Skeletal isotopic responses of the Scleractinian coral Isopora palifera to experimentally controlled water temperatures

Abstract

We cultivated Isopora palifera clone colonies at six different temperatures for testing the utility of its skeletal δ 18 O as a paleotemperature proxy. Specimens cultivated at higher temperatures exhibited lower calcification rates, especially at 31.0°C, than those cultured at lower temperatures. The skeletal δ 18 O of the specimens cultured at 21.1-29.5°C correlated strongly with water temperature, and δ 18 O-temperature sensitivity was -0.15‰ °C -1 . When we removed the thermal factor from the skeletal δ 18 O and δ 13 C trends at 21.1-29.5°C by subtracting the estimated equilibrium values of inorganic aragonite from the analyzed δ 18 O and δ 13 C values, we found that the calcification rate variation has little influence on the isotopic compositions of the specimens examined. Thus, the skeletal δ 18 O of I. palifera corals without severe bleaching can be a good temperature proxy at temperatures below ~30°C.

Geochemistry-based coral palaeoclimate studies and the potential of ‘non-traditional’ (non-massive Porites) corals: Recent developments and future progression

“…The ERSST dataset is generated from smoothed SST data with local and short-term variations removed (Smith et al, 2008). Nishida et al (2014) calculated a similar temperature sensitivity of −0.15‰/°C for incubated I. palifera from Japan, however, both geochemical sampling procedures also failed to consider ultrastructure variations in geochemistry or provide a detailed screening for diagenesis, which may also reduce the sensitivity of a calibration equation. Halving the sampling resolution from every 1 mm to 2 mm was noted to result in significant decreases (N0.05‰) in the δ 18 O seasonal amplitude, thus Lemley (2012) recommend that future Isopora research maintains at least a 1 mm sampling resolution.…”

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

“…Our δ 18 O‐SST sensitivity falls between Isopora δ 18 O‐SST sensitivities from the Felis et al [] bulk samples (−0.218‰ °C −1 ) and those reported by Lemley [] from work on Isopora from Myrmidon Reef (18°15′S, 147°23′E), Papua New Guinea (5°6′S, 145°48′E), and Heron Island (−0.15 to −0.16‰ °C −1 ). Additionally, Nishida et al [] conducted an incubation study of I. palifera and calculated the same temperature sensitivity of −0.15‰ °C −1 . In a review of “nontraditional” corals in paleoceanographic studies, Sadler et al [] suggested the shallower sensitivities of Lemley [] and Nishida et al [] reflect smoothing in the ERSST data product and/or a lack of consideration for diagenesis and skeletal ultrastructure.…”

“…Additionally, Nishida et al [] conducted an incubation study of I. palifera and calculated the same temperature sensitivity of −0.15‰ °C −1 . In a review of “nontraditional” corals in paleoceanographic studies, Sadler et al [] suggested the shallower sensitivities of Lemley [] and Nishida et al [] reflect smoothing in the ERSST data product and/or a lack of consideration for diagenesis and skeletal ultrastructure. While our study corroborates the Lemley [] and Nishida et al [] δ 18 O‐SST sensitivities by reporting sensitivities smaller than −0.23‰ °C −1 even after our application of multiple data products and high‐resolution sampling (see supporting information), it is possible that these values could more closely approach the accepted biogenic aragonite SST sensitivity after rescaling that addresses skeletal mass accumulation in the tissue layer as suggested by Gagan et al [].…”

“…Studies since the conclusion of IODP 325 suggest that branching to submassive forms of Isopora contain high‐resolution, near‐monthly resolvable, geochemical records within their aragonite skeletons [ Lemley , ] that make them suitable for coral‐based climatic reconstructions. Recent calibrations [ Lemley , ; Nishida et al , ] did not use high‐resolution (i.e., subannual) sampling, nor did they include skeletal trace metals, leaving the full suite of potential paleothermometers unexplored. Felis et al [] applied an average of well‐established Porites sensitivities to Sr/Ca data from fossil Isopora collected during IODP 325 to measure glacial‐interglacial SST change on the GBR.…”