Persistent East Equatorial Pacific Carbon Storage at the Middle Pleistocene Transition

15 pages, 5 figuresThe Middle Pleistocene Transition (MPT, ~641–920 ka) represents a period of the Quaternary climate when, in the absence of substantial changes in orbital forcing, the climate progressively shifted to the 100 ka asymmetrical glacial–interglacial cyclicity characterizing the current climate. The causes of this change remain still uncertain but several lines of evidence suggested the carbon storage of the deep ocean played a relevant role. Here we evaluate the contribution of the eastern deep tropical Pacific to the global ocean carbon sequestration and storage between 760 and 1,040 ka. We present multi‐proxy records for export production and the redox environment at the seabed from Ocean Drilling Program Site 1242 located in the deep East Equatorial Pacific. Our data indicate the development of suboxic bottom waters during early marine isotopic stage (MIS) 23 and glacial MIS 22, suggesting the capture and storage of respired carbon. Redox‐sensitive elements suggest the progressive oxygenation of the deep ocean initiated at the end of the glacial MIS 22, continued across deglaciation and ended with the accomplishment of full interglacial MIS 21. We describe this pattern as a “less complete deglacial ventilation” in that it differs from the mid‐late Pleistocene Pacific deep ocean ventilation pattern which occurs during deglaciations. The ventilation of the deep Pacific Ocean extending beyond deglaciation might have contributed to a persistent deep ocean carbon sequestration, which might have resulted in lowered atmospheric CO2 values that could have influenced the internal response of the climate system contributing to the development of the 100 ka climate variabilityThe laboratory technical assistance of Victor González Guitián to perform elemental analysis was funded by Xunta de Galicia through the program GRC‐ED431C 2017/55. This study was funded by the project CGL2016‐79878‐R (Spanish Ministerio de Economía, Industria y Competividad within the state program Investigación Desarrollo e Innovación Orientada a los Retos de la Sociedad)Peer reviewe