Abrupt glacial climate shifts controlled by ice sheet changes

Zhang, Xu; Lohmann, Gerrit; Knorr, Gregor; Purcell, Catherine

doi:10.1038/nature13592

Cited by 240 publications

(241 citation statements)

References 97 publications

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“…These results are broadly consistent with previous research (e.g. Zhang et al, 2014Zhang et al, , 2017, but the timing and duration of the most sensitive interval of time and the likelihood that a forcing produces a longer-term cooling event may ultimately depend on a complex interplay between ice volume and atmospheric CO 2 (Zhang et al, 2017). Atmospheric pCO 2 during the YD initiation was relatively high (∼ 240 ppmv) and could therefore affect the timing of ideal conditions for abrupt climate change in conjunction with ice volume, but their precise interdependence is still unclear.…”

Section: Sensitivity To Ice Volumesupporting

confidence: 83%

“…Zhang et al, 2014Zhang et al, , 2017, and here we investigate this further by examining the timing of Greenland stadials relative to ice volume (estimated using Red Sea sea level; Siddall et al, 2003). The timings of 55 stadial initiations as compiled in the INTIMATE (INTegration of Ice core, MArine, and TErrestrial) initiative (Rasmussen et al, 2014) are compared relative to ice volume, and indeed a strong bias towards intermediate ice volume conditions exists, with 73 % of the millennial-scale cooling events occurring during only 40 % of the range of sea level across the interval from 0 to 120 ka BP (Fig.…”

Section: Sensitivity To Ice Volumementioning

confidence: 99%

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Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly

2018

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Abstract. The Younger Dryas is considered the archetypal millennial-scale climate change event, and identifying its cause is fundamental for thoroughly understanding climate systematics during deglaciations. However, the mechanisms responsible for its initiation remain elusive, and both of the most researched triggers (a meltwater pulse or a bolide impact) are controversial. Here, we consider the problem from a different perspective and explore a hypothesis that Younger Dryas climate shifts were catalysed by the unusually sulfurrich 12.880 ± 0.040 ka BP eruption of the Laacher See volcano (Germany). We use the most recent chronology for the GISP2 ice core ion dataset from the Greenland ice sheet to identify a large volcanic sulfur spike coincident with both the Laacher See eruption and the onset of Younger Dryasrelated cooling in Greenland (i.e. the most recent abrupt Greenland millennial-scale cooling event, the Greenland Stadial 1, GS-1). Previously published lake sediment and stalagmite records confirm that the eruption's timing was indistinguishable from the onset of cooling across the North Atlantic but that it preceded westerly wind repositioning over central Europe by ∼ 200 years. We suggest that the initial short-lived volcanic sulfate aerosol cooling was amplified by ocean circulation shifts and/or sea ice expansion, gradually cooling the North Atlantic region and incrementally shifting the midlatitude westerlies to the south. The aerosol-related cooling probably only lasted 1-3 years, and the majority of Younger Dryas-related cooling may have been due to the seaice-ocean circulation positive feedback, which was particularly effective during the intermediate ice volume conditions characteristic of ∼ 13 ka BP. We conclude that the large and sulfur-rich Laacher See eruption should be considered a viable trigger for the Younger Dryas. However, future studies should prioritise climate modelling of high-latitude volcanism during deglacial boundary conditions in order to test the hypothesis proposed here.

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Section: Sensitivity To Ice Volumesupporting

confidence: 83%

Section: Sensitivity To Ice Volumementioning

confidence: 99%

Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly

2018

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“…This echoes the results of experiment TOP that suggested that any change in the heat transported by the AMOC is but one constituent of the heat transported by the ocean and that changes in the shallow, wind-driven circulation are equally important. Zhang et al (2014) also found a dramatic increase in the AMOC in their model simulations of a White Mountain, but they did not report how the equatorial heat transport was different. We will note that a very much stronger AMOC is not a consistent feature of White Mountain simulations: other simulations of HadCM3 with the same height of ice sheet but using a land-sea mask of the LGM, rather than the preindustrial that we show here, do not show a large increase in their AMOC.…”

Section: Alb/topmentioning

confidence: 92%

Green Mountains and White Plains: The Effect of Northern Hemisphere Ice Sheets on the Global Energy Budget

