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Abstract:
High-latitude cold-water coral (CWC) reefs are particularly vulnerable due to enhanced CO2 uptake in these
regions. For both modern and fossil Lophelia pertusa
samples, retrieved along the Norwegian margin from Lopphavet
(70.6°N) over Sula to Oslofjord (59°N), we have analysed the
boron isotope systematics (δ11B) as a potential seawater pH proxy [1]. This case study investigated potential heterogeneities within single specimens and recent regional to
local variations Analyses were undertaken using MC-ICP-MS based bulk (solution) analyses and continuous laser ablation
(LA) profiles, as well as secondary ion mass spectrometry
(SIMS) spot measurementsin combination with fluorescence microscopy. The latter provided a fast pre-screening
routine for phase-specific subsampling. Bulk analyses of around 5 mg milled from the massive thecal walls from samples of the main transect sites resulted in a recent average δ11B value of 26. 7‰(±0.3, 2SD). In contrast, an adjacent subsample dominated by centres of calcification (COC) gave 22.65‰, hence
an offset of about-3 ‰, with an approximately 40% lower B/Ca
ratio. LA profiles [2] showed significant δ11B single sample
heterogeneities of up to 10 ‰. Supporting preliminary SIMS results yielded similar ranges, and indicate multiple COC
zones as the source of low δ11B values. This suggests stronger
isotope fractionation occurred with lower B concentrations in
the COC compared to the theca during mineralisation.
