scholarly journals Centennial-scale variability of the British Ice Sheet: Implications for climate forcing and Atlantic meridional overturning circulation during the last deglaciation

2007 ◽  
Vol 22 (1) ◽  
pp. n/a-n/a ◽  
Author(s):  
Paul C. Knutz ◽  
Rainer Zahn ◽  
Ian R. Hall
Keyword(s):  
Ice Sheet ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Climate Forcing ◽  
Last Deglaciation ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
The Last Deglaciation

scholarly journals Drivers of the evolution and amplitude of African Humid Periods

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Laurie Menviel ◽  
Aline Govin ◽  
Arthur Avenas ◽  
Katrin J. Meissner ◽  
Katharine M. Grant ◽  
...  
Keyword(s):  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Interglacial Period ◽  
Last Deglaciation ◽  
Last Interglacial ◽  
Overturning Circulation ◽  
Last Interglacial Period ◽  
Meridional Overturning ◽  
Northern Hemispheric ◽  
The Last Deglaciation

AbstractDuring orbital precession minima, the Sahara was humid and more vegetated, providing potential corridors for Hominins migration. Uncertainties remain over the climatic processes controlling the initiation, demise and amplitude of these African Humid Periods. Here we study these processes using a series of transient simulations of the penultimate deglaciation and Last Interglacial period, and compare the results with a transient simulation of the last deglaciation and Holocene. We find that the strengthening of the Atlantic Meridional Overturning Circulation at the end of deglacial millennial-scale events exerts a dominant control on the abrupt initiation of African Humid Periods as the Atlantic Meridional Overturning Circulation modulates the position of the Intertropical Convergence Zone. In addition, residual Northern Hemispheric ice-sheets can delay the peak of the African Humid Period. Through its impact on Northern Hemispheric ice-sheets disintegration and thus Atlantic Meridional Overturning Circulation, the larger rate of insolation increase during the penultimate compared to the last deglaciation can explain the earlier and more abrupt onset of the African Humid Period during the Last Interglacial period. Finally, we show that the mean climate state modulates precipitation variability, with higher variability under wetter background conditions.

scholarly journals Impact of North Atlantic – GIN Sea exchange on deglaciation evolution of Atlantic Meridional Overturning Circulation

2011 ◽  
Vol 7 (1) ◽  
pp. 521-534
Author(s):  
J. Cheng ◽  
Z. Liu ◽  
F. He ◽  
B. L. Otto-Bliesner
Keyword(s):  
North Atlantic ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Transient Simulation ◽  
Last Deglaciation ◽  
Overturning Circulation ◽  
Sensitivity Experiments ◽  
Meridional Overturning ◽  
The Last Deglaciation ◽  
Mean State

Abstract. The Bølling-Allerød (BA) warming is the most pronounced abrupt climate change event during the last deglaciation. Two notable features of the BA onset are found in our transient simulation of the last deglaciation with CCSM3: the first is the occurrence of an overshoot in the Atlantic Meridional Overturning Circulation (AMOC, about 20 Sv as to 13 Sv at Last Glacial Maximum) and the second is the subsequent transition of AMOC from a glacial (about 13 Sv) to an interglacial mean state (about 18 Sv). Here, we present two new sensitivity experiments to explicitly illustrate the impact of North Atlantic – GIN Sea exchange on the deglaciation evolution of the AMOC. In these sensitivity experiments, the oceanic exchange during the BA onset is inhibited by introducing a Partial Blocking scheme. In response to this, the deep-water formation in the GIN Sea is reduced by 80% compared to the transient simulation. This in turn results in a reduced AMOC overshoot followed by a lower mean state of the AMOC. Our results therefore suggest that, oceanic processes were more important than the external forcings and atmospheric processes for the AMOC evolution during the BA onset.

scholarly journals Millennial variability of terrigenous transport to the central-southern Peruvian margin during the last deglaciation (18–13 kyr BP)

2022 ◽  
Author(s):  
Marco Yseki ◽  
Bruno Turcq ◽  
Sandrine Caquineau ◽  
Renato Salvatteci ◽  
José Solis ◽  
...  
Keyword(s):  
South America ◽  
Walker Circulation ◽  
Atlantic Meridional Overturning Circulation ◽  
Intertropical Convergence Zone ◽  
Meridional Overturning Circulation ◽  
Last Deglaciation ◽  
Overturning Circulation ◽  
Meridional Overturning ◽  
The Last Deglaciation ◽  
End Members

