Ecological training set of freshwater ostracods in Canadian and Siberian periglacial regions

Quantified palaeoenvironmental reconstructions are essential to estimate the impact of future climate changes on ecosystems. Based on faunistic data from regional multireference sites and limnological surveys, ecological training sets can be used to build transfer functions to infer major environmental variables (e.g., temperature, conductivity, DOC, and pH value) in a greater study area. The remote Polar regions are affected by bigger amplitude of climate change than elsewhere on this planet and make ecological training sets in this region so important.Freshwater ostracods from Arctic nvironments have the potential to hindcast glacial/interglacial and stadial/interstadial alaeoclimate variations. Various methods can be applied to fossil assemblages such as indicator species approach, modern analoguetechniques and transfer functions based on ecological training sets.The present training set combines data from the Canadian (Southampton Island at 63-65°N; Bylot Island at 72-73°N) and the Siberian (Central Yakutia at 61°N; Northeast Yakutia at 66°N; Lena Delta at 72°N) high latitudes with reference areas in Central Canada (Whapmagoostui-Kuujjuarapik at 50-55°N; Churchill at 58°N). A total of 75 localities were sampled during field work in 2005-2007. In general, life conditions for aquatic organisms such as freshwater ostracods in the high latitude regions are extremeand limited by short open water periods during the summer and strong variations of water temperatures in the shallow waters. The host waters in periglacial regions are affected by permafrost and thermokarst processes and mostly represented as polygonal ponds or thermokarst lakes in different stages of their development. Generally, the waters in our study area have a mean pH-value of 7.6, ranging from pH 6.0 to pH 9.2. They are characterised by low ionic contents (Condmean = 231μS*cm−1), but the training set includes sites between 4.4 μS*cm−1 (e.g., on Bylot Island) and 1433 μS*cm−1 (e.g., in Central Yakutia). A principal component analysis reveals that 88.5 % of the variability of the environmental data is explained by the first ordination axis corresponding to pH, conductivity and major cations (i.e., Ca, Na). The studied ostracod assemblages are characterised by dominance of single species indifferent regions, e.g., Cyclocypris ovum on Bylot Island, Fabaeformiscandona pedata in the Lena Delta. In general, the species diversity in northern latitudes is relatively low due to the harsh environmental conditions affecting ostracods ontogeny. In total, 16 species were used in the presented data set.Further implementation of the ecological training set into transfer functions for one or more variables are prosperous

Ostracods as ecological and isotopic indicators of lake water salinity changes: the Lake Van example

Ostracods are common lacustrine calcitic microfossils. Their faunal assemblage and morphological characteristics are important ecological proxies, and their valves are archives of geochemical information related to palaeoclimatic and palaeohydrological changes. In an attempt to assess ostracod ecology (taxonomic diversity and valve morphology) combined with valve geochemistry (δ18O and δ13C) as palaeosalinity indicators, we analysed sedimentary material from the International Continental Scientific Drilling Program (ICDP) Ahlat Ridge site from a terminal and alkaline lake, Lake Van (Turkey), covering the last 150&thinsp;kyr. Despite a low species diversity, the ostracod faunal assemblage reacted sensitively to changes in the concentration of total dissolved salts in their aquatic environment. Limnocythere inopinata is present throughout the studied interval, while Limnocythere sp. A is restricted to the Last Glacial period and related to increased lake water salinity and alkalinity. The presence of species belonging to the genus Candona is limited to periods of lower salinity. Valves of Limnocytherinae species (incl. L. inopinata) display nodes (hollow protrusions) during intervals of increased salinity. Both the number of noded valves and the number of nodes per valve appear to increase with rising salinity, suggesting that node formation is related to hydrological changes (salinity and/or alkalinity). In contrast to Lake Van's bulk δ18O record, the δ18O values of ostracod valves do record relative changes of the lake volume, with lower values during high lake level periods. The δ13C values of different species reflect ostracod habitat preferences (i.e. infaunal vs. epifaunal) but are less sensitive to hydrological changes. However, combined with other proxies, decreasing Holocene δ13C values may indicate a freshening of the lake water compared to the low lake level during the Last Glacial period. The Lake Van example underscores the significance and value of coupling ostracod ecology and valve geochemistry in palaeoenvironmental studies of endorheic lake basins.</p

СУТНІСТЬ ТА ПРОЦЕС ФОРМУВАННЯ ІНТЕГРОВАНИХ МАРКЕТИНГОВИХ КОМУНІКАЦІЙ

Проаналізовано сутність, характеристика, принципи інтегрованих комунікацій та розкрито особливості процесу їх формування на підприємствах України.; The essence, characteristics and principles of integrated communications are analyzed. The peculiarities of the process of their formation on the enterprises are discovered

Using multiple chronometers to establish a long, directly-dated lacustrine record:Constraining &gt;600,000 years of environmental change at Chew Bahir, Ethiopia

