Boron isotope composition of the cold-water coral Lophelia pertusa along the Norwegian margin : zooming into a potential pH-proxy by combining bulk and high-resolution approaches

• Published in: Chemical Geology
• Main Authors: Jurikova, Hana, Liebetrau, Volker, Raddatz, Jacek, Fietzke, Jan, Trotter, Julie, Rocholl, Alexander, Krause, Stefan, McCulloch, Malcolm, Rüggeberg, Andres, Eisenhauer, Anton
• Other Authors: University of St Andrews. School of Earth & Environmental Sciences
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: Aragonite precipitation; Biomineralisation; Diagenesis; Isotope geochemistry; Laser ablation; MC-ICP-MS; Ocean acidification; pH and carbon cycle reconstruction; SIMS; QE Geology; Geology; Geochemistry and Petrology; DAS; SDG 13 - Climate Action; SDG 14 - Life Below Water; QE; Lopphavet; Lophelia pertusa
• Online Access: http://hdl.handle.net/10023/20246; https://doi.org/10.1016/j.chemgeo.2019.01.005

This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 643084 (BASE-LiNE Earth) and the collaborative research initiative CHARON (DFG Forschergruppe 1644 - Phase II) funded by the German Research Foundation. J.R. acknowledges funding from DFG project ISOLDE DU 45/1 and 45/3 and ECHO RA 2156/1. J.T. and M.M. are supported by the Australian Research Council fellowship FL120100049, CE140100020 and acknowledge support from research project DP0986505. High-latitude cold-water coral reefs are particularly vulnerable to climate change due to enhanced CO2 uptake in these regions. To evaluate their physiological functioning and potential application as pH archives, we retrieved both recent and fossil samples of Lophelia pertusa along the Norwegian margin from Oslofjord (59°N), over to Trondheimsfjord, Sula and Lopphavet (70.6°N). Boron isotope analyses (δ11B) were undertaken using solution-based and laser ablation multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS; LA-ICP-MS), and secondary ion mass spectrometry (SIMS). Epi-fluorescence microscopy was employed to provide a rapid pre-screening routine for structure-specific subsampling in the coral skeleton. This integrated approach enabled us to assess heterogeneities within single specimens, as well as to investigate the role of local environmental influences including recent and past variations. All three mass spectrometry methods show substantial differences in the δ11B of the theca wall (TW) and the centres of calcification (COC's). Micro-bulk subsamples milled from the theca wall of modern specimens originating from different habitats but with comparable seawater pH (8–8.16) gave consistent δ11B values averaging 26.7 (±0.2‰, 2σ, n = 4), while COC subsamples systematically deviated towards lower B/Ca (by ~40%) and depleted δ11B values (minimum 22.7 ± 0.3‰, 2σ), implying a difference of at least 4‰ between TW and COC. SIMS and LA-ICP-MS ...