 |
| Titel |
Two-way coupled ice sheet-earth system simulations: Consequences of raising CO2 concentration for Greenland and the interacting climate system |
| VerfasserIn |
Christian Rodehacke, Miren Vizcaino, Uwe Mikolajewicz |
| Konferenz |
EGU General Assembly 2013
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083469
|
|
|
|
|
|
| Zusammenfassung |
| The observed distinct warming in the Arctic and the northward flow of tropical water masses
seem to trigger enhanced melting of the Greenland ice sheet, which adds more fresh water
into the ambient ocean. A continuation of the observed accelerated melting during the last
decade would stabilize the water column in the adjacent deep water formation sides. With
our fully coupled ice sheet-earth system model we approach the questions if this
weakens the formation of deep water masses and reduces the thermohaline driven
meridional overturning circulation (MOC). We have performed idealized future
projections to investigate the response of the interaction under raising atmospheric
carbon dioxide concentration with our two-way coupled ice sheet-earth system model
system.
We will present the building blocks of our fully coupled system, which includes a
physical based calculation of the ice sheet’s surface mass balance and ice sheet-ocean
interaction; The ESM instead is subject to orographic changes and receives fresh water fluxes,
for example. Since the behavior of an ice sheet in the near future is controlled by both the
external forcing and by its initial conditions, we have performed Latin Hyper Cube (LHC)
simulations with the ice sheet model over more than one glacial-interglacial cycle
utilizing standard techniques to obtain a reasonable initial state. According to several
quantities the best performing LHC member is exposed afterwards to boundary
conditions determined from energy balance calculations again obtained from simulated
forcing fields. Finally the fully coupled system is brought into a quasi-equilibrium
under pre-industrial conditions before idealized scenarios have been started. In
contrast to commonly used strategies, our coupled ice sheet inherits the memory of a
glacial cycle simulations obtain exclusively from ESM fields. Furthermore we use a
mass conserving scheme, do neither apply flux corrections nor utilize anomaly
coupling.
Under different CO2 forcing scenarios — for example, raising CO2 by 1%/year until four
times the pre-industrial concentration (4xCO2) has reached, abrupt raise to 4xCO2 — the
response of the coupled system is analyzed. For instance, an abrupt CO2 forcing leads to an
immediate response of the Greenlandic ice sheet. The surface mass balance turns strongly
negative within a couple of years, causing skyrocketing melting rates and sea level rise. The
contribution of the ocean-ice sheet interaction decreases instead, because the ice sheets
retreats from the coast and is therefore less susceptible to an eroding ocean. The
additionally released fresh water and the heat both have to potential to stifle the
MOC. However sensitivity experiments indicate that the additional fresh water has a
negligible influence on the MOC with a time scale of a century or more in our model
system.
For the study we have used the current CMIP5 earth system model MPI-ESM that
comprises the atmosphere model ECHAM6 (T63L47), the vegetation model JSBACH and the
ocean biogeochemical model MPIOM / HAMOCC (GR15L40, nominal horizontal resolution
of 1.5° with one pole over Greenland). The ESM is coupled to the Parallel Ice Sheet
Model (PISM) covering Greenland, where PISM has a horizontal resolution 10
km. |
|
|
|
|
|
|