Middle to Late Jurassic equatorial seawater temperatures and latitudinal temperature gradients based on stable isotopes of brachiopods and oysters from Gebel Maghara, Egypt

Stable isotope (δ18O, δ13C) analyses of brachiopod and oyster shells from the Gebel Maghara, Egypt, were used to reconstruct the first detailed dataset on peri-equatorial water temperatures during the Middle to Late Jurassic. Throughout this time interval, temperatures remained relatively constant around an average of 25.7 °C. Slightly warmer conditions existed in the Early Bathonian (~ 27.0 °C), while the Kimmeridgian shows the lowest temperatures (~ 24.3 °C). As expected for a tropical palaeolatitude, the seasonality was very low (< 2 °C) as reconstructed by high-resolution stable isotope analyses of two oyster shells. Latitudinal temperature gradients in the Middle Jurassic were much steeper than previously expected and comparable to today. During the Kimmeridgian (Late Jurassic), temperatures in Europe were generally warmer leading to weaker latitudinal gradients. On average, water temperatures reconstructed from stable isotopes for Jurassic localities above the thermocline are lower than Recent sea-surface temperatures (based on currently used estimates for the δ18O value of seawater).