@article{VanderMeerenMischkeSunjidmaaetal.2012,
  author    = {Van der Meeren, T. and Mischke, Steffen and Sunjidmaa, N. and Herzschuh, Ulrike and Ito, E. and Martens, K. and Verschuren, Dirk},
  title     = {Subfossil ostracode assemblages from Mongolia quantifying response for paleolimnological applications},
  series = {Ecological indicators : integrating monitoring, assessment and management},
  volume    = {14},
  journal   = {Ecological indicators : integrating monitoring, assessment and management},
  number    = {1},
  publisher = {Elsevier},
  address   = {Amsterdam},
  issn      = {1470-160X},
  doi       = {10.1016/j.ecolind.2011.07.004},
  pages     = {138 -- 151},
  year      = {2012},
  abstract  = {Ostracodes (Ostracoda, Crustacea) are aquatic micro-crustaceans with a significant representation in the fossil record. If the environmental influence on the species composition of their communities is robustly quantified, past changes in ostracode communities reflected in fossil assemblages can be used for paleo-environmental reconstruction. We analyzed ostracode assemblages in recently deposited surface sediments from 56 lakes in western and central Mongolia, and simultaneously recorded local water chemistry and solute concentration in order to elucidate the distribution of individual ostracode species in relation to these broad environmental gradients. Multivariate analysis indicated that the species variation in ostracode assemblages could be mainly attributed to variations in percent calcium (\%Ca) relative to total cation content, mean annual precipitation, calcium concentration, alkalinity, percent bicarbonate relative to total anion content, and mean July temperature. This matches well with the results of a similar analysis on presence/absence data of living ostracodes in nearshore samples, even though some differences exist between the faunal composition of both datasets. The documented response of ostracode species to environmental variation tracks the typical solute evolutionary pathway for surface waters in this region, characterized by calcite precipitation and consequent depletion in dissolved calcium. Hence, the best quantitative inference model (WA-PLS model with R-jack(2) = 0.70, RMSEP = 0.40) for paleolimnological application was obtained for \%Ca. Comparison between this model and a specific conductance (SC) inference model based on the same dataset, and based on ostracode datasets from different regions, indicated that the \%Ca inference model suffers less than the SC inference model from a step-change in reconstructed values. The statistical power of different inference models based on Mongolian ostracodes are variously affected by the common dominance of a single euryhaline species (Limnocythere inopinata), limited faunal turnover in the freshwater portion of the salinity gradient, and the bimodal frequency distribution of SC among regional lakes. The latter probably represents true scarcity of lakes with intermediate salinity rather than a biased representation in our dataset. In a broader context of ostracode ecology, and with respect to regional paleolimnological applications, we highlight the potential of fossil Mongolian ostracode assemblages to trace past hydrological shifts associated with changes in groundwater inflow.},
  language  = {en}
}
@article{VerschurenDamsteMoernautetal.2009,
  author    = {Verschuren, Dirk and Damst{\´e}, Jaap S. Sinninghe and Moernaut, Jasper and Kristen, Iris and Blaauw, Maarten and Fagot, Maureen and Haug, Gerald H.},
  title     = {Half-precessional dynamics of monsoon rainfall near the East African Equator},
  issn      = {0028-0836},
  doi       = {10.1038/Nature08520},
  year      = {2009},
  abstract  = {External climate forcings-such as long-term changes in solar insolation-generate different climate responses in tropical and high latitude regions(1). Documenting the spatial and temporal variability of past climates is therefore critical for understanding how such forcings are translated into regional climate variability. In contrast to the data- richmiddle and high latitudes, high-quality climate-proxy records from equatorial regions are relatively few(2-4), especially from regions experiencing the bimodal seasonal rainfall distribution associated with twice-annual passage of the Intertropical Convergence Zone. Here we present a continuous and well-resolved climate-proxy record of hydrological variability during the past 25,000 years from equatorial East Africa. Our results, based on complementary evidence from seismic-reflection stratigraphy and organic biomarker molecules in the sediment record of Lake Challa near Mount Kilimanjaro, reveal that monsoon rainfall in this region varied at half-precessional (similar to 11,500-year) intervals in phase with orbitally controlled insolation forcing. The southeasterly and northeasterly monsoons that advect moisture from the western Indian Ocean were strengthened in alternation when the inter-hemispheric insolation gradient was at a maximum; dry conditions prevailed when neither monsoon was intensified and modest local March or September insolation weakened the rain season that followed. On sub-millennial timescales, the temporal pattern of hydrological change on the East African Equator bears clear high-northern-latitude signatures, but on the orbital timescale it mainly responded to low-latitude insolation forcing. Predominance of low-latitude climate processes in this monsoon region can be attributed to the low-latitude position of its continental regions of surface air flow convergence, and its relative isolation from the Atlantic Ocean, where prominent meridional overturning circulation more tightly couples low-latitude climate regimes to high-latitude boundary conditions.},
  language  = {en}
}
@article{WolffHaugTimmermannetal.2011,
  author    = {Wolff, Christian Michael and Haug, Gerald H. and Timmermann, Axel and Damste, Jaap S. Sinninghe and Brauer, Achim and Sigman, Daniel M. and Cane, Mark A. and Verschuren, Dirk},
  title     = {Reduced interannual rainfall variability in East Africa during the last Ice Age},
  series = {Science},
  volume    = {333},
  journal   = {Science},
  number    = {6043},
  publisher = {American Assoc. for the Advancement of Science},
  address   = {Washington},
  issn      = {0036-8075},
  doi       = {10.1126/science.1203724},
  pages     = {743 -- 747},
  year      = {2011},
  abstract  = {Interannual rainfall variations in equatorial East Africa are tightly linked to the El Nino Southern Oscillation (ENSO), with more rain and flooding during El Nino and droughts in La Nina 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.},
  language  = {en}
}
@article{WolffKristenJennySchettleretal.2014,
  author    = {Wolff, Christian Michael and Kristen-Jenny, Iris and Schettler, Georg and Plessen, Birgit and Meyer, Hanno and Dulski, Peter and Naumann, Rudolf and Brauer, Achim and Verschuren, Dirk and Haug, Gerald H.},
  title     = {Modern seasonality in Lake Challa (Kenya/Tanzania) and its sedimentary documentation in recent lake sediments},
  series = {Limnology and oceanography},
  volume    = {59},
  journal   = {Limnology and oceanography},
  number    = {5},
  publisher = {Wiley},
  address   = {Waco},
  issn      = {0024-3590},
  doi       = {10.4319/lo.2014.59.5.1621},
  pages     = {1621 -- 1636},
  year      = {2014},
  abstract  = {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 Nino-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.},
  language  = {en}
}