<i>Acropora</i>
            interbranch skeleton Sr/Ca ratios: Evaluation of a potential new high‐resolution paleothermometer

Sadler, James; Nguyen, Ai Duc; Leonard, Nicole D.; Webb, Gregory E.; Nothdurft, Luke D.

doi:10.1002/2015pa002898

Cited by 10 publications

(22 citation statements)

References 79 publications

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“…This high resolution (~3-hour sampling) record correlates well with water temperature data collected by the moorings of the Great Barrier Reef Mooring Array representing the outer shelf and shelf break water temperatures at 10 and 11 m depth [Sadler et al, 2016]. Such similarity between datasets suggests that the MAPCO2 system provides water temperature data representative of both the local and wider marine environment [Sadler et al, 2016].…”

Section: Water Temperature Datasetsmentioning

confidence: 66%

“…Due to the high sub-sampling resolution, the resulting Sr/Ca ratios were smoothed with a four-point running mean prior to regression against water temperature, in a similar manner to the modern Acropora Sr/Ca calibration study [Sadler et al, 2016].…”

Section: Modern Coral Coresmentioning

confidence: 99%

“…(2σ) ka, Table 6-2, Supplementary Table 6-1) collected from a shallow rotary core on the leeward reef flat of Heron Reef Webb et al, 2016] was also used for paleoclimate reconstruction using a site specific calibration developed by Sadler et al [2016].…”

Section: Modern Coral Coresmentioning

confidence: 99%

“…Subsamples were collected at approximately 0.33-0.5 mm sampling resolution from the interbranch skeleton displaying strong annual density banding patterns as per Sadler et al [2016].…”

Section: Modern Coral Coresmentioning

confidence: 99%

“…The derived equation was then applied to sub-fossil Porites samples recovered from rotary cores from the windward Heron Reef margin. We also evaluated the paleoclimate record of a similarly aged corymbose Acropora sample from a leeward margin core using a site-specific calibration developed by Sadler et al [2016], to provide the first mid-Holocene paleoclimate records for the southern GBR. …”

Section: Introductionmentioning

confidence: 99%

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Reef cores as records of Holocene water temperatures of the southern Great Barrier Reef: Geochemical analysis of traditional (Porites) and non-traditional (Acropora) reef building corals

Sadler¹

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In order to accurately predict future climate variations induced by natural and anthropogenic forcings, we require a detailed understanding of the Earth's climate system. With such temporally limited instrumental records, proxy-based reconstructions are an invaluable source of climate information. Current paleoclimate databases indicate a lack of records representing the southern hemisphere and tropics; key regions that can be represented by high resolution, coral geochemistry-based climate reconstructions.Reef coring techniques allow the recovery of significant proportions of coral material from throughout the Holocene, Pleistocene and beyond. Given the high species diversity of IndoPacific coral reefs, the presence of massive Porites commonly used for climate reconstruction is likely to be limited in reef cores. Corymbose Acropora, however, displays a high abundance in modern and fossil reef records and thus could act as a major source of new climate information from the Earth's recent history.Previous investigations of Acropora geochemistry have focused on branches, with significant levels of secondary thickening smoothing environmental signals otherwise recorded by the Sr/Ca ratio paleothermometer. This project investigates the potential of Acropora interbranch skeleton as a climate archive, following the identification of annual density banding patterns in computed tomography scans. Scanning electron microscopy based documentation of structure and growth patterns reveal that inter-branch skeleton is atypical for Acropora.Low linear extension rates, a simplified skeletal structure with limited secondary aragonite deposition, approximately horizontal density bands and seasonal cyclicity in Sr/Ca ratios bear a greater resemblance to massive corals such as Porites. These observations, combined with a high abundance in past and present Indo-Pacific reefs, suggest that inter-branch skeletal growth in Acropora may prove to be a valuable source of untapped paleoclimate information.A site-specific calibration for Acropora inter-branch skeleton Sr/Ca ratios to water temperature was conducted using modern corymbose Acropora colonies and concomitant instrumental water temperature records from the lagoon and fore-reef slope of Heron Reef, southern Great Barrier Reef (GBR). Large inter-colony differences in Sr/Ca ratios were observed in the modern cores, suggesting that inter-branch skeleton may not be a suitable archive for absolute temperature reconstruction. Normalisation of each Sr/Ca record to the corresponding core mean does, however, remove these inter-colony differences and allows the reconstruction of the seasonal water temperature amplitude with a sensitivity of −0.05 ii mmol/mol/°C. Application of the resulting transfer equation to the modern inter-branch skeleton Sr/Ca record successfully identified the greater seasonal temperature range of the lagoon compared to the adjacent reef slope. A site-specific calibration also was completed for southern GBR Porites at Heron Reef using the reef slope water te...

