Transition in Biomineralization Mechanisms From Early to Late Stages of Deep-Sea Bamboo Corals: Insights From fs-LA-ICP-TOFMS Elemental Imaging

The elemental compositions of deep-sea corals are invaluable proxies in high-resolution reconstructions of deep-sea paleo-oceanographic conditions, but the incorporation of minor and trace elements into their skeletons and associated biomineralization are poorly understood. In this study, multielement (Cd, P, Ba, K, S, Co, Mn, Fe, Sr, Na, and Mg) and fluorescence imaging of skeletal cross-sections of a subapical branch and middle-basal trunk of a deep-sea bamboo coral, Jasonisis sp. (collected from the seafloor in front of the Mariana arc (11.95355°N, 141.47446°E) at a depth of 1,385.9 m in October 2019) were undertaken using femtosecond laser ablation-inductively coupled plasma time-of-flight mass spectrometry and laser scanning confocal microscopy, respectively. The spatial associations of minor and trace elements and their organic compositions, and associated growth patterns (cyclic rings) of early- (the subapical branch and the near-core region of the middle and basal trunk) and late-stage (the middle-basal trunk excluding near-core regions) coral skeletons were determined simultaneously. The consistent distribution patterns of most elements and the presence of distinct rings correspond to growth patterns associated with nutrient-like elements such as Cd, P, and Ba and organic components within the late skeleton. This likely suggest a significant role of nutrients in the biomineralization process during the late stage. The distinct elemental patterns, exhibiting positive correlation among specific elements (e.g., P, S, Mn, Co, and Cd) and negative correlations with others (e.g., Na and Mg), along with the lower organic content observed in the early skeleton, suggest a unique mineralization mechanism during the initial growth stage, with kinetic processes playing a dominant role. Therefore, combined multielement and organic composition mapping of different parts of coral skeletons provides comprehensive insight into coral growth and the incorporation of trace elements.