Approaches to unravel seasonality in sea surface temperatures using paired single‐specimen foraminiferal δ 18 O and Mg/Ca analyses

Seasonal changes in surface ocean temperature are increasingly recognized as an important parameter of the climate system. Here we assess the potential of analyzing single‐specimen planktonic foraminifera as proxy for the seasonal temperature contrast (seasonality). Oxygen isotopes and Mg/Ca ratios were measured on single specimens of Globigerinoides ruber , extracted from surface sediment samples of the Mediterranean Sea and the adjacent Atlantic Ocean. Variability in δ 18 O and Mg/Ca was then compared to established modern seasonal changes in temperature and salinity for both regions. The results show that (1) average δ 18 O‐derived temperatures correlate with modern annual average temperatures for most sites, (2) the range in δ 18 O‐ and Mg/Ca‐derived temperature estimates from single‐specimen analysis resembles the range in seasonal temperature values at the sea surface (0–50 m) in the Mediterranean Sea and the Atlantic Ocean, and (3) there is no strong correlation between Mg/Ca‐ and δ 18 O‐derived temperatures from the same specimens in the current data set, indicating that other parameters (salinity, carbonate ion concentration, symbiont activity, ontogenesis, and natural variability) potentially affect these proxies.