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Section: Water Temperature Datasetsmentioning

confidence: 66%

Section: Modern Coral Coresmentioning

confidence: 99%

Section: Modern Coral Coresmentioning

confidence: 99%

“…Subsamples were collected at approximately 0.33-0.5 mm sampling resolution from the interbranch skeleton displaying strong annual density banding patterns as per Sadler et al [2016].…”

Section: Modern Coral Coresmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Reef cores as records of Holocene water temperatures of the southern Great Barrier Reef: Geochemical analysis of traditional (Porites) and non-traditional (Acropora) reef building corals

Sadler¹

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Reef core insights into mid-Holocene water temperatures of the southern Great Barrier Reef

et al. 2016

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The tropical and subtropical oceans of the Southern Hemisphere are poorly represented in present‐day climate models, necessitating an increased number of paleoclimate records from this key region to both understand the Earth's climate system and help constrain model simulations. Here we present a site‐specific calibration of live collected massive Porites Sr/Ca records against concomitant in situ instrumental water temperature data from the fore‐reef slope of Heron Reef, southern Great Barrier Reef (GBR). The resultant calibration, and a previously published Acropora calibration from the same site, was applied to subfossil coral material to investigate Holocene water temperatures at Heron Reef. U‐Th‐dated samples of massive Porites suggest cooler water temperatures with reduced seasonal amplitude at ~5.2 ka (2.76–1.31°C cooler than present) and ~7 ka (1.26°C cooler than present) at Heron Reef. These results contrast the previous suggestion of a mid‐Holocene Thermal Maximum in the central GBR around 5.35 ka and 4.48 ka, yet may be explained by differences in temperature of the shallow ponded reef flat (central GBR) and the deeper reef slope waters (this study) and potential large reservoir correction errors associated with early radiocarbon dates. Combining coral‐based water temperature anomaly reconstructions from the tropical and subtropical western Pacific indicates a coherent temperature response across the meridional gradient from Indonesia and Papua New Guinea down to the southern GBR. This similarity in reconstructed temperature anomalies suggests a high probability of an earlier expression of a mid‐Holocene Thermal Maximum on the GBR between ~6.8 and 6.0 ka.

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A modern Sr/Ca‐δ¹⁸O‐sea surface temperature calibration for Isopora corals on the Great Barrier Reef

2017

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Isopora (Acroporidae) is a genus of often encrusting, branching to submassive corals that are common in many shallow habitats on modern and fossil Indo‐West Pacific reefs. Although abundant, Isopora is largely absent from paleoceanographic literature. The scarcity of large Porites and the abundance of Isopora retrieved from the Great Barrier Reef (GBR) on Integrated Ocean Drilling Program Expedition 325 focused paleoceanographic attention on Isopora. Here we provide the first independent high‐resolution calibration of both Sr/Ca and δ18O for temperature analyses based on Isopora and demonstrate its consistency with Porites records. We developed modern skeletal Sr/Ca‐ and δ18O‐sea surface temperature (SST) calibrations based on five modern Isopora colonies from Heron Island in the southern GBR. Pairing the coral Sr/Ca record with monthly SST data yielded Sr/Ca‐SST sensitivities from −0.061 ± 0.004 (centered) to −0.083 ± 0.007 (raw) mmol/mol °C−1 based on reduced major axis regressions. These sensitivities are in the middle of the range of published Porites values and overlap most published values for Isopora, −0.075 ± 0.011 to −0.065 ± 0.011 mmol/mol °C−1. The δ18O‐SST sensitivities range from −0.184 ± 0.014 (centered) to −0.185 ± 0.014 (raw) ‰ °C−1, assuming that all seasonal variation in δ18O was due to SST. These δ18O‐SST sensitivities are smaller than the widely accepted value of −0.23‰ °C−1 for biogenic aragonite but are at the upper end of high‐resolution Porites‐defined sensitivities that are consistently less than the aforementioned established value. Our results validate the use of Isopora as an alternative source of paleoceanographic records in habitats where large massive Porites are scarce or absent.

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Acropora interbranch skeleton Sr/Ca ratios: Evaluation of a potential new high‐resolution paleothermometer

Cited by 10 publications

References 79 publications

Reef cores as records of Holocene water temperatures of the southern Great Barrier Reef: Geochemical analysis of traditional (Porites) and non-traditional (Acropora) reef building corals

Reef cores as records of Holocene water temperatures of the southern Great Barrier Reef: Geochemical analysis of traditional (Porites) and non-traditional (Acropora) reef building corals

Reef core insights into mid-Holocene water temperatures of the southern Great Barrier Reef

A modern Sr/Ca‐δ¹⁸O‐sea surface temperature calibration for Isopora corals on the Great Barrier Reef

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Acropora interbranch skeleton Sr/Ca ratios: Evaluation of a potential new high‐resolution paleothermometer

Cited by 10 publications

References 79 publications

Reef cores as records of Holocene water temperatures of the southern Great Barrier Reef: Geochemical analysis of traditional (Porites) and non-traditional (Acropora) reef building corals

Reef cores as records of Holocene water temperatures of the southern Great Barrier Reef: Geochemical analysis of traditional (Porites) and non-traditional (Acropora) reef building corals

Reef core insights into mid-Holocene water temperatures of the southern Great Barrier Reef

A modern Sr/Ca‐δ18O‐sea surface temperature calibration for Isopora corals on the Great Barrier Reef

Contact Info

Product

Resources

About

A modern Sr/Ca‐δ¹⁸O‐sea surface temperature calibration for Isopora corals on the Great Barrier Reef