Hi Tim,

Using the keywords: marine, organic carbon, and atmospheric CO2 with a search on my ref database (over 30,000 refs just on stable isotopes) the selection, as given below, was generated (including abstracts). Maybe not all hits yet ‘exactly’ what you looked for, but at least contains info of the type you wanted. Playing with keywords might improve this also (did not want to do that myself for ‘restricted time reasons’).
I expect to make this database, together with some more helpful info for stable isotopes, available within half a year – I will announce this on the list (if allowed).

Best wishes and hope it helps.

Searching result is:

Craig, H. (1953). "The geochemistry of the stable carbon isotopes." Geochim. Cosmochim. Acta 3(2-3): 53-92 doi: 10.1016/0016-7037(53)90001-5.
    Several hundred samples of carbon from various geologic sources have been analyzed in a new survey of the variation of the ratio C13/C12 in nature. Mass spectrometric determinations were made on the instruments developed by H. C. Image and his co-workers utilizing two complete feed systems with magnetic switching to determine small differences in isotope ratios between samples and a standard gas. With this procedure variations of the ratio C13/C12 can be determined with an accuracy of ±0.01% of the ratio.
The results confirm previous work with a few exceptions. The range of variation in the ratio is 4.5%. Terrestrial organic carbon and carbonate rocks constitute two well defined groups, the carbonates being richer in C13 by some 2%. Marine organic carbon lies in a range intermediate between these groups. Atmospheric CO2 is richer in C13 than was formerly believed. Fossil wood, coal and limestones show no correlation of C13/C12 ratio with age. If petroleum is of marine organic origin a considerable change in isotopic composition has probably occurred. Such a change seems to have occurred in carbon from black shales and carbonaceous schists. Samples of graphites, diamonds, igneous rocks and gases from Yellowstone Park have been analyzed. The origin of graphite cannot be determined from C13/C12 ratios. The terrestrial distribution of carbon isotopes between igneous rocks and sediments is discussed with reference to the available meteoritic determinations.Isotopic fractionation between iron carbide and graphite in meteorites may indicate the mechanism by which early fractionation between deep seated and surface terrestrial carbon may have occurred.

Maberly, S. C., J. A. Raven, et al. (1992). "Discrimination between 12C and 13C by marine plants." Oecologia 91(4): 481-492 doi: 10.1007/BF00650320.
    The natural abundance13C/12C ratios (as
δ13C) of organic matter of marine macroalgae from Fife and Angus (East Scotland) were measured for comparison with the species' ability to use CO2 and HCO 3  -  for photosynthesis, as deduced from previously published pH-drift measurements. There was a clear difference in δ13C values for species able or unable to use HCO 3  - . Six species of Chlorophyta, 12 species of Phaeophyta and 8 species of Rhodophyta that the pH-drift data suggested could use HCO 3  -  had δ13C values in the range -8.81‰ to -22.55‰. A further 6 species of Rhodophyta which the pH-drift data suggested could only use CO2 had δ13C values in the range -29.90‰ to-34.51‰. One of these six species (Lomentaria articulata) is intertidal; the other five are subtidal and so have no access to atmospheric CO2 to complicate the analysis. For these species, calculations based on the measured δ13C of the algae, the δ13C of CO2 in seawater, and the known13C/12C discrimination of CO2 diffusion and RUBISCO carboxylation suggest that only 15–21% of the limitation to photosynthesisin situ results from CO2 diffusion from the bulk medium to the plastids; the remaining 79–85% is associated with carboxylation reactions (and, via feedback effects, down-stream processes). This analysis has been extended for one of these five species,Delesseria sanguinea, by incorporating data onin situ specific growth rates, respiratory rates measured in the laboratory, and applying Fick's law of diffusion to calculate a boundary layer thickness of 17–24 μm. This value is reasonable for aDelesseria sanguinea frondin situ. For HCO 3  -  -using marine macroalgae the range of δ13C values measured can be accommodated by a CO2 efflux from algal cells which range from 0.306 of the gross HCO 3  -  influx forEnteromorpha intestinalis (δ13C=-8.81‰) in a rockpool to 0.787 forChondrus crispus (δ13C=-22.55‰). The relatively high computed CO2 efflux for those HCO 3  -  -users with the more negative δ13C values implies a relatively high photon cost of C assimilation; the observed photon costs can be accommodated by assuming coupled, energy-independent inorganic carbon influx and efflux. The observed δ13C values are also interpreted in terms of water movement regimes and obtaining CO2 from the atmosphere. Published δ13C values for freshwater macrophytes were compared with the ability of the species to use CO2 and HCO 3  -  and again there was an apparent separation in δ13C values for these two groups. δ13C values obtained for marine macroalgae for which no pH-drift data are available permit predictions, as yet untested, as to whether they use predominantly CO2 or HCO 3  -

Beerling, D. J. (1997). "Interpreting environmental and biological signals from the stable carbon isotope composition of fossilized organic and inorganic carbon." J. Geol. Soc. London 154(2): 303-309 doi: 10.1144/gsjgs.154.2.0303.
    Stable carbon isotope studies on marine and terrestrial organic and inorganic carbon provide a means for detecting global climate change and for reconstructing past concentrations of atmospheric CO2. Comparison between the CO2 estimates reconstructed from carbon isotope studies for the past 150Ma show good agreement with the predictions of a long-term carbon-cycle model based on mass-balance studies. Further, the CO2 estimates from these sources over the entire Phanerozoic show agreement with the fossil record of leaf stomatal density change—a feature inversely related to the concentration of atmospheric CO2. Isotopic studies on temporal sequences of fossilized terrestrial organic matter have contributed to palaeoecological studies on shifts in the dominance of plants with the C4 photosynthetic pathway in ecosystems and historical changes in the metabolic processes of leaves of individual species. The long-term perspective offered by these studies provides critical information for assessing the responses of biological systems to future global environmental change.

