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Abstract
Abstract. Orbital forcing does not only exert direct insolation effects, but also alters climate indirectly through feedback mechanisms that modify atmosphere and ocean dynamics and meridional heat and moisture transfers. We investigate the regional effects of these changes by detailed analysis of atmosphere and ocean circulation and heat transports in a coupled atmosphere-ocean-sea ice-biosphere general circulation model (ECHAM5/JSBACH/MPI-OM). We perform long term quasi equilibrium simulations under pre-industrial, mid-Holocene (6000 years before present – yBP), and Eemian (125 000 yBP) orbital boundary conditions. Compared to pre-industrial climate, Eemian and Holocene temperatures show generally warmer conditions at higher and cooler conditions at lower latitudes. Changes in sea-ice cover, ocean heat transports, and atmospheric circulation patterns lead to pronounced regional heterogeneity. Over Europe, the warming is most pronounced over the north-eastern part in accordance with recent reconstructions for the Holocene. We attribute this warming to enhanced ocean circulation in the Nordic Seas and enhanced ocean-atmosphere heat flux over the Barents Shelf in conduction with retreat of sea ice and intensified winter storm tracks over northern Europe.
Highlights
Changes of insolation distribution due to variations in the Earth’s orbit around the sun are considered the dominant external forcing of glacial-interglacial cycles throughout the Quaternary (Milankovic, 1941; Hays et al, 1976; Imbrie et al, 1992)
Subject of the present study are effects of orbital forcing on regional climate and the role of orbitally induced changes in atmospheric and oceanic circulation and the associated heat transports in the Holocene (6000 years before present – yBP) and the last interglacial period, the Eemian (125 000 yBP), compared to pre-industrial climate in a fully coupled atmosphere-oceansea ice-biosphere general circulation model (GCM)
We present results obtained from two time-slice simulations with a comprehensive GCM compared to a control run under pre-industrial conditions: one of Holocene climate, 6000 yBP, and one of Eemian climate, 125 000 yBP
Summary
Changes of insolation distribution due to variations in the Earth’s orbit around the sun are considered the dominant external forcing of glacial-interglacial cycles throughout the Quaternary (the last 2.5 million years) (Milankovic, 1941; Hays et al, 1976; Imbrie et al, 1992). Their impact on the climate of interglacial periods has been studied in previous coupled atmosphere-ocean modeling work mainly focussing on the atmosphere component of the climate system (e.g., Braconnot et al, 2007a,b).
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