Carbon Isotope Changes Research Articles

Experimentally-controlled carbon and oxygen isotope exchange between bioapatites and water under inorganic and microbially-mediated conditions

Modern bone and enamel powders have reacted at 301 K with 13C- and 18O-labelled waters under inorganic and microbial conditions. The aim of the study is to investigate the resistance of stable isotope compositions of bioapatite carbonate (δ 13C, δ 18Oc) and phosphate (δ 18Op) to isotopic alteration during early diagenesis. Rapid and significant carbon and oxygen isotope changes were observed in the carbonate and phosphate fractions of bone apatite before any detectable change occurred in the crystallinity or organic matter content. These observations indicate that chemical alterations of bone apatite are likely to start within days of death. Enamel crystallites are much more resistant than bone crystallites, but are not exempt of alteration. Non removable carbon and oxygen isotope enrichments were measured in the carbonate phase of bone (50–90%) and enamel (40%) after the acetic acid treatment. This result indicates that a significant part of 13C and 18O-labelled coming from the aqueous fluid has been durably incorporated into the apatite structure, probably through isotopic exchange or secondary carbonate apatite precipitation. As a result, acetic acid pre-treatments that are currently used to remove exogenous material by selective dissolution, are not adequate to restore pristine δ 13C and δ 18Oc values of fossil apatites. Under inorganic conditions, kinetics of oxygen isotope exchange are 10 times faster in carbonate than in phosphate. On the opposite, during biologically-mediated reactions, the kinetics of oxygen isotope exchange between phosphate and water is, at least, from 2 to 15 times faster than between carbonate and water. Enamel is a more suitable material than bone for paleoenvironmental or paleoclimatical reconstructions, but interpretations of δ 18Op or δ 13C values must be restricted to specimens for which no or very limited trace of microbial activity can be detected.

Early Cretaceous carbon isotopic and marine environmental changes in northern Oyubari area, Hokkaido

Early Cretaceous carbon isotopic and marine environmental changes in northern Oyubari area, Hokkaido

Geochemical and organic carbon isotope studies across the continental Permo–Triassic boundary of Raniganj Basin, eastern India

Organic carbon isotope and geochemical changes across a continental interior Permo–Triassic boundary section from the Raniganj Basin, India, indicate a ∼9‰ drop in organic carbon δ 13C in the Early Triassic and synchroneity of this event throughout the Pangea. The study demands a common causative mechanism for the perturbation of the global carbon reservoir and not a combination of multiple causes. A global sea-level fall and oxidation of marine gas hydrates possibly increased the 12CO 2 input in the ocean–atmosphere system which caused a climatic shift from humid to warm semi-arid type and consequent extinction of land plants. Simultaneous increase in erosion from near-barren lands, change in the erosional base level and provenance deposited the boundary sandstone with positive europium anomaly and debris flow type matrix rich conglomerate. No extraterrestrial source, therefore, is needed to explain this Eu anomaly. The response of the terrestrial plant community to this perturbation of the carbon reservoir was, however, sluggish and the δ 13C drop took place slowly, being maximal in the Early Triassic only.

Stable carbon isotope changes during artificial charring of propagules

Charred organic remains are ubiquitous in the archaeological and fossil record and are often used to interpret past environments and climate. This study focuses on the physical and chemical alteration that takes place during heating (i.e. charring). Modifications to the internal and external morphology were noted alongside the change in molecular and stable carbon isotope signature. Molecular analyses were undertaken using direct temperature resolved mass spectrometry and the stable carbon isotopes determined using isotope ratio mass spectrometry. The results of this study document a general enrichment in 13C/12C composition of charred material which could reflect the changes observed in both the molecular composition and the relative proportions of the molecules formed. These results indicate that spurious results might be inferred when comparing the stable carbon isotope signature of charred/charcoalified material with uncharred organic matter

Climate history of the middle reach of the Yangtze river over the past 9000 years: A speleothem isotopic record from Za cave, Hubei, China

