Comparisons On Sterol Biomarkers From Algae Cultures, Suspended Particles And Marine Sediments In The East China Sea And The Yellow Sea

Due to dominant contribution of diatoms for marine productivity, it is significantto reconstruct diatom productivity for understanding the evolution of marineproductivity and climate change. Brassicasterol as diatoms indicator has been widelyused to reconstruct diatom productivity, whereas some studies indicated theoccurrences of this compound in some dinoflagellates, coccolithforids, cryptophytesand its uncommon distribution in diatoms. The results of algae culture suggest that24-methylenecholesterol could be more suitable for indicating diatoms comparingwith brassicasterol owing to its high concentration and more common distribution indiatoms. However, this result has not been investigated in suspended particles andsediment samples. In this study, sterol compounds in dominant alga, suspendedparticles and sediments from the East China Sea and the Yellow Sea were measured.The results indicate that24-methylenecholesterol has relatively higher abundancesand more common occurrence in diatoms in comparion with brassicasterol. Inaddition,24-methylenecholesterol is detected in dinoflagellate Prorocentrumdonghaiense, while brassicasterol is found in all of three cultured dinoflagellatespecies. The distribution patterns of24-methylenecholesterol contents in suspendedparticles and sediments are in accord with brassicasterol, but brassicasterol contentshave higher values, which could be due to better preservation of brassicasterol.Therefore, the comparison of brassicasterol with24-methylenecholesterol indicatessedimentary brassicasterol could be more reliable diatoms indicator for diatomsreconstruction in the East China Sea and the Yellow Sea.Brassicasterol content in sediments is affected by the production and subsequentpreservation. In order to accurately reconstruct diatom productivity, preservationefficiency should be considered. Middelburg model (1989) is used to evaluate degradation process of brassicasterol in sediment cores10694and DH5-1. Thedifference between measured data and modeled data is used to reflect the change ofdiatom export productivity. Brassicasterol curves of the core10694after1975s andDH5-1after1873s are similar to their modeled degradation curves while thedifferences between measured data and modeled data can still observed suggestingboth the degradation and diatoms production affect brassicasterol contents in thesecores. However, brassicasterol curve of the core10694before1975s is different frommodeled degradation curve, suggesting export production controlled the changes ofbrassicasterol contents before1975s. The differences between measured and modeledbrassicasterol contents in core10694suggest increasing diatom productivity since1930, which could be related with increased nutrient supply in the euphotic zonecaused by strengthened East Asia Winter Monsoon and anthropogenic discharge.Similar increasing diatom productivity observed since1930in core DH5-1isinterpreted as a result of increased nutrient concentration of Changjiang Diluted Water(CDW) and strengthened East Asia Winter Monsoon.