A high-resolution multi-proxy record from Lake Van, eastern Anatolia, derived from a lacustrine sequence cored at the 357m deep Ahlat Ridge (AR), allows a comprehensive view of paleoclimate and ...environmental history in the continental Near East during the last interglacial (LI). We combined paleovegetation (pollen), stable oxygen isotope (δ18Obulk) and XRF data from the same sedimentary sequence, showing distinct variations during the period from 135 to 110ka ago leading into and out of full interglacial conditions. The last interglacial plateau, as defined by the presence of thermophilous steppe-forest communities, lasted ca. 13.5ka, from ~129.1–115.6ka BP.
The detailed palynological sequence at Lake Van documents a vegetation succession with several climatic phases: (I) the Pistacia zone (ca. 131.2–129.1ka BP) indicates summer dryness and mild winter conditions during the initial warming, (II) the Quercus-Ulmus zone (ca. 129.1–127.2ka BP) occurred during warm and humid climate conditions with enhanced evaporation, (III) the Carpinus zone (ca. 127.2–124.1ka BP) suggest increasingly cooler and wetter conditions, and (IV) the expansion of Pinus at ~124.1ka BP marks the onset of a colder/drier environment that extended into the interval of global ice growth. Pollen data suggest migration of thermophilous trees from refugial areas at the beginning of the last interglacial. Analogous to the current interglacial, the migration documents a time lag between the onset of climatic amelioration and the establishment of an oak steppe-forest, spanning 2.1ka. Hence, the major difference between the last interglacial compared to the current interglacial (Holocene) is the abundance of Pinus as well as the decrease of deciduous broad-leaved trees, indicating higher continentality during the last interglacial. Finally, our results demonstrate intra-interglacial variability in the low mid-latitudes and suggest a close connection with the high-frequency climate variability recorded in Greenland ice cores.
•The new high-resolution pollen data reflects an intra-interglacial instability.•Lake Van proxy data suggest a strong teleconnection with the North Atlantic circulation.•LI is no analogue to the climate condition of the current interglacial.•Correlations have been established between the Lake Van and southern Europe.
The Dead Sea, located at the deepest place on continent and between the subtropical Mediterranean zone and the desert, reflects in its water composition and levels, and sedimentary records the ...hydrological conditions in the southern Levant region. Temporal variations in rainfall and temperatures of the Holocene Levant are reconstructed here from pollen data recovered from a sediment core drilled at the Ein Gedi shore, applying a novel biome model based on Bayesian statistics. Our results suggest that the region was arid and warm in the early Holocene period (∼10–6.5 ka cal BP), wetter and colder in the mid Holocene (6.3–3.3 ka cal BP), and drier and warmer in the late Holocene (∼3.2 ka cal BP to present). These periods comprise multi-centennial climate cycles that are characterized by rapid changes in temperature and precipitation reflecting Sea Surface Temperature (SST) and atmospheric conditions over the Atlantic Ocean. The pollen record responds within a short time interval to the climate conditions and marks rapid shifts from Mediterranean to desert environmental conditions and back in the southern Levant region. We also evaluate our results in the light of possible disturbances of the natural vegetation, e.g. the possibility of forest decrease, since the Neolithic.
► We present temporal rainfall and temperature variations in the Levant (Near East) during the last 10,000 years. ► The reconstruction is based on the longest and most continuous pollen record of the Holocene Dead Sea. ► The pollen record marks rapid shifts from Mediterranean to desert conditions and back. ► We apply a novel biome model based on Bayesian statistics to quantify the variability of climate parameters. ► The results compares favorably with reconstructions of the lake levels of the Dead Sea.