Despite eastern Africa being a key location in the emergence of Homo sapiens and their subsequent dispersal out of Africa, there is a paucity of long, well-dated climate records in the region to contextualize this history. To address this issue, we dated a ∼293 m long composite sediment core from Chew Bahir, south Ethiopia, using three independent chronometers (radiocarbon, 40Ar/39Ar, and optically stimulated luminescence) combined with geochemical correlation to a known-age tephra. The site is located in a climatically sensitive region, and is close to Omo Kibish, the earliest documented Homo sapiens fossil site in eastern Africa, and to the proposed dispersal routes for H. sapiens out of Africa. The 30 ages generated by the various techniques are internally consistent, stratigraphically coherent, and span the full range of the core depth. A Bayesian age-depth model developed using these ages results in a chronology that forms one of the longest independently dated, high-resolution lacustrine sediment records from eastern Africa. The chronology illustrates that any record of environmental change preserved in the composite sediment core from Chew Bahir would span the entire timescale of modern human evolution and dispersal, encompassing the time period of the transition from Acheulean to Middle Stone Age (MSA), and subsequently to Later Stone Age (LSA) technology, making the core well-placed to address questions regarding environmental change and hominin evolutionary adaptation. The benefits to such studies of direct dating and the use of multiple independent chronometers are discussed. Highlights • Four independent dating methods applied to ∼293 m lake core from southern Ethiopia. • Reveals 620 ka high-resolution sedimentary record near key fossil hominin sites. • Mean accumulation rate of 0.47 mm/a comparable to other African lacustrine sediments. • Accumulation rate fell to 0.1 mm/a during MIS 2, likely due to reduced sediment supply. • Use of multiple independent chronometers is a powerful approach in lake settings

Hydroclimate changes in eastern Africa over the past 200,000 years may have influenced early human dispersal

Abstract: Reconstructions of climatic and environmental conditions can contribute to current debates about the factors that influenced early human dispersal within and beyond Africa. Here we analyse a 200,000-year multi-proxy paleoclimate record from Chew Bahir, a tectonic lake basin in the southern Ethiopian rift. Our record reveals two modes of climate change, both associated temporally and regionally with a specific type of human behavior. The first is a long-term trend towards greater aridity between 200,000 and 60,000 years ago, modulated by precession-driven wet-dry cycles. Here, more favorable wetter environmental conditions may have facilitated long-range human expansion into new territory, while less favorable dry periods may have led to spatial constriction and isolation of local human populations. The second mode of climate change observed since 60,000 years ago mimics millennial to centennial-scale Dansgaard-Oeschger cycles and Heinrich events. We hypothesize that human populations may have responded to these shorter climate fluctuations with local dispersal between montane and lowland habitats

ICDP workshop on the Lake Tanganyika Scientific Drilling Project: a late Miocene–present record of climate, rifting, and ecosystem evolution from the world's oldest tropical lake

The Neogene and Quaternary are characterized by enormous changes in global climate and environments, including global cooling and the establishment of northern high-latitude glaciers. These changes reshaped global ecosystems, including the emergence of tropical dry forests and savannahs that are found in Africa today, which in turn may have influenced the evolution of humans and their ancestors. However, despite decades of research we lack long, continuous, well-resolved records of tropical climate, ecosystem changes, and surface processes necessary to understand their interactions and influences on evolutionary processes. Lake Tanganyika, Africa, contains the most continuous, long continental climate record from the mid-Miocene (∼10 Ma) to the present anywhere in the tropics and has long been recognized as a top-priority site for scientific drilling. The lake is surrounded by the Miombo woodlands, part of the largest dry tropical biome on Earth. Lake Tanganyika also harbors incredibly diverse endemic biota and an entirely unexplored deep microbial biosphere, and it provides textbook examples of rift segmentation, fault behavior, and associated surface processes. To evaluate the interdisciplinary scientific opportunities that an ICDP drilling program at Lake Tanganyika could offer, more than 70 scientists representing 12 countries and a variety of scientific disciplines met in Dar es Salaam, Tanzania, in June 2019. The team developed key research objectives in basin evolution, source-to-sink sedimentology, organismal evolution, geomicrobiology, paleoclimatology, paleolimnology, terrestrial paleoecology, paleoanthropology, and geochronology to be addressed through scientific drilling on Lake Tanganyika. They also identified drilling targets and strategies, logistical challenges, and education and capacity building programs to be carried out through the project. Participants concluded that a drilling program at Lake Tanganyika would produce the first continuous Miocene–present record from the tropics, transforming our understanding of global environmental change, the environmental context of human origins in Africa, and providing a detailed window into the dynamics, tempo and mode of biological diversification and adaptive radiations.© Author(s) 2020. This open access article is distributed under the Creative Commons Attribution 4.0 License

The Lake CHAd Deep DRILLing project (CHADRILL) - targeting ~ 10 million years of environmental and climate change in Africa

