A coupled climate model simulation of Marine Isotope Stage 3 stadial climate
1Linné Flow Centre, Department of Mechanics, KTH, 10044 Stockholm, Sweden
2Swedish Meteorological and Hydrological Institute, 60176 Norrköping, Sweden
3Swedish Nuclear Fuel and Waste Management Co (SKB), Box 5864, 10240 Stockholm, Sweden
4Swedish Meteorological and Hydrological Institute, 60176 Norrköping, Sweden
5LNEG – Laboratorio Nacional de Energia e Geologia, Unidade de Geologia Marinha, Estrada da Portela, Zambujal, 2610-143 Amadora, Portugal
6Department of Geological Sciences, Stockholm University, 10961 Stockholm, Sweden
Abstract. We present a coupled global climate model (CGCM) simulation, integrated for 1500 years to quasi-equilibrium, of a stadial (cold period) within Marine Isotope Stage 3 (MIS 3). The simulated Greenland stadial 12 (GS12; ~44 ka BP) annual global mean surface temperature (Ts) is 5.5 °C higher than in the simulated recent past (RP) climate and 1.3 °C lower than in the simulated Last Glacial Maximum (LGM; 21 ka BP) climate. The simulated GS12 climate is evaluated against proxy data of sea surface temperature (SST). Simulated SSTs fall within the uncertainty range of the proxy SSTs for 30–50% of the sites depending on season. Proxy SSTs are higher than simulated SSTs in the Central North Atlantic, in contrast to earlier simulations of MIS 3 stadial climate in which proxy SSTs were found to be lower than simulated SST. The annual global mean Ts only changes by 0.10 °C from model years 500–599 to the last century of the simulation, indicating that the climate system may be close to equilibrium already after 500 years of integration. However, significant regional differences between the last century of the simulation and model years 500–599, with a maximum of 8 °C in temperature and 65% in precipitation in Southeastern Greenland in boreal winter, exist. Further, the agreement between simulated and proxy SST is improved from model years 500–599 to the last century of the simulation. El-Niño-Southern Oscillation (ENSO) teleconnections in mean sea level pressure (MSLP) are analysed for the last 300 years of the GS12, LGM and RP climate simulations. In agreement with an earlier study, we find that GS12 and LGM forcing and boundary conditions induce major modifications to ENSO teleconnections. However, significant differences in the teleconnection patterns are found between a 300-year time-slice starting after 195 model years and the last 300 years of the simulation. Thus we conclude that both the mean state and the variability of the simulated GS12 climate is dependent on the equilibration. The Atlantic Meridional Overturning Circulation (AMOC) slows down by 50% in the GS12 climate as compared to the RP climate. This slowdown is attained without freshwater forcing in the North Atlantic region, a method used in other studies to force an AMOC shutdown. The results presented here suggest that stadial climate, rather that interstadial climate, should be interpreted as a near-equilibrium MIS 3 climate, in contradiction to an earlier modelling study.