7 Ma. Northern Hemisphere ice sheets began to fluctuate under orbital control, expanding and contracting every 41 ka before ~800 ka and every 100 ka since (Bintanja and van de Wal 2008; Sosdian and Rosenthal 2009) (Fig. 2a). The mid-Pleistocene OSI-906 mouse transition ~800 ka was associated with a cooling of deep ocean water and a substantial thickening of the ice sheets during subsequent glacial phases. During the longer cooler glacial phases of each cycle temperatures, rainfall and sea levels learn more were
all lower. During each short interglacial phase sea levels have been within ~10 m of today’s level (0 m). In contrast, mean sea levels have declined gradually from −16 ± 10 m 2.6 Ma, to an average of −62 ± 50 m during the last million years (Figs. 2a and 3b). The ± estimates are not uncertainties but the normal glacial-interglacial sea level fluctuations, of which there were ~48 since 2.4 Ma. During periods when sea levels were below −30 m extensive coastal plains emerged across the Sunda Shelf and the region’s area doubled and provided dry land habitat between continental Asia, Borneo and Bali (Fig. 3a). For example, during the last glacial cycle sea levels fell
from +6 m at 120 ka, to between −124 and −130 m during the last glacial maximum (LGM) 19–26 ka, before rising quickly to +2.5–5.0 m between 4,850 and 4,450 years ago, and then falling to 0 m at 3 ka (Horton et al. 2005; Sathiamurthy and Voris 2006; Clark et al. 2009; Hanebuth et al. 2009). During the extreme conditions of the LGM, when the Sunda plains reached their greatest extent, Erastin purchase mean annual temperatures on land at sea level were 5–6°C lower than today’s (Kershaw et al. 2007). The biogeographic significance
of the Sunda plains will be discussed further below. Fig. 2 a Global sea level fluctuations estimated from deep-ocean foraminiferal δ18O isotope ratios over the last 4 Ma (data from Lisiecki and Raymo 2005 as transformed by Naish and Wilson 2009 and simplified by hand). b Maximum Resveratrol fluctuations in tropical lowland forest extent in Southeast Asia during the last 1 Ma (after Cannon et al. 2009). This particular curve was produced assuming an equatorial temperature change of −3°C and shows the maximal area of forest in km2 × 106. More detailed projections for three forest types under this and other paleoclimatic models are provided by Cannon et al. (2009) Fig. 3 Outline maps of Southeast Asia when sea levels are at a 120 m below, b 60 m below, and c 2 m above and 25 m above today’s sea level. Sundaland had its greatest areal extent about 20 ka when sea levels fell below −120 m. The average areal extent of Sundaland in the last million years occurred when sea levels were at −62 m. Sea levels are expected to rise 1–2 m above today’s level in the next 100–300 years. More detailed maps are provided by Sathiamurthy and Voris (2006) who show regional geography at 5-meter increments of sea level change between −120 m and +5 m.