Climatic instabilities of the last 70,000 years in the subtropical eastern North Atlantic: exploring vegetation and hydrological responses on the SW Iberian Margin using a land-sea direct comparison

Abstract

This PhD addresses the long-term and rapid vegetation and climate changes in SW Iberia during the Last Glacial and Holocene, covering the last ~70 ka. The Last Glacial and deglaciation, are among the main targets of the palaeoclimate community for understanding dynamic changes in the Earth System. To date, several studies have revealed the sensitive record of vegetation response to climate changes preserved in marine cores of the Iberian margin. So far, a detailed analysis of the Last Glacial is therefore not completed; MIS3 has been heavily targeted, but MIS2 has been less studied; and a complete full set of data for studying the climatic instabilities of Heinrich Stadials (HSs) 6-1 is missing. Open questions remain about the nature, timing and drivers of abrupt events on the SW Iberian Margin. Two exceptional marine sedimentary records were analysed: Site U1385 (IODP Expedition 339 SW Iberian margin, off Lisbon), and core D13882 from the near coastal Lisbon mud-patch. Delivering the highest resolution multiproxy data by analysing pollen and Sea Surface Temperatures (SSTs) in a sedimentary record was the main challenge. The methodology used is a land-sea direct correlation approach. This method allows the comparison in the same stratigraphic sample between terrestrial and oceanic tracers, which are interpreted in terms of correlative atmospheric and oceanic conditions. The key findings are presented in form of four research papers. The first presents the first independent radiocarbon chronology for the Last Glacial at Site U1385 using Bayesian age-depth modelling, incorporating the results of 38 new AMS radiocarbon dates obtained in the framework of this PhD/NERC funding. The second presents the new high-resolution pollen and SST record of U1385 for the Last Glacial, providing a detailed examination of the long-term and millennial scale vegetation and oceanographic changes with a special view to deepening the understanding of millennial climate variability, including characterisation of the unique terrestrial and oceanic “fingerprint” of each of the six HSs. The third considers in more detail the rapid expansion of forest in the Western Mediterranean during the deglaciation, with a detailed discussion around the role of profound atmospheric CO2 changes at this time. The final paper examines the time-transgressive nature of the Early Holocene forest maximum in Iberia and its connection with orbital drivers, based on the analysis of the D13882 record and comparison with other Iberian Margin marine pollen records. In summary, this research project encompasses a broad scientific spectrum: age (Last Glacial, Deglaciation and Holocene), cycles (Glacial/Interglacial, Dansgaard-Oeschger), and long-term vs short term, different triggers (orbital vs internal factors). It represents an exploration of key and relevant Quaternary themes and works toward exploring and testing new hypotheses. Finally, several directions for further research are indicated. The future increase in temporal resolution to a decadal scale (~50 years), samples permitting, represents one such direction.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	William Fletcher (Supervisor) & Abi Stone (Supervisor)