What does kyr bp mean

The most popular kyr cycle is certainly the eccentricity one. Actually, the periods of the most important spectral components of e used in Berger are , 14 , , 99 and yr. The derivative of eccentricity is definitely showing a spectrum dominated by the kyr cycle with the same spectral components as e itself.

The inclination of the Earth orbital plane on the ecliptic does not display any kyr cycle, but it is not the case for its inclination on the reference plane for which cycles of 98 and years appear.

Finally the frequency modulation of obliquity is characterised by cycles kyr and 97 kyr long. For inso- lation, it is known that there is only a very weak signal around kyr coming from e itself. However, if we consider the seasonal cycle at the equator, its amplitude varies with cycles of kyr , kyr , 41 kyr , 10 kyr and 5 kyr , all related to e.

Although all these cycles are close to the kyr cycle found in geological data, the origin of this kind of cycle can be best identified by comparing the proxy record to the re- sponse of the climate system to the astronomical forcing. This forcing signal which contains, in one way or another, the astronomical characteristics mentioned above is, at least, partly distorted and transformed, a modification which can only be estimated through climate models.

Such a climate model has been developed in the early 80Ss in Louvain-la-Neuve and used since to simulate the last and next glacial-interglacial cycles. Are Avellino cal BP and Pompeii twin plinian eruptions? Pre-eruptive constraints and degassing history. Somma-Vesuvius activity started 35 ky ago and is characterized by numerous eruptions of variable composition and eruptive style, sometimes interrupted by long periods of unrest. The 79 AD eruption embodies the most famous eruption since it's responsible of the destruction of Pompeii and Herculanum and it's the first described eruption.

The Avellino eruption represents the last plinian event that preceded the Pompeii eruption. The eruptive sequence is similar to the 79 AD plinian eruption, with an opening phase preceding a main plinian fallout activity which ended by a phreatomagmatic phase. The fallout deposit displays a sharp colour contrast from white to grey pumice, corresponding to a magma composition evolution.

We focus our study on the main fallout deposit that we sampled in detail in the Traianello quarry, 9 km North-North East of the crater, to investigate the degassing processes during the eruption, using volatile content and textural observations.

Density and vesicularity measurements were obtained on a minimum of pumice clasts sampled in 10 stratigraphic levels in the fallout deposit. On the basis of the density distribution, bulk geochemical data, point analytical measurements on glasses melt inclusions and residual glass and textural observations were obtained simultaneously on a minimum of 5 pumice clasts per eruptive unit.

The pre-eruptive conditions are constrained by systematic Cl measurements in melt inclusions and matrix glass of pumice clasts. Hajdas, Irena; Ivy, Susan D. For the extension of the radiocarbon calibration curve beyond 14C y BP , laminated sediment from Lake Soppensee central Switzerland was dated. The radiocarbon time scale was obtained using accelerator mass spectrometry AMS dating of terrestrial macrofossils selected from the Soppensee sediment.

Because of an unlaminated sediment section during the Younger Dryas 14C y BP , the absolute time scale, based on counting annual layers varves , had to be corrected for missing varves. The Soppensee radiocarbon-verve chronology covers the time period from to 14C y BP on the radiocarbon time scale and to calendar y BP on the absolute time scale.

The good agreement with the tree ring curve in the interval from to cal y BP cal y indicates calendar year proves the annual character of the laminations. Circum-Mediterranean fire activity and climate changes during the mid Holocene environmental transition cal yr BP. In this contribution I will present a synthesis of mid- to late-Holocene fire activity from the Mediterranean basin and explore the linkages among fire, climate variability and seasonality, and people through several climatic and ecological transitions.

Regional fire histories were created from 36 radiocarbon-dated sedimentary charcoal records, available from the Global Charcoal Database. During the mid-Holocene "Thermal Maximum", charcoal records from the northern Mediterranean suggest the region was more fire prone while records from the southern Mediterranean indicate a decrease in fire activity associated with wetter-than-present summers.