Magioncalda, R., C. Dupuis, et al. (2004). "Paleocene-Eocene carbon isotope excursion in organic carbon and pedogenic carbonate: Direct comparison in a continental stratigraphic section." Geology 32(7): 553–556 doi: 10.1130/G20476.1.
    The negative carbon isotope excursion at the Paleocene-Eocene boundary is a chemo stratigraphic marker widely used for correlation of marine and continental stratigraphic sections. It is linked to massive dissociation of sedimentary methane hydrates and helps to explain an important greenhouse thermal event (Paleocene–Eocene thermal maximum), marine extinctions, and mammalian faunal change on three continents. We show that the carbon isotope excursion recorded in dispersed organic carbon (DOC) from fine-grained terrestrial sedimentary rocks at Polecat Bench, Wyoming, is very similar to that described in two high-resolution studies of pedogenic soil-nodule carbonate from the same section. All show a rapid onset, an ~40 m series of excursion values, and a slower recovery. However, the carbon isotope excursion in soil-nodule carbonate starts and ends 3–5 m lower stratigraphically than that in DOC. We hypothesize that enhanced diffusion of atmospheric CO2 and subsurface diagenesis in an environment of good drainage and elevated temperature and pCO2 may explain this offset. The reliability of
δ13C in DOC is attributed to mixing and averaging of isotopic signals from different organic compounds and tissues.

Dromart, G., J.-P. Garcia, et al. (2003). "Ice age at the Middle–Late Jurassic transition?" Earth Planet. Sci. Lett. 213(3-4): 205-220 doi: 10.1016/S0012-821X(03)00287-5.
    A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine invertebrate fauna (ammonites) and isotopic thermometry (
δ18O values of shark tooth enamel) indicates a severe cooling at the Middle–Late Jurassic transition (MLJT), about 160 Ma ago. The magnitude of refrigeration (1–3°C for lower middle latitudes) and its coincidence in time with an abrupt global-scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time. Ice sheets may have developed over the high-latitude mountainous regions of Far-East Russia. The drastic cooling just post-dated the Middle–Late Callovian widespread deposition of organic-rich marine sediments (e.g. northwestern Europe, Central Atlantic, and Arabian Peninsula). This thermal deterioration can thus be ascribed to a downdraw in atmospheric CO2 via enhanced organic carbon burial which acted as a negative feedback effect (i.e. the inverse greenhouse effect). The glacial episode of the MLJT climaxed in the Late Callovian, lasted about 2.6 Myr, and had a pronounced asymmetrical pattern composed of an abrupt (0.8 Myr) temperature fall opposed to a long-term (1.8 Myr), stepwise recovery. The glacial conditions at the MLJT reveal that atmospheric CO2 levels could have dropped temporarily to values lower than 500 ppmv during Mesozoic times.

Arens, N. C. and A. H. Jahren (2000). "Carbon isotope excursion in atmospheric CO2 at the Cretaceous-Tertiary Boundary: Evidence from terrestrial sediments." Palaios 15(4): 314-322 doi: 10.1669/0883-1351(2000)015<0314:CIEIAC>2.0.CO;2.
    A −1.5‰ to −2‰ carbon isotope excursion immediately above the clay layer that defines the Cretaceous-Tertiary (K/T) boundary has been reported in marine sediments world wide. This paper reports a similar −1.5‰ to −2.8‰ carbon isotope excursion recorded by C3 land plants from three temporally-controlled, stratigraphically-constrained terrestrial sections in the Western Interior of North America (Garfield County, Montana, and Slope County, North Dakota). Carbon isotope measurements of bulk sedimentary organic carbon were well-correlated with those of isolated plant cuticle, suggesting that the terrestrial organic carbon signature in these sediments parallels that of plant cuticle. Carbon isotope signatures were also independent of rock type and depositional environment, showing that the carbon isotope signature of plants, although altered, is not biased taphonomically. Because the signature in terrestrial facies records the isotope composition of paleoatmospheric CO2, this record—combined with that from marine sections—offers additional insight into changes in carbon cycling underlying the K/T negative carbon isotope excursion. For example, radiometric age determinations from the Hell Creek Road locality in Montana bracket the atmospheric carbon isotopic recovery between 65.00 ± 0.05 Ma and 65.16 ± 0.04 Ma. This reflects a more rapid recovery for the terrestrial biosphere than for that of the marine realm, perhaps due to lower extinction rates in land plants than in marine primary producers.

Weissert, H. (1989). "C-Isotope stratigraphy, a monitor of paleoenvironmental change: A case study from the early cretaceous." Surv. Geophys. 10(1): 1-61 doi: 10.1007/BF01901664.
    Today's disturbance of the global carbon cycle induced by anthropogenic processes has raised new interest in the history of the global carbon cycle and its relationship to climate and other geochemical cycles. Carbon-isotope stratigraphy proves to be most useful as a monitor of the history of the carbon-cycle during the last 200 million years. In the introductory paragraphs of this review the mode of functioning of the global carbon-cycle is summarized and the connection between carbon-cycle and carbon isotope geochemistry is documented. A case study on the disturbance of the global carbon cycle during the Aptian-Albian is presented. The disturbance of the carbon cycle lasting up to millions of years is recorded in the carbon-isotope stratigraphy of pelagic sediments. It is superimposed on high frequency sedimentological cycles, related to climate and oceanographic cycles of 20, 40 or 100 ky duration. The data reviewed suggest that the change in the global carbon system was linked to a global acceleration of geochemical cycles triggered by a long-term change in atmospheric CO2 controlled by the rate of sea-floor formation and by volcanic activity. Increased accumulation rates of terrestrial material and terrestrial organic matter in marine sediments may be used as an indicator of an intensified hydrological cycling resulting in higher water-discharge rates. An intensification of the Aptian-Albian water cycle is further reflected in continental sediments monitoring a period of elevated humidity. An increase in water discharge rates should have affected the transfer rate of dissolved nutrients from continents to oceans. Elevated concentrations of phosphorus may have led to an increase in Aptian-Albian oceanic productivity enhancing the transfer of marine organic matter from the oceanic into the sedimentary reservoir. Increased productivity, increased bulk sedimentation rates and poorly oxygenated deep-water led to increased preservation of marine and terrestrial organic matter in marine sediments. The accelerated output of marine organic carbon from the oceanic reservoir is ultimately registered in the positive carbon-isotope excursion of the marine carbonate carbon-isotope stratigraphy.

