The Last Deglaciation in Antarctica: Further Evidence of a “Younger Dryas” Type Climatic Event

In the tropical Mérida Andes (northwestern Venezuela), glacial landforms were found at altitudes between 2600 and 5000 m, corresponding to 600 km2 of ice cover during the maximum glacial extension. However, the lack of sufficient absolute age data prevents detailed reconstruction of the timing of the last deglaciation. On the northwestern flank of the Mucuñuque Massif, successive moraines and striated eroded basement surfaces were sampled for cosmogenic 10Be investigation. Their compilation with published data allows the establishment of a detailed chronology of the post-LGM glacier history. The oldest moraines (18.1 and 16.8 ka) correspond to the Oldest Dryas. Successive moraine ridges indicate stops in the overall retreat between the LGM and the Younger Dryas. The cold and short Older Dryas stadial has been identified. Results indicate that most of the ice withdrew during the Pleistocene. The dataset supports an intensification of the vertical retreat rate from ~ 25 m/ka during the late Pleistocene to ~ 310 m/ka during the Pleistocene/Holocene. Afterwards, the glacier was confined and located in the higher altitude zones. The altitude difference of the Younger Dryas moraines in the Mucubají, La Victoria and Los Zerpa valleys indicates a strong effect of valley orientation on the altitude of moraine development.

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A New 14C Calibration Data Set for the Last Deglaciation Based on Marine Varves

Radiocarbon ◽

10.1017/s0033822200018361 ◽

1997 ◽

Vol 40 (1) ◽

pp. 483-494 ◽

Cited By ~ 43

Author(s):

Konrad A. Hughen ◽

Jonathan T. Overpeck ◽

Scott J. Lehman ◽

Michaele Kashgarian ◽

John R. Southon ◽

...

Keyword(s):

Global Climate ◽

Ice Core ◽

Younger Dryas ◽

Core Layer ◽

Cariaco Basin ◽

Calibration Data ◽

Last Deglaciation ◽

Data Set ◽

The Last Deglaciation ◽

Calibration Data Set

Varved sediments of the tropical Cariaco Basin provide a new 14C calibration data set for the period of deglaciation (10,000 to 14,500 years before present: 10–14.5 cal ka bp). Independent evaluations of the Cariaco Basin calendar and 14C chronologies were based on the agreement of varve ages with the GISP2 ice core layer chronology for similar high-resolution paleoclimate records, in addition to 14C age agreement with terrestrial 14C dates, even during large climatic changes. These assessments indicate that the Cariaco Basin 14C reservoir age remained stable throughout the Younger Dryas and late Allerød climatic events and that the varve and 14C chronologies provide an accurate alternative to existing calibrations based on coral U/Th dates. The Cariaco Basin calibration generally agrees with coral-derived calibrations but is more continuous and resolves century-scale details of 14C change not seen in the coral records. 14C plateaus can be identified at 9.6, 11.4, and 11.7 14C ka bp, in addition to a large, sloping “plateau” during the Younger Dryas (∼10 to 11 14C ka bp). Accounting for features such as these is crucial to determining the relative timing and rates of change during abrupt global climate changes of the last deglaciation.

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Climate bifurcation during the last deglaciation

Climate of the Past Discussions ◽

10.5194/cpd-8-321-2012 ◽

2012 ◽

Vol 8 (1) ◽

pp. 321-348 ◽

Cited By ~ 2

Author(s):

T. M. Lenton ◽

V. N. Livina ◽

V. Dakos ◽

M. Scheffer

Keyword(s):

Climate Variability ◽

Early Warning ◽

Bifurcation Point ◽

Younger Dryas ◽

Cold Climate ◽

Meridional Overturning Circulation ◽

Last Deglaciation ◽

Overturning Circulation ◽

Slowing Down ◽

The Last Deglaciation

Abstract. The last deglaciation was characterised by two abrupt warming events, at the start of the Bølling-Allerød and at the end of the Younger Dryas, but their underlying causes are unclear. Some abrupt climate changes may involve gradual forcing past a bifurcation point, in which a prevailing climate state loses its stability and the climate tips into an alternative state, providing an early warning signal in the form of slowing responses to perturbations. However, the abrupt Dansgaard-Oeschger (DO) events during the last ice age were probably triggered by stochastic fluctuations without bifurcation or early warning, and whether the onset of the Bølling-Allerød (DO event 1) was preceded by slowing down or not is debated. Here we show that the interval from the Last Glacial Maximum to the end of the Younger Dryas, as recorded in three Greenland ice cores with two different climate proxies, was accompanied by a robust slowing down in climate dynamics and an increase in climate variability, consistent with approaching bifurcation. Prior to the Bølling warming there was a robust increase in climate variability but no consistent slowing down signal, suggesting this abrupt change was probably triggered by a stochastic fluctuation. The Bølling warming marked a distinct destabilisation of the climate system, which excited an internal mode of variability in Atlantic meridional overturning circulation strength, causing multi-centennial climate fluctuations. There is some evidence for slowing down in the transition to and during the Younger Dryas. We infer that a bifurcation point was finally approached at the end of the Younger Dryas, in which the cold climate state, with weak Atlantic overturning circulation, lost its stability, and the climate tipped irreversibly into a warm interglacial state. The lack of a large triggering perturbation at the end of the Younger Dryas, and the fact that subsequent meltwater perturbations did not cause sustained cooling, support the bifurcation hypothesis.

