What are those stripes?

The Miracle Lake

Lake Suigetsu Varves

Lake Suigetsu is the largest lake of the Five Lakes of Mikata (area: 4.15 km , depth: 34 m).
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Striped patterns called “varves” have formed at the bottom of this lake through the accumulationof sediment over 70,000 years. Sediment core research was carried out in 1993, 2006 and 2012,
in order to research and study the varves. The 70,000 consecutive years’ worth of varves and theresults from research of them are attracting attention from both Japan and around the world.

The Sea of Japan
Lake Hiruga
Lake Kugushi
Lake Suigetsu
Lake Suga
Lake Mikata
The Five Lakes of Mikata (Fukui Prefecture)

The Five Lakes of Mikata, designated as one of
the country’s places of scenic beauty, refers collectively
to Lakes Kugushi, Hiruga, Suigetsu, Mikata and Suga
located within the Wakasa Bay Quasi-National Park.
Remains from the Jomon period have been
discovered in the area around the lakes. They wereregistered as a Ramsar Site in 2005, being consideredinternationally important wetlands.

(Photo provided by Wakasa Mikata Jomon Museum)2

The key to unlocking mysteries of the past was
hidden in striped patterns beneath the lakebed!

Varves(shown in the photo on the right) are formed by deposits ofdifferent types of materials depending on the season. A varve is a pair oflight and dark colored stripes that corresponds to one year, and important
clues to understanding the history of climate change and natural disasters
are recorded in these stripes.
Through analysis of the varves, highly accurate data on the naturalenvironment (air temperature, water temperature, vegetation, etc.) andnatural disasters (earthquakes, tsunami, floods, volcanic activities, etc.)that occurred in the past can be obtained and research is advancing
worldwide.
Furthermore, the varves are used to calibrate radiocarbon dating that
identifies the chronology of fossils and relics, and the IntCal13 calibration
curve, utilizing data obtained from the Lake Suigetsu varves, was publishedin September 2013. This has led to the Lake Suigetsu varves being
regarded in archaeology and geology as a global standard measure,
dramatically improving the accuracy of dating more than ever before.
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Varves of
Lake Suigetsu

The favorable conditions that allowed
the world’s best varves to form

The process of varve formation
Why do the striped patterns form in the varves?
At the bottom of Lake Suigetsu, deposits of soil and organic matter such as the remains ofplankton occur from spring to autumn, and those of mineral matter such as iron that has precipitatedin the lake water and yellow sand from the continent occur from late autumn to winter. The striped
pattern is formed by pairs of light and dark colored layers which correspond to a year’s time, with thedark layers containing more organic matter, and the light layers containing more mineral matter.
The varved sediment of Lake Suigetsu, averaging to a 0.7 mm thickness per year, has been
deposited over 70,000 years.

The topography and surrounding environmentof Lake Suigetsu
Topography and surrounding environment have a strong influence on varve formation. Lake
Suigetsu has several conditions that have allowed the pairs of stripes to accumulate without disturbanceand form each year. The four main conditions are listed below. As lakes with such favorable conditions
for varve formation are a rarity around the globe, it is fittingly known as the miracle lake.

1 A topography with nolarge feeding rivers

The lakebed is left undisturbed by the
inflow of soil and stones, and large
amounts of water such as from heavy rain,
due to the lake’s depth and the absence ofany large rivers directly feeding it.

2 A topography

When did the striped patterns form?
Varves allow the year a stripe formed to be identified, by being able to count the pairs that form
each year, as with tree rings, in the striped pattern. For example, the 1,000th pair of stripes from thesurface can be identified as that which formed 1,000 years ago, or the 10,000th pair of stripes as thatwhich formed 10,000 years ago.

surrounded by mountains

The lake water is kept from being stirred up
as the surrounding mountains block winds
and prevent waves from building up.

