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

Broecker, Wallace S.; Andree, Michael; Wölfli, W.; Oeschger, H.; Bonani, Georges; Kennett, James P.; Peteet, D. M.

doi:10.1029/pa003i001p00001

Cited by 395 publications

(137 citation statements)

References 41 publications

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“…A pulse of fresh water (glacial melt water) into the North Atlantic is believed to have caused this anomaly via affects on the THC (Broecker et al 1988;Bard et al 1990;Hughen et al 2000). The response and stability of the THC in HadCM3 to both fresh water and anthropogenic forcing have been explored in previous studies (Thorpe et al 2001;.…”

Section: (B) Climate Scenarios and Simulationsmentioning

confidence: 99%

Contrasting simulated past and future responses of the Amazonian forest to atmospheric change

Cowling

Betts

Cox

et al. 2004

Phil. Trans. R. Soc. Lond. B

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Modelling simulations of palaeoclimate and past vegetation form and function can contribute to global change research by constraining predictions of potential earth system responses to future warming, and by providing useful insights into the ecophysiological tolerances and threshold responses of plants to varying degrees of atmospheric change. We contrasted HadCM3LC simulations of Amazonian forest at the last glacial maximum (LGM; 21 kyr ago) and a Younger Dryas-like period (13-12 kyr ago) with predicted responses of future warming to provide estimates of the climatic limits under which the Amazon forest remains relatively stable. Our simulations indicate that despite lower atmospheric CO 2 concentrations and increased aridity during the LGM, Amazonia remains mostly forested, and that the cooling climate of the Younger Dryas-like period in fact causes a trend toward increased above-ground carbon balance relative to today. The vegetation feedbacks responsible for maintaining forest integrity in past climates (i.e. decreased evapotranspiration and reduced plant respiration) cannot be maintained into the future. Although elevated atmospheric CO 2 contributes to a positive enhancement of plant carbon and water balance, decreased stomatal conductance and increased plant and soil respiration cause a positive feedback that amplifies localized drying and climate warming. We speculate that the Amazonian forest is currently near its critical resiliency threshold, and that even minor climate warming may be sufficient to promote deleterious feedbacks on forest integrity.

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Section: (B) Climate Scenarios and Simulationsmentioning

confidence: 99%

Contrasting simulated past and future responses of the Amazonian forest to atmospheric change

Cowling

Betts

Cox

et al. 2004

Phil. Trans. R. Soc. Lond. B

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“…Several authors have investigated this issue for past climates and future climate projections. The discharge of meltwater from the northern hemisphere ice sheets has been proposed as the triggering mechanism for abrupt climate change in the past at the time of the Younger Dryas (Broecker et al 1988;Maier-Reimer and Mikolajewicz 1989). Fichefet et al (2003) found a substantial weakening of the NAMOC in response to increased meltwater fluxes from the GrIS in a twenty-first century simulation.…”

Section: Introductionmentioning

confidence: 99%

Long-term ice sheet–climate interactions under anthropogenic greenhouse forcing simulated with a complex Earth System Model

et al. 2008

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Several multi-century and multi-millennia simulations have been performed with a complex Earth System Model (ESM) for different anthropogenic climate change scenarios in order to study the long-term evolution of sea level and the impact of ice sheet changes on the climate system. The core of the ESM is a coupled coarseresolution Atmosphere-Ocean General Circulation Model (AOGCM). Ocean biogeochemistry, land vegetation and ice sheets are included as components of the ESM. The Greenland Ice Sheet (GrIS) decays in all simulations, while the Antarctic ice sheet contributes negatively to sea level rise, due to enhanced storage of water caused by larger snowfall rates. Freshwater flux increases from Greenland are one order of magnitude smaller than total freshwater flux increases into the North Atlantic basin (the sum of the contribution from changes in precipitation, evaporation, run-off and Greenland meltwater) and do not play an important role in changes in the strength of the North Atlantic Meridional Overturning Circulation (NAMOC). The regional climate change associated with weakening/ collapse of the NAMOC drastically reduces the decay rate of the GrIS. The dynamical changes due to GrIS topography modification driven by mass balance changes act first as a negative feedback for the decay of the ice sheet, but accelerate the decay at a later stage. The increase of surface temperature due to reduced topographic heights causes a strong acceleration of the decay of the ice sheet in the long term. Other feedbacks between ice sheet and atmosphere are not important for the mass balance of the GrIS until it is reduced to 3/4 of the original size. From then, the reduction in the albedo of Greenland strongly accelerates the decay of the ice sheet.

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Section: Introductionmentioning

confidence: 99%

“…Initial support for this theory included elevated δ 18 O values in Gulf of Mexico sediment dating from the early YD (implying that meltwater was rerouted elsewhere) (Broecker et al, 1988;Flower and Kennett, 1990;Teller, 1990). The meltwater was originally proposed to have travelled to the North Atlantic via the St Lawrence Valley, but results have so far revealed only limited geological evidence of a massive flux of freshwater coincident with the YD initiation (Broecker, 2006a;Rayburn et al, 2011). The freshwater pulse may have followed another route to the ocean, and other research has proposed the Mackenzie Valley (Condron and Winsor, 2012;Murton et al, 2010) as a possible alternative and the Fennoscandian Ice Sheet as an alternate source .…”

Section: Introductionmentioning

confidence: 99%

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

Cited by 395 publications

References 41 publications

Contrasting simulated past and future responses of the Amazonian forest to atmospheric change

Contrasting simulated past and future responses of the Amazonian forest to atmospheric change

Long-term ice sheet–climate interactions under anthropogenic greenhouse forcing simulated with a complex Earth System Model

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

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