For the first time a biological source for the long-chain alkyl 1,14-diols and 12-hydroxy methyl alkanoates, lipids widely occurring in the marine water column and sediments, has been identified. Cultures of Proboscia indica and Proboscia alata, rhizosolenoid diatoms belonging to the widespread diatom genus Proboscia, contain C28, C28:1, C30, and C30:1 alkyl 1,14-diols, and C27 and C29 12-hydroxy methyl alkanoates as major neutral lipids. These components form a substantial fraction of lipid fractions from sediment traps or sediments, especially in areas with an elevated primary production such as upwelling regions. Examination of literature data reveals that as much as 20 to 35% of the total lipid flux in the Arabian Sea is derived from Proboscia diatoms during the start of the upwelling season. Their rapid transfer to the water-sediment interface may explain why corresponding 1,14-keto-ols, inferred oxidation products of diols, are hardly formed. These interpretations are supported by compound-specific carbon isotopic analysis of long-chain keto-ols and diols in surface sediments of the Arabian Sea. The data indicate that long-chain alkyl 1,14-diols and 12-hydroxy methyl alkanoates can be applied as indicators for high-nutrient conditions in the photic zone.