Model-Paleodata analysis of an orbitally driven mechanism for the onset of the warmest interglacials like MIS 11, 31, 49 etc.

Abstract:

Global climate during Quaternary and Late Pliocene (present–3.1 Ma) is characterized by alternating glacial and interglacial conditions. Recently, several interglacials have been identified as warmer than others, like 9, 11, 31, 49, 55, 77, 87 and 91, and are termed as “Superinterglacials”. Our proposed theory associates these superinterglacials with variations in the behavior of the Northern Hemisphere (NH) ice sheets with respect to the Southern Hemisphere (SH) ice sheets. At lower eccentricities, with the effect of precession being minimal, the NH ice sheets vary in-phase with SH. At higher eccentricities, NH ice sheets vary out-of-phase with SH ice sheets and are forced by precession driven local insolation changes.

Model results indicate that during periods of low eccentricity, favorable forcing (high obliquity, high CO2) leads to unusually long interglacial conditions in both NH and SH. Using an ensemble of GCM simulations covering MIS 11, 31 and 49 we show that SH ice-sheets follow boreal summer insolation at lower eccentricities, switching to austral summer insolation at higher eccentricities. This switch provides the necessary orbital forcing for prolonged interglacial climates, much longer than expected from global oxygen isotope records. The prolonged warm conditions in the SH preconditions the poles to produce a large response during the superinterglacials. Recent paleodata studies have shown the existence of such extra-long interglacials in the NH during MIS 15-13 (preceding MIS 11) using grain-size records from Chinese loess (Q Hao, 2015). In this study we work with a collection of paleoclimate records though Pleistocene and correlate with our modeling results. Global records such as benthic δ18O capture the integrated signals of ice volume from both hemispheres, making it difficult to isolate the behaviour of the NH and SH ice sheets. Hence we focus on paleodata records, which capture the NH and SH ice volume signals individually, like the Chinese loess records serving as a proxy for Arctic climate variability or benthic records from Shackleton site (IODP U1385) which provides a long term continuous record of the SH signal. Using combination of model results and paleodata, we analyze future climate trends during astronomical analogues of the superinterglacials like MIS 11 and 31.