A study of geomorphological formation in coastal region for the northern migration of coral reef development with global warming

在全球变暖的时代，珊瑚礁的形成预计会向北迁移。西北太平洋是珊瑚礁大小和分布逐渐缩小到纬度极限的罕见之地。通过钻探研究了4个不同纬度地区(谷儿岛-马格吉岛地区、托卡拉群岛、冲绳岛、小川群岛)的生物礁发育情况。琉球北部北纬30度附近(谷桥岛-马格吉岛地区)的生物礁发育具有以下特征：1)启动生长滞后于海平面上升；2)由于主要生物礁发育停止不到2000年，生物礁发育持续时间短；3)在1~2m/ka之间上升速度缓慢。特定地点的生物礁形成和狭小的生物礁发育时间范围可能是高纬度生物礁生长的特征。小的高纬度生物礁可以在短地质时期内形成。然而，礁石发育的时间和地点很难预料。与琉球北部相比，小川群岛的礁石地形、内部结构和发育都是独一无二的。有必要对小川群岛的珊瑚礁进行进一步调查。

The northern migration of the coral reef formation is expected in the era of global warming. The northwestern Pacific is rare place where the reef-size and reef-distribution decrease gradually to the latitudinal limit. This study discusses the reef development in four reef area of different latitudes (Tanegashima-Magejima area, Tokara Islands, Okinawa Island, Ogasawara Islands) by drillings.The reef development in the northern Ryukyus around the latitude of 30 degree N (Tanegashima-Magejima area) characterized by follows: 1) lagged start-up growth behind the sea level rise, 2) short duration of reef development as the major reef development ceases less than 2,000 years, 3) slow upward growth rate between 1 to 2 m/ka. The site-specific reef formation and the narrow time range of reef development may characterize the high-latitude reef growth. The small high-latitude reef may build in the short geological time period. However, the timing and locality of reef development is hard to expect.In Ogasawara Islands, reef topography, internal structure and development are unique comparing with the northern Ryukyus. The further investigation is necessary for coral reefs in Ogasawara Islands.