2019 AGU abstract supports Younger Dryas “exacerbated” by cosmic impact

Sharma, 2013

This week is “abstract reveal” week for the enormous annual conference of the American Geophysical Union (AGU) held each December (See Tusk at 2009 AGU). So each year around this time I search the AGU website for any coming presentations concerning the Younger Dryas and cosmic impact.

Fall Meeting 2019 San Fran turned up an interesting hit. Mukul Sharma, a geochemistry genius who has been in and out of the YDIH publishing maelstrom for years, presents a poster from a distinguished team led by Ji-Hye Seo and other Geo-forensic experts.

It is intriguing that Sharma et al. envision a stochastic volcanic eruption immediately preceding an extraordinarily energetic cosmic impact. It seems like it should be the other way around.

“These signals suggest that volcanism potentially induced the YD cooling, which may have been further exacerbated by an extra-terrestrial impact”

 

C11C-1305 Younger Dryas Trigger Through the Lens of GRIP Ice Core

Monday, December 9, 2019, Moscone South

The Younger Dryas (YD) abrupt cooling event (~12,900 yr to 11,600 yr) represents a brief return to severe cold conditions in mid-to-high- latitudes in the Northern Hemisphere. The cooling is thought to have resulted from freshwater flooding of the northeast Atlantic and/or the Arctic Oceans that prevented deep water formation and promoted extensive southward expansion of sea-ice. Two different triggers that would lead to freshwater capping the north Atlantic have been proposed: (1) catastrophic drainage of proglacial Lake Agassiz and (2) a meteorite impact-related partial destabilization and/or melting of the Laurentide ice sheet. However, the physical evidence for these triggers remains elusive. Recent revision in the age of Laacher See volcano (Volcanic Explosivity Index = 6) in Eifel, Germany has led to the suggestion that the YD event was triggered by emplacement in the stratosphere of large amounts volcanic sulfur and halogens with sustained cooling resulting from a positive feedback involving sea ice expansion and/or AMOC shutdown. Thus, building of sea-ice rather than freshwater capping provides a trigger according to this hypothesis. Here, we use GRIP ice core to investigate whether the YD was engendered by a one-time catastrophic event or whether it was an integral part of a sequence of events that unfolded as the last ice-age came to a close. We sampled GRIP ice core every 9 cm from a depth of 1659.35 m to 1664.30 m corresponding to a time-resolution of 2-3 years spanning 12,939-12,810 yr b2k. Decontaminated ice-core was analyzed for δ¹⁸O, δD, major cations and anions, trace-elements, and osmium and lead isotopes. We find that a massive volcanic eruption occurred at 12,918 yr b2k and that immediately following the eruption the d-excess increases from 4 to 9 permil over a period of 37 years indicating a profound increase in sea-ice. During this time period, ratio of fluxes mantle to continental derived osmium also increases. Additionally, there is evidence of a 20-fold increase in extra-terrestrial osmium flux ~12,819 yr b2k following which the δ¹⁸O values display a steep and sustained decline to –40 permil. These signals suggest that volcanism potentially induced the YD cooling, which may have been further exacerbated by an extra-terrestrial impact.

Authors

• Ji-Hye Seo

  • Dartmouth College
• Changhee Han

  • Inha University
• Joergen Peder Steffensen

  • Niels Bohr Institute – University of Copenhagen
• Erich C Osterberg

  • Dartmouth College
• Sungmin Hong

  • Inha University
• Mukul Sharma

  • Dartmouth College