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  1. Element-calcium ratios in the skeleton of cold-water coral Desmophyllum dianthus represent potential archives for paleo-reconstruction of several ocean properties including temperature and nutrient concentrations. However, relatively large uncertainties in these proxy calibrations and heterogeneity in the skeletal composition have limited its application to date. We address these issues by analyzing corals cultured under systematically varied seawater conditions (phosphate, barium, temperature, pH, feeding frequency) over a two-year period, and refine the calibration of P/Ca, Ba/Ca, U/Ca, and Li/Mg proxies for seawater phosphate, barium, carbonate ion concentration, and temperature, respectively. Composition of the corals is determined using laser-ablation ICPMS, with robust plasmamore »conditions established using the Normalized Argon Index [1], and proxy element incorporation is evaluated for influences of temperature, pH, and feeding frequency. The aragonite precipitated during the stages of the culturing experiment is identified using fluorescent and geochemical labelling of the skeleton through calcein and lead isotopes, respectively. This approach allows us to resolve monthly and annual increments in these slow growing (1-2mm/year) organisms, and also to evaluate the influence of calcification rate on the composition. We address the issue of heterogeneity by adapting methods for LA-ICPMS imaging to create macroscale images to reveal the full pattern of skeletogenesis and related compositional variability of D. dianthus. Preliminary images suggest that heterogeneity stems from the asymmetric precipitation of aragonite, and from centers of calcification (also known as early mineralization zones) that complicate the interpretation of elemental signals throughout the skeleton, but also help to identify new skeletal regions suitable for proxy measurement. Finally, we also discuss the role of endolithic organisms in some of these specimens. [1] Fietzke, J. & Frische, M. (2016), J. Anal. At. Spectrom. 31, 234–244.« less
  2. Cold-Water Corals (CWCs), and most marine calcifiers, are especially threatened by ocean acidification (OA) and the decrease in the carbonate saturation state of seawater. The vulnerability of these organisms, however, also involves other global stressors like warming, deoxygenation or changes in sea surface productivity and, hence, food supply via the downward transport of organic matter to the deep ocean. This study examined the response of the CWC Desmophyllum dianthus to low pH under different feeding regimes through a long-term incubation experiment. For this experiment, 152 polyps were incubated at pH 8.1, 7.8, 7.5 and 7.2 and two feeding regimes formore »14 months. Mean calcification rates over the entire duration of the experiment ranged between −0.3 and 0.3 mg CaCO 3 g −1 d −1 . Polyps incubated at pH 7.2 were the most affected and 30% mortality was observed in this treatment. In addition, many of the surviving polyps at pH 7.2 showed negative calcification rates indicating that, in the long term, CWCs may have difficulty thriving in such aragonite undersaturated waters. The feeding regime had a significant effect on skeletal growth of corals, with high feeding frequency resulting in more positive and variable calcification rates. This was especially evident in corals reared at pH 7.5 (Ω A = 0.8) compared to the low frequency feeding treatment. Early life-stages, which are essential for the recruitment and maintenance of coral communities and their associated biodiversity, were revealed to be at highest risk. Overall, this study demonstrates the vulnerability of D. dianthus corals to low pH and low food availability. Future projected pH decreases and related changes in zooplankton communities may potentially compromise the viability of CWC populations.« less