A stalagmite in Qingjiang, Hubei, has yielded the records of hydrogen and oxygen as well as carbon isotopic changes and provided a climate history of 9000 years. The hydrogen isotopic ratio in fluid inclusions and the oxygen isotopic ratio in stalagmite calcite are controlled by meteoric water, which is in response to ambient temperature or precipitation amount. The carbon isotopic ratio, sensitive to the nature of vegetation, also can be used to reconstruct the climate history. The carbon-14 and U-series dated stalagmite records reveal that climate oscillated in the middle reach of Yangtze river over the past 9000 years: (1) 9.0-6.5 kaBP, a cooler and more humid condition; (2) 6.5-4.0 kaBP, with warmer and drier weather; (3) 4.0-2.0 kaBP, cold weather with heavy precipitation, and (4) 2.0 kaBP to present, tendency to be warmer and drier.

Long- and short-term carbon fluctuations in the Eastern Mediterranean during the late Holocene

Research Article| December 01, 2001 Long- and short-term carbon fluctuations in the Eastern Mediterranean during the late Holocene Bettina Schilman; Bettina Schilman 1Geological Survey, 30 Malkhei Israel, Jerusalem 95501, Israel Search for other works by this author on: GSW Google Scholar Ahuva Almogi-Labin; Ahuva Almogi-Labin 1Geological Survey, 30 Malkhei Israel, Jerusalem 95501, Israel Search for other works by this author on: GSW Google Scholar Miryam Bar-Matthews; Miryam Bar-Matthews 1Geological Survey, 30 Malkhei Israel, Jerusalem 95501, Israel Search for other works by this author on: GSW Google Scholar Laurent Labeyrie; Laurent Labeyrie 2Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Gif-sur-Yvette, France Search for other works by this author on: GSW Google Scholar Martine Paterne; Martine Paterne 2Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Gif-sur-Yvette, France Search for other works by this author on: GSW Google Scholar Boaz Luz Boaz Luz 3Institute of Earth Sciences, Hebrew University, Jerusalem 91904, Israel Search for other works by this author on: GSW Google Scholar Author and Article Information Bettina Schilman 1Geological Survey, 30 Malkhei Israel, Jerusalem 95501, Israel Ahuva Almogi-Labin 1Geological Survey, 30 Malkhei Israel, Jerusalem 95501, Israel Miryam Bar-Matthews 1Geological Survey, 30 Malkhei Israel, Jerusalem 95501, Israel Laurent Labeyrie 2Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Gif-sur-Yvette, France Martine Paterne 2Laboratoire des Sciences du Climat et de l'Environnement (CEA-CNRS), Gif-sur-Yvette, France Boaz Luz 3Institute of Earth Sciences, Hebrew University, Jerusalem 91904, Israel Publisher: Geological Society of America Received: 21 Mar 2001 Revision Received: 25 Jun 2001 Accepted: 20 Jul 2001 First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2001) 29 (12): 1099–1102. https://doi.org/10.1130/0091-7613(2001)029<1099:LASTCF>2.0.CO;2 Article history Received: 21 Mar 2001 Revision Received: 25 Jun 2001 Accepted: 20 Jul 2001 First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bettina Schilman, Ahuva Almogi-Labin, Miryam Bar-Matthews, Laurent Labeyrie, Martine Paterne, Boaz Luz; Long- and short-term carbon fluctuations in the Eastern Mediterranean during the late Holocene. Geology 2001;; 29 (12): 1099–1102. doi: https://doi.org/10.1130/0091-7613(2001)029<1099:LASTCF>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract A high-resolution record of carbon isotope changes during the late Holocene was obtained in core GA-112 from the easternmost Mediterranean. Over the past 3600 yr, a gradual 13C-depletion trend shown by both planktonic and benthic foraminifera corresponds to a global rise in atmospheric CO2. The global and local trends suggest that aridification and biomass destruction in the Nile basin played a major role in the global CO2 rise in the late Holocene. Superimposed on the general δ13C trend are four mirror- image cycles in δ13C of planktonic and benthic foraminifera. Higher planktonic δ13C values reflect periods of high productivity off the coast of Israel. Simultaneously, decrease in the benthic δ13C values occurred because of degradation of higher organic-matter fluxes to the sediment. Therefore, large differences between the two records indicate periods of high productivity. The Eastern Mediterranean productivity fluctuations respond to a periodical replenishment of nutrients to the mixed layer via Nile runoff. Historical data of the Nile flood fluctuations for the past ∼1400 yr show a remarkable coincidence between high and low Nile floods and high and low Eastern Mediterranean productivity levels, which are correlated with the periodic monsoonal activity over the Nile headwaters. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

