The release of 14C-depleted carbon from the deep ocean during the last deglaciation: Evidence from the Arabian Sea

During the last deglaciation the concentration of CO2 in the atmosphere increased and the radiocarbon activity (Δ14C) of the atmosphere declined in two steps corresponding in timing to Heinrich Stadial 1 and the Younger Dryas. These changes have been attributed to the redistribution of 14C-depleted carbon from the deep ocean into the upper ocean and atmosphere. Recently, reconstructions of Δ14C in intermediate waters of the eastern tropical Pacific have revealed pulses of very old water during the deglaciation, consistent with the release of 14C-depleted carbon from the deep ocean at this time. Here, we present reconstructions of intermediate water Δ14C from the northern Arabian Sea near the coast of Oman. These reconstructions record significant aging of intermediate waters in the Arabian Sea during Heinrich Stadial 1 and, to a lesser extent, during the Younger Dryas. The timing and magnitude of 14C depletion in the Arabian Sea during Heinrich Stadial 1 is very similar to that previously observed in the eastern North Pacific near Baja California, indicating that similar mechanisms were involved in controlling Δ14C at these two sites. The most parsimonious explanation of the Δ14C records from the Arabian Sea and Baja California remains the release of 14C-depleted carbon from the deep ocean by renewal of upwelling and mixing in the Southern Ocean. These 14C-depleted waters would have been incorporated into thermocline and intermediate water masses formed in the Southern Ocean and spread northward into the Pacific, Indian and Atlantic Ocean basins.