Variation in deglacial coralgal assemblages and their paleoenvironmental significance: IODP Expedition 310

Global and Planetary Change 76 (2011) 1–15

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Variation in deglacial coralgal assemblages and their paleoenvironmental significance: IODP Expedition 310, “Tahiti Sea Level” Elizabeth Abbey a,b,⁎, Jody M. Webster a,b, Juan C. Braga c, Kaoru Sugihara d, Carden Wallace e, Yasufumi Iryu f, Donald Potts g, Terry Done h, Gilbert Camoin i, Claire Seard i a

School of Earth and Environmental Sciences, James Cook University, Townsville, Qld 4811, Australia School of Geosciences, The University of Sydney, NSW 2006, Australia Departamento de Estratigrafia y Paleontologia, Universidad de Granada, E-18002 Granada, Spain d Center for Global Environmental Research (CGER), National Institute for Environmental Studies (NIES), 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan e Museum of Tropical Queensland, Townsville, Qld 4810, Australia f Department of Earth and Planetary Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan g Department of Earth and Evolutionary Biology, University of California, Santa Barbara, CA 95604, USA h Australian Institute of Marine Science, PMB #3, Townsville MC, Qld 4810, Australia i CEREGE, CNRS-Collége de France-IRD, B.P. 80, F-13545 Aix-en-Provence cedex 4, France b c

a r t i c l e

i n f o

Article history: Received 21 June 2010 Accepted 19 November 2010 Available online 26 November 2010 Keywords: IODP Expedition 310 “Tahiti Sea Level” Tahiti coralgal assemblages last deglaciation paleoenvironmental change

a b s t r a c t 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 (b 10–15 m) corals and coralline algal assemblages developed continuously throughout both sites from 16 ka to ca. 8 ka, suggesting that coralgal assemblage variation is more influenced by factors such as turbidity and water chemistry than sea-level rise alone. © 2010 Elsevier B.V. All rights reserved.

1. Introduction Coral reef systems are valuable recorders of environmental changes, as they can display specific and predictable zonation patterns related to depth or light attenuation and hydrodynamic energy regimes (Rosen, 1971; Done, 1982; Faure and Laboute, 1984; Veron, 2000), and are highly sensitive to variations in water chemistry and physical factors, such as temperature and turbidity (Buddemeier and Hopley, 1988; Kleypass, 1996). Fossil coral reef systems can be preserved in the rock record, thus providing detailed information about the past ambient ⁎ Corresponding author. School of Geosciences, Madsen Building (F09), The University of Sydney, NSW 2006, Australia. Tel.: +61 2 9036 6539; fax: +61 2 9351 3644. E-mail address: [email protected] (E. Abbey). 0921-8181/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.gloplacha.2010.11.005

conditions of a region. The presence or absence of certain corals and coralline algae in the fossil record, in particular those with known environmental sensitivities, is especially valuable for reconstructing paleoenvironments. Combined with U-series and 14C dating, fossil coral reefs have been used to reconstruct climate conditions and sea-level rise during the last deglaciation in the Caribbean (Fairbanks, 1989; Bard et al., 1990a) and the Indo-Pacific (Chappell and Polach, 1991; Edwards et al., 1993; Bard et al., 1996). Distinct drowned reef terraces constructed of monospecific shallowwater coral Acropora palmata have been identified off Barbados and used to constrain deglacial sea-levels, but the Indo-Pacific lacks a similarly wide-spread finite coral sea-level indicator (Davies and Montaggioni, 1985). Instead, pioneering work lead by Pirazzoli and Montaggioni (1988) used coral assemblages (especially Acropora robusta

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group) rather than monospecific communities to constrain paleowater depths to within ±6 m in French Polynesia (Bard et al., 1996; Montaggioni et al., 1997; Cabioch et al., 1999a; Camoin et al., 2004). Using these modern comparisons, accurate paleoenvironmental reconstructions can be made, which are important not only for sea-level studies, but also for understanding how reefs and their component coralgal assemblages respond to a variety of environmental perturbations. Several periods of rapid climate and sea-level change have been recognized during the last deglaciation through the identification of punctuated reef growth sequences showing periods of drowning and subsequent regeneration (Blanchon and Shaw, 1995; Montaggioni, 2005). The timing of these reef drowning events is then used to develop a chronology for sea-level rise behavior. Using this method, at least two massive meltwater inputs contributing to accelerated sea-level rise are thought to have occurred during the last deglaciation. A meltwater pulse around 13.8 to 14.7 ka was identified in the Caribbean (MWP-1A by Fairbanks, 1989; Fairbanks et al., 2005), the western Pacific (Hanebuth et al., 2000) and central Pacific (Bard et al., 1996; Webster et al., 2004) that resulted in a rise in sea-level of 15 m in less than 500 years, but evidence from prior drilling in Tahiti remains controversial, as the reef record only extends to 13.8 ka (Bard et al., 1996). A second, smaller meltwater pulse was also identified between ca. 10 and 11 ka in Barbados (Fairbanks, 1989; Bard et al., 1990b; MWP-1B of Fairbanks, 1990; Bard et al., 1996), the Huon Peninsula (Chappell and Polach, 1991) and Mayotte Reef (Colonna et al., 1996), however, recent investigations into previously undated cores from Tahiti reveal evidence to the contrary (Bard et al., 2010). The intervening period between these debated sea-level accelerations, known as the Younger Dryas (12.5 ka, Fairbanks, 1990), saw a brief return to a near glacial climate state. While the search for reef growth hiatuses on Tahiti has received much attention, few detailed studies of coralgal community variability in space and time during periods of growth and drowning have been undertaken. As the last deglaciation was a time of significant sealevel and climate fluctuations, it represents a prime period to observe how coral reefs respond to dramatic environmental perturbations. In conjunction with the known sensitivities of the studied corals and algae, spatial and temporal variability may offer insight into the most influential factors of reef initiation, development and death. As a far field site, removed from the glacio-isostatic influence of ice sheet loading and unloading, and also tectonically stable, Tahiti is an ideal location to study the influence of deglacial sea-level rise on coralgal communities. A series of drill holes (P6–P10) of the reefs offshore Papeete Harbor (Fig. 1) has revealed that reef growth was continuous and coralgal assemblages varied through time during the last 13 ka (Montaggioni et al., 1997; Cabioch et al., 1999a; Bard et al., 2010), but the only evidence for reef growth prior to this time comes from dredged material (15 ka in situ coral, Camoin et al., 2006). For the first time, drilling by the IODP in Sep–Oct 2005 has recovered cores from thirtyseven boreholes from three widely spaced sites that extend the reef record to 16 ka (Camoin et al., 2007a).These new records will allow for an unprecedented investigation of both the stratigraphic and smallscale (meters) to large-scale (island-wide) spatial variations in coralgal assemblages on Tahiti during deglacial sea-level rise. The present study concerns sixteen continuous vertical drill holes at two sites on Tahiti. Here we present a detailed analysis of the deglacial coralgal assemblages during the development of the Tahiti reef. The primary aims of our study are: (1) to document the characteristics of the coral and algal assemblages at the two sites, (2) to reconstruct their paleoenvironmental setting, and (3) to define their stratigraphic and spatial variations and discuss their implications for paleoenvironmental variation during deglacial sea-level rise. 1.1. Study sites The two sites studied lay offshore Tiarei and Maraa, Tahiti, French Polynesia (Central Pacific Ocean, Fig. 1). Tahiti is a tropical intraplate

