Silicate, linearly interpolated from CARS2000 mean and seasonal fields to 0.1 degree spaced grid, at depths of 0, 150, 500, 1000 and 2000 metres. The loess filter used to create CARS2000 resolves at each point a mean value and a sinusoid with 1 year period (and in some cases a 6 month period sinusoid - the "semi-annual cycle".) The provided "annual amplitude" is simply the magnitude of that annual sinusoid. CARS is a set of seasonal maps of temperature, salinity, dissolved oxygen, nitrate, phosphate and silicate, generated using Loess mapping from all available oceanographic data in the region. It covers the region 100-200E, 50-0S, on a 0.5 degree grid, and on 56 standard depth levels. Higher resolution versions are also available for the Australian continental shelf. The data was obtained from the World Ocean Atlas 98 and CSIRO Marine and NIWA archives. It was designed to improve on the Levitus WOA98 Atlas, in the Australian region. CARS2000 is derived from ocean cast data, which is always measured above the seafloor. However, for properties which do not change rapidly near the seafloor, this would not lead to a significant error. All the limitations of CARS2000 also apply here.