In the context of orbitally-induced summer insolation decrease, South Mediterranean wet conditions could be linked to the Afro-Asian summer monsoon which weakened after ca. Relatively abrupt changes in fire regime observed at ca. Charcoal records of past fire activity appear sensitive to both orbitally-forced climate changes and shorter lived excursions which may be related to cold events apparent in the North Atlantic record of ice-rafted debris.

In contrast, they suggest: 1 Teleconnections between the Mediterranean area and other climatic regions, in particular the North Atlantic and the low-latitude monsoon areas, influenced past fire regimes; 2 Gradual forcing, such as changes in orbital parameters, may have triggered more abrupt shifts in fire regime, either directly or indirectly through these teleconnections.

The seismic-stratigraphic record of lake-level fluctuations in Lake Challa: Hydrological stability and change in equatorial East Africa over the last kyr. Seismic-reflection data from crater lake Challa Mt. Extrapolation of a well-constrained age model on the cored upper part of the sequence suggests that these lake-level fluctuations represent a detailed and continuous record of moisture-balance variation in equatorial East Africa over the last kyr. Climate history near the East African equator reflects variation in the precessional forcing of monsoon rainfall modulated by orbital eccentricity, but precession-driven moisture fluctuations were less extreme than those observed in northern and southern tropical Africa.

This long period of moist glacial climate and a short, relatively modest LGM drought can be attributed to greater independence of western Indian Ocean monsoon dynamics from northern high-latitude glaciation than those in the tropical Atlantic Ocean.

This rather persistent moist glacial climate regime may have helped maintain high biodiversity in the tropical forest ecosystems of the Eastern Arc mountains in Tanzania. Paleosols in low-order streams and valley heads in the Araucaria Plateau - Record of continental environmental conditions in southern Brazil at the end of MIS 3. The Araucaria Plateau is a geomorphological unit that occupies approximately three-quarters of the terrain in the southern region of Brazil.

The plateau displays different altitudinal levels to kyr BP BP and The calibrated ages are related to Marine Isotope Stage 3 MIS 3 , in which the last period of global warming occurred approximately kyr cal. We obtained the following conclusions: a the properties of paleosols reflect pedological processes that are adjusted to the paleoenvironmental conditions at the end of MIS 3 and the transition to MIS 2 Last Glacial Maximum ; b aplasmogenic partial acidolysis was the predominant.

Ostracods and sediment geochemistry as indicators of hydrologic and climatic variability in the central part of the Mexican Chihuahuan Desert over the last 27 ka cal BP. The lacustrine basin covers an area of approximately 1, km2 and is surrounded by mountains up to ca.

This basin was formed by tectonic processes and the basement is formed by volcanic felsic rocks of Tertiary age. Four sediment cores were obtained from central and western part of the basin to reconstruct hydrologic and climate variability during the late Pleistocene and Holocene. In this work, we present paleo-ecology of ostracods and sedimentary geochemistry from two sediment cores cm and cm long collected from the western basin margin.

The age model was constructed from 8 AMS radiocarbon dates and the longest profile represents the last 27 cal ka BP. The results were divided into two zones for interpretation. Zone 1 covers ca. This suggests greater interaction between water and sediment, lower evaporation and relatively higher lake level in the basin. Sediments of the last 17 cal ka BP cm Zone 2 are characterized by below average water-sediment interaction, higher carbonate precipitation and deposition of allochthonous organic matter terrestrial origin.

This view is not without its critics, due in part to the uncertainty regarding the timing and rate of expansion and the difficulty in identifying the point at which agriculture first arrived in a particular location. Evidence for potential 'episodes' of Mesolithic agricultural activity in the UK has been identified in the UK pollen record, but this data is very tentative.

Cereal pollen is typically present in very low concentrations requiring very large, time consuming counts and differentiating early cereal pollen from local grasses is very problematic, particularly in areas where the local grasses were domesticated.

