Sea-level changes over the past 6,000 years in the Society and Tuamotu Islands, French Polynesia
Abstract
Tropical coral reefs are unique recorders of sea-level and environmental changes. They are therefore of pivotal importance to resolving the rates of millennial-scale eustatic changes, to clarifying the mechanisms that drive glacial-interglacial cycles and to constraining geophysical models. A detailed regional study of Late Holocene (i.e., the past 6,000 years) relative sea-level changes is based on coral reef records of two high islands from the Society Islands (Bora Bora, Moorea) and two atolls from the Tuamotu Archipelago (Rangiroa, Tikehau), French Polynesia, South-Central Pacific. Different sea-level indicators, such as in situ coral colonies, bivalves and exposed coral conglomerates, were used in order to reconstruct relative sea-level changes. A special attention has been given to microatolls which are circular coral colonies that grow predominantly laterally as their upward growth is constrained by the water level, thus providing an accurate record of the low-tide level. The reconstruction of sea-level changes has been based on the accurate dating (U/Th (MC-ICPMS) dating with a 2σ error of 3-36 years) of pristine coral and bivalve samples and the precise measurement of their position (especially altitude) via GPS (vertical and horizontal precision of 1-3 cm and a few millimetres, respectively). Former studies have reported that sea level in French Polynesia was approximately 1 m higher than present between 5,000 and 1,250 yrs BP and that a highstand was reached between 2,000 and 1,500 yrs BP (Pirazzoli and Montaggioni, 1988) and persisted until 1,200 yrs BP in the Tuamotu Archipelago (Pirazzoli and Montaggioni, 1986). In contrast to these former studies, our study reveals that sea level reached its present level at around 5,000 yrs BP and continued to rise from at least 4,951 to 2,535 yrs BP when it was at least 1.3 m above the present level. These results will be integrated in a regional study of Late Holocene sea-level changes in various islands from French Polynesia which cover a range of latitudes (14-23°S) with the aim of isolating the eustatic and isostatic component signals through geophysical modeling.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMPP51D..08H
- Keywords:
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- 4556 OCEANOGRAPHY: PHYSICAL Sea level: variations and mean;
- 4220 OCEANOGRAPHY: GENERAL Coral reef systems