At present, Lake Chad ( ~13°0 N, ~14° E) is a shallow freshwater lake located in the Sahel/Sahara region of central northern Africa. The lake is primarily fed by the Chari-Logone river system draining a ~600 000 km2 watershed in tropical Africa. Discharge is strongly controlled by the annual passage of the intertropical convergence zone (ITCZ) and monsoon circulation leading to a peak in rainfall during boreal summer. During recent decades, a large number of studies have been carried out in the Lake Chad Basin (LCB). They have mostly focused on a patchwork of exposed lake sediments and outcrops once inhabited by early hominids. A dataset generated from a 673m long geotechnical borehole drilled in 1973, along with outcrop and seismic reflection studies, reveal several hundred metres of Miocene-Pleistocene lacustrine deposits. CHADRILL aims to recover a sedimentary core spanning the Miocene-Pleistocene sediment succession of Lake Chad through deep drilling. This record will provide significant insights into the modulation of orbitally forced changes in northern African hydroclimate under different climate boundary conditions such as high CO2 and absence of Northern Hemisphere ice sheets. These investigations will also help unravel both the age and the origin of the lake and its current desert surrounding. The LCB is very rich in early hominid fossils (Australopithecus bahrelghazali; Sahelanthropus tchadensis) of Late Miocene age. Thus, retrieving a sediment core from this basin will provide the most continuous climatic and environmental record with which to compare hominid migrations across northern Africa and has major implications for understanding human evolution. Furthermore, due to its dramatic and episodically changing water levels and associated depositional modes, Lake Chad's sediments resemble maybe an analogue for lake systems that were once present on Mars. Consequently, the study of the subsurface biosphere contained in these sediments has the potential to shed light on microbial biodiversity present in this type of depositional environment. We propose to drill a total of ~1800m of poorly to semi-consolidated lacustrine, fluvial, and eolian sediments down to bedrock at a single on-shore site close to the shoreline of present-day Lake Chad. We propose to locate our drilling operations on-shore close to the site where the geotechnical Bol borehole (13°280 N, 14°440 E) was drilled in 1973. This is for two main reasons: (1) nowhere else in the Chad Basin do we have such detailed information about the lithologies to be drilled; and (2) the Bol site is close to the depocentre of the Chad Basin and therefore likely to provide the stratigraphically most continuous sequence

Recurrent explosive eruptions from a high-risk Main Ethiopian Rift volcano throughout the Holocene

Corbetti caldera is the southernmost large volcanic system in Ethiopia, and has been categorized at the highest level of uncertainty in terms of hazard and risk. Until now, the number and frequency of past explosive eruptions at Corbetti has been unknown, due to limited studies of frequently incomplete and patchy outcrop sequences. Here we use volcanic ash layers preserved in sediments from three Main Ethiopian Rift lakes to provide the first detailed record of volcanism for the Corbetti caldera. We show that lake sediments yield more comprehensive, stratigraphically-resolved dossiers of long-term volcanism than often available in outcrop. Our eruptive history for Corbetti spans the last 10 k.y. and reveals eruptions at an average return period of ~900 years. The threat posed by Corbetti has, until now, been underestimated. Future explosive eruptions, similar to those of the past 10 k.y. would blanket nearby Awassa and Shashamene, currently home to ~260,000 people, with pumice fall deposits and would have significant societal impacts. A lake sediment tephrostratigraphic approach shows significant potential for application throughout the East African Rift system, and will be essential to better understanding volcanic hazards in this rapidly developing region.Martin-Jones was funded by a Natural Environment Research Council (NERC) Algorithm Ph.D. (grant NE 10983–01). Field work at Lake Chamo was funded by the German Research Foundation (DFG) within the scope of the CRC 806 (Our Way to Europe). Smith acknowledges funding from the Natural Environment Research Council (grant NE/ L013932/1), Brown and Frank acknowledge DFG SPP 1488 grant KO2870/4–1

Exotic aerosols in the Falkland Islands: a record of South American dust and pollen transport to the South Atlantic since 13 ka.

South America is thought to be a major contributor of dust to the Southern Ocean and Antarctica and therefore to affect the hemispheric energy balance and carbon cycle. However, Patagonia is an arid and deflated landscape without any continental records of dust flux. The Falkland Islands, downwind of Patagonia, offer an opportunity to recover such a record from the blanketing peat accumulation.A short peat core taken in 2013 from East Falkland was dated by 14C, analysed by iTrax XRF scanner, LOI and DBD, and pollen analysis. The peat extends back to approximately 13 ka and ceases at around 2 ka (probably due to turf cutting). LOI and iTrax confirm a component of inorganic, siliceous minerals which we infer to be dust transported from South America. The transport of aerosols from South America is confirmed by the presence of exotic pollen (e.g. Araucariaceae), also found by Turney et al. (2016) for the last 2.6 ka. mDust fluxes were high from 13 ka until around 10 ka and remained low except for a brief excursion around 8 ka. A similar pattern was found at a site in the Beagle Channel (Vanneste et al., 2016. Sci Reports), except that at the Falklands the post-ACR/YD decrease in dust flux was delayed by up to 1 kyr. The results support the Patagonian origin of dust to the South Atlantic and suggest a dominantly glacial origin