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The stable carbon isotopic composition of organic material in platform derived sediments: implications for reconstructing the global carbon cycle
Author(s) -
OEHLERT AMANDA M.,
LAMBWOZNIAK KATHRYN A.,
DEVLIN QUINN B.,
MACKENZIE GRETA J.,
REIJMER JOHN J. G.,
SWART PETER K.
Publication year - 2012
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.2011.01273.x
Subject(s) - total organic carbon , carbonate , diagenesis , geology , carbon cycle , sedimentary depositional environment , carbon fibers , total inorganic carbon , pelagic zone , δ13c , isotopes of carbon , dissolved organic carbon , geochemistry , pelagic sediment , mineralogy , cycling , paleontology , oceanography , environmental chemistry , sedimentary rock , stable isotope ratio , carbon dioxide , chemistry , ecology , materials science , ecosystem , structural basin , composite number , composite material , biology , quantum mechanics , physics , organic chemistry , history , archaeology
In pelagic carbonate sediments, the degree to which the δ 13 C values of inorganic and organic fractions co‐vary has been used to interpret rates of production, burial and decomposition of organic carbon. This relationship is relatively consistent through time, permitting estimates of organic carbon production and preservation. However, as the majority of pelagic sediments older than 200 Myr have been subducted, carbonate sediments deposited in epeiric seas and platforms are often substituted for pelagic carbonates in analyses of ancient global carbon cycling. There are well‐known pitfalls to using shallow marine carbonate materials, including diagenesis, semi‐isolation of depositional environments and input of different types of sediments with varying inorganic δ 13 C (δ 13 C inorganic ) values, which can obscure any global signatures. One method used to assess whether global changes in δ 13 C are accurately represented by δ 13 C inorganic records is to examine variations in the δ 13 C of co‐occurring organic material (δ 13 C organic ). If a δ 13 C organic record co‐varies with a co‐occurring δ 13 C inorganic record, it is argued that the signals must be related to variations in the global carbon cycle. This assumption has been investigated by analysing the isotopic composition of the organic carbon preserved in the uppermost 150 m of periplatform sediments recovered during ODP Leg 166 from the western margin of Great Bahama Bank. The δ 13 C organic values measured in this study were compared to previously published δ 13 C inorganic records measured on identical samples, thus allowing a study of the correlation between the two records through time. These analyses showed that the correlation coefficient between δ 13 C inorganic and δ 13 C organic increased from the proximal location (Site 1005, r 2 = 0·1), to the distal site (Site 1006, r 2 = 0·63). The importance of platform‐derived carbonate and organic material at the proximal location, Site 1005, is reflected in the absence of a co‐variation between inorganic and organic δ 13 C records, which exhibit no correlation on the platform itself. In contrast, the co‐variance in δ 13 C values at the basinal location, Site 1006, is explained by a two‐point mixing model, which demonstrates the importance of both pelagic and platform‐derived carbonate and organic carbon in generating the positive correlation between the organic and inorganic δ 13 C values; this results in a correlation between δ 13 C inorganic and δ 13 C organic records at Site 1006 that is unrelated to global carbon cycling. Such data question the applicability of using δ 13 C organic values to support the ability of δ 13 C inorganic values to record global carbon cycling in carbonates recovered from environments where multiple sources of carbonate and organic carbon contribute to the bulk δ 13 C signal.