Deciphering local from global signals in Portimão Bank sedimentary dynamics

Paleoenvironmental studies play a pivotal role in addressing contemporary environmental challenges, enhancing our understanding of Earth's history, and informing climate change preparedness strategies. The PC06 sediment core, retrieved at the base of the Portimão Bank (PB) at a depth of 3,520 meters, southwest of the Gulf of Cadiz, specifically provides a valuable contribution spanning 49,000 cal. years BP to the present. This is a multidisciplinary study including sedimentological (grain size, carbonates, organic matter, smear slides and sand fraction composition) and geochemical analyses (based on XRF data) to elucidate the paleoenvironmental changes and related depositional processes over that time. Based on the obtained results four main sedimentary units with distinct lithofacies characterize the stratigraphy of the core; from bottom to top, they are as follows: A- Pyritic mud, B- Pyritic organic-rich mud, C- Clay-rich mud, and D- Pelagic mud. These sedimentary units show a transition from terrigenous mud deposition (A to C) to biogenic sedimentation (unit D) during the Holocene. The units A to C are marked by significant silt peaks and high D50 values, which suggests the influence of bottom currents from the deep waters of the North Atlantic, particularly during the Heinrich events (HE) 5 and 1, while unit D is characterize by a high percentage of planktonic foraminifera and coccolithophorids. Furthermore, units A to C are slightly coarser than unit D. Those observations could be interpreted as variations in the environmental changes at two different temporal scales: i) from the glacial (A to C) to interglacial (D) periods; and ii) a short-scale local variations during the A to C unit sedimentation related to the presence of pyrite. This multidisciplinary analysis yields valuable insights into the interaction of local and global signals, refining our understanding of Portimão Bank sedimentary dynamics throughout the studied period.

 

This work is a contribution of the MONTERA (CTM 2009-14157-C02 CSIC), EDUCOAST (PT-INNOVATION-067) and EMSO-PT (PINFRA/22157/2016) projects.