Contrasting intensity of aragonite dissolution in glacial vs. interglacial intervals of a sea-level controlled subtropical carbonate succession

Aragonite and high-Mg calcite are abundant in modern, neritic temperate water systems but are nearly absent from their fossil counterparts. Dissolution of these metastable mineral phases will often leave no visible trace in the sedimentary record. Furthermore, it has been proposed that dolomitization is driven by reflux of mesohaline, aragonite undersaturated waters and that dolomite crystal growth is tightly coupled to aragonite dissolution in a temperate carbonate slope system. This study aims to clarify the processes responsible for this aragonite loss and associated dolomite formation in temperate carbonates. Biomarkers and microscopic techniques in combination with pore water analysis are used to investigate sediment cores from IODP Site U1460 on the outer ramp of the western Australian Shelf. It is shown that synsedimentary aragonite dissolution is negligible but increases significantly in a burial depth of ~ 5 m. This increase is controlled by the onset of incipient sulfate reduction, which is also interpreted to lower the kinetic inhibition for dolomite formation. However, the intensity of aragonite dissolution does not increase linearly but shows clear variations based on the availability of reactive organic matter, which is higher in interglacial compared to glacial intervals. Aragonite dissolution and Mg2+ loss from high-Mg calcite contribute to the precipitation of dolomite preferentially in interglacial sediments. This mechanism provides an indirect link between dolomite formation, aragonite dissolution, and orbital cycles. The outcome of this study contributes to a better understanding of the timing and mechanism of aragonite dissolution. (Poster)