South Atlantic and benthic foraminifer δ13C deviations: implications for reconstructing the Late Quaternary deep-water circulation

Benthic foraminifer species Cibicidoides wuellerstorfi and related genera are assumed to secrete calcite very close to the carbon isotope values of the ambient bottom-water ΣCO 2. Recently, attention has been focused on substantial productivity-linked δ 13C depletions. To examine further the productivity effect on benthic δ 13C deviations, we present data from the South Atlantic between 15 and 35°S, including water samples from 10 hydrographic stations and related surface-sediment measurements on C. wuellerstorfi. We compare open-ocean data with observations in the Namibia Upwelling area. As a result, δ 13C ΣCO 2 values as well as phosphate concentrations in water samples of the upwelling realm differ significantly from those of the open-ocean realm at least in the upper and mid-depth water masses (SACW, AAIW, UCDW). However, deviations from the Redfield fractionation, caused by air–sea fractionation, remain constant within each water mass, which means that the carbon isotope changes toward upwelling areas are exclusively determined by biological cycling. In addition to lower δ 13C ΣCO 2 values in upwelling areas, a depletion in the δ 13C of epibenthic foraminifer calcite is observed, which is most likely explained by the decay of organic matter, reducing the 13C/ 12C ratio in the pore water and influencing the carbon isotopic composition of the C. wuellerstorfi shells of highly productive areas. The paleoceanographic implication of this effect for reconstructing the Late Quaternary deep-water circulation is discussed using carbon isotope records of several sediment cores within and outside the Namibia upwelling area.

Climate and vegetation history of the midcontinent from 75 to 25 ka: A speleothem record from crevice cave, missouri, USA

Four Missouri stalagmites yield consistent overlapping records of oxygen and carbon isotopic changes and provide a climate and vegetation history with submillennial resolution from 75 to 25 thousand years ago (ka). The thorium-230-dated records reveal that between 75 and 55 ka, the midcontinental climate oscillated on millennial time scales between cold and warm, and vegetation alternated among forest, savanna, and prairie. Temperatures were highest and prairie vegetation peaked between 59 and 55 ka. Climate cooled and forest replaced grassland at 55 ka, when global ice sheets began to build during the early part of Marine Oxygen Isotope Stage 3.

Global δ 13 C changes across the Paleocene-Eocene boundary: criteria for terrestrial-marine correlations

Abstract The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high δ 13 C values in the late Paleocene to values that are 2 to 3 lower in the early Eocene. The shift is recorded in fossil carbonates from each ocean basin and represents a large change in the distribution of 12 C between the ocean and other carbon reservoirs. Superimposed upon this long-term shift are several distinct carbon isotopic negative excursions that are also recorded globally. These carbon isotopic ‘events’ near the Paleocene-Eocene boundary provide stratigraphic information that can facilitate intersite correlations between marine and non-marine sequences. Here we present a detailed marine carbon isotopic stratigraphy across the Paleocene-Eocene boundary that is constrained by calcareous nannofossil and planktonic foraminifera biostratigraphy and magnetostratigraphy. We show that several distinct carbon isotopic changes are recorded in uppermost Paleocene and lowermost Eocene marine biogenic carbonate sediments. At least one of these isotopic changes in the ocean’s carbon isotopic composition was transmitted to terrestrial carbon reservoirs, including plant biomass via atmospheric CO 2 . As a consequence of this exchange of 12 C between the ocean and terrestrial carbon reservoirs, it is possible to use carbon isotope stratigraphy to correlate the uppermost Paleocene and lowermost Eocene non-fossiliferous terrestrial sediments of the Paris Basin with marine sequences.

