CORDIS - EU research results

Natural responses to past North Atlantic Oscillations: Southern Iberian Peninsula vs. United Kingdom. Analogues for future environmental changes

Final Report Summary - NAOSIPUK (Natural responses to past North Atlantic Oscillations: Southern Iberian Peninsula vs. United Kingdom. Analogues for future environmental changes)

The main goal of the NAOSIPUK project is to reconstruct the North Atlantic Oscillation (NAO) for the Holocene. Several Holocene climatic records are being studied in two areas with different NAO responses: southern Iberian Peninsula and central/northern UK. Different approaches have been carried out to reconstruct the past environments of the different sites. Among these, pollen and charcoal studies, organic and inorganic geochemistry analyses, sedimentary and geophysical surveys are being of great importance.

The NAO has been one major climate mode that naturally affects weather and climate patterns across Europe at present and during the last hundred years. These oscillations have important economic and social consequences for the future of impacted regions, regarding changes in agricultural harvests, water management, energy supply and demand, and fishery yields. The NAO is caused by the difference between surface sea-level pressure of the Subtropical (Azores) High and the Subpolar Low. The NAO has two modes. In the positive mode warm and moist air across northern Europe gives rise to dry conditions over southern Europe. The negative mode reflects more meridional atmospheric flow with a shift to cold and dry conditions in northern Europe and warm and wet conditions in southern Europe. In this way, high latitude sites like the UK, usually receive more rainfall and experience more frequent extreme wet weather events such as flooding, whereas lower latitudes like southern Spain, experience drier conditions and more severe drought events during NAO positive conditions. In this project we have used the comparison of high resolution Holocene records from regions that display an opposite response to the NAO modes as natural analogues for past, present and futures scenarios.

To achieve this main objective other secondary questions had to be answered:
• What were the responses of past continental environments from Western Europe to abrupt climate events, especially rainfall changes during the Holocene? What were the responses from sensitive areas (such as southern Iberian Peninsula), in comparison with the global response of the Northern Hemisphere?
• Were the environmental responses from continental ecosystems fast or slow?
• Which relationships can be established between these climate changes, the environmental responses and the NAO mode?
• Is there any difference between the ecosystem response to long-term NAO variability in Southern Iberian Peninsula and the United Kingdom both prior to and after human-induced warming?
These questions are being answered by achieving the following six specific objectives and using a multidisciplinary approach. These main objectives were:
(1) To select the most appropriate, high-resolution climate archive from areas with different NAO influence, with the best preservation features and presence of key biomarkers.
(2) To determine the source of the organic matter: terrestrial, algal, or aquatic (using n-alkanes / traditional isotopic analyses).
(3) To establish the precipitation/evaporation balance of the environments, and the terrestrial and aquatic community response.
(4) To assay for the presence of other useful biomarkers, such as long-chain alkenones (LCAs) and / or diols that can be used to determine lake paleotemperatures.
(5) To assess the biogeochemical response of the lakes / peat bogs to past climatic fluctuations under “natural conditions”.
(6) To evaluate the human impact on these environments since the Industrial Revolution compared to the long-term natural trend.

In the last two years we have analysed five Holocene and/or latest Pleistocene sedimentary records from southern Spain, and two from the UK. However, one extra sedimentary records have been taken in the UK and will be analysed by our research network during the next years. Different analyses have been conducted, such as analyses of the composition of the bulk organic matter of the sediments to understand the source of organic matter, or biomarkers analyses. The biomarkers extracted from the sediment (specific compound of the sediment organic matter), such as leaf waxes (n-alkanes), algae-related compounds (diols and alkenones), and bacteria-related compounds (hopanes), have been analysed to specify the source of the organic matter, temperature ranges, as well as hydrological changes.

The studies of the Spanish sites are more advanced than the UK ones, as most of the sediment cores were already collected at the beginning of the project. Our preliminary results show that the palaeoenvironmental indexes developed from n-alkanes agree with the variations deduced from the carbon and nitrogen atomic ratios, as well as the carbon isotopic composition from bulk sediments in southern Spanish bogs. Interestingly, these indexes show opposite trends during the same periods in some of the records, which will help us to distinguish regional versus local effects of climate change, human impacts, and aeolian dust inputs. During the late Holocene solar forces and NAO fluctuations mainly drive the environmental evolution in some of those sites. Abrupt environmental changes are identified during the last hundred years, agreeing with the regional and global industrial development.

The regional comparison between central / northern UK and southern Spain shows a more stable middle Holocene (from ~7000 to ~5000 Cal yr BP) at higher latitudes. On the other hand, the environmental and climatic changes in southern Spain are quite abrupt during this period. This might be related to the beginning or increasing influence of the NAO during the middle Holocene.

Once the data of the Spanish and UK sites have been fully studied we could propose a climate model to understand the teleconnection between middle-low and high latitudes, identify the forces driving the environmental changes in the ecosystems, as well as the so-called natural vs. human-induced environmental change, which is a milestone to understand.