Land bridges of Japan

Due to changes in sea level, Japan has at various times been connected to the continent by land bridges (陸橋, rikukyō), with continental Russia to the north via the Sōya Strait, Sakhalin, and the Mamiya Strait, and with the Korean Peninsula to the southwest, via the Tsushima Strait and Korea Strait.[1]: 962  Land bridges also connected the Japanese Islands with each other. These land bridges enabled the migration of terrestrial fauna from the continent and their dispersal within Japan.[1]: 961 

Geological background

Around 25 million years ago, the Sea of Japan began to open, separating Japan from the continent and giving rise to the Japanese island arc system of today.[2]: 1  The Sea of Japan as a back-arc basin was open both to the northeast and to the southwest by 14 Ma,[2]: 14  while marine transgression further contributed to the isolation and insulation of Japan.[1]: 961  Due to the level of tectonic activity in the area and significant subsidence of the Japanese Islands since the Miocene, exact quantification of historic sea level changes is problematic.[1]: 962 

Northern land bridge

Based on current depths, a 55 m (180 ft) reduction in sea level would be sufficient to connect Hokkaidō with the mainland.[3]: 1135  The Sōya land bridge (宗谷陸橋) and Mamiya land bridge (間宮陸橋) — sometimes referred to jointly as the Saghalien land bridge (樺太陸橋)[4] or Sakhalin land bridge — are thus thought to have been in place during most glacial periods.[1]: 962 [3]: 1135 

Western land bridge

With a minimum depth of 130 m (430 ft) and based in part on the appearance in Japan of Proboscidea, the Tsushima land bridge (津軽陸橋) and Korean land bridge (朝鮮陸橋) — sometimes referred to jointly as the Korean land bridge[4] — are understood to have been in place at 1.2 Ma, 0.63 Ma, and 0.43 Ma.[1]: 962 [5]: 314 

Kuril land bridge

A Kuril land bridge (千島陸橋) has been insufficient to connect Hokkaidō with Kamchatka during the Quaternary.[4] The southern Kuril land bridge that connected Kunashiri and the Lesser Kurils to Hokkaidō during the Early Holocene was insufficient with the rising sea level at around 6,000 BP.[6]: 133 

Seto land bridges

Honshū, Shikoku, and Kyūshū are separated by shallow straits that rarely exceed 50 m (160 ft) in depth.[3]: 1135  Consequently, they were frequently connected together as a single land mass.[1]: 962 [3]: 1135 

Tsugaru land bridge

The Tsugaru Strait, with a depth in excess of 130 metres (430 ft), represents a more significant faunal boundary, known as Blakiston's Line.[3]: 1135  The most recent age of the Tsugaru land bridge (津軽陸橋) is uncertain.[7]

Ryūkyū land bridge

The Ryūkyū Islands, separated by deeper straits still (the Tokara Gap), have been isolated from the main islands throughout the Quaternary.[1]: 962  The Ryūkyū land bridge (琉球陸橋) was sufficient temporarily to connect Miyako-jima with Taiwan during the late Middle Pleistocene, allowing for the migration of the Steppe mammoth (Mammuthus trogontherii).[4][8] During this period, the Miyako Strait was sufficient to prevent the land bridge reaching Okinawa Island.[8]

See also

References
  1. Millien-Parra, Virginie; Jaeger, Jean-Jacques (1999). "Island Biogeography of the Japanese Terrestrial Mammal Assemblages: An Example of a Relict Fauna". Journal of Biogeography. 26 (5): 959–972. doi:10.1046/j.1365-2699.1999.00346.x. JSTOR 2656237. S2CID 85597772.
  2. Taira, A.; Ohara, Y.; Wallis, S.R.; Ishiwatari, A.; Iryu, Y. (2016). "Geological evolution of Japan: an overview". In Moreno, T.; Wallis, S.; Kojima, T.; Gibbons, W. (eds.). The Geology of Japan. London: The Geological Society. p. 1. ISBN 978-1-86239-743-9.
  3. McKay, Bailey D.; Ebach, Malte (2012). "A new timeframe for the diversification of Japan's mammals". Journal of Biogeography. 39 (6): 1134–1143. doi:10.1111/j.1365-2699.2011.02666.x. JSTOR 23258800. S2CID 86359818.
  4. Shikama Tokio (1962). "Quaternary Land Connections of Japanese Islands with Continent from the Viewpoints of Palaeomammalogy" 化石哺乳類等よりみた日本列島と大陸との陸地接続 [Quaternary Land Connections of Japanese Islands with Continent from the Viewpoints of Palaeomammalogy]. The Quaternary Research (Daiyonki Kenkyū) (in Japanese and English). 2 (4–5): 146–153. doi:10.4116/jaqua.2.146.
  5. Taruno Hiroyuki 樽野博幸 (2010). "The stages of land bridge formation between the Japanese Islands and the continent on the basis of faunal succession" 哺乳類化石の変遷から見た日本列島と大陸間の陸橋の形成時期 [The stages of land bridge formation between the Japanese Islands and the continent on the basis of faunal succession]. The Quaternary Research (Daiyonki Kenkyū) (in Japanese and English). 49 (5): 309–314. doi:10.4116/jaqua.49.309. ISSN 0418-2642.
  6. Razjigaeva, Nadezhda G.; et al. (2013). "Holocene climatic changes and vegetation development in the Kuril Islands". Quaternary International. 290–291: 126–138. Bibcode:2013QuInt.290..126R. doi:10.1016/j.quaint.2012.06.034.
  7. Yashima Kunio; Miyauchi Takahiro (1990). "The Tsugaru Land Bridge problem related to Quaternary coastal tectonics, Northeast Japan" 津軽陸橋問題と第四紀地殻変動 [The Tsugaru Land Bridge Problem Related to Quaternary Coastal Tectonics, Northeast Japan]. The Quaternary Research (Daiyonki Kenkyū) (in Japanese and English). 29 (3): 267–275. doi:10.4116/jaqua.29.267.
  8. Kawamura Ai; Chang, Chun-Hsiang; Kawamura Yoshinari (2016). "Middle Pleistocene to Holocene mammal faunas of the Ryukyu Islands and Taiwan: An updated review incorporating results of recent research". Quaternary International. 397: 117–135. Bibcode:2016QuInt.397..117K. doi:10.1016/j.quaint.2015.06.044.
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