Flow Cytometry is employed to increase the concentration of cereal type grains in a sample, whilst also providing a more 'targeted' sample for aDNA analysis. The results so far provide clear evidence for an early phase of 'Mesolithic' agriculture in the catchment, spanning only two centuries to Cal yr BP. It occurred over years before the main transition into permanent and intensive agriculture in the catchment, at a time of significant changes in regional climate and sea-level.

The results from Mere Tarn provide the earliest. Identification of contrasting seasonal sea ice conditions during the Younger Dryas. The presence of the sea ice diatom biomarker IP25 in Arctic marine sediments has been used in previous studies as a proxy for past spring sea ice occurrence and as an indicator of wider palaeoenvironmental conditions for different regions of the Arctic over various timescales [e. The current study focuses on high-resolution palaeo sea ice reconstructions for northern Norway during the last ca.

Within this study, particular emphasis has been placed on the identification of the sea ice conditions during the Younger Dryas and the application of different biomarker-based proxies to both identify and quantify seasonal sea ice conditions. Firstly, the appearance of the specific sea ice diatom proxy IP25 at ca. The near continuous occurrence of IP25 for the next ca. At ca. Similarly, a high resolution record from the Kveithola Through, western Barents Sea, showed clearly higher IP25 concentrations during the Younger Dryas stadial compared to the Holocene.

For both marine records, the IP25 concentrations were also combined with those of the open water phytoplankton biomarker brassicasterol to generate PBIP25 data from which more quantitative measurements of sea ice were determined. The contrasting seasonal sea ice conditions during the Younger Dryas were further verified. The high-resolution sedimentological and geochemical analysis of a sediment sequence from Lake Savine Western Mediterranean Alps, France led to the identification of event layers for the last years.

Because human activity could influence the flood chronicle, the presence of pastures was reconstructed through ancient DNA, which suggested that the flood chronicle was mainly driven by hydroclimate variability.

Weather reanalysis of historical floods allow to identify that mesoscale precipitation events called "East Return" events were the main triggers of floods recorded in Lake Savine. The first part of this palaeoflood record kyr BP was characterized by increases in flood frequency and intensity in phase with Northern Alpine palaeoflood records.

By contrast, the second part of the record i. These results suggest a palaeohydrological transition at approximately 4 kyr BP , as has been previously described for the Mediterranean region. This may have resulted in a change of flood-prone hydro-meteorological processes, i. At a centennial timescale, increases in flood frequency and intensity corresponded to periods of solar minima, affecting climate through atmospheric changes in the Euro-Atlantic sector.

The recording of starch grains attributable to Avena oat caryopses expands our information about the food plants used for producing flour in Europe during the Paleolithic and about the origins of a food tradition persisting up to the present in the Mediterranean basin.

The quantitative distribution of the starch grains on the surface of the grinding stone furnished information about the tool handling, confirming its use as a pestle-grinder, as suggested by the wear-trace analysis. The particular state of preservation of the starch grains suggests the use of a thermal treatment before grinding, possibly to accelerate drying of the plants, making the following process easier and faster.

The study clearly indicates that the exploitation of plant resources was very important for hunter—gatherer populations, to the point that the Early Gravettian inhabitants of Paglicci were able to process food plants and already possessed a wealth of knowledge that was to become widespread after the dawn of agriculture. The study clearly indicates that the exploitation of plant resources was very important for hunter-gatherer populations, to the point that the Early Gravettian inhabitants of Paglicci were able to process food plants and already possessed a wealth of knowledge that was to become widespread after the dawn of agriculture.

Paleoceanography of the Gulf of Alaska during the past 15, years: results from diatoms, silicoflagellates, and geochemistry. High-resolution records of diatoms, silicoflagellates, and geochemistry covering the past 15, years were studied in three cores from the Gulf of Alaska GOA. Core EWJC in an oceanic setting on the Kayak Slope displays a paleoceanographic record similar to that at several locations on the California margin during deglaciation. Sea ice-related diatoms increased in abundance during the YD, indicating cooler, but less productive waters.

