Exploring abrupt climate change induced by comets and asteroids during human history

Science News: Signs of giant comet impacts found in cores

Copious ammonium may be evidence of a 50-billion-ton strike at the end of the ice age
A new study cites spikes of ammonium in Greenland ice cores as evidence for a giant comet impact at the end of the last ice age, and suggests that the collision may have caused a brief, final cold snap before the climate warmed up for good.
In the April Geology, researchers describe finding chemical similarities in the cores between a layer corresponding to 1908, when a 50,000-metric-ton extraterrestrial object exploded over Tunguska, Siberia, and a deeper stratum dating to 12,900 years ago. They argue that the similarity is evidence that an object weighing as much as 50 billion metric tons triggered the Younger Dryas, a millennium-long cold spell that began just as the ice age was loosing its grip (SN: 6/2/07, p. 339

3 Responses

  1. Good stuff! However, this is hardly new news, as the greenland Ice Cores have been indicating not only significant ammonium spikes, but also what seem to be enigmatic nitrate increases during the Younger Dryas. The link can easily be made (as is done in my book “Sudden Cold An Examination of the Younger Dryas Cold Reversal”

  2. This post is about the best fit I could find for this comment.

    In this ice core paper, Johnsen et al 1992

    The Summit [ice core site] location on the top of the ice sheet (Fig. 1) s an almost ideal depositional environment in which to recover an ice core; the flow pattern is simple, because there is no horizontal ice movement at present, and little in the past, when the ice divide might have been slightly displaced from its present position.Johnsen et al 1992 – Irregular glacial interstadials in a new Greenland ice core” http://www.rci.rutgers.edu/~jdwright/johnsenetal.pdf

    I’ve said many times here that steep-slope (mountainous) ice flows, and the opposite, that ice on the flat (or contained within a basin) does not flow. This simple statement confirms that they KNOW that there is some ice that flows and some that doesn’t. And I would bet that if you ask them why the ice at Summit does not flow, they will assert one of those two conditions – flat or basin. And YET, when you talk to them about ice on the flat Canadian Shied (the Laurentide), they will change tunes and tell you all about ice advances (movement!) and ice retreat (melting). Either ice can flow on flat ground or in basins, or it can’t. They can’t have their cake and eat it, too.

    Furthermore, the Summit surface temperature seldom rises above the freezing point, in contrast to Dye 3 [ice core site] where summer melting often causes post-depositional changes in the firn, for example absorption of additional soluble gases from the atmosphere.

    I CHALLENGE them to get any coherent signal out of this ice core – because of the very reason they state here. If the icw on top melts to some unnown degree in some or most or all summers, then there can be no KNOWLEDGE about the accumulation of ice over time. If it is melting NOW each summer, then it would have melted SOME or perhaps all of the summers – and HOW MUCH IS LOST? AND HOW MANY TIMES IN THE RECORD? The record is useless. Driklling and coring in a steep slope has EXACTLY the qualites NOT to have in an ice core.

    I paraphrase their own words from above:

    …the flow pattern is NOT simple, because there IS DEFINITELY horizontal ice movement at present, and MUCH in the past, when the ice layers below WERE MORE THAN slightly displaced (AND TO UNKNOWABLE AND VARYING DEGREES) from its present position.

    Glaciers and ice sheets are not equivalent animals. Discussing either one as if it acts like the other can only be erroneous thinking. How could it be otherwise – if one is on the flat and cannot move, while the other is on a slope, in a valley, and MUST move?

    Invoking high, deep ice and that the vertical weight of gravity somehow delivers a horizontal internal flow over hundreds and hundreds of kms is invalid, IMVHO.

    And if they are wrong on this, then every sentence in every paper that depends on ice sheets on the flat moving anywhere is defunct. Add in friction and protuberances (hills, ridges, etc.) as impediments to movement, and the problem for them gets even worse and more erroneous.

  3. Seriously…

    In design, we often had to deal with movement of objects over sloped and flat surfaces. When this came up, we would have to reference the correct formulas for force requirements, and the formulas for slopes were DIFFERENT than for horizontal flat surfaces. BOTH had to deal with friction and breakaway force (AN IMPORTANT POINT in itself!), but if we did not have a downward slope wroking with us, then the “normal” force only had to deal with overcoming friction and breakaway force.

    Movement was not possible until the breakaway force was overcome, and THEN we had to deal only with SLIDING FRICTION.

    These are basic basic basic basic principles for mechanical movement. And believe me, an ice mass moving IS a mechanical movement.


    –Normal force (due to gravity).

    –Slope (brings trigonometry into it; at zero angular degrees the horizontal thrust from the “normal force” is ALWAYS zero. This is taught Geology 101.)

    –Coefficient of Friction. (applies to sliding friction, but not breakaway force)

    –Breakaway force. (force necessary to overcome the adhesion between the substrate and the object to move)

    –Surface roughness (adds to the Coefficient of friction, and is due to the interlocking at the microscopic – or even the macroscopic – level

    –Temperature (can and does affect both Coefficient of Friction AND the Breakaway force.

    –Lubrication (can reduce the required breakaway force and the Coefficient of Friction – but never to zero)

    –Additional formulae are required for the flow of fluids (and rheids).

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