Roberts

Valdes

2017

Journal of Climate

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. ABSTRACTThe changes in the global energy budget in response to imposing an ice sheet's topography, albedo, or topography and albedo combined are examined. The albedo of the ice sheet (here called a ''White Plain'') causes an outgoing top of the atmosphere radiation anomaly over the ice sheet that is balanced by an incoming anomaly in the Southern Hemisphere. This causes a northward transport of heat across the equator that is carried equally by the ocean and atmosphere. The topography of the ice sheet (''Green Mountain'') causes an incoming radiation anomaly over the ice sheet that is balanced predominantly by an outgoing anomaly to the south of the ice sheet, with a smaller outgoing flux in the Southern Hemisphere. The heat is transported across the equator by the atmosphere alone. The combined topography and albedo of the ice sheet (''White Mountain'') cause an outgoing radiation anomaly over the ice sheet that is balanced equally by an incoming flux in the Southern Hemisphere and to the south of the ice sheet. Heat is transported across the equator by the ocean alone.With varying ice sheet geometry generally linear relationships between the various energy fluxes and the varying height and area of the ice sheet are found. In both the White Plain and White Mountain cases the ocean is always a significant carrier of heat across the equator, and in the White Mountain case it is preeminent.

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“…With aid of the comprehensive coupled climate model COSMOS 8,9 we explore the governing mechanism of AMOC stability associated with atmospheric CO 2 changes. Two experiments were conducted with gradual changes in atmospheric CO 2 under intermediate (CO2_Hys) and maximum (LGM_0.15_CO2) ice volumes (Supplementary Table 1 Supplementary Fig.…”

Section: Gradual Co 2 Changes As a Forcing Factormentioning

confidence: 99%

Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state

et al. 2017

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Glacial climate is marked by abrupt, millennial-scale climate changes known as Dansgaard-Oeschger cycles. The most pronounced stadial coolings, Heinrich events, are associated with massive iceberg discharges to the North Atlantic. These events have been linked to variations in the strength of the Atlantic meridional overturning circulation. However, the factors that lead to abrupt transitions between strong and weak circulation regimes remain unclear. Here we show that, in a fully coupled atmosphere-ocean model, gradual changes in atmospheric CO 2 concentrations can trigger abrupt climate changes, associated with a regime of bi-stability of the Atlantic meridional overturning circulation under intermediate glacial conditions. We find that changes in atmospheric CO 2 concentrations alter the transport of atmospheric moisture across Central America, which modulates the freshwater budget of the North Atlantic and hence deep-water formation. In our simulations, a change in atmospheric CO 2 levels of about 15 ppmv-comparable to variations during Dansgaard-Oeschger cycles containing Heinrich events-is su cient to cause transitions between a weak stadial and a strong interstadial circulation mode. Because changes in the Atlantic meridional overturning circulation are thought to alter atmospheric CO 2 levels, we infer that atmospheric CO 2 levels may serve as a negative feedback to transitions between strong and weak circulation modes.A brupt climate changes associated with Dansgaard-Oeschger (DO) events as recorded in Greenland ice cores are characterized by rapid warming from stadial to interstadial conditions. This is followed by a phase of gradual cooling before an abrupt return to cold stadial conditions 1,2 . A common explanation for these transitions involves changes in the Atlantic meridional overturning circulation (AMOC) 3 , perhaps controlled by freshwater perturbation (for example, refs 4,5) and/or Northern Hemisphere ice sheet changes (for example, refs 6-8). To reproduce the abrupt transitions into and out of cold conditions across the North Atlantic (that is, AMOC weak or 'off' mode 3 ), a common trigger mechanism is related to the timing of North Atlantic freshwater perturbations 9,10 that is mainly motivated by unequivocal ice-rafting events during Heinrich Stadials (HS) 11 . However, recent studies suggest that the Heinrich ice-surging events are in fact triggered by sea subsurface warming associated with an AMOC slow-down 12,13 . Furthermore, the duration of ice-rafting events does not systematically coincide with the beginning and end of the pronounced cold conditions during Heinrich Stadials 14,15 . This evidence thus challenges the current understanding of glacial AMOC stability 5,8 , suggesting the existence of additional control factors that should be invoked to explain abrupt millennial-scale variability in climate records. In contrast to the north, the rapid climate transitions are characterized by interhemispheric anti-phased variability, with more gradual changes in southern high latitudes 16...

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Abrupt glacial climate shifts controlled by ice sheet changes

Cited by 240 publications

References 97 publications

Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly

Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly

Green Mountains and White Plains: The Effect of Northern Hemisphere Ice Sheets on the Global Energy Budget

Abrupt North Atlantic circulation changes in response to gradual CO2 forcing in a glacial climate state

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