Helium isotopes near the Indonesian Throughflow
Ma. Teresa Escobar, Atmosphere and Ocean Research Institute University of Tokyo, Tokyo, Japan, Naoto Takahata, Atmosphere and Ocean Research Institute University of Tokyo, Kashiwa, Japan, Hajime Obata, The University of Tokyo, Atmosphere and Ocean Research Institute, Kashiwa, Japan and Yuji Sano, Marie Core Research Institute, Kochi University, Nankoku, Japan
Abstract:
Helium isotopes in the ocean are very useful tracers of hydrothermal input and deep-sea circulation. Unlike other geochemical proxies, noble gases are inert and does not react with other materials in the water column. Previous studies in the Indian Ocean showed that helium isotopes in the region were mainly from the midocean ridge, convergent boundaries in the northwest, and input from the Pacific ocean via currents that go through the Indonesian archipelago. The Indonesian Throughflow (ITF) plays a significant role in global climate because it serves as a branch of the global conveyor belt. However, its deep flow is not well known. We tried to investigate the deep current over the Indonesian sills into the eastern Indian Ocean using helium isotopes. The ITF brings water masses with the helium isotopic signature of the Pacific but it also undergoes changes through mixing and local sources along the way.
We present recent helium isotope data from International Indian Ocean Expedition (IIOE-2) onboard R/V Hakuho Maru at the east Indian Ocean in December 2018. Samples were collected with Niskin bottles attached to a CTD-Carousel Multisampler System. Seawater was introduced into copper tubes then sealed with stainless steel clamps for storage. Dissolved gas from the samples were purified on a purification line equipped with charcoal traps, Ti-getter, cryogenic pump, and QMS. Helium isotopes were measured using a Helix SFT Noble Gas Mass Spectrometer at AORI, UTokyo. To contribute to the efforts of understanding long term changes in the ITF, we compare our data with those from previous expeditions and share our insights on the source and distribution of helium isotopes.