Abstract. Reconstructing precipitation and wind from the geological record could help to understand the potential changes in precipitation and wind dynamics in response to climate change in Peru. The last deglaciation offers natural experimental conditions to test precipitation and wind dynamics response to high latitude forcing. While considerable research has been done to reconstruct precipitation variability during the last deglaciation in the Atlantic sector of South America, the Pacific sector of South America has received little attention. This work aims to fill this gap by reconstructing types of terrigenous transport to the central-southern Peruvian margin (12° S and 14º S) during the last deglaciation (18–13 kyr BP). For this purpose, we used grain-size distribution in sediments of marine core M77/2-005-3 (Callao, 12º S) and G14 (Pisco, 14º S). We analyzed end-members (EM) to identify grain-size components and reconstruct potential sources and transport processes of terrigenous material across time. We identified four end-members for both Callao and Pisco sediments. In Callao, we propose that changes in EM4 (101 μm) and EM2 (58 μm) contribution mainly reflect hydrodynamic energy and diffuse sources, respectively, while EM3 (77 um) and EM1 (11 μm) variations reflect changes in aeolian and fluvial inputs, respectively. In Pisco, changes in the contribution of EM1 (10 μm) reflect changes in river inputs while EM2 (52 μm), EM3 (75 μm) and EM4 (94 μm) reflect an aeolian origin linked to surface winds. At millennial-scale, our record shows an increase of the fluvial inputs during the last part of Heinrich Stadial 1 (~ 16–14.7 kyr BP) at both locations. This increase was linked to higher precipitation in Andes related to a reduction of the Atlantic Meridional Overturning Circulation and meltwater discharge in North Atlantic. In contrast, during Bølling-Allerød (~ 14.7–13 kyr BP), there was an aeolian input increase, associated with stronger winds and lower precipitation that indicate an expansion of the South Pacific Subtropical High. These conditions would correspond to a northern displacement of the Intertropical Convergence Zone-South Subtropical High system associated with a stronger Walker circulation. Our results suggest that variations in river discharge and changes in surface wind intensity in the western margin of South America during the last deglaciation were sensitive to Atlantic Meridional Overturning Circulation variations and Walker circulation on millennial timescales. In the context of global warming, large-scale precipitation and fluvial discharge increases in the Andes related to Atlantic Meridional Overturning Circulation decline and southward displacement of the Intertropical Convergence Zone should be considered.

scholarly journals Climate and ice sheet evolutions from the last glacial maximum to the pre-industrial period with an ice-sheet–climate coupled model

2021 ◽  
Vol 17 (5) ◽  
pp. 2179-2199
Author(s):  
Aurélien Quiquet ◽  
Didier M. Roche ◽  
Christophe Dumas ◽  
Nathaëlle Bouttes ◽  
Fanny Lhardy
Keyword(s):  
Ice Sheet ◽  
Atlantic Meridional Overturning Circulation ◽  
Meridional Overturning Circulation ◽  
Freshwater Flux ◽  
Oceanic Circulation ◽  
Last Deglaciation ◽  
Grounding Line ◽  
Meridional Overturning ◽  
Reference Experiment ◽  
The Last Deglaciation

Abstract. The last deglaciation offers an unique opportunity to understand the climate–ice-sheet interactions in a global warming context. In this paper, to tackle this question, we use an Earth system model of intermediate complexity coupled to an ice sheet model covering the Northern Hemisphere to simulate the last deglaciation and the Holocene (26–0 ka). We use a synchronous coupling every year between the ice sheet and the rest of the climate system and we ensure a closed water cycle considering the release of freshwater flux to the ocean due to ice sheet melting. Our reference experiment displays a gradual warming in response to the forcings, with no abrupt changes. In this case, while the amplitude of the freshwater flux to the ocean induced by ice sheet retreat is realistic, it is sufficient to shut down the Atlantic meridional overturning circulation from which the model does not recover within the time period simulated. However, with reduced freshwater flux we are nonetheless able to obtain different oceanic circulation evolutions, including some abrupt transitions between shut-down and active circulation states in the course of the deglaciation. The inclusion of a parameterisation for the sinking of brines around Antarctica also produces an abrupt recovery of the Atlantic meridional overturning circulation, absent in the reference experiment. The fast oceanic circulation recoveries lead to abrupt warming phases in Greenland. Our simulated ice sheet geometry evolution is in overall good agreement with available global reconstructions, even though the abrupt sea level rise at 14.6 ka is underestimated, possibly because the climate model underestimates the millennial-scale temperature variability. In the course of the deglaciation, large-scale grounding line instabilities are simulated both for the Eurasian and North American ice sheets. The first instability occurs in the Barents–Kara seas for the Eurasian ice sheet at 14.5 ka. A second grounding line instability occurs ca. 12 ka in the proglacial lake that formed at the southern margin of the North American ice sheet. With additional asynchronously coupled experiments, we assess the sensitivity of our results to different ice sheet model choices related to surface and sub-shelf mass balance, ice deformation and grounding line representation. While the ice sheet evolutions differ within this ensemble, the global climate trajectory is only weakly affected by these choices. In our experiments, only the abrupt shifts in the oceanic circulation due to freshwater fluxes are able to produce some millennial-scale variability since no self-generating abrupt transitions are simulated without these fluxes.

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