Our field data from the Upper Palaeolithic site of Al-Ansab 1 (Jordan) and from a pollen sequence in the Dead Sea elucidate the role that changing Steppe landscapes played in facilitating ...anatomically modern human populations to enter a major expansion and consolidation phase, known as the "Early Ahmarian", several millennia subsequent to their initial Marine Isotope Stage 4/3 migration from Africa, into the Middle East. The Early Ahmarian techno-cultural unit covers a time range between 45 ka-37 ka BP. With so far more than 50 sites found, the Early Ahmarian is the first fully Upper Palaeolithic techno-cultural unit exclusively and undisputedly related to anatomically modern human populations. In order to better understand the potentially attractive features of the Early Ahmarian environmental context that supported its persistence for over 8,000 years, we carried out a decennial research program in Jordan and in the Dead Sea. This included (1) a geoscientific and archaeological survey program in the Wadi Sabra (Jordan) with a particular focus on excavations at the Early Ahmarian site of Al-Ansab 1 alongside the detailed analysis of Quaternary sediments from the same area and (2) palaeobotanical research based on Quaternary lake deposits from the Dead Sea. Our pollen data from the Dead Sea indicate slow, low frequency vegetational variation with expanding Artemisia steppe, from 60 to 20 ka BP (MIS 3-2). Here, we see a reciprocal assimilation of southern and northern Levantine vegetation zones thereby enhancing a long-lasting south-to-north steppe corridor. The same integration process accelerated about 40 ka ago, when forested areas retreated in the Lebanese Mountains. The process then extended to encompass an area from Southern Lebanon to the Sinai Peninsula. We argue that, at the same time, the carriers of the Early Ahmarian techno-cultural unit extended their habitat from their original Mediterranean biome (in the North) to the Saharo-Arabian biome (to the South). Our excavation of Al-Ansab 1, a campsite at the eastern margins of the Early Ahmarian settlement area, indicates far reaching annual movements of small, highly mobile hunter-gatherer groups. We assume a low degree of settlement complexity, still allowing for habitat extension of the Early Ahmarian into the margins of the Levantine corridor. Due to our radiometric dates, our combined archaeological and environmental record sheds light on an evolved phase of the Early Ahmarian, around 38 ka ago, rather than the starting phase of this techno-cultural unit. Possible application of our model to the starting phase of the Early Ahmarian remains an aspect of future research.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Natural disturbances such as volcanic eruptions provide a unique opportunity to study past ecological dynamics. Here we illustrate the response of terrestrial and aquatic ecosystems to ...volcanic eruptions in connection to prevailing climate conditions. We selected five volcaniclastic depositions in the Lake Van (Turkey) sediments from different interglacial/glacial periods (Marine Isotope Stages 3 to 9e). Using high-resolution pollen data, non-pollen palynomorphs, and microscopic charcoal particles we attempted to disentangle climatic and volcanic forcing of natural environmental disturbances. Our results highlights that the thickness of subsequent volcanic deposits and the respective climatic conditions strongly influence the impact on terrestrial and aquatic ecosystems. The most common response to ash deposition is a shift towards herbaceous taxa and abrupt fire activity. The affected herbaceous vegetation recovers to pre-eruption levels in 20 to 40 varve-years. The lake water experiences intensified productivity due to subsequent nutrient input and significant increase in aquatic microfossils. Our findings pave the way for disentangling climatic and volcanic forcing of natural environmental disturbances.
• Here, palaeobotanical and genetic data for common beech (Fagus sylvatica) in Europe are used to evaluate the genetic consequences of long-term survival in refuge areas and postglacial spread. • ...Four large datasets are presented, including over 400 fossil-pollen sites, 80 plant-macrofossil sites, and 450 and 600 modern beech populations for chloroplast and nuclear markers, respectively. • The largely complementary palaeobotanical and genetic data indicate that: (i) beech survived the last glacial period in multiple refuge areas; (ii) the central European refugia were separated from the Mediterranean refugia; (iii) the Mediterranean refuges did not contribute to the colonization of central and northern Europe; (iv) some populations expanded considerably during the postglacial period, while others experienced only a limited expansion; (v) the mountain chains were not geographical barriers for beech but rather facilitated its diffusion; and (vi) the modern genetic diversity was shaped over multiple glacial-interglacial cycles. • This scenario differs from many recent treatments of tree phylogeography in Europe that largely focus on the last ice age and the postglacial period to interpret genetic structure and argue that the southern peninsulas (Iberian, Italian and Balkan) were the main source areas for trees in central and northern Europe.
