Experimental proxy calibration in cold water corals

Abstract

Cold-water corals (CWCs) display an almost cosmopolitan distribution over a wide range of depths. Similar to their tropical counterparts, they provide continuous, high-resolution records of up to a century or more. Several CWC elemental and isotopic ratios have been suggested as useful proxies, but robust calibrations under controlled conditions in aquaria are needed. Whereas a few such calibrations have been performed for tropical corals, they are still pending for CWCs. This reflects the technical challenges involved in maintaining these slow-growing animals alive during the long-term experiments required to achieve sufficient skeletal growth for geochemical analyses. We will show details of the set up and initial stages of a long-term experiment being run at the ICM (Barcelona), where live specimens (>150) of Desmophyllum dianthus sampled in the Comau Fjord (Chile) are kept under controlled and manipulated chemistry (pH, phosphate, barium) and feeding conditions. With this set up, we aim to experimentally calibrate specific elemental ratios including P/Ca, Ba/Ca, B/Ca and U/Ca as proxies of nutrient dynamics, pH, and carbonate ion concentration. Regarding geochemistry, we will analyze coral skeletons using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS), which will allow running quantitative analyses on spot sizes of tens of microns. We will also attempt measurements using NanoSIMS, to resolve nano-scale details in relative composition. Preliminary data obtained from these techniques will be presented, together with suitable parameters to monitor coral growth and physiology including skeletal growth, coral calcification and respiration