Oxygen and Hydrogen Isotopic Composition of Fluid Inclusion Water in Cold-water Coral Skeletons Captures Metabolic Activity?
Abstract
Cold water corals residing in the deeper water masses of the global ocean are a potentially valuable archives of paleoceanographic change. However, over the past decades it became clear that many of the proxy records that work so well for tropical symbiotic corals are of little use for these deeper-dwelling a-symbiotic taxa. Here we present a new approach to extracting proxy records from cold-water corals. We have extracted microscopic amounts of fluid water trapped in modern cold-water coral aragonite and analyzed the oxygen (δ18O) and hydrogen (δ2H) isotope ratios of that water.
We primarily targeted the cold-water coral species Lophelia pertusa from the Logachev Mound Province in the North Atlantic Ocean. The results display a clear trend in δ2H and δ18O values that suggest that mixing of seawater and metabolic water in the coral tissue affected the water as it was captured in the coral skeleton. An observed significant offset from the theoretical seawater - metabolic water mixing line for these specimens can be explained if the water was primarily transported into the coral skeleton as hydrated amorphous calcium carbonate. The fluid inclusion waters analyzed are not in isotopic equilibrium with host aragonite. Other cold-water coral taxa from the same area show similar isotope fractionation, as do several symbiotic tropical corals. It seems therefore that the isotope patterns observed represent the internal water pool of the corals and isotope fractionation links to the calcification processes. Lophelia pertusa data that are available to us now, seem to suggest that increased metabolic rates lead to lower δ2H and δ18O values of the inclusion water in the coral skeleton, which potentially allows for reconstruction of metabolic rates in corals back in time.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP42B..08V
- Keywords:
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- 0419 Biomineralization;
- BIOGEOSCIENCESDE: 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCESDE: 4924 Geochemical tracers;
- PALEOCEANOGRAPHYDE: 4994 Instruments and techniques;
- PALEOCEANOGRAPHY