Coccolithophore paleoproductivity variability as a proxy of ocean surface dynamics and climate variability in the Gulf of Cadiz during the Mid-Brunhes Event (MIS 12-11)

This study focuses on high-resolution analyses of coccolithophore assemblages from a sediment core retrieved at IODP Site U1386, located in the Gulf of Cádiz. This area plays a crucial role in studying the Atlantic-Mediterranean water exchange. Our samples span the Termination V period (MIS 12-11, 434-404 kyr) that roughly corresponds with Mid-Brunhes Event, a major global climatic shift in glacial-interglacial cycles during the Quaternary. The main objective is to reconstruct coccolithophore paleoproductivity variations and use it as an indicator of surface ocean dynamics and environmental conditions during this critical interval of global environmental change.

Our results reveal higher paleoproductivity during the interglacial period (MIS 11), with an average of 8.33 × 10⁹ coccoliths/g, compared to lower paleoproductivity during the glacial period (MIS 12), with an average of 4.23 × 10⁹ coccoliths/g. This difference is also reflected in nannoplankton assemblage composition: with cold-water species such as Coccolithus pelagicus subsp. pelagicus dominating during the glacial, and an increase in warm-water species during the interglacial. These patterns are consistent with a cooling in sea surface temperatures (SST) during the glacial period and warming during the interglacial, and with benthic δ¹⁸O values, which were higher in the glacial and lower in the interglacial, reflecting an increase in Northern Hemisphere ice cover during the cold period. Our data, along with previous studies, suggest that MIS 12 in the study region was characterized by severe climatic conditions, with intensified circulation of subpolar surface water masses into the study region and a potential southward migration of the polar front. In contrast, during MIS 11, the climate was warmer, with intensified influence from subtropical surface water masses. Additionally, we observe a significant decrease in paleoproductivity around 430 kyr, coincident with severe SST cooling and peaks in ice-rafted debris (IRD), which could correlate with Heinrich type Event 4 (Ht-4), previously observed in the Iberian margin.