Carbon Isotope Record Research Articles

Marine Late Triassic-Jurassic carbon-isotope excursion and biological extinction records: New evidence from the Qiangtang Basin, eastern Tethys

The mass extinction event of the Late Triassic is relatively poorly-known among the five major extinction events in the Phanerozoic. Moreover, the typical marine Triassic-Jurassic (T-J) records are absent in regions other than the western Tethys and Boreal realms, and thus major questions remain as to the global significance and cause(s) of the event. Especially in the eastern Tethys, no marine sedimentary records of the T-J transition are known from open marine facies, and thus the extent and significance of the marine T-J transition are unclear. We show the first high-resolution carbonate carbon-isotope record, geochemistry, palaeontologic and lithological data from a marine T-J section (Wenquan section). In the columnar profile, we place the T-J boundary at the top of grainstone layers representing the shallowest water deposit. Our results reveal that the carbonate carbon-isotope record contains two different excursions in the Wenquan section of northern Tibet, China. These are consistent with the “initial” and “main” negative carbon-isotope excursions (CIEs) found in the global stratotype section and point (GSSP), strongly suggesting their global nature. A biological crisis together with paleoceanographic changes was identified near the main CIE. This means that a mass of isotopically light carbon was rapidly released into the air and oceans, resulting in environmental changes and biological crisis. • The first high-resolution record of the T-J boundary from the Tibet, East Tethys. • The distinct twice negative CIEs are consistent with the CIEs found in the global GSSP profile. • A biological crisis together with paleoceanographic changes was discovered.

The Carbon-Isotope Record of the Sub-Seafloor Biosphere

Sub-seafloor microbial environments exhibit large carbon-isotope fractionation effects as a result of microbial enzymatic reactions. Isotopically light, dissolved inorganic carbon (DIC) derived from organic carbon is commonly released into the interstitial water due to microbial dissimilatory processes prevailing in the sub-surface biosphere. Much stronger carbon-isotope fractionation occurs, however, during methanogenesis, whereby methane is depleted in 13C and, by mass balance, DIC is enriched in 13C, such that isotopic distributions are predominantly influenced by microbial metabolisms involving methane. Methane metabolisms are essentially mediated through a single enzymatic pathway in both Archaea and Bacteria, the Wood–Ljungdahl (WL) pathway, but it remains unclear where in the pathway carbon-isotope fractionation occurs. While it is generally assumed that fractionation arises from kinetic effects of enzymatic reactions, it has recently been suggested that partial carbon-isotope equilibration occurs within the pathway of anaerobic methane oxidation. Equilibrium fractionation might also occur during methanogenesis, as the isotopic difference between DIC and methane is commonly on the order of 75‰, which is near the thermodynamic equilibrium. The isotopic signature in DIC and methane highly varies in marine porewaters, reflecting the distribution of different microbial metabolisms contributing to DIC. If carbon isotopes are preserved in diagenetic carbonates, they may provide a powerful biosignature for the conditions in the deep biosphere, specifically in proximity to the sulphate–methane transition zone. Large variations in isotopic signatures in diagenetic archives have been found that document dramatic changes in sub-seafloor biosphere activity over geological time scales. We present a brief overview on carbon isotopes, including microbial fractionation mechanisms, transport effects, preservation in diagenetic carbonate archives, and their implications for the past sub-seafloor biosphere and its role in the global carbon cycle. We discuss open questions and future potentials of carbon isotopes as archives to trace the deep biosphere through time.

Prosopis sp. tree-ring oxygen and carbon isotope record of regional-scale hydroclimate variability during the last 9500 years in the Atacama Desert

