Sediment waves in the Caroline Basin suggest evidence for Miocene shifts in bottom water flow in the western equatorial Pacific

Abstract

We describe abyssal sediment waves in seismic profiles from the Caroline Basin, western Pacific Ocean, which indicate bottom currents at this location have shaped the seabed beginning in the early to mid-Miocene. Our evidence is based on 2D high-resolution multi-channel seismic data we collected in 2013 during a site survey for IODP Expedition 363. Drilling within this grid (at IODP Site U1490) was completed in late 2016 and we expect results will provide the age and composition needed to evaluate the paleoceanographic implications of the geomorphologic history we describe. Our seismic grid reveals roughly 150ms (two-way travel time; roughly 135m) of sediment waves with 10–40ms wave heights (roughly 9–36m) and 1–2km wavelengths. These waves most likely accumulated in carbonate-rich sediments, based on DSDP Site 62 (450km to the south but lacking evidence of bottom currents in profiles or cores). The wave-like bedforms in our survey grid are independent of underlying structures and may have developed in response to an early Neogene intensification of bottom water flow documented at ODP Site 1124 in the SW Pacific (Carter et al., 2004). Steady growth and slow NW migration of the waves in the survey grid continued for much of the Miocene. Above ~250ms (roughly 212m) below the seafloor lateral migration halted and wave growth slowed. Today waves are present on the seafloor due to vertical aggradation along the flank of a gentle ridge at the northern edge of our survey grid. We propose this evolution of wave morphology is linked to global climatic events that drove thermohaline circulation throughout the world's oceans.