Evidence from tree rings and ice cores suggest that parts of Europe, Asia and North America saw protracted cooling in the 530’s, which has been linked to drought and famine. Some scientists hypothesize that Halley’s Comet may have caused this, by leaving a dust trail that the Earth later intercepted during its orbit. Dust in the air could have blocked the sun’s rays. Abbott finds evidence in ice cores drilled from Greenland: as much as 10 times more dust is found in the layer corresponding to 533 A.D. than at other intervals, she says. This dust is rich in markers of extraterrestrial origins such as nickel and iron oxide spherules. She finds that neither volcanism nor solar cycles can fully explain the cooling seen in various records during this decade. Furthermore, spikes of the ice-core dust appear to match the timing of the Eta Aquarid meteor shower, known to be triggered by Halley.
TITLE: What caused terrestrial dust loading and climate downturns between 533 and 540 A.D.?
AUTHORS (FIRST NAME, LAST NAME): Dallas H Abbott1, Dee L Breger3, Pierre E Biscaye1, John Arthur Barron4, Robert A Juhl2, Patrick McCafferty5
INSTITUTIONS (ALL): 1. Lamont-Doherty Earth Obs, Palisades, NY, United States.
2. Independent Researcher, Tokyo, Japan.
3. Micrographic Arts, Saratoga Springs, NY, United States.
4. USGS, Menlo Park, CA, United States.
5. Queens University, Belfast, Ireland.
ABSTRACT BODY: Sn-rich particles, Ni-rich particles and cosmic spherules are found together at four stratigraphic levels in the GISP2 ice core between 360 and 362 meters depth. Using a previously derived calendar-year time scale, these particles span a time of increased dust loading of the Earth’s atmosphere between 533 and 540 A.D. The Sn enrichments suggest a cometary source for the dust. The late spring timing of extraterrestrial input best matches the Eta Aquarid meteor shower associated with comet 1P/Halley. The increased flux of cometary dust could explain a modest climate downturn in 533 A.D. The profound global dimming during 536 and 537 A.D. cannot be explained merely by a combination of cometary dust and a modest volcanic eruption. We found tropical marine microfossils at the end 535-start 536 A.D. level that we attribute to a low-latitude explosion in the ocean. This additional source of dust is probably needed to explain the solar dimming in 536-537 A.D. In addition, we found high-latitude marine diatoms and silicoflagellates at a second time horizon, circa 538 A.D. Some of the fossils are pre-Pleistocene in age, as old as Eocene. Both of these fossil-bearing stratigraphic levels contain enrichments of nitrate and ammonium in their supernatant water.
KEYWORDS: 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE Aerosols and particles, 4306 NATURAL HAZARDS Multihazards, 0724 CRYOSPHERE Ice cores, 6015 PLANETARY SCIENCES: COMETS AND SMALL BODIES Dust.
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Previously Presented Material: 10% previously presented at March 2013 meeting on Volcanism, Impacts and Mass Extinctions-material is submitted to a special GSA volume from that meeting