The hyper-arid core of the Atacama Desert is one of the most persistently arid environments in the world, yet there is evidence of significant hydroclimate variability during the Holocene. The timing of regional scale pluvial or humid periods has important implications for understanding the drivers of South American climate variability as well as the development of agriculture by prehistoric cultures. Here we present oxygen (δ18O) and carbon (δ13C) isotope values from ancient Prosopis sp. tree-ring cellulose as a record relative humidity (RH) and water availability (via intrinsic water–use efficiency) over century–long intervals throughout the past 9.5 ka in the northern Atacama Desert (19–21°S). These data provide the first high–resolution (ca. annual) evidence for decreasing water availability and increasing climate variability in the Atacama from the early-to late- Holocene. Intrinsic water–use efficiency steadily increases over the Holocene indicating a lowering of the water table and a reduction in the availability of groundwater resources in the region. As water availability decreases, δ18O-based estimates of RH show increased variance beginning ~4.9 ka. This change in RH coincides with the onset of modern day Central Andean atmospheric circulation patterns and previously documented humid periods in the southern Altiplano (22–24°S). Subannual tree-ring isotope analysis of modern and early Holocene (8.3 ka) trees show a similar seasonal cycle in carbon isotope values that correlates with modern annual changes in temperature; however, the early Holocene interseasonal variability is greater than modern seasonality. δ18O values of the Atacama tree-rings are highly correlated with those of the Sajama ice core from the Bolivian Andes, demonstrating a teleconnection between high-altitude Andean precipitation and water availability in the Atacama Desert. These reconstructions together provide a record of Holocene water availability and ephemeral recharge related to changes in ENSO and South American monsoon.

Carbon-isotope record and paleoceanographic changes prior to the OAE 1a in the Eastern Tethys: Implication for the accumulation of organic-rich sediments

Abstract The Barremian and Aptian correspond to periods of marked changes in the atmosphere-ocean system, and offer valuable information about global tectonic events. Here, we present integrated high-resolution carbonate carbon-isotope (δ13Ccarb) and geochemical data that precede the Early Aptian oceanic anoxic event (OAE 1 a) in the Qiangtang Basin (Eastern Tethys). We identified a characteristic and well-correlatable Barremian-Lower Aptian carbon-isotope pattern that can be categorized into 10 Segments. The most notable features of the δ13Ccarb record are multiple negative carbon-isotope excursions in the Barremian-Aptian, and each is possibly linked to environmental changes. Two carbon isotopic plateaus are observed in the Upper Barremian, which are generally related to increased primary productivity, and to the concomitant development of dys-to anaerobic conditions. Our data indicate the development of anoxic conditions during shale deposition, which occurred under the conditions of a semi-enclosed lagoon environment. Such conditions, were likely localized, and not the primary mechanism responsible for the deposition of organic-rich sediments within the Shenglihe succession. The deposition of organic-rich shales was very likely due to global/regional warming. Rising temperatures and hydrological cycle strengthening during shale deposition are believed to have increased primary productivity, and thus resulted in the expansion of the local oxygen minimum zone within the water column.

Late Devonian carbon isotope chemostratigraphy: A new record from the offshore facies of South China

We present a new biostratigraphically constrained carbon isotope record from the Lali section (South China) to document perturbations in the Late Devonian carbon cycle. Positive carbon isotope excursions (CIEs) are most important components of the Late Devonian long-term carbon isotope cycle: Frasnes (+2‰), Middlesex (+1‰), Lower Kellwasser (+3‰), Upper Kellwasser (+3‰) and Upper annulata (+1‰) events, as well as a small positive CIE (+1‰) in the Famennian expansa-aculeatus zones were recorded. It is noteworthy that no significant carbon isotope shifts are found for the Rhinestreet, Nehden, Condroz and Enkeberg events. The Late Devonian long-term carbon isotope curve from South China is in agreement with contemporaneous world-wide trends in Euramerica (Europe and North America) and Gondwana. Global data suggests a higher Famennian δ13Ccarb baseline (about +2.5 ‰) than that of the Frasnian (about +1‰). Previous studies have related the positive CIE to ocean anoxia, but its ultimate driver remains unclear. Other interpretations include the spread of land plants or increased tectonic activity, but these explanations are questionable due to the relative short durations of the CIEs compared to long-term processes of plant evolution and plant cover extension as well as tectonic movements.

