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A critical review of marine sedimentaryδ 13 C org ‐ p CO 2 estimates: New palaeorecords from the South China Sea and a revisit of other low‐latitude δ 13 C org ‐ p CO 2 records
Author(s) -
Kienast Markus,
Calvert Stephen E.,
Pelejero Carles,
Grimalt Joan O.
Publication year - 2001
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2000gb001285
Subject(s) - terrigenous sediment , sedimentary rock , geology , glacial period , sedimentary organic matter , oceanography , latitude , physical geography , paleontology , geography , geodesy
In an attempt to understand better the local biogeochemistry of the South China Sea (SCS) and to unravel the contribution of this marginal low‐latitude basin to changes in atmospheric CO 2 concentrations, we analyzed the carbon isotopic composition of organic matter (δ 13 C org ) in four sediment cores from throughout the SCS covering the last 220 kyr. Higher values (around −19.5 to −20.5‰) mark glacial stages, while lower values (around −21 to −22.5‰) are characteristic of interglacials. Following well established procedures, the δ 13 C org records are converted to local p CO 2 estimates. On the basis of these and other low‐latitude δ 13 C org − p CO 2 estimates from the literature, we present a critical evaluation of the use of δ 13 C of bulk sedimentary organic matter to hindcast past changes in local CO 2 (aq). Three crucial pitfalls are identified. (1) Given the present inability to quantify precisely the time‐varying amount of terrigenous C org input to marine sediments, absolute values of p CO 2 estimates based on bulk sedimentary C org are questionable. (2) None of the low‐latitude sedimentary δ 13 C org − p CO 2 records shows the expected correlation between temporal changes in upwelling intensity and CO 2 estimates, most likely due to the antagonistic influences of CO 2 (aq) and phytoplankton growth rate on δ 13 C org . (3) A detailed comparison of marine δ 13 C org − p CO 2 records with the Vostok CO 2 record reveals significant differences in phasing, specifically at the end of the last deglaciation and during the oxygen isotope stage 5/4 transition. However, in areas where equilibrium between oceanic and atmospheric CO 2 occurs, for example the SCS and the Mediterranean, the timing of changes in δ 13 C org should agree with the CO 2 record from ice cores if δ 13 C org is a reliable proxy for changes in CO 2 (aq). Taken together, the compilation of records presented here cautions the use of δ 13 C org as an unambiguous tracer of dissolved molecular CO 2 in the surface ocean and calls for a re‐evaluation of the role of the low‐latitude ocean on temporal changes in atmospheric CO 2 .