An Integrated Atmosphere - Ocean - Ice Sheet Model Approach
The rapid growth of ice sheets in Antarctica at the Eocene-Oligocene (E-O) transition about 35 million years ago (Ma) is an outstanding
event in Cenozoic climate evolution, which in general is characterized by long-term cooling from relatively warm and ice-free conditions
at 65–58 Ma to the buildup of massive ice-sheets in both hemispheres, beginning at about 10 Ma (see Figure 1). The reasons for the
Cenozoic Antarctic glaciation are still discussed, hypothesizing changes in heat transports induced by the opening of circum-Antarctic
seaways, decreasing atmospheric carbon dioxide concentrations, and changes in orbital forcing. These mechanisms may have served as a
trigger and pacemaker for ice-sheet growth.
A clear answer about the climatic effects of Cenozoic seaway opening in the Southern ocean has not been given yet, since previous
coupled modeling studies suffered from simplified representations of the ocean. However, a three-dimensional oceanic flow regime
is of paramount importance for realistic patterns of heat and moisture fluxes to force the atmosphere, and hence to obtain realistic
atmospheric fluxes of heat and moisture which drive the waxing and waning of Antarctic sheets. The analysis of different flow regimes
in the coupled atmosphere-ocean system during the E-O transition can give significant clues for our understanding of Cenozoic climate
variability.
This research project investigates the Cenozoic Antarctic glaciation by means of an integrated atmosphere-ocean-ice sheet model approach,
which goes beyond previous modeling efforts. We apply the comprehensive climate model COSMOS (Jungclaus et al., 2006), composed of
general circulation models of the atmosphere (ECHAM5; Roeckner et al., 2003) and the ocean (MPI-OM; Marsland et al., 2003), which
are coupled by the OASIS3 coupler in combination with a three-dimensional ice sheet model for Antarctica (by Huybrechts, 1993).
Climate and ice sheet models are iteratively coupled (see Figure 2 for a sketch of the coupling scheme).
In a series of sensitivity studies we examine the effects of the above-mentioned hypotheses on the build-up of Antarctic
sheets. As a first result, Figure 3 shows the modelled thickness of Antarctic ice sheets obtained from the control simulation
for present-day conditions (Cristini et al., 2009). The results are largely in line with observations, indicating that our
model approach can be also applied to other Cenozoic time slices.
Fig.1: Evolution of the global climate over the past 65 million years (taken from Zachos et al., 2008). The climate
curve is a stacked deep-sea benthic foraminiferal oxygen-isotope curve based on marine sediment records.
Fig.2: Scheme of the coupling procedure between the climate model COSMOS and the ice sheet model ISM. COSMOS
consists of general circulation models for the atmosphere (ECHAM5) and the ocean (MPIO-OM) which are coupled by the
coupler OASIS3. COSMOS exchanges net precipitation (P-E), surface atmospheric temperature (SAT), Antarctic surface
elevation and albedo with the ISM in an iteratively procedure.
Fig.3: Modeled thickness of Antarctic ice sheets as obtained from the control simulation for present-day
conditions (Cristini et al., 2009).
Scientists
Gerrit Lohmann
Alfred-Wegener-Institute Bremerhaven
Martin Butzin
Universität Bremen
Klaus Grosfeld
Alfred-Wegener-Institute Bremerhaven
Philippe Huybrechts
Alfred-Wegener-Institute Bremerhaven
Luisa Cristini
Alfred-Wegener-Institute Bremerhaven
Research areas
Antarctica
Publications
Cristini et al., Grosfeld K, Butzin M, Thoma M, Werner M, Huybrechts P, Lohmann G, 2009. The Antarctic Ice
Sheet in the global climate system: a coupled climate-ice sheet modelling approach (in prep.)
Huybrechts P, 1993. Glaciological Modelling of the Late Cenozoic East Antarctic Ice Sheet: Stability or
Dynamism?, Geografiska Annaler, 75A, 221–238.
Jungclaus JH, Botzet M, Haak H, Marotzke J, Mikolajewicz U, Roeckner E, Keenlyside N, Latif M, Luo JJ, 2006. Ocean
Circulation and Tropical Variability in the Coupled Model ECHAM5/MPI-OM, Journal of Climate, 19, 3952–3972.
Marsland SJ, Haak H, Jungclaus JH, Latif M, Röske F, 2003. The Max-Planck-Institute global ocean/sea ice model
with orthogonal curvilinear coordinates, Ocean Modelling, 5, 91–127.
Roeckner E, et al., 2003. The atmospheric general circulation model ECHAM 5. Part I: model description, Report No.
349, Max Planck Institute for Meteorology, Hamburg.
Zachos JC, Dickens GR, Zeebe RE, 2008. An early Cenozoic perspective on greenhouse warming and carbon-cycle dynamics,
Nature, 451, 279–283.
Homepage
---
Research funding organisation
German Research Foundation
Project numbers: BU 2243/1, LO-1372/2
Funding period: August 2007 – July 2010