Stratigraphy and isotope geochemistry of the pre-Sturtian Ugab Subgroup, Otavi/Swakop Group, northwestern Namibia

The Islay carbon isotope anomaly is a late Tonian negative δ13C excursion that has been documented in marine carbonates globally. It has in the past been thought to be causally linked to the onset of Cryogenian glaciation ca. 717 Ma. However, recent work suggests that this anomaly is instead closer to ca. 739–735 Ma and that it may be one of two distinct late Tonian carbon isotope anomalies. Here we present the litho- and chemo-stratigraphy of the late Tonian Ugab Subgroup of the Otavi/Swakop Group in northwestern Namibia. Carbon isotope data from two separate outcrop belts, the Summas Mountains and the Vrede Domes, indicate that the Ugab Subgroup strata exposed in the former inlier are older than those of the latter, with only approximately 100 m of stratigraphic overlap. We use detailed measured sections to develop a sequence stratigraphic framework for the Ugab Subgroup in each outcrop belt, and correlate strata across the two exposures to construct a composite carbonate δ13C record for the late Tonian in Namibia. This carbon isotope profile of the Ugab Subgroup shows two separate pre-Sturtian negative anomalies, consistent with findings in northern Canada, Svalbard, Scotland, and Ethiopia. Our results are an important contribution to the pre-Cryogenian carbon isotope record, as these data may serve as the first definitive documentation of both anomalies within a single basin.

Variations in the East Asian winter monsoon from 3500 to 1300 cal. yr BP in northern China and their possible societal impacts

Changes in paleoenvironments from 3500 to 1300 cal. yr BP have been documented by a high-resolution grain-size and organic carbon isotope record in core Z8 from the Shandong mud wedge in the southern Yellow Sea (YS). The sensitive grain-size component, sorting coefficients and δ13Corg values were used to identify the paleohydrologic variations and the intensity of the East Asian winter monsoon (EAWM). The coarse fraction of sediment, together with organic isotope and sea surface temperature (SST) data, shows a weak EAWM during 3500–2300 cal. yr BP, a gradual increase in the EAWM from 2300 to 1700 cal. yr BP and an enhanced EAWM since 1700 cal. yr BP. Superimposed on this general trend, several prominent short-lived strong EAWM episodes peaked at approximately 3300, 3100, 2900, 2750, 2620, 2220, 1900, 1700 and 1400 cal. yr BP. The paleoenvironmental record matches ancient Chinese historical climate records as well as socioeconomic changes, with lower economic levels occurring during stronger EAWM episodes. The results show that prosperous stages of ancient Chinese dynasties mainly occurred in weak EAWM periods, while collapses and/or changes in ancient Chinese dynasties generally occurred during cold periods with a strong EAWM. We suggest that the persistent short-lived strengthening of the EAWM could have exerted a remarkable influence on ancient agricultural societies through decreases in both winter temperature and monsoonal precipitation.

Biochemostratigraphy of an upper Albian–Turonian succession from the southeastern Neo-Tethys margin, SW Iran

A Neo-Tethyan upper Albian–Turonian (hemi-)pelagic carbonate succession (Sarvak Formation), accessible in outcrop in the Zagros, SW Iran, was investigated using sedimentology, microfacies analysis, planktonic foraminifera biostratigraphy, and carbon-isotope stratigraphy. The succession contains six biozones including Thalmanninella (Th.) appenninica, Th. globotruncanoides, Rotalipora cushmani, Whiteinella archaeocretacea, Helvetoglobotruncana Helvetica, and Marginotruncana schneegansi. Some of these biozones show variable stratigraphic positions throughout the Tethyan and Boreal realms that hinder correlation of the studied Iranian section with European reference sections. Therefore, the correlation of the existing biostratigraphic framework was complemented by carbonate carbon-isotope stratigraphy based on bulk carbonate material. Despite the low resolution of the presented carbon-isotope record, pronounced global events including the late Turonian Events, Cenomanian/Turonian Boundary (CTB) Event (OAE 2), and Albian/Cenomanian Boundary (ACB) Event can be distinguished. The δ13C excursions provide global synchronous time-lines for correlation. The distinguished biozones were compared among the sections regarding their stratigraphic positions relative to these time-lines. The correlation tentatively suggests that the biostratigraphic datum marking the ACB is diachronous with an SE–NW trend. First appearance datum (FAD) of Th. appenninica varies from the upper Albian to the lower Cenomanian. The FAD of Th. globotruncanoides is also variable from the upper Albian to the lower Cenomanian. However, the middle Cenomanian–Turonian biozones including Rotalipora cushmani and Whiteinella archaeocretacea zones are synchronous. Elevated pCO2 contributed to the gradual increase of the SST (sea surface temperature) during the Cenomanian, and the dramatic climax at the earliest Turonian. This trend closely correlates with the change from the diachronous ACB-biozones to synchronous CTB-biozones. Possibly, increasing SSTs provided temperature-tolerance range for the species throughout different latitudes, and assisted their rapid distribution. Moreover, the warming raised the sea level from the latest Albian to Turonian that inundated landbridges, resulting in an enhanced marine circulation and faster distribution of planktonic species throughout the Neo-Tethys Ocean.

