Insights into the nature of climate and vegetation changes over the last 28,000 years using combined pollen and leaf-wax biomarker analyses from the SW Iberian Margin

• Main Author: Cutmore, Anna Victoria
• Other Authors: Tzedakis, P, Maslin, M, Eglinton, T
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UCL (University College London) 2021
• Subjects: North Atlantic
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10131446/1/A.Cutmore_PhD_Thesis_2021.pdf; https://discovery.ucl.ac.uk/id/eprint/10131446/

This thesis aims to enhance the current understanding of the response of SW Iberian ecosystems to abrupt and orbital-scale climate changes. The last ~28 thousand years can provide such insight, containing several abrupt North Atlantic climate events superimposed on orbital-scale global changes. This study presents new high-resolution pollen and leaf-wax n-alkane records combined with palaeoceanographic proxies from the same deep-sea cores (SHAK06-5K and MD01-2444) on the Southwestern (SW) Iberian Margin. The chronology of these records is based on high-resolution Accelerator Mass Spectrometry radiocarbon dating of planktonic foraminifer Globigerina bulloides from cores SHAK06-5K and MD01-2444. Changes in temperate and steppe records during the Last Glacial Maximum and subsequent deglaciation are closely coupled with changes in sea surface temperatures (SSTs), and global ice volume. This coupling continues during the onset of the Holocene, with the peak in thermophilous woodland lagging the boreal insolation maxima by ~2 kyr. This possibly arises from the persistence of residual high-latitude ice-sheets into the Holocene. A close correlation between rapid oscillations in pollen percentages and millennial/centennial-scale variations in SSTs, planktonic 18O, and lithology suggests extrinsically-forced SW Iberian ecosystem changes in response to abrupt North Atlantic climate events. In contrast, the abrupt thermophilous woodland decline at ~7.8 thousand years before present (cal ka BP) indicates an intrinsically-mediated abrupt vegetation response to the gradually declining boreal insolation, resulting in the crossing of an ecological threshold. The leaf-wax n-alkane 13C record from SHAK06-5K combined with the pollen record from the same core and modern leaf-wax n-alkane 13C data from SW Iberia suggest that this geochemical proxy is directly or indirectly driven by SW Iberian climate variations. Two potential mechanisms are proposed: i) n-alkane 13C is directly controlled by changes in regional moisture ...