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Renita Aranha

Geochemistry, microstructure and growth banding in Stylaster campylecus parageus and Primnoa pacifica - Implications for commonly observed deep sea corals as paleoceanographic archives

Renita Aranha
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Evan Edinger

Earth Sciences, Memorial University of Newfoundland

2008 - 2010

Marine Biodiversity, MB-18: Pacific Coral and Sponge

renita.aranha@mun.ca

A sclerochronological study of two common cold-water corals from the Northeast Pacific, Stylaster campylecus parageus and Primnoa pacifica, was performed on specimens collected in 2008 from Dixon Entrance, BC, and the Olympic Coast National Marine Sanctuary, Washington State. SEM imaging of S. campylecus revealed the presence of growth banding and extensive skeletal remineralization. Profiles of Na/Ca, Mg/Ca, Sr/Ca and Ba/Ca could, however, be obtained with Secondary Ion Mass Spectrometry. Sr/Ca values were observed to display two maxima over distances covering approximately 12 growth bands, with corresponding minima in Mg/Ca and Na/Ca. These cyclical co-variations were interpreted to be primarily influenced by surface water productivity. This cyclicity in the trace element profiles, in the context of a documented biannual increase in productivity, suggested that the growth bands are monthly. The average radial growth rate of S. campylecus was 1.4 ± 0.1 mm.yr-1, and the average axial growth rate was 17.3 ± 1.1 mm.yr-1. Temperature changes cannot account for the variation in Mg/Ca and Sr/Ca in either S. campylecus or P. pacifica. These variations appear instead to be modulated by surface water productivity. The annual radial growth rate of P. pacifica varied between 0.23 and 0.58 mm.yr-1 in the samples studied - considerably higher than growth rates of a similar species in the North Atlantic. Geographic variation in growth rates is likely influenced by primary productivity.

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