[M-GI25] Holocene paleoenvironment, paleoclimate, and paleohazards in the Pacific Islands

[MGI25-06] Holocene development of coral reefs and reef islands in the Pacific

★Invited Papers

*Hiroya Yamano^1,2 (1.The University of Tokyo, 2.National Institute for Environmental Studies)

Keywords:coral reef, reef island, sea-level change

Reef islands on coral reefs are small and low-lying, and they are thus considered to be vulnerable to environmental changes. Though their structure looks simple, recent developments in geomorphological studies of reef islands, as well as those of coral reefs that serves as the foundation, indicate remarkable variations in their constituents and developmental history.

In general, coral reefs reached its present position by ~4000 years ago, in response to stabilization of sea levels after ceasing of ice-sheet melting. As the coral reefs grew laterally to form reef flats under relatively stable sea levels, carbonate sediments derived from reef-building organisms (e.g., corals and foraminifera) distributed on the reef were transported and accumulated to form reef islands.

However, reef-island development and constituents in the Pacific showed that 1) the onset of island evolution ranges from 5500 years ago to 2000 years ago, 2) the sediments are from rubble-dominated to sand dominated, and 3) the dominant constituents are corals or foraminifera. These variations could be due to local sea-level history caused by hydro-isostacy, wave energy, and biogeography. As the case studies are still limited, more studies could help identify the controlling factors and set up conservation and intervention planning to maintain reef islands in an era of environmental change.