In this paper, we use high-resolution lacustrine pollen and grain-size records from Balikun Lake to infer vegetation, lake evolution, and climate in arid western China during MIS2. This cold and dry LGM climate triggered a substantial lowering of lake level; 3 an extremely cold and dry climate prevailing from Our results challenge the traditional view of cold and wet climatic conditions and high lake levels in arid western China during the LGM, and we propose that changes in local temperature modulated by July insolation was an indispensable factor in triggering vegetation evolution in the Balikun region during MIS2.

Vibrio parahaemolyticus Cal R down regulates the thermostable direct hemolysin TDH gene transcription and thereby inhibits hemolytic activity. TDH, encoded by tdh gene, is a major virulent determinant of V.

All KP positive strains contain tdh1 and tdh2 genes, but tdh2 is predominantly responsible for KP. Cal R is a regulatory protein that was originally identified as a repressor of swarming motility and T3SS1 gene expression in V. The results showed that His- Cal R protected a single region from bp to bp upstream of tdh2 against DNase I digestion, and a transcriptional start site located at 42 bp upstream of tdh2 was detected and its transcribed activity was inhibited by Cal R.

Moreover, the KP test results showed that the hemolytic activity of V. The data demonstrated that Cal R is a repressor of the tdh2 transcription and thereby inhibits the hemolytic activity of V.

Published by Elsevier B. Deglaciation of Fennoscandia. Stroeven, Arjen P. To provide a new reconstruction of the deglaciation of the Fennoscandian Ice Sheet, in the form of calendar-year time-slices, which are particularly useful for ice sheet modelling, we have compiled and synthesized published geomorphological data for eskers, ice-marginal formations, lineations, marginal meltwater channels, striae, ice-dammed lakes, and geochronological data from radiocarbon, varve, optically-stimulated luminescence, and cosmogenic nuclide dating.

This is summarized as a deglaciation map of the Fennoscandian Ice Sheet with isochrons marking every years between 22 and 13 cal kyr BP and every hundred years between Deglaciation patterns vary across the Fennoscandian Ice Sheet domain, reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins.

For example, the ice sheet margin in the high-precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice-marginal deposits in many fjords and coastal valleys. Retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern Sweden and rapid retreat of the calving ice margin in the Baltic Basin.

Our reconstruction is consistent with much of the published research. However, the synthesis of a large amount of existing and new data support refined reconstructions in some areas.

For example, the LGM extent of the ice sheet in northwestern Russia was located far east and it occurred at a later time than the rest of the ice sheet, at around cal kyr BP.

We also propose a slightly different chronology of moraine formation over southern Sweden based on improved correlations of moraine segments using new LiDAR data and tying the timing of moraine formation to Greenland ice core cold stages.

Retreat rates vary by as much as an order. An age scale synchronisation between the Talos Dome and the EPICA Dome C ice cores was carried on through the identification of several common volcanic signatures for the last 42 kyr.

Using this tight stratigraphic link we transferred the EDC age scale to the Talos Dome ice core producing a new age scale for the last 12 kyr. We estimated the discrepancies between the modeled TALDICE-1 age scale and the new one during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones.

Except for a very few cases, R ranges between 0. At this stage our approach does not allow us unequivocally to find out which of the models is affected by errors, but, taking into account only the historically known volcanic events, we found that discrepancies up to years appears in the last two millennia in the TALDICE-1 model, while our new age scale shows a much better agreement with the volcanic absolute horizons. Thus, we propose for the Talos Dome ice core a new age scale covering the whole Holocene obtained by a direct transfer, via our stratigraphic link, from the EDC modelled age scale by Lemieux-Dudon et al.