volcanic island situated at 17°50 S and 149°20 W in the Society Archipelago. Subsidence rates deduced from the ages of subaerial lavas beneath the Pleistocene reef range from 0.15 mm year− 1 (Le Roy, 1994) to 0.25 mm year− 1 (Bard et al., 1996). Weather patterns are seasonal, with the austral summer months bringing heavy rain and occasional cyclones, and the winter months being relatively drier and cooler. Rainfall on Tahiti is variable by location; the west side of the island is the driest and receives an average of 1500 mm year− 1, and the southern and eastern sides may receive up to 4000 mm year− 1 (Crossland, 1928a; Crossland, 1928b; Williams, 1933; Dupont, 1993). Suspended sediments and nutrient flux in the lagoon are also seasonally variable, where Secchi disk depth can be reduced by 50% in the wet months (Gabrie and Salvat, 1985). Dominant winds blow from the northeast or the southeast and create strong swells on the eastern side of the island. Tahiti's modern reef consists of fringing and discontinuous barrier reefs. The outer reef slope is made up of spurs and groves sloping seaward at 20°. Along the south and west coasts, the reef flat is wide and separated from the fringing reef by only a very shallow lagoon, and on the north and east coast the reef flat is very narrow and separated by wide lagoons locally reaching depths of 35 m (Williams, 1933; Dupont, 1993). 2. Methods 2.1. IODP drilling operations and recovery Transects of holes were drilled from three regions around Tahiti using the mission specific platform, the DP Hunter, offshore Faa'a, Tiarei and Maraa (Camoin et al., 2007b), IODP Sites TAH-01A, TAH-02A and TAH-03A respectively (Fig. 1). Water depths at these locations range from 41.6 to 117.5 m. During drilling, the core barrel was advanced in 1.5 m increments, and core depths were measured with ±0.1 m accuracy (Inwood et al., 2008). Cores are 65 mm in diameter and were recovered at depths ranging from 41.6 to 161.8 m. Average recovery exceeds 90% when primary cavities and macroporosity are considered (Inwood et al., 2008). Sixteen holes were analyzed for the purpose of this study. Paired cores are defined as those positioned within 5 to 20 m from one another, and cores may be separated by distances of up to 350 m at a site (Fig. 1, e.g., Maraa). Differences in the depths of Pleistocene substrates of sea floor drilling targets can also vary by 25 to 30 m. Three pairs (M0021A/B, M0023A/B, and M0024A/25B) and one trio (M0009B/D/E) of cores have been examined from Tiarei (Fig. 4). One pair was recovered from the inner ridge (M0023A/B) and the remaining cores were recovered from the outer ridge. Together they form two transects; a landward–seaward transect extends from the inner ridge to the outer ridge, and a NW–SE trending transect spans 200 m parallel to shore (Fig. 1). Seven holes from Maraa were examined, including two pairs (M0015A/B and M0016A/B). Coring in Maraa reached the Pleistocene basement at a variety of depths, between 107 and 123 meters below sea level (mbsl) in the outermost holes (M0015A/B, M0016A/B, and M0018A) and between 85 and 95 mbsl in the innermost holes (M0007A and M0017A). 2.2. Core logging and fossil identification A combination of petrographic thin sections, slabbed core material, and high-resolution digital line-scan images of the archive half of core sections was used during logging. Drilling penetrated two major lithologic units; an upper unit (Unit I) consisting of a deglacial package which is underlain by a lower unit (Unit II), identifiable by visible diagenetic properties of the sediments caused by subaerial exposure and meteoric diagenesis during sea-level lowstand (Camoin et al., 2007b; Thomas et al., 2009; Fujita et al., 2010). All cores investigated herein intersected the contact between Unit I and Unit II, but only detailed logging of Unit I was carried out for this study. Cores were

E. Abbey et al. / Global and Planetary Change 76 (2011) 1–15

3 0 10

18 0

Hole M0025B

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Hole M0009D 1 60

149°10' Hole M0021B

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Moorea

Site M0019 Site M0020

140

Tiarei Site M0009 Site M0021 Site M0023 Site M0024 Site M0025

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Hole M0009E Hole M0009B 149°50'W

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14 24'15"

17 29'30"

Tahiti 17°40'

N Mara a Site M0007 Site M0015 Site M0016 Site M0017 Site M0018

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17°50' 149°33'0"

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Hole M0007A 0

5

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Hole M0015A Hole M001 8A 180

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17°46'0"

Hole M0015B Hole M0016A 140 200

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Fig. 1. Study site locale (1) and locations of drilling in Tiarei (1a) and Maraa (1b).

examined to identify corals, coralline algae, and mollusks, as well as to characterize the distribution, morphology and context of the biota. Coral growth forms were given quantitative definitions as described in IODP Proceedings (Camoin et al., 2007b). In situ corals were distinguished from drilling disturbance or allochthonous rubble using a suite of criteria established by previous drilling studies (Lighty et al., 1982; Montaggioni et al., 1997; Montaggioni and Faure, 1997; Cabioch et al., 1999a,b; Camoin et al., 2001; Webster and Davies, 2003; Camoin et al., 2004). The reliability of these criteria can vary with growth form, but include (1) orientation of well-preserved corallites, (2) orientation of acroporid, pocilloporid, and poritid branches, (3) coral colonies capped by thick (few cm) coralline algal crusts, and (4) the presence of macroscopic and microscopic sediment geopetals in cavities and mollusk chambers and valves. Coral and coralline algae observations were subdivided into 10 cm intervals, rounded to the nearest 5 cm at the bottom of each core section. In order to calculate reef framework volume, each 10 cm length was given a value corresponding to an estimation of the ratio of coralgal material to any surrounding microbialite. The thickest coralline algal crusts within each 10 cm interval were recorded, and the occurrence of vermetid gastropods within the crusts was noted. Corals were described to the lowest taxonomic level in consultation with taxonomic guides and by comparisons to modern specimens

(Veron and Pichon, 1976; Veron and Pichon, 1977, 1979, 1982; Veron and Wallace, 1984; Veron, 1986, 2000; Wallace, 1999). Using a comparison of the biozonation of the fossil corals' modern counterparts, the paleoenvironmental settings were reconstructed. Detailed taxonomic observations of the coralline algae were undertaken using over 400 ultra-thin sections. Since all identified coralline species are living today in Tahiti and other areas of the Pacific Ocean, their present-day environmental distribution (depth range) has also been used to interpret the paleoenvironmental settings of the in situ coralgal frameworks. In all in situ samples the interpreted paleowater depth is the shallowest depth range of the coralline species cooccurring in the sample. We have followed the depth distribution of living corallines indicated by Cabioch et al. (1999b), Payri et al. (2000), and Littler and Littler (2003). 2.3. Radiocarbon dating and X-ray diffraction Samples of coral and encrusting coralline algae were inspected under magnification and mechanically cleaned with a dentil drill and then ultra sonically cleaned in Milli-RO water. Samples were then submerged in 10% H2O2 for 24 h to remove organic carbon. 500– 1000 mg of each coral and coralline algae sample was etched with HCl to a minimum of 40% loss by weight. Sub-samples of 12–20 mg were

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subsequently hydrolyzed and graphitized. Radiocarbon ages were measured by accelerator mass spectrometry (AMS) on the ANTARES facility installed at ANSTO (Fink et al., 2004). AMS ages were converted to calendar years BP using CALIB Rev 5.0.1 (Stuiver and Reimer, 1993) using the marine calibration dataset-marine04.14c (Hughen et al., 2004) and a reservoir deviation of 82 ± 42 (ΔR). Splits of each pre-treated coral sample were powdered for X-ray diffraction (XRD) to quantify contamination and possible carbonate recrystalization. The measurements were carried out using a PANalytical X'Pert Pro Diffractometer with Cu Kα radiation and XRD data were collected over a 2θ range of 5° to 80°. Approximately 50 mg of powdered coral was used for each test and aragonite standards with 0.1, 0.5, 2.0, 10.0 and 20.0% calcite were used for calibration. 3. Results 3.1. Coral taxonomy Twenty-six species from twelve genera in seven scleractinian families were identified from Tiarei and Maraa (Table 1), but due to the nature of the material and the difficulty associated with identifying corals to species level in cores, it is most meaningful to compare observations only to the family or genus level. All twelve identified coral genera are present in Tiarei cores, but Porites and Montipora are very dominant. Taxonomic distribution varies spatially at Tiarei, most notably for Acropora, which are virtually absent from the outer ridge (M0009, M0021, M0024, and M0025), but common on the inner ridge (M0023). Maraa has similar species richness, only lacking the rare Fungia seen in Tiarei cores, but a more even occurrence of coral genera. In addition to Porites and Montipora, Acropora and Pocillopora are also very common genera at Maraa. Again, Acropora is not distributed evenly across all holes at Maraa; it is common in all holes with the exception of M0016B and M0018A. 3.2. Coral assemblages and paleoenvironmental interpretation In situ coralgal framework has been divided into ecological assemblages based on dominant corals and associated secondary corals (Table 2, Fig. 2). Coral growth form (morphology), taxonomy, associated biota (e.g., coralline algae and vermetid gastropods), and in situ coralgal material density were also taken into consideration in the definition and characterization of each coral assemblage. Paleoenvironmental interpretations are based on comparisons with analogous Table 1 Coral taxa identified from Maraa (m) and Tiarei (t). Family ACROPORIDAE Acropora spmt Acropora aculeus?m Acropora cytheream? Acropora gemmiferat Acropora secale?m Montipora sp.mt Montipora aequituberculatamt Montipora tuberculosamt Montipora verrucosamt Montipora cf venosam Family AGARICIIDAE Leptoseris sp.mt Leptoseris explanatam?t Leptoseris solidamt Pachyseris sp.mt Pachyseris speciosamt Pavona sp.mt Pavona explanulatat Pavona maldivensismt Pavona variansmt

