The ACER pollen and charcoal database: a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard–Oeschger (D–O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D–O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73–15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U∕230Th, optically stimulated luminescence (OSL), 40Ar∕39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft AccessTM at https://doi.org/10.1594/PANGAEA.870867

The ACER pollen and charcoal database: A global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

This is the final version of the article. Available from Copernicus Publications via the DOI in this record.Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard-Oeschger (D-O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D-O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73-15ka) with a temporal resolution better than 1000years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U/230Th, optically stimulated luminescence (OSL), 40Ar/39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft Access™ at https://doi.org/10.1594/PANGAEA.870867.The members of the ACER project wish to thank the QUEST-DESIRE (UK and France) bilateral project, the INQUA International Focus Group ACER and the INTIMATE-COST action for funding a suite of workshops to compile the ACER pollen and charcoal database and the workshop on ACER chronology that allow setting the basis for harmonizing the chronologies. Josué M. Polanco-Martinez was funded by a Basque Government postdoctoral fellowship (POS_2015_1_0006) and Sandy P. Harrison by the ERC Advanced Grant GC2.0: unlocking the past for a clearer future

The Hominin Sites and Paleolakes Drilling Project:Inferring the environmental context of human evolution from eastern African rift lake deposits

Funding for the HSPDP has been provided by ICDP, NSF (grants EAR-1123942, BCS-1241859, and EAR-1338553), NERC (grant NE/K014560/1), DFG priority program SPP 1006, DFG-CRC-806 “Our way to Europe”, the University of Cologne (Germany), the Hong Kong Research Grants Council (grant no. HKBU201912), the Peter Buck Fund for Human Origins Research (Smithsonian), the William H. Donner Foundation, the Ruth and Vernon Taylor Foundation, Whitney and Betty MacMillan, and the Smithsonian’s Human Origins Program.The role that climate and environmental history may have played in influencing human evolution has been the focus of considerable interest and controversy among paleoanthropologists for decades. Prior attempts to understand the environmental history side of this equation have centered around the study of outcrop sediments and fossils adjacent to where fossil hominins (ancestors or close relatives of modern humans) are found, or from the study of deep sea drill cores. However, outcrop sediments are often highly weathered and thus are unsuitable for some types of paleoclimatic records, and deep sea core records come from long distances away from the actual fossil and stone tool remains. The Hominin Sites and Paleolakes Drilling Project (HSPDP) was developed to address these issues. The project has focused its efforts on the eastern African Rift Valley, where much of the evidence for early hominins has been recovered. We have collected about 2 km of sediment drill core from six basins in Kenya and Ethiopia, in lake deposits immediately adjacent to important fossil hominin and archaeological sites. Collectively these cores cover in time many of the key transitions and critical intervals in human evolutionary history over the last 4 Ma, such as the earliest stone tools, the origin of our own genus Homo, and the earliest anatomically modern Homo sapiens. Here we document the initial field, physical property, and core description results of the 2012–2014 HSPDP coring campaign.Publisher PDFPeer reviewe

Lithological and topographic impact on soil nutrient distributions in tectonic landscapes: implications for Pleistocene human-landscape interactions in the southern Kenya Rift

International audienceTectonically active regions are characterized by complex landscapes comprising soils with heterogeneous physicochemical properties. Spatial variability of nutrient sources enhances landscape biodiversity and creates heterogeneous habitats potentially attractive for animals and humans. In this study, we analyze the role of geological processes in the distributions of soil nutrients in the southern Kenya Rift, a key region in the interpretation of early human-landscape interactions. Our aim is to determine how spatial variations in rock chemistry, as well as topographic gradients and localized zones of rock fracturing from tectonic faulting determine the distributions of plant-available soil nutrients in soils. We hypothesize that present-day soil nutrient levels reflect the long-term chemical and geomorphological characteristics of the landscape and underlying parent material, and that regions with high nutrient availability occur along pathways correlating with locations of hominin fossil sites. Analyses of 91 topsoil samples from the main geological units show that Calcium (Ca) deficiencies predominately occur in shallow soils developed on trachytic volcanic rocks and granitic gneisses, while high Ca levels are associated with basaltic parent material and sedimentary deposits of mixed sources. XRF analysis of rock samples confirms that CaO levels in trachyte rocks are significantly lower than those in basalts, and Ca mobilization in basalt is more effective than in trachyte. Along two toposequences in densely faulted basaltic and trachytic rocks, we observed slope dependent soil nutritional gradients and a systematic increase of the concentrations of Ca, Mg and SOC in topsoils of colluvial sediments downslope of active normal faults. Known hominin sites in the region are located either along corridors of long-term Ca availability or at short-term nutrient hotspots potentially related to active CO2 degassing along active fault zones. This implies a strategic advantage of Ca-rich regions for hominin subsistence strategies, such as provision of predictable constraints on the distribution and mobility of grazing animals in complex tectonic landscapes. Our study implies that geological processes impact nutrient distributions in the southern Kenya Rift. Results of this study have further implications for understanding the role of soils in the interpretation of hominin-landscape interactions in the early stages of human evolution

At the heart of the African Acheulean: the physical, social and cognitive landscapes of Kilombe