3 An absence of life at thelake bottom

An aerial photograph after heavy rain. The brown-looking Lake
Mikata has had sand and mud washed into it, but the muddy
water has not flowed into Lake Suigetsu pictured above it.
A photographic record showing the favorable conditions forvarve formation. (Photo provided by Fukui Shimbun)

As the lake water is not stirred up, a layer that lacks oxygen forms in the deep parts. In otherwords, living things are unable to exist at the bottom of Lake Suigetsu, meaning that the varves
are not disturbed by them.

The 1,000th pair = 1,000 years ago

By counting the numberof varves (1 pair of stripes
equivalent to 1 year) from thesurface, we can find out
how many years ago they
were formed.

4 The lake is not filled up

Lakes in general become filled up with sediment over time, such as with soil and sand fromupstream. Lake Suigetsu, however, has continued to subside due to the influence fromsurrounding faults for a long time. This has resulted in the lake not filling up with sediment,
instead allowing a steady accumulation of sediment on the lakebed.

The 10,000th pair = 10,000 years ago■ Lake Suigetsu Varves
A sediment core approximately 73 meters in length was obtainedin the 2006 research, the first 45 meters of which contained welldefined varves. Around 70,000 years’ worth of stripes were counted with
uninterrupted varves, being the first of this type ever seen around the world.
The section between 45 and 64 meters consisted of mud
sediment. It is speculated that this was due to the shallowness of
Lake Suigetsu during this period.
Varves appear again from the 64-meter mark, with sedimentfrom the deepest section being believed to be that from about
150,000 years ago.

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A diagram of Lake Suigetsu varves5

What we can learn from the varves
Varves, which allow chronology to be identified by year, contain substances such as leaves,pollen, volcanic ash and yellow sand. By analyzing them, it is possible to reconstruct past events year
by year, including changes in air temperature, water temperature and climate.
The varves of Lake Suigetsu, having accumulated over 70,000 years, are a source tounderstanding valuable information about the natural environment in the past.

What we can learn about past climate change from the varves
From leaves and pollen containedin varves
Fossil leaves and pollen contained in the varves
enable us to identify the species of plants that grewaround the lake, andlearn about the climate
and environment at
the time. Studying thechanges of such species
leads to an understandingof variations in the climate
and environment, with
A fossil leaf contained in
the varves giving us athe varves of Lake Suigetsu
detailed understanding of(Photo provided by the Lakethe conditions at the time
Suigetsu Project)
year by year.

Fallen leaves
and pollen

From changes in the appearanceof sedimentation
Upon close inspection of the very thinly depositedvarves, areas of thick accumulations and differencesin color are noticeable. These are indications ofearthquakes and floods. When an earthquake occurs,
it causes a large amount of soil and sand from aroundthe lake to flow in, forming a thick layer of sediment. A
difference in the way sediment forms is also apparent
after a flood has occurred.
By studying the varves of Lake Suigetsu,
12 examples were found of thick layers caused
by earthquake over the last 30,000 years. This
record of earthquakes and floods is expected to
be used in the future for disaster prediction.
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30,000 years ago, the area around

30,000 years ago

the lakes was grassland with sparse coniferous
trees such as spruces under a cold and dry
climate. Thereafter, following the glacial period,
the vegetation around the lakes graduallyturned into a temperate forest with deciduous
broad-leaved trees such as beeches.

12,000 years ago, after a period of

instability during which the temperature would
fluctuate quite considerably, it gradually changed
into a warm climate. As for the vegetation, there
was a stretch of forest containing trees such as
beeches, oaks, and walnuts. It is believed to bearound this period that the Jomon people began
to live around the lakes.

Yellow sand fromthe continent

Volcanic
ashes

From volcanic ash and yellow
sand contained in varves
Varves also contain yellow sand, which werecarried on the prevailing westerlies from the Asian
continent, and volcanic ashes. Other things that canbe identified include the date of a volcanic eruption(using the volcanic ashes), and changes in the
direction of the westerlies (using the yellow sand).