Family FAVIIDAE Favia spmt Favia pallida?t Leptastrea sp.mt Leptastrea purpureat Leptastrea transversamt Montastrea sp.mt Montastrea curtamt Family FUNGIIDAE Fungia sp.t Fungia danaet Family POCILLOPORIDAE Pocillopora sp.mt Pocillopora damicornist Pocillopora eydouximt Pocilopora verrucosat Family SIDERASTREIDAE Psammocora sp.mt Family PORITIDAE Porites sp.mt Porites lichen/rusmt Porites lobatamt Porites lobata/solidamt

modern and fossil Indo-Pacific reef communities and discussed in the following paragraphs. Based on this coral composition and comparison with modern reef zonation and ecology in the Indo-Pacific, we identified seven coral assemblages and their paleoenvironments (Table 3). Assemblage 1 (cA1) is dominated by branching (b2 cm) and robust branching (N2 cm) Pocillopora (P. eydouxi), massive (N2 cm) and encrusting (b2 cm) Montipora (e.g., M. aequituberculata and M. tuberculosa), branching and massive Porites, and associated encrusting Porites and massive Faviids (e.g., Montastrea curta). Coralgal frameworks are dense and cm-thick coralline algae are present locally (Fig. 2A). In most of the Indo-Pacific, this community can be found on modern windward reef crests, from the upper forereef to the outer reef flat (Montaggioni, 2005). Fossil and modern robust branching assemblages can be found in reef-edge environments in water depths less than 6 m on Tahiti (Pirazzoli and Montaggioni, 1988; Montaggioni et al., 1997; Sugihara et al., 2006) and Moorea (Bouchon, 1985). Assemblage 2 (cA2) is characterized by massive Porites and minor Montipora. Massive Leptastrea transversa, branching Porites, Acropora and Pocillopora are occasionally associated with this assemblage (Fig. 2B). Framework is very dense and algal crusts are often only thin and localized, but can reach 1 cm maximum thickness. In modern reefs, Porites are commonly found as colonizers where water conditions are poor (low salinity, Moberg et al., 1997; high sedimentation, Veron, 2000). Similar modern Indo-Pacific communities tend to dominate sheltered environments on reef flats, patch reefs, and backreef zones from 0 to 25 m water depth (Done, 1982; Bouchon, 1985; Veron, 1986; Montaggioni et al., 1997; Cabioch et al., 1999a). Assemblage 3 (cA3) is dominated by branching corals, mainly Porites (e.g., P. lichen/rus) and Pocillopora (P. eydouxi), some Pavona maldivensis, and rare encrusting corals (e.g., M. tuberculosa, M. aequituberculata, L. transversa, and Pavona varians) (Fig. 2C). Coralgal frameworks are dense and cm thick crusts of algae commonly form over branch tips. Modern branching communities in the Indo-Pacific are commonly found on semi-exposed to sheltered environments on the mid-forereef, inner reef flat, and backreef zones up to 20 m deep (Montaggioni, 2005). Similar modern branching assemblages on Moorea can be found in less than 10 m water depth (Bouchon, 1985), but fossil assemblages of branching Porites nigrescens on Tahiti occupy more variable water depths to a maximum of 30 m (Cabioch et al., 1999a). Assemblage 4 (cA4) is dominated by robust branching Acropora, commonly with 2 cm thick algae on branch tips (Fig. 2D). Robust Acropora are typically found in high-energy environments on the reef crest and upper reef slope (Done, 1982; Montaggioni and Faure, 1997; Cabioch et al., 1999b). Robust branching communities (though primarily Pocillopora) inhabit the modern reefs of Tahiti and Moorea in less than 6 m water depth (Bouchon, 1985; Sugihara et al., 2006). Robust fossil assemblages that dominate the Papeete cores have been interpreted as indicative of similarly shallow paleoenvironments in less than 10 m water, and perhaps less than 6 m (Pirazzoli and Montaggioni, 1988; Montaggioni and Camoin, 1993; Montaggioni et al., 1997; Cabioch et al., 1999a,b). Assemblage 5 (cA5) is characterized primarily by abundant tabular or tabular-branching Acropora (e.g., A. cytherea and A. secale), branching Porites, and Pocillopora (Fig. 2E). Encrusting corals are also common and diverse (e.g., M. cf aequituberculata, M. venosa, L. cf transversa, and P. varians). Corals and algae form relatively dense frameworks with algal crusts reaching 4 cm thickness locally. Modern tabular-branching communities commonly occur in semi-exposed or sheltered environments on the upper and mid-forereef, reef flat, and backreef slope no deeper than 20 m, but are commonly between 2 and 15 m water depth in Tahiti and the Indo-Pacific (Done, 1982; Montaggioni, 2005; Sugihara et al., 2006). This fossil assemblage is likely to represent a lowerenergy paleoenvironmental setting in 5–15 m water depth on Tahiti (Montaggioni et al., 1997; Cabioch et al., 1999a).

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Table 2 Coral assemblages and their paleoenvironmental interpretations. Coral assemblage

Key components

Additional components

Assemblage 1 cA1

Massive and encrusting Montipora (e.g., M. aequituberculata, M. tuberculosa), robust Pocillopora (e.g., P. eydouxi), branching Porites, and associated encrusting Porites and Faviids (e.g., Montastrea curta) Massive Porites, Montipora, associated branching Porites, Acropora, and Pocillopora Branching Porites (e.g., P. lichen/rus), Pocillopora, Pavona maldivensis, associated encrusting Porites, Montipora (e.g., M. tuberculosa, M. aequituberculata), and Faviids (e.g., L. transversa) Robust branching Acropora and associated Pocillopora Tabular and rare branching Acropora (e.g., A. secale), branching and encrusting Porites, Montipora (e.g., M. cf aequituberculata, M. venosa), Faviids (e.g., L. cf transversa), Agariciids (e.g., P. varians), and associated Pocillopora Branching and encrusting Porites (e.g., P. lobata), Montipora (e.g., M. aequituberculata, M. tuberculosa, M. verrucosa), Agariciids (e.g., Pavona maldivensis, P. varians, rare Pachyseris speciosa), Faviids (e.g., L. transversa, M. curta). Occurs with tabular Acropora (e.g., Acropora cytherea) and massive Porites in Maraa only Montipora (e.g., M. tuberculosa), Agariciids (e.g., P. varians, Pachyseris sp., Leptoseris solida.), Faviids (e.g., M. curta, L. transversa)

Algae up to 3 cm thick, commonly with Tiarei vermetid gastropods.

Less than 10 m, high energy

Thin algal crusts. Vermetid gastropods uncommon. Algae commonly thick, up to 4 cm. Vermetid gastropods commonly associated. Algae up to 2 cm thick common. Thick algae is localized, reaching 4 cm. Vermetid gastropods in the thickest crusts. Algae commonly thin with localized thickening up to 4 cm. Vermetid gastropods uncommon.

All sites

Less than 25 m, turbid Less than 30 m

Maraa All sites

Less than 10 m Less than 20 m

All Sites

Less than 30 m

All sites

Generally deeper than 20 m or turbid

Assemblage 2 cA2 Assemblage 3 cA3

Assemblage 4 cA4 Assemblage 5 cA5

Assemblage 6 cA6

Assemblage 7 cA7

Assemblage 6 (cA6) is comprised of a very diverse suite of corals and growth forms. Branching and encrusting Porites (e.g., P. lobata) and Montipora (e.g., M. aequituberculata, M. tuberculosa, and M. verrucosa) are common, as are Pavona (e.g., P. maldivensis and P. varians) and Faviids (e.g., L. transversa and M. curta) (Fig. 2F). Pachyseris speciosa is present, but rare. Less dense frameworks are common, and algae range from millimeters to centimeters thick. This assemblage is somewhat variable between sites, where in Maraa minor tabular Acropora and massive Porites are also present. These taxa have broad environmental distributions and tolerate a wide range of hydrodynamic energy regimes. The relatively high number of coral species present in this assemblage is typical of the high species richness found in water depths of 10–20 m on the outer reef slope of Moorea (Bouchon, 1985), however, analogous modern communities have not been identified from Tahiti. Consequently, the paleoenvironmental setting of this assemblage can only be constrained to semi-exposed to well-protected environments in water depths less than 30 m. Assemblage 7 (cA7) is dominated by encrusting corals. Montipora tuberculosa, P. varians, M. curta, L. transversa, and well-developed colonies of P. speciosa are common (Fig. 2G). Leptoseris solida can also be observed. Associated coralline algae can range from thin and/or laminated up to 4 cm thick. This assemblage can be found on the modern outer reef slope in 30 m water depth in Moorea (Bouchon, 1985) and Tahiti (Sugihara et al., 2006). However, in modern IndoPacific reefs, encrusting corals dominate a variety of environments, ranging from deep outer reef slopes in excess of 20 m water depth where irradiation is minimal, to high-energy reef crests and slopes in less than 15 m water depth where water is turbid (Montaggioni, 2005). 3.3. Coralline algal assemblages and paleoenvironmental interpretation Coralline red algae are common components of deglacial reefs in the studied cores. Corallines are observed growing on or intergrown with corals and other encrusting organisms in reef framework (Fig. 2A–G). Twenty-eight species of coralline algae have been identified in all the studied cores, but coralline species richness is not evenly distributed in the different sites and throughout cores. Plants with very thin laminar thalli are commonly microtized, with no diagnostic characters preserved and cannot usually be identified. Therefore, they have not been taken into account in the species richness comparisons. All algal genera and species identified in the cored sequences are still living in French Polynesia and other IndoPacific reefs (Cabioch et al., 1999b; Littler and Littler, 2003). These living coralline algae species show depth-related habitat preferences

Algae are thin or laminated.