Lake Van sediment cores from the Ahlat Ridge and Northern Basin drill sites of the ICDP project PALEOVAN contain a wealth of information about past environmental processes. The sedimentary sequence ...was dated using climatostratigraphic alignment, varve chronology, tephrostratigraphy, argon–argon single-crystal dating, radiocarbon dating, magnetostratigraphy, and cosmogenic nuclides. Based on the lithostratigraphic framework, the different age constraints are compiled and a robust and precise chronology of the 600,000 year-old Lake Van record is constructed. Proxy records of total organic carbon content and sediment color, together with the calcium/potassium-ratios and arboreal pollen percentages of the 166-m-long event-corrected Ahlat Ridge record, mimic the Greenland isotope stratotype (NGRIP). Therefore, the proxy records are systematically aligned to the onsets of interstadials reflected in the NGRIP and synthesized Greenland ice-core stratigraphy. The chronology is constructed using 49 age control points derived from visual synchronization with the Greenland ice-core stratigraphy using the GICC05 timescale, an absolutely-dated speleothem timescale (e.g., Hulu, Sanbao, Linzhu cave) and the Epica Dome C timescale. In addition, the uppermost part of the sequence is complemented with four ages from Holocene varve chronology and three calibrated radiocarbon ages. Furthermore, nine argon–argon ages and a comparison of the relative paleointensity record of the magnetic field with reference curve PISO-1500 confirm the accuracy of the age model. Also the identification of the Laschamp event via measurements of 10Be in the sediment confirms the presented age model. The chronology of the Ahlat Ridge record is transferred to the 79-m-long event-corrected composite record from the Northern Basin and supplemented by additional radiocarbon dating on organic marco-remains. The basal age of the Northern Basin record is estimated at ∼90 ka. The variations of the time series of total organic carbon content, the Ca/K ratio, and the arboreal pollen percentages illustrate that the presented chronology links ice-marine-terrestrial stratigraphies and that the paleoclimate data are suited for reconstructions and modeling of the Quaternary and Pleistocene climate evolution in the Near East at millennial timescales. Furthermore, the chronology of the last 250 ka can be used to test other dating techniques.
•Long lacustrine drill cores were dated using a suite of age constraints.•A robust chronology of the 600,000 year-old Lake Van record is constructed.•Proxy records are aligned to the NGRIP/GLT syn ice-core stratigraphy.•Ar/Ar ages, 14C, relative paleointensity and 10Be confirm the age model.
A well-dated suite of Lake Van climate-proxy data covering the last 360 ka documents environmental changes over 4 glacial/interglacial cycles in Eastern Anatolia, Turkey. The picture of cold and dry ...glacials and warm and wet interglacials emerging from pollen, organic carbon, authigenic carbonate content, elemental profiling by XRF and lithological analyses is inconsistent with classical interpretation of oxygen isotopic composition of carbonates pointing to a more complex pattern in Lake Van region. Detailed analysis of glacial terminations allows for the constraining of a depositional model explaining different patterns observed in all the proxies. We hypothesize that variations in relative contribution of rainfall, snowmelt and glacier meltwater recharging the basin have a very important role for all sedimentary processes in Lake Van. Lake level of glacial Lake Van, predominantly fed by snowmelt, was low, the water column was oxic, and carbonates precipitating in the epilimnion recorded the light isotopic signature of inflow. During terminations, increasing rainfall and significant supply of mountain glaciers' meltwater contributed to lake level rise. Increased rainfall enhanced density gradients in the water column, and hindered mixing leading to development of bottom-water anoxia. Carbonates precipitating during terminations show large fluctuations in their isotopic composition. Full interglacial conditions in Lake Van are characterized by high or slowly falling lake level. Rainfall and snowmelt feed the lake but due to re-established mixing, the isotopic composition of authigenic carbonates is heavier and closer to that of evaporation-influenced lake water than that of runoff representing snowmelt and atmospheric precipitation.
