EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Abrupt Bølling‐Allerød Warming Simulated under Gradual Forcing of the Last Deglaciation

Takashi Obase1 and Ayako Abe-Ouchi1,2
Takashi Obase and Ayako Abe-Ouchi
  • 1The University of Tokyo, Atmosphere and Ocean Research Institute, Kashiwa, Japan
  • 2National Institute of Polar Research, Tachikawa, Japan

During the last deglaciation, a major global warming trend was punctuated by abrupt climate changes, likely related to Atlantic meridional overturning circulation (AMOC). One problem is that an abrupt increase in the AMOC during the Bølling‐Allerød (BA) transition occurred when the melting of Northern Hemisphere ice sheets was significant, which tended to weaken the AMOC. Here, from transient simulations of the last deglaciation using an atmosphere‐ocean general circulation model, we show that an abrupt increase in the AMOC during the BA transition could occur without reduction in glacial meltwater. The abrupt increase in the AMOC accompanied abrupt warming in Greenland and sea ice retreat in the North Atlantic, consistent with proxies and previous modeling studies. The results imply that abrupt BA warming during the middle stage of the last deglaciation was a response to gradual warming under the presence of meltwater from continental ice sheets.

How to cite: Obase, T. and Abe-Ouchi, A.: Abrupt Bølling‐Allerød Warming Simulated under Gradual Forcing of the Last Deglaciation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12398,, 2020

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Presentation version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-12398, Sandra Gomes, 06 May 2020

    Dear Takashi Obase,

    Thank you for sharing your interesting and insightful presentation. I work with proxy data and my understanding of models is quite limited. Recently I look into the results of TRace21ka and if I am not wrong there is a temperature decrease for the Iberian peninsula (similar to the one observed during the YD) at around 14 ka, also the pollen records do show it. Does your simulation detect that?

    Thank you for your time and availability.


    Sandra Gomes

  • AC1: Comment on EGU2020-12398, Takashi Obase, 06 May 2020

    Dear Sandra,
    Thank you for a question. I checked the time series of SST off the Iberian peninsula, and I found SST at 14 ka was cooler than the temperature peak in BA transition (~14.7 ka). I don't know the extent of the cooling from Trace21ka experiment, but the extent of cooling in our simulation might be smaller, as the meltwater flux is kept to a constant value during 16-13 ka BP.