The main purpose of the present study is to use foraminifera to create a separate account on coastal environmental changes in the area. For this purpose foraminifera were sampled at 20 cm intervals from an 8.

This core was taken by vibracoring. Foraminifera were extracted, identified, counted separately and finally multiple variable analyses cluster, PCA were used to identify paleo-environments represented by different species assemblages.

Three distinct foraminiferal communities represented by 18 species indicating three biofacies could be recognized. As indicated by dominating Millioids spp. Increasing sea level and intensified storminess during this period might have prevented barrier growth.

This open bay environment converted to more brackish closed bay environment possibly due to the growth of the Santa Rosa Barrier around 3 kyrs BP and that environment exists till today. Abundance of Ammonia-Elphdium - Bolivina spp provide evidence for this transition. These results are comparable with physical and chemical proxy records of the same core as well as other published regional records. It contains a 17 kyr long, stratigraphically continuous sedimentary sequence dated by 30 AMS 14C ages.

Temperature and humidity display rapid and significant changes over the Holocene. The rapid transition from a cold mean annual temperature MAT 3.

During the Holocene, MAT varied from ca. Warm periods 11,,, , cal yr BP were separated by colder intervals. The last 2. The Holocene remained dry until cal yr BP.

Then, precipitations increased to reach a maximum between and cal yr BP. A rapid decrease occurred until cal yr BP and the late Holocene was dry. The highest rainfall intervals correlate with the highest activity of ENSO.

Variability in solar output is possibly the main cause for this millennial to decadal cyclicity. Observation of 23 supernovae that exploded kyr.

This paper describes the rigorous method, using the signature of volcanic sulphate, which was employed for the last 42 kyr of the record. Using this tight stratigraphic link, we transferred the EDC age scale to the Talos Dome ice core, producing a new age scale for the last 12 kyr. We estimated the discrepancies between the modelled TALDICE-1 age scale and the new scale during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones.

At this stage our approach does not allow us to unequivocally identify which of the models is affected by errors, but, taking into account only the historically known volcanic events, we found that discrepancies up to yr appear in the last two millennia in the TALDICE-1 model, while our new age scale shows a much better agreement with the volcanic absolute horizons. Kovacs, Shawn E. High salinity of the meteoric WM during the wet mid-Holocene is attributed to increased turbulent mixing between the meteoric and underlying marine WM.

Increased precipitation, in terms of amount, frequency, and intensity e. Conversely, during dry periods reduced precipitation and flow in the meteoric WM would result in lower salinity. Karst properties and Holocene sea-level rise also seem to have an effect on the aquifer. This study demonstrates that calcite raft deposits can be used as paleo-environmental recorders documenting the effects of sea level and climate change on aquifer condition.

Here we exploit sub-fossil New Zealand kauri trees to report the first securely dated, decadally-resolved atmospheric radiocarbon 14 C record spanning GS Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but probably due to an equatorward migration of the Polar Front, reducing the advection of southwesterly air masses to high latitudes. Our findings suggest opposing hemispheric temperature trends were driven by atmospheric teleconnections, rather than AMOC changes.

Here we exploit sub-fossil New Zealand kauri trees to report the first securely dated, decadally-resolved atmospheric radiocarbon 14C record spanning GS Hydrological and climate changes in southeast Siberia over the last 33 kyr.

Paleoenvironmental and paleoclimate changes in intracontinental Siberia were reconstructed by continuous, high-resolution records biogenic silica, U, total organic carbon and N, total S, and grain size from a sediment core retrieved from the Buguldeika Saddle, Lake Baikal, dating back to the last 33 cal. The Holocene climate was wet relative to the last glacial period. The climate became gradually warm and wet from the early to middle Holocene, followed by a shift at ca.

This suggests that the climate system transition from the glacial to interglacial state occurred at that time. In the last glacial, the deposition of carbonate mud from the Primorsky Range was associated with Heinrich events H3 and H1 and the Selenga River inflow during the Last Glacial Maximum was caused by meltwater of mountain glaciers in the Khamar-Daban Range.

