2:15 PM - 2:30 PM
[BPT03-03] Search for diatom biomarkers by lipid analysis of diatom species from North Pacific Ocean
Keywords:Diatom, Steroid, North Pacific Ocean, Biomarkers, Primary productivity
Diatoms are one of the most diverse and abundant phytoplankton in the world, containing over 30,000 species estimated (Mann & Vanormelingen, 2013). They are also important in the biogeochemical cycle, by 20% contribution to the global primary production, which is equivalent to all rainforests combined (Armbrust, 2009). Diatom diversity radically increased around the Eocene/Oligocene boundary and the late Miocene, alongside a decrease in diversity of dinoflagellates and coccolithophorids (Falkowski et al., 2004). Therefore, the evaluation of the diatom primary productivity is essential for understanding long time-scale biogeochemical cycle and marine ecosystem as well as paleoceanographic variation. Biomarker proxies can provide the quantitative estimates of diatom productivity during geological times, especially during the Neogene. However, until recently diatom biomarker analysis has been limited to Atlantic and Southern Ocean species and cultures. In the present study, we analyzed lipid biomarkers of typical North Pacific diatom cultures and searched for effective diatom biomarkers as a proxy.
The diatom cultures studied were collected from the North Pacific and harvested. We used 6 species, Chaetoceros debilis, Neodenticula seminae, Proboscia alata, Rhizosolenia hebetata, Stephanopyxis nipponica, and Thalassiosira nordenskioeldii, which are major species in North Pacific Ocean. Lipids were extracted with dichloromethane/methanol, and separated to aliphatic, aromatic, ketone-ester, and polar fractions. Lipids were identified and quantified via GC-MS and GC-FID.
We identified various biomarkers including fatty acids, sterols, and long-chain alkenes. Sterol compositions in the species varied; cholesterol (C27 Δ5) and ostreasterol (C28 Δ5,24) were commonly identified. Ostreasterol is thought to be diatom biomarker because of its detection from only diatom. We examined the possibility of sterols as a comprehensive diatom productivity proxy in geological marine sediments. Also, there were two key biomarkers detected specifically from certain species; 24-norsterol (C26 Δ5,22E), which is thought to be the precursor of 24-norcholestane found in Neogene diatomaceous sediments, was detected from C. debilis. However, the producer(s) of 24-norsterol was unclear. In our study, the 24-norsterol was firstly identified from a cosmopolitan diatom C. debilis. 22-dehydrocholesterol (C27 Δ5,22E) was abundantly detected from N. seminae with high contribution over 75% of total sterols. Considering the most dominance of N. seminae in the North Pacific, the 22-dehydrocholesterol can be typical diatom biomarker in the North Pacific. In addition, C25 HBI alkenes from R. hebetata, and long-chain alkyl-diols from P. alata were unique biomarkers to these species. The significance of these biomarkers and its application as North Pacific diatom productivity proxy will also be discussed.
References
Mann & Vanormelingen., 2013., Journal of Eukaryotic Microbiology, 60, 414-420.
Armbrust., 2009., Nature, 459, 185-192.
Falkowski et al., 2004., Science, 305, 354-360.
The diatom cultures studied were collected from the North Pacific and harvested. We used 6 species, Chaetoceros debilis, Neodenticula seminae, Proboscia alata, Rhizosolenia hebetata, Stephanopyxis nipponica, and Thalassiosira nordenskioeldii, which are major species in North Pacific Ocean. Lipids were extracted with dichloromethane/methanol, and separated to aliphatic, aromatic, ketone-ester, and polar fractions. Lipids were identified and quantified via GC-MS and GC-FID.
We identified various biomarkers including fatty acids, sterols, and long-chain alkenes. Sterol compositions in the species varied; cholesterol (C27 Δ5) and ostreasterol (C28 Δ5,24) were commonly identified. Ostreasterol is thought to be diatom biomarker because of its detection from only diatom. We examined the possibility of sterols as a comprehensive diatom productivity proxy in geological marine sediments. Also, there were two key biomarkers detected specifically from certain species; 24-norsterol (C26 Δ5,22E), which is thought to be the precursor of 24-norcholestane found in Neogene diatomaceous sediments, was detected from C. debilis. However, the producer(s) of 24-norsterol was unclear. In our study, the 24-norsterol was firstly identified from a cosmopolitan diatom C. debilis. 22-dehydrocholesterol (C27 Δ5,22E) was abundantly detected from N. seminae with high contribution over 75% of total sterols. Considering the most dominance of N. seminae in the North Pacific, the 22-dehydrocholesterol can be typical diatom biomarker in the North Pacific. In addition, C25 HBI alkenes from R. hebetata, and long-chain alkyl-diols from P. alata were unique biomarkers to these species. The significance of these biomarkers and its application as North Pacific diatom productivity proxy will also be discussed.
References
Mann & Vanormelingen., 2013., Journal of Eukaryotic Microbiology, 60, 414-420.
Armbrust., 2009., Nature, 459, 185-192.
Falkowski et al., 2004., Science, 305, 354-360.