Intra-interglacial climate variability: model simulations of Marine Isotope Stages 1, 5, 11, 13, and 15

Abstract

Abstract. Using the Community Climate System Model version 3 (CCSM3) including a dynamic global vegetation model, a set of 13 time slice experiments was carried out to study global climate variability between and within the Quaternary interglacials of Marine Isotope Stages (MISs) 1, 5, 11, 13, and 15. The selection of interglacial time slices was based on different aspects of inter-and intra-interglacial variability and associated astronomical forcing. The different effects of obliquity, precession, and greenhouse gas (GHG) forcing on global surface temperature and precipitation fields are illuminated. In most regions seasonal surface temperature anomalies can largely be explained by local insolation anomalies induced by the astronomical forcing. Climate feedbacks, however, may modify the surface temperature response in specific regions, most pronounced in the monsoon domains and the polar oceans. GHG forcing may also play an important role for seasonal temperature anomalies, especially at high latitudes and early Brunhes interglacials (MIS 13 and 15) when GHG concentrations were much lower than during the later interglacials. High-versus low-obliquity climates are generally characterized by strong warming over the Northern Hemisphere extratropics and slight cooling in the tropics during boreal summer. During boreal winter, a moderate cooling over large portions of the Northern Hemisphere continents and a strong warming at high southern latitudes is found. Beside the well-known role of precession, a significant role of obliquity in forcing the West African monsoon is identified. Other regional monsoon systems are less sensitive or not sensitive at all to obliquity variations during interglacials. Moreover, based on two specific time slices (394 and 615 ka), it is explicitly shown that the West African and Indian monsoon systems do not always vary in concert, challenging the concept of a global monsoon system on astronomical timescales. High obliquity can also explain relatively warm Northern Hemisphere high-latitude summer temperatures despite maximum precession around 495 ka (MIS 13). It is hypothesized that this obliquity-induced high-latitude warming may have prevented a glacial inception at that time.

Hybrid insolation forcing of Pliocene monsoon dynamics in West Africa

“…The concept of insolation gradients is supported by recent climate model studies (Mantsis et al, 2014) simulating an enhanced mid-latitude eddy circulation (which is important for the heat and moisture transport from low to high latitudes) in response to low obliquity (resulting in a strong LIG during summer), and a concomitant shift of the poleward boundaries of the tropical rain belt towards the Equator. In addition, weakening of the inter-hemispheric gradient leads to diminished cross-equatorial heat transport and a weaker Hadley circulation during winter (Reichart, 1997;Bosmans et al, 2015a). Further model simulations corroborate the importance of an obliquity-induced insolation gradient forcing for West African monsoon variability (Rachmayani et al, 2016).…”

“…The indication for LIG forcing during weak precession cycles of the Pliocene is less pronounced than during the Late Pleistocene suggesting that the obliquity forcing of the summer LIG is reinforced by the intensification of the Northern Hemisphere glaciation. LIG-induced climate shifts during the last glacial cycle are more severe than during the Pliocene due to increased ice-albedo feedbacks (Raymo and Nisancioglu, 2003). In addition, the duration of humid-arid periods seems to increase in the course of the last glacial cycle, reflecting the shift from one dominant forcing to another, i.e.…”

“…On orbital timescales, the periodicity of glacialinterglacial cycles with the high-to-low-latitude contrast in insolation (i.e. latitudinal insolation gradient) forces moisture fluxes poleward via strong gradients, thus triggering ice sheet growth (Raymo and Nisancioglu, 2003). In this context, most studies focus on high latitudes, and studies considering a latitudinal gradient forcing of tropical monsoon systems are limited to the last glacial cycle (e.g.…”

“…This intra-hemispheric insolation gradient leads to differential heating between the cold polar regions and the hot tropics and creates the latitudinal temperature/pressure gradient, which ultimately controls the poleward heat and moisture transport, a mechanism that has been invoked in the so-called "gradient hypothesis" by Raymo and Nisancioglu (2003) to explain the strong obliquity rhythm of glacial-interglacial cycles between 0.8 and 3.0 Ma (the "41 kyr world"). Another gradient hypothesis is favoured by Bosmans et al (2015b), who suggest that the inter-hemispheric insolation gradient drives winds and associated cross-equatorial moisture transport deep into the African continent linked with an intensification of the Hadley cell during winter (Reichart, 1997). The same mechanism has been invoked by Leuschner and Sirocko (2003) defining the Indian summer monsoon index.…”

Transient simulations of the present and the last interglacial climate using the Community Climate System Model version 3: effects of orbital acceleration

“…In equilibrium simulations, the boundary conditions are not varied temporally but rather kept fixed under the assumption that the Earth system is in equilibrium with them (e.g. Braconnot et al, 2007;Lunt et al, 2013;Milker et al, 2013;Rachmayani et al, 2016). Evidently, only limited information regarding the temporal evolution of the dynamic system is obtained by the time slice approach.…”