Coralline algae as recorders of past climatic and environmental conditions

Calcifying marine organisms can be used as recorders, or proxies, of past environmental conditions if they lock physical or chemical signals within their skeletal material. Coralline algae lay down regular growth bands and the study of their structure and composition has gained increasing attention as a technique for reconstructing past environments in tropical, temperate and polar regions. Structurally, growth band width and percentage calcification have been used as records of historic light availability (e.g. due to cloud cover and sea ice extent). The chemical composition of their high Mg calcite skeleton has received significantly more attention, being used to reconstruct temperature, salinity, dissolved inorganic carbon, upwelling patterns and wider climate indices. At the ecosystem level, such reconstructions have been used to shed light on the drivers of past changes in marine productivity. Against a backdrop of projected ocean acidification coralline algae show significant potential for reconstructing historic changes in ocean acidification-driven marine carbonate chemistry. Due to their global distribution, coralline algae are becoming a regularly used tool for understanding environmental and ecosystem change, particularly in areas where other proxies are not available or instrumental records are sparse.