The rapid decline in precipitation during the early Holocene may have been a response to the 8. However, such great rates of accumulation come with a price as features of interest are often deeply buried and may only be adequately recovered using drilling technologies. Here we present a full-vector geomagnetic reconstruction for the last 70, yrs from ultrahigh resolution records obtained through ODP drilling Leg on the Chilean Margin. ODP Site The chronology is constrained by AMS radiocarbon dates and tuning of alkenone sea surface temperature to Antarctic ice core temperature records back to 70, years BP.

To the north, ODP Sites The Site chronology indicates that the Laschamp event, centered at 41, yrs BP , has a duration in reverse polarity of only yrs, with polarity transitions occurring in less than yrs within a yr long interval of low RPI.

The path of virtual geomagnetic pole VGP positions for the Laschamp excursion at Site is generally consistent with the hypothesis of a simple field geometry. A high-resolution sedimentary charcoal record from Lago dell'Accesa in southern Tuscany reveals numerous changes in fire regime over the last BP and provides one of the longest gap-free series from Italy and the Mediterranean region. Charcoal analyses are coupled with gamma density measurements, organic-content analyses, and pollen counts to provide data about sedimentation and vegetation history.

A comparison between fire frequency and lake-level reconstructions from the same site is used to address the centennial variability of fire regimes and its linkage to hydrological processes. Our data reveal strong relationships among climate, fire, vegetation, and land-use and attest to the paramount importance of fire in Mediterranean ecosystems. The mean fire interval MFI for the entire Holocene was estimated to be yr, with a minimum around 80 yr and a maximum around yr.

Between BP , up to eight high-frequency fire phases lasting yr generally occurred during shifts towards low lake-level stands ca 11,, 10,, , , , , , , and cal.

Therefore, we assume that most of these shifts were triggered by drier climatic conditions and especially a dry summer season that promoted ignition and biomass burning. At the beginning of the Holocene, high climate seasonality favoured fire expansion in this region, as in many other ecosystems of the northern and southern hemispheres.

Human impact affected fire regimes and especially fire frequencies since the Neolithic ca cal. Burning as a consequence of anthropogenic activities became more frequent after the onset of the Bronze Age ca cal. The anthropogenic phases with maximum fire activity corresponded to greater sensitivity of the vegetation and triggered. Distal deltaic deposits document hydrological variability during the past 30 kyrBP in Lake Towuti, Indonesia.

Vogel, Hendrik; Russell, James M. Lake Towuti 2. The Mahalona River constitutes the largest tributary and connects Lake Towuti with the two upstream lakes Matano and Mahalona. Tracing past variability of Mahalona River discharge is therefore an important puzzle piece for the understanding of depositional dynamics in Lake Towuti as well as catchment hydrology and hydrological connectivity between the Malili Lakes.

Distal deltaic deposits can help identifying past variability in river discharge and delta dynamics. Using highly resolved seismic reflection data collected between we identified a stack of acoustically laminated reflections in Towuti's extensive and morphologically flat deep northern basin. For detailed characterization of these acoustic features we collected a c. MWD appear mostly homogenous silt- to finesand-sized siliciclastics with high amounts of terrestrial plant macrofossils with only thin cm basal sand layers and clay caps Testing the Hypothesis of Fire Use for Ecosystem Management by Neanderthal and Upper Palaeolithic Modern Human Populations.

Background It has been proposed that a greater control and more extensive use of fire was one of the behavioral innovations that emerged in Africa among early Modern Humans, favouring their spread throughout the world and determining their eventual evolutionary success. We would expect, if extensive fire use for ecosystem management were a component of the modern human technical and cognitive package, as suggested for Australia, to find major disturbances in the natural biomass burning variability associated with the colonisation of Europe by Modern Humans.

