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

[MGI25-04] ENSO events recorded in coral skeletons

★Invited Papers

*Tsuyoshi Watanabe¹, Atsuko Yamazaki² (1.Hokkaido University /KIKAI Institute for coral reefs sciences, 2.Graduate School of Environmental Studies, Nagoya University)

Keywords:Coral skeleton, El Niño, Holocene, Global warming

El Niño-Southern Oscillation (ENSO) is a phenomenon in which sea surface pressure in the atmosphere and water temperature and ocean currents in the oceans change like a seesaw in the east and west Pacific Ocean near the equator. These phenomena are collectively referred to as the El Niño phenomenon. Although El Niño events are currently monitored by buoys and satellites in the equatorial Pacific Ocean, the strength and frequency of El Niño events and their influence on the interaction of atmosphere and oceans in different climatic backgrounds in the past are not well understood. One method for reconstructing past El Niño events is to use the skeletons of reef-building corals that inhabit shallow waters in tropical and subtropical regions. Reef-building corals, which form coral reefs, continue to grow for hundreds of years, forming annual rings on their calcium carbonate (aragonite) skeletons. The oxygen isotope ratios of the calcium carbonate skeletons of these corals record both the sea surface temperature and the oxygen isotope ratio of the seawater during the period of coral growth. For example, in the western Pacific region, the warm water mass moves eastward during El Niño periods, resulting in cooler temperatures and drier conditions due to reduced precipitation brought by the monsoon. La Niña periods are hotter and wetter due to precipitation brought by the monsoon. Each of these modes is recorded in the pattern of coral skeletal variability as lower values of oxygen isotope ratios during El Niño and higher values during La Niña. In the central and eastern Pacific, the corals there may record changes in water temperature and sea level associated with the east-to-west movement of warm water masses, as well as changes in ocean currents and wind direction. Thus, using long-lived living samples and fossil coral skeletons, it is possible to reconstruct El Niño events from the past to the present and their effects on the surrounding environment, and there is potential for predicting the mechanism of El Niño occurrence and its future. In this talk, I will review recent studies using coral skeletons to reconstruct past El Niño events and discuss how they affected the lives of the people who lived in each location.