Presentation Information
[AOS25-P13]Extraction method–dependent EEM–PARAFAC signatures of fluorescent organic matter in marine sediments
*Shigenobu Takeda1, Keita Saito1, Yuka Tatera1, Yoshiko Kondo2 (1.Japan Coast Guard, 2.Nagasaki University)
Keywords:
Marine sediments,FDOM,Alkaline extraction,PARAFAC analysis
Fluorescent dissolved organic matter (FDOM) in marine sediments provides valuable information on the sources and diagenetic alteration of sedimentary organic matter. However, differences in extraction protocols among previous studies complicate the interpretation and intercomparison of excitation–emission matrix (EEM) fluorescence characteristics and parallel factor analysis (PARAFAC)-derived components. Here, we evaluate how commonly used extraction methods influence the composition and recovery of sedimentary FDOM.
Sediment samples were collected from three Japanese coastal regions—the Sea of Okhotsk, Suruga Bay, and the northern Okinawa Trough. Water extraction was conducted by shaking freeze-dried sediments with ultrapure water for 24 h at 20°C. Alkaline extraction was performed using two approaches: (1) 24 h shaking with 0.1 M NaOH at 20°C and (2) ultrasonic treatment (three 10-min cycles) with 0.5 M NaOH at 60°C. For ultrasonic extraction, we also assessed the effect of 6 M HCl pre-treatment. Pore water obtained by centrifugation was analyzed for comparison. Extracts were analyzed using EEM fluorescence spectroscopy, and fluorescent components were resolved by PARAFAC analysis.
PARAFAC modeling identified five fluorescent components, comprising three humic-like and two protein-like components. For humic-like components, alkaline extraction was more effective than water extraction, and fluorescence intensities were higher for ultrasonic extraction than for 24 h shaking extraction. In addition, acid pre-treatment—reported to promote the dissociation of coordination bonds between humic substances and Ca or Fe—resulted in further increases in fluorescence intensity. In contrast, humic-like fluorescence was scarcely detectable in pore waters. Protein-like components also exhibited higher fluorescence intensities under ultrasonic alkaline extraction, consistent with the pattern observed for humic-like components. However, acid pre-treatment tended to reduce tryptophan-like fluorescence in some cases.
These results demonstrate that extraction methodology exerts strong control over EEM–PARAFAC signatures of sedimentary FDOM. Our findings provide important constraints for interpreting existing datasets obtained using different extraction protocols and suggest that ultrasonic alkaline extraction with acid pre-treatment is appropriate for characterizing humic-like organic matter in marine sediments.
Sediment samples were collected from three Japanese coastal regions—the Sea of Okhotsk, Suruga Bay, and the northern Okinawa Trough. Water extraction was conducted by shaking freeze-dried sediments with ultrapure water for 24 h at 20°C. Alkaline extraction was performed using two approaches: (1) 24 h shaking with 0.1 M NaOH at 20°C and (2) ultrasonic treatment (three 10-min cycles) with 0.5 M NaOH at 60°C. For ultrasonic extraction, we also assessed the effect of 6 M HCl pre-treatment. Pore water obtained by centrifugation was analyzed for comparison. Extracts were analyzed using EEM fluorescence spectroscopy, and fluorescent components were resolved by PARAFAC analysis.
PARAFAC modeling identified five fluorescent components, comprising three humic-like and two protein-like components. For humic-like components, alkaline extraction was more effective than water extraction, and fluorescence intensities were higher for ultrasonic extraction than for 24 h shaking extraction. In addition, acid pre-treatment—reported to promote the dissociation of coordination bonds between humic substances and Ca or Fe—resulted in further increases in fluorescence intensity. In contrast, humic-like fluorescence was scarcely detectable in pore waters. Protein-like components also exhibited higher fluorescence intensities under ultrasonic alkaline extraction, consistent with the pattern observed for humic-like components. However, acid pre-treatment tended to reduce tryptophan-like fluorescence in some cases.
These results demonstrate that extraction methodology exerts strong control over EEM–PARAFAC signatures of sedimentary FDOM. Our findings provide important constraints for interpreting existing datasets obtained using different extraction protocols and suggest that ultrasonic alkaline extraction with acid pre-treatment is appropriate for characterizing humic-like organic matter in marine sediments.