The Schandelah Scientific Drilling Project: A 25-million year record of Early Jurassic palaeo-environmental change from northern Germany

With the aim to understand prolonged and repeated marine anoxia after the Triassic-Jurassic mass- extinction event, a continuously cored, 338 metre thick succession of Rhaetian to Toarcian sediments was retrieved close to the village of Schandelah near Braunschweig (Lower Saxony, northern Germany). Here, preliminary biostratigraphical, lithological, sedimentological, geochemical, and geophysical borehole data are presented and discussed. Based on the presence of ammonites, ostracods, benthic foraminifers, calcareous nannofossils, and palynomorphs, all major Late Triassic and Early Jurassic stage boundaries and many of the standard Lower Jurassic ammonite zones could be defined. The deltaic Rhaetian sand- and siltstone succession (Exter Fm) contains evidence for seismic activity probably related to large-scale geodynamic processes. The Hettangian (Lias Alpha) is represented by a thick heterolithic succession composed of shallow marine sandy and silty beds with intercalated organic-rich shale, representing deposition on a shoreface with frequent storm activity. Progressive deepening during the Sinemurian to Toarcian resulted in repeated deposition of laminated organic-rich facies. Periods of relative sea-level fall likely occurred during the Late Hettangian, the Late Sinemurian, and Early Pliensbachian, where a series of hardgrounds occur indicating erosion on the sea floor followed by sea level rise leading to omission, and increased reworking. One of the most conspicuous features of the Lower Jurassic in the Schandelah-1 core is the presence of abundant authigenic carbonates (glendonites,concretions, beef-calcite) within the Upper Pliensbachian with partly very negative C-isotope values (down to –37‰ V-PDB) suggesting the anaerobic oxidation of methane. A high-resolution organic carbon isotope record based on 485 analyses shows two major negative carbon isotope excursions (CIEs) within the lowermost Hettangian and Lower Toarcian, respectively. Both excursions coincide with the onset of black shale deposition and are well-known features of these time-intervals in other regions. Despite the fact that black shale deposition also characterizes parts of the Sinemurian and Pliensbachian in similar facies, no large negative CIEs are apparent. The Schandelah-1 core thus provides an unique archive of sedimentary, biotic and geochemical records of long-term Triassic-Jurassic palaeo-environmental change in the European Epicontinental Seaway.

The Cenomanian/Turonian boundary interval deep-sea deposits in the Zagros Basin (SW Iran): Bioevents, carbon isotope record and palaeoceanographic model

The Cenomanian/Turonian (C/T) boundary interval, spanning the upper part of the Sarvak Formation in the Zagros Basin (Izeh Zone), has been studied to determine the timing and the possible cause of biotic turnovers, coinciding with the intense environmental perturbations during the Oceanic Anoxic Event 2 (OAE2). The upper Cenomanian strata in the study section, composed of light-colour marlstone/organic-rich marlstone and shale bedding couplets, record fluctuations in microfossil assemblages and organic carbon contents. We suggest that the organic-poor layers, characterized by high abundance of radiolarians, were deposited during cold periods under surface water eutrophication (upwelling) and ventilated seafloor. In contrast, water column stratification during warm periods enhanced organic matter preservation and allowed deposition of organic-rich strata. Continued stratification and also increased runoff and primary productivity during warm intervals of OAE2 led to expansion of oxygen minimum zone (OMZ), which may have caused extinctions of deep followed by intermediate water planktic foraminifera. Such conditions may have led to significant decreases in the abundance and diversity of planktic foraminifera and dominance of the biserial genus Planoheterohelix (“Heterohelix” shift event). The δ13C curve in the study interval reveals the diagnostic features of global C/T boundary carbon isotope record, including three positive peaks (A, B and C) within the Whiteinella archaeocretacea Biozone. These carbon isotope features and the most important bioevents in the study section are stratigraphically listed below: 1- Highest occurrences (HOs) of Th. greenhornensis and Th. deeckei, 2- HO of R. cushmani and δ13C peak A, 3- HO of “G”. bentonensis, 4- Onset of “Heterohelix” shift event, 5- δ13C peak B, 6- δ13C peak C, 7- Filament event, 8- Lowest occurrence (LO) of H. helvetica, and 9- Holywell event.

