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A multiproxy oxygen and carbon isotope (δ13C and δ18O), growth rate, and trace element stalagmite paleoenvironmental record is presented for the Early Holocene from Ethiopia. The annually laminated stalagmite grew from 10.6 to 10.4 ka and from 9.7 to 9.0 ka with a short hiatus at ~9.25 ka. Statistically significant and coherent spectral frequencies in δ13C and δ18O are observed at 15-25 and 19-23 years, respectively. The observed ~1‰amplitude variability in stalagmite δ18O is likely forced by nonequilibrium deposition, due to kinetic effects during the progressive degassing of CO2 from the water film during stalagmite formation. These frequencies are similar to the periodicity reported for other Holocene stalagmite records from Ethiopia, suggesting that multidecadal variability in stalagmite δ18O is typical. Several processes can lead to this multidecadal variability and operate in different directions. A hydroclimate forcing is likely the primary control on the extent of the partial evaporation of soil and shallow epikarst water and associated isotopic fractionation. The resulting oxygen isotope composition of percolation water is subsequently modulated by karst hydrology. Further isotopic fractionation is possible in-cave during nonequilibrium stalagmite deposition. Combined with possible recharge biases in drip-water δ18O, these processes can generate multidecadal δ18O variability. [ABSTRACT FROM AUTHOR]

Paleoanthropologists have long speculated about the role of environmental change in shaping human evolution in Africa. In recent years, drill cores of late Neogene lacustrine sedimentary rocks have yielded valuable high-resolution records of climatic and ecosystem change. Eastern African Rift sediments (primarily lake beds) provide an extraordinary range of data in close proximity to important fossil hominin and archaeological sites, allowing critical study of hypotheses that connect environmental history and hominin evolution. We review recent drill-core studies spanning the Plio–Pleistocene boundary (an interval of hominin diversification, including the earliest members of our genus Homo and the oldest stone tools), and the Mid–Upper Pleistocene (spanning the origin of Homo sapiens in Africa and our early technological and dispersal history). Proposed drilling of Africa's oldest lakes promises to extend such records back to the late Miocene. High-resolution paleoenvironmental records are critical for understanding external drivers of human evolution. African lake basin drill cores play a critical role in enhancing hominin paleoenvironmental records given their continuity and proximity to key paleoanthropological sites. The oldest African lakes have the potential to reveal a comprehensive paleoenvironmental context for the entire late Neogene history of hominin evolution. [ABSTRACT FROM AUTHOR]

We introduce a new method to compute plant distribution in Ethiopia under paleoclimatic conditions using fuzzy logic. Using a published map of the potential vegetation for Ethiopia we decipher the boundary conditions for the main vegetation units shown, reflecting modern climatic conditions for temperature and precipitation in this region. Fuzzy logic using these climatic values on a GIS platform then derived the computational map of the potential vegetation. Comparing it with the original map shows a general correspondence of about 90%. By changing the underlying climate parameters, we then used this model for hypothetical paleoclimatic conditions to simulate the vegetational response on these changed climate settings. Finally, vegetational response maps for Ethiopia are presented for two scenarios: (i) a colder and drier condition (such as the Last Glacial Maximum) and (ii) a warmer and wetter condition (such as the last interglacial) than today. [ABSTRACT FROM AUTHOR]

