Origins and fate of dissolved sterols in the Weddell Sea, Antarctica

Dissolved sterols were investigated in the autumnal Weddell Sea, where stratification is weak and global bottom water formation takes place. Among 25 compounds identified, the zoosterol cholest-5-en-3β-ol exhibited highest concentrations. 24-Methycholesta-5,22E-dien-3β-ol and cholesta-5,22E-dien-3β-ol followed next in abundance. Levels of cholest-5-en-3β-ol remained roughly unchanged throughout the water column. Phytosterol concentrations decreased by a factor of 20 towards the bottom, but displayed a similar pattern. In general, the distribution of dissolved sterols was neither correlated to oceanographic features nor to biological ones, but reflected dissolution of particles with different sinking rates. Low levels in newly formed bottom water are consistent with extensive degradation in source waters on the shelf. From geographical and seasonal comparisons a degradation half-life of three weeks was estimated for phytosterols in surface waters. This half-life is slightly shorter than reported earlier in a warm oligotrophic ocean. Newly formed bottom water does not contribute significantly to sterol export into adjacent oceans.