Soil formation occurs through numerous physical and chemical weathering processes acting to alter the parent rock on the Earth's surface. Samples of surface soils were collected over a range of elevations (2000-3600 m) from profiles directly overlying basaltic to more felsic parent rocks, over a region in NW Ethiopia. The soils were investigated to determine their chemical composition and X-ray diffraction was used to identify and quantify individual mineral phases. The data set was analyzed using non-parametric statistics (Spearman's Rank and Mann-Whitney U tests) to compare the soils forming over the two parent rocks. Principal component analysis (PCA) was used to identify the mineral alteration assemblage and formation during pedogenesis. The extent of alteration was quantified using several chemical weathering indices (Chemical Index of Alteration = CIA; Chemical Index of Weathering = CIW), including an index calculated by multivariate analyses of the soil chemical composition data (weathering "W" index). Further to this we devised and tested a new weathering index (W-min) using multivariate analysis of the soil mineralogy, to estimate the extent of weathering and physico-chemical proprieties of the parent rock from which the soil formed.The soils present a fair to advanced stage of alteration, with abundant iron (Fe) oxides (up to 40 wt%) and phyllosilicates (up to 57 wt%), including kaolinite-smectite (K-S) mixed-layer phases. The K-S was composed of either 30-50% kaolinite or 94-98% kaolinite layers. Discrete kaolinite was also present. The bimodal K-S mineralogical composition is likely due to two precursor phases: feldspar for the kaolinite-rich K-S and volcanic glass for the smectite-rich K-S. K-S with intermediate composition (50-94% kaolinite) was rare, due to its instability. Statistical analysis showed significant differences between the chemical compositions of the soils developed on the two different parent volcanic compositions. The soils overlying the more felsic parent rocks were less altered than those overlying the flood basalt. When comparing the weathering indices calculated in this study, we conclude that while the CIA and CIW may be more readily determined, the W and W-min indices can elucidate information on the composition of the original rock from which they formed. The W index is more sensitive to certain variables when compared with the newly derived mineralogical if index; however the W-min, index takes into account mineral phases within the sample, which provides a more detailed interpretation of weathering rates than chemistry alone. In addition the W-min, index correlated with meteorological variables, such as elevation (and consequently temperature and precipitation), known to influence the degree of pedogenesis. The W-min index can be used to enhance our understanding of the processes that occur during weathering processes to supplement information gained from traditional chemical weathering indices.

Understanding social-ecological system dynamics is a major research priority for sustainable management of landscapes, ecosystems and resources. But the lack of multi-decadal records represents an important gap in information that hinders the development of the research agenda. Without improved information on the long-term and complex interactions between causal factors and responses, it will be difficult to answer key questions about trends, rates of change, tipping points, safe operating spaces and pre-impact conditions. Where available long-term monitored records are too short or lacking, palaeoenvironmental sciences may provide continuous multi-decadal records for an array of ecosystem states, processes and services. Combining these records with conventional sources of historical information from instrumental monitoring records, official statistics and enumerations, remote sensing, archival documents, cartography and archaeology produces an evolutionary framework for reconstructing integrated regional histories. We demonstrate the integrated approach with published case studies from Australia, China, Europe and North America.

A growing number of proxy, historical and instrumental data sets are now available from continental Africa through which past variations in temperature can be assessed. This paper, co-authored by members of the PAGES Africa2k Working Group, synthesises published material to produce a record of temperature variability for Africa as a whole spanning the last 2000 years. The paper focuses on temperature variability during the ‘Medieval Climate Anomaly’ (MCA), ‘Little Ice Age’ (LIA) and late 19th–early 21st centuries. Warmer conditions during the MCA are evident in records from Lake Tanganyika in central Africa, the Ethiopian Highlands in northeastern Africa, and Cango Cave, the Kuiseb River and Wonderkrater in southern Africa. Other records covering the MCA give ambiguous signals. Warming appears to have been greater during the early MCA (c. ad 1000) in parts of southern Africa and during the later MCA (from ad 1100) in Namibia, Ethiopia and at Lake Tanganyika. LIA cooling is evident in Ethiopian and southern African pollen records and in organic biomarker data from Lake Malawi in southeastern tropical Africa, while at Lake Tanganyika the temperature depression appears to have been less consistent. A warming trend in mean annual temperatures is clearly evident from historical and instrumental data covering the late 19th to early 21st centuries. General warming has occurred over Africa since the 1880s punctuated only by a period of cooling in the mid 20th century. The rate of temperature increase appears to have accelerated towards the end of the 20th century. The few long high-resolution proxy records that extend into the late 20th century indicate that average annual temperatures were 1–2°C higher in the last few decades than during the MCA.

