Annual Layers of Ice

Tree-rings and lake varves are not the only system that build annual layers that can be measured and counted. Snow and ice also follow annual patterns in their formation and deposition that allow a number of ways to determine the annual layers.

To introduce the basic methods we will start with a fairly simple but dramatic set of annual ice layers:

The Quelccaya Ice Cap
This information comes from an on-line slide show:

http://www.ncdc.noaa.gov/paleo/slides/slideset/index20.htm (3)

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(Slide 1) The Peruvian altiplano is a high plateau ranging in altitude from 3500 to over 4000 meters above sea level. Though the altiplano is a cold, harsh environment, large herds of hardy llamas such as these hint at the richness of South America's high grasslands. The Quelccaya ice cap rises in the background, 55 km2 of ice that provides important clues on climatic change and variability in the South American tropics. The ice sheet's summit elevation is 5670 m and its maximum summit thickness is 164 m.
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<img src="http://herballure.com/ForumExtras/Images/hrfxilqccy.jpg">
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(Slide 3) The Quelccaya cap terminates abruptly and spectacularly in a 55 m ice cliff. The annual accumulation layers clearly visible in the photograph are an average of .75 m thick. While snow can fall during any season on the altiplano, most of it (80-90%) arrives between the months of November and April. The distinct seasonality of precipitation at Quelccaya results in the deposition of the dry season dust bands seen in the ice cliff. These layers are extremely useful to the paleoclimatologist because they allow ice core records to be dated very accurately using visual stratigraphyy, which is simply the visual identification of annual dust layers in ice records (in most ice cores, annual layers become indistinct at depth, forcing paleoclimatologists to rely on less-accurate ice-flow models to establish chronologies; at Quelccaya, on the other hand, annual layers are visible throughout the core).
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(Slide 6) An array of forty-eight solar panels provided enough electricity to recover two ice cores to bedrock, one 154.8 m long covering the last 1350 years, and the other 163.6 m long and 1500 years old.
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(Slide 11) Two of the analyses performed on the cores are presented here, accumulation and the oxygen isotope ratio (known as dO-18). Accumulation is a measure of annual layer thickness normalized to account for the compression of ice layers at depth and corrected for ice flow dynamics. The oxygen isotope ratio (a measure of the ratio of heavy oxygen (O-18) to light oxygen (O-16)) is a proxy measure for paleotemperature, though it also reflects changes in snow surface processes and water-vapor history.
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One of the most salient features in the last millennium of climate history is the Little Ice Age, a loosely-defined period of cold temperatures and increased climatic variability that has been documented in many parts of the globe.* As this figure shows, the Little Ice Age is identified in the Quelccaya climate record as a period of 'colder' (more negative) dO-18 roughly bracketed between 1550 A.D. and 1900 A.D.
Note that they are talking about correlating layers with climate information provided by dO-18. We'll also come across this in other measurement systems. This is the proportion of a "heavy" isotope of oxygen in the atmosphere (O-16 is "normal" weight oxygen)

see http://en.wikipedia.org/wiki/Oxygen-16 (1)
and http://en.wikipedia.org/wiki/Oxygen-18 (2)

While this series of layers only date back to ~500AD they are important for a couple of reasons: they show visible layers, and they allow calibration of the oxygen isotope ratio (dO-18) as a measure of layers and of climate. These layers also show a period of sever weather that is known from history (the Little Ice Age) and the effects of a volcanic eruption nearby that occurred in 1600 AD. These results can then be applied to other ice cores.

The Dunde Ice Cap
Continuing from the same slide show:

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(Slide 14) The Dunde Ice Cap (pronounced Dun-duh) is extremely remote, perched on the mountain range separating China's highest desert, the Qaidam Basin, from its more famous counterpart, the Gobi. For over 40,000 years, snow has been piling up on this 60 km^2 ice cap deep in China's sparsely inhabited interior. A team of paleoclimatologists from the United States and China came here in 1987 to uncover the climatic secrets locked in Dunde's icy depths.
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(Slide 17) Since Quelccaya is at the edge of the moist Amazon Basin while Dunde is wedged between two deserts, it is not surprising that accumulation rates are much higher at Quelccaya. Indeed, the annual average accumulation at Quelccaya in meters of water equivalent is 1.15 m compared to just .43 m at Dunde. Like Quelccaya, around 80% of Dunde's precipitation falls during the wet season. The dry season is clearly identified in the core record by the layers of dust from surrounding deserts visible in this ice segment.
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Since snow accumulates more slowly at Dunde, ice from its ~140 m cores is significantly older than that from Quelccaya. While Quelccaya provides high-resolution clues to the last 1500 years of climate, Dunde stretches back over 40,000 years, well into the last ice age.
The same kind of alternating layers of dust and snow as at Quelccaya, the same kind of climate information from the oxygen isotope ratio (dO-18), data that matches known climate markers, including the last ice age, data that also showed up in Lake Suigetsu climate information. Research on the Dunde Ice Cores is continuing, including analysis of the dust and pollen as markers not just of climate but of environment.

