1:45 PM - 2:00 PM
[MIS22-01] Biomarker analysis of suspended particles in sea surface layers of the northwestern Pacific off the eastern Hokkaido to the Sanriku coast
Keywords:SPOM, Biomarkers, Sterol, Fatty acid, Northwest Pacific Ocean
The biological pump globally exports particulate organic carbon (POC) from sea surface to deep waters. Recently, the biological pump system is noticed for fixation and sequestration of atmospheric CO2 as geoengineering using marine carbon cycling. The POC export is known to promote mainly by the aggregates of living organisms, detritus, fecal pellet, and inorganic matter (Alldredge et al. 1993). The export flux of POC is thought to be controlled by multiple biological systems, which are not only primary productivity but also food web including grazing by predator and microbial decomposition. To understand such complex food web, more refractory lipid compounds, biomarkers, can be useful for tracing the POC and evaluating quantitatively for fixation and sequestration of CO2. In the present study, we analyzed lipid biomarkers of suspended particulate organic matter (SPOM) in surface to subsurface waters to examine applicability of the biomarkers as the quantitative tracers of food web in marine environment.
We used the SPOM samples collected from sea surface and subsurface layers (0 to 100 m) of the northwestern Pacific off the eastern Hokkaido to the Sanriku coast (A line) during the Hokkou-maru HK2405 cruise (May 10 to 21, 2024) by filtrating with GF/F glass filters. 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.
In the site of the northwestern Pacific off Hokkaido (A-07 site), C8-C22 fatty acids including C20:5 (EPA) and C22:6 (DHA), which are produced by mainly microalgae such as diatom and zooplankton, respectively, were identified as major lipids. The DHA and EPA were hardly detected in SPOM samples from the sea surface, while their concentrations and relative abundances in total fatty acids were highest in chlorophyll maximal depth. The DHA and EPA in the SPOM from chlorophyll max depth might be derived mainly from the zooplankton such as labyrinthula through the exchange of these fatty acids during grazing diatom. Also, diatomaceous steroids, brassicasterol, occelasterol, and ostreasterol, were abundantly detected in the subsurface layers. C29 sterols such as β-sitosterol, which are usually produced by terrestrial plants, were significantly detected in all SPOM samples. The β-sitosterol concentrations varied with depth as similar to those of DHA and EPA, while the relative abundances of β-sitosterol increased with depth, suggesting that refractoty terrigenous organic matter were more highly contributed as the origin of β-sitosterol at deeper depths. In addition, we could detect long-chain alkyl diols, which are produced by diatom genus Proboscia and eustigmatophyte, as well as long-chain alkenones, which are produced by Haptophyte (coccolithophorid) genus Gephyrocapsa, in all SPOM samples. The concentrations of the alkenones were very low, so that productivity, contribution in primary production, and export flux of Haptophyte were likely to be low in A-07 site in spring season.
We used the SPOM samples collected from sea surface and subsurface layers (0 to 100 m) of the northwestern Pacific off the eastern Hokkaido to the Sanriku coast (A line) during the Hokkou-maru HK2405 cruise (May 10 to 21, 2024) by filtrating with GF/F glass filters. 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.
In the site of the northwestern Pacific off Hokkaido (A-07 site), C8-C22 fatty acids including C20:5 (EPA) and C22:6 (DHA), which are produced by mainly microalgae such as diatom and zooplankton, respectively, were identified as major lipids. The DHA and EPA were hardly detected in SPOM samples from the sea surface, while their concentrations and relative abundances in total fatty acids were highest in chlorophyll maximal depth. The DHA and EPA in the SPOM from chlorophyll max depth might be derived mainly from the zooplankton such as labyrinthula through the exchange of these fatty acids during grazing diatom. Also, diatomaceous steroids, brassicasterol, occelasterol, and ostreasterol, were abundantly detected in the subsurface layers. C29 sterols such as β-sitosterol, which are usually produced by terrestrial plants, were significantly detected in all SPOM samples. The β-sitosterol concentrations varied with depth as similar to those of DHA and EPA, while the relative abundances of β-sitosterol increased with depth, suggesting that refractoty terrigenous organic matter were more highly contributed as the origin of β-sitosterol at deeper depths. In addition, we could detect long-chain alkyl diols, which are produced by diatom genus Proboscia and eustigmatophyte, as well as long-chain alkenones, which are produced by Haptophyte (coccolithophorid) genus Gephyrocapsa, in all SPOM samples. The concentrations of the alkenones were very low, so that productivity, contribution in primary production, and export flux of Haptophyte were likely to be low in A-07 site in spring season.