Distribution Paleoenvironmental interpretation

All sites

and some of them have relatively narrow depth ranges in their modern distribution. The depth ranges of four identified fossil coralline algae assemblages can be used independently from the corals to interpret the paleowater depth of the studied reef framework deposits (Table 3). Assemblage 1 (aA1) is characterized by centimeter thick plants of Hydrolithon onkodes (Fig. 3A) and extends to 10 m depth. Thick crusts of this species are very common on coral colonies both in present-day and previously cored deglacial reefs off Papeete (Montaggioni et al., 1997; Cabioch et al., 1999a). Other species, such as Hydrolithon gardineri, Lithophyllum kotschyanum and Pneophyllum conicum (=Negoniolithon conicum) are also common in this shallow water assemblage. Assemblage 2 (aA2) is characterized by species such as H. gardineri, Hydrolithon munitum, Hydrolithon reinboldii and P. conicum occurring with thin crusts of H. onkodes, which can extend from 0 to 20 m (Fig. 3B). Assemblage 3 (aA3) is characterized by Lithophyllum prototypum (reported as Titanoderma tessellatum by other authors such as Cabioch et al., 1999b), knobby plants of Mesophyllum erubescens, and Lithothamnion prolifer (Fig. 3C). These species mainly occur between 15 and 30 m, but the latter can live in deeper waters, down to 40–50 m (Keats et al., 1996). Assemblage 4 (aA4) is characteristic of paleoenvironments below 20–25 m, and is defined by the lack of shallower coralline assemblages and the dominance of frameworks of foliose plants of Mesophyllum funafutiense growing on or intergrown with laminar corals, and thin encrusting plants of Lithoporella melobesioides, with occurrences of Hydrolithon breviclavium and Lithothamnion species (Fig. 3D). 3.4. Radiocarbon dating Fourteen specimens were selected from Maraa for radiocarbon dating, including six corals and eight crusts of coralline algae. XRD analyses of coral specimens confirm very low levels of calcite in all but the oldest sample (Table 4). The radiocarbon results confirm a postglacial timing of reef development and are consistent with previously published radiometric dating results from Tiarei (Fig. 4). 3.5. Spatial, stratigraphic, and chronologic changes in coralgal assemblages The purpose of surveying on both small scales (meters) and large scales (island-wide) is to establish baseline variability. With an understanding of small scale variation, the significance of large scale

6

E. Abbey et al. / Global and Planetary Change 76 (2011) 1–15

Fig. 2. Coral reef limestone showing principle components of (A) Assemblage 1 corals dominated by Montipora (1) and Pocillopora (2); (B) Assemblage 2 corals dominated by massive Porites (1); (C) Assemblage 3 corals dominated by branching corals (e.g., Porites (1) and Pocillopora) and very minor associated encrusting corals (e.g., Porites (2)); (D) Assemblage 4 dominated by robust branching Acropora (1); (E) Assemblage 5 corals dominated by tabular Acropora (1), branching corals (e.g., Pocillopora) (2), and encrusting and platy corals (e.g., Porites (3) and Agariciids (4)); (F) Assemblage 6 corals dominated by encrusting (1) and branching (2) Porites, Montipora, Agariciids (3) and Faviids; (G) Assemblage 7 corals dominated by Pachyseris speciosa, Pavona varians (1) and Montipora (2).

variation, or lack thereof, can be identified. On Tahiti, closely and widely spaced cores show a range of stratigraphic coralgal assemblage variability between them. Published U/Th and 14C chronology can be

found in Asami et al. (2009, corals), Heindel et al. (2009, corals and microbialites), Inoue et al. (2010, corals) and Westphal et al. (2009, microbialites). More detailed chronology has been undertaken for

E. Abbey et al. / Global and Planetary Change 76 (2011) 1–15

7

Table 3 Algal assemblages and their paleoenvironmental interpretation. Algal assemblage

Key components

Additional components

Maximum depth

Assemblage 1 aA1

Thick Hydrolithon onkodes (locally Mastophora species)

10 m

Assemblage 2 aA2

Thin H. onkodes, H. gardineri, P. conicum

Assemblage 3 aA3

Mesophyllum erubescens (depth range 15–30 m), L. prototypum Mesophyllum funafutiense, Hydrolithon breviclavium, Lithoporella

Hydrolithon gardineri, Hydrolithon murakoshii, Hydrolithon munitum, Hydrolithon reinboldii, Pneophyllum conicum, Neogoniolithon frutescens, Spongites sulawensis, Spongites fruticulosus, Spongites sp., Lithophyllum cuneatum, Lithophyllum insipidum, Lithophyllum kotschyanum, Lithophyllum incrassatum, Lithophyllum prototypum, Lithophyllum gr. Pustulatum H.murakoshii, H. munitum, Hydrolithon rupestre, N. frutescens, Spongites sp., L. insipidum, L. kotschyanum, Lithophyllum prototypum, L. incrassatum, L. gr. pustulatum, Lithothamnion prolifer Lt. prolifer, H.murakoshii, H. munitum, H. rupestre, L. insipidum, L. incrassatum, L. gr. pustulatum, H. reinboldii, L. gr. pustulatum, Lithothamnion sps., Sporolithon sps.

Assemblage 4 aA4

sea-level reconstructions (Deschamps et al., in prep.), reef accretion history (Camoin et al., in prep.) and microbialite development (Seard et al., 2010). Details of 14C dating performed for this study can be found in Table 4. 3.5.1. Tiarei 3.5.1.1. Seaward core transect. Coring on the outer ridge reached the Pleistocene basement at ca. 119 mbsl (meters below sea-level) in four holes — M009D, M009B, M0024A, and M0025B,and the basement was reached at ca. 111 mbsl in three holes — M009E, M0021A, and M0021B (Fig. 4). The first corals to populate the basement substrate in every hole on the outer ridge, regardless of timing of initiation, are Montipora (e.g., M. aequituberculata and M. tuberculosa), Porites and Pocillopora (e.g., P. eydouxi) (cA1). This assemblage has a stratigraphic thickness of 1 to 6 m with thick and thin coralline algal crusts of H. onkodes and H. gardineri (algae Assemblage 1 and 2). All communities forming on the ca. 119 mbsl substrate transition into extensive massive Porites communities (cA2) ranging from 2 to 10 m in stratigraphic thickness at ca. 118 mbsl and 15.3 ka. Thick crusts of H. onkodes associated with vermetid gastropods also characterize this stratigraphic interval. No massive Porites communities (cA2) develop on the 111 mbsl basement substrate following the initial coral assemblage. Instead, a dense framework of branching Porites (cA3) and thick and thin crusts of H. onkodes (aA1 and aA2) extend for 5 m or more. At 115–110 mbsl and ca. 14.8 ka, massive Porites in the deeper holes are replaced by the same dense framework of branching Porites as is seen in shallower holes. In all outer ridge holes, with the exception of M0009D where a significant gap in recovery precludes the assessment of the presence or absence of Assemblage 5 in this stratigraphic interval, branching Porites (e.g., P. lichen/rus) continues and/or alternates with massive Porites (e.g., P. lobata/solida). Both communities are succeeded by a diverse coral assemblage of branching and encrusting Porites, Montipora, Agariciids, and Faviids (cA6) at depths ranging from 110 to 100 mbsl in association with thick and thin crusts of H. onkodes (aA1). With the exception of M0024A, cA6 is then replaced by the ultimate succession of encrusting and platy corals (e.g., L. transversa, Pachyseris, Pavona) (cA7). Corallines associated with this assemblage are thin and laminar crusts of M. funafutiense and Lithoporella (aA4). Deeper holes M0009B/D/E and M0025B transition into this final assemblage 98 to 108 mbsl and development of this assemblage is variable, from 1 to 4 m in thickness. In shallower holes (M0021A/B), the transition into cA7 occurs at ca. 85 mbsl and reef growth terminates at ca. 82 mbsl. 3.5.1.2. Landward hole transect. Holes M0023A and M0023B on the inner ridge reached the Pleistocene basement between 95 and 98 mbsl (Fig. 4). The first community to occupy the substrate is a dense framework of branching Porites and Pocillopora (e.g., P. eydouxi) (cA3) and up to 2 cm thick crusts of H. onkodes with Mastophora (aA1) and associated vermetid gastropods. This assemblage is extensive, up to