Results indicate that fire regime follows the Dansgaard-Oeschger climatic variability and its impacts on fuel load. No major disturbance in natural fire regime variability is observed at the time of the arrival of Modern Humans in Europe or during the remainder of the Upper Palaeolithic 40—10 kyr cal BP. A late glacial to early Holocene lacustrine and peat succession, rich in conifer remains and including some palaeolithic flint artefacts, has been investigated in the Palughetto intermorainic basin Venetian Pre-Alps.

The geomorphological and stratigraphical relationships, 14C dates and pollen analyses allow a reconstruction of the environmental history of the basin and provide significant insights into the reforestation and peopling of the Pre-Alps.

The onset of peat accumulation is dated to BP , coinciding with reforestation at middle altitudes that immediately post-dates the immigration of Larix decidua and Picea abies subsp.

Plant macrofossils point to the expansion of spruce about BP , so far one of the earliest directly dated in the late glacial period of southern Europe. The previous hypothesis of an early Holocene spruce immigration in the Southern Alps from Slovenia needs reconsideration. Organic sedimentation stopped at the end of the Younger Dryas and was followed by the evolution of hydromorphic soils containing lithic artefacts, anthropic structures and wood charcoal.

The typological features of the flint implements refer human occupation of the site to the end of the recent Epigravettian. Charcoals yielded dates either consistent with, or younger than, the archaeological chronology, in the early and middle Holocene. Bayesian chronological analyses consistent with synchronous age of 12,, Cal B.

The Younger Dryas impact hypothesis posits that a cosmic impact across much of the Northern Hemisphere deposited the Younger Dryas boundary YDB layer, containing peak abundances in a variable assemblage of proxies, including magnetic and glassy impact-related spherules, high-temperature minerals and melt glass, nanodiamonds, carbon spherules, aciniform carbon, platinum, and osmium.

Bayesian chronological modeling was applied to dates from 23 stratigraphic sections in 12 countries on four continents to establish a modeled YDB age range for this event of 12,, Cal B. This range overlaps that of a peak in extraterrestrial platinum in the Greenland Ice Sheet and of the earliest age of the Younger Dryas climate episode in six proxy records, suggesting a causal connection between the YDB impact event and the Younger Dryas.

The widespread distribution of the YDB layer suggests that it may serve as a datum layer. Kennett, James P. Randolph, Jr. Potential climatic mechanisms associated with the mega drought at cal yr BP : linking proxy data with modern climate analogues. Roughly years ago, a year long mega drought occurred in the central Rocky Mountains, as indicated by pollen evidence from lake sediments from Long Lake, south-eastern Wyoming.

However, pollen evidence does not record the climate mechanisms that caused the drought; they only provide evidence that the drought occurred. A modern climate analogue technique using North American Regional Reanalysis data was applied to the sedimentary data in order to identify possible synoptic and dynamic patterns that may have caused the mega drought at cal yr BP. Our results suggest warm and dry conditions were a result of anomalously higher-than-normal geopotential heights that were centred over the Great Plains beginning in the spring and persisting through the fall.

Drought conditions during the growing seasons was the result of the anomalous high-pressure ridge, which suppressed moisture transport via the low level jet from the Gulf of Mexico, as well as brought in dry continental air from in the interior region of North America. The conditions associated with modern analogues offer a potential climate mechanism that caused the mega drought years ago, and likely led to the changes in vegetation composition as evidenced by the pollen record from Long Lake, Wyoming.

We conducted a detailed study of natural remanence and rock magnetic properties on sediments cores from lake Moreno South-Western Argentina. Based on these measurements, we constructed a paleosecular variation PSV record Irurzun et al. The Declination and Inclination logs of the characteristic remanent magnetization for the cores as function of shortened depth are obtained. The data from all cores were combined to obtain a composite record using the Fisher method.