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Rapid changes in the oceanic fronts in the Norwegian Sea during the last deglaciation: implications for the Younger Dryas cooling event

Marine Geology ◽

10.1016/s0025-3227(98)00070-x ◽

1998 ◽

Vol 152 (1-3) ◽

pp. 177-188 ◽

Cited By ~ 11

Author(s):

D Klitgaard-Kristensen ◽

T.L Rasmussen ◽

H.P Sejrup ◽

H Haflidason ◽

Tj.C.E van Weering

Keyword(s):

Younger Dryas ◽

Last Deglaciation ◽

Norwegian Sea ◽

Oceanic Fronts ◽

Rapid Changes ◽

The Last Deglaciation

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A Speleothem Record of Younger Dryas Cooling, Klamath Mountains, Oregon, USA

Quaternary Research ◽

10.1016/j.yqres.2005.06.008 ◽

2005 ◽

Vol 64 (2) ◽

pp. 249-256 ◽

Cited By ~ 55

Author(s):

David A. Vacco ◽

Peter U. Clark ◽

Alan C. Mix ◽

Hai Cheng ◽

R. Lawrence Edwards

Keyword(s):

Climate Change ◽

Northern Hemisphere ◽

Younger Dryas ◽

Sampling Interval ◽

Temperature Variability ◽

Early Holocene ◽

Last Deglaciation ◽

Klamath Mountains ◽

Scale Temperature ◽

The Last Deglaciation

AbstractA well-dated δ18O record in a stalagmite from a cave in the Klamath Mountains, Oregon, with a sampling interval of 50 yr, indicates that the climate of this region cooled essentially synchronously with Younger Dryas climate change elsewhere in the Northern Hemisphere. The δ18O record also indicates significant century-scale temperature variability during the early Holocene. The δ13C record suggests increasing biomass over the cave through the last deglaciation, with century-scale variability but with little detectable response of vegetation to Younger Dryas cooling.

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Climate bifurcation during the last deglaciation?

Climate of the Past ◽

10.5194/cp-8-1127-2012 ◽

2012 ◽

Vol 8 (4) ◽

pp. 1127-1139 ◽

Cited By ~ 27

Author(s):

T. M. Lenton ◽

V. N. Livina ◽

V. Dakos ◽

M. Scheffer

Keyword(s):

Climate Variability ◽

Early Warning ◽

Bifurcation Point ◽

Climate Changes ◽

Younger Dryas ◽

Cold Climate ◽

Last Deglaciation ◽

Overturning Circulation ◽

Slowing Down ◽

The Last Deglaciation

Abstract. There were two abrupt warming events during the last deglaciation, at the start of the Bølling-Allerød and at the end of the Younger Dryas, but their underlying dynamics are unclear. Some abrupt climate changes may involve gradual forcing past a bifurcation point, in which a prevailing climate state loses its stability and the climate tips into an alternative state, providing an early warning signal in the form of slowing responses to perturbations, which may be accompanied by increasing variability. Alternatively, short-term stochastic variability in the climate system can trigger abrupt climate changes, without early warning. Previous work has found signals consistent with slowing down during the last deglaciation as a whole, and during the Younger Dryas, but with conflicting results in the run-up to the Bølling-Allerød. Based on this, we hypothesise that a bifurcation point was approached at the end of the Younger Dryas, in which the cold climate state, with weak Atlantic overturning circulation, lost its stability, and the climate tipped irreversibly into a warm interglacial state. To test the bifurcation hypothesis, we analysed two different climate proxies in three Greenland ice cores, from the Last Glacial Maximum to the end of the Younger Dryas. Prior to the Bølling warming, there was a robust increase in climate variability but no consistent slowing down signal, suggesting this abrupt change was probably triggered by a stochastic fluctuation. The transition to the warm Bølling-Allerød state was accompanied by a slowing down in climate dynamics and an increase in climate variability. We suggest that the Bølling warming excited an internal mode of variability in Atlantic meridional overturning circulation strength, causing multi-centennial climate fluctuations. However, the return to the Younger Dryas cold state increased climate stability. We find no consistent evidence for slowing down during the Younger Dryas, or in a longer spliced record of the cold climate state before and after the Bølling-Allerød. Therefore, the end of the Younger Dryas may also have been triggered by a stochastic perturbation.

