IMPACT OF INDUCED STRESS ON THE SKELETAL GEOCHEMISTRY OF CORALS GROWN IN BIOSPHERE 2

Abstract

Skeletal geochemical records of Porites spp. corals are well-established tools for reconstructing past climates. The response of these corals to environmental stress can also provide critical insights into the optimal environmental conditions for growth. In particular, corals grown under controlled conditions offer new information on how natural reefs respond to extreme conditions, ocean acidification, and thermal stress. Here we use corals collected from the University of Arizona’s Biosphere 2 ocean that was previously marked with dye to analyze the impact of stress from an environmental change on the corals’ skeletal composition and growth. Following collection, we milled powders along a transect of optimal growth and analyzed their trace element content using an inductively coupled plasma-mass spectrometer. We found that the established temperature proxies Li/Mg and Sr/Ca declined with depth and therefore age but with a notable offset between these proxies during the stressor event and associated coral growth anomalies. By separating the record into two periods of stress, first from the coral's transition to the Biosphere 2 ocean and then second during the early experiment, there’s an indication these events caused active transport via the Ca-ATPase pump in the skeleton to decline as well as Rayleigh fractionation to weaken (m = -0.149). With established links between skeletal U/Ca and B/Ca and the carbonate chemistry of the coral's calcifying fluid, our results suggest a decrease in the vital carbonate ion causing a decrease in skeletal growth. These results highlight the impact of stress on coral calcification and the paleoclimate reconstructions developed from the geochemistry of the coral skeleton.