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Temporal and spatial variability of western Indian Ocean reefs: climatic and environmental record

Objective

To produce a high quality data base covering the last
20.000 years and defining the environmental
changes in the tropical areas of the western Indian Ocean
(of special interest is the spatial evolution of the southern
limit of the intertropical belt).
To reconstruct changes in sea level on
a regional scale, and thus to integrate the results in a global
palaeoceanographic framework.


The data set is based on the record from the study of coral reefs
of the main sea surface parameters (temperature, salinity) at
various time scales, and provides information on some aspects of
climate dynamics (e.g. patterns of short-term palaeoclimatic
variations, monsoon variability, relationships between monsoon
intensity and El Nino-Southern Oscillation).
The data set is based on the record from the study of coral reefs


The work will concentrate on the study of 3 reef sites
latitudinally distributed along the Mozambique Channel:
Seychelles (4º S); Mayotte, Comoro Islands (14º S) and
Tulear, Madagascar (23º 30'S). It concerns two distinct time
scales: 1-1,000 years and 1,000 to 20,000 years, at different
levels of spatial and temporal resolution, involving
high-frequency (seasonal or pluri-annual) and low-frequency
(century to millenium) forcing trends.

The 1-1,000 yrs time scale will be investigated by drilling
individual massive coral heads (Porites). In each of the three
sites of study, the selection of coral heads with overlapping
chronologies will produce a composite record that may cover a
millenium at resolution of up to seasonal frequency. The methods
used will be principally geochemical, including stable isotopes
(delta 18O, delta 13C), trace elements (Sr/Ca),
coupled with
measurements of growth and production rates of coral skeletons
(sclerochronology). Isotope analyses will be performed on each
seasonal band of the skeletons in order to get a high-resolution
record. Trace elements analyses will be made for periods
characterized by sharp fluctuations of sea surface temperatures
demonstrated by delta 18O excursions. Accurate ages will
be provided by AMS 14C dating.

The 1,000-20,000 yrs time scale will be investigated from cores
made through around 25 m thick reef sequences and from available
material provided by previous sampling of submerged reef slopes
using submersible. This study seeks to see how far the
high-resolution in coral growth bands may be applied to key
periods within a longer time scale (e.g. 10 years proxy
variations over 8,000 yrs). The minimal resolution will be of
100 years. The climate variability will be defined with oxygen
and carbon isotope data obtained from cored coral colonies
(massive Porites and branching Acropora). Since a continuous
record cannnot be expected on this time scale, high resolution
measurements will be performed only at various well-dated levels.

In addition, sea level curves will be reconstructed through U/Th
radiometric dates (alpha-counting method; Thermal Ionization
Mass spectometry) obtained from in-place corals, coupled with
palaeobathymetry information deduced from biological assemblages
significant as sea level indicators.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Université d'Aix-Marseille I (Université de Provence)
Address
3 Place Victor Hugo
13331 Marseille
France

Participants (9)

Bureau de Recherches Géologiques et Minières (BRGM)
France
Address
Avenue Du Concyr
45060 Orléans
CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
France
Address
Europole Mediteraneen De L'arbois, Cerege
13545 Gardanne
Centre National de la Recherche Scientifique (CNRS)
France
Address
Avenue De La Terrasse
91198 Gif-sur-yvette
Christian-Albrechts Universität Kiel
Germany
Address
Wischhofstraße 1-3
24148 Kiel
HEIDELBERGER AKADEMIE DER WISSENCHAFTEN
Germany
Address
Im Neuenheimer Feld 366
69120 Heidelberg
NATIONAL RESEARCH COUNCIL OF ITALY
Italy
Address
Via Gobetti 101
40129 Bologna
UNIVERSITY OF GLASGOW
United Kingdom
Address
East Kilbridge Nel Technology Park
G75 0QU Glasgow
University of Glasgow
United Kingdom
Address
University Avenue
G12 8QQ Glasgow
Università degli Studi di Bologna
Italy
Address
42,Via Irnerio
40126 Bologna