EGU2020-21845
https://doi.org/10.5194/egusphere-egu2020-21845
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Reconstructing abrupt climate changes of the last deglaciation & Holocene: Pollen & biomarker analyses from the Portuguese Margin

Anna Cutmore1, Blanca Ausin2,3, Timothy Eglinton2, Mark Maslin1, and Chronis Tzedakis1
Anna Cutmore et al.
  • 1University College London, Geography, London, United Kingdom of Great Britain and Northern Ireland (anna.cutmore.15@ucl.ac.uk)
  • 2Geological Institute, ETH Zürich, Zurich 8092, Switzerland
  • 3Department of Geology, University of Salamanca, Salamanca 37008, Spain

In light of the current rate of anthropogenic climate change, it is becoming increasingly critical to enhance knowledge of past abrupt climate events and subsequent responses of the Earth system. One period that can provide such insight is the last ~28 kyr, with several abrupt changes occurring over the course of the deglaciation. The Portuguese Margin has been an ideal location to study the impacts of these abrupt climate events on marine and terrestrial environments.  The combined effect of the narrow continental shelf and close proximity to the Tagus and Sado rivers, lead to the rapid delivery of a high quantity of sediment, including our pollen and biomarker proxies, to the Tagus Abyssal Plain. Joint terrestrial and palaeoceanographic analyses from the same sediment samples enable an in situ assessment of the relative timing of changes in palaeoceanographic and terrestrial proxies.

 

Here we document the response of western Iberian vegetation to millennial and centennial-scale changes, particularly changes in moisture availability, over the deglaciation and Holocene, by combining (for the first time at a Portuguese Margin site) pollen and leaf-wax isotopic biomarker records (δ13C and δD) from core SHAK06-5K. A high-resolution pollen record (every 2cm) and lower-resolution n-alkane δ13C and δD records spanning 28kya are compared with high-resolution XRF sediment and planktonic foraminiferal d18O analyses from the same core.  The sequence is supported by high-resolution age control, based on 40 Accelerator mass spectrometry (AMS) 14C dates from monospecific samples of the planktonic foraminifera, Globigerina bulloides.

 

Our pollen record indicates the rapid response of regional vegetation to centennial changes and millennial-scale climate events, with forest expansion during the warm interglacial/ interstadial Bølling-Allerød and Holocene, and forest contraction and steppe expansion during cold glacial/ stadial conditions of the Last Glacial Maximum and Younger Dryas. Comparing our pollen and n-alkane biomarker data with the XRF Zr:Sr ratio and planktonic foraminiferal δ18O records, a clear synchroneity can be seen in the timing of millennial-scale changes in all records.  The millennial-scale changes in our leaf wax n-alkane δD and δ13C records can be explained by both vegetation composition and growing season water availability. 

How to cite: Cutmore, A., Ausin, B., Eglinton, T., Maslin, M., and Tzedakis, C.: Reconstructing abrupt climate changes of the last deglaciation & Holocene: Pollen & biomarker analyses from the Portuguese Margin, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21845, https://doi.org/10.5194/egusphere-egu2020-21845, 2020

Comments on the presentation

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Presentation version 1 – uploaded on 05 May 2020
  • CC1: Comment on EGU2020-21845, Sandra Gomes, 06 May 2020

    Hi Anna, 

    Thank you for your presentation and sharing your preliminary interesting and needed results/understanding about leaf wax n-alkane δD and δ13C records. We have met at INQUA and I am working in the IM too. 

    I am curious about your Eurosiberian pollen curve, because it is quite similar to your temperate curve; what taxa do you include on it? 

    What type of plants do you think are represented by your leaf wax n-alkane δD and δ13C ? 

    and what do you think about the low levels δ13C observed during the HS2 which are comparable with the BA? 

    Thank you

    Sandra 

    sandra.domingues@manchester.ac.uk

     

     

     

  • AC1: Comment on EGU2020-21845, Anna Cutmore, 07 May 2020

    Hi Sandra,

    Thanks for your message- nice to hear from you. I'll send you an email with some more details!

    Best wishes,

    Anna

    • AC2: Reply to AC1, Anna Cutmore, 11 May 2020

      Just to quickly sumarise my more lengthy email (!):

      1. Our Eurosiberian summary curve includes all trees and shrubs, excluding Pinus and Cedrus, and Mediterranean and Pioneer taxa (the temperate curve includes Mediterranean taxa)

      2. Based on previous research of sediment deposition at our core site, we are assuming that the biomarkers are sourced primarily from within the Tagus basin (with a small contribution from the Sado). Although the pollen record can give us an indication of the composition of the taxa contributing to this signal, variations in pollen production, distribution and preservation of different species means that we cannot use this as a direct measure. I'm hoping the concentration results from our modern Tagus basin leaf-wax n-alkane samples might provide a clearer picture.

      3. At present, I'm hesitant to make any climatic inferences from the BA as it's currently only one data point (we do have another 8 samples for this period, so I will be able to update you when the lab reopens and we are able to run the samples). However, looking at HS2, it does appear that water availability is decreasing over this period, coinciding with a rise in semi-desert taxa.

      Thanks for your questions and interest,

      Anna

      • CC2: Reply to AC2, Sandra Gomes, 11 May 2020

        Thank you Anna for your time and availability.