http://tamino.wordpress.com January 3rd 2009 … a blog with the title Open Mind that reported a year ago on the Firestone et al (2008) claim that a comet was responsible for the YD boundary event – a sudden reversion to cold almost glacial conditions in high latitudes of the northern hemisphere. However, the cooling episode does not appear in Antarctic ice cores (at Byrd station for example). For a long time the prevailing theory for the cause of the YD event was the release of a vast quantity of fresh water into the North Atlantic from a suspected large inland lake held back by glacial ice. When this hypothetical ice dam melted, a couple of thousand years after the end of the Ice Age, this melted and released fresh water poured into the ocean, decreasing the salinity of the surface water and in turn the density of the surface water which prevented it from sinking into the deep ocean and recircling back towards the tropics. Ocean currents circulate heated surface water around the world’s oceans and in the North Atlantic sink and return to the equatorial zone beneath the Gulf Stream and it’s river of warm water emanating from the Caribbean – but with an ultimate origin in the equatorial zones of the Pacific and Indian oceans. This is known as thermohaline circulation – the transportation of heat from the tropics to the poles. Robbed of the Gulf Stream as a result of the influx of fresh water the North Atlantic was thought to have entered a deep freeze – and you may note also it is a favourite idea of AGW advocacy. However, along came Firestone, West and colleagues and the YD impact theory. The cold weather is instead blamed on loading of the atmosphere by cometary debris and dust.
http://anthropology.net December 16th 2009 … has a debate on the YD boundary event with a response by Richard Firestone.
At www.realclimate.org of January 2009 the YD comet theory was also discussed but in general was not regarded as very likely. It was never the less not as critical as one might expect and suggested waiting until further evidence was found. However, a comet impact might take some of the thunder out of global warming as the cool episode that followed is generally attributed to climate change – a scary scenario that involved cold temperatures striking NW Europe and North America and the shut down of the Gulf Stream. Worth reading.
Meanwhile, http://cosmictusk.com has a report from February on the claim that an asteroid cluster was blamed for an airburst over Australia as a result of dust found in Antarctic ice cores. There were two big impactors it is argued, one at 481,000 years ago and the other at 434,000 years ago (see also www.sciencedaily.com of July 2008 id0807 10103903
The similar, but different story pops up on Daily Galaxy (www.dailygalaxy.com of 9th March) which reports there is a crater hiding a mile beneath the Antarctic ice sheet that was created by a 50km wide object – that struck the earth at the Permian-Triassic boundary event when almost all animal life is thought to have died out. The impact was responsible for the creation of a Rift Valley, it is argued, between what is now Australia and the Antarctic continent. The two continental sections did not actually split apart at that point in time – this happened much later.