The potential of seep carbonates to preserve the seawater isotope compositions

Abstract

Abstract The isotopic compositions of authigenic minerals of marine sediments are potential proxies for reconstructing paleoenvironmental conditions. However, the reliability and applicability of this tracer remain elusive due to the limited spatial distribution scope and alteration during early diagenesis. Here we report isotopic measurements of seep carbonates (calcium, molybdenum, strontium, neodymium) generated by gas hydrate dissociation, sampled from a core drilled at the South China Sea. Our results show that there is approximately −1.2‰ calcium isotopic fractionation between aragonite and seawater. On the other hand, the molybdenum, strontium, and neodymium isotopic compositions are similar to those found in modern seawater. These results indicate that aragonite-dominated seep carbonate, which preferentially precipitates in proximity to the seawater-sediment interface, can preserve the pristine seawater isotopic signatures. Therefore, we infer that aragonite-dominant seep carbonate is a promising archive for coeval seawater chemistry.