20 m

30 m Greater than 20–25 m

15 m thick, and continues until ca. 81 mbsl. Tabular Acropora develops in M0023B (cA5) and alternates with cA4. Acropora does not become dominant in M0023A, where instead a diverse suite of branching Porites and encrusting Montipora and Agariciids (cA6) alternates with massive Porites (Assemblage 2) ca. 12.6 ka. H. onkodes and Mastophora pacifica (aA1 and aA2) are common throughout both holes until ca. 73 mbsl. An encrusting and platy coral community (e.g., L. transversa and P. varians) (cA7) associated with M. funafutiense (aA4) develops in both holes at ca. 73 mbsl ca. 11.2 ka and growth continues until the tops of holes at ca. 67 mbsl. 3.5.2. Maraa 3.5.2.1. M0016 and M0018. Massive P. lobata communities (cA2) initiated in three outermost holes (M0016A, M0016B, and M0018A) on the basement substrate at ca. 120 mbsl ca. 15–14 ka (Fig. 5). These communities are associated with thin crusts of H. onkodes typical of aA2 and persist through several meters of core to 115 to 110 mbsl. At 115 mbsl massive Porites is succeeded by branching Porites and P. maldivensis with associated M. cf verrucosa (cA3) in M0016A and M0018A, and branching and encrusting Porites and Montipora with associated P. varians (cA6) in M0016B. Thick and thin crusts of H. onkodes (aA1 and aA2) and vermetid gastropods are common. cA3 and cA6 alternate for 15 m through these outermost holes and algal assemblages aA1 and aA2 reach thicknesses up to 6 cm. At ca. 100 mbsl, growth of cA6 and algal assemblage aA2 terminate in M0016B without the development of an encrusting community (i.e., cA6) or deep-water corallines (i.e., aA4). Branching colonies of Porites, A. cytherea and P. maldivensis continue through M0016A and M0018A for another 10 m. At ca. 90 mbsl, corals in M0016A and M0018A become dominated by encrusting and platy forms of Montipora and P. varians (cA6 and cA7) with only minor branching corals. Coralline algae crusts are thinner and Mesophyllum is dominant in M0016A, but H. onkodes continues to be associated with the corals in cA7 until ca. 85 mbsl. At ca. 85 mbsl, Pachyseris, L. solida and P. varians are dominant in both holes with associated M. curta, and thin crusts of M. funafutiense and Lithoporella are common (aA4). Reef growth terminates in both holes at 81 mbsl ca. 8.8 ka. 3.5.2.2. M0015. At ca. 110 mbsl and ca. 13.9 ka, reef growth is initiated in M0015A by branching Porites and robust branching Pocillopora (cA3) with thick crusts of H. onkodes and Mastophora and in M0015B by massive Porites (cA2) and thin crusts of H. onkodes (aA2) (Fig. 5). Massive P. lobata remains dominant in M0015B from 108 to 106 mbsl, but then reverts to branching Porites and robust branching Pocillopora, which continues with up to 4 cm thick crusts of H. onkodes in both M0015A and M0015B to ca. 90 mbsl. A brief interval of tabular Acropora (cA5) interrupts this branching Porites assemblage at ca. 97 mbsl in both holes. At ca. 90 mbsl and ca. 12.0 ka, coral growth becomes dominated by tabular Acropora, branching Porites, robust Pocillopora (cA5) and

8

E. Abbey et al. / Global and Planetary Change 76 (2011) 1–15

Fig. 3. (A) Sample 5B4 showing a thick plant of Hydrolithon onkodes with partly buried thallus of Lithophyllum cuneatum characteristic of very shallow waters (b 10 m, Assemblage 1). (B) Sample 18A (4) showing knobby plants of Mesophyllum erubescens that typically extend down to 25 m (Assemblage 3). (C) Sample 18A3 (4) showing laminar, terraced plants of Lithophyllum prototypum (also referred to as Titanoderma tessellatum) that mainly occur in the shallower 25 m (Assemblage 3). (D) Sample 15B1 showing Mesophyllum funafutiense 1 forming frameworks of foliose plants typical of deep water and shade assemblages (Assemblage 4).

crusts of H. onkodes/H. gardineri and N. conicum up to 1 cm thick. Tabular Acropora extends continuously through M0015A until ca. 80 mbsl, but is interrupted in short intervals in M0015B at ca. 87 and ca. 83 mbsl where it is replaced by branching and encrusting Porites and Montipora (cA6) and massive Porites (cA2). Associated corallines within this interval include L. prolifer, M. funafutiense and Lithoporella (aA3 and aA4). Tabular corals (cA5) resume with thick crusts of H. onkodes (aA1) at ca. 81 mbsl in M0015B until ca. 79. At ca. 79 mbsl, corals become dominated by Leptoseris and P. speciosa with P. varians, Montipora (cA7) and thin (1–2 mm) crusts of coralline algae dominated by M. funafutiense and laminar Lithothamnion (aA4). Reef growth is terminated ca. 73 mbsl and 9.2–8.6 ka. 3.5.2.3. M0007 and M0017. Reef growth in the innermost holes, M0007A and M0017A, initiated on the Pleistocene substrates ca. 85 and ca. 95 mbsl respectively (Fig. 5). A community of massive M. curta, L. cf transversa and branching Pocillopora and Porites (cA1) is the first to colonize the basement in M0017A ca. 13.2 ka. Branching P. lichen/rus

(cA3) alternates with massive Porites (cA2) and a brief interval of tabular Acropora (cA5) until ca. 85 mbsl. Associated algae reach 2 cm thickness and consist of H. onkodes, H. gardineri and Mastophora (aA1) with vermetid gastropods locally. Reef growth in M0007A is initiated by robust Pocillopora (cA3) and associated with 2 cm thick crusts of coralline algae and vermetid gastropods. In both innermost holes, corals transition to a tabular Acropora dominated community with robust Pocillopora and branching Porites (cA5). A distinct community of exclusively robust branching Acropora (cA4) develops from 82 to 78 mbsl (ca. 12.2 ka) and 77 to 73 mbsl (ca. 12.9 ka) in M0017A and M007A respectively, above which reef growth returns to tabular and branching Acropora (A. secale) with branching Porites, Pocillopora and minor encrusting corals (M. cf venosa, L. transversa, and P. varians) (cA5). This community extends until ca. 70 mbsl in hole M0017A, throughout which thin crusts of H. onkodes (aA2) overgrown by Mesophyllum, Lithothamnion and Lithoporella develop. Corals transition into an encrusting assemblage of Montipora and P. varians (cA7) with thin crusts of M. funafutiense, Lithothamnion and Lithoporella (aA4)

E. Abbey et al. / Global and Planetary Change 76 (2011) 1–15

9

Table 4 Summary of coral and algal radiocarbon dating results and calibration. IODP code

ANSTO lab code

14

C agea

14 C error

Corrected error

Median calibrated agea

2σ calibrated age rangea

Material

17A4R1_1–3 15B2R1_57–65 18A1R1_16–22 15A2RCC_12–14 15A20R1_61–67 17A18R1_44–58 7A33R1_63–69 17A21R1_16–19 16A31R1_35–43 15B37R1_57–63 15A36R1_37–42 16B17R1_16–23 18A21R1_30–33 16B23R1_65–70

OZM176 OZM182 OZM178 OZM168 OZM169 OZM172 OZM183 OZM177 OZM173 OZM171 OZM170 OZM174 OZM179 OZM175

5565 8200 8350 8640 10,740 10,820 11,480 11,770 12,410 12,470 12,580 12,590 12,730 13,210

± 50 ± 60 ± 60 ± 70 ± 70 ± 80 ± 70 ± 70 ± 90 ± 80 ± 80 ± 80 ± 80 ± 90

± 131 ± 146 ± 146 ± 163 ± 163 ± 181 ± 163 ± 163 ± 199 ± 181 ± 181 ± 181 ± 181 ± 199

5857 8598 8809 9202 11,994 12,159 12,937 13,171 13,787 13,848 13,948 13,957 14,128 15,007