Increased Stability in Carbon Isotope Records Reflects Emerging Complexity of the Biosphere

Preference for certain stable isotopes (isotope fractionation) during enzyme-mediated reactions is a universal aspect of life. For instance, carbon isotopes are fractionated during anabolic (e.g., photosynthate production) and catabolic (e.g., methanogenesis) reactions. These biological processes exert a major control on ambient micro-scale chemical conditions as well as the large-scale exogenic carbon reservoir. Combined with the ubiquity of bio-mediated carbonate mineral nucleation and obligate enzymatic skeletonization, these biochemical reactions and their control on the exogenic carbon pool are known to leave distinct imprints on carbonate minerals which accumulate as sediments throughout Earth’s history. Here, we study the evolution of the marine carbonate-carbon isotope record based on database compilations from the Precambrian and the Phanerozoic. By looking at the frequency distribution of the amplitude of stratigraphic variation at various temporal resolutions, we assess trends in the carbonate-carbon isotope variability. Part of this variation can only be explained by authigenic and diagenetic carbonate mineral additions, which carry metabolic carbon isotope signatures created in the vicinity of cells and secluded (sub-)seafloor micro-environments. It can be envisioned that compartmentalization (membrane enclosed regions), the accumulation of extracellular polymeric substances (biofilms), and restricted fluid exchange in the early diagenetic environment can create sharp isotope gradients that lead to a high-order of micro-scale carbon isotope variability being imprinted in carbonate rock. The frequency of the high-amplitude variation diminishes with the development of more complex life (metazoan-dominated biosphere); presumably through the dispersing action of bioturbation (eradicating these micro-environments), increased grazing pressure and the advent of obligate biomineralization. On the other hand, stark chemical gradients in a world dominated by unicellular life (prokaryotes and to a lesser extent eukaryotes) are thought to leave a distinctly more variable C isotope signature in carbonate rock. An enhanced understanding of the biogenicity of carbonate carbon isotope signatures at multiple spatial and temporal scales provides a baseline that is usable in the search for signs of (past) extraterrestrial life.

Carbon Isotope Record of Trace n‐alkanes in a Continental PETM Section Recovered by the Bighorn Basin Coring Project (BBCP)

AbstractContinental sedimentary records of early Paleogene hyperthermals are typically limited to weathered, often discontinuous, outcrop exposures. In 2011, the Bighorn Basin Coring Project (BBCP) collected the first continuous terrestrial records of the Paleocene‐Eocene Thermal Maximum (PETM) in the Bighorn Basin, Wyoming. Organic matter preservation was poor during the PETM, even in core material. Concentrations of leaf waxes during the PETM are too low for compound‐specific carbon isotope analysis by conventional means. However, the recent development of picomolar‐scale compound‐specific isotope analyses (pico‐CSIA) has reduced sample requirements and enabled measurements of carbon isotope ratios of n‐alkanes across the PETM in the Basin Substation core. While the prominent, negative carbon isotope excursion in total organic carbon that typically identifies the PETM in the sedimentary record is absent from the core, lithostratigraphic, biostratigraphic, and chemostratigraphic data suggest that the most likely position of the PETM is from ~87.82‐ to ~50‐m composite depth. This ~40‐m interval coincides with the lowest weight percent organic carbon, n‐alkane abundances, and n‐alkane δ13C values and the highest n‐alkane average chain lengths. Comparison of the n‐alkane isotope record from the core with that from organic‐rich rocks exposed in the SE Bighorn Basin suggests that n‐alkanes in the core fail to express the full magnitude of the carbon isotope excursion. We hypothesize that floodplain sediments at Basin Substation contain a mixture of PETM and reworked fossil n‐alkanes. Low total organic carbon suggests that PETM climate accelerated organic matter decay rates and floodplains may have acted as a carbon source during the PETM.

