Inter-annual variation in atmospheric Δ¹⁴C over the Northern Indian Ocean

Abstract

Radiocarbon (¹⁴C) in atmospheric CO₂ over the Northern Indian Ocean was measured between 1993 and 2001, by collecting remote maritime air from ship cruises. The Δ¹⁴C of atmospheric CO₂ over this region decreased from 120±3‰ in 1993 to 85±2‰ in 2001, consistent with the global exponential decreasing trend. The Δ¹⁴C values measured in spring of 2001 over the Bay of Bengal and the Arabian Sea were 86±2‰ and 85±3‰, respectively, thus indistinguishable within error limits. Significant inter-annual variations in Δ¹⁴C were observed over this region. Input of ¹⁴C-free fossil fuel CO₂ from the South Asian continent significantly influence springtime Δ¹⁴C values over the Northern Indian Ocean, through transport by meridional atmospheric circulation. Additional variations are possibly caused by enhanced inputs of ¹⁴C-rich biogenic CO₂, during El Niño/Southern Oscillation events.