5681–6011 8406–8846 8589–8995 9001–9402 11,632–12,354 11,832–12,404 12,841–13,081 12,993–13,304 13,549–14,017 13,666–14,042 13,765–14,143 13,770–14,154 13,860–14,605 14,597–15,403

Coral Coralline Coral Coral Coralline Coralline Coralline Coralline Coralline Coral Coralline Coralline Coral Coral

a b

algae

algae algae algae algae algae algae algae

Description

Percent calcite

P. varians Thin crustsb (2 mm) P. varians L. solida Thick crusts (1 cm) Very thick crusts (N1 cm) Very thick crusts (N1 cm) Thick crusts (1 cm) Very thick crusts (N1 cm) P. lobata Very thick crusts (N1 cm) Thick crusts (1 cm) P. rus(?) P. lobata

b 1% N/A b 1% b 1% N/A N/A N/A N/A N/A b 1% N/A N/A b 1% 2–3%

Years BP. 15B2R1_57–65 Coralline algae species include Mesophyllum funafutiense(?), Lithoporella, laminar Lithothamnion, H. murakoshii(?), H. reinboldii and Peyssonnelia.

they are replaced by 1 m of branching Porites and Pocillopora rubble at the top of the hole.

which develop until reef growth terminates at ca. 60 mbsl ~5.9 ka. Tabular Acropora develops in hole M0007A until 64.5 mbsl where corals transition over 1 m into massive Porites (cA2) with L. prolifer and M. erubescens (aA3) and thin crusts of Mesophyllum and Lithoporella. Massive Porites alternates with encrusting and branching Porites, Pocillopora, and Montipora (cA6) until ca. 53 mbsl. Thin coralline algal crusts of Mesophyllum and Lithothamnion (aA4) replace aA3, and encrusting Porites, M. tuberculosa, P. varians and Leptastrea (cA7) replace cA6. In situ corals and algae develop until ca. 45 mbsl, where 65

4. Discussion 4.1. Integration of coralline and coral interpretations In most cases, coralline assemblage paleoenvironmental interpretation is consistent with the associated coral assemblage paleoenvironmental

Coral assemblages

Coralline algal assemblages

cA7, encrusting Pachyseris speciosa, Leptoseris solida and Montipora. Thin coralline algal crusts.

70

aA4, Mesophyllum funafutiense intergrown with laminar corals, thin encrusting Lithoporella melobesioides. aA3, knobby Mesophyllum erubescens, Lithophyllum prototypum and Lithothamnion prolifer. aA2, thin crusts of Hydrolithon onkodes with H. gardineri, H. munitum, H. reinboldii, and Pneophyllum conicum.

cA6, encrusting and branching corals. Thick and thin coralline algal crusts. cA5, encrusting, branching, and tabular corals. Thick and thin coralline algal crusts cA3, branching Porites and robust Pocillopora. Thick coralline algal crusts.

75

aA1, thick crusts of Hydrolithon onkodes. Coralgal framework percent (Grey, 0-100%) and thickness of encrusting coralline algae (Red, 0-6cm).

cA2, massive Porites. Thin coralline algal crusts.

80

cA1, robust Pocillopora and Montipora. Thick and thin coralline algal crusts.

V

Associated Vermetid gastropods

Lithology 85

Coral-algal fragments and/or microbialite. Unit II, older Pleistocene reef

90

mbsl

95

100

105

23A 23B Inner Ridge

110

115

120

125

21A

21B

9E

9D 9B Outer Ridge

24A

25B

130 Fig. 4. Cores retrieved from Tiarei: Stratigraphic distribution of coral and algal assemblages, algae thickness, and coralgal framework density. Coral assemblages are defined by associated species/genera/families, growth form and framework density. Algae and framework observations are averaged in 10 cm intervals; algae thickness is recorded as the thickest crust in a given interval, and framework values are the average of a 10 cm interval. See Tables 3 and 4 for complete coral and algal assemblage descriptions.

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E. Abbey et al. / Global and Planetary Change 76 (2011) 1–15

Coral assemblages

Coralline algal assemblages

cA7, encrusting Pachyseris speciosa, Leptoseris solida and Montipora. Thin coralline algal crusts.

40 45 50

cA6, encrusting and branching corals. Thick and thin coralline algal crusts.

aA3, knobby Mesophyllum erubescens, Lithophyllum prototypum and Lithothamnion prolifer.

cA5, encrusting, branching, and tabular corals. Thick and thin coralline algal crusts.

aA2, thin crusts of Hydrolithon onkodes with H. gardineri, H. munitum, H. reinboldii, and Pneophyllum conicum. aA1, thick crusts of Hydrolithon onkodes.

cA4, robust branching Acropora. cA3, branching Porites and robust Pocillopora. Thick coralline algal crusts.

55

Coralgal framework percent (Grey, 0-100%) and thickness of encrusting coralline algae (Red, 0-6cm).

cA2, massive Porites. Thin coralline algal crusts.

60

aA4, Mesophyllum funafutiense intergrown with laminar corals, thin encrusting Lithoporella melobesioides.

V

5.86

9.8

Associated Vermetid gastropods

cA1, robust Pocillopora and Montipora. Thick and thin coralline algal crusts.

65

Lithology Coral-algal fragments and/or microbialite.

70

Unit II, older Pleistocene reef 8.60 9.20

75 80

12.2

mbsl

8.81 12.9

85

12.2

90 12.0 13.2

95

17A

7A 100

Landward

105 13.9

13.9

13.4

110 13.8

14.0

115

14.1

120 15.0

125

15A

15B

130

16A

16B

18A

Seaward

Fig. 5. Cores retrieved from Maraa: Stratigraphic distribution of coral and algal assemblages, algae thickness, and coralgal framework density. Coral assemblages are defined by associated species/genera/families, growth form and framework density. Algae and framework observations are averaged in 10 cm intervals; algae thickness is recorded as the thickest crust in a given interval, and framework values are the average of a 10 cm interval. See Tables 2 and 3 for complete coral and algal assemblage descriptions.

interpretation (e.g., thick crusts of shallow-water H. onkodes [aA1] are associated with shallow-water robust branching Acropora [cA4], and deep-water L. melobesioides and M. funafutiense [aA4] are associated with deep-water P. speciosa and Leptoseris [cA7]; Figs. 6 and 7). However, algal species typical of deeper assemblages may occur with those characteristic of shallower depths in the same sample. In these instances, the maximum depth range of the shallowest coralline present defines coralline assemblages and their paleoenvironmental significance. In samples from the studied holes, species typical of the deepest-water assemblage (aA4), such as M. funafutiense and L. melobesioides, can appear overgrowing species characteristic of aA1–3 or encrusting the same coral branch on a different side, usually immediately predating microbial crusts. As light penetration is one of the major controlling factors in coralline distribution (Adey, 1979; Adey, 1986), the presence of crevices, caves and cavities influence species distribution in a similar manner to water depth. Shade habitats are dominated by the same corallines as those living in open deep environments. These species can be found at the same depth as those exclusive to shallow water but in darker habitats. Similarly, shallowwater species can be overgrown by shade species when the framework substrate in which they grew becomes overshadowed by new coral growth. Therefore, only the algal assemblage indicative of the shallowest range for the paleowater depth interpretation is relevant to the overall coralgal paleoenvironmental interpretation.

4.2. Coralgal assemblage variations in space Maraa and Tiarei coral assemblages show distinct patterns in spatial distribution that appear to be controlled by the depth and nature of the Pleistocene basement and proximity to the island. Massive Porites are common in outer cores in both Tiarei (e.g., M0024A/25B; Fig. 4) and Maraa (e.g., M0015A/B and M0016A/B; Fig. 5) where they form thick sections, yet are rare and/or less developed in inner cores. Porites species, especially domal forms, tend to be very hardy and resistant to low temperature, low salinity, high terrigenous input and reduced water circulation (Marshall and Orr, 1931; Manton, 1935; Wells, 1954; Scoffin and Stoddart, 1978; Martin et al., 1989; Schlöder and D'Croz, 2004). Porites are often found at the base of cores retrieved from the Great Barrier Reef, where it is interpreted as indicating a lag in initial colonization due to locally adverse conditions (Davies and Hopley, 1983; Hopley et al., 2007). Inimical conditions on the outer edge of the reef may have been caused by the resuspension of sediments during the early stages of sea-level rise, creating an environment too harsh for more sensitive genera, such as Acropora (van Woesik and Done, 1997; Loya et al., 2001). Low salinity and poor water quality may have also been exacerbated at Tiarei where the island's largest river and drainage basin (Papenoo R.) is responsible for the removal of 24.6× 10− 2 km3 kyr− 1 of debris — more than ten times the erosion rate of drainage basins near Maraa (Hildenbrand et al., 2008). Fossilized

