Red coralline algae and climate change: growth, magnesium concentration variability and the development of a new palaeoclimate proxy
Pauly, Maren Isabelle
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Past ocean acidification recorded in the geological record facilitates the understanding of rates and influences of contemporary pCO2 enrichment. High resolution proxies of pCO2 and pH can be used to reconstruct components of the palaeocarbonate system. At present, most pH reconstructions are made using boron isotopes, however, there is some uncertainty associated with vital effects and isotopic fractionation. In addition to contemporary ocean acidification, marine organisms currently experience thermal stress associated with increasing atmospheric temperatures. Here we present a study of the influences of multiple stressors on the growth and structure of a marine carbonate, predicted to occur within this century, and a novel structural proxy for carbonate chemistry; Mg-O bond strength in coralline algae. Free living Lithothamnion glaciale algae were incubated in control (380ppm pCO2), moderate acidification (750ppm pCO2) and high acidification (1000ppm pCO2) at ambient and enhanced (+2°C) temperature conditions for 24 months. Coralline algae growth (linear extension) was highly dependent on temperature, with +2°C samples experiencing significantly reduced growth. No significant correlation was found between pCO2 and growth, indicating L. glaciale’s ability to acclimatize. Relative magnesium concentration and Mg-O bond strength within the high-Mg skeleton cyclically over an annual cycle. For all seasons there was a positive linear relationship between pCO2 concentration and bond strength mediated by positional disorder of the calcite lattice. Structural preservation of the carbonate chemistry system in coralline algal high Mg calcite represents an alternative approach to reconstructing marine carbonate chemistry parameters based on skeletal structure rather than chemistry.