Lake Suigetsu is one of 5 lakes that were formed from volcanic eruptions. The reason this lake was targeted for study is because scientists are fully aware of the problems of assigning layers of sediments to the equivalent of annual rings and this lake has all the features that one could hope to find in a location that will likely avoid many of those problems. Annual varves are thought to be the result of different compositions of sediments and organic material in the spring/summer vs the fall/winter. To avoid the problem of false layers produced in many places by floods or inconsistent seasonality a location that is protected and exhibits a strong season signal is best. Lake Suigetsu fits those requirements. For example, the Hasu River enters Lake Mikata where the sediments suspended in the river, even during a large flood, will fall out. Water then flows through a narrow but shallow channel into Lake Suigetsu which is surrounded by high cliffs on all sides and has almost no input of water from the surrounding area save a very few very small creeks. The result of this is that the waters of Lake Suigetsu have very little suspended sediment and the surrounding walls limit the wind on its surface so the waters are not disrupted. Thus the center of the lake is extremely stable and unlikely to be disturbed by floods, large storms, etc… Input to the sediment on the bottom mostly comes from material falling into the lake from the air (leaves, pollen, volcanic ash, dust) or from differential growth of organisms (algae) over the year. What is amazing about most of the varves of Lake Suigetsu is that even microscopically the varves formed 1000 years ago look the same as those formed 40,000 years ago. Even as one moves in the core from varves formed in the past several hundred years when the climate was known from this region and varves were formed one each year back to 10s of thousands of years ago, the varves have the same characteristics. This provides even more confidence that the varves represent annual years and that the climatic influences on this lake in the past have been very similar to those of the present.
There is strong seasonality in this region with summer and winter monsoons. The high precipitation in the winter along with cold/freezing water and decaying plant material and algae results in deposition of both different organics (eg. pollen in spring vs lack of pollen in winter) in summer vs winter but higher sediments during the winter. The result is alternating bands of material. These layers are very very thin because in the very middle of this lake, were the cores were taken, the total amount of material that settles to the bottom of the lake amounts to less than 1mm per year. I want to stress here that climatologist and biogeochemists has spent considerable time documenting the layers in multiple cores in this lake. They have counted layers by multiple methods including by eye and by computer assisted techniques and more recently by various scans of the cores using other methods of imaging which highlight differences in organic content which can accentuate the winter season layers making the reads more accurate. Careful and independent counts of the annual layers have been performed and more than 800 samples of leaves and other organic content (pollen grains etc..) have been selected from the cores for carbon 14 dating. In addition, 40Argon/39Argon dating has been performed on tephra (ash) layers found in the cores sections (see picture to the right for an example) and two other types of dating methods have been performed on the cores (please see the Science article for details, additional papers about varves and chronology around the world can be found in this issue of Quaternary Science Reviews). The multiple cores from the sediments in this lake have been examined by many scientists overt the past 20 years. Over that time the quality of the data has improved as assumptions about varves have been tested with new techniques and new forms of dating allow further independent dating methods have increased confidence in the varve counts.
Initial studies in the early 1990s found a tight correlation between varve count and C14 dates of organics in the layers going back 40,000 varve years. There is obviously a correlation with age and depth of the column as well (see figure to the right). The most recent analysis reported in Science and detailed further in several other papers published or in press today are now taking the varve counts back to 60,000 years. Several ash layers have been dated with other radiometric dating techniques and they show dates that fall on the line of varve counts. Over 800 samples of organic material have been C14 dated and each of those has been sent to at least two (sometimes 3!) radiocarbon labs for independent verification of the C14 dates. Incredible rigor in selecting samples for C14 dates and blind testing at multiple labs has been done because one of the primary goals of the Suigetsu varve counting group is to test and calibrate the C14 clock.
Consider also that there are more than 30 visible ash layers which form discrete almost pure glass crystal layers that lie between varve layers. These would have formed from airborne ash from volcanoes in the area. That ash would have fallen directly into the lake and settle quickly to the bottom. Had this ash been brought in by the river it would have been mixed with other sediments. These ash layers attest to the fact that this lake had very clear undisturbed waters during the whole period that these varves formed. In addition to the 30 visible layers there are at least 100 additional ash deposits that are so fine that they can only be identified by microscope. These would represent ash from very distant or small volcanic explosions that brought a very small amount of ash fallout to the lake. The advantage of these ash deposits is that some of them can also be radiometrically dated and those dates compared to the varve/layer counts. When this is done an ash layer found at varve count 9000 is found to have a radiometric date of around 9000 years. This represents yet another independent verification that both the varve counts accurately reflect the passage of time in the forms of annual layers.
Over the years there have been multiple cores taken from the lake which have had their varve layers counted multiple independent times by multiple methods. C14 dating has been performed by multiple groups over a period of 20 years and other forms of dating have continued to confirm that the varves in this lake represent individual years. When this data is combined with data from other locations and tree ring data a very compelling picture of a consistent chronology extending back a minimum of 50,000 years appears. Below is a composite figure showing the relationship of tree rings, varves and C14 dates compiled from multiple studies from different locations in the world. What we see is an amazing correlation of these data points.
In response some creationists try to argue that rapid sedimentation can cause the appearance of varve like layers which could be mistaken as annual years when they really represent catastrophic events. They point to examples of lakes and other fossils varve sites (ancient preserved lakes with varved rock) where there is evidence of multiple varves produced in a single year. The strategy is to suggest either implicitly or explicitly that because exceptions can be found to varves representing individual years that all reports of varves should be discredited. The Lake Suigetsu cores were examined because exactly because they are in a location that provides the optimal conditions and the range of material enables multiple lines of independent evidence. For the record the picturesque lakes at Interlaken in Switzerland while not going back quite as far, also challenge Gen 1 readings.
What does this all mean? Simply put both the YEC and OEC view of this creation being 6,000 years old doesn’t match the observable facts of 45-60,000 years of continuous life.
[This article was taken with minor modifications from http://thenaturalhistorian.com/2012/11/12/varves-chronology-suigetsu-c14-radiocarbon-callibration-creationism/%5D
See also the project site http://www.suigetsu.org/index.html