Western Pacific physical and biological controls on atmospheric CO2 concentration over the last 700 kyr

We present new geochemical evidence of changes in the vertical dissolved inorganic carbon (DIC) distribution in the western tropical Pacific over the last 700 kyr, derived from stable carbon isotope (ä13C) signals recorded in epifaunal benthic (Cibicidoides wuellerstorfi) and thermocline-dwelling planktonic (Pulleniatina obliquiloculata) foraminifera extracted from the Calypso Core MD06-3047. We further analyse the results of a transient numerical experiment of the Last Glacial Maximum (LGM) and the last deglaciation performed with the carbon isotope-enabled earth system model LOVECLIM, to understand the deglacial changes in DIC distribution and verify the proxy-based hypothesis. During glacial periods of the past 700 kyrs, the distinct negative deep water ä13CDIC values obtained from the benthic foraminifera suggest a carbon increase in the deep ocean, which could have been caused by weakening of deep Southern Ocean (SO) ventilation and enhanced marine biological productivity driven by dust-induced iron fertilization. During glacial terminations, a decrease of thermocline ä13CDIC associated with an increase in deep water ä13CDIC indicate a reduced vertical DIC gradient and the net transmission of 12C from the deep waters to the thermocline, caused mainly by the physical process (enhanced SO ventilation). On longer time scales, the largest increase in the Pacific deep carbon reservoir ä13CDIC during the marine isotope stage (MIS) 12/11 transition coincided with the mid-Brunhes climatic shift, which implies that the extent of oceanic carbon release during this interval was much larger than that during other deglaciations since 700 ka B.P. We infer that this could have been caused by reorganization of the oceanic carbon system. These findings provide new insights into the Pleistocene evolution of the carbon-cycle system in the Pacific Ocean