[A-CG30] Multi-scale ocean-atmosphere interaction in the tropics

[ACG30-P04] Variations of sea surface temperature and salinity using coral Sr/Ca and δ¹⁸O in the Java Sea and the Lombok Strait.

*Ai Genda¹, Ali Arman², Minoru Ikehara³, Atsushi Suzuki⁴, Mayuri Inoue¹ (1.Graduate School of National Science and Technology, Okayama University, 2.National Nuclear Energy Agency of Indonesia (BATAN), 3.Center of Advanced Marine Core Research, Kochi University, 4.Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology)

The Indonesian Throughflow (ITF) runs from the Pacific into the Indian Ocean through the Indonesian archipelago. The ITF modulate heats and water budget between the Pacific and the Indian Ocean, and therefore the ITF plays an important role in climate change. In addition, during northwest monsoon, sea surface currents drive low salinity and buoyant water from the Java Sea to the southern Makassar Strait. This water caps surface flow through the Makassar Strait and called "freshwater plug". In contrast, during southeast monsoon, sea surface currents remove freshwater plug from the southern Makassar Strait. Thus, it is suggested that behavior of freshwater plug would affect variation of Asia monsoon and climate change. However, instrumental records have accumulated only for decades in the Indonesian Seas partially due to the complex topography. In this study, we reconstructed sea surface environments using Sr/Ca and oxygen isotopic ratios (δ¹⁸O) in coral skeleton collected from Seribu Islands and Bali Island. While both coral Sr/Ca and δ¹⁸O depend on sea surface temperature (SST), coral δ¹⁸O also depend on seawater δ¹⁸O which mostly correspond to salinity. Therefore, both SST and salinity can be reconstructed from based on coral Sr/Ca and δ¹⁸O.
Coral samples used in this study were collected from two sites: one is the Seribu Islands located in the Java Sea where freshwater plug appears and the other is the southeast of Bali Island in the Lombok Strait, which is one of outlet of ITF connecting to the Indian Ocean. Seribu's and Bali's records covered about 70-year from 1931-2002 and 50-year from 1962-2012, respectively. In 1997 when positive Indian Ocean Dipole mode and El Niño occurred, Bali's record show large anomaly (cool SST and drought), whereas Seribu's record shows only a slightly change. Furthermore, it seems that a relatively big change of marine environments like a regime shift has occurred in the Lombok Strait around late 1990s with no clear change in the Java Sea. We will show and discuss the temporal and spatial change of the variation of SST and salinity based on coral Sr/Ca and δ¹⁸O in both sites over the past decades.