Preprints
https://doi.org/10.5194/bg-2022-180
https://doi.org/10.5194/bg-2022-180
04 Oct 2022
 | 04 Oct 2022
Status: a revised version of this preprint is currently under review for the journal BG.

Deep-sea stylasterid δ18O and δ13C maps inform sampling scheme for paleotemperature reconstructions

Theresa M. King and Brad E. Rosenheim

Abstract. Deep-sea corals have the potential to provide high resolution paleotemperature records to evaluate oceanographic changes in settings that are vulnerable to current and future warming. The geochemical records preserved in coral skeletal carbonate, however, are limited by their large offsets from isotopic equilibrium with seawater. These "vital effects" are the result of biological influences (kinetic and metabolic) on the calcification of coral skeletons and are well known to drive oxygen and carbon stable isotope ratios (δ18O and δ13C, respectively) away from an environmental signal. Additionally, vital effects as they pertain to deep-sea branching corals are not well understood, thus hindering the utility of paleoceanographic archives with a vast latitudinal range. Here we describe the likely growth structure of a deep-sea stylasterid coral taxon and demonstrate the optimal sampling location for paleotemperature reconstructions. We sampled two coral specimens over cross sections through their primary growth axes to create skeletal δ18O and δ13C maps. Such maps reveal a consistent trend of increasing isotopic values toward the innermost portion of the coral slices; the average center values being ~1 ‰ closer to seawater equilibrium values than a traditional bulk sample. The difference between the higher center and lower bulk δ18O values result in temperature difference as much as 5.1 °C (±1.8 °C) between the sampling methods. These results support a two-step biomineralization consisting of a rapid initial skeletal construction, followed by a slower infilling concentrated towards the center, not yet described for this coral taxon. We anticipate this work to initiate efforts to sample deep-sea branching corals, potentially informing advanced visualization techniques to achieve the most accurate paleotemperature reconstructions.

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Theresa M. King and Brad E. Rosenheim

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-180', Anonymous Referee #1, 04 Jan 2023
    • AC1: 'Reply on RC1', Theresa King, 02 Feb 2023
  • RC2: 'Comment on bg-2022-180', Anonymous Referee #2, 12 Jan 2023
    • AC2: 'Reply on RC2', Theresa King, 02 Feb 2023
Theresa M. King and Brad E. Rosenheim
Theresa M. King and Brad E. Rosenheim

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Short summary
Corals can record ocean properties such as temperature in their skeletons. These records are useful for where and when we have no instrumental record like in the distant past. However, coral growth must be understood to interpret these records. Here, we analyze slices of a branching deep sea coral from Antarctica to determine how to best sample these corals for past climate work. We recommend sampling from the innermost portion of coral skeleton for accurate temperature reconstructions.
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