Compound-Specific Radiocarbon Analysis of Organic Compounds from Mount Fuji Proximal Lake (Lake Kawaguchi) Sediment, Central Japan

Abstract

Differential sources of sedimentary organic compounds in a volcanic region were revealed by determining radiocarbon content (Δ14C) of organic compounds in surface sediments from Lake Kawaguchi, at the northern foot of Mount Fuji, central Japan. The Δ14C values of C16 fatty acid (−124‰) and chlorophyll a (Chl a) (−133‰) were similar to the Δ14C of dissolved inorganic carbon (DIC) in surface water (−117‰), suggesting that a significant portion of these compounds originated from modern primary producers with a reservoir age of ~1000 years. On the other hand, a large offset between the Δ14C values of Chl a (−133‰) and those of 132, 173-cyclopheophorbide-a-enol (−169‰) and pheophytin a (−179‰) suggested contributions from older pigments. In addition, the Δ14C of long-chain (C24, C26, and C28) fatty acids (−183 to −75‰) showed a large offset from that of a plant leaf remain (0‰) within sediments, demonstrating that the long-chain fatty acids were affected by substantial contributions from pre-aged terrestrial materials. Overall, the sedimentary organic compounds gave 14C ages older than the plant leaf fragment within sediments; however, the similarity between Δ14C of the C16 fatty acid and DIC implies potential for applying compound-specific radiocarbon analysis as a dating tool in volcanic lake environments.

Dating Lake Sediments Using Compound‐Specific 14C Analysis of C16 Fatty Acid: A Case Study From the Mount Fuji Volcanic Region, Japan

“…The 14 C age of the plant leaf within the Kg layer (2,979 ± 31 years BP) yielded a calibrated age of 3,149 ± 54 cal BP. This is almost identical to the age of the Kg eruption (3,149 ± 12 cal BP; Tani et al, 2013), which confirms the previous finding that the plant leaf remains are the most precise recorder of age in lacustrine sediments (Nakamura et al, 2012;Yamamoto et al, 2020). The 14 C offset between the C 16 fatty acid and a plant leaf from the Kg interval (1,003 ± 73 14 C years) is consistent (within error) with the C 16 fatty acid in the core top sediments (983 ± 56 years BP) and the modern lake reservoir age (1,058 ± 35 C years) estimated in June 2017 from Lake Kawaguchi surface water DIC (Δ 14 C = −117 ± 2‰; Yamamoto et al, 2020) and atmospheric CO 2 (Δ 14 C = 7 ± 3‰ [an average of CO 2 data from five stations available]; ICOS RI, 2019).…”

“…We selected C 16 , C 24 , and C 26 fatty acids as the target compounds because of their high abundance in the Lake Kawaguchi sediments, as compared to other homologs. A previous study in the surface sediment from Lake Kawaguchi revealed that the carbon in C 16 fatty acid derives from contemporary primary producers such as diatoms, whereas the C 24 and C 26 fatty acids received substantial contributions from pre‐aged materials (Yamamoto et al., 2020).…”

“…(c) Bathymetric map of Lake Kawaguchi with the location of core KA-1 (created from data provided by the Geospatial Information Authority of Japan). that the carbon in C 16 fatty acid derives from contemporary primary producers such as diatoms, whereas the C 24 and C 26 fatty acids received substantial contributions from pre-aged materials (Yamamoto et al, 2020).…”

Organic carbon accumulation and productivity over the past 130 years in Lake Kawaguchi (central Japan) reconstructed using organic geochemical proxies

“…4c), suggesting that the values were not solely influenced by the source of organic matter and productivity within the lake. Nevertheless, we cannot fully rule out the possibility that the Suess effect may be overestimated for the d 13 C TOC since Yamamoto et al (2020) have recently reported a 14 C age of 937 ± 22 yr BP from the lake DIC in Lake Kawaguchi, suggesting potential influence of exogenous old carbon sources and groundwater.…”

“…The C 16 fatty acid can be abundantly produced by phytoplankton, as well as other organisms such as terrestrial plants, animals, and bacteria (Harwood 1996). However, identical radiocarbon isotope ratios (D 14 C) between the sedimentary C 16 fatty acid and dissolved inorganic carbon (DIC) in surface water, as well as chlorophyll a in the sediment, suggest that it originates from contemporary primary producers like diatoms (Yamamoto et al 2020).…”