Kuypers, M. M. M., R. D. Pancost, et al. (1999). "A large and abrupt fall in atmospheric CO2 concentration during Cretaceous times." Nature 399: 342-345 doi: 10.1038/20659.
    Marine carbonates and organic matter show a sharp increase in their 13C/12C isotope ratio at the Cenomanian/Turonian (C/T) boundary, in the Cretaceous period. This isotopic shift resulted from an increase in the rate of sedimentary burial of 13C-depleted organic carbon in response to the C/T 'oceanic anoxic event'. The enhanced burial rate should have led to a significant drop inthe atmospheric CO2 concentration, which could explain the apparent climate cooling of early Turonian times. Here we present stable carbon isotope data for specific compounds from terrestrial leaves and marine phytoplankton, and quantify the abruptness and magnitude of the atmospheric CO2 concentration change. Isotope shifts in leaf-wax components extracted from abyssal sediments in the northeastern tropical Atlantic Ocean—the components are wind-delivered from Africa—indicate a sudden change in plant communities of the north African continent. Specifically, the data suggest that plants using the C3-type photosynthetic pathway were succeeded by plants using the C4-type pathway. If C4plants can outcompete C3 plants only at atmospheric CO2 concentrations below 500 p.p.m.v. (ref. 5), the observed vegetation change indicates a far larger reduction in C/T CO2 concentration—some 40–80%—than previously suggested. The isotopic excursion in the marine phytoplankton compounds is consistent with this estimate. We infer that this dramatic fall in the atmospheric CO2 concentration was abrupt, occurring in just 60,000 years.

Hesselbo, S. P., H. C. Jenkyns, et al. (2007). "Carbon-isotope record of the Early Jurassic (Toarcian) Oceanic Anoxic Event from fossil wood and marine carbonate (Lusitanian Basin, Portugal)." Earth Planet. Sci. Lett. 253(3-4): 455-470 doi: 10.1016/j.epsl.2006.11.009.
    The Toarcian Oceanic Anoxic Event (OAE) in the Early Jurassic (~ 183 Ma ago) was characterized by widespread near-synchronous deposition of organic-rich shales in marine settings, as well as perturbations to several isotopic systems. Characteristically, two positive carbon-isotope excursions in a range of materials are separated by an abrupt negative shift. Carbon-isotope profiles from Toarcian fossil wood collected in England and Denmark have previously been shown to exhibit this large drop (~ − 7‰) in
δ13C values, interpreted as due to an injection of isotopically light CO2 into the ocean–atmosphere system. However, the global nature of this excursion has been challenged on the basis of carbon-isotope data from nektonic marine molluscs (belemnites), which exhibit heavier than expected carbon-isotope values. Here we present new data, principally from fossil wood and bulk carbonate collected at centimetre scale from a hemipelagic section at Peniche, coastal Portugal. This section is low in organic carbon (average TOC = ~ 0.5%), and the samples should not have suffered significant diagenetic contamination by organic carbon of marine origin. The carbon-isotope profile based on wood shows two positive excursions separated by a large and abrupt negative excursion, which parallels exactly the profile based on bulk carbonate samples from the same section, albeit with approximately twice the amplitude (~ − 8‰ in wood versus ~ − 3.5‰ in carbonate). These data indicate that the negative carbon-isotope excursion affected the atmosphere and, by implication, the global ocean as well. The difference in amplitude between terrestrial organic and marine carbonate curves can be explained by greater water availability in the terrestrial environment during the negative excursion, for which there is independent evidence from marine osmium-isotope records and, plausibly, changes in atmospheric CO2 content, for which independent evidence is also available. The Peniche succession is also notable for the occurrence of re-deposited sediments: their lowest occurrence coincides with the base of the negative excursion and their highest occurrence coincides with its top. Thus, slope instability and sediment supply could have been strongly linked to the global environmental perturbation, an association that may misleadingly simulate the effects of sea-level fall.

