Glacial dysoxia in the deep subpolar North Atlantic during the Mid-Pleistocene Transition

The transition from 41-kyr to 100-kyr climate cycles during the Mid-Pleistocene Transition (MPT; 1250-700 kyr), occurred in the absence of any significant shift in orbital forcing. The increase of carbon storage in the deep ocean between Marine Isotope Stage (MIS) 24-22 has been suggested as a main internal factor leading to the transition to 100-kyr glacial cycles. We present sedimentary redox proxies and benthic foraminifera assemblages that demonstrate persistent dysoxic conditions during the MPT at IODP Site U1314 (subpolar North Atlantic). During glacials between 940 and 870 kyr, benthic foraminifera species typical of high porewater oxygen concentration disappeared, and concentrations of manganese oxides and reactive phosphorus mineral phases, both influenced by redox state, showed reductions exceeding 50%. Here, we show that higher freshwater supply associated with ice-rafted delivery caused a reduction in deep-water convection, decreasing bottom-water oxygenation and favoring carbon storage in the subpolar North Atlantic during the MPT.