Unintelligent Design
22 Apr '13 21:082 editsOriginally posted by sonhouseThe reason for studying the ice core data is to gain a climate record. Dating is a side issue and loses accuracy the deeper the core sample. Also it must be assumed whether these layers are a result of a single year or a single season. The common assumption has been a single year. The following is what Wikipedia has to say about it:
The whole point of studying ice core data is to see what years have thicker layers. Of course ice buildup varies year to year but the record of thin V thick is left in the core. How could it be otherwise?
You have a year where you get 1 mm of ice then a year with 2 mm of ice, those thicknesses do not go away or change, it is 1 mm now and 1 mm 10,000 yea ...[text shortened]... even CLOSE to where just that pressure would make much of a difference in the layer thicknesses.
CLIMATE RECORD:
As the ice forms from the incremental build up of annual layers of snow, lower layers are older than upper, and an ice core contains ice formed over a range of years. The properties of the ice and the recrystallized inclusions within the ice can then be used to reconstruct a climatic record over the age range of the core, normally through isotopic analysis. This enables the reconstruction of local temperature records and the history of atmospheric composition.
Ice cores contain an abundance of information about climate. Inclusions in the snow of each year remain in the ice, such as wind-blown dust, ash, bubbles of atmospheric gas and radioactive substances. The variety of climatic proxies is greater than in any other natural recorder of climate, such as tree rings or sediment layers.
DATING BY ICE CORES:
Upper layers of ice in a core correspond to a single year or sometimes a single season. Deeper into the ice the layers thin and annual layers become indistinguishable. If the summer temperatures do get above freezing, any ice core record will be severely degraded or completely useless, since meltwater will percolate into the snow.
Shallow cores, or the upper parts of cores in high-accumulation areas, can be dated exactly by counting individual layers, each representing a year. Deeper into the core the layers thin out due to ice flow and high pressure and eventually individual years cannot be distinguished.
Dating is a difficult task. Five different dating methods have been used for Vostok cores, with differences such as 300 years at 100 m depth, 600yr at 200 m, 7000yr at 400 m, 5000yr at 800 m, 6000yr at 1600 m, and 5000yr at 1934 m.
Different dating methods makes comparison and interpretation difficult. Matching peaks by visual examination of Moulton and Vostok ice cores suggests a time difference of about 10,000 years but proper interpretation requires knowing the reasons for the differences.
http://en.wikipedia.org/wiki/Ice_core
I also found the following statement interesting, for they still have many problems to overcome in accurate dating.
There are great problems relating the dating of the included bubbles to the dating of the ice, since the bubbles only slowly "close off" after the ice has been deposited.
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