Maruoka, T., C. Koeberl, et al. (2007). "Carbon isotopic compositions of organic matter across continental Cretaceous–Tertiary (K–T) boundary sections: Implications for paleoenvironment after the K–T impact event." Earth Planet. Sci. Lett. 253(1-2): 226-238 doi: 10.1016/j.epsl.2006.10.028.
    To assess the environmental perturbation induced by the impact event that marks the Cretaceous–Tertiary (K–T) boundary, concentrations and isotopic compositions of bulk organic carbon were determined in sedimentary rocks that span the terrestrial K–T boundary at Dogie Creek, Montana, and Brownie Butte, Wyoming in the Western Interior of the United States. The boundary clays at both sites are not bounded by coals. Although coals consist mainly of organic matter derived from plant tissue, siliceous sedimentary rocks, such as shale and clay, may contain organic matter derived from microbiota as well as plants. Coals record
δ13C values of plant-derived organic matter, reflecting the δ13C value of atmospheric CO2, whereas siliceous sedimentary rocks record the δ13C values of organic matter derived from plants and microbiota. The microbiota δ13C value reflects not only the δ13C value of atmospheric CO2, but also biological productivity. Therefore, the siliceous rocks from these sites yields information that differs from that obtained previously from coal beds.
Across the freshwater K–T boundary at Brownie Butte, the
δ13C values decrease by 2.6‰ (from − 26.15‰ below the boundary clay to − 28.78‰ above the boundary clay), similar to the trend in carbonate at marine K–T sites. This means that the organic δ13C values reflect the variation of δ13C of atmospheric CO2, which is in equilibrium with carbon isotopes at the ocean surface. Although a decrease in δ13C values is observed across the K–T boundary at Dogie Creek (from − 25.32‰ below the boundary clay to − 26.11‰ above the boundary clay), the degree of δ13C-decrease at Dogie Creek is smaller than that at Brownie Butte and that for marine carbonate.
About 2‰ decrease in
δ13C of atmospheric CO2 was expected from the δ13C variation of marine carbonate at the K–T boundary. This δ13C-decrease of atmospheric CO2 should affect the δ13C values of organic matter derived from plant tissue. As such a decrease in δ13C value was not observed at Dogie Creek, a process that compensates the δ13C-decrease of atmospheric CO2 should be involved. For example, the enhanced contribution of 13C-enriched organic matter derived from algae in a high-productivity environment could be responsible. The δ13C values of algal organic matter become higher than, and thus distinguishable from, those of plant organic matter in situations with high productivity, where dissolved HCO3− becomes an important carbon source, as well as dissolved CO2. As the δ13C-decrease of atmospheric CO2 reflected a reduction of marine productivity, the compensation of the δ13C decrease by the enhanced activity of the terrestrial microbiota means that the microbiota at freshwater environment recovered more rapidly than those in the marine environment.
A distinct positive
δ13C excursion of 2‰ in the K–T boundary clays is superimposed on the overall decreasing trend at Dogie Creek; this coincides with an increase in the content of organic carbon. We conclude that the K–T boundary clays include 13C-enriched organic matter derived from highly productive algae. Such a high biological productivity was induced by phenomena resulting from the K–T impact, such as nitrogen fertilization and/or eutrophication induced by enhanced sulfide formation. The high productivity recorded in the K–T boundary clays means that the freshwater environments (in contrast to marine environments) recovered rapidly enough to almost immediately (within 10 yr) respond to the impact-related environmental perturbations.

Isozaki, Y., H. Kawahata, et al. (2007). "A unique carbon isotope record across the Guadalupian–Lopingian (Middle–Upper Permian) boundary in mid-oceanic paleo-atoll carbonates: The high-productivity “Kamura event” and its collapse in Panthalassa." Global Planet. Change 55(1-3): 21-38 doi: 10.1016/j.gloplacha.2006.06.006.
    Middle to Upper Permian shallow marine carbonates in the Kamura area, Kyushu (SW Japan), were derived from a paleo-atoll complex developed on an ancient seamount in mid-Panthalassa. The Capitanian (Upper Guadalupian) Iwato Formation (19 m-thick dark gray limestone) and the conformably overlying Wuchiapingian (Lower Lopingian) Mitai Formation (17 m-thick light gray dolomitic limestone) are composed of bioclastic limestone of subtidal facies, yielding abundant fusulines. A secular change in stable carbon isotope ratio of carbonate carbon (
δ13Ccarb) was analyzed in the Kamura section in order to document the oceanographic change in the superocean Panthalassa with respect to the mass extinction across the Guadalupian–Lopingian boundary (G–LB). The Iwato Formation is characterized mostly by unusually high positive δ13Ccarb values of + 4.9 to + 6.2‰, whereas the Mitai Formation by low positive values from + 1.9 to + 3.5‰. The negative excursion occurred in three steps around the G–LB and the total amount of the negative shifts reached over 4‰. A remarkably sharp drop in δ13Ccarb values, for 2.4‰ from 5.3 down to 2.9‰, occurs in a 2 m-thick interval of the topmost Iwato Formation, after all large-shelled fusulines and bivalves disappeared abruptly. Such a prominent high positive δ13Ccarb plateau interval in the end-Guadalupian followed by a large negative shift across the G–LB was detected for the first time, and this trend in the mid-superoceanic sequence is correlated chemostratigraphically in part with the GSSP (Global Stratotype Section and Point) candidate for the G–LB in S. China. The present results prove that the end-Guadalupian event was doubtlessly global in context, affecting circum-Pangean basins, Tethys, and Panthalassa. The end-Guadalupian interval of a high positive plateau in δ13Ccarb values over + 5‰ is particularly noteworthy because it recorded an unusually high bio-productivity period that has not been known in the Permian. This end-Guadalupian high-productivity event, newly named “Kamura event”, suggests burial of a huge amount of organic carbon, draw-down of atmospheric CO2 and resultant global cooling at the end of Guadalupian, considerably after the Gondwana glaciation. The low temperatures during the Kamura event may have caused the end-Guadalupian extinction of large-shelled Tethyan fusulines and bivalves adapted to warm climate. On the other hand, the following event of ca. 4‰ negative shift in δ13Ccarb values across the G–LB indicates a global warming in the early Lopingian. This may have allowed radiation of the new Wuchiapingian fauna, and this trend appears to have continued into the Mesozoic. These observations are in good agreement with the global sea-level curve in the Middle–Late Permian. The smooth and gradual pattern of the negative shift suggests that the causal mechanism was not of catastrophic nature (e.g. bolide impact, sudden melting of methane hydrate) but was long and continuous.

