2025/01/02 by Iris Arndt, Miguel Bernecker, Tobias Erhardt +9 · 1 voice
Earth and Planetary Sciences · #Geology and Paleoclimatology Research #Paleontology and Stratigraphy of Fossils #Geological and Geophysical Studies
paper · doi:10.1016/j.palaeo.2024.112711
Giant clams ( Tridacna ) are well-suited archives for studying past climates at (sub-)seasonal timescales, even in ‘deep-time’ due to their high preservation potential. They are fast growing (mm-cm/year), live several decades and build large aragonitic shells with seasonal to daily growth increments. Here we present a multi-proxy record of a late Miocene Tridacna grown on the western margin of the Makassar Strait (Indonesia). By analysing daily elemental cycle lengths using our recently developed Python script Daydacna, we build an internal age model, which indicates that our record spans 20,916 ± 1220 days (2 SD), i.e. ~57 ± 3 years. Our temporally resolved dataset of elemental ratios (El/Ca at sub-daily resolution) and stable oxygen and carbon isotopes (δ 18 O and δ 13 C at seasonal to weekly resolution) was complemented by dual clumped isotope measurements, which reveal that the shell grew in equilibrium with seawater. The corresponding Δ 47 value yields a temperature of 27.9 ± 2.4 °C (2 SE) from which we calculate a mean oxygen isotopic composition of the late Miocene tropical seawater of −0.43 ± 0.50 ‰. In our multi-decadal high temporal resolution records, we found multi-annual, seasonal and daily cycles as well as multi-day extreme weather events. We hypothesise that the multi-annual cycles (slightly above three years) might reflect global climate phenomena like ENSO, with the more clearly preserved yearly cycles indicating regional changes of water inflow into the reef, which altogether impact isotopic water signatures, temperature and nutrient availability. In addition, our chronology indicates that twice a year a rainy and cloudy season, presumably related to the passing of the ITCZ, affected light availability and primary productivity in the reef, reflected in decreased shell growth rates. Finally, we find irregularly occurring extreme weather events likely connected to heavy precipitation events that led to increased runoff, high turbidity, and possibly reduced temperatures in the reef. • We present the first >50-year long palaeoclimate record at sub-daily resolution. • Tridacna records seasonal precipitation and wind patterns driven by ITCZ movements. • Dual clumped isotope data reveal: Tridacna grow shells in equilibrium with seawater. • Late Miocene specimen records 27.9 ± 2.4 °C (2 SE) with a δ 18 O sw of −0.43 ± 0.50 ‰. • Elemental and isotopic cycles between 2 and 7 years indicate ENSO-like patterns.