Carbon Isotope Stratigraphy of the Upper Kharaib and Shuaiba Formations: Implications for the Early Cretaceous Evolution of the Arabian Gulf Region

The carbon isotope profiles of shallow-marine carbonates from the Barremian-Aptian Kharaib and Shuaiba formations of the Arabian Gulf region range between 0.5 and 7^pmil ^dgr13C PDB (Peedee belemnite). Systematic variations can be correlated with isotope profiles reported from Tethyan pelagic limestone sequences. The detailed correspondence between the isotopic signature of the relatively well-dated pelagic limestones and the poorly dated shallow-water limestones from the Arabian Gulf region suggests that global marine carbon isotope changes apparently affected deep-sea and shallow-water carbonate sediments similarly and at a similar time resolution. Although oxygen isotopes have been reset during diagenesis, carbon isotopes appear to have maintained their primary marine signature through time. No evidence has been found to connect carbon isotope trends to subaerial exposure or later meteoric diagenesis. In combination with other data, the investigated carbon isotope profiles can be used for basin-to-platform and regional correlations beyond the current resolution of biostratigraphy in shallow-water limestones. Carbon isotope stratigraphy confirms significant hiatuses in the investigated shallow-water carbonate sequences. Using carbon isotope trends as a proxy for sea level fluctuations, the carbon isotope cycles of the late Early Cretaceous of the Arabian Gulf region may represent four cycles of rising and falling sea level with a duration corresponding to that of third-order sea level fluctuations. Regional correlations derived from isotope trends provide a scenario for the larger scale stratigraphic evolution of the Arabian peninsula during the end of the Early Cretaceous. Differential rates of aggradation between realms influenced by siliciclastics and those characterized by siliciclastic-poor (clean) carbonate deposition apparently caused the development of a pronounced basin-platform topography during the early Aptian (Shuaiba intrashelf basin and platform).

Coastal Massachusetts pond development: edaphic, climatic, and sea level impacts since deglaciation

Kettle ponds in the Cape Cod National Seashore in southeastern Massachusetts differ in their evolution due to depth of the original ice block, the clay content of outwash in their drainage basins, and their siting in relation to geomorphic changes caused by sea-level rise, barrier beach formation, and saltmarsh development. Stratigraphic records of microfossil, carbon isotope, and sediment changes also document late-glacial and Holocene climatic changes. The ponds are separated into 3 groups, each of which follow different development scenarios. Group I ponds date from the late-glacial. They formed in clay-rich outwash, have perched aquifers and continuous lake sediment deposition. The earliest pollen and macrofossil assemblages in Group I pond sediments suggest tundra and spruce-willow parklands before 12 000 yr B.P., boreal forest between 12 000 and 10 500 yr B.P., bog/heath initiation and expansion during the Younger Dryas between 11 000 and 10 000 yr B.P., northern conifer forest between 10 500 and 9500 yr B.P., and establishment of the Cape oak and pitch pine barrens vegetation after 9500 yr B.P. Sedimentation rate changes suggest lowered freshwater levels between 9000 and 5000 yr B.P. caused by decreased precipitation on the Atlantic Coastal Plain. Lake sediment deposition began in the middle Holocene in Group II ponds which formed in clay-poor outwash. These ponds date from about 6000-5000 yr B.P. In these ponds sediment deposition began as sea level rose and the freshwater lens intersected the dry basins. The basal radiocarbon dates of these ponds and stable carbon isotope analyses of the pond sediments suggest a sea-level curve for Cape Cod Bay. Holocene topographic changes in upland and the landscape surrounding the ponds is reconstructed for this coastal area. Group III ponds in the late Holocene landscape of the Provincelands dunes originated as interdunal bogs about 1000 yr B.P. and became ponds more recently as water-levels increased. Peat formation in the Provincelands reflects climatic changes evident on both sides of the Atlantic region.

