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

Abstract

During the last deglaciation the concentration of CO 2 in the atmosphere increased and the radiocarbon activity (Δ 14C) 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 Δ 14C 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 Δ 14C 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 Δ 14C at these two sites. The most parsimonious explanation of the Δ 14C 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.