd 106 – 126 Kilimanjaro [Tanzania]; Lake Challa; Tanzania; Bacteria (microorganisms); core analysis; lacustrine deposit; lacustrine environment; lipid; membrane; microbial community; paleotemperature; soil biota; suspended particulate matter; water temperature https://www.scopus.com/inward/record.uri?eid=2-s2.0-84902329365&doi=10.1016%2fj.gca.2014.04.042&partnerID=40&md5=492afc3ee3392a7e2ca7e1e2d31c6389 Cited by: 78; All Open Access, Green Open Access Laura K. Buckles Johan W.H. Weijers Dirk Verschuren Jaap S. Sinninghe Damsté article Verschuren201372 2013 English 18168957 10.2204/iodp.sd.15.09.2013 Scientific Drilling 72-76 Ghent University, Limnology Unit, K.L., Ledeganckstraat 35, B-9000 Ghent, Belgium; University of Nairobi, Department of Geology, Chiromo Campus, P.O. Box 30197, Nairobi 00100, Kenya; Palynology and Palaeobotany Section, National Museums of Kenya, P.O. Box 40658, Nairobi 00100, Kenya; Office of the Prime Minister, P.O. Box 74434, Nairobi 00200, Kenya 15 https://www.scopus.com/inward/record.uri?eid=2-s2.0-84877833251&doi=10.2204%2fiodp.sd.15.09.2013&partnerID=40&md5=7af28582042289c69cfb02ee73e188df cited By 8 D. Verschuren D.O. Olagod S.M. Rucina P.O. Odhengo article Wolff2011743 Interannual rainfall variations in equatorial East Africa are tightly linked to the El Niño Southern Oscillation (ENSO), with more rain and flooding during El Niño and droughts in La Niña years, both having severe impacts on human habitation and food security. Here we report evidence from an annually laminated lake sediment record from southeastern Kenya for interannual to centennial-scale changes in ENSO-related rainfall variability during the last three millennia and for reductions in both the mean rate and the variability of rainfall in East Africa during the Last Glacial period. Climate model simulations support forward extrapolation from these lake sediment data that future warming will intensify the interannual variability of East Africa's rainfall. 2011 English 00368075 10.1126/science.1203724 Science 333 743-747 Helmholtz Centre Potsdam GeoForschungsZentrum (GFZ-German Research Centre for Geosciences), Climate Dynamics and Landscape Evolution, Telegrafenberg, D-14473 Potsdam, Germany; Deutsche Forschungsgemeinschaft (DFG) Graduate School 1364, University of Potsdam, Institute of Geosciences, Karl-Liebknecht Strasse 24, D-14476 Potsdam, Germany; DFG Leibniz Center for Earth Surface Process and Climate Studies, University of Potsdam, D-14476 Potsdam, Germany; Geological Institute, Department of Earth Sciences, Eidgenössische Technische Hochschule (ETH-Swiss Federal Institute of Technology), Zürich, CH-8092 Zurich, Switzerland; International Pacific Research Center, School of Ocean and Earth Science and Technology, University of Hawai'i, 2525 Correa Road, HI 96822, United States; Faculty of Geosciences, Utrecht University, Post Office Box 80021, 3508 TA Utrecht, Netherlands; Department of Marine Organic Biogeochemistry, Nederlands Instituut Voor Zeeonderzoek (NIOZ-Royal Netherlands Institute for Sea Research), Post Office Box 59, 1790 AB Den Burg, Netherlands; Department of Geosciences, Princeton University, Princeton, NJ 08544, United States; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964-8000, United States; Limnology Unit, Department of Biology, Ghent University, Ledeganckstraat 35, 9000 Gent, Belgium 6043 rain, annual variation; climate modeling; El Nino-Southern Oscillation; flooding; food security; lacustrine deposit; paleoclimate; Pleistocene; precipitation intensity, Africa; article; climate; El Nino; food security; glacial period; lake sediment; priority journal; seasonal variation, Kenya https://www.scopus.com/inward/record.uri?eid=2-s2.0-79961241131&doi=10.1126%2fscience.1203724&partnerID=40&md5=40813f4a44e1a848cdb32d6826fa5956 cited By 130 C. Wolff G.H. Haug A. Timmermann J.S. Sinninghe Damsté A. Brauer D.M. Sigman M.A. Cane D. Verschuren