Environmental constraints on Holocene cold-water coral reef growth off Norway: Insights from a multi-proxy approach
High-latitude cold-water coral (CWC) reefs are particularly susceptible due to enhanced CO2 uptake in these regions. Using precisely dated (U/Th) CWCs (Lophelia pertusa) retrieved during research cruise POS 391 (Lopphavet 70.6°N, Oslofjord 59°N) we applied boron isotopes (δ11B), Ba/Ca, Li/Mg and U/C...
Published in: | Paleoceanography |
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Main Authors: | , , , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
AGU (American Geophysical Union)
2016
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Subjects: | |
Online Access: | https://oceanrep.geomar.de/id/eprint/33787/ https://oceanrep.geomar.de/id/eprint/33787/1/palo20367.pdf https://doi.org/10.1002/2016PA002974 |
Summary: | High-latitude cold-water coral (CWC) reefs are particularly susceptible due to enhanced CO2 uptake in these regions. Using precisely dated (U/Th) CWCs (Lophelia pertusa) retrieved during research cruise POS 391 (Lopphavet 70.6°N, Oslofjord 59°N) we applied boron isotopes (δ11B), Ba/Ca, Li/Mg and U/Ca ratios to reconstruct the environmental boundary conditions of CWC reef growth. The sedimentary record from these CWC reefs reveals a lack of corals between ∼ 6.4 and 4.8 ka. The question remains if this phenomenon is related to changes in the carbonate system or other causes. The initial postglacial setting had elevated Ba/Ca ratios, indicative of meltwater fluxes showing a decreasing trend towards cessation at 6.4 ka with a oscillation pattern similar to continental glacier fluctuations. Downcore U/Ca ratios reveal an increasing trend, which is outside the range of modern U/Ca variability in L. pertusa, suggesting changes of seawater pH near 6.4 ka. The reconstructed BWT at Lopphavet reveals a striking similarity to Barent Sea-Surface and sub-Sea-Surface-Temperature records. We infer that meltwater pulses weakened the North Atlantic Current system resulting in southward advances of cold and CO2 rich Arctic waters. A corresponding shift in the δ11B record from ∼ 25.0‰ to ∼ 27.0 ‰ probably implies enhanced pH-up regulation of the CWCs due to the higher pCO2 concentrations of ambient seawater, which hastened Mid-Holocene CWC reef decline on the Norwegian Margin. |
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