Annually laminated speleothems have the potential to provide information on high‐frequency climate variability and, simultaneously, provide good chronological constraints. However, there are distinct types of speleothem annual laminae, from physical to chemical, and a common mechanism that links their formation has yet to be found. Here, we analyzed annually laminated stalagmites from 23 caves and 6 continents with the aim to find if there are common mechanisms underlying their development. Annually laminated stalagmites are least common in arid and semiarid climates, and most common in regions with a seasonality of precipitation. At a global scale, we observe faster growth rates with increasing mean annual temperature and decreasing latitude. Changepoints in average growth rates are infrequent and age‐depth relationships demonstrate that growth rates can be approximated to be constant. In general, annually laminated stalagmites are characterized by centennial‐scale stability in calcite precipitation due to a sufficiently large and well‐mixed water source, a time series spectrum showing first‐order autoregression due to mixing of stored water and annual recharged water, and an inter‐annual flickering of growth acceleration, bringing growth rates back to the long‐term mean. Climate forcing of growth rate variations is observed where a multi‐year climate signal is strong enough to be the dominant control on calcite growth rate variability, such that it retains a climate imprint after smoothing of this signal by mixing of stored water. In contrast, long‐term constant growth rate of laminated stalagmites adds further robustness to their unparalleled capacity to improve accuracy of chronology building. Plain Language Summary: Growth layers, or laminae, are found in many biological and geological records. Stalagmites, mineral precipitates found in caves, can contain annual laminae. Stalagmites grow upwards from water which drips onto them from overlying fractures and voids. For annually laminated stalagmites, it is not known where and for how long they form, and why. Here, we review and statistically analyze a global data set of laminated stalagmites. They are less common in water‐limited climates and are only found in regions with seasonal precipitation. The annual average laminated stalagmite vertical growth is 0.093 mm, increasing with warmer temperatures. Stalagmite accumulation rate is relatively unchanging over time. This is because their drip water source has enough volume and a stable chemical composition to be a buffer to rapid changes. Year‐to‐year, we see a "flickering," where accumulation rate returns toward the long‐term average, also due to this buffering effect. For an environmental signal to be preserved in stalagmite laminae thickness requires a large perturbation, such as wet or dry years associated with the El Niño‐Southern Oscillation, that can override the buffering of the overlying water source. The long‐term constant growth rate of laminated stalagmites provides an unparalleled capacity for precise chronology building. Key Points: Laminated stalagmites are characterized by centennial‐scale stability in accumulation rateStrong multi‐year climate signals may retain an imprint in annual growth rate after smoothing of this signal by mixing with stored waterLong‐term constant growth rate of laminated stalagmites benefits accurate chronology building [ABSTRACT FROM AUTHOR]

Abstract Oxygen and carbon (δ18Ο/δ13C) isotope, growth rate and trace element data are reported for a U-Th dated, annually-laminated stalagmite, GM1 from Goda Mea Cave, Ethiopia. The stalagmite grew intermittently around the last interglacial. The proxy records are used to develop a conceptual growth model of the stalagmite and to assess its potential for revealing a climate signal in this climatically sensitive northeastern African region during an important period in the evolution of Homo sapiens and dispersal of Anatomically Modern Humans out of Africa. Speleothem deposition is of short-duration occurring at ∼129 ka, ∼120 ka, in an undated growth phase, and at ∼108 ka; probably due to tectonic activity. δ18Ο composition is very stable within growth phases (1σ variability < 0.76‰), as are Mg/Ca, Sr/Ca and Ba/Ca, all indicative of well-mixed source-waters. A shift to positive δ18Ο values and increased variability in Mg/Ca, Sr/Ca and Ba/Ca prior to growth hiatuses is observed, indicating a loss of the well-mixed water source prior to growth cessation. Mean δ18Ο composition (−3.82 to −7.77‰) is lower than published modern and Holocene stalagmites from the region. Geochemical data, statistical analyses, and a conceptual model of stalagmite growth, demonstrate that climatic conditions recorded by GM1 were wetter than the Holocene. The ∼129 ka growth phase particularly presents an annual record of the relative Intertropical Convergence Zone (ITCZ) position. The GM1 record, the oldest high-resolution continental climate record from Ethiopia so far published, presents evidence that any early human migrations which occurred during MIS 5 are likely to have occurred during a wet event in northeast Africa. Highlights • Stalagmite GM1 discontinuously deposited at ∼129 ka, 120 ka, an undated growth phase, and ∼108 ka. • Multi-proxy analysis necessary to identify climatic from karstic signal. • Low δ18O at ∼129 ka and ∼108 ka attributed to wetter climatic conditions. • The first annually-resolved stalagmite record of the last interglacial from Ethiopia. • The earliest Modern Human dispersal out of Africa occurred during humid climate conditions. [ABSTRACT FROM AUTHOR]

Our understanding of the impact of climate-driven environmental change on prehistoric human populations is hampered by the scarcity of continuous paleoenvironmental records in the vicinity of archaeological sites. Here we compare a continuous paleoclimatic record of the last 20 ka before present from the Chew Bahir basin, southwest Ethiopia, with the available archaeological record of human presence in the region. The correlation of this record with orbitally-driven insolation variations suggests a complex nonlinear response of the environment to climate forcing, reflected in several long-term and short-term transitions between wet and dry conditions, resulting in abrupt changes between favorable and unfavorable living conditions for humans. Correlating the archaeological record in the surrounding region of the Chew Bahir basin, presumably including montane and lake-marginal refugia for human populations, with our climate record suggests a complex interplay between humans and their environment during the last 20 ka. The result may contribute to our understanding of how a dynamic environment may have impacted the adaptation and dispersal of early humans in eastern Africa. [ABSTRACT FROM AUTHOR]