Experimental paleo-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 (annual to seasonal) 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 experimental proxy calibrations have been performed for tropical corals, they are still pending for CWCs. This reflects the technical challenges involved in maintaining these slow-growing creatures alive in aquaria during the long-term experiments required to achieve sufficient skeletal growth for geochemical analyses. In this presentation we will show details of the set up and initial results of a long-term experiment being run at the ICM aquaria facilities in Barcelona, where live specimens (>150) of the CWC Desmophyllum dianthus, 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. We present preliminary results using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS), which allows 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 monitoring parameters regarding coral growth and physiology including skeletal growth, coral calcification and respiration