Stable (δ13C, δ18O) and strontium () isotopes through the Paleocene at Gebel Aweina, eastern Tethyan region

Abstract Stable ( δ 13 C, δ 18 O) and strontium ( 87 Sr 86 Sr ) isotopic records have been established through the Paleocene section at Gebel Aweina, in the Eastern Desert, Egypt. The section has been formed in a shelf-upper bathyal environment and, spans the interval from planktonic foraminiferal Zones P1d to P6a or P6b. Integrated evaluation of isotopic results and scanning electron microscope observations suggest that, strontium and whole-rock δ 13 C records reflect primarily original isotopic trends, whereas δ 18 O and foraminiferal δ 13 C values have been severely affected by diagenesis. The whole-rock δ 13 C record exhibits a continuous increase of 4‰ from the early Paleocene to middle late Paleocene. The increase is followed by a stepwise δ 13 C decrease of the same magnitude through the late late Paleocene and onwards. The gross trends of this δ 13 C record have earlier been registered in many coeval deep-sea sections, but there are also some significant disparities. At Aweina, for example, the Paleocene carbon isotopic changes have a higher amplitude. In the deep sea, the mid-to-late Paleocene δ 13 C increase has been interpreted to reflect high biological productivity and/or changes in the global carbon mass balance. The δ 13 C decrease in the upper part of the Aweina section can be identified as the Paleocene-Eocene transitional long-term (> 10 3 kyr) negative δ 13 C shift, which may reflect a major reorganisation in global oceanic circulation patterns. The well-known latest Paleocene, deep-sea, benthic foraminiferal extinction event has been found in the upper part of the Aweina section, and coincides with a distinct and rapid δ 13 C decrease of 1.5‰ The benthic extinction event and the associated δ 13 C anomaly thus represent important stratigraphic markers also in more shallow environments. The Gebel Aweina δ 13 C record shows considerably lower values compared to the global δ 13 C record during early and early late Paleocene and in the latest Paleocene. In the early late Paleocene (foraminiferal Zones P3a to the base of P4) the Aweina δ 13 C values increase rapidly by 1.5‰, and converge with the global record; thereafter the two records covary up to the benthic extinction event, after which they diverge. The convergence between the records may reflect sea-level rise and more open water-mass exchange between the eastern Tethys and the world ocean. The similarity of pilot δ 13 C records from Greece and Tunisia with the Aweina record support this interpretation. Diagenetic processes, however, cannot be ruled out, and further studies are required to determine the significance of the 13 C depletions in the eastern Tethyan sediments. The 87 Sr 86 Sr ratios through the Paleocene at Gebel Aweina are remarkably invariable close to a value of 0.7077. This is the same trend that has been reported in some earlier detailed studies conducted on well-preserved calcitic material from the Paleocene, indicating original Sr-isotopic signatures at Gebel Aweina. The homogeneity of Sr-isotopic ratios throughout the Paleocene contrasts with the prominent changes observed in the carbon isotope record, indicating a decoupling of the mechanisms regulating the mass fluxes of these elements. The invariable Sr-isotopic ratios suggest stable conditions as regards to relative changes in mass fluxes of riverine and/or hydrothermal Sr during the Paleocene.

Patterns of faunal turnover and diversity in the Neogene Siwaliks of Northern Pakistan

