is a lake in the Hokuriku region of

Honshu , historically called , is the largest and most populous island of Japan. It is located south of Hokkaidō across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyūshū across the Kanmon Straits. The island se ...

, Japan, which is one of the Mikata Five Lakes located in Mihama and Wakasa,

Fukui Prefecture is a prefecture of Japan located in the Chūbu region of Honshū. Fukui Prefecture has a population of 778,943 (1 June 2017) and has a geographic area of 4,190 km2 (1,617 sq mi). Fukui Prefecture borders Ishikawa Prefecture to the north, G ...

(west-central

), close to the coast of the

Wakasa Bay is a bay located in the Chūbu region of Japan, and spans the coasts of Kyoto Prefecture, and Fukui Prefecture. Geography Wakasa Bay is the area south of the straight line from Cape Kyoga on the west of Tango Peninsula to Cape Echizen on the ...

in the

Sea of Japan The Sea of Japan is the marginal sea between the Japanese archipelago, Sakhalin, the Korean Peninsula, and the mainland of the Russian Far East. The Japanese archipelago separates the sea from the Pacific Ocean. Like the Mediterranean Sea, i ...

. Since 1993, it has been attracting the attention of scientists because of the undisturbed nature of the water for many thousands of years. It is possible to identify the annual deposits of silt in a similar manner that tree rings are identified. The area of the lakes is now part of the Wakasa Bay National Park.

Mikata five lakes

All five lakes have different concentrations of salt. Lake Mikata is a fresh water lake, and Lake Hiruga contains ocean water. Lake Kugushi and Lake Hiruga are connected with Wakasa Bay. The primary inflow of fresh water is from the Hasu River to Lake Mikata. The size and the depth of the lakes are as follows, *Lake Mikata: fresh water lake; area of 3.56 km², 5.8 m deep *Lake Suigetsu: brackish water lake; area of 4.16 km², 34.0 m deep *Lake Suga: brackish water lake; area of 0.91 km², 13.0 m deep *Lake Kugushi: brackish water lake; area of 1.40 km², 2.5 m deep *Lake Hiruga : ocean water lake; area of 0.92 km², 38.5 m deep The lakes are all connected with channels or canals.

"Because Lake Kugushi opens into Wakasa Bay through a narrow and shallow river (Hayase River), seawater enters Lake Suigetsu periodically via Lake Kugushi during high tide."

Lake Suga may be seen as the eastern part of Lake Suigetsu, since the two are joined by a wide channel.

Radiocarbon dating

The

varve A varve is an annual layer of sediment or sedimentary rock. The word 'varve' derives from the Swedish word ''varv'' whose meanings and connotations include 'revolution', 'in layers', and 'circle'. The term first appeared as ''Hvarfig lera'' (va ...

s of Lake Suigetsu allow a chronology to be established, because of the leaf fragments embedded in them, which have been used to

calibrate In measurement technology and metrology, calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Such a standard could be another measurement device of known ...

the Carbon-14 time scale beyond the range of the absolute tree-ring calibration. In late 2009, the journal Radiocarbon announced agreement on the INTCAL09 standard, which extends a more accurate calibration curve to 50,000 years. The results of research on varves in Lake Suigetsu, Japan announced in 2012 realised this aim. "In most cases the radiocarbon levels deduced from marine and other records have not been too far wrong. However, having a truly terrestrial record gives us better resolution and confidence in radiocarbon dating," said

Christopher Bronk Ramsey Christopher Bronk Ramsey is a British physicist, mathematician and specialist in radiocarbon dating. He is a professor at the University of Oxford and is the incumbent Director of the Oxford Radiocarbon Accelerator Unit (ORAU), a post he has held ...

. "It also allows us to look at the differences between the atmosphere and oceans and study the implications for our understanding of the marine environment as part of the global carbon cycle." Results were published in 2012 in the journal

Science Science is a systematic endeavor that Scientific method, builds and organizes knowledge in the form of Testability, testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earli ...

increasing the calibration from 12,593 to 52,800 years. The only inflow to Lake Suigetsu is through a shallow channel from the neighbouring Lake Mikata and there is little outflow. Consequently, only the finest sediment comes into the lake. The water is

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

(deoxygenated) preventing the growth of organisms and due to seasonal variations it is usually but not always possible to distinguish the annual deposits visually. It has taken almost twenty years to overcome the consequent problems, using multiple cores and new detection techniques to complete the sequence.

References

External links

Lake Suigetsu - Location
www.suigetsu.org

- www.suigetsu.org - Main page {{Authority control Suigetsu Radiocarbon dating Landforms of Fukui Prefecture Wakasa, Fukui

Mikata five lakes

Radiocarbon dating

See also

References

External links