Abrupt intrinsic and extrinsic responses of southwestern Iberian vegetation to millennial‐scale variability over the past 28 ka

Anna Cutmore,Laurie Menviel,Vasiliki Margari,Negar Haghipour,Belen Martrat,Francesco Muschitiello,David Hodell,Timothy Eglinton,Polychronis C Tzedakis,Blanca Ausín,Mark Maslin

doi:10.1002/jqs.3392

Abstract

ABSTRACTWe present new high‐resolution pollen records combined with palaeoceanographic proxies from the same samples in deep‐sea cores SHAK06‐5K and MD01‐2444 on the southwestern Iberian Margin, documenting regional vegetation responses to orbital and millennial‐scale climate changes over the last 28 ka. The chronology of these records is based on high‐resolution radiocarbon dates of monospecific samples of the planktonic foraminifera Globigerina bulloides, measured from SHAK06‐5K and MD01‐2444 and aligned using an automated stratigraphical alignment method. Changes in temperate and steppe vegetation during Marine Isotope Stage 2 are closely coupled with sea surface temperature (SST) and global ice‐volume changes. The peak expansion of thermophilous woodland between ~10.1 and 8.4 cal ka bp lags behind the boreal summer insolation maximum by ~2 ka, possibly arising from residual high‐latitude ice‐sheets into the Holocene. Rapid changes in pollen percentages are coeval with abrupt transitions in SSTs, precipitation and winter temperature at the onset and end of Heinrich Stadial 2, the ice‐rafted debris event and end of Heinrich Stadial 1, and the onset of the Younger Dryas, suggesting extrinsically forced southwestern Iberian ecosystem changes by abrupt North Atlantic climate events. In contrast, the abrupt decline in thermophilous elements at ~7.8 cal ka bp indicates an intrinsically mediated abrupt vegetation response to the gradually declining boreal insolation, potentially resulting from the crossing of a seasonality of precipitation threshold.

Highlights

Situated in a transition zone between temperate central Europe and arid North Africa, the western Mediterranean is heavily affected by mid‐latitude and sub‐tropical interactions, making it sensitive to variations in the general circulation (Giorgi and Lionello, 2008; Lionello, 2012)
We present two new high‐resolution pollen records of the last 28 ka combined with palaeoceanographic analyses and a radiocarbon (14C) chronology supported by 47 14C dates from deep‐sea cores SHAK06‐5K and MD01‐2444 on the SW Iberian Margin, to: 1. investigate the response of SW Iberian vegetation to orbital variability over Marine Isotope Stage (MIS) 2 and the Holocene; 2. investigate the absolute timing of millennial‐scale SW Iberian vegetation changes over the past 28 ka, and the relative timing of abrupt vegetation and oceanographic changes over this period using existing palaeoceanographic analyses from cores SHAK06‐5K and MD01‐2444; and
A range of pollen and spores were identified in SHAK06‐5K and MD01‐2444, which include angiosperms, gymnosperms, pteridophytes and bryophytes

Summary

Introduction

Situated in a transition zone between temperate central Europe and arid North Africa, the western Mediterranean is heavily affected by mid‐latitude and sub‐tropical interactions, making it sensitive to variations in the general circulation (Giorgi and Lionello, 2008; Lionello, 2012). Between October and March, the strengthened Icelandic low and weakened Azores High result in southward‐shifted westerlies; these dominant and strong southwesterly winds create down‐welling over the Iberian Margin continental shelf (Ambar andand Fiúza, 1994; Vitorino et al, 2002), and drive the poleward Portugal Coastal Counter current (PCCC). This winter cooling of surface waters combined with high energy waves creates well mixed surface waters to ~100 m (Vitorino et al, 2002). The source of terrestrial sediment transported to the SW Iberian Margin has remained constant over the last 28 ka, primarily supplied by the Tagus catchment basin

Materials and methods

Results and discussion

Conclusions