Description: Material cored during the Integrated Ocean Drilling Program (IODP) Expedition 310 'Tahiti Sea Level' revealed that the fossil reef systems around Tahiti are composed of two major stratigraphic sequences: (i) a last deglacial sequence; and (ii) an older Pleistocene sequence. The older Pleistocene carbonate sequence is composed of reef deposits associated with volcaniclastic sediments and was preserved in Hole 310-M0005D drilled off Maraa. Within an approximately 70-m-thick older Pleistocene sequence (33.22-101.93 m below seafloor; 92.85-161.56 m below present sealevel) in this hole, 11 depositional units are defined by lithological changes, sedimentological features, and paleontological characteristics and are numbered sequentially from the top of the hole downward (Subunits P1-P11). Paleowater depths inferred from nongeniculate coralline algae, combined with those determined by using corals and larger foraminifers, suggest two major sealevel rises during the deposition of the older Pleistocene sequence. Of these, the second sealevel rise is associated with an intervening sealevel drop. It is likely that the second sealevel rise corresponds to that during Termination II (TII, the penultimate deglaciation, from Marine Isotope Stages 6 to 5e). Therefore, the intervening sealevel drop can be correlated with that known as the 'sealevel reversal' during TII. Because there are limited data on the Pleistocene reef systems in the tropical South Pacific Ocean, this study provides important information about Pleistocene sealevel history, the evolution of coral reef ecosystems, and the responses of coral reefs to Quaternary climate changes.

Description: Fossil reefs are valuable recorders of paleoenvironmental changes during the last deglaciation, and detailed characterizations of coralgal assemblages can improve understanding of the behavior and impacts of sea-level rise. Drilling in 2005 by the Integrated Ocean Drilling Program (IODP) Expedition 310 explored submerged offshore reefs from three locations around Tahiti, French Polynesia and provides the first look at island-wide variability of coralgal assemblages during deglacial sea-level rise. We present the first detailed examination of coral and coralline algal taxonomy and morphology from two sites on Tahiti (offshore Tiarei and offshore Maraa). Sixteen cores ranging in depth from 122 m to 45 m below sea-level represent reef growth from 16 ka to ca. 8 ka (Camoin, G.F., Iryu, Y., McInroy, D.B. and the IODP Expedition 310 Scientists, 2007. IODP Expedition 310 reconstructs sea level, climatic, and environmental changes in the South Pacific during the last deglaciation. Scientific Drilling, 5: 4-12). Twenty-six coral species, twelve coral genera and twenty-eight coralline algal species were identified from 565 m of core and over 400 thin sections. Based on these data, and in comparison with modern and fossil analogs, seven coral and four algal assemblages have been identified in the deglacial sequences in Tahiti, representing a range of environments from less than 10 m to greater than 20-30 m water depth. Deglacial reef initiation varied at sites based on the available substrate, and early colonizers suggest water conditions at all sites were unfavorable to sensitive corals, such as Acropora, prior to ca. 12.5 ka. Mainly shallowwater (b10-15 m) corals and coralline algal assemblages developed continuously throughout both sites from 16 ka to ca. 8 ka, suggesting that coralgal assemblage variation ismore influenced by factors such as turbidity and water chemistry than sea-level rise alone.

Description: The present study investigates the influence of environmental (temperature, salinity) and biological (growth rate, inter-generic variations) parameters on calcium isotope fractionation (d44/40Ca) in scleractinian coral skeleton to better constrain this record. Previous studies focused on the d44/40Ca record in different marine organisms to reconstruct seawater composition or temperature, but only few studies investigated corals. This study presents measurements performed on modern corals from natural environments (from the Maldives for modern and from Tahiti for fossil corals) as well as from laboratory cultures (Centre Scientifique de Monaco). Measurements on Porites sp., Acropora sp., Montipora verrucosa and Stylophora pistillata allow constraining inter-generic variability. Our results show that the fractionation of d44/40Ca ranges from 0.6 to 0.1 per mil, independent of the genus or the environmental conditions. No significant relationship between the rate of calcification and d44/40Ca was found. The weak temperature dependence reported in earlier studies is most probably not the only parameter that is responsible for the fractionation. Indeed, sub-seasonal temperature variations reconstructed by d18O and Sr/Ca ratio using a multi-proxy approach, are not mirrored in the coral's d44/40Ca variations. The intergeneric variability and intrageneric variability among the studied samples are weak except for S. pistillata, which shows calcium isotopic values increasing with salinity. The variability between samples cultured at a salinity of 40 is higher than those cultured at a salinity of 36 for this species. The present study reveals a strong biological control of the skeletal calcium isotope composition by the polyp and a weak influence of environmental factors, specifically temperature and salinity (except for S. pistillata). Vital effects have to be investigated in situ to better constrain their influence on the calcium isotopic signal. If vital effects could be extracted from the isotopic signal, the calcium isotopic composition of coral skeletons could provide reliable information on the calcium composition and budget in ocean.

