Reconstructing Paleoseasonality from Accretionary Skeletal Carbonates—Challenges and Opportunities

Abstract

Seasonal temperature variation at any location is most strongly regulated by the annual cycle of solar insolation, which is controlled by latitude and orbital parameters; other factors are continentality, albedo feedbacks, stratification and advection, and water depth. Seasonal minima, maxima, and range vary with change in mean annual temperature (MAT) across latitudes; seasonal variation in ocean-water temperature is highest in the mid-latitudes. Seasonal temperature range at depth is likely to be less than that at the sea surface. The chemistry of accretionary biogenic carbonate can preserve a record of seasonal temperature variation experienced by an organism over some portion of its ontogeny. Sampling early parts of ontogenies will yield a more complete temperature record because growth is faster (so temporal resolution is higher) and more likely to be continuous throughout the year. Biases due to preferential season of growth can be recognized by characteristic patterns of isotope data when plotted versus distance along the ontogenetic trajectory. Multiple years are needed to reliably characterize seasonal temperature range and inter-annual variability for a stratigraphic horizon in a given region; single-shell studies are less useful in this regard unless they contain very long records. Data from multiple time intervals or regions using the same taxon, sampled the same way, and from the same facies can establish meaningful trends in average temperature and seasonal range. Deep-time studies exploring seasonal temperature extremes and ranges can be coupled with proxies for mean annual temperature to offer a more complete understanding of changing climate conditions through time.