Diamond isotope compositions indicate altered igneous oceanic crust dominates deep carbon recycling

A long-standing unresolved problem in understanding Earth's deep carbon cycle is whether crustal carbon is recycled beyond arc depths. While isotopic signatures of eclogitic diamonds and their inclusions suggest deep recycling of crustal material, the crustal carbon source remains controversial; seafloor sediment – the widely favored crustal carbon source – cannot explain the combined carbon and nitrogen isotopic characteristics of eclogitic diamonds. Here we examined the carbon and oxygen isotopic signatures of bulk-rock carbonate for 80 geographically diverse samples from altered mafic-ultramafic oceanic crust (AOC), which comprises 95 vol% of the crustal material in subducting slabs. The results show: (i) AOC contains carbonate with δ13C values as low as −24‰, indicating the presence of biogenic carbonate; (ii) carbonate in AOC was mainly formed during low-temperature (<100°C) alteration processes. Modeling accounting for this newly recognized carbon source in the oceanic crust with formation temperatures <100°C yields a global carbon influx of 1.5±0.3 × 1012 molC/yr carried by subducting AOC into the trench, which is 50–90% of previous estimates, but still of the same order of the carbon influx carried by subducting sediments into the trench. The AOC can retain carbon better than sediment during subduction into the asthenosphere, transition zone and lower mantle. Mixing of asthenospheric and AOC fluids provides the first consistent explanation of the diverse record of carbon and nitrogen isotopes in diamonds, suggesting that AOC, instead of sediment, is the key carrier of crustal carbon into the deep mantle.

Holocene interaction of maritime and continental climate in Central Europe: New speleothem evidence from Central Germany

Abstract Central European climate is strongly influenced by North Atlantic (Westerlies) and Siberian High circulation patterns, which govern precipitation and temperature dynamics and induce heterogeneous climatic conditions, with distinct boundaries between climate zones. These climate boundaries are not stationary and shift geographically, depending on long-term atmospheric conditions. So far, little is known about past shifts of these climate boundaries and the local to regional environmental response prior to the instrumental era. High resolution multi-proxy data (stable oxygen and carbon isotope ratios, S/Ca and Sr/Ca) from two Holocene stalagmites from Blesberg Cave (Thuringia) are used here to differentiate local and pan-regional environmental and climatic conditions Central Germany through the Holocene. Carbon isotope and S/Ca and Sr/Ca ratios inform us on local Holocene environmental changes in and around the cave, while δ18O (when combined with independent records) serves as proxy for (pan-)regional atmospheric conditions. The stable carbon isotope record suggests repeated changes in vegetation density (open vs. dense forest), and increasing forest cover in the late Holocene. Concurrently, decreasing S/Ca values indicate more effective sulfur retention in better developed soils, with a stabilization in the mid-Holocene. This goes in hand with changes in effective summer infiltration, reflected in the Sr/Ca profile. Highest Sr/Ca values between 4 ka and 1 ka BP indicate intensified prior calcite precipitation resulting from reduced effective moisture supply. The region of Blesberg Cave is sensitive to shifts of the boundary between maritime (Cfb) and continental (Dfb) climate and ideally suited to reconstruct past meridional shifts of this divide. We combined the Blesberg Cave δ18O time series with δ18O data from Bunker Cave (western Germany) and a North Atlantic Oscillation (NAO) record from lake SS1220 (SW Greenland) to reconstruct the mean position of the Cfb-Dfb climate boundary. We further estimate the dynamic interplay of the North Atlantic Oscillation and the Siberian High and their influence on Central European climate. Repeated shifts of the Cfb-Dfb boundary over the last 4000 years might explain previously observed discrepancies between proxy records from Europe. Detailed correlation analyses reveal multi-centennial scale alternations of maritime and continental climate and, concurrently, waning and waxing influences of Siberian High and NAO on Central Europe.