Zedef, V., M. J. Russell, et al. (2000). "Genesis of vein stockwork and sedimentary magnesite and hydromagnesite deposits in the ultramafic terranes of southwestern Turkey: A stable isotope study." Econ. Geol. 95(2): 429-445 doi: 10.2113/95.2.429.
    Vein stockworks and lacustrine developments of cryptocrystalline magnesium carbonates of Neogene and Quaternary age occur within the partially serpentinized, discontinuous ultramafic belts of southwestern Turkey. They are comparable to the Neogene cryptocrystalline magnesite bodies elsewhere in the Alpine orogen to the northwest and southeast. Our previous work (Fallick et al., 1991) suggested that cool (<100°C) modified meteoric water was the mineralizer, that ultramafic rock was the source of the magnesium, but that there were three separate sources of the (bi)carbonate. These sources were distinguishable by their stable isotope composition as follows: (1) low-temperature carbonate with {delta}18O(SMOW) values of ~36 per mil and {delta}13C(PDB) values of ~4 per mil, derived from atmospheric CO2; (2) moderate-temperature carbonate with {delta}18O(SMOW) values of +28 per mil and {delta}13C(PDB) values of –15 per mil, derived by decarboxylation of organic-rich sediments; and (3) higher temperature carbonate with {delta}18O(SMOW) values of ~19 per mil and {delta}13C(PDB) values of ~3 per mil, assumed to have been generated by thermal contact metamorphism of Paleozoic marine limestone at depth. In general these magnesite deposits were found to fall into two groups, comprising carbonate generated on two mixing lines. The first group spanned the putative mixing line from the "atmospheric" source (1) to "organically derived" source of CO2 (2). The second group extended between atmospheric source (1) and the "thermal" source (3), although there were concentrations either around the atmospheric end, or precisely at the contact metamorphic end of the line.
In the present study we found that large stockwork deposits at Helvacibaba and Koyakci Tepe have {delta}13C(PDB) and {delta}18O(SMOW) values averaging ~–12 and ~+27 per mil, respectively, indicating a derivation mainly by oxidation of organic-rich metasediments perhaps underthrust at depth (end-member 2), with some involvement of atmospheric carbon dioxide as bicarbonate in the circulating, hot, and modified meteoric water (end-member 1). Calcite veinlets in a meta-argillite of the Cambro-Ordovician Seydisehir Formation, most likely to have been underthrust beneath the stockworks, yielded {delta}13C(PDB) values of –20 per mil, consistent with, though not proving, oxidized organic carbon being one of the sources of carbonate. The {delta}18O(SMOW) values of these same veinlet carbonates are also rather low (22{per thousand}), indicating precipitation from heated ground water, though their age is unknown.
The major stratiform magnesite deposit at Hirsizdere in the center of the Menderes graben has {delta}13C(PDB) and {delta}18O(SMOW) values averaging ~3 and ~25 per mil, respectively, and thus appears to be an example of the hydrothermal-sedimentary (i.e., exhalative) type (Ilich, 1968). In contrast, the hydromagnesite stromatolites presently growing in Salda Gölü (Lake Salda) are apparently developing at cool ground-water seepages. The gross morphology of the Salda Gölü stromatolites and the hydromagnesite sediments derived therefrom is reminiscent of that revealed in the Bela Stena magnesite pit in Serbia. These lacustrine deposits have mean {delta}13C(PDB) values of ~4 and ~2 per mil and mean {delta}18O(SMOW) values of ~36 and ~33 per mil, respectively, i.e., they both plot broadly over the atmospheric CO2-meteoric water field (end-member 1), consistent with microbially mediated precipitation at cool ground-water seepages in enclosed evaporating lakes.

Gröcke, D. R. (2002). "The carbon isotope composition of ancient CO2 based on higher-plant organic matter." Phil. Trans. R. Soc. Lond. A Mathem. Phys. Eng. Sci. 360(1793): 633-658 doi: 10.1098/rsta.2001.0965.
    Carbon isotope ratios in higher-plant organic matter (
δ13Cplant) have been shown in several studies to be closely related to the carbon isotope composition of the ocean-atmosphere carbon reservoir, and, in particular, the isotopic composition of CO2. These studies have primarily been focused on geological intervals in which major perturbations occur in the oceanic carbon reservoir, as documented in organic carbon and carbonates phases (e.g. Permian-Triassic and Triassic-Jurassic boundary, Early Toarcian, Early Aptian, Cenomanian-Turonian boundary, Palaeocene-Eocene Thermal Maximum (PETM)). All of these events, excluding the Cenomanian-Turonian boundary, record negative carbon isotope excursions, and many authors have postulated that the cause of such excursions is the massive release of continental-margin marine gas-hydrate reservoirs (clathrates). Methane has a very negative carbon isotope composition (δ13C, ca. 60‰) in comparison with higher-plant and marine organic matter, and carbonate. The residence time of methane in the ocean-atmosphere reservoir is short (ca. 10 yr) and is rapidly oxidized to CO2, causing the isotopic composition of CO2 to become more negative from its assumed background value (δ13C, ca. -7‰). However, to date, only the Early Toarcian, Early Aptian and PETM are well-constrained chronometric sequences that could attribute clathrate release as a viable cause to create such rapid negative δ13C excursions. Notwithstanding this, the isotopic analysis of higher-plant organic matter (e.g. charcoal, wood, leaves, pollen) has the ability to (i) record the isotopic composition of palaeoatmospheric CO2 in the geological record, (ii) correlate marine and non-marine stratigraphic successions, and (iii) confirm that oceanic carbon perturbations are not purely oceanographic in their extent and affect the entire ocean-atmosphere system. A case study from the Isle of Wight, UK, indicates that the carbon isotope composition of palaeoatmospheric CO2 during the Mid-Cretaceous had a background value of 3‰, but fluctuated rapidly to more positive (ca. +0.5‰) and negative values (ca. 10‰) during carbon cycle perturbations (e.g. carbon burial events, carbonate platform drowning, large igneous province formation). Hence, fluctuations in the carbon isotope composition of palaeoatmospheric CO2 would compromise our use of palaeo-CO2 proxies that are dependent on constant carbon isotope ratios of CO2.

Joachimski, M. M. and W. Buggisch (2002). "Conodont apatite
δ18O signatures indicate climatic cooling as a trigger of the Late Devonian mass extinction." Geology 30(8): 711-714 doi: 10.1130/0091-7613(2002)030<0711:CAOSIC>2.0.CO;2.
    The oxygen isotopic composition of conodont apatite from two Frasnian-Famennian boundary sections was measured in order to reconstruct variations in marine paleotemperatures during the late Frasnian mass-extinction event. The measured conodont apatite
δ18O values reveal two positive excursions with maximum amplitudes of +1‰ to +1.5‰ that parallel positive excursions in the carbonate carbon isotopic composition. The +3‰ excursions in carbonate δ13C have been interpreted as consequences of enhanced organic carbon burial rate resulting in a decrease in atmospheric CO2 concentration. Climatic cooling as a potential consequence of lower atmospheric CO2 concentration is confirmed by the conodont apatite δ18O records, which translate into cooling of low-latitude surface waters by 5–7 °C. Repeated cooling of the low latitudes during the late Frasnian had a severe impact on the tropical shallow-water faunas that were probably adapted to warm surface-water temperatures and severely affected during the late Frasnian crisis. These prominent variations in ocean-water temperature were stressful to the tropical shallow-water fauna and potentially culminated in low origination rates of new species, one of the major factors of the decline in diversity during the latest Frasnian.