Description: The topographic survey of the studied outcrops is based on several thousands of measurements per study site and the measurement of the sample elevation with reference to sea level using a real-time kinematic GPS Trimble R8. The maximum vertical (Z) and horizontal (X and Y) elevation errors are of ± 2.0 cm and a few millimetres, respectively. During the measurement, the surveys were related to the French Polynesian Geodetic Network (Réseau Géodésique de Polynésie Française; RGPF), to operating tide gauges or tide gauge data sets, to probes that were deployed during the field work, to the instantaneous sea level or to modern adjacent microatolls growing in a similar environment than their fossil counterparts. In the absence of geodetic datum or tide gauges, probes were deployed for four to five days in order to measure the sea-level position and to compare the data to the elevation of modern microatolls. The relative sea-level curve, which is presented in this paper, is based on data acquired on islands for which longer tidal records and geodetic data are available. After acquisition, the raw data were processed with the aims: 1) to estimate the elevation of individual dated fossil microatolls based on local tide gauge parameters, and 2) to compare the elevation of all dated fossil microatolls according to the same vertical reference. The link between tide gauge data and the position of the living and fossil microatolls can be established using RGPF. However, a topographic reference at the scale of French Polynesia (4,167 km^2), which is mandatory to achieve the second objective, does not exist, as tide gauge observations are incomplete and the NGPF (Nivellement Général de Polynésie Française) vertical datum that is associated to the RGPF is not homogeneous at this regional scale. The official geodetic system in French Polynesia is the RGPF, which is associated with the NGPF vertical datum. The French Polynesian Geodetic Network is a semi-dynamic system with different levels established by the Naval Hydrographic and Oceanographic Service (Service Hydrographique et Océanographique de la Marine; SHOM) in cooperation with the National Geographic Institute (Institut Géographique National; IGN). The selection of microatolls for dating has been based on the lack of erosion features, the absence of local moating effects and their mineralogical preservation, demonstrating that our database is robust. The chemical preparation, mass-spectrometer measurements and age dating were performed in the years 2014 to 2016 mostly directly after field collection. The data are presented in Supplementary Table 2 following recommendations from Dutton et al. (2017). The best-preserved samples, as indicated by X-ray Powder Diffraction (XRD) measurements, comprise 97.5% aragonite on average (n = 281). Additionally, no secondary aragonite or calcite crystals were revealed by thin section and Scanning Electron Microscope (SEM) observations.

Description: The widespread occurrence of microbialites in the last deglacial reef frameworks (16-6 Ka BP) implies that the accurate study of their development patterns is of prime importance to unravel the evolution of reef architecture through time and to reconstruct the reef response to sea-level variations and environmental changes. The present study is based on the sedimentological and chronological analysis (14C AMS dating) of drill cores obtained during the IODP Expedition #310 "Tahiti Sea Level" on the successive terraces which typify the modern reef slopes from Tahiti. It provides a comprehensive data base to investigate the microbialite growth patterns (i.e. growth rates and habitats), to analyze their roles in reef frameworks and to reconstruct the evolution of the reef framework architecture during sea-level rise. The last deglacial reefs from Tahiti are composed of two distinctive biological communities: (1) the coralgal communities including seven assemblages characterized by various growth forms (branching, robust branching, massive, tabular and encrusting) that form the initial frameworks and (2) the microbial communities developed in the primary cavities of those frameworks, a few meters (1.5 to 6 m) below the living coral reef surface, where they heavily encrusted the coralgal assemblages to form microbialite crusts. The dating results demonstrate the occurrence of two distinctive generations of microbialites: the "reefal microbialites" which developed a few hundred years after coralgal communities in shallow-water environments, whereas the "slope microbialites" grew a few thousands of years later in significantly deeper water conditions after the demise of coralgal communities. The development of microbialites was controlled by the volume and the shape of the primary cavities of the initial reef frameworks determined by the morphology and the packing of coral colonies. The most widespread microbialite development occurred in frameworks dominated by branching, thin encrusting, tabular and robust branching coral colonies which built loose and open frameworks typified by a high porosity (〉 50%). In contrast, their growth was minimal in compact coral frameworks formed by massive and thick encrusting corals where primary cavities yielded a low porosity (~ 30%) and could not host a significant microbialite expansion.