People’s lifestyles and changes in theenvironment around the Five Lakes of Mikata

Volcanic
eruption

Flood

The lakeside with sparse coniferous trees

12,000 years ago

5,700 years ago

Around, forestsof evergreen broad-leaved trees, such as
camellias, and those of cedars stretchedout. Many relics have been excavated fromareas around the lakes, where those relics,
including the Torihama Shell Midden, tell how
the people of the Incipient-to-Early Jomon
period (between 12,000 years ago and 5,500
years ago) lived. Owing to the woodlands
abundant with nuts, etc., and lakes thatprovided many fish, it was most likely a very
inhabitable place abundant with food.

The lakeside transition from coniferous
trees to deciduous broad-leaved trees

5,700 years ago

Flood
Flood
Earthquake
Flood

Sections of Lake Suigetsu varves

Flood

Dugout canoes made of cedar displayed at the
Wakasa Mikata Jomon Museum. They wereexcavated from ruins around Lake Mikata locatedto the south of Lake Suigetsu.

The lakeside in the Jomon period
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The Varves of Lake Suigetsu —A Global Standard Scale for Dating
Radiocarbon Dating and the
Global Standard
The radiocarbon dating to identify the ages offossils and relics is an age determination method,which uses a substance called radiocarbon (carbon 14)
contained in animals, plants, and other things.
The amount of carbon 14 halves every 5,730
years after the death of the animal or plant. Therefore,
examining the amount of residual carbon 14 in theobject, such as the remains of a living thing, allows us toestimate the number of years that have passed since thedeath of the organism.
However, the amount of carbon 14 contained in
an animal or plant varies depending on the date, andis not uniform. This leads to an inaccuracy of the dateestimated from the carbon-14 content alone, and theerror needs to be compensated. It is necessary toaccurately determine the amount of carbon 14 for thatdate in order to calibrate the error.
Tree rings give the most effective samples forevaluating the amount of carbon 14 contained in remains
up to about 13,000 years from present. Counting thenumber of tree rings and measuring the carbon-14
content of each ring enable us to determine an accurate
date in relation to the carbon-14 content, which can beapplied to other objects. For dates older than 13,000
years ago, as it is difficult to acquire such old tree
samples, ocean basin varves and shallow-water coral
were conventionally used. Unfortunately, the use of
these aquatic materials entailed uncertainty due to suchfactors as the carbon dioxide contained in the seawater.
Since the varves of Lake Suigetsu have been
continuously deposited without a break for 70,000 years,
it is possible to identify the date by counting the numberof stripes, as with tree rings. Furthermore, measuring
the amount of carbon 14 contained in the fossil leaves inthe varves enabled us to accurately identify the amountof carbon 14 for the date when the same leaves had
fallen. This made it possible to identify radiocarbon dates
anywhere in the world, by comparing the measured
radiocarbon level with the data from Lake Suigetsu,
and finding the stripe that contains a fossil leaf withthe equivalent radiocarbon level. The varves of Lake
Suigetsu are used as the most accurate “global standard
timescale” for determining age.
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Carbon 14
Carbon 14 contained in leaves
and other organic materials

The half-life ofCarbon 14

5,730 years

Carbon 14 produced in theatmosphere is absorbed by plants throughphotosynthesis, and into animals via thefood chain. The amount of carbon 14 inanimals and plants continuously decreases
after their death as it ceases to be taken
in anymore. This nature, as well as the
5,730-year half-life of carbon 14, allows thedating. The concentration of carbon 14 in
the atmosphere varies from year to year
because this element is sensitive to changes
in the geomagnetic field and solar activity.
Currently, the limit of measurement
using the amount of carbon 14 is that up to
approximately 50,000 years ago.