Melezhik, V. A., A. E. Fallick, et al. (2000). "Palaeoproterozoic magnesite-stromatolite-dolostone-'red bed' association, Russian Karelia: palaeoenvironmental constraints on the 2.0 Ga-positive carbon isotope shift." Norsk Geol. Tidsskrift 80(3): 163-186 doi: 10.1080/002919600433724.
    The ca. 2000 Ma Tulomozerskaya Formation, Russian Karelia, is composed of an 800 m-thick magnesite-stromatolite-dolostone-'red bed' succession with the most 13C-rich dolostones (up to +18‰ V-PDB) that have ever been reported. Terrigenous 'red beds' are developed throughout the sequence and represent three main depositional settings: (1) a braided fluvial system over a lower energy, river-dominated coastal plain, (2) a low-energy, barred lagoon or bight, and (3) a non-marine, playa lake. A significant component of the sequence consists of biostromal and biohermal columnar stromatolites accreted in shallow-water, low-energy, intertidal zones, barred evaporitic lagoons and peritidal evaporitic environments. Only a small portion of stromatolites might have been accreted in relatively 'open' marine environments. The red, flat-laminated, dolomitic and magnesite stromatolites formed in evaporative ephemeral ponds, coastal sabkhas and playa lakes. Tepees, mudcracks, pseudomorphs after calcium sulphate, halite casts, and abundant 'red beds' in the sequence suggest that (1) terrestrial environments dominated over aqueous, and (2) partial or total decoupling took place between the stromatolite-dominated depositional systems and the bordering sea. The greatest enrichment in 13C occurs in the playa magnesite (up to +17.2‰) and in the laminated dolomitic stromatolites accreted in ephemeral ponds (up to +16.8‰), whereas the dolostones from more open environments are less rich in 13C (+5.6 to +10.7‰). The isotopic shift (ca. 5‰) induced by global factors (i.e. accelerated accumulation of organic material in an external basin) was augmented by that driven by a series of local factors (restriction, evaporation, biological photosynthesis). The latter enhanced a global
δ13C value due to an isotopic disequilibrium between atmospheric CO2 and dissolved inorganic carbon in the local aquatic reservoirs precipitating the carbonate minerals. The interplay between global and local factors should be taken into account when interpreting the Palaeoproterozoic carbon isotope excursion and its implications.

Kaiser, S. I., T. Steuber, et al. (2006). "Geochemical evidence for major environmental change at the Devonian–Carboniferous boundary in the Carnic Alps and the Rhenish Massif." Palaeogeogr., Palaeoclim., Palaeoecol. 240(1-2): 146-160 doi: 10.1016/j.palaeo.2006.03.048.
    A positive carbon isotope excursion is reported for the global Hangenberg Event near the Devonian–Carboniferous boundary, one of the most significant Phanerozoic mass extinction events. The
δ13C excursion occurs both in micritic limestones and in sedimentary organic matter of black shales and limestones from different palaeogeographical regions, which were precisely correlated by conodont biostratigraphy. The excursion indicates global change in the isotopic composition of marine dissolved inorganic carbon and atmospheric CO2. This resulted from the increased burial of organic matter by globally widespread deposition of black shales.
δ18O values of conodont apatite indicate that globally widespread black shale deposition was preceded by increasing temperature, probably with a thermal gradient between equatorial and higher latitudes (~ 20 °S). The main regressive interval of the event, correlated previously with a short-lived glacial episode in Gondwana, yielded no material for geochemical analyses, but low temperatures are recorded in overlying beds and increase again during the terminal Devonian. Early Carboniferous sea-surface temperatures were similar to those of the Late Devonian.
This pattern of increased organic carbon burial, and changes in climate and sea level, is similar to that of several other extinction events of the Phanerozoic. It supports the hypothesis that increased organic carbon burial and oceanic anoxia can trigger mass extinctions, glaciations and eustatic sea-level change.

Galli, M. T., F. Jadoul, et al. (2005). "Anomalies in global carbon cycling and extinction at the Triassic/Jurassic boundary: evidence from a marine C-isotope record." Palaeogeogr., Palaeoclim., Palaeoecol. 216(3-4): 203-214 doi: 10.1016/j.palaeo.2004.11.009.
    This study investigates whether the end-Triassic biotic crisis was coupled with a perturbation of the marine C-isotope budget. The marine C-isotope signature serves as a proxy of the marine carbon reservoir and ultimately of the global C cycle. A continuous shallow water marine limestone succession from the Western Southern Alps (Bergamasc Alps, northern Italy) provides information on the end-Triassic biotic crisis and on the evolution of the marine carbon reservoir across the Triassic/Jurassic (T/J) boundary. The established carbonate C-isotope curve is marked by a negative C-isotopepulse coinciding with the disappearance of the end-Triassic benthic faunal assemblage and a widespread Rhaetian carbonate platform drowning event. The negative spike is followed by a positive C-isotope excursion starting at the palynological T/J transition. The negative C-isotope pulse may have resulted from the sudden release of gas hydrates. The positive isotope excursion records a global change in organic carbon burial rates, probably in response to elevated atmospheric CO2 levels at a time of massive volcanic activity in the Central Atlantic Magmatic Province. High CO2 levels were responsible for the end-Triassic biocalcification crisis, carbonate platform collapse, and, possibly, the sudden release of methane from gas hydrate.

