Calibration studies on mollusc shells in the Peru-Chile coastal region submitted to ENSO impacts.
Abstract
Mollusc shells have an exceptional potential for high resolution paleoclimatic records and, unlike corals, ice cores and even tree rings, have the advantage to be widely distributed along the world coastlines. For the reconstruction of seasonal or intra annual climate variability, this kind of fast-growing biogenic material is particularly suitable. Several preliminary studies involving stable isotope variations within modern, as well as Early and Middle Holocene, bivalve shells from Peru and northern Chile showed relatively short-lived excursions which depict thermal anomalies linked to regional ENSO impacts. The Eastern Pacific region (30^oS-1^oS) which is actually the area where the strongest SST signal of ENSO is obtained, and where abundant archaeological shell deposits and fossiliferous marine terrace units are preserved, thus offers a great opportunity to develop a new proxy for paleo-ENSO studies. Oxygen isotope data were classically obtained through series of sub-samples along the major growth axis of marine molluscs. However this traditional approach only provides a rough evidence for the record of anomalous conditions during weeks or months. Recent technical developments allowing a much higher resolution in the geochemical measurements and in the microstructural observations of the sampled material, associated to a better understanding of the biomineralisation processes, renewed significantly the modality of the calibration studies. The CONCHAS project involves coupled measurements of seawater parameters and variations of geochemical and isotopic composition at a daily, or subdaily, scale. The studies bear upon half a dozen species of molluscs (bivalves and one gastropod) and include inter-specific comparisons on individuals growing in a given environment (natural or controlled artificially). The first results indicate clearly that all the factors that control the growth rate of the carbonate skeleton and the precise timing of the biomineral deposition must be taken into account prior to any interpretation of the variations of the geochemical composition. A large part of the so-called "vital effect" can now be reduced, simply by understanding how the shell is being formed days after days. Similarly, the specific paleo-temperature equations will thus be better resolved if the data used correspond to subsamples well identified in time (duration and date of shell increment formation) and can be confidently related to instrumentally measured environmental parameters.
- Publication:
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EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....13681O