The fluvial Neogene Siwalik formations of northern Pakistan contain a long and richly fossiliferous sequence of terrestrial vertebrate faunas in which patterns of faunal turnover and changes in diversity can be documented and analyzed for intervals having durations of 0.5 m.y. The complete sequence extends from circa 18.5 to 1 Ma, but the part between 18.5 and 5.5 Ma is best sampled, and most intervals within it are well represented. Thirteen orders of Siwalik mammals have been identified, with well-sampled intervals having 50 or more species. Most Siwalik mammals, however, are either rodents or artiodactyls. Bovids are the most common and most speciose of the larger mammals, while murid and “cricetid” rodents dominate the small mammal assemblages. Between 18.5 and 5.5 Ma species diversity varied considerably. Among artiodactyls and rodents the number of species first increased between 15 and 13 Ma and then fell. Data on stratigraphic ranges of rodents and artiodactyls show that faunal change in the Siwaliks was episodic, occurring during short intervals with high turnover followed by longer periods with considerably less change. Maxima of first appearances occurred at approximately 13.5 and 8.5 Ma, while maxima of last occurrences were at 12.5 and 8.0 Ma. Some of the observed faunal events can be correlated to climatic and environmental changes. The Middle Miocene diversification occurred during a period of global cooling, while the latest Miocene decline in diversity and increased turnover accompanied oxygen and carbon isotopic changes that correlate to globally increasing seasonality and aridity. Other correlations are ambiguous. The marked decrease in diversity and the major turnover events between 13 and 8 Ma do not correspond to known local or global events. The Neogene Siwaliks and Paleogene Bighorn-Crazy Mountains sequence in Wyoming and Montana share many similarities. They have equivalent levels of temporal resolution and similar levels of completeness of their fossil records. Siwalik ordinal abundance and diversity patterns differ markedly from those of the Paleogene, but generic, and probably species, diversity was approximately the same, although the Siwalik faunas may have been slightly less diverse. Over time, changes in diversity were of comparable magnitude, with monotonic trends persisting for more than 5 million years. The magnitude of faunal turnover was also similar, ranging from less than half to 3.5 times that expected. In both sequences faunal change appears to have been episodic, with strong pulses between intervals of low turnover. The Siwaliks, in contrast to the Paleogene sequence, may have had more distinct pulses and longer intervals between pulses. Neither sequence has peaks of first occurrences coinciding with peaks of last occurrences.

Diagenetic evolution of the Carnian Wetterstein platforms of the Eastern Alps

ABSTRACTThe carbonate platforms of the Wetterstein Formation of the Eastern Alps (Drau Range and Northern Calcareous Alps) show a distinct facies zonation of reefs and lagoons. While some lagoonal areas were episodically emerged and formed lagoonal islands, others remained permanently flooded. The scale of near surface, meteoric or marine diagenesis was related to this lagoonal topography. At shallow burial depth, cementation was dominated by altered marine solutions, which additionally caused recrystallization of metastable constituents of the sediment and earlier marine cements (high magnesian calcite, aragonite) connected with a carbon and oxygen isotopic change to more negative values.Deeper burial cementation shows a succession with two types of saddle dolomite and three types of blocky calcite. Carbon and oxygen isotopic values of these cements show a trend towards more negative values from the first to the last generation, in the following succession: clear saddle dolomite—zoned blocky calcite—cloudy saddle dolomite—post‐corrosion blocky calcite—replacive blocky calcite. Fluid inclusion studies of the carbonate cements are interpreted to indicate a deeper burial temperature development that first increases from 175 to 317°C, followed by a temperature decrease to 163–260°C, and subsequent increase up to 316°C, whereby the samples of the Drau Range always show the lowest values. Calculations of the isotopic composition of the water, from which the carbonate cements were precipitated, yielded positive δ18O values from 6.66 to 17.81%o (SMOW), which are characteristic for formation and/or metamorphic waters. Also, the isotopic compositions of the palaeofluids probably changed during deeper burial diagenesis, following the temperature development.

An Oceanographic Explanation for the Apparent Carbon Isotope‐Cadmium Discordancy in the Glacial Antarctic?

The seeming discordance between the glacial to interglacial changes in the carbon isotope ratio and cadmium content of benthic foraminifera from the deep Antarctic has cast a shadow on the reliability of these proxies as valid of paleocirculation indicators. The problem is that while cadmium content shows little glacial to interglacial change [Lea and Boyle, 1990; Boyle, 1992], the carbon isotope change is larger than at any other place in the ocean [Curry et al., 1988; Ïññü et al., 1990;Charles and Fairbanks, 199O]. Even after correction for the 0.35‰ glacial to interglacial change in the isotope ratio for mean ocean‐atmosphere carbon, a difference of 0.5 to 0.6‰ remains. On the basis of Redfield ratios for today's ocean, this is equivalent to a 25% increase in cadmium content which is not seen. This puzzle has been with us for several years.