•Lake Van climate-proxy data document changes in Turkey for the last 360 ka.•Switch from snowmelt-fed to rainfall-fed runoff control the δ18O of carbonates.•Most Lake Van data imply dry glacial/wet interglacial conditions in Eastern Mediterranean.•But oxygen isotopes show a more complex pattern.
Despite ongoing discussions on hydroclimatic conditions in the southern Levant during the Last Glacial, detailed knowledge about the Levantine paleovegetation, which is an important indicator for the ...paleoclimate, is limited. To investigate the paleovegetation in northern Israel, we analyzed the pollen assemblage of a sediment core that was drilled at the Ohalo II archaeological site on the southwestern shore of the Sea of Galilee (Lake Kinneret). We refined the lithology and the age-depth model with the help of five new radiocarbon dates. The core comprises a continuous sediment profile of mainly laminated authigenic calcites and detrital material that deposited between ca. 28,000 and 22,500 years before present, when the Sea of Galilee rose above the modern lake level stand and temporarily merged with Lake Lisan, the precursor of the Dead Sea. The well-dated and high-resolution pollen record suggests that steppe vegetation with grasses, other herbs, and dwarf shrubs predominated in northern Israel during the investigated period. In contrast to the Holocene, there was no continuous vegetation belt of the Mediterranean biome in the vicinity of the Sea of Galilee. Mediterranean elements such as deciduous oaks only occurred in limited amounts and were probably patchily distributed. These results disagree with previous pollen-based hypotheses from the region that assumed the spread of Mediterranean forest during glacial periods. While the pollen data may indicate semiarid conditions in northern Israel and give no evidence of increased effective moisture, previous hydroclimatic studies suggested increased precipitation rates that are consistent with high lake levels (Sea of Galilee/Lake Lisan). Thus, we discuss factors influencing the pollen assemblage and the plant cover.
•Well-dated and high-resolution pollen record from Last Glacial Sea of Galilee/Lake Lisan.•Dominance of steppe vegetation in northern Israel during the MIS 2 lake level high stand.•Discussion of apparent conflicts between pollen data and other regional climate proxies.
Fossil long-chain alkenones have been used for several decades to reconstruct past ocean surface water temperatures and gained recent interest as a paleotemperature proxy for continental lake ...settings. However, factors besides temperature can affect alkenone distributions in haptophyte algae, and alkenone compositions can differ between haptophyte species. Alkenone-biosynthesizing haptophyte algae are genetically much more diverse in lakes than in the marine realm, and species-level variations in alkenone compositions could have implications for alkenone paleothermometry. Here, we performed a paired analysis of alkenone distributions and haptophyte species compositions using ancient DNA in up to 270 ka-old sediments of Lake Van in Turkey to reveal a possible species-effect on fossil alkenone distributions and paleotemperature estimates. The same predominant haptophyte in Lake Van today prevailed also since the last ∼100 ka. However, a calibration of alkenone paleotemperature especially in the oldest analyzed intervals is complicated due to a more complex haptophyte species composition predominated by a haptophyte (LVHap_6), which is phylogenetically different from sequences recovered from currently existing lakes including Lake Van and from haptophyte species existing in culture. The predominance of LVHap_6 coincided with the presence of alkenone MeC38:3 and relatively high MeC37:3/4 (2.4) and MeC38:4/5 ratios (3.0). Uk37 index values in the sediment core over the last 270 ka reflect relative changes in past temperature and are additionally linked to haptophyte species composition. A sustained period of high salinity, as indicated by pore-water salinity measurements, could potentially have triggered the succession of haptophytes as sources of alkenones in Lake Van.
•Alkenone analyses in a record from Eastern Anatolia covering the past 270 ka.•New insight into the influence of haptophyte species on alkenone distribution.•Semi-quantitative link between Uk37 index and past temperatures in Lake Van.
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