EGU2020-13928, updated on 12 Jun 2020
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Reconstruction of regional humidity variations during the Younger Dryas - Holocene transition in NW Iberia using lipid biomarker stable isotope ratios

Oliver Rach1, Oliver Heiri2, Castor Muñoz Sobrino3, Andrea Vieth-Hillebrand4, and Dirk Sachse1
Oliver Rach et al.
  • 1German Research Centre for Geosciences (GFZ), Organic Surface Geochemistry Lab, Section 4.6, Potsdam, Germany
  • 2Department of Environmental Sciences, Geoecology, University of Basel
  • 3Department Bioloxía Vexetal e Ciencias do Solo, University of Vigo
  • 4German Research Centre for Geosciences (GFZ), Organic Geochemistry, Section 3.2, Potsdam, Germany

The impact of global temperature changes on hydroclimate, especially on regional spatial scales, is difficult to predict with global climate models. These models are generally too coarse in resolution and do not fully constrain complex atmospheric processes. We can study past climatic changes to understand the evolution of hydroclimate and identify its mechanisms on regional scales. The Younger Dryas (YD) cold period ca. 12.000 years ago was the last major abrupt climate change in Earth history and as such provides us with a natural laboratory to better understand impacts of such change on both global and regional scales. Increasingly, high resolution datasets from terrestrial archives throughout Europe are being developed which suggest atmospheric controls on abrupt changes in local ecosystems, such as the southward movement of the jet stream during the YD period. Therefore, regions located at the boundary between major moisture sources are particularly interesting, such as NW Iberia, which is situated between Atlantic and Mediterranean moisture sources and their effects. Here we present terrestrial lipid biomarker (n-alkane) stable hydrogen (δ2Hwax) and carbon (δ13Cwax) isotope records from lake Laguna de la Roya (LR) (NW Iberia), covering the YD. In combination with pollen and chironomid reconstructed temperature data, we aim to identify the evolution of atmospheric conditions during the YD in NW Iberia. Since LR is located close to the Atlantic Ocean and the reconstructed maximum YD sea-ice extent, we are specifically interested in amplitude and variability of local hydroclimatic changes compared to more continental sites during the YD-Holocene transition. During the YD, La Roya δ2Hwax values were characterized by ~6‰ more negative values compared to the preceding Allerød, indicative of colder and drier conditions, which is supported by local temperature reconstruction and pollen analysis. More continental records from western Europe such as Lake Meerfelder Maar (MFM) showed ~12‰ more negative values during YD. This doubling in depletion of MFM samples compared to LR could be, in part, attributed to the stronger temperature drop in continental Europe of about 4-6°C. For the same time at LR, the chironomid data show a drop of only 2.5°C. In general, δ2Hwax from LR were more positive, on average, compared to MFM, by ~27‰ in the Allerød and ~33‰ during the YD. However, in the Holocene both records converge to an average difference of 15‰, which is close to the modern measured 10‰ difference in δ2Hprecipition (source water for δ2Hwax) and consistent with a shared Atlantic moisture origin and subsequent Rayleigh rainout towards the East. Considering possible temperature related depletions in the LR δ2Hwax record during YD, the 27‰ difference in the Allerød implies additional influences on the recorded signal. A different moisture source area (Mediterranean) for LR during Allerød/YD period, and/or increased air mass transport distances from LR to MFM compared to Holocene conditions can explain the δ2Hwax differences. These findings suggest significant changes in the atmospheric circulation at the YD-Holocene transition when the jet stream shifted northward due to lower seasonal sea-ice expansions and intensification of the Atlantic Meridional Overturning Circulation.

How to cite: Rach, O., Heiri, O., Muñoz Sobrino, C., Vieth-Hillebrand, A., and Sachse, D.: Reconstruction of regional humidity variations during the Younger Dryas - Holocene transition in NW Iberia using lipid biomarker stable isotope ratios, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13928,, 2020

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Presentation version 1 – uploaded on 28 Apr 2020
  • CC1: Comment on EGU2020-13928, Sandra Gomes, 06 May 2020

    Dear Olivier,

    I really like your study since there is a need to better understand the hydroclimate in the IP.  I was just curious to know if you have performed an analysis in other IP continental cores, or other IP locations to confirm/test your suggested moisture Mediterranean source?


    • AC1: Reply to CC1, Oliver Rach, 06 May 2020

      Thanks for your comment. Currently we are working on this record and the idea of the change between the moistore sources. There are currently not many stable hydrogen iostope records avaiable for the IP... especially not hydrogen records. A colleague is working on a n-alkane d2H rocord from western Italy for the same period. Maybe this helps us to identify more the characteristics of the Med.- moisture source. The stable carbon isotope data (here not presented) which show more or less stable conditions during Allerod and YD show also higher varibaility and changes at the Holocene/YD transition. This imply some significant changes also in the ecosystem at the YD/Holocene transition. 

      • CC2: Reply to AC1, Sandra Gomes, 07 May 2020


        Dear Oliver,


        Thank you for your response.  It is true that is not many records analysed, and with the ambiguous hydroclimate proxy data, reconstructions proxies are required.   Are you targeting other intervals or just working with the YD, the pollen records of Laguna de Roya spans to the HS1.




        • AC2: Reply to CC2, Oliver Rach, 07 May 2020

          Hey Sandra,

          currently we are only working on the YD. The analysis of the YD period at La Roya is part of a bigger project. In the main project (called "STEEPclim" by Dirk Sachse) we analyze on a temporal high resolution scale several lake records from different location all over Europe. The aim of the project is to understand to temporal and spatial development of the YD in Europe. Here you can find more inforamtion on that:

          However, I think the location of La Roya is quite interesting. Maybe in future we can go on with the analysis. This depends also on our partners. 

  • CC3: Comment on EGU2020-13928, Sandra Gomes, 07 May 2020

    Thank you, Oliver ...very helpful. Maybe you already came across it, possibly it can be useful

    Thank you for your availability and all the best for your research.


    Sandra Gomes

  • CC4: Comment on EGU2020-13928, Sandra Gomes, 07 May 2020

    I was trying to share the link for the following article but it disappeared 

    Naughton, F., Costas, S., Gomes, S.D., Desprat, S., Rodrigues, T., Goñi, M.S., Renssen, H., Trigo, R., Bronk-Ramsey, C., Oliveira, D. and Salgueiro, E., 2019. Coupled ocean and atmospheric changes during Greenland stadial 1 in southwestern Europe. Quaternary Science Reviews212, pp.108-120.