Discovery of the Toba Ash ( c. 70 ka) in a high-resolution core recovering millennial monsoonal variability off Pakistan

Abstract

A discrete Toba Ash layer in the northeastern Arabian Sea was detected near the base of a 20.2 m long piston core (289KL) recovered from the oxygen minimum zone off the Indus delta. In addition to the Toba Ash, we discovered two highly disseminated, vitreous, rhyolitic ‘ash layers’ in two annually laminated box cores: a ‘Younger Ash’ (about ad 1885–1900), and an ‘Older Ash’ (about ad 1815–1830). The glass shards were probably derived from eruptions of Indonesian volcanoes, although it was not possible to correlate these two ashes with well-known historical eruptions. We discuss source, transport and deposition of distal ash-fall layers in the Arabian Sea, which are derived from violent ultra-Plinian eruptions on the Indonesian volcanic archipelago, as well as their use for palaeoclimatic correlation. Core 289KL has a complete, high-resolution stratigraphic record of the past 75 ka with 21 interstadials (IS) or Dansgaard-Oeschger (D-O) cycles and equivalents of Heinrich events H1–H6. The high-frequency record of this core shows rapid climate oscillations with periods around 1.5 ka and can be tuned precisely to the δ18O record of a Bay of Bengal core and to the GISP-2 ice core from Greenland. The Toba event (70 ± 4 ka bp), which is well documented in the Arabian Sea and Bay of Bengal records at the end of IS-20, as well as in the Greenland ice, is an excellent stratigraphic marker horizon to validate this correlation. The apparent synchronous appearance of the various D-O oscillations and Heinrich events, which has been documented for many northern hemisphere localities, can be explained only by fairly rapid atmospheric circulation changes. Changes in the intensity of the Indian summer monsoon are tightly coupled with suborbital climate oscillations in the northern hemisphere via atmospheric moisture and heat circulation.

The 74 ka Toba super-eruption and southern Indian hominins: archaeology, lithic technology and environments at Jwalapuram Locality 3

“…Sediment organic content remains below 2% through Phases 1 and 2, which demonstrates that organic turnover was high through this period. This period coincides in part with the high sedimentation seen in Arabian Sea cores (Schultz et al, 2002;Von Rad et al, 2002) for the initial climatic deterioration from the peak of DansgaardeOeschger (DeO) interstadial 20, dated approximately 77 ka in the North Greenland ice core (Andersen et al, 2004) and 73 ka in the Greenland Summit ice record (Dansgaard et al, 1993). The soil carbonate oxygen isotope record for Locality 3 through Phases 1e3 reveals a distinct cooling/drying trend throughout the period leading to the Toba eruption (Fig.…”

Palaeoenvironmental response to the ∼74 ka Toba ash-fall in the Jurreru and Middle Son valleys in southern and north-central India

“…In fact, the onset of periods of loess deposition in China ∼71 ka Huang et al, 2001) and in Pakistan ∼74 ka (Dennell et al, 1992) represents evidence of a post-Toba shift in Asian monsoonal dynamics, where the summer south-west monsoon weakened and the winter northeast monsoon strengthened. This would have resulted in increased aridity in areas of northern India in particular, supported by marine core evidence from the Bay of Bengal and Arabian Sea that indicates decreased fluvial input during this period (Kudrass et al, 2001;von Rad et al, 2002). Therefore, arid conditions and drought likely persisted in the Middle Son valley during both OIS 4 and the stadial in between D-O 19 and 20, having been caused by a depressed south-west monsoon and significantly stronger north-east monsoon.…”

Weakening and strengthening of the Indian monsoon during Heinrich events and Dansgaard-Oeschger oscillations

“…Because of this fine tuning it is not possible to interpret lead or lag relationships between the two records although lead and lag relationships among the proxies measured from the same core are certainly valid. An additional time control point is given by the Toba Ash layer identified in core SO130-289KL at 18.43 m subbottom depth ( Figure 2) von Rad et al, 2002;Storey et al, 2012].…”