Multi-proxy analyses of mussels from the Brazos River (Texas, USA)

Abstract: Oxygen isotope sclerochronology with mollusk shells is complicated in subtropical regulated rivers by irregular shell δ18O patterns. We performed multi-proxy analyses (δ18O, δ13C, clumped isotopes) from serially-sampled freshwater mussels in two species (Amblema plicata and Cyrtonaias tampicoensis), two specimens each, from the Brazos River, Texas to age specimens and test whether they accurately record environmental conditions such as river discharge and water source. Oxygen isotopic measurements are similar to predicted aragonite δ18O values based on temperature and water 18O, but the record is complex and irregular. To better resolve the chronologies, we performed clumped isotope analyses on select shell intervals. Clumped isotope temperatures (T(Δ47)) ranged from 19° to 36°C. Summer T(Δ47) values were 3-5°C higher than measured temperatures, suggesting an offset in paleothermometer calibration. Chronologies based on Δ47 and δ18O reveal specimen ages of 3-4 years and winter growth cessation or dramatic slowing in both C. tampicoensis and A. plicata, highlighting thermal limitations on growth and potential biases in environmental reconstructions. Carbon isotope trends were similar between conspecific shells, but differed between species, with mean 13C of -9‰ for A. plicata and -12‰ for C. tampicoensis. These findings argue for more direct environmental control on the A. plicata shell 13C chronology, which correlates with upstream dam releases. Furthermore, a relationship between river discharge and water δ18O can be used to reconstruct the timing of high discharge based on shell δ18O.

Other Description: Van Plantinga, A. A., & Grossman, E. L. (2018). Stable and clumped isotope sclerochronologies of mussels from the Brazos River, Texas (USA): Environmental and ecologic proxy. Chemical Geology.