East African paleoenvironments are highly variable, marked by extreme fluctuations in moisture availability, which has far-reaching implications for the origin, evolution and dispersal of Homo sapiens in and beyond the region. This paper presents results from a pilot core from the Chew Bahir basin in southern Ethiopia that records the climatic history of the past 45 ka, with emphasis on the African Humid Period (AHP, similar to 15-5 ka calBP). Geochemical, physical and biological indicators show that Chew Bahir responded to climatic fluctuations on millennial to centennial timescales, and to the precessional cycle, since the Last Glacial Maximum. Potassium content of the sediment appears to be a reliable proxy for aridity, showing that Chew Bahir reacted to the insolation-controlled humidity increase of the AHP with a remarkably abrupt onset and a gradual termination, framing a sharply defined arid phase (similar to 12.8-11.6 ka calBP) corresponding to the Younger Dryas chronozone. The Chew Bahir record correlates well with low- and high-latitude paleoclimate records, demonstrating that the site responded to regional and global climate changes. (C) 2012 Elsevier Ltd and INQUA. All rights reserved.

Magnetic and geochemical core data spanning the last 17,000years are correlated with new seismic stratigraphy from Lake Tana, Ethiopia, to infer past lake-level change and hence effective precipitation. The data confirm that low lake-level coincides with Heinrich Event 1 (H1) in the North Atlantic, as previously shown from diatom and pollen evidence (Lamb et al., 2007). The lake deepened at 15.3calkyr BP and abruptly returned to freshwater conditions, when the lake overflowed into the Blue Nile. Low runoff and lake levels and therefore rainfall are inferred between 13.0 and 12.5calkyr BP and may represent southerly suppression of the ITCZ and the associated monsoon front at the time of the Younger Dryas. Two drought episodes occurred at 8.4 and 7.5calkyr BP, and are also interpreted as a southward shift in the monsoon front. The first of these events appears to have preceded and been more significant than the 8.2calkyr BP. Precipitation declined after 6.8calkyr BP, although we do not see an abrupt end to the African Humid Period. This period culminated in a dry episode at ~4.2calkyr BP, supporting the view that reduced Nile flow was a contributing factor to the demise of the Egyptian Old Kingdom.

Introduction Based on the 2007 census conducted by the Central Statistical Agency of Ethiopia (CSA, 2008), the Tigray Region has an estimated total population of 4,314,456; among which 19.5% are urban inhabitants. The region is primarily agricultural and the majority of the population is employed in this sector. Agriculture is dependent on unreliable rainfall. Livestock play an important role in the rural economy of Tigray. They are sources of draft power for tillage and transportation, cash income from sale of livestock and livestock products, food such as milk for household consumption and manure to maintain soil fertility. Tigray has 47 districts (woredas) and among them, Degua Temben is one, which has a relatively cool temperature. Hagere Selam is the capital of the Degua Temben District, where all the district offices are located.

