| Archive for Earth Sciences Forum This site is dedicated to the Earth Sciences. We are here for you to discuss issues regarding any aspect of the Earth sciences, at all levels of knowledge. Questions are welcomed, as are open scientific debates. Enjoy!!! |
| Andre |
The 100,000 year cycle.When we look at the longest ice core isotope record we see this:
But ice cores are not the only place where we harvest isotopes. The ocean floor accumulates remains of small skeletons of foraminifera. As the accumulation is much slower, it's possible to collect cores with fossil foraminifera going back hundreds of million of years, telling us much about the past. That is, if we understand the language of the proxies. Let's look at a marvelous compilation of the oxygen isotopes of foraminifera shells from 57 of those marine sediment cores of the Ocean Drilling Program over here: **Image link deleted for shape of the thread. Please see the link here:** Ref: Lisiecki, L. E., and M. E. Raymo (2005), A Pliocene-Pleistocene stack of 57 globally distributed benthic d18O records, Paleoceanography, 20, PA1003, doi:10.1029/2004PA001071 This covers the last 5.3 million years. We are especially interested in the youngest part, say the last half million. Let's compare that with the ice core: 
Dozens of scientists have been crushing their brains about this. This is the take of Spencer Weart:
But that is what we would call a challenge. |
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| NileQueen |
How precise can the dating be at 130,000 years ago or so?
Your vertical line looks like the ocean and the ice core record are operating in sync. and contemporaneous. One is not appearing to lead the other at this spot. |
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| Andre |
All about the dating here There are many tricks to date these records. Sometimes radioactive dating of many unstable isotope series is possible, magnetic orientation can be fitted to the known magnetic polarisation. Sometimes volcanic tephra layers can be identified. Then there is estimation of annual accumulation. All of those should match a bit. And then finally there is the tuning to Milankovitch cycles and other proxies. This however is circular reasoning, using the hypothesis as data to prove the same hypothesis equals to a=a.
Exactly, well if tune both to Milankovitch then again that circular reasoning eliminates lead - lag. But there are other ways to judge which signal leads which one, looking at the shape of the spikes. We'll get to that. See what the authors say about the ocean lag:
Is that really so? Any oceanographers around? I read somewhere that the Thermohaline Current cycles in about 1500 years. So, I would infer that a subducting molecule in the Northern Atlantic would take on the average 1000-1500 years to emerge somewhere again after a long journey around the world in the deep ocean. But if that is true for the first water molecule, how long will it take for the complete oceans to mix homogeneous. I would be surprised if that would be 1000 years as well, considering how long it takes to mix two pots of paint homogeneously. So if I make a high resolution comparision of the last 30,000 years it just so appears that the Deep sea benthic stack started on its way up 23,000 years ago while the EPICA dome C ice core "temperature" -isotopes waited to about 18,700 years. Which leads which? 
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