Simultaneous changes in carbon isotopes, sea level, and conodont biozones within the Cambrian-Ordovician boundary interval at Black Mountain, Australia

Carbon isotope profiles of marine carbonate units within the Cambrian-Ordovician boundary section at Black Mountain, western Queensland, Australia, reveal cyclical changes in δ13C within the Georgina basin during the boundary interval. Minimum values in the δ13C profile are found in strata bearing lithostratigraphic evidence for sea-level drop and also correlate strongly with conodont assemblage zone boundaries. These relations indicate that direct mechanistic links existed between carbon cycles, changes in sea level, and conodont evolution.

Upper Pleistocene oxygen and carbon isotopic changes of core SCS-15B at the South China Sea

The Upper Pleistocene oxygen and carbon isotopic records of G. sacculifer in core SCS-15B at the South China Sea resemble those from Pacific and Indian deep-sea cores. The δ 18O data show that the oxygen isotope stages can be recognized to stage 7. Using the time scale of Martinson et al. (1987. Quat. Res. 27, 1–29), sedimentation rates of SCS-15B are compared with a nearby core SCS-15A. Results indicate that there was a discrepancy of sedimentation rates between these two cores during the last interglacial period. Comparison with the benthic record between the last glacial maximum and Holocene implies that there may exist a temperature effect in the benthic record. The δ 13C data show that two minimum spikes occur at oxygen isotope stage transitions 6/5 and 2/1 as found in other oceans.

Carbon isotope fractionation and changes in the flux and composition of particulate matter resulting from biological activity during a sediment trap experiment in Lake Greifen, Switzerland1

Sediment traps were deployed in Lake Greifen, a hard‐water eutrophic, Swiss lake, for 2 weeks in May and June 1983. Oxygen, pH, and suspended particle concentrations indicated a sharp increase in productivity during the experiment. Carbon isotope composition of the dissolved inorganic carbon recorded the balance between photosynthesis and respiration and showed possible evidence of diffusion of atmospheric CO2 across the water‐atmosphere interface, most likely to replace CO2 used during photosynthesis. Allochthonous mineral debris from resuspended sediments or river input was a major component of the sedimenting material. Due to removal of CO2, large, newly formed calcite crystals precipitated when photosynthesis increased. The carbon isotope ratio of trap calcite and the composition of trap amino acids showed the influence of the detrital input on the more dominant isotopic signal of authigenic calcite. Sediment calcite is enriched in 13C relative to authigenic calcite in the sediment traps. This enrichment is likely due to fractionation during precipitation in the surface waters or during dissolution in the water and sediments due to CaCO3 undersaturation. We found extensive loss of material from unpoisoned sediment traps in the cuphotic zone, most likely due to zooplankton feeding.

The carbon isotope record of dolostones as a stratigraphic tool: A case study from the upper cretaceous shelf sequence, Israel

Accumulation of evidence on past global changes in carbon isotopes in marine carbonate rocks points to the usefulness of the carbon isotope record as a stratigraphic tool. This method will be important in sections with a poor representation of indicative fauna, such as dolostones. Isotope analyses of dolostone sequences from the Upper Cenomanian-Turonian sequence of Israel suggest that on the average a depletion of 1.1% in δ 13C ratio can be detected across the boundary. The Israeli trend agrees with the δ 13C record across this boundary reported from sections with detailed biostratigraphic records.

Statistics of the AD Record of Climatic and Carbon Isotopic Change

The AD time series of Δ14C, δ13C, and cosmic ray fluxes, Q, were analyzed for similarities. Two cases of significant correlation between Q and tree-ring δ13C were encountered, for which up to 25% of the variance can be attributed to changes in the tree's isotope fractionation that related to solar induced climatic changes. However, it is possible that the demonstrated correlation is fortuitous because actual climate proxy records generally do not correlate significantly with the Q record.