In 2014, Bin Chen et al. claimed that the primary reservoir of this element on Earth is the inner core. The downward flux of this element is plotted against depth on the Martin curve. The ratio of this element to nitrogen determines whether soil nitrogen undergoes immobilization or remineralization. Abundance of this element is regulated by negative feedback in which silicate weathering causes burial of this element in the seafloor, which also occurs as a result of the biological pump. Two fractions (10[1])of this element notated DOM and POM are distinguished by particle size. Mangrove forests and tidal marshes are of interest (10[1])in “blue” methods for sequestering this element. For 10 (10[1])points, name this element whose biogeochemical cycling may involve fixation of its inorganic dioxide into organic matter. ■END■