The Tigray Plateau of Ethiopia and Eritrea is vulnerable to environmental change, yet environmental influences on the rise and fall of the civilizations that once existed there are almost unexplored. We sampled sections of gully walls for palaeoenvironmental proxies from two sites: 1) Adi Kolen on the southern outskirts of the Plateau's most developed former empire, the Aksumite, and 2) Adigrat near polities dating to at least ca. 3000cal yr BP. A multi-proxy approach for examining local variation in palaeoenvironments was evaluated that included stable isotopic and elemental analyses (δ13CSOM, δ15N, %TOC, and %TN) of soil, and charcoal identification. An increase in δ15N values from older soils in Adi Kolen (4400cal yr BP) and Adigrat (2900cal yr BP) until 1200cal yr BP is not explained by changes in δ15N that occur with time in an unchanging environment. It may instead indicate an overall decrease in rainfall from the earlier times until 1200cal yr BP. In one Adigrat section, the decreases in organic δ13C and increases in C/N molar ratios from older to younger soil could have resulted from changes that occur over time, per se. In the remaining sections, however, δ13CSOM trends more likely reflect changes in the biomass of C4 relative to C3 plants (% C4 biomass). Changes in% C4 biomass may reflect climate and/or land use. Deciphering which may be aided by analyses of the other proxies. Identified charcoal suggests that both sites supported some juniper forest types until very recently but that forests may have been a more important and dynamic component of Adigrat's vegetation history than Adi Kolen's. If environment affected the trajectories of the kingdoms of the Tigray Plateau, these results suggest that the exact nature of the changes in climate differed among kingdoms. The kingdoms prior to 1200cal yr BP may have been exposed to increasing aridity punctuated with relatively wetter intervals. Thereafter, general changes in climate are not apparent. Land clearing dynamics are likely to have had a more consistent effect on the trajectories of kingdoms than climate changes.

Bush encroachment is a significant phenomenon in savanna environments as it affects wildlife and local livelihoods by preventing new pasture generation. In this article we present a 2000-year record of vegetation change in the Dara range of the Mago National Park, southwestern Ethiopia, an area inhabited by Mursi agro-pastoralists. We use an interdisciplinary approach to understand whether bush encroachment in this area is a recent event or a transitional state of the savanna and describe the local understanding of encroachment as a species-specific process. The vegetation record was obtained from a fossil hyrax midden, a type of sediment already used in Southern Africa but never before in East Africa. Six encroaching phases, led by Capparaceae and Grewia, were found over the last two millennia. The system proved to be resilient, with alternating open and encroached phases, and showed a non-linear response to environmental change, thereby fitting the control theory hypothesis for hysteresis loops. Determining the thresholds conditioning the system's resilience could help to improve savanna management for both local people and National Park authorities.

Landslide hazard is one of the crucial environmental constraints for the development of Ethiopia, representing a limiting factor for urbanization and infrastructures. The high relief and the rugged topography induced by a strong Plio-Quaternary uplift, the occurrence of clayey horizons within the sedimentary sequences, the dense network of tectonic fractures and faults, the thick eluvial mantles on volcanic outcrops, and the thick colluvial–alluvial deposits at the foot of steep slopes are the predisposing factors for a large variety of mass movements. Heavy summer rainfall is the main triggering factor of most landslides, some of which undergo a step-like evolution with long-lasting quiescence intervals. First generation movements are commonly restricted to shallow phenomena, such as soil slips or mud flows in eluvial–colluvial material. Fast moving slope failures, such as rock slides, topplings and falls, are also triggered by earthquakes. To mitigate the landslide risk, any first priority measure should include adequate drainage of slopes in order to reduce water infiltration. On the other hand, appropriate site selection for buildings, transferring risky settlements, accurate geological control of works, and education campaigns are all strongly recommended.

