Regional insolation forcing of late Quaternary climate change in the Southern Hemisphere

Abstract

In agreement with the Milankovitch orbital forcing hypothesis it is often assumed that glacial-interglacial climate transitions occurred synchronously in the Northern and Southern hemispheres of the Earth. It is difficult to test this assumption, because of the paucity of long, continuous climate records from the Southern Hemisphere that have not been dated by tuning them to the presumed Northern Hemisphere signals. Here we present an independently dated terrestrial pollen record from a peat bog on South Island, New Zealand, to investigate global and local factors in Southern Hemisphere climate changes during the last two glacial-interglacial cycles. Our record largely corroborates the Milankovitch model of orbital forcing but also exhibits some differences: in particular, an earlier onset and longer duration of the Last Glacial Maximum. Our results suggest that Southern Hemisphere insolation may have been responsible for these differences in timing. Our findings question the validity of applying orbital tuning to Southern Hemisphere records and suggest an alternative mechanism to the bipolar seesaw for generating interhemispheric asynchrony in climate change.

Antarctic lakes suggest millennial reorganizations of Southern Hemisphere atmospheric and oceanic circulation

“…Such correspondence between Antarctica and midlatitudes of the Southern Hemisphere has been proposed for the initiation and termination of the LGM (30), but has only recently been suggested for millennial time scales (31). Vandergoes et al (30) and Kaiser et al (31) both further suggested that the climatic link between Antarctica and the temperate midlatitudes was through variations in sea-ice extent, the Antarctic Circumpolar Current, and the westerlies, a hypothesis supported by upwelling data (36) and modelling (34). Although we cannot test this scenario directly, our proposal that high lake levels are linked to northward shifts in the pressure and storm systems around Antarctica, is consistent with this concept.…”

Altered Ecologies: Fire, climate and human influence on terrestrial landscapes: Terra Australis 32

“…However, as described above, forest persisted in the north throughout the LGM and forest pollen increased sharply in North Island sites around 18,000 years ago (Newnham et al 2003), several thousand years before there was any significant increase in atmospheric CO 2 concentration. Similarly, a mid-LGM warming and period of forest expansion evident in some NZ pollen records (Vandergoes et al 2005;Alloway et al 2007;) coincides with minimum atmospheric CO 2 concentration. If there was a CO 2 effect on flowering, it certainly was insufficient to prevent adequate forest pollen representation.…”

“…However, there has been a trend towards dating lake, swamp and playa sequences using pollen preparations or bulk sediment dates on relatively inorganic materials (e.g. Gillespie et al 1991;Magee 1995;Chester and Prior 2004;Vandergoes et al 2005;Cupper 2006;). In the latter case, the carbon being dated in organic poor sediments is likely to be effectively similar to a pollen preparation concentrate.…”

The timing and cause of glacial advances in the southern mid-latitudes during the last glacial cycle based on a synthesis of exposure ages from Patagonia and New Zealand

“…Barrell et al (2013) suggested that full glacial conditions may have begun around 28.8 ka based on a large increase in herb pollen around this time (Vandergoes et al, 2005). Climatic amelioration occurred around 18 ka, based on pollen assemblages and speleothem records (Williams et al, 2015).…”