Bottom water characteristics and paleoceanographic evolution of Central Southern Pacific Ocean across the Mid-Brunhes Transition

The varying strength and length of historical and forthcoming interglacial periods hold significant relevance for human society. The interglacials occurring after the Mid-Brunhes Transition (MBT; ∼430 kyr) displayed warmer temperatures and elevated CO₂ in the atmosphere compared to those preceding that period. However, the reason behind this climatic shift remains under debate. Here, we have analysed sediment core samples from International Ocean Discovery Program Site U1540 located in the Central South Pacific to study the assemblages of benthic and planktic foraminifera, as well as Iceberg-rafted debris (IRD), in order to understand the causes of increased atmospheric CO₂ during interglacial periods following the MBT. During the pre-MBT interglacials, CSP bottom water was more oxic, and corrosive marked by a higher abundance of highly oxic and corrosive-resistant Antarctic Bottom Water (AABW) indicator species Nuttallides umbonifera (%), which reduced significantly during and post-MBT interglacials. This study suggests that the influence of AABW decreases during MIS 11 and other interglacials after the MBT, which is marked by ∼10 % reduction in oxic benthic foraminifera species (%) and N. umbonifera (%) as compared to the pre-MBT interglacials. This reduction in AABW volume might have influenced the sequestration of atmospheric CO₂ in the deep ocean, leading to an increase of ∼30 ppm in atmospheric CO₂ during and after the MBT interglacials compared to levels before the MBT. During post-MBT interglacials, a significant reduction in sea-ice and icebergs shoaled the thermocline, which is marked by minimal IRD and abundance of Globoconella inflata. The oxygenated Lower Circumpolar Deep Water follows the Antarctic Circumpolar Current strength and shows 100 kyr periodicity in bottom water current strength.