Skip to main content

Environmental sensitivity of the Iberian peninsula to climate change

Final Report Summary - IBERIAN CLIMATE (Environmental sensitivity of the Iberian peninsula to climate change)

The Iberian Peninsula lies in the boundary between tropical and subtropical climates, which amplifies the climatic signals from the northern hemisphere through both atmospheric and water circulation feedbacks, making it an ideal site to monitor Northern hemisphere climate changes. The project approaches these issues by concentrating on episodes of rapid climate changes in Iberia that occurred at millennial to centennial timescales during the last glacial-interglacial climatic cycle. The aim of the project is to produce a quantitative reconstruction of the Iberian Peninsula past climate variability (temperature and precipitation) using organic geochemistry (biomarkers) and pollen records, in lake sediments to establish the relation between those changes and those observed in both ice cores from Greenland and paleotemperature records from marine sediments from the continental Iberian margin. Climatic parameters will include temperature TEX86 (SST and lake temperatures), MBT-CBT (from branched GDGTs in marine and lacustrine sediments), salinity, precipitation, paleoproductivity (biomarker abundance).
The main results and conclusions of the project:
We validated the use of the MBT-CBT pH and temperature proxy in the Iberian Peninsula. The MBT-CBT proxy is based on the distribution of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in soils. The CBT quantifies soil pH and the MBT relates to mean annual air temperature. However other factors such as the hydrological conditions have been suggested to influence the MBT. A set of 25 soil samples of the Iberian Peninsula with a wide range of hydrological regimes was analysed to assess the effect of the hydrological conditions on the MBT-CBT. We found that CBT is significantly correlated to soil pH confirming it as a robust proxy for soil pH. In contrast the MBT index was not correlated to MAT and only weakly correlated to annual mean precipitation. Instead we found a significant correlation between MBT and the Aridity index (AI), a parameter quantifying water availability in soils. The AI can explain 70 % of the residuals of MAT estimation and 50 % of the actual variation of the MBT. Therefore in the study area the branched GDGT distribution is strongly controlled by soil water availability (Menges et al. 2014). We believe that the bdGDGT producing organisms found in Spanish soils are more constrained by low water content than temperature itself. This resulted in 2 oral presentations, a poster and a Biogeochemistry publication. These results raised great concerns for the use of the MBT-CBT as a temperature proxy which has also been reported from other studies and was discussed at length at the GDGT-NIOZ workshop where these results were presented. On the positive side changes in MBT-CBT it arid to semiarid regions could potentially indicate water availability in soils making it an invaluable tool for paleorecontrustion of hydric conditions. This would grant further investigation which is unfortunately outside the scope of this project but we hope to pursue in the future.
As expected from the soil end-member results the MBT-CBT does not show a significant temperature trend when applied downcore on a lake sediment record. However, when a different temperature proxy the TEX86 SST is applied we were able to record the little ice age (LIA) period as well as the medieval warm period during the Holocene. These results indicate that continental climatic changes were simultaneous to those previously recorded by marine sediments in the Iberian margin and North Atlantic. We presented this as a poster at the EGU 2014 within the BG6.1 session and are currently preparing a publication.
Potential Impact:
• GDGT Proxies are enhancing the paleoclimatologist tool-kit by providing new ways to reconstruct paleoenvironmental parameters that could not be studied otherwise. Thanks to the fellowship Dr. Huguet has significantly contributed to constrain the use of the better known GDGT proxies such as TEX86, MBT-CBT and BIT.
• Moreover the fellow that further expand the paloclimatological information that can be extracted from sedimentary records.
• Reliable continental temperature and climatic records are scarce making the outcome of this project of relevant to the organic geochemistry and the wider paleoclimatic community.