RECONSTRUCTING SEASONAL-SCALE PRECIPITATION PATTERNS FROM HIGH RESOLUTION OXYGEN ISOTOPE SCLEROCHRONOLOGY OF COASTAL TURRITELLID GASTROPODS

Turritellid gastropods are aragonitic marine mollusks which are particularly abundant and widespread in the fossil record. With fast growth rates and a shallow coastal living environment, they have the potential to be excellent recorders of ancient subannual climate variation – both seasonal temperature changes and fluctuations in δ¹⁸O_sw. Previous sclerochronological studies of turritellids have investigated seasonal temperature ranges by converting δ¹⁸O to temperature, assuming an invariant δ¹⁸O_sw. However, this approach is complicated by naturally variant δ¹⁸O_sw in the marginal marine environments where turritellids live, driven by seasonally variable freshwater delivery related to local rainfall patterns. We produce 22 new high-resolution oxygen isotope profiles of modern turritellid shells, and compare these and other published records to instrumental temperature and precipitation data in order to assess the potential of turritellids to record past sea surface temperatures and seasonal precipitation patterns. We find that the annual range in shell δ¹⁸O is related to seasonal precipitation variance (the difference in rainfall between wettest and driest month, SPV), once seasonal changes in sea surface temperature are accounted for. We demonstrate the effects of alignment vs. misalignment of precipitation and temperature maxima on δ¹⁸O profiles using modeled synthetic data. This empirical relationship between δ¹⁸O_range, SST and SPV can be used to reconstruct paleoenvironmental conditions, particularly in the tropics where seasonal precipitation has a strong effect on δ¹⁸O.