Calibration of the Oxygen Isotopic Composition of Bivalve Shells (Protothaca Thaca, Veneridae) From the Northern Chile Coast.
Abstract
High resolution serial samplings of molluscan shells have been realized to obtain oxygen isotopic records of the seasonal variations of sea surface temperature (SST) and proved to be relevant in the detection of short-lived ENSO impacts in western South America. This study concerns the oxygen isotopic analyses of a bivalve shell Protothaca thaca, a near-shore species living along the South American coasts in the latitudinal zone between 12° S and 45° S, which commonly lives some five years. The living shells were sampled in May 1992 and December 2000 on the North Chile coast in Antofagasta Bay (23° 46'S/70° 28'W), the last ones having survived the strong 1997-98 El Niño event and the 1998-2000 La Niña episode. The sampling of the aragonitic external layer was realized from half a cm away from the umbo along the growth axis (approximately 60 or 70 mm) at about one mm interval. The variations of the oxygen isotopic compositions reported as a function of the distance from the umbo show a typical cyclic pattern which mimics the seasonal SST variations: the low \delta18O values correspond to shell calcification in summer waters while the high \delta18O values correspond to shell calcification during winter. The oxygen isotopic curves were compared with daily SST data obtained at Antofagasta during the January 1987-January 2001 period in order to determine the age of each isotopic peak. The growth curve determined for individual shells has an exponential expression where the parameters differ slightly for each shell. It is clear that micro-environmental and biological parameters within each individual play a role in the calcification process, growth rate and isotopic fractionation. However it is shown that a common pattern of oxygen isotopic variations is registered by different individuals from a given locality. The experimental relationship between temperature and the oxygen isotopic composition of Protothaca thaca was finally deduced as follows: T° C = 18.5 -5.00 (\delta18O shell - \delta18O water) This equation is very similar to other equations proposed for aragonitic shells; the slight differences in the equation parameters reflect altogether specific isotopic fractionation and local environmental factors.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFMPP11A0449E
- Keywords:
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- 3344 Paleoclimatology;
- 4267 Paleoceanography;
- 4546 Nearshore processes