Temperature and Monsoon Tango in a Tropical Stalagmite: Last Glacial-Interglacial Climate Dynamics

Abstract

High-resolution paleoclimate data on stable isotopes in a stalagmite were coupled to glycerol dialkyl glycerol tetraethers (GDGTs). The Indian Summer Monsoon (ISM) transitioned from limited rainfall during the Last Glacial Maximum (LGM) to intense precipitation during early Holocene (22 to 6 ka). This was associated with changes in stalagmite growth, abundance of branched (br) and isoprenoid (iso) GDGTs, as well as δ18O, δ13C, Sr/Ca and GDGT-derived signals providing both temperature and moisture information. The reconstructed mean annual air temperature (MAAT) of the most modern stalagmite sample at ~19 °C, matches the surface and cave MAAT, but was ~4 °C lower during LGM. Warming at the end of LGM occurred before ISM strengthened and indicate 6 ka lag consistent with sea surface temperature records. The isotope records during the Younger Dryas show rapid progressions to dry conditions and weak monsoons, but these shifts are not coupled to TEX86. Moreover, change to wetter and stronger ISM, along with warmer Holocene conditions are not continuous indicating a decoupling of local temperatures from ISM.

The Indian Summer Monsoon from a Speleothem δ18O Perspective—A Review

“…Orbital-scale records are available from Bittoo cave [13] from north India and Belum cave [54] from peninsular India. Mawmluh cave [16,17,46] from the northeast currently covers the Last Glacial Maximum, and Heinrich stadials. Records from peninsular Valmiki cave covers the later phase of Heinrich event 1 [50] and the last deglaciation [49].…”

“…Records from peninsular Valmiki cave covers the later phase of Heinrich event 1 [50] and the last deglaciation [49]. Bittoo [13], Kalakot [44], and Timta [15] caves from north India and Mawmluh [16,17,46] cave from northeast India cover the Bølling-Allerød (BA) and Younger Dryas (YD) periods. Sahiya [10,12] cave from north India, Mawmluh [45] and Umsynrang [61] caves from northeast India, and Kotumsar [57] cave from peninsular India cover significant periods of the Holocene.…”

The Indian Summer Monsoon from a Speleothem d¹⁸O Perspective – a Review

“…Similarly, the temperature reconstruction given by the stalagmite GDGT proxy indicates little temperature change in this region during the YD event. This suggests that δ 18 O variation is not controlled by local temperature change but by larger circulation changes triggered by a distal North Atlantic event [46]. And the coupled analysis of δ 18 O and δ 13 C further indicate that the δ 18 O variation between the BA and into the YD may be more representative of a change in seasonality of rainfall associated with a weaker ISM [17].…”

“…Records from peninsular Valmiki cave covers the later phase of Heinrich event 1 [50] and the last deglaciation [49]. Bittoo [13], Kalakot [44] and Timta [15] caves from north India and Mawmluh [16,17,46] cave from northeast India cover the Bølling-Allerød (BA) and Younger Dryas (YD) periods. Sahiya [10,12] cave from north India, Mawmluh [45] and Umsynrang [61] caves from northeast India and Kotumsar [57] cave from peninsular India encompass significant periods of the Holocene.…”

“…Glycerol Dialkyl Glycerol Tetraether (GDGT) [46], δ 13 C and ice volume corrected δ 18 O [17] measured from stalagmites in this region give additional information on the controls on δ 18 O variation. For example, the ice volume corrected δ 18 O suggest that ice volume and SST changes account for only 1/4th (~1‰) of the δ 18 O change from the glacial to deglacial, the larger part is attributable to change in ISM strength [17].…”