GeologyRocksMilankovitch Cycles
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I think one of the major
Mon, 01/14/2008 - 19:18I think one of the major problems with doing this is that the climatic record in geology is more and more sporadic the further back in time you go. Even if we would put all the cycles together like u mentioned it may be very hard to impossible to correlate them with what the geology has available for us. There are theories that say that we only see 5% of the actuall geological sedimentation and any other rocks that have ever existed. Now image pieces this often very obscured record into the right places of your climate curves. There may be multiple peaks at various levels and chosing which one corresponds to which may be nothing more than anyones guess.
It is however possible to re-model past climates by means of Isotope studies (i am thinking esp. of d18O here).
I have been going thru my class stuff and I actually found a graphic comparing Insolation (depending on the angle of the axial tilt) with d18O and dust using the EPICA Dome C Ice core data. It seems to correspond somehow.
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Milankovitch Cycles
Mon, 01/14/2008 - 19:21The problem with Milankovitch Cycles in the geological record is this ...
Although the process may be cyclic, what you don't know exactly is the sedimentation rate, so you don't know how many years your cycle represents.
You could try using varves (annual layers of sediment ) but you don't tend to get varve sequences matching the length of several Milankovitch Cycles to do the analysis.
Having said all that, some authors think that they have detected Milankovitch Cycles in the layered Lias rocks of Dorset, and elsewhere in the UK.
Rather than use time domain, the sequence is analysed in the frequency domain and spectral peaks (metres/cycle) matched to Milankovitch Cycles (years/cycle).
(Caveat - I'm not an expert on this)
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Thanks for the response
Mon, 01/14/2008 - 20:12Thanks for the response chaps. It looks like I am in water over my head but at least my idea was not torpedoed on sight.
Mathias wrote: There are theories that say that we only see 5% of the actuall geological sedimentation and any other rocks that have ever existed.
That gave me pause for thought. I generally assumed geological records were gospel. Seems I need to be more cautious when I read reports on geological events.
What got me thinking along these lines is the current murky debate on global warming. The geological record shows past global temperatures have at times been higher than at present and I was wondering if I could see any correlation with Milankovitch cycles. Being an AGW sceptic I believe the major cause is directly driven by the sun. Marginal changes of CO2 in the order of .02% just seems unbelievable. Massive increases in CO2 could shortly follow global temperature rise if CO2 is released big time from clathrates and thawing tundra. Anyway, musn't clutter this site with my ramblings.
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Found some more evidence for
Thu, 01/17/2008 - 07:37Found some more evidence for Milankovitch cycles and climate forcing.
Mathias wrote:
It is however possible to re-model past climates by means of Isotope studies (i am thinking esp. of d18O here).
Nice one! See this site for more detail:
http://www2.ocean.washington.edu/oc540/lec02-22/
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There are means to recognise
Thu, 01/17/2008 - 22:20There are means to recognise if in any outcrop, drill core or other situation has time intervals that have not survived, had no sedimentation, or whatever. The older deposits get the more and more difficult it becomes. Ice cores are to my knowledge pretty complete in the time they represent.
Anways. I am not an expert of this matter. I am more into mineral deposits and exploration.
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Milankovitch Cycles
Submitted by Richard on Mon, 01/14/2008 - 13:41.Hi, all. A query from a non Geological type. Hope someone can advise or give pointers.
I am currently looking at Milankovitch Cycles on this site:
http://www.homepage.montana.edu/~geol445/hyperglac/time1/milankov.htm
What I am trying to find, it may not even be possible, but here goes, is a timeline showing the three Milankovitch Cycles superimposed on each other and past climatic events that may have been a directly or even partially caused by such cycles.
What I imagine is just one cycle of the 100.000 year Eccentricity cycle and then two or more cycles of the 41,000 year Axial Tilt cycle with finally five or more cycles of the 23,000 year Precession cycles. Once the relationship of the cycles is estabilished it should be possible to extend the cycles back into the past and check out major climatic events that show up in the Geological record.
Currently "the Earth is at perihelion very close to the winter solstice" in the Precession cycle which goes a long way to explaining why Northern Hemisphere winters are a bit warmer than average.
Richard