mole_content_of_biogenic_silica_expressed_as_silicon_in_sea_floor_sediment mol m-2 [MLM2] "Content" indicates a quantity per unit area. Biogenic silica is a hydrated form of silica (silicon dioxide) with the chemical formula SiO2.nH2O sometimes referred to as opaline silica or opal. It is created by biological processes and in sea water it is predominantly the skeletal material of diatoms. "Biogenic" means influenced, caused, or created by natural processes. The phrase "expressed_as" is used in the construction "A_expressed_as_B", where B is a chemical constituent of A. It means that the quantity indicated by the standard name is calculated solely with respect to the B contained in A, neglecting all other chemical constituents of A.
The surface called "sea floor" means the lower boundary of the ocean. "Sea floor sediment" is sediment deposited at the sea bed.