Paper Number: 1539
Reconstructing Mid- to Late Holocene sea-level changes from coral microatolls, French Polynesia
Hallmann, N.1, Camoin, G.1, Eisenhauer, A.2, Vella, C.1, Samankassou, E.3, Botella, A.4, Milne, G.A.4, Pothin, V.1, Dussouillez, P.1 and Fleury, J.1
1 CEREGE UMR 7330, Europôle Méditerranéen de l'Arbois, BP80, 13545 Aix-en-Provence cedex 4, France, hallmann@cerege.fr
2 GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel, Wischhofstraße 1-3, 24148 Kiel, Germany
3 University of Geneva, Rue des Maraîchers 13, CH-1205 Geneva, Switzerland
4 University of Ottawa, Department of Earth Sciences, Ottawa, Ontario K1N 6N5, Canada
___________________________________________________________________________
Sea-level change during the Mid- to Late Holocene has a similar amplitude to the sea-level rise that is likely to occur before the end of the 21st century providing a unique opportunity to study the coastal response to sea-level change and to reveal an important baseline of natural climate variability prior to the industrial revolution.
Mid- to Late Holocene relative sea-level change in French Polynesia was reconstructed using coral reef records from twelve islands, which represent ideal settings for accurate sea-level studies because: 1) they can be regarded as tectonically stable during the relevant period (slow subsidence), 2) they are located far from former ice sheets (far-field), 3) they are characterized by a low tidal amplitude, and 4) they cover a wide range of latitudes which produces significantly improved constraints on GIA (Glacial Isostatic Adjustment) model parameters.
Absolute U/Th dating of in situ coral colonies and their accurate positioning via GPS RTK (Real Time Kinematic) measurements is crucial for an accurate reconstruction of sea-level change. We focus mainly on the analysis of coral microatolls, which are sensitive low-tide recorders, as their vertical accretion is limited by the mean low water springs level. Growth pattern analysis allows the reconstruction of low-amplitude, high-frequency sea-level changes on centennial to sub-decadal time scales.
A sea-level rise of less than 1 m is recorded between 6 and 3–3.5 ka, and is followed by a gradual fall in sea level that started around 2.5 ka and persisted until the past few centuries. The reconstructed sea-level curve therefore extends the Tahiti sea-level curve [1], and is in good agreement with a geophysical model tuned to fit far-field deglacial records [2].
References:
[1] Deschamps P et al. (2012) Nature 483: 559-564
[2] Bassett S et al. (2005) Science 309: 925-928