Marine carbon reservoir, Corg-Ccarb coupling, and the evolution of the Proterozoic carbon cycle

Abstract

The post-2.0 Ga Proterozoic C isotope record reveals two distinct, yet interrelated trends: a stepwise increase in average ␦ 13 C from ϳ0‰ (calculated with respect to the Peedee belemnite isotope standard) prior to ca. 1.3 Ga to Ͼ؉5‰ in the Neoproterozoic, and a concomitant increase in the magnitude of isotopic excursions. Steady-state and nonsteady-state models suggest that these fundamental changes are best explained by a combination of evolving burial fluxes and a secular decrease in the size of the marine dissolved inorganic carbon (DIC) reservoir. The DIC reservoir size affects the sensitivity of the isotopic system to biogeochemical perturbation. Major rearrangements of carbon cycling during the Proterozoic, in part related to the evolving marine carbon reservoir, permit elevated ␦ 13 C values to be sustained for geologically long time spans. Recognition of this dependence on DIC reservoir size provides, for the first time, a direct link between changing carbonate precipitation styles and the marine C isotope record and may help constrain estimates of Proterozoic pCO 2 .

Platform-induced clay-mineral fractionation along a northern Tethyan basin-platform transect: implications for the interpretation of Early Cretaceous climate change (Late Hauterivian-Early Aptian)

“…þ2&; e.g., Fö llmi et al, 2006). This is explained by a buffering effect on the marine d 13 C record, through accelerated water cycle and increased delivery of Dissolved Inorganic Carbon (DIC) to the ocean under more humid climate conditions (e.g., Bartley and Kah, 2004;Godet et al, 2006).…”

Changes in the Si / P weathering ratio and their effect on the selection of coccolithophores and diatoms

“…The removal of C from Earth's surface reservoirs is constrained by the kinetics of chemical weathering reactions as it controls the burial of organic C, via input of dissolved nutrients to the ocean basins, and CaCO 3 , via alkalinity flux. The degree of coupling of organic C and CaCO 3 15 burial fluxes depends on the extent to which organic productivity is dominated by calcifying organisms (Bartley and Kah, 2004). A tight biological coupling becomes effective in the planktonic realm with the ecological success of planktonic calcifiers during the Mesozoic (Ridgwell, 2005).…”

C- and Sr-isotope stratigraphy of the São Caetano complex, Northeastern Brazil: a contribution to the study of the Meso-Neoproterozoic seawater geochemistry

“…Alternatively, Bartley and Kah (2003) and Frank et al (1997Frank et al ( , 2003 proposed that these slightly fluctuating C-isotope pathways should have been related to large changes in the biochemical cycles and in the mass balance between the inorganic (C carb ) and organic (C org ) carbon reservoirs; which would have resulted in 13 C depleted-anoxic deep ocean and 13 C-rich shallow marine waters.…”

“…Therefore, establishing factors that affected the seawater geochemistry during this time span has remained difficult. Based on the available data, it has been proposed that the early Mesoproterozoic C-and Sr-isotope composition of seawater remained in an apparent long-lasting steady state (Buick et al 1995, Brasier andLindsay 1998), while the middle-late Mesoproterozoic-early Neoproterozoic composition of seawater seems to have registered stronger perturbations in the geochemical cycles as a result of miscellaneous factors (Brasier and Lindsay 1998, Kah et al 1999, Bartley et al 2000, 2001, Bartley and Kah 2003, Frank et al 1997.…”

“…Few works (e.g Knoll et al 1995, Hall and Veizer 1996, Frank et al 1997, Kah et al 1999, 2001, Bartley et al 2001, Azmy et al 2001, Maheshwari et al 2002, Bartley and Kah 2003 have supplied reliable chemostratigraphic information for the construction of well constrained C-and Sr-isotope secular variation curves. Therefore, establishing factors that affected the seawater geochemistry during this time span has remained difficult.…”