Lake Ashenge, a closed-basin lake near the northernmost penetration of summer monsoon rains, is well placed to provide a continental record of past changes in the strength of the African monsoon system. Diatom and oxygen isotope analyses of the lake sediments confirm that the overall trend of climate change during the past 17,000 years was driven by precessional forcing, punctuated by abrupt shifts that may be linked to changes in Atlantic surface temperatures. The lake level was low from at least 17.2 to 16.2 cal kyr BP, and then rose between 16.2 and 15.2 cal kyr BP, which may represent a temporary reactivation of the monsoonal circulation system following its reduced activity during the Last Glacial Maximum. The lake was significantly low between 13.6 and similar to 11.8 cal kyr BP coinciding approximately with the Younger Dryas, but beginning 900 years before its recognised onset in the Greenland ice-core record. A major sedimentary hiatus, covering the interval 11.8 to 7.6 cal kyr BP, was probably caused by an early Holocene lowstand, the precise timing of which cannot be determined because pre-lowstand sediments were eroded from the core site. The lake filled to its overflow from 7.6 cal kyr BP until 5.6 cal kyr BR when the sediments record an abrupt lake response to the regional transition to and conditions that mark the end of African Humid Period. Evidence is also presented for climate changes which may have been associated with the rise and fall of Aksum. Ethiopia's first great civilisation. (C) 2009 Elsevier B.V. All rights reserved.

No abstract available. doi:10.2204/iodp.sd.8.10.2009

A long history of supporting sophisticated but unsustainable kingdoms make,, the Tigray Plateau of the northern Ethiopian highlands a promising region for the study of relationships between palaeoenvironmental change and the trajectories of human civilizations. The natural vegetation above 2200 m elevation is thought to be forests dominated by Juniperus procera. Nonetheless, this hypothesis is not supported in the vegetation cover now and is scarcely studied in the palaeorecord. To examine changes in vegetation, climate, and land use, we identified buried charcoalized wood and estimated the percentage of organic carbon from C-4 plants (%C-4 carbon) from delta C-13 values of bulk organic matter in the soils of gully walls in the boundaries of the ancient Aksumite Empire Charcoal ranged in age from ca. 13.700 to 110 cal yr BP. Juniperus procera occurred in even the youngest samples, although at lower percentages of the total charcoal than in older samples Nevertheless, rapidly regenerating angiosperms usually dominated or co-dominated charcoal even in some of the oldest strata A shift towards higher% C-4 carbon and % total organic carbon (%TOC) in soils younger than 3300 cal yr BP began during a period when agricultural uses of land may have increased in order to support the needs of growing societies A shift towards higher % C4 carbon but lower %TOC began at ca. 6000 cal yr BP. however, during a period when no charcoal was found and no changes in human societal complexity are known. These results indicate that jumper forest types have long been present at >2200 m in the Tigray Plateau but that they have rarely been the dominant natural vegetation. Furthermore. lack of repeatable correspondence between factors suggests that the causes of similar shifts in vegetation composition were not always the same (C) 2009 Elsevier B V All rights reserved

How did environmental history, particularly climate, affect the evolution of our hominin ancestors and closely related species? The formulation of testable hypotheses about the climate‐evolution connection is impeded by limited numbers of hominin specimens and the geographic and temporal gaps that characterize their fossil record. Additionally, knowledge of Earth's environmental history close to these fossil finds remains limited. Scientists interested in the problem currently make use of temporally and geographically discontinuous outcrop exposures at the fossil sites, and/or deep‐sea or lake paleoclimate records geographically distant from the hominin fossils, to address the Earth history side of this equation.

We investigated genetic variation of 273 individuals from 25 populations of the monotypic species Hagenia abyssinica (Rosaceae) from the highlands of Ethiopia at three chloroplast microsatellite loci. The objectives were to infer the factors that shaped the genetic structure and to reconstruct the recolonization history of the species. Six haplotypes that were phylogenetically grouped into two lineages were identified. Homology of the three loci to the respective regions of the chloroplast genome was confirmed by sequencing. The chloroplast haplotypes found in Hagenia showed a clear pattern of congruence between their geographical distribution and genealogical relationships. A very low haplotype diversity within populations ( h S = 0.079, v S = 0.058) and a very high population differentiation ( G ST = 0.899, N ST = 0.926) was observed, reflecting very low mixing between recolonizing lineages. Restricted gene flow through seeds, rare long-distance dispersal, contiguous range expansion and mutation shaped the genetic structure of Hagenia . Fossil pollen records suggested that the trend of postglacial recolonization of Hagenia was first in the south and latter went to the north in Ethiopia.