Sediment Waves Beneath the West Pacific Warm Pool on Eauripik Rise: A Direct Indicator of Long-Term Bottom Current Flow

Abstract:

Variations in ocean dynamics of the western Pacific warm pool (WPWP) have significant impacts on global climate, and understanding this relationship can improve predictions of future climate trends. We report on progress towards establishing a history of water column structure and air-sea interaction of this critical part of the global climate system. Sites proposed and now approved for future drilling by IODP Exp. 363 were surveyed with 2D high-resolution multi-channel seismic grids during cruise 1313 of the R/V Roger Revelle in September 2013. Here we describe observations at proposed site WP2 on the northern Eauripik Rise, near the northern limb of the WPWP. Approximately 400 m of buried sediment waves, with amplitudes of 10-20 m and wavelengths of 1-2 km, are prevalent throughout the ~ 10 x 15 km survey grid. Abyssal sediment waves provide direct evidence of circulation in the deep sea, and can be tied to indirect circulation indicators in sediment cores. Additionally, changes in circulation indicated by changes in bedform geometry can be associated with climatic oscillations. The sediment waves were mapped, characterized, and converted to depth using seismic stacking velocities. Biostratigraphy at DSDP Site 62, 450 km south of WP2 on Eauripik Rise provided age constraints on several horizons correlated between these locations. The oldest waves at WP2 (~ 15 Ma; 400 mbsf) migrate north and increase in amplitude upsection until a key horizon at roughly 280 mbsf is reached. At this level wave migration stops, though wave heights continue to decrease until at seafloor all seismic evidence of current-controlled deposition has disappeared. This morphologic shift, suggested from available data to occur ~10 Ma, indicates a change from strong, long-term current-controlled sedimentation to conditions with little to no bottom current flow. Drilling at WP2 will pinpoint the time of this change and will aid the understanding of the evolution of the WPWP since the middle Miocene, in particular the changes in deep Pacific circulation at the northern limb of the WPWP, with applications to global climate changes.