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

1998 ◽  
Vol 152 (1-3) ◽  
pp. 177-188 ◽  
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

scholarly journals Hydrographic shifts south of Australia over the last deglaciation and possible interhemispheric linkages

2021 ◽  
pp. 1-12
Author(s):  
Matthias Moros ◽  
Patrick De Deckker ◽  
Kerstin Perner ◽  
Ulysses S. Ninnemann ◽  
Lukas Wacker ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Southern Hemisphere ◽  
Critical Role ◽  
Temperature Response ◽  
South Australia ◽  
Last Deglaciation ◽  
Tight Coupling ◽  
Oceanic Fronts ◽  
The Last Deglaciation ◽  
Circumpolar Current

Abstract Northern and southern hemispheric influences—particularly changes in Southern Hemisphere westerly winds (SSW) and Southern Ocean ventilation—triggered the stepwise atmospheric CO2 increase that accompanied the last deglaciation. One approach for gaining potential insights into past changes in SWW/CO2 upwelling is to reconstruct the positions of the northern oceanic fronts associated with the Antarctic Circumpolar Current. Using two deep-sea cores located ~600 km apart off the southern coast of Australia, we detail oceanic changes from ~23 to 6 ka using foraminifer faunal and biomarker alkenone records. Our results indicate a tight coupling between hydrographic and related frontal displacements offshore South Australia (and by analogy, possibly the entire Southern Ocean) and Northern Hemisphere (NH) climate that may help confirm previous hypotheses that the westerlies play a critical role in modulating CO2 uptake and release from the Southern Ocean on millennial and potentially even centennial timescales. The intensity and extent of the northward displacements of the Subtropical Front following well-known NH cold events seem to decrease with progressing NH ice sheet deglaciation and parallel a weakening NH temperature response and amplitude of Intertropical Convergence Zone shifts. In addition, an exceptional poleward shift of Southern Hemisphere fronts occurs during the NH Heinrich Stadial 1. This event was likely facilitated by the NH ice maximum and acted as a coup-de-grâce for glacial ocean stratification and its high CO2 capacitance. Thus, through its influence on the global atmosphere and on ocean mixing, “excessive” NH glaciation could have triggered its own demise by facilitating the destratification of the glacial ocean CO2 state.

The chronology of the last Deglaciation: Implications to the cause of the Younger Dryas Event

1988 ◽  
Vol 3 (1) ◽  
pp. 1-19 ◽  
Author(s):  
W. S. Broecker ◽  
M. Andree ◽  
W. Wolfli ◽  
H. Oeschger ◽  
G. Bonani ◽  
...  
Keyword(s):  
Younger Dryas ◽  
Last Deglaciation ◽  
The Last Deglaciation ◽  
Younger Dryas Event

Timing of the last Deglaciation in the Sierra Nevada of the Mérida Andes, Venezuela

2013 ◽  
Vol 80 (3) ◽  
pp. 482-494 ◽  
Author(s):  
Julien Carcaillet ◽  
Isandra Angel ◽  
Eduardo Carrillo ◽  
Franck A. Audemard ◽  
Christian Beck
Keyword(s):  
Sierra Nevada ◽  
Late Pleistocene ◽  
Younger Dryas ◽  
Ice Cover ◽  
Published Data ◽  
Last Deglaciation ◽  
The Last Deglaciation ◽  
Absolute Age ◽  
Glacial Landforms

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.

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

Radiocarbon ◽  
1997 ◽  
Vol 40 (1) ◽  
pp. 483-494 ◽  
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.

scholarly journals Climate bifurcation during the last deglaciation

2012 ◽  
Vol 8 (1) ◽  
pp. 321-348 ◽  
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.

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

2005 ◽  
Vol 64 (2) ◽  
pp. 249-256 ◽  
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.

scholarly journals Climate bifurcation during the last deglaciation?

2012 ◽  
Vol 8 (4) ◽  
pp. 1127-1139 ◽  
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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