Mantle ³He distribution and deep circulation in the Indian Ocean

Abstract

The World Ocean Circulation Experiment Indian Ocean helium isotope data are mapped and features of intermediate and deep circulation are inferred and discussed. The 3He added to the deep Indian Ocean originates from (1) a strong source on the mid‐ocean ridge at about 19°S/65°E, (2) a source located in the Gulf of Aden in the northwestern Indian Ocean, (3) sources located in the convergent margins in the northeastern Indian Ocean, and (4) water imported from the Indonesian Seas. The main circulation features inferred from the 3He distribution include (1) deep (2000–3000 m) eastward flow in the central Indian Ocean, which overflows into the West Australian Basin through saddles in the Ninetyeast Ridge, (2) a deep (2000–3000 m) southwestward flow in the western Indian Ocean, and (3) influx of Banda Sea Intermediate Waters associated with the deep core (1000–1500 m) of the through flow from the Pacific Ocean. The large‐scale 3He distribution is consonant with the known pathways of deep and bottom water circulation in the Indian Ocean.

Distribution of helium-3 plumes and deep-sea circulation in the central Indian Ocean

“…The δ 3 He values increased downward, and maxima of about 15% were observed at mid-depth (2000 -3000 m); they then decreased to about 10% in the bottom water. It is well known that at mid-depth, Indian Ocean waters are affected by mantle helium with a high δ 3 He value, possibly derived from the Central Indian Ridge (Östlund et al 1987;Jamous et al 1992;Jean-Baptiste et al 1992;Srinivasan et al 2004). Figure 2 shows a vertical cross section of δ 3 He in the central Indian Ocean along our sampling stations.…”

“…To investigate the source of the helium-3 plume found in the Arabian Sea (ER5 to 7), we inferred deep currents from the lateral δ 3 He distribution. Srinivasan et al (2004) reported that the helium-3 plume around 20°S seemed to flow eastward at 2000-3000 m depth, based on the δ 3 He distribution. In order to check whether the helium-3 plume apparently flows northward from the Central Indian Ridge around 20°S to the region adjacent to the Indian subcontinent, we investigated the relationship between temperature and salinity in deep seawater.…”

“…4; one is located around 20°S on the Central Indian Ridge; the other is located in the Gulf of Aden (Srinivasan et al 2004). Helium-3 plumes were also found around 5°N over the Carlsberg Ridge (Ray et al 2008(Ray et al , 2012 but the plume depth was deeper (> 3000 m depth) than for the other hydrothermal sites (the Central Indian Ridge and the Gulf of Aden).…”

“…The hydrothermal plume found at 20°S in our cruise may be originated from the Central Indian Ridge near the Rodriguez Triple Junction. This area is one of the most active sources of hydrothermal helium-3 in the Indian Ocean (Srinivasan et al 2004). …”

“…This plume-shaped 3 He anomaly, which was originated from volcanic activity on the ridge, spread eastward by abyssal currents at the depth of the crest. After the GEO-SECS survey, the Indigo Cruises (Jamous et al 1992) and the WOCE (World Ocean Circulation Experiment) cruises (Srinivasan et al 2004) obtained helium isotope data in a large area of the Indian Ocean. The WOCE was the largest internationally coordinated oceanographic program and a comprehensive global hydrographic survey of physical and chemical properties during the 1990s.…”