Overview of the Calibration Curve (IntCal13)
and the Roles and Meaning of Lake Suigetsu
Professor Takeshi Nakagawa, Ritsumeikan University
We humans are instinctively
interested in our own origin— who we are, and where weare from. When and why did
our ancestors leave Africa,
what dangers have we faced,and how have we been able tosurvive up to the present time?
This is not only a question ofanthropology and archaeology,
but also an important issue
about philosophy and values.
In connection, a timescale thatcan measure a long period oftime in the order of thousandsor tens of thousands of years isnecessary to answer questions
such as, “When exactly did the
Neanderthal die out and why
did they make way for Homosapiens?” and “When did theJomon people produce theirearthenware for the first time?”
Needless to say, there were nosuch devices as mechanicalclocks or atomic watches in thosedays. A specific timescale has
been used in the field of geology,
and continued efforts have been
dedicated to improve its accuracy.
Lake Suigetsu in Fukui Prefecture
has played an important role inbringing about a tremendous leapin the quality of the timescale,almost to the point of perfection.
The most common method
used around the world tomeasure time within the periodranging up to 50,000 years
ago is radiocarbon (14C)
dating. However, the dateobtained from the amount ofresidual carbon 14 alone is notnecessarily accurate, and aconversion table, or a calibration
model, to convert the measured
value to a true value is required
for accurate dating.
The conversion table must
not differ depending on the
researcher, and must be unified
based on an international
agreement. At present, the mostwidely used calibration modelin the world is known as IntCal,
which was first proposed in 1998
and updated in 2004 and 2009.
IntCal is, so to speak, a global
standard timescale to define
geological points in time, justlike the meter standard and theRoyal Greenwich Observatory.
The IntCal was updated again,
and announced as IntCal13
in September 2013. The datafrom Lake Suigetsu, which was
not adopted in the previous
version IntCal03, was fully
incorporated in IntCal13 as its
outstanding quality was highly
appreciated.
As there is a rule with IntCal to
avoid excessive dependence
on data from only one location,

Fossil leaves from Lake Suigetsu(Photo provided by the Lake Suigetsu Project)
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data fromplacesother thanLake Suigetsu was also
incorporated in IntCal13.
Nevertheless, it is obvious thatthe presence of Lake Suigetsu
is overwhelming among theelements constituting IntCal13.
This refers to the aspects of theamount of data used, the abilityof dating through calibration,and the “purity” of the datawith which it is not necessary
to take into account the oldcarbon coming from deep-sea
water, limestone, etc.
IntCal13 is a standard scaleof history created with thetremendous efforts of many
researchers, the foundationsof which are supported by
Lake Suigetsu. In relation
to the study of history andarchaeology, Lake Suigetsu
is the equivalent of the Royal
Greenwich Observatory
for people in contemporarysociety. It is expected thatthe use of IntCal13 will shedlight on past events in detailand greatly facilitate progressin the understanding of ourroots, enhancing our insight
into the future based on thisunderstanding.

Progress of the Research into
the Varves of Lake Suigetsu
Future Prospects of Applied Development

The First Research in 1993

Associate Professor Hitoshi Yonenobu,

Lakebed sediment was first collectedfrom Lake Suigetsu in 1991. The researchteam lead by Emeritus Professor Yoshinori
Yasuda (International Research Center forJapanese Studies) conducted exploratory
boring and discovered the existence ofvarved sediment for the first time in Asia.
In 1993, the team extracted approximately
75 meters of sediment. Based on theanalysis of fossil pollen taken from thevarves, research findings on paleoclimaticchanges before and after the beginning of
the Jomon period were published.

School of Natural and Living Sciences Education, Naruto University of Education

What does “knowing the past” exactly mean?
James Hutton, a Scottish geologist in the 18th century,
said, “The present is the key to the past,” and laid afoundation for modern geology. At present, under theconcept that the past is the key to understanding thefuture, the history of climatic changes is being actively
researched in detail throughout the world. The sixth
Assessment Report of the Intergovernmental Panelon Climate Change, which was reported in the media
on September 27, 2013, was a result of examining
and compiling the content of such research. Providing
solutions for such urgent issues that should be solved
through international cooperation is, of course, an
important role for the science that looks into the past.

