pH variations during the last and current interglacial stages at the western Iberian margin

The intricate interplay among atmospheric CO2 concentrations, surface ocean pH dynamics, and their profound impact on marine ecosystems is of paramount importance in the context of contemporary climate change. Pre-industrial atmospheric CO2 concentrations oscillated in phase with glacial-interglacial cycles, showcasing low levels during glacial periods and elevated concentrations during interglacial periods. Nevertheless, this natural variability has been significantly disrupted due to the surge in anthropogenic CO2 emissions over recent decades. According to the Intergovernmental Panel on Climate Change, if global atmospheric CO2 concentrations persist in rising at the current rate, it is anticipated that the average ocean pH will decrease by 0.3 pH units in surface waters by the conclusion of this century. This scenario could exacerbate the impacts already observed in marine calcifying organisms, including in marine calcifying organisms such as planktonic foraminifera, affecting their diversity, abundance, and calcification. The main objective of this study is to understand the surface ocean pH evolution in a seasonal upwelling region, during two distinct interglacial periods in Earth's history: the Marine Isotopic Stage 5e (MIS 5e), the last interglacial without anthropogenic influence; and the Holocene, the present interglacial but subjected to anthropogenic influence. In upwelling regions, the upwelling of aged and CO2-rich subsurface waters together with high rates of primary production and respiration, is expected to regionally amplify ocean acidification. This study concentrates on the reconstruction of surface ocean pH using boron isotopes in a surface planktonic foraminifera species, Globogerinoides bulloides. This species is typically found in upwelling regions and was preserved in the marine sediment corer MD03-2699 (39°02.20′N, 10°39.63′W). Our preliminary findings indicate a pH difference between MIS 5e and the Holocene, with lower pH values during the Holocene.  It is argued that during the Holocene, a potential increase in wind intensity may have triggered a strong and persistent upwelling increasing productivity and respiration, consequently leading to lower pH. Additionally, the increase of atmospheric CO2, reconstructed from Antarctic ice cores during this period could also contribute to the ocean pH reduction. These variations in upwelling and/or atmospheric CO2 could be a pivotal factor influencing the observed pH differences, contributing to our comprehension of natural pH variations on the western Iberian margin through advanced pH reconstruction techniques and other multi-proxy environmental data integration for both periods in the region.