The Permian-Triassic transition in ocean island setting: Environmental disturbances and new high-resolution carbon-isotope record from the Qiangtang Basin, NW China

The Permian-Triassic boundary (PTB) events such as carbon-isotope excursion, volcanism, and environmental disturbances are not well understood in an ocean island setting. Here, we develop a new case study for the Permian-Triassic transition in the Qiangtang Basin, Tibet, by combining existing biostratigraphy, new carbon-isotope data, sedimentological data, UPb zircon age, mineralogical and geochemical data. These new data defined the Permian-Triassic transition age as about 252.3 ± 0.9 Ma, corresponding to the lowermost sea level. A long-term negative carbonate carbon isotope trend is present at the same stratigraphic level in different depositional environments, strongly suggesting its global nature. However, our new ocean island setting is characterized by an abrupt shift in carbon isotope values across the level, which is different from many chemostrtigraphic studies that show a gradual shift in carbon isotope values across the event horizon. The most likely explanation for the abrupt shift in δ13C values is a sedimentary hiatus at this level in the study section. Three-stage climatic models through the PTB in the ocean island setting are identified: Stage 1 is characterized by a warm and humid climate with moderate chemical weathering; while a hot and humid climate with intense chemical weathering dominates stage 2; the climate in stage 3 is a relatively hot and arid climatic condition with weak chemical weathering.

North Atlantic influences on climate conditions in East-Central Europe in the late Holocene reflected by flowstone compositions

A stalagmitic flowstone deposit from the Béke Cave (called Nagy-tufa deposit), East-Central Europe is characterized by complex, climate related textural and geochemical records as documented from a drill core (BNT-2 core) covering the period of 4 to 1 ka cal BP. The core location was monitored in an earlier study. Based on monitoring, textural and chemical relationships, it has been hypothesized that the stable carbon isotope signal of the flowstone deposit is a regional humidity record, indicating wet periods 3.8 to 3.4, 3.0 to 2.8 and 2.0 to 1.6 ka cal BP, and a prominent dry period between 2.1 and 2.7 ka cal BP. Furthermore, stable H isotope data of inclusion-hosted water were used to reconstruct the atmospheric temperatures that fit independent regional paleotemperature records, indicating warm conditions around 2.7 ka BP and a relatively cold period between 2.5 and 1.5 ka BP. Comparisons with regional speleothem records and reconstructed North Atlantic Oscillation data indicate that the Late Holocene paleohumidity changes recorded by the BNT-2 stable carbon isotope record can be detected in the entire Western-Central European region with further links to the North Atlantic realm.

Arido-eustasy: A new example of non-glacial eustatic sea level change

Sea level fluctuation is common in the stratigraphical record and is partly explained by periodic polar glaciation. Such fluctuation in the absence of polar glaciation, during the warm periods of Earth's history, is poorly understood and currently under discussion. Here, I reconsider the palaeo-environmental information extracted from the variation in the carbon-isotope record and explain the phenomenon by coupling the levels of marine and fresh-water reservoirs through long-term wet and arid climate modes. The arido-eustasy model produces a standard anti-covariation pattern of marine organic and carbonate carbon-isotope records, which may appear throughout the geochemical record of the last 200 Myr. Under the model, orbitally forced periods of extremely wet climate result in environmental crisis, sea level falls, and carbon cycle perturbations, during which negative excursions in the marine organic carbon-isotope record of sediments containing matter from terrestrial vegetation should be understood as a proxy reporting periods of high precipitation rather than changes in the global carbon reservoir. I propose that the early Toarcian oceanic anoxic event is an example of arido-eustasy.

Influence of the High Arctic Igneous Province on the Cenomanian/Turonian boundary interval, Sverdrup Basin, High Canadian Arctic