Boring site on the lake
Sediment core tube
leading to the bottom of
the lake. The entrance
to the 70-thousand-yeartime tunnel.

The Second Research in 2006
In 2006, the research team lead byProfessor Takeshi Nakagawa (Newcastle
University, UK) conducted four boringsand successfully formed a perfectsediment core of approximately 73 meters
long. The team spent a number of years
counting the stripes of the extracted
sediment core (designated as SG06), as
well as applying radiocarbon dating tofossil leaves contained in the core sample.
The research results were published in theAmerican academic journal “Science” in
2012, and in the following year, the varvesof Lake Suigetsu became the global
standard timescale for dating within aperiod of up to 50,000 years ago.

This cottage,
nicknamed“Suigetsu Hilton,”accommodated
the researchers
during the 2006
research.

Four sedimentcore samples werecombined to form
continuous varves
extending to approx.
73 meters with no
missing parts.

The Third Research in 2012
The 2012 research was conductedby a team lead by Professor Ryuji Tada
(Graduate School of Science, Universityof Tokyo). Their research included study
on changes in the westerlies over theyears using the yellow sand and othersubstances contained in the varves, andthe estimation of precipitation based on
the rate of sedimentation of clay flowing
in from rivers.

Research dealing with phenomena that changewith the passage of time (historical science) requires
an accurate perception of the order of occurrenceof events, as well as of the timing and time lags at
different places, in order to correctly think about thecausal relationships between matters. In this respect,a high-precision chronological scale is necessary.
Recently, archaeologists from our research group(the “Pan Pacific Environmental Changes andCivilizations” Project for the Grant-in-Aid for Scientific
Research on Innovative Areas by the Ministry of
Education, Culture, Sports, Science and Technology;
lead by Kazuo Aoyama, professor, Ibaraki University)
conducted thoroughgoing excavation of remnants

for the initial to terminal phases
at Seibal, a representativearchaeological site of the Maya
civilization in Guatemala, andcollaborating natural scientists carried out carbon-14
dating of many samples.
The results of dating were applied to IntCal curves,which are often referred to as wiggles, using a Bayesianstatistics method, and greatly accurate estimation of theduration of the civilization was obtained. The outcome
produced evidence against the traditionally prevailinghypothesis that this ancient city is the oldest public ritual
construction of the Maya civilization and that the Maya
civilization arose due to the unidirectional influence of
the adjacent Olmeca civilization.
The application of IntCal13 to a large number ofcarbon-14 dates will also lead to the progress ofarchaeological research in Japan based on accurate
chronological axes.
Efforts toward this areready to start, andenhanced accuracyof chronologicalframeworks from thelate Paleolithic period
and the Jomon period
across historicaltimes is expected.
Ruins of Seibal(Photo provided by Professor Kazuo
Aoyama, Ibaraki University)

Varves Around the World
Varves have been discovered in several placesin the world including the Eifel district in Germany,
the Cariaco Basin in Venezuela, Monticchio in Italy,
and Lake Sihailongwan in China. Varves have also
been found in other places in Japan, apart from
Lake Suigetsu; namely, Lake Ichinomegata (Akita
Prefecture), Lake Togo (Tottori Prefecture), and Lake
Fukami (Nagano Prefecture).

As with the varves of Lake Suigetsu, research is
conducted on various subjects including the naturalenvironment in the past, natural disasters such as
earthquakes and floods, and the relationship between thelifestyle of people and history. It is expected that researchoutcomes in the future will contribute to the elucidation ofvarious things such as global warming, the mechanism ofnatural disasters, and the history of humankind.

Prof. Takeshi Nakagawa working on
the preservation of collected varves

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Printed in June 2014