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:
    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:
    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:
    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:
    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

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:
    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

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:
    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.
The 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: 
    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: 
    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: 
    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 

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 

Delta Isotopes Consultancy

Dr. Pier A. de Groot
Pastoor Moorkensstraat 16
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Isotope Scientists).

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Techniques”, with a link to the Elsevier web site on the handbook (marked: 
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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 
( <file://> ) 

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


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