A question or so about varves.

[David B]

I've just watched yet another tv science doc - this time about worldwide climatic event that happened around AD 535, which in this documentary has been tentatively attributed to a bang at Krakatoa, bigger than the 19th century one.

I've read about this c535 event before, and it has been attributed to both a volcanic event, source unknown, and to a possible impact event.

It does seem, though, that there was a big event at that time, from dendrochronological evidence, ice core evidence, historical accounts, and imputed from a comparative dearth of historical accounts in the decades after the event, as I recall.

My question is - do any of the experts know of any signatures of this event in analysis of varves.

A further question is - has anyone looked specifically for signatures of this event in the varve record?

Further questions - would it be a good idea to look, and what might one look for?

Ash?

Evidence of lots of sulphuric and/or sulphurous acid?

Vegetation changes?

David B (wonders, without confidence, if demonstrating a signature of an event at 535ish, in varves dated to 535ish, might make at least some sort of impact on those who deny that varves demonstrate an earth older than a YEC interpretation)

[espritch]

If it was volcanic, I imagine there could have been an increase in acid rain which would negatively affect diatom growth, so you might find associated varves with lower than normal diatom content. You could also check for changes in water temperature recorded as differing oxygen isotope ratios in the diatom shells (apparently, water temperature has a measurable effect on these ratios).

If it was an impact event, there might be elevated iridium levels. Of course this might produce acid rain as well.

I have no idea if any effort has been made to find such signals in varves.

[Jet Black]

I'll ask around some of my contacts. I'm not aware of anything in particular though.