Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 300 (2010): 215-225, doi:10.1016/j.epsl.2010.09.029.
Description:
Deep-sea scleractinian corals precipitate aragonite skeletons that provide valuable
archives of past ocean conditions. During calcification biological mediation causes variability in
trace metal incorporation and isotopic ratios of the aragonite such that signals caused by
environmental controls can be overwhelmed. This complicates the interpretation of geochemical
proxies used for paleo-reconstructions. In this study we examine the environmental controls on
the Mg/Li ratio of 34 individuals from seven genera of deep-sea scleractinian corals:
Desmophyllum, Balanophyllia, Caryophyllia, Enallopsammia, Flabellum, Trochocyanthus, and
Lophelia. In addition we examine the distributions of Mg and Li in Desmophyllum and
Balanophyllia using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS).
Both Mg/Ca and Li/Ca ratios increased by more than a factor of 2 in the center of
calcification regions compared to the outer, fibrous regions of the coral skeleton. As a result,
replicate ~10 mg subsamples of coral show less variability in the Mg/Li ratio than Mg/Ca.
Microscale Mg and Li results are consistent with Rayleigh-type incorporation of trace metals
with additional processes dominating composition within centers of calcification. Comparison of
Mg/Li to seawater properties near the site of collection shows that the ratio is not controlled by
either carbonate ion or salinity. It appears that temperature is the major control on the Mg/Li
ratio. For all 34 samples the temperature correlation (R2=0.62) is significantly better than for
Mg/Ca (R2=0.06). For corals of the family Caryophyllidae the R2 value increases to 0.82 with
the exclusion of one sample that was observed to have an altered, chalky texture. Despite this
excellent correlation the scatter in the data suggests that the Mg/Li ratio of deep-sea corals
cannot be used to reconstruct temperature to better than approximately ±1.6°C without better
temperature control and additional calibration points on modern coral samples.
Description:
Financial Support was provided by the USGS WHOI Co-operative agreement, NSF-ANT grant numbers 0636787 and 80295700 and the WHOI Ocean Life Institute. David Case was supported by the WHOI Summer Student
Fellowship.
Keywords:
Biomineralization
;
Paleoceanography
;
Deep-sea coral
;
Mg/Ca
;
Mg/Li
;
Thermometry
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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