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Tracking aquatic change using chlorine-specific carbon and nitrogen isotopes: The last glacial-interglacial transition at Lake Suigetsu, Japan

Lookup NU author(s): Professor Takeshi Nakagawa

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Abstract

Joint carbon and nitrogen isotope measurements were made from chlorins (chlorophyll a, phaeophytin a and pyrophaeophytin a) extracted from the last glacial-interglacial transition sediments of Lake Suigetsu, central Japan. These data highlight both the potential and difficulty of using chlorin-specific isotopes to track aquatic change from lake sediments. delta C-13 and delta N-15 of the three chlorins show coherent patterns with time, supporting the theory that phaeophytin a and pyrophaeophytin a are early diagenetic products of chlorophyll a and that despite this transition, their isotopic signatures remain intact. However, our data suggest that the isotopic composition of phaeophytin a and pyrophaeophytin a can be imprecise proxies for the isotope composition of chlorophyll a, possibly owing to the complex array of factors which affect the synthesis, transformation and sedimentation of these phaeopigments in nature. The total accumulation of organic matter in Lake Suigetsu appears to be controlled by the balance of allocthonous and authocthonous material as reflected by the C/N ratio. However, both bulk organic and chlorin-specific delta C-13 show similar changes, suggesting that the first order variability in bulk organic delta C-13 reflects aquatic change. By contrast, there is no similarity between chlorin and bulk delta N-15, suggesting that interpretation of bulk delta N-15 in this setting is compromised by diagenetic alteration. The isotopic composition of chlorins are interpreted to reflect the response of aquatic primary productivity to post-glacial environmental change. However, further research into the synthesis and transformation of chlorins in the modern environment is required in order to facilitate a more rigorous approach to interpreting isotope ratios in chlorins extracted from sediments.

Publication metadata

Author(s): Tyler J, Kashiyama Y, Ohkouchi N, Ogawa N, Yokoyama Y, Chikaraishi Y, Staff RA, Ikehara M, Ramsey CB, Bryant C, Brock F, Gotanda K, Haraguchi T, Yonenobu H, Nakagawa T

Publication type: Article

Publication status: Published

Journal: Geochemistry, Geophysics, Geosystems

Year: 2010

Volume: 11

Issue: 9

Print publication date: 23/09/2010

ISSN (print):

ISSN (electronic): 1525-2027

Publisher: American Geophysical Union

URL: http://dx.doi.org/10.1029/2010GC003186

DOI: 10.1029/2010GC003186

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