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doi:10.2204/iodp.proc.320321.206.2013

Methodology

All biogenic silica (opal) analyses were conducted at the Center for Marine Environmental Sciences (MARUM; University of Bremen, Bremen, Germany). Opal procedures followed Müller and Schneider (1993), who modified the method originally proposed by DeMaster (1981). The wet-chemical leaching technique involves the extraction of biogenic silica using hot alkaline solutions, measurements by using inductively coupled plasma–emission spectroscopy (ICP-ES) coulometry, and correction for nonbiogenic silica released from coexisting aluminosilicates and quartz (Müller and Schneider, 1993).

An important advantage of the automated extraction method used in our measurements is that the method provides complete biogenic silica recovery and corrects for the nonbiogenic silica. The method determines only one element (Si), and no assumption with respect to the sediment composition has to be made (Müller and Schneider, 1993). A weak point in the manual technique is that the linear slope and the extrapolated intercept values are based on only a few measurements (usually three or four). Based on replicate measurements of silicon standard solutions, the precision of the analytical system is better than +0.5% (Müller and Schneider, 1993).

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