Younger Dryas cooling began with a series of eruptions in Iceland followed by an impact

초록

The Younger Dryas (YD) abrupt cooling event (12,900 yr to 11,600 yr; yr = before 2000 A.D. ) is thought to have resulted from meltwater discharges in the northeast Atlantic and/or the Arctic Oceans that prevented deep water formation. The potential forcing mechanisms include 1) catastrophic freshwater drainage of proglacial Lake Agassiz, 2) a meteorite impact-induced partial destabilization and melting of the Laurentide Ice Sheet, and 3) large volcanic sulfate and halogen loading in the stratosphere from the eruption of Laacher See volcano, Germany. However, the physical evidence for these mechanisms remains elusive. Moreover, there is recent evidence that high latitude North Atlantic Deep Water formation may have slowed down ~400 years before the YD onset due to freshwater release from the Fennoscandian Ice Sheet. Here, we use the GRIP ice core to investigate whether there was a one-time event or a series of events that led to the YD cooling. We sampled the GRIP ice core from 12,939 yr to 12,810 yr at a 2.5 year time-resolution. Decontaminated ice samples were analyzed to determine ?18O, d-excess, major ions, trace-elements, Ir, and Os and Pb isotopes. In addition, we analyzed Laacher See tephra for Pb isotopes. We report that the isotopic signals at the YD onset in GRIP show no evidence of the Laacher See eruption or a meteorite impact. Instead, the initiation of YD cooling follows and coincides with multiple volcanic eruptions in the Northern Volcanic Zone in Iceland. Moreover, there is evidence of a 24-fold increase in extra-terrestrial Os flux 12,820 yr ago. We hypothesize that an increase in volcanism in Iceland resulting from isostatic rebound combined with rising sea level likely caused a part of the southern Icelandic Ice Sheet to collapse. YD cooling was initiated by freshwater flux to the North Atlantic from the destabilization of the Icelandic Ice Sheet. Cooling appears to be further exacerbated by an impact some 80 years after the onset of the YD.