Comparison between stacked inclination and declination records of lake Moreno and results obtained in previous works, lake Escondido Gogorza et al. This agreement made possible to transform the stacked curves into time series that spans the interval 11 and 21 14C kyr B. Rock magnetic properties of the sediments cores showed uniform magnetic mineralogy and grain size, suggesting that they were suitable for relative paleointensity studies. Coherence analysis showed that the normalized records were not affected by local environmental conditions.

The recorded pseudo-Thellier paleointensity was compared with records obtained from conventional normalizing methods. Comparing the paleointensity curves with others obtained previously in other lakes in the area has allowed us to reach reliable conclusions about centennial-scale features. References: Gogorza, C. Earth, Planets and Space, V51 2 , Gogorza, C. Terrestrial biosphere changes over the last kyr.

Hoogakker, B. Global average areas of grassland and dry shrubland, desert, and tundra biomes show large-scale increases during the Last Glacial Maximum, between ca. These changes are reflected in BIOME4 simulations of global net primary productivity, showing good agreement between the two models.

Such changes are likely to affect terrestrial carbon storage, which in turn influences the stable carbon isotopic composition of seawater as terrestrial carbon is depleted in 13C. Viehberg, Finn A. Transcontinental dispersal of modern humans from the Near East to the Balkans in the Middle and Upper Palaeolithic is expected to have followed the coastline i.

A multiproxy approach enabled us to reconstruct the environmental history. We included biological proxies i. Geomorphological findings in the lake basin and geochemical analyses hint to changing lake water levels at least since 40 ka cal BP that lasted until c.

This supports the theory of persisting dry climate conditions before the onset of the Holocene also inferred from geochemical sediment proxies i. The identified animal remains in the cave sequence change from larger ungulates to smaller ungulates and increase in fish and shellfish. It is proposed that the compositional change in game is not solitarily caused by technology advances, but also by environmental and climatic changes as inferred from sediment archives of Lake Iznik.

Bischoff, J. The Sima de los Huesos site of the Atapuerca complex near Burgos, Spain contains the skeletal remains of at least 28 individuals in a mud breccia underlying an accumulation of the Middle Pleistocene cave bear U. Earlier dating estimates of to kyr were based on U-series and ESR methods applied to bones, made inaccurate by unquantifiable uranium cycling. We report here on a new discovery within the Sima de los Huesos of human bones stratigraphically underlying an in situ speleothem.

Finite dates on the upper part suggest a speleothem growth rate of c. This rate, along with paleontological constraints, place the likely age of the hominids in the interval of to kyr.

All rights reserved. A tree grows a new ring each year, and the thickness can be matched to different years. Scientists have compiled a sequence of tree rings spanning thousands of years, and compared the 14C in them. These are then compared to different 14C dates, which allows them to be calibrated. Along with tree rings, other materials are used to calibrate: ice cores, sedimentary layering, cave deposits, and volcanic eruptions.

On the left-hand axis is the radiocarbon concentration expressed in BP years and the bottom axis shows calendar years. The grey histogram shows possible ages for the sample the higher the histogram the more likely that age is.

The results of calibration are often given as an age range. As the above example from the ORAU shows, the BP date is what is returned during the dating analysis of a material, say a piece of bone. From this a calibrated date is calculated, and given in a range of dates, written as cal BC.

Above, the abbreviations are all used without punctuations, but it is common to see them with punctuations, e. AD Thanks for this great scientific article i liked it therefore I noted it. Though, may I ask about, how radio carbon work to find out the age of the death date?

Also does it have any formula? Could you also tell me what is the C14 contraction? Among them are:. Reimer and colleagues point out that this is just the latest in calibration sets, and further refinements are to be expected.

For example, they've discovered evidence that during the Younger Dryas 12,—12, cal BP , there was a shutdown or at least a steep reduction of the North Atlantic Deep Water formation , which was surely a reflection of climate change; they had to throw out data for that period from the North Atlantic and use a different dataset.

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Kris Hirst is an archaeologist with 30 years of field experience. Her work has appeared in scholarly publications such as Archaeology Online and Science.

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