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reef framework dominated by branching Porites (cA3), which developed in Maraa inner sites before the dominance of Acropora. Abundance of crustose corallines in the Great Barrier Reef strongly depends on sediment influx and water clarity (Fabricius and De'ath, 2001). Similarly, in Mediterranean Messinian reefs, species richness is much higher in reefs facing the open oceans than in reefs in intermontane basins affected by river discharge of terrigenous sediment (Braga et al., 2009). The high species richness of corallines in Maraa observed to be associated with the low-tolerance Acropora assemblage (cA5) in cores supports the notion that these algae were sensitive to the poor water quality of Tiarei during deglaciation.

microbialites that encase the corals from the last deglaciation contain more terrestrial volcanoclastic grains at Tiarei than Maraa, suggesting this is also the trend historically (Camoin et al., 2007a; Westphal et al., 2009). The reduced effect of river discharge in Maraa is apparent by the frequency of tabular and branching Acropora (cA5) in cores (e.g., M0007A, M0017A, and M0015A/B; Fig. 5) and may also play an important role in the differential diversity observed between the northeastern and southwestern sides of the island. The total species richness of coralline algae in the deglacial reefs in Tahiti, twenty-eight species, resembles the highest records of present-day reefs in the Pacific and Indian oceans. This number only refers to coralline species with thalli thicker than 20 μm (see Results, Section 3.3). Adey et al. (1982) reported twenty-seven species in the Hawaiian Islands (sampling down to 85 m); Verheij (1994) found twenty species in the upper 65 m in the Spermonde Archipelago in Indonesia; Iryu et al. (1995) identified nineteen species (sampling down to 50 m) in the Ryukyu Islands; and South and Skelton (2003) and N'Yeurt et al. (1996)) reported twenty-one and seventeen species, respectively, from the Fiji Islands with no indication of sampling depth limit. The reported species numbers in present-day reef areas are patently affected by taxonomic procedures and sampling depth (and probably the surveyed area) and, thus, other accounts record substantially lower species richness. There is a markedly higher coralline algal diversity in the Acroporadominated paleoenvironments in the deglacial reefs in Tahiti. A total of twenty-three species can be identified in samples within the encrusting coral of assemblages cA4 and cA5 in Maraa, while only sixteen species occur in coeval reef framework in Tiarei (Table 5). In a similar pattern, only twenty coralline species have been found in the

4.3. Coralgal assemblage variations in time Coralgal assemblage variations occur as vertical transitions from cA1 to cA7 and aA1 to aA4. Reverse transitions occur, but only between cA2 to cA6 and aA1 and aA2. Based on our understanding of the modern analogs of the coralgal assemblages, these community transitions within a core may represent the response of reef growth to changing paleoenvironmental conditions (e.g., sea-level rise puts communities at greater depth leading to dominance of depth-tolerant coralgal assemblages), but vertical assemblage transitions may also be produced by ecological succession and vertical reef accretion, or lateral growth during sea-level still stands (backstepping and/or progradation, i.e. Walther's Law, described in Webster and Davies, 2003). Individual assemblages form extensive vertical intervals within cores at all sites, suggesting long periods of stable paleoenvironmental conditions on Tahiti. For example, branching Porites (cA3) develops through more than 12 m of nearly uninterrupted core recovery in

Coral assemblages 65

Paleowater depth (m) 0 10 20 30+

Coralline algal assemblages aA4, Mesophyllum funafutiense intergrown with laminar corals, thin encrusting Lithoporella melobesioides. aA3, knobby Mesophyllum erubescens, Lithophyllum prototypum and Lithothamnion prolifer.

cA7, encrusting Pachyseris speciosa, Leptoseris solida and Montipora. Thin coralline algal crusts.

0 10 20 30+

cA6, encrusting and branching corals. Thick and thin coralline algal crusts. cA5, encrusting, branching, and tabular corals. Thick and thin coralline algal crusts

70

75

aA2, thin crusts of Hydrolithon onkodes with H. gardineri, H. munitum, H. reinboldii, and Pneophyllum conicum.

cA4, robust branching Acropora.

aA1, thick crusts of Hydrolithon onkodes.

cA3, branching Porites and robust Pocillopora. Thick coralline algal crusts.

Associated Vermetid gastropods

V

Lithology

cA2, massive Porites. Thin coralline algal crusts.

80

0 10 20 30+

0 10 20 30+

Coral-algal fragments and/or microbialite.

cA1, robust Pocillopora and Montipora. Thick and thin coralline algal crusts.

Unit II, older Pleistocene reef

85

0 10 20 30+

90

95

mbsl

0 10 20 30+

100

105

0 10 20 30+

0 10 20 30+

23A 23B Inner Ridge

0 10 20 30+

110 2

115

120

125

21A

21B

9E

9D

9B

24A

25B

Outer Ridge 130 Fig. 6. Interpreted paleowater depth intervals in cores from Tiarei. Water depths are based on published accounts of fossil and modern Indo-Pacific reefs.

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E. Abbey et al. / Global and Planetary Change 76 (2011) 1–15

Coral assemblages 40 Paleowater depth (m) 0

Coralline algal assemblages

cA7, encrusting Pachyseris speciosa, Leptoseris solida and Montipora. Thin coralline algal crusts. cA6, encrusting and branching corals. Thick and thin coralline algal crusts. cA5, encrusting, branching, and tabular corals. Thick and thin coralline algal crusts.

10 20 30+

45 50

cA4, robust branching Acropora.

55

cA3, branching Porites and robust Pocillopora. Thick coralline algal crusts.

0

10 20 30+

aA1, thick crusts of Hydrolithon onkodes. Coralgal framework percent (Grey, 0-100%) and thickness of encrusting coralline algae (Red, 0-6cm).

cA2, massive Porites. Thin coralline algal crusts.

60

aA4, Mesophyllum funafutiense intergrown with laminar corals, thin encrusting Lithoporella melobesioides. aA3, knobby Mesophyllum erubescens, Lithophyllum prototypum and Lithothamnion prolifer. aA2, thin crusts of Hydrolithon onkodes with H. gardineri, H. munitum, H. reinboldii, and Pneophyllum conicum.

V

Associated Vermetid gastropods

cA1, robust Pocillopora and Montipora. Thick and thin coralline algal crusts.

Lithology

65

Coral-algal fragments and/or microbialite. Unit II, older Pleistocene reef

70

0

10 20 30+

0

10 20 30+

75 0

mbsl

80

10 20 30+

0

10 20 30+

0

10 20 30+

85 90 95

17A

7A 100

Landward

105 110 115 120 125

15A

15B

130

16A

16B

18A

Seaward Fig. 7. Interpreted paleowater depth intervals in cores from Maraa. Water depths are based on published accounts of fossil and modern Indo-Pacific reefs.

M0023A (Fig. 6). This is consistent with previous observations of continuously shallow reef assemblages spanning 11 ka to present in Papeete Harbor (Montaggioni et al., 1997). The depth range of Assemblage aA3 partly overlaps those of aA2 and aA4, but adds a certain degree of resolution to the paleodepth interpretation, which cannot be attained with the species characteristic of the other assemblages. Its identification in Maraa probably reflects a higher development of deeper reef-framework facies before the drowning of the reef in this area compared to Tiarei. 4.4. Paleoenvironmental variations during the last deglaciation The ecological characteristics of deglacial reefs on Tahiti are variable based on the initial depth of the Pleistocene basement, the local hydrodynamic energy regime and local water quality — these factors are discussed in the following section in the context of reef initiation, growth and death. 4.4.1. Deglacial reef initiation The initial communities to occupy the Pleistocene basement were variable both between sites and within sites due to a range of optimum to sub optimum substrates. Shallow water and/or high-energy coralgal assemblages (cA1 and cA3, aA1 and aA2) formed on most basement substrates in Tiarei (Fig. 6) and also in the inner, upslope substrates in Maraa (Fig. 7), yet intermediate depth and lower-energy massive Porites (cA2, aA2) formed on the outer substrates in Maraa. This

discrepancy in paleowater depth of 5 to 10 m between the pioneer communities suggests that while deglacial reef initiation took place rapidly and in shallow paleowater depths in Tiarei and in the inner Maraa holes, reef initiation occurred with some delay and therefore in deeper paleowater depths in the outer Maraa holes. We argue that the nature of the Pleistocene basement substrate may have influenced this variable composition of the initial colonizing coralgal assemblages between sites. In cores where branching corals (cA1 and cA3) are the pioneer communities (all Tiarei sites and Maraa sites M0007A, M0015A/ B, and M0017A), the substrates are mainly composed of coralgal bindstone, coral framework or large coral debris (Camoin et al., 2007b). These substrate types appear to be ideal for the development of the high-energy and shallow coralgal assemblages on Tahiti's windward margin and shallow communities on Maraa's inner leeward margin, but unfavorable substrates of loose sand and rudstones may have retarded reef initiation in the outer Maraa holes.

