Environmental and diagenetic records from trace elements in the Mediterranean coral Cladocora caespitosa

Trace element contents in coralline aragonite have long been used as proxies to record environmental growth conditions such as sea surface temperature (SST). In this study we explored whether trace element contents in modern and fossil corals (Cladocora caespitosa) from the Mediterranean could help constrain SST temperature and seasonality of climate in late Pleistocene interglacials. In modern Adriatic C. caespitosa, the individual corallite Sr/Ca signal captures seasonal variation with up to 68% of the variance related to SST. A similar but weaker relationship is shown by Mg/Ca. However, published equations to quantify absolute water temperature from Sr and Mg contents in modern C. caespitosa did not yield consistent or credible results, because each corallite exerts a strong, non-predictable ‘vital effect’. With no constant species-specific offset from equilibrium, temperature-trace element relationships become, at best, colony specific and unsuitable for absolute palaeotemperature reconstruction. Despite this, temperature-related cyclicity in Sr and Mg is preserved in corallites up to at least MIS 7 age, allowing identification of seasonality in SST. In addition, unusual trace element anomalies in modern C. caespitosa can inform on events such as sediment discharge into the coastal zone. Partial diagenetic alteration of fossil C. caespitosa skeletons from aragonite to calcite destroys original SST driven cyclic trace element signals and is an effective indicator of corallite preservation quality.