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

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.