Hasegawa, T., L. M. Pratt, et al. (2003). "Upper Cretaceous stable carbon isotope stratigraphy of terrestrial organic matter from Sakhalin, Russian Far East: a proxy for the isotopic composition of paleoatmospheric CO2." Palaeogeogr., Palaeoclim., Palaeoecol. 189(1-2): 97-115 doi: 10.1016/S0031-0182(02)00634-X.
    Time-stratigraphic patterns of stable carbon isotopic ratios recorded in terrestrial organic matter from Cenomanian–Maastrichtian successions for the Russian Far East can be correlated to those of carbonate carbon from well-studied successions for other parts of the world. Age-indicative biostratigraphy based on regional ammonoids and inoceramid bivalves are well established in Japan and can be applied to the whole Cretaceous succession except for the Upper Cenomanian–Lower Turonian and the upper part of the Maastrichtian (zones lacking macrofossils). Globally correlative carbon isotopic events previously documented with carbonate carbon from Europe and with carbonate carbon and marine organic matter from the U.S. Western Interior are recognized with similar magnitude through uppermost Cenomanian–Lower Campanian. In ascending order these events are: positive ‘spike’ across the Cenomanian–Turonian boundary; step-like leveled segment followed by negative shift (Lower–Middle Turonian); trough-like negative excursion (Middle–Upper Turonian); positive rebound coupled with following broad peak (Coniacian); and positive peak (basal Campanian) followed by modest negative excursion. The parallel fluctuation of the
δ13C value between the terrestrial organic matter and carbonate suggests carbon isotopic equilibrium between surface seawater and atmospheric CO2 and demonstrates that the isotopic curve of terrestrial organic carbon can be used to monitor carbon isotopic fluctuations of CO2 in the ocean–atmosphere system. In the Upper Campanian and Maastrichtian, a negative δ13C excursion within chron 33r and a following rapid rebound can be correlated with the same distinctive carbon isotopic feature of carbonate observed in the deep sea cores from South and North Atlantic, the Indian, and the Pacific Oceans. Within this interval, the δ13C value of terrestrial organic matter also reflects carbon isotopic fluctuation of the global CO2 reservoir with relatively minor regional/local ‘noise’.

Weissert, H. and H. Mohr (1996). "Late Jurassic climate and its impact on carbon cycling." Palaeogeogr., Palaeoclim., Palaeoecol. 122(1-4): 27-43 doi: 10.1016/0031-0182(95)00088-7.
    The climate of the Late Jurassic has been characterized by high atmospheric CO2 levels and by a monsoonal rainfall pattern. In this study we traced the evolution of the global carbon cycle through the Late Jurassic with the help of carbonate carbon isotope stratigraphy. The Oxfordian-Tithonian
δ13C curve is marked by one major positive carbon isotope excursion with an amplitude Δδ13C > 1.0‰ (Middle to Late Oxfordian) and a second, minor positive excursion with an amplitude Δδ13C < 1.0‰ (Late Kimmeridgian). The Early Kimmeridgian and Early Tithonian δ13C-values fluctuate around δ13C = +2‰±0.3‰ and contrast with the less positive δ13C-values of Early Oxfordian and Late Tithonian age (δ13C = +1‰±0.5‰). A comparison of the Late Jurassic carbonate carbon isotope curve with the occurrence of organic-rich sediments suggests that not only fluctuations in organic carbon burial but also in carbonate carbon burial had an impact on the C-isotoperecord. The Oxfordian C-isotope excursion appears to correspond to a time of overall increased organic carbon burial triggered by increased nutrient transfer from continents to oceans during a time of rising global sea level. However, episodes of enhanced organic carbon burial during the Kimmeridgian and Early Tithonian are not reflected by prominent spikes in the C-isotope record. Favourable conditions for carbonate platform growth at a time of high global sealevel may have resulted in the stabilisation of the C org/C carb burial ratio and hence maintained the δ13C record at steady but relatively positive values. The Middle and Late Tithonian C-isotope values drop below δ13C = +1.5‰. A similar shift to less positive C-isotope values was recognized in other C-isotope records from the Tethys and Atlantic Oceans and reflects a decrease in the C org/C carb burial ratio possibly related to a reorganisation of the global climate system.
Globally widespread marine black shale-mature quartzose sandstone assemblages suggest that the relative efficiency of the Late Jurassic carbon pumps was controlled by weathering, erosion and runoff causing widespread marine eutrophication. Eutrophication favoured the organic carbon pump but it diminished the carbonate-platform growth potential. The monsoonal rainfall distribution pattern may explain why Late Jurassic carbonate platforms experienced less severe growth crises than Early Cretaceous carbonate platforms.

Erez, J., A. Bouevitch, et al. (1998). "Carbon isotope fractionation by photosynthetic aquatic microorganisms: experiments with Synechococcus PCC7942, and a simple carbon flux model." Can. J. Bot. 76(6): 1109-1118 doi: 10.1139/cjb-76-6-1109.
    Stable carbon isotopes (12C and 13C) are widely used to trace biogeochemical processes in the global carbon cycle. Natural fractionation of carbon isotopes is mainly due to the discrimination of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) against 13C during photosynthesis. In marine and other aquatic microorganisms, this fractionation is lowered when the dissolved CO2 (CO2(aq)) is decreasing, but the underlying mechanisms are poorly understood. Cultured Synechococcus PCC7942 showed maximum isotopic fractionations of -33omicron (in delta 13C units) relative to the total inorganic carbon (Ci) when CO2(aq) is above 30 m M. As the culture grew, pH increased, CO2(aq) was lower than 1 m M, and the Ci concentrating mechanism was induced although the Ci was above 3 mM. The isotopic fractionation was drastically reduced to values of -1 to -3 omicron relative to Ci. A simple carbon isotope flux model suggests that during the first stages of the experiment the total uptake (F1) was roughly three- to four-fold greater than the photosynthetic net accumulation (F2). When the Ci concentrating mechanism was induced, the leakage of CO2 from the cells declined, the cells started to utilize HCO3- and the F1/F2 ratio decreased to values close to 1. Based on this model the isotopic variability of oceanic phytoplankton suggests that the F1/F2 ratio may be above 3 in high latitudes and ~1.1 in equatorial waters, where the Ci concentrating mechanism is probably induced. Attempts to reconstruct past atmospheric CO2 levels and paleoproductivity should take into account the effects of the Ci concentrating mechanism on the isotopic fractionation of aquatic primary producers.