4.4.2. Deglacial reef growth Following reef initiation on Tahiti, most coral assemblages between ca. 120 and ca. 110 mbsl developed in somewhat deeper conditions as indicated by the prevalence of massive Porites (cA2) and scarcer algae crusts (aA2). A shallowing-upwards sequence begins at ca. 110 mbsl with the development of extensive branching communities (cA3). The alternating pattern of branching (cA3 and cA4), tabular (cA5) and branching–encrusting corals (cA6) between ca. 110 mbsl and the bottoms of the drowning sequence suggests that paleoenvironmental

E. Abbey et al. / Global and Planetary Change 76 (2011) 1–15

Tahiti waters from 12.7 to 9.8 ka. Such variations did not affect the persistent development of Acropora after ~ 12.5 ka.

Table 5 Algal distribution relative to coral assemblage and site. Acropora interval (branching + tabular), Maraa

Branching Porites interval, Maraa

Branching encrusting interval, Tiarei (coeval to Acropora in Maraa)

Hydolithon breviclavium Hydolithon gardineri Hydolithon murakoshii Hydolithon munitum Hydolithon onkodes Lithoporella sp. Mastophora sp. Neogoniolithon fosliei Neogoniolithon frutescens Pneophyllum conicum laminar Spongites sp. Lithophyllum acrocamptum (= L. incrassatum) Lithophyllum cuneatum Lithophyllum insipidum Lithophyllum gr. kotschyanum Lithophyllum prototypum Lithophyllum gr. pustulatum Lithothamnion prolifer laminar Lithothamnion sp. Mesophyllum erubescens Mesophyllum funafutiense Sporolithon sp. Total = 22

H. gardineri H. murakoshii H. onkodes Hydorlithon rupestre Lithoporella sp. Mastophora pacifica Neogoniolithon sp. P. conicum Spongites sulawensis Lithophyllum acrocamptum L. cuneatum L. insipidum

H. breviclavium H. gardineri H. murakoshii H. onkodes H. reinboldii M. pacifica Lithoporella sp. P. conicum Spongites sp. L. acrocamptum L. cuneatum L. insipidum

L. gr. kotschyanum L. prototypum L. gr. pustulatum

L. gr. pustulatum L. prolifer laminar Lithothamnion sp. Mesophyllum sp.

L. prolifer laminar Lithothamnion sp.

4.4.3. Deglacial reef death Deep-water coralgal communities (cA7, aA4) replace shallow assemblages in Tiarei at the tops of cores ca. 11 ka on the inner ridge, though the timing on the outer ridge is unknown (Fig. 6). Some algal transitions suggest the deepening was abrupt, most notably in M0021A and B where shallow H. onkodes and Mastophora (aA1) occur at ca. 85 mbsl, immediately prior to deep-water coralgal assemblages (cA7 with aA4). In Maraa, deep-water assemblages begin forming at the tops of cores between 85–80 mbsl in outer cores (cA7 with aA3 and aA4), and 70–55 mbsl in inner cores (cA7 with aA4). Two Maraa cores (M0007A and M0016A) show a stratigraphically extended transition from shallow (b10 m) to intermediate (15–30 m) to deep (N20 m), suggesting the change in paleowater depth occurred over a somewhat longer time period than is indicated in Tiarei cores (Fig. 7). This discrepancy in paleowater depth signals may also be attributed to variable hydrodynamic and oceanographic conditions between the southwestern and northeastern sides of the island. 5. Conclusions

M. erubescens M. funafutiense

Total = 19

13

Total = 16

conditions (turbidity, energy, salinity) may have fluctuated near the tolerance limits of the different coral assemblages. However, where associated algae have been identified, paleowater depths can be constrained to no deeper than 20 m, and often less than 10 m (Figs. 6 and 7). These shallow- to intermediate-depth (0–20 m) reefs are variable in cores, accreting up to 10 m or more in some places to a maximum height of ca. 80–85 mbsl on Tiarei's outer ridge and Maraa's outer holes. The consistent appearance of Acropora within assemblages (especially sites M0007A, M0017A, and M0015A/B) and the increased coralline species richness from ca. 90 mbsl and ~ 12.5 ka to the tops of cores could indicate improving water quality through time. Records of paleoclimate variability, particularly precipitation, are scarce in the central subtropical Pacific Ocean. However, data from the main Hawaiian Islands indicate that climate may have varied considerably during the early deglacial (Last Glacial Maximum to 10 ka), especially precipitation (Hotchkiss and Juvik, 1999). Deglacial pollen records from Oahu indicate a dramatic increase in rainfall (~ 200%) beginning ca. 17 ka that was sustained until ca. 13 ka before returning to present levels after this time. Similarly high rainfall on Tahiti during this interval may have reduced salinity and increased turbidity, leading to the observed reduction in species richness. The appearance of Acropora at 12.5 ka seems to be consistent with that seen in the Papeete cores, however, a brief period of Acropora growth took place at an earlier interval as well, around 13.75 ka (Bard et al., 1996; Montaggioni et al., 1997; Cabioch et al., 1999a). The timing of the Acropora appearance is coincident with or subsequent to local oceanographic and atmospheric changes, but it is unclear if these changes had a direct relationship with the shift in the coral communities. Recent palaeoclimate work on Tahiti corals suggests that from 12.7 to 9.8 ka (Inoue et al., 2010) water temperatures were likely 2–4 °C cooler than modern and 1–2 °C cooler than 14.2–13 ka (Cohen and Hart, 2004; Asami et al., 2009; Inoue et al., 2010). This indicates that cooler water temperatures did not hinder profuse Acropora growth in Tahiti, which was coincident with minimum recorded SST values. Data from Inoue et al. (2010) also suggest higher variability and slightly higher average values of nutrient content of

Based on a detailed examination of the stratigraphic and spatial coralgal assemblage variation in Tiarei and Maraa, and in comparison with previously published coralline algae records, we draw the following conclusions: 1. Seven coral assemblages and four algal assemblages are present in the fossil reefs of Tahiti. In comparison with analogous modern and fossil assemblages, their paleoenvironmental settings can be identified and represent shallow upper reef slope (b10 m), intermediate (10–20 or 15–30 m) and deep forereef slope (N20–30 m). 2. Reef initiation was variable across sites and community composition was dependent upon the available substrate, those composed of reef framework and large rubble being the most optimum for rapid colonization. 3. The low abundance of Acropora in Tiarei and in the outer cores of Maraa suggests that early conditions were unsuitable for sensitive reef builders on Tahiti, especially in Tiarei due to the influence of the Papenoo River. However, conditions were sufficiently improved by 13–12 ka for Acropora to thrive and coralline algae to diversify, which may be explained by reduced runoff related to a transition into a drier climate on the island. 4. The persistence of shallow-water and intermediate-depth coralgal assemblages indicates that the fossil barrier reef developed near sea-level for much of the last deglaciation. This suggests that variations in coralgal assemblages developing from 15 ka to 12 ka may be more strongly influenced by environmental factors associated with sea-level rise (e.g., turbidity and water chemistry), rather than simply its deepening effects. 5. In all cases in Tahiti's submerged terraces, reef growth was terminated and cores are capped by distinctly deep-water coralgal assemblages, characteristic of deep reef growth and imminent drowning. Whether or not this drowning took place contemporaneously across all sites will be determined as more detailed chronology is presented. Acknowledgements This research used samples and data provided by the Integrated Ocean Drilling Program (IODP). We wish to acknowledge the Expedition 310 Scientists, as well as Bremen Core Repository members for support and collaboration during offshore/onshore parties. We would like to thank the support of ANSTO, including Geraldine Jacobsen and technicians for assistance with AMS, and

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Gordon Thorogood for support with XRD analyses. Funding was provided to E.A. by the School of Earth and Environmental Sciences at James Cook University, the School of Geosciences at the University of Sydney, the Australian Institute of Marine Science in a partnership with James Cook University (AIMS@JCU), the Australian Institute for Nuclear Science and Engineering (AINSE) and the Australian Nuclear Science and Technology Organisation (ANSTO). J.M.W. was provided support from James Cook University as part of a New Staff Development Grant and by the University of Sydney. Financial support was issued to Y.I. in part by grants-in-aid for scientific research, Japan Society for the Promotion of Science (18340163). We would also like to thank Lucien Montaggioni for his helpful review. References Adey, W.H., 1979. Crustose coralline algae as microenvironmental indicators in the Tertiary. In: Gray, J., Boucot, A.J. (Eds.), Historical Biogeography, Plate Tectonics and the Changing Environment. 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