Milankovitch theory of ice ages: Hypothesis of ice-sheet linkage between regional insolation and global climate

Abstract

J. D. Hays, J. Imbrie, and N. J. Shackleton (1976, Science 194, 1121–1132) showed that the astronomical theory explained many features of late Quaternary ice-age climates, but they did not specify the physical mechanisms involved. Here it is proposed that interlocked variations of ice-sheet heat sinks in both polar hemispheres amplified and transmitted Milankovitch summer half-year insolation changes (a version of the astronomical theory) between 45° and 75°N into the globally synchronous climate changes recorded in geologic records. It is suggested that late Quaternary ice sheets had terrestrial components (grounded above sea level, melting margins, fluctuations controlled by climate) and marine components (grounded below sea level, drained largely by ice streams, limited melting margins, fluctuations controlled primarily by sea level and secondarily by climate, interior surface elevations coupled to downdraw through ice streams). Northern Hemisphere ice sheets were largely marine (with minor melting margins) in the Arctic and terrestrial (with major melting margins) in the midlatitudes. West Antarctic and peripheral East Antarctic ice was marine-based and lacked melting margins. Because of their geographic array, these terrestrial and marine components formed an ice-sheet system whose variations were coupled on a global scale. Milankovitch summer isolation changes near midlatitude Northern Hemisphere melting margins controlled most variations of this system, because advance or retreat of melting margins initiated concurrent eustatic sea-level change. Such sea-level change afforded the critical interlocking mechanism between terrestrial and marine components because it forced simultaneous expansion or contraction of marine margins in both polar hemispheres. This initiated an amplifying feedback loop among all marine components and influenced interior downdraw through ice streams. Arctic summer insolation change was less important because northern melting margins were relatively minor. Its greatest influence was on surface ablation of ice streams that controlled interior downdraw. This affected eustatic sea level and activated global linkage of marine sectors. By analogy with present-day Antarctica, late Quaternary ice sheets were enormous planetary heat sinks due to their reflective and radiative surface characteristics. It is suggested that the effectiveness of these ice-sheet heat sinks varied with their areal extent and interior surface elevation. Thus, it is postulated that concurrent growth or decay of these interlocked ice-sheet heat sinks in both polar hemispheres served as the global amplifier of regional Milankovitch summer insolation.