KlimaCampus Kolloquium: Millennial scale climate variability and ice age cycle
Date
16.11.2023
Time
15:15 h
Place
- Bundesstr. 53, room 022/023
- Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg
Glacial periods were punctuated by abrupt millennial scale climate changes, such as Dansgaard-Oeschger events, Boeling-Allerod and Younger Dryas. Although glacial abrupt climate changes were shown to have a strong link to the Atlantic Meridional overturning circulation (AMOC) changes and the glacial background climate, simulating the millennial scale climate change and understanding its condition with fully coupled ocean-atmosphere GCM have been challenging. Here we present several cases of millennial scale climate variability simulated with our Japanese Atmosphere Ocean coupled GCM, MIROC4m. A series of long transient experiments (> 10,000 years) were performed systematically with different steady glacial conditions (CO2 level, obliquity, precession, ice sheet size and meltwater amount) in order to study the dependence of millennial scale variability on the background climate and summarize the results as phase diagrams. We found that a sweet spot of millennial scale oscillation exists under a certain condition, while the AMOC is in a stable strong (weak) mode of about 18 (10) Sv (Sverdrup) without the oscillation. In the sweet spot, self-sustained oscillation with bipolar seesaw pattern appears and shifts between interstadials with strong AMOC and stadials with weak AMOC occur. The interval between abrupt events ranges from 1000 years to more than 5000 years, while an abrupt shift from stadial to interstadial mode occurs in about 100 years, just like geological evidence, ice core analysis and the deep-sea cores. The mechanism of the millennial scale climate variability as well as its threshold of occurrence, which is likely related to the thermal condition of global climate, can be now discussed.