At the termination of the Younger Dryas , Populus underwent another widespread decline, this time in response to competition from boreal and temperate taxa as the climate abruptly warmed. Late glacial-early Holocene pollen assemblages with high quantities of Populus pollen often lack modern analogues and thus confound quantitative paleoclimatic reconstructions; our results provide a context to interpret these assemblages.

Furthermore, while Populus may continue to expand in the future in response to human disturbance and increasing temperatures, its sensitivity to competition may eventually put it at risk as global warming accelerates.

Lateglacial landscape and vegetation change and the younger dryas climatic oscillation in New Zealand. Lateglacial sequences in New Zealand show progressive afforestation and landscape stabilization reflecting a warming climate. Between 14, BP and 11, BP, afforestation and landscape stability was achieved throughout most of the North Island and the northwest sector of the South Island. In the South Island, scrub and tree ferns were replacing previous grasslands in the east by 11, BP, and broadleaved forest was spreading in the west.

No significant reversals of these trends occurred and afforestation was complete by BP. Glaciers of the high central part of the Southern Alps made a series of advances between 14, and BP Most of these advances are poorly dated but two moraines are of Younger Dryas age.

The cause of the northern hemisphere Younger Dryas cooling is still uncertain, and expected Southern Hemisphere responses may differ according to the mechanism proposed for the cooling. Poor chronological resolution and apparent conflict between the various types of evidence for climatic change make detection of an unambiguous Younger Dryas in New Zealand problematical.

Positive anomaly in platinum group elements and the presence of shocked diamonds: Two question marks at the Younger Dryas. Recently, a large size impact was proposed as the cause of the global changes taking place at the Younger Dryas YD some 12,9 kyr ago. Impact evidence was reported in a C-rich black layer of broad geographic distribution. The impact markers consist of a large anomaly in the concentration of platinum group elements PGE and the presence of nanodiamonds, in particular lonsdaleite, which hexagonal structure is believed to be of shock origin.

The impact is proposed to have occurred on the North American continent. Therefore, an alternative hypothesis is that a cometary projectile exploded fully within the atmosphere spreading PGE and shock formed diamonds, without any target rock contribution, all around the Northern hemisphere.

At all sites analyzed the PGE pattern is typical of that of the continental crust. In several craters Popigai, Ries or at the KT boundary nanodiamonds have been reported associated with shocked materials. The Lommel nanodiamonds present in the Younger Dryas layer do resemble nanodiamonds found in carbon spherules of unknown origin previously reported in top soil from several localities in Belgium and Germany.

2018–19 North American winter

The C stable isotopic. Minimal geological methane emissions during the Younger Dryas -Preboreal abrupt warming event. Methane CH 4 is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods measuring emissions and top-down approaches measuring atmospheric mole fractions and isotopes for constraining these geological emissions have been associated with large uncertainties.

Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane 14 CH 4 in the past atmosphere and show that geological methane emissions were no higher than Assuming that past geological methane emissions were no lower than today, our results indicate that current estimates of today's natural geological methane emissions about 52 teragrams per year are too high and, by extension, that current estimates of anthropogenic fossil methane emissions are too low.

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Our results also improve on and confirm earlier findings that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas -Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs marine methane hydrates, permafrost and methane trapped under ice to 19 per cent or less 95 per cent confidence.

To the extent that the characteristics of the most recent deglaciation and the Younger Dryas -Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur. Abrupt release of terrigenous organic carbon to the Laptev Sea at termination of the Younger Dryas.

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Tesi, T. Based on analysis of a piston core collected in from the Lena River paleo delta, now Laptev Sea, we show that rapid and massive organic carbon OC deposition took place into the marine system at the termination of the Younger Dryas when the Arctic region experienced a large and extremely fast climate change. The OC appears to be a few thousand years old at time of deposition ca.

Altogether our results indicate that fast climate warming exerts first-order control on large-scale carbon redistribution. Because the Younger Dryas -Preboreal transition occurred within a few decades, we infer that the abrupt and large release of terrigenous OC was essentially driven by rapid changes in the permafrost stability i. Interestingly, only surface and sub-surface carbon pools i.

Petrenko, Vasilii V. Methane CH4 is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane 14CH4 in the past atmosphere and show that geological methane emissions were no higher than The controversial Younger Dryas impact hypothesis suggests that at the onset of the Younger Dryas an extraterrestrial impact over North America caused a global catastrophe.

The main evidence for this impact—after the other markers proved to be neither reproducible nor consistent with an impact—is the alleged occurrence of several nanodiamond polymorphs, including the proposed presence of lonsdaleite, a shock polymorph of diamond.

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Our accelerator mass spectrometry radiocarbon dates of 14 individual charcoal particles are internally consistent and show that wildfires occurred well after the proposed impact. In addition we present evidence for the occurrence of cubic diamond in glass-like carbon. No lonsdaleite was found.

The relation of the cubic nanodiamonds to glass-like carbon, which is produced during wildfires, suggests that these nanodiamonds might have formed after, rather than at the onset of, the Younger Dryas. Our analysis thus provides no support for the Younger Dryas impact hypothesis. Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences. Moore, Christopher R. Randolph; Goodyear, Albert C.

Victor; Bunch, Ted E. In order to evaluate its geographic extent, fire-assay and inductively coupled plasma mass spectrometry FA and ICP-MS elemental analyses were performed on 11 widely separated archaeological bulk sedimentary sequences. We expect the Pt anomaly to serve as a widely-distributed time marker horizon datum for identification and correlation of the onset of the YD climatic episode at 12, Cal B.