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Cirque glacier activity in arctic Norway during the last deglaciation

Quaternary Research ◽

10.1016/j.yqres.2007.07.006 ◽

2007 ◽

Vol 68 (3) ◽

pp. 387-399 ◽

Cited By ~ 22

Author(s):

Øyvind Paasche ◽

Svein Olaf Dahl ◽

Jostein Bakke ◽

Reidar Løvlie ◽

Atle Nesje

Keyword(s):

Regional Distribution ◽

Lacustrine Sediments ◽

Younger Dryas ◽

Last Deglaciation ◽

Visual Interpretation ◽

Dry Period ◽

Equilibrium Line Altitude ◽

Glacial Retreat ◽

Magnetic Parameters ◽

The Last Deglaciation

AbstractNumerous cirques of the Lofoten–Vesterålen archipelago in northern Norway have distinct moraine sequences that previously have been assigned to the Allerød-Younger Dryas (∼ 13,400 to 11,700 yr BP) interval, constraining the regional distribution of the equilibrium-line altitude (ELA) of cirque and valley glaciers. Here we present evidence from a once glacier-fed lake on southern Andøya that contests this view. Analyses of radiocarbon dated lacustrine sediments including rock magnetic parameters, grain size, organic matter, dry bulk density and visual interpretation suggest that no glacier was present in the low-lying cirque during the Younger Dryas-Allerød. The initiation of the glacial retreat commenced with the onset of the Bølling warming (∼ 14,700 yr BP) and was completed by the onset of Allerød Interstade (∼ 13,400 yr BP). The reconstructed glacier stages of the investigated cirque coincide with a cool and dry period from ∼ 17,500 to 14,700 yr BP and a somewhat larger Last Glacial Maximum (LGM) advance possibly occurring between ∼ 21,050 and 19,100 yr BP.

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Early Younger Dryas glacier culmination in southern Alaska: Implications for North Atlantic climate change during the last deglaciation

Geology ◽

10.1130/g46058.1 ◽

2019 ◽

Vol 47 (6) ◽

pp. 550-554 ◽

Cited By ~ 6

Author(s):

Nicolás E. Young ◽

Jason P. Briner ◽

Joerg Schaefer ◽

Susan Zimmerman ◽

Robert C. Finkel

Keyword(s):

Climate Change ◽

North Atlantic ◽

Younger Dryas ◽

Last Deglaciation ◽

North Atlantic Climate ◽

The Last Deglaciation

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Antarctic-like temperature variations in the Tropical Andes recorded by glaciers and lake levels during the last deglaciation

10.5194/egusphere-egu21-12951 ◽

2021 ◽

Author(s):

Léo Martin ◽

Pierre-Henri Blard ◽

Jérôme Lavé ◽

Vincent Jomelli ◽

Maarten Lupker ◽

...

Keyword(s):

Younger Dryas ◽

Cosmic Ray ◽

Temperature Reconstruction ◽

Warming Trend ◽

Last Deglaciation ◽

Tropical Andes ◽

Tropical Regions ◽

The North ◽

The Last Deglaciation ◽

The Antarctic

The climatic reorganizations that occurred in the Southern and Northern hemispheres during the last deglaciation are thought to have affected the continental tropical regions. However, the respective impact of North and Southern climatic changes in the Tropics are still poorly understood. In the Norhtern Tropical Andes, moraines records indicate that the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) stage was more represented than the Younger Dryas (12.9-11.7 ka BP) (Jomelli et al., 2014). However, further South, in the Altiplano basin (Bolivia), two cold periods of the North Hemisphere (Heinrich Stadial 1a (16.5-14.5 ka) and Younger Dryas) are synchronous with (i) major advances or stillstands of paleo-glaciers and with (ii) the highstands of the giant palaeo-lakes Tauca and Coipasa (Martin et al., 2018). Therefore, additional geochronological records of paleoglaciers fluctuations are necessary to address the respective impacts of North and South Hemisphere on the glacial dynamics in the region.We present new Cosmic Ray Exposure (CRE) ages from glacial landforms of the Bolivian Andes that extend pre-existing datasets for four different sites spreading from 16 to 21&#176;S. We reconstruct the Equilibrium Line Altitudes (ELA) associated with each moraine with the AAR method and use them in an inverse algorithm that combines both the palaeo-glaciers and palaeo-lake budgets to derive temperature and precipitation reconstructions. Our temperature reconstruction (&#916;T vs. Present) shows a consistent trend through the four glacial sites with a progressive warming from &#916;T= -5&#176;C (17 ka BP) to &#8211;2.5&#176;C (15-14.5 ka BP, at the end of the Tauca highstand). This is followed by a return to colder conditions, around -4&#176;C, during the ACR (15.5-12.9 ka BP). The Coipasa highstand is coeval with another warming trend followed by &#916;T stabilization at the onset of the Holocene (circa 10 ka BP), around -3&#176;C. Precipitation is mainly characterized by increases during the lake highstands, modulated by the distance from the glacial sites to the center of the paleolakes that are moisture sources (recycling processes).These new results highlight the decorrelation of the glacier dynamics to the temperature signal in regions that are characterized by high precipitation variability. They also provide a theoretical frame to explain how both regional and global forcings can imprint the paleo-glacial records. Our results strongly suggest that during the last deglaciation (20 &#8211; 10 ka BP), in the Tropical Andes, atmospheric temperatures follow the Antarctic variability, while precipitation is driven by the changes occurring in the Northern Hemisphere.ReferencesJomelli et al., Nature, 2014; Martin et al., Sc. Advances, 2018

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