Processes controlling the formation of the Mertz Drift, George Vth continental shelf, East Antarctica: evidence from 3.5 kHz sub-bottom profiling and sediment cores

Recently discovered sediment drift deposits on the Antarctic continental shelf provide access to information on the Holocene palaeoceanography of the bottom current regime within deep shelf basins that were previously inaccessible. The George Vth Basin on the East Antarctic margin has been identified by oceanographers as an important source of Antarctic Bottom Water, hence the Holocene history of bottom current activity here may be relevant to variations in bottom water export. The analysis of seismic and sediment core data indicates that the Holocene history of sedimentation on the Mertz Drift occurred in response to a progressively changing bottom current regime. The stratigraphic horizons that mark the onset of different phases of deposition are diachronous within the Mertz Drift. Rapidly accumulating, laminated siliceous mud and diatom ooze (SMO) that comprises the bulk was deposited first on the eastern side of the drift (5000–3500 years BP) and later on the lobate, southwestern side (3000 and 2000 years BP). This spatial variation in timing of rapid SMO deposition is attributed to a gradual increase in bottom current speed over the mid- to late Holocene. The deposition of true drift-style sedimentary features is restricted to a small area in the southwestern corner of the Mertz Drift, with the remaining parts characterised by drape and fill deposits. An estimation of the mass flux of sediment reaching the drift suggests that the modern, stronger bottom currents need carry only a very low suspended sediment concentration to explain the measured 10-fold reduction in sediment accumulation rates after 3000 years BP. Cores from the Mertz Drift and from a perched basin located 60 km to the east contain the same lithologic units and have the same approximate age. Thus the palaeoenvironmental interpretations based on the Mertz Drift can be extrapolated over the entire George Vth Basin region.