Emplacement of Large Igneous Provinces (LIPs) had a major effect on global climate, ocean chemistries as traced in sedimentary records and biotic turnovers. The linkage between LIPs and oceanic anoxic events has been documented with the Cenomanian/Turonian boundary event and Oceanic Anoxic Event 2 (OAE2). The Caribbean LIP and High Arctic Large Igneous Province (HALIP) are regarded as possible triggers. The pericratonic Arctic Sverdrup Basin is the partial location of the HALIP, where little is known about sedimentary, geochemical and biotic responses to the HALIP phases. Sedimentary strata at Glacier Fiord, Axel Heiberg Island, exhibit a dynamic Cretaceous polar carbon burial history within the lower to middle Cenomanian Bastion Ridge Formation and upper Cenomanian to Turonian part of the Kanguk Formation. We present the first initial 187Os/188Os (Osi) composition profile for a polar Cenomanian/Turonian boundary interval (∼100–93.9 Ma) linked to recently dated magmatic phases of the Strand Fiord Formation, part of the HALIP. The carbon isotope record coupled with the Osi profile show two events in the upper Cenomanian interval marked by positive carbon perturbations and shifts to more non-radiogenic Osi compositions. The earlier short-lived event is interpreted as result of weathering of the surrounding Strand Fiord volcanics causing a local non-radiogenic Osi signal. Coinciding transgressive shorelines let to an increase in marine and terrestrially derived organic matter. Subsequently, injection of mantle-derived basalts into organic rich sediments is credited with causing the release of methane documented in a distinct negative carbon isotope excursion. We speculate that the methane release of the HALIP was an important contribution for rapid global warming caused by increasing atmospheric CO2 levels associated with the OAE2 event likewise recognized in the Sverdrup Basin. As climate cooled in the middle and late Turonian, carbon burial decreased under increasingly oxygenated benthic conditions. Epifaunal foraminiferal species, adapted to low oxygen conditions, persisted during the OAE2. Our Cenomanian to Turonian multiproxy record of the Sverdrup Basin distinguishes between local and global signals within a restricted High Arctic basin. Our results demonstrate the interplay between basin tectonism and sea-level change, increased weathering during transgressive phases, seafloor processes such as hydrothermal activity and methane release and biotic response to a complex paleoceanography. With future reliable dated frameworks this unique polar record will facilitate correlations to other polar basins and records of lower paleolatitudes.

Long-term summer warming trend during the Holocene in central Asia indicated by alpine peat α-cellulose δ13C record

The long-term cooling or warming trend is one of the most important aspects of Holocene paleoclimatic research. However, there are currently significant discrepancies among climatic simulation results, sedimentary and synthesized Holocene temperature records. These discrepancies call for new Holocene temperature records with a robust chronology and unambiguous indicative significance. Here, we present a ca. 45-year-resolution alpine peat α-cellulose carbon isotopic (δ13C) record from the Altai Mountains in central Asia. The chronology of the record has been well-constrained by 22 AMS 14C dates of the peat α-cellulose samples. Based on detailed modern-process study results, the indicative significance of the record has been carefully determined as summer temperature indicator. The record reveals an overall trend of increasing summer temperature for the past ca. 11 ka with a warmer early (from ca. 8–6 ka BP) and late (from ca. 4–0 ka BP) Holocene and colder middle Holocene (from ca. 6–4 ka BP). The general pattern of a warmer early and late Holocene and colder middle Holocene is consistent with previously reported temperature records from central Asia, the Tibetan Plateau, and North China. The long-term warming trend in our summer temperature record is consistent with recently reported winter temperature records from high latitudes of continental Eurasia. All these results further support the reliability of our summer temperature record from central Asia. The better understandings about the Holocene temperature history and its possible driven mechanism(s) can be benefited potentially from more reliable Holocene temperature records, including our record reported in this paper.

Paleoenvironment Variability during Termination I at the Reykjanes Ridge, North Atlantic

The micropaleontological study (radiolarians and foraminifera) of the sediment core AMK-340, Reykjanes Ridge, North Atlantic, combined with the radiocarbon dating and oxygen and carbon isotopic record, provided data for the reconstruction of the summer paleotemperature across the upper 100 meters water depth range, and paleoenvironments during the Termination I in the age interval of 14.5–8 ka. The response of the main microfossil species to the paleoceanographic changes within the Bølling-Allerød (BA) warming, the Younger Dryas (YD) cold event and final transition to the warm Holocene, was different. The BA warming was well captured by the radiolarian and benthic foraminiferal records, but not the planktic one. The high abundances of the cold-water radiolarian species Amphimelissa setosa as a Greenland/Iceland Sea indicator marked a cooling at the end of the BA and at the start of the YD at 13.2–12.3 ka. The micropaleontological and isotopic data together with the paleotemperature estimates for the Reykjanes Ridge at 60°N document that, after the warm BA, the middle YD ca. 12.5–12.2 ka was the next significant step toward the Holocene warming. The start of the Holocene interglacial conditions was reflected in large representation of the microfossils being indicators of the open boreal North Atlantic environments indicating increasing warmth.