Bomb-radiocarbon in the Northern Indian Ocean

Abstract

Bomb-radiocarbon is a useful tracer to study ocean circulation and air-sea CO₂ exchange processes. In the present study bomb radiocarbon distribution in dissolved inorganic carbon of the Northern Indian Ocean around late 2010s has been evaluated. In the late 2010s surface waters in the Northern Indian Ocean had ∆¹⁴C values ranging between 9 and 17 ‰ which is comparable or even higher than that of the contemporaneous atmospheric ∆¹⁴C values. Water column measurements showed that the bomb ¹⁴C inventory in the Arabian Sea and the Bay of Bengal has increased between 1990s and 2010s. During the same period, the eastern and western equatorial Indian Ocean showed either no change or a slight decline in the water column bomb ¹⁴C inventory. These bomb ¹⁴C inventory values were also used to estimate the air-sea CO₂ exchange rate and net CO₂ flux over the Northern Indian Ocean region. Bomb ¹⁴C-based estimate of net CO₂ flux from the Arabian Sea is 75 ± 24 Tg C yr⁻¹ and the Bay of Bengal is 1 ± 7 Tg C yr⁻¹, which is comparable to the estimates reported by previous investigations in the region. The present observations show that the bomb ¹⁴C is being transferred to the deeper depths of the ocean, emphasizing the need for continued ¹⁴C measurements to gain further insights into subsurface processes in the region.