Pedersen, T. F. and P. Bertrand (2000). "Influences of oceanic rheostats and amplifiers on atmospheric CO2 content during the Late Quaternary." Quat. Sci. Rev. 19(1-5): 273-283 doi: 10.1016/S0277-3791(99)00085-2.
    Although a clear explanation has yet to emerge for the observed decline in atmospheric CO2 content during glacial episodes, numerous hypotheses have been offered. Selected examples are reviewed or evaluated here. A strengthened biological pump resulting from intensified upwelling at low latitudes was suggested early on as a likely direct cause of the glacial CO2 drawdown. Two problems have since arisen with this hypothesis. First, on some upwelling continental margins, for example off California, Oregon, northwestern Mexico, Peru, and parts of NW Africa, organic matter accumulation decreased, in some areas markedly, during the Last Glacial Maximum (LGM). Second, upwelled cool CO2-rich water degasses carbon dioxide in warm regions, and for a key area such as the modern equatorial Pacific to become a net sink for atmospheric CO2, rather than a source as it is today, the rate of downward organic carbon export must exceed the rate of degassing. Recent sedimentary carbon and nitrogen isotopic data suggest however that the equatorial Pacific has remained a strong CO2 source for at least the last 40,000 yr and probably much longer. Although the direct extraction of carbon from surface waters and burial in the sediments in productive regions now appears unlikely to provide the sought-for explanation, indirect effects related to export productivity may hold the key. These can modulate the chemical character of the ocean so as to increase its uptake of CO2 (a rheostat effect) or they could increase indirectly the nutrient inventory of the sea (an amplifier effect). For example, it is now recognized that denitrification was greatly reduced during glacial maxima in all three principal oxygen minimum zones in the oceans, i.e. the subtropical north and south Pacific and the Arabian Sea. The implication is that nitrate, the limiting nutrient in the modern ocean, must have been more abundant during glacial periods, and that this surfeit would have supported increased export production in the meso or oligotrophic areas that are today nitrate-limited. Dust may represent another rheostat. Increases in atmospheric turbidity during glacials are clearly recorded by ice and marine sediment cores in both hemispheres. In addition to fostering enhanced export production by adding needed iron to nitrate-rich areas, it has been suggested recently that increased dust inputs to nitrate-depleted regions during glacials might have encouraged growth of iron-hungry N2 fixing cyanobacteria, thus alleviating nitrate limitation. No sedimentary
δ15N data yet exist to support this hypothesis, but it remains viable. Finally, regional changes in physical hydrography may have played a major and hitherto underestimated role. For example, in the glacial Southern Ocean south of the Polar Front, recent nitrogen isotopeand other data imply that the upper water column was well stratified during the LGM. By limiting upwelling, this would have reduced the ocean-atmosphere CO2 ‘leak’ in the area. This could have made a significant contribution to the pCO2 drawdown.

Zeebe, R. E., D. A. Wolf-Gladrow, et al. (1999). "On the time required to establish chemical and isotopic equilibrium in the carbon dioxide system in seawater." Marine Chem. 65(3-4): 135-153 doi: 10.1016/S0304-4203(98)00092-9.
    Dissolved inorganic carbon in sea water plays a key role in understanding the properties of the oceanic carbon reservoir within the global carbon cycle. For instance, fluxes between the atmosphere and the ocean are estimated using the stable carbon isotopes 12C and 13C of atmospheric CO2 and its dissolved forms within the ocean. Likewise, the investigation of carbon uptake by marine phytoplankton or the reconstruction of past oceans via stable isotope analysis demand a sound understanding of the sea water chemistry and associated carbon isotope fractionation. Chemical and isotopic disequilibrium is of particular interest when small length and time scales are considered. For example, within the microenvironment of marine plankton or within the surface boundary layer of the ocean (gas exchange atmosphere-ocean) the seawater carbonate chemistry deviates appreciably from equilibrium. It can be shown that a time-dependent description of the carbonate system is indispensable when time scales smaller than 90 s are involved (length scale of the diffusive boundary layer 10−4 m). Properties of the equilibrium state of the carbonate system in sea water are well known. However, hitherto there is little detailed work on the disequilibrium state of the chemical and in particular on the isotopic properties of the system. Here we present analytical and numerical techniques to determine the relaxation time of the chemical system including
νCO2, HνCO−3, νCO2−3, H+, OH−, B(OH)3, and B(OH)4−, where ν=12, 13, and 14. The calculated relaxation time for chemical equilibrium at a temperature of 25°C and a salinity of 35 at pH 8.2 is 15.9 s (only 12C species), while the time calculated for isotopic equilibrium is 17.5 s (all carbon isotopes considered).

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From: "Heaton, Timothy HE" <[log in to unmask]>
Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
Date: Thu, 23 Aug 2007 11:51:59 +0100
To: <[log in to unmask]>
Conversation: Isotope changes in marine organic carbon
Subject: [ISOGEOCHEM] Isotope changes in marine organic carbon

Does anyone know of any recent reviews on carbon isotope changes of marine ORGANIC carbon through geological time? Especially studies that relate marine orgainc d13C to atmospheric CO2 changes.

Tim H.E. Heaton

NERC Isotope Geosciences Laboratory
British Geological Survey

Keyworth, Nottingham NG12 5GG, England
(www.bgs.ac.uk/nigl/index.htm <file://www.bgs.ac.uk/nigl/index.htm> )

Tel. +44(0)115 936 3401
Email: [log in to unmask]


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