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Internal waves and tides; Reflection seismics; Sapropel S1; Seismic oceanography; Levant Basin; Contour currents
Abstract:
Internal waves are widely present in world's oceans propagating in stratified ocean layers such as the seasonal pycnocline. At continental shelves and slopes, breaking of internal waves may create turbulence of sufficient energy to erode and transport sediments. In this study, we investigate the late Pleistocene to Recent impact of internal waves on the morphology of the Israeli Mediterranean continental slope. Based on mooring data, we show that the internal wave spectrum on the upper slope contains significant energy at near-inertial and semidiurnal tidal frequencies. Sediment subbottom profiler data show two fields of nearly contour parallel sediment waves located in water depths of 80 m–130 m and 190 m–350 m, respectively. A zone of flat seafloor morphology and remarkably constant slope inclination of 1.0°–1.2° separates both sediment wave fields. The entire stretch of seafloor between 80 m and 350 m corresponds to depths of major ocean density stratification, supporting the propagation of internal waves. In addition, this area is critically inclined with respect to semidiurnal internal tides and supercritically inclined with respect to near-inertial waves, two scenarios previously related to internal wave breaking. We propose that breaking internal waves control the inclination of the Israeli continental slope and contribute to sediment starvation within the zone of flat seafloor morphology. The formation of sediment waves is attributed to high-frequency trailing internal waves of similar wavelengths as sediment waves, observed within a seismic image of the water column. We correlate subbottom profiler data to a radiocarbon dated sediment core. No sediment waves formed from 16 cal ka–8 cal ka, indicating that the seafloor impact of internal waves ceased during a time of rapid sea level rise and fresh water input in the Eastern Mediterranean realm. The end of this period coincides with the formation of sapropel S1.
