THREE STRIKES? EARTH NOT OUT

A portion of the GISP2 ice core covering the time from A.D. 532 to 542 was calendar-year dated using ion data and historical accounts [1]. This portion of the GISP2 ice core contains assemblages of two or more marine diatom species at three different stratigraphic levels. The first level is A.D. late 535 early 536. The diatom assemblage and one silicoflagellate are tropical to subtropical [2]. The second level covers early A.D. 541 to late 541. It contains two Azpeitia, one likely Azpeitia nodulifera, a common tropical diatom species. It also contains two centric marine diatom valves, in addition to specimens of Thalassiothrix, Synedra, Triceratium and a possible radiolarian fragment. Overall, the assemblage is consistent with a tropical-marine source. The third level covers late A.D. 538 to early 539. The diatom assemblage is high-latitude with mixed ages from the last 5.3 Ma to Eocene. The best match to this assemblage is found at Ocean Drilling sites in the eastern half of Norwegian-Greenland Sea, where no active volcanoes exist. The two low-latitude assemblages date to the same time as frost rings in bristlecone pines from the summers of A.D. 536 and A.D. 541. In addition, there are 9 lunar halos (inferred atmospheric dimming) in S. China throughout A.D. 541. Although there is no frost ring evidence from North America at the time of the high-latitude (third) assemblage, S. China recorded severe frosts, famine and atmospheric dimming. The coincidence of atmospheric dimming in China with high concentrations of marine diatoms in the ice core could provide further support for our calendar-year dating. Ion data show the two most prominent peaks in non-seasalt sulfate in early A.D. 536 and late A.D. 541. Because sulfate can take 6 to 18 months to fall out after a volcanic eruption [3], the sulfate data are consistent with a volcanic source for the low-latitude diatoms. If so, the volcanic cone must have been at least partially submarine so that its eruption could inject diatom-bearing marine sediment into the atmosphere. An alternative source for the diatoms involves a strike of an extraterrestrial body into the ocean. Present data do not allow us to discriminate between these two hypotheses. [1] Abbott et al., 2014a. GSA Spec. Paper 505, Ch. 22. [2} Abbott et al., 2014b, GSA Spec. Paper 505, Ch 23. [3] Koffman et al., 2011, Fall AGU, #V11D-2539.