http://geology.geoscienceworld.org/cgi/content/abstract/26/2/135 (5)

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High pollen concentrations between 10 000 and 4800 yr B.P. suggest that the summer monsoon probably extended beyond its present limit to reach Dunde and westernmost Tibet in response to orbital forcing. The summer monsoon retreated time-transgressively across the Qinghai-Tibetan Plateau during the middle Holocene. Relatively humid periods occurred at 2700-2200, 1500-800, and 600-80 yr B.P., probably as a result of neoglacial cooling. Prominent pollen changes during the Medieval Warm Period (790-620 yr B.P.) and the Little Ice Age (330-80 yr B.P.) suggest that the vegetation in the Qinghai-Tibetan Plateau region is sensitive to abrupt, century-scale climatic changes, such as those anticipated in scenarios of greenhouse warming.
http://www.springerlink.com/content/wu102k4348572506/ (6)

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The insoluble microparticle concentrations and size distributions and oxygen isotope abundances (dO-18) in two 1-meter ice cores from the margin of the Dunde ice cap (38° 06 'N; 96° 24 'E; 5325 masl) drilled in 1986 and three ice cores drilled to bedrock at the summit of the ice cap in 1987 suggest the presence of Wisconsin/Würm Glacial Stage (LWGS) ice in the subtropics.
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Additionally, the morphological properties of the particles in the LWGS ice are identical to those of the thick, extensive loess deposits of central china which accumulated during the cold, dry glacial stages of the Pleistocene. When the climatic and environmental records are fully extracted from the three deep cores they will provide a very detailed record of variations in particulates (soluble and insoluble), stable isotopes, net balance, pollen and perhaps atmospheric gases of CO2 and methane through the Holocene into the last glacial in the subtropics on the climatically important Tibetan Plateau.
http://en.wikipedia.org/wiki/Wisconsin_glaciation (4)

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The Wisconsin (in North America), Devensian (in the British Isles), Midlandian (in Ireland), Würm (in the Alps), and Weichsel (in northern central Europe) glaciations are the most recent glaciations of the Pleistocene epoch, which ended around 10,000 BCE. The general glacial advance began about 70,000 BCE, and reached its maximum extent about 18,000 BCE.
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The name Devensian glaciation is used by British geologists and archaeologists and refers to what is often popularly meant by the latest Ice Age.
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It was the final glacial phase of the Pleistocene and its deposits have been found overlying material from the preceding Ipswichian interglacial and lying beneath those from the following Flandrian stage of the Holocene.
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The latter part of the Devensian includes Pollen zones I-IV, the Allerød and Bølling Oscillations and the Older and Younger Dryas climatic stages.
Thus we see evidence of the end of the last glaciation period in the dust and pollen in the layers of ice from the Dunde Ice Cap in addition to the evidence of the dO-18 ratios. Data that also makes the concept of a world wide flood (WWF) within this period difficult, as the dust every year is of the same type and the thickness of ice and dust layers are the same from year to year indicating that the ice cap has not changed locations nor floated on water at any time in its history.

These climate changes locked in the ice layers are at the same distribution as the climate changes locked in the varves of Lake Suigetsu, they correlate because they are both annual systems.

Minimum age of the earth > 40,000 years based on this data.

And this is but the tip of the iceberg.

Enjoy.

References
(1) Anonymous "Oxygen-16" Wikipedia. updated 7 Dec 2006. accessed 10 Jan 2007 from http://en.wikipedia.org/wiki/Oxygen-16
(2) Anonymous "Oxygen-18" Wikipedia. updated 7 Dec 2006. accessed 10 Jan 2007 from http://en.wikipedia.org/wiki/Oxygen-18
(3) Anonymous "Paleo Slide Set: Low Latitude Ice Cores: High Resolution Records of Climatic Change and Variability in the Tropics and Subtropics" NOAA Paleoclimatology. updated 20 Jul 2004. accessed 10 Jan 2007 from http://www.ncdc.noaa.gov/paleo/slides/slideset/index20.htm
(4) Anonymous "Wisconsin glaciation" Wikipedia. updated 15 Jan 2007. accessed 19 Jan 2007 from http://en.wikipedia.org/wiki/Wisconsin_glaciation
(5) Kam-biu Liu, et al, "A pollen record of Holocene climatic changes from the Dunde ice cap, Qinghai-Tibetan Plateau" Geology; February 1998; v. 26; no. 2; p. 135-138 accessed 19 Jan 2007 from http://geology.geoscienceworld.org/cgi/content/abstract/26/2/135
(6) Thompson, Lonnie G., "Wisconsin/Würm glacial stage ice in the subtropical dunde ice cap, China" GeoJournal Vol 17, No 4 Dec 1988 DOI 10.1007/BF00209440 P517-523, SpringerLink Date 20 Oct 2004 accessed 19 Jan 2007 from http://www.springerlink.com/content/wu102k4348572506/
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