THREE SCALES OF BANDING AND TRACE/MINOR ELEMENT VARIATION IN THE SKELETON OF THE DEEP-SEA GORGONIAN CORAL PRIMNOA RESAEDEFORMIS

There is increasing interest in the climatic and environmental records in the skeletons of deep-sea corals. Specimens of the deep-sea gorgonian coral Primnoa resaedeformis were collected by nearshore fishermen from the Northeast Channel, off the SE coast of Nova Scotia, from a depth of 280 m. This coral secretes a two-component skeleton: calcite, and a horny protein “gorgonin”. Younger examples have primarily organic skeletons, with calcite becoming more prevalent with age.

Examination of polished thin sections with Nomarski interference microscopy shows monthly growth bands, 15-30 microns wide, assembled into annual bands about 250 microns wide. Delineation of the banding is facilitated by segregations of fibres of gorgonin, which are tangentially oriented. In the outer calcite layers, annual and monthly bands are seen as faint organic stains that are superimposed on finescale laminations. Laminae range from <1 micron to 6 microns in width and are visible in transmitted light. It is possible that these laminae are daily.

Chemical analysis of the skeletons was performed by laser-ablation ICP-MS for Mg/Ca, Mn/Ca, Sr/Ca, Cd/Ca, Ba/Ca and U/Ca ratios (precision ~8%). Variation in Sr/Ca across all samples is within machine error. All other elemental ratios are enriched in the presence of gorgonin, rendering the inner skeleton an unreliable source of paleoclimatic information. Values in the outer calcite zones show less variability and agreement between spots of co-eval skeleton. Mg/Ca ratios are the most promising source of paleotemperatures; variation in this ratio is large enough to be resolved by LA-ICPMS.