Modelling the climate, ice sheet and thermohaline circulation during the ice age termination
Abstract
One of the challenges of earth system modeling is to explain the mechanism of ice age cycle by simulating it and to understand the uniqueness or necessity of the present state of climate and cryosphere. Whether Milankovitch cycle or CO2 is the driver and why the dominant periodicity of ice age cycle switched from 40 ka cycle to 100ka cycle and why a sharp termination occur for each ice age cycle have been remained unsolved. Here we simulate the glacial cycle and investigate the origin of saw-tooth shape 100ka cycle using a three dimensional ice sheet model with the input examined by GCM. The model is forced by the orbital parameters (Berger, 1978) and atmospheric CO2 content obtained by ice cores (Vostok, EPICA and DomeF), whose dating is partly given by a new method using the N2/O2 ratio. The ice sheet model includes the thermo-mechanical coupling process of ice sheet with the process of delayed isostatic rebound with a typical time constant. In order to estimate the climate sensitivity to Milankovitch forcing and atmospheric CO2 indicated by ice core data we used an atmospheric GCM (part of MIROC GCM) coupled to a slab ocean and full MIROC AOGCM in part of the work. Within the range of possibilities of the model, ice age cycles with a saw-tooth shape 100 ka cycle, the major NH ice sheets’ volume and the geographical distribution at the glacial maximum are successfully simulated. Moreover the role of Atmospheric stationary wave feedback are found to be important to sharpen the termination. It is shown by sensitivity studies that this 100ka cycle is mainly obtained by the slowly acting ice sheet response to Milankovitch forcing even without the CO2 cycle. The CO2 change amplifies the cycle and affects the global climate change, while the delay of crustal rebound sharpens the termination of every ice age cycle. In order to study the effect of thermohaline circulation, the sensitivity of AOGCM (by MIROC) is separately studied by applying time slice experiments of every 2000 years during the deglaciation (LGM, 19ka, 17ka, 15ka, 13ka, 11ka , 9ka) and hosing to some of the time slices. Some new results and perspective on modelling the change of climate, ice sheet and thermohaline circulation since LGM is presented and discussed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP14C..07A
- Keywords:
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- 0726 CRYOSPHERE / Ice sheets;
- 1620 GLOBAL CHANGE / Climate dynamics;
- 1626 GLOBAL CHANGE / Global climate models;
- 4900 PALEOCEANOGRAPHY