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Co-ordinated Research Programme on Nuclear and Isotopic Studies of the El Niņo Phenomenon in the Ocean

El Niņo has been recognized as a very important environmental problem affecting the climate of the Pacific region (as well as the whole of the Earth), and has significant local effects lasting up to several years with important consequences on fish populations and rainfall, including the formation of cyclones. The economic aspects of El Niņo's impact on both the marine environment and the Earth's climate in general have been regarded as a most influential environmental phenomenon. One of the most important parameters in determining the climate on Earth is the temperature record of the ocean. It is believed, therefore, that sea-surface temperature and its coupling with atmospheric processes is the most important phenomenon in the long-term climate record.

Isotopic investigations of the El Niņo phenomenon are based on the fact that during an El Niņo event sea-surface temperature increases and is accompanied by larger evaporation losses and isotopic fractionation, resulting in changes of D/H, 18O/16O, 13C/12C and 14C/12C isotopic ratios in seawater. It has been recognised that corals archive isotopic records in their annual bands and therefore could be used for the reconstruction of past ocean temperature records if an appropriate absolute chronology of their growth could be established. This can be accomplished by independent radionuclide dating of coral bands using 210Pb and Th/U dating methods. Coral is a calcium carbonate material and it has been found that incorporation of other elements like Sr and U into coral also depends on sea-surface temperature, therefore Mg/Ca, Sr/Ca and U/Ca ratios have been used for reconstruction of past sea-surface temperatures, although there are still many unresolved problems. Further investigations included deep-sea sediments, especially in areas where there are no corals. The applications of nuclear and isotopic techniques in El Niņo investigations have been carried out mostly on seawater and coral samples collected in the western Equatorial Pacific.

The CRP is co-ordinating efforts in the use of nuclear and isotopic techniques for studying isotope records in corals, seawater and sediment, with the aim of studying transfer of radioactive and stable isotopes from seawater to corals and sediments and to derive past temperature records in the Pacific Ocean. For this purpose, analysis of natural-radiogenic (210Pb, 226Ra, Th and U isotopes), natural-cosmogenic (10Be, 14C,) and anthropogenic (3H, 14C) radionuclides will be carried out on seawater, coral and sediment samples collected in the Pacific region using radiometric and mass spectrometry techniques (Inductively Coupled Mass Spectrometry - ICPMS, Accelerator Mass Spectrometry - AMS, and Thermal Ionisation Mass Spectrometry - TIMS). These analyses will enable to develop floating absolute chronologies for corals (and sediments) going back several hundreds of years, so the temperature records obtained by analysis of stable isotopes in corals can be developed for the same time period. Such isotopic records will enable to search for El Niņo signals in the past, to better understand its characteristics and predict ocean-atmosphere coupling in the future. They will allow more detailed studies on the processes involved (e.g. seawater-coral interactions), thus improving the possibilities for better understanding the El Niņo phenomenon in the ocean. Further work will include isotopic studies in ice cores (10Be) and tree-rings (14C), so marine investigations could be confronted and supplemented by terrestrial archives of the ENSO phenomena.

The IAEA-MEL has a long tradition and wide experience in the use of nuclear and isotopic techniques in marine environmental studies. These techniques have been successfully applied in such research projects as the investigation of long-term climatic records in the Mediterranean Sea, the investigation of water level changes in the Caspian Sea, in environmental studies in the Japan Sea, etc. The CRP is focusing specifically on the development and refinement of high sensitive nuclear and isotopic techniques that may be applied to problems involving seawater-atmosphere interactions, transport and archiving of radioactive and stable isotopes in corals and sediments, and the development of floating coral chronologies going back in time over at least the last five hundred years.

The CRP is fully integrated with the on-going Subprogramme H.1. Recognizing the important role of nuclear and isotopic methods in marine environmental studies a new project H.1.03 "Climate Change Studies Using Isotopic Records in the Marine Environment" has been launched for the biennium 2004 - 2005, fully concentrating on the investigation of climate change using marine isotopic archives.

The objectives of the CRP can be summarised as:

It is expected that the CRP, by co-ordinating the efforts of several laboratories, will bring new scientific information on the El Niņo phenomenon in the ocean.

The laboratories participating in the CRP are from the following Member States:

The first research coordination meeting of the CRP is planned for October 2004 in Monaco where CRP plan will be developed. Regular meetings and communication will ensure proper co-ordination and successful implementation of the CRP. The recommended time frame of the CRP is 4 years (2004-2008). It is intended that the CRP group will select for the CRP work two or three reference sites. All individual methodologies would be applied to the selected areas in order to integrate and validate the results, and to formulate a standard, viable strategy for El Niņo investigations. Standardization of sampling techniques, sample preparation, analytical procedures, and data interpretation across the reference sites will form an essential part of the CRP.