Kilombe is known as an extensive late Lower Pleistocene Acheulean site complex in the Rift Valley in Kenya. We report here on recent research which has explored a longer stratigraphic succession around the sites, casting light on landscape development and occupation through much of the last million years. With its position near the Equator the site complex is close to the geographic and chronological heart of the Acheulean, and ideally suited to investigations, because of the extent of preservation of ancient landscape, and the potential for dating and recovery of environmental information The new surveys have concentrated on studying the site area in its local setting near the foot of Kilombe volcano, which became extinct in the early Pleistocene, and formerly held a crater lake, currently under investigation. In 2011, bifaces were also found at the mouth of the volcano gorge. Events on the Acheulean main site terminated with a volcanic eruption which deposited the 3-banded tuff (3BT), now dated to ca. 990,000 years, but the sequence continues above this level, and is capped locally by an ashflow tuff (AFT) some 7 metres thick, the product of a landscape-transforming eruption probably deriving from an ancestor of the present day Menengai. To the east and west, the sequence then resumes with major exposures of tuffaceous sediments belonging to the Middle and Upper Pleistocene, and containing Middle Stone Age and Later Stone Age artefacts. These provide the chance to study newer landscapes within the same catchment. The Kilombe main site permits very rare opportunities to compare large numbers of bifaces and other artefacts which are of the same age across a distance of around 200 metres, and so build up a picture of local variability within a site complex. The site area allows comparisons – within the complex to explore its structure of variation, on a regional scale of site catchment, and then externally to help evaluate issues across the greater Acheulean world and through the Middle Stone Age. Although the development of the MSA can be seen only sketchily at present, the preservation of both contexts and artefacts demonstrates the potential to elaborate a longer record

Diversity and ecology of tropical African fungal spores from a 25,000-year palaeoenvironmental record in southeastern Kenya

Fossil fungal spores and other non-pollen palynomorphs (NPPs) are powerful environmental proxies in European palaeoecological and archaeological contexts. However, their application on other continents, and particularly in the tropics, is hampered by uncertain equivalence with morphologically similar taxa in Europe, and incomplete knowledge of their ecology in the new local contexts. Here we use fossil NPP assemblages in a 25,000-year sediment record from Lake Challa, a steep-sided crater lake near Mt. Kilimanjaro in southeasternKenya, to assess NPP diversity in atropical-African context and the equivalence of African taxa with their European counterparts. We recovered a total of 65 well-defined NPP types, of which 61 are fungal spores, and 42 could be linked to known taxa. We provide diagnoses and illustrations of 61 recovered taxa, 58 of which have not been documented before. Using the Challa pollen record of past regional vegetation dynamics and two independent proxies of past temperature and rainfall, we also assessed the association of individual fungal taxa with particular species and biomes of tropical-African vegetation, and with the history of regional climate change. We often found strong correspondence between the stratigraphic distribution of individual fungal spore taxa and the occurrence of specific vegetation types. Changing climate conditions appear to have had a strong impact on the ability of fungi to play a role in the decomposition of dead plants. For fungal spore assemblages, the most prominent change in regional palaeoenvironments over the past 25,000 years occurred at the start of the wet early Holocene, following Younger Dryas drought. Epicoccum purpurascens is common in the Glacial and Late-Glacial parts of the sequence, but shows a strong decline during the early Holocene. Coniochaeta cf. ligniaria occurs throughout the record but shows dramatic fluctuations that appear to relate to major changes in humidity. Correlation between fungal abundance and humidity is also observed in taxa for which the Challa region provided suitable habitat from ca. 16,500 cal. yr BP (e.g., Curvularia) or from the Late-Glacial to Holocene transition (e.g., Tetraploa aristata, Dictyoarthrinium cf. sacchari, cf. Byssothecium, types HdV-1032 and HdV-1033, cf. Alternaria, cf. Brachysporium, cf. Helminthosporium, Spegazzinia tessarthra and cf. Lasiodiplodia theobromae). Many of these taxa did not occur, or were rare, during both wet and dry phases of the Glacial period, suggesting an additional temperature effect on their occurrence in tropical African environments. A possibly dominant role of temperature is revealed in the stratigraphic distribution of Acrodictys, which appears at the onset of deglacial climate warming ca. 17,500 cal. yr BP and remains common throughout both wet and dry phases of the Holocene. Spores of the dung-inhabiting fungus Sporormiella occur throughout the 25,000-year record without notable fluctuations, suggesting little changes in the overall population density of large herbivores in the region

Half-precessional dynamics of monsoon rainfall near the East African equator: Implications for Indian Ocean ITCZ migration over the past 25,000 years

We present a detailed reconstruction of hydrological changes near the equator in East Africa from before the LGM to the present, using proxies extracted from the sediment record of Lake Challa on the lower east slope of Mt. Kilimanjaro (3° S, 36° E). Our results show that monsoon rainfall in this region varied at half-precessional (~11,500-year) intervals, because the southeasterly and northeasterly Indian Ocean monsoons, which together create the bimodal seasonal distribution of equatorial rainfall, were strengthened in alternation when the inter-hemispheric insolation gradient was maximized. Dry conditions prevailed when neither monsoon was particularly strong, and minima in local March or September insolation weakened the rain season that followed. The distinct timing of late-glacial drought on the equator (20.5-16.5 ka BP) does not fit well with NH glaciation being its primary driver. It is best attributed to partial failure of the short rain season due to modest local September insolation, perhaps exacerbated by the southeasterly monsoon being weakened by northern cooling still affecting the North African land mass. Our data further highlight that orbital-scale ITCZ ‘migration’, or shifts in its mean annual latitudinal position, mainly relates to variation in how far the ITCZ is displaced into the NH or SH during summer and winter; the cross-equatorial position of the East African region with twice-annual ITCZ passage is not much affected. On (sub)millennial time scales the temporal pattern of hydrological change on the East African equator bears clear signatures of northern high-latitude climate variability, but on the orbital time scale it mainly responded to low-latitude insolation forcing. Important keys to this history are the low-latitude position of its continental regions of convergence and its relative isolation from the Atlantic Ocean domain, where strong meridional overturning circulation more tightly coupled tropical climate regimes to high-latitude climate dynamics