This Pt datum will facilitate the dating and correlating of archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control. Toomey, Michael; Korty, Robert L. The risk posed by intensification of North Atlantic hurricane activity remains controversial, in part due to a lack of available storm proxy records that extend beyond the relatively stable climates of the late Holocene. Despite potentially hostile conditions for cyclogenesis in the tropical North Atlantic at that time, our record and numerical experiments suggest that strong hurricanes may have regularly affected Florida.

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. In , Firestone et al. Up to now, the evidence for this proposed impact has been heavily debated Pinter et al. Two years later, Mahaney et al. However, the data presented consisted of an SEM image of the surface of a quartz grain only, and in following work Mahaney et al.

Instead, they showed grains with oriented cracks along their edges, which they claimed to be related to the 'mass impact and extreme heat' from incoming ejecta material. However, oriented cracks are not accepted evidence for an impact French, Koeberl, Possible shocked quartz grains were isolated using density separation, mounted in epoxy and polished.

No evidence for oriented cracks along grain edges, like those reported by Mahaney et al.

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Transmitted light microscopy showed that a number of grains contained tectonic deformation lamellae. One grain from the Usselo horizon contains at least two sets of closely spaced, straight, and narrow lamellae, similar to PDFs. In SEM-CL imaging however, only some of these lamellae showed up as non-luminescent, while most had the same intensity as the host grain.

It is possible that these lamellae represent planar fractures, which also form by low pressure shock processes. It must be noted that even if. The Younger Dryas Stadial marks the final succession of climatic fluctuations of the last Glacial. Whilst well studied in records from Europe and Greenland, few high resolution records are available from East Asia. Here we present a high resolution, multi-proxy study of the Lake Suigetsu Japan sediments using the 'SG06' composite profile. Firstly, our results show that the climatic equivalent of the Younger Dryas at Lake Suigetsu shows no major lead or lag in comparison to records from the North Atlantic region, which was postulated by an earlier project on the Suigetsu sediments 'SG93'.

Furthermore, some of the analysed proxies from the SG06 core show a sub-division of the Younger Dryas Stadial. The timing of this sub-division is similar to the bi-partition of the Younger Dryas Stadial observed in a number of European records e. Lane et al. This bi-partition was related to a northward shift of the westerly wind jet in the North Atlantic region. Our findings imply that the underlying climatic mechanism operated on a hemispheric rather than just on a regional scale. References: Lane et al. Younger Dryas cooling and the Greenland climate response to CO2. Such YD cooling implies a muted Greenland climate response to atmospheric CO 2 , contrary to physical predictions of an enhanced high-latitude response to future increases in CO 2.

Our results thus suggest that Greenland climate was warmer during the YD relative to the OD in response to rising atmospheric CO 2 , consistent with sea surface temperature reconstructions and physical predictions, and has a sensitivity approximately twice that found in climate models for current climate due to an enhanced albedo feedback during the last deglaciation. Younger Dryas glacial stillstands on the Bolivian Altiplano: pattern and climatic implications. Modifications of the global climate during the last deglaciation have been characterized by regional reorganization that may have in turn amplified or attenuated the global changes.

Notably, the respective influences of the Southern and Northern Hemispheres are poorly understood in the Tropics. This underlines the importance of studying past climate variations in the Tropics, particularly in the poorly documented tropical moutain areas. Cosmogenic exposure dating applied to the glacial landscapes provides temporal constraints on glacier fluctuations in response of climate variations. This permits high-resolution reconstructions of regional climates. In this work we present new cosmogenic ages from two different locations of the Bolivian Altiplano, the Nevado Sajama volcano S On the Sajama, new cosmogenic 3He dates support a late local glacial maximum, synchronous with the plaeolake Tauca highstand ca.

Our data document also several recession episodes with the youngest one, characterized by an ELA of m, that seems to correspond to the Younger Dryas YD stadial ca. In the Zongo valley, two recessional moraines have indistinguishable cosmogenic 10Be ages of ca.

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Upstream, we identified an intermediate recessional moraine that could either be synchronous with Heinrich 1 or with the Antarctic Cold Reversal episode. Upward along the valley, a Younger Dryas stadial is clearly established by well-clustered cosmogenic 10Be ages, yielding a moraine age of ca. The onset of the Holocene has been generally considered rapid and uninterrupted in the circum-Atlantic region.

Loss-on-ignition LOI - an index of organic carbon profiles from 18 lateglacial-aged lakes in Nova Scotia, Canada, together with chironomid-inferred temperature reconstructions at 5 sites, demonstrate that the rapid warming from the Younger Dryas GS-1 to the Holocene was interrupted by a cooling of 1.

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The resulting inflection or reversal on the rising temperature curve has also been identified at 35 sites outside Nova Scotia from terrestrial and marine settings, indicating that this cool step is a robust feature throughout the North Atlantic and is likely the result of major oceanic and atmospheric reorganization of the Holocene climate system. Origin and provenance of spherules and magnetic grains at the Younger Dryas boundary. In support of this hypothesis, varying peak abundances of magnetic grains with iridium and magnetic microspherules have been reported at the Younger Dryas boundary YDB.

The late deglacial interval from approximately 13 to 11 kyr BP contains some of the best documented abrupt climate changes in the Past, the Younger Dryas YD. It is also an interval when the bipolar climatic signature of millennial-scale changes in the Atlantic meridional overturning circulation AMOC is well expressed.