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Reliable radiocarbon (14C) ages of foraminifera are a prerequisite to generate robust high-resolution age-depth models or to obtain precise understanding of past carbon cycle dynamics. With the advance of small-scale 14C measurements, instrumental precision and levels of contamination (extraneous carbon introduced during sample pretreatment or analysis) became increasingly important to consider. To reduce the effect of carbon contamination, an attempt can be made to remove it by leaching the surface with weak acids. Alternatively, mathematical corrections (e.g., subtraction) based on processing blanks can be applied. We report on 14C analyses of monospecific foraminifera samples compared between different blank corrections (correction against 14C-free CO2, IAEA-C1 and foraminifera) and sample treatments (i) to examine whether chemical pretreatment and mathematical blank subtraction are comparable, and (ii) to determine limitations hindering reliable 14C dating with ever smaller sample sizes. The data show that chemical pretreatment of foraminifera corrected against IAEA-C1 does remove surface contamination and that the same effect can be achieved for untreated samples that were mathematically corrected for blank values determined from sample size-matched 14C-free foraminifera. Leaching only has a beneficial effect on 14C data for older samples, where the isotopic difference between untreated and chemically pretreated samples exceeds the analytical precision.

The Bølling-Allerød interstadial (14.7-12.9 kyr BP), during the last deglaciation, was characterized by rapid retreat of ice sheets and significant sea level rise (Meltwater Pulse 1A, MWP-1A; 14.7-14.3 kyr BP). Yet, the response of the terrestrial cryosphere during this period of abrupt climate change remains elusive. Here we present a multi-proxy analysis of a sediment record from the upper slope of the Svalbard continental margin that encompasses the last 30 kyr. We show that the Last Glacial Maximum was characterised by the deposition of bedrock material locally sourced by the Barents Sea Ice Sheet. Instead, during MWP-1A permafrost-derived material rich in biospheric carbon became the dominant source of sediments despite the lack of any direct connection with permafrost deposits. Our results suggest massive erosion of Yedoma permafrost deposits during abrupt sea level rise followed by long-range sea ice transport within the Transpolar Drift towards the Arctic Ocean gateway. Overall, we show how permafrost is susceptible to large-scale remobilization in a scenario of rapid warming and sea level rise.

Fjords have been identified as carbon burial hotspots, sequestering about 18 MtC annually, with most recent estimates suggesting 61±16% of sedimentary organic carbon (OC) to be labile. Towards higher latitudes and catchment glaciation the relative contribution of petrogenic OC increases in fjord sediments. Enhanced melting and mass loss due to anthropogenic climate change is expected to increase sedimentary runoff from glaciers and ice-sheets in the coming decades, including previously locked-up petrogenic OC. Since petrogenic OC has an accumulated history of pre-depositional degradation, sequestration, and diagenesis, it has commonly been regarded as non-bioavailable to today’s microbes and is typically not considered a carbon source in climate models. However, over the last two decades, several studies discussed microbial utilization of petrogenic OC. While glacially derived dissolved OC was identified as being highly bio-available in the water column, the bio-availability of its particulate counterpart is virtually unexplored, especially after redeposition. To investigate the bio-availability of sedimentary petrogenic OC and its carbon feedback potential to the atmosphere, we extracted and determined intact polar lipids (indicative of living microbes) and their radiocarbon signature down core in three sediment cores in a proximal-to-distal transect in Hornsund fjord, Svalbard. By applying an isotope mass balance, we were able to show that local subsurface bacteria use between 5 ± 2% and 55 ± 6% (average of 25 ± 16%) of petrogenic OC for their biosynthesis. Thus, providing evidence that particulate petrogenic OC is bio-available after redeposition and is used as an important substrate in the subsurface. This suggests a potential positive feedback of increased petrogenic OC supply to fjord sediments via its bacterial utilization and subsequent carbon release in a warming climate. Further, we observe increased bio-availability of petrogenic OC along both the distal-to-proximal transect and down core. We hypothesize that the spatial and temporal variability of petrogenic carbon utilization is related to the availability of recently synthesized marine OC as well as to the distance to glacial termini, thus to sediment accumulation rate and oxygen availability.

Rapid Arctic warming accelerates permafrost thaw, causing an additional release of terrestrial organic matter (OM) into rivers and, ultimately, after transport via deltas and estuaries, to the Arctic Ocean nearshore. The majority of our understanding of nearshore OM dynamics and fate has been developed from freshwater rivers despite the likely impact of highly dynamic estuarine and deltaic environments on the transformation, storage, and age of OM delivered to coastal waters. Here, we studied particulate organic carbon (POC) dynamics in the Lena River delta and compared them with POC dynamics in the Lena River main stem along a ∼ 1600 km long transect from Yakutsk, downstream to the delta. We measured POC, total suspended matter (TSM), and carbon isotopes (δ13C and Δ14C) in POC to compare riverine and deltaic OM composition and changes in OM source and fate during transport offshore. We found that TSM and POC concentrations decreased by 70 % during transit from the main stem to the delta and Arctic Ocean. We found deltaic POC to be strongly depleted in 13C relative to fluvial POC. Dual-carbon (Δ14C and δ13C) isotope mixing model analyses indicated a significant phytoplankton contribution to deltaic POC (∼ 68 ± 6 %) and suggested an additional input of permafrost-derived OM into deltaic waters (∼ 18 ± 4 % of deltaic POC originates from Pleistocene deposits vs. ∼ 5 ± 4 % in the river main stem). Despite the lower concentration of POC in the delta than in the main stem (0.41 ± 0.10 vs. 0.79 ± 0.30 mg L−1, respectively), the amount of POC derived from Yedoma deposits in deltaic waters was almost twice as large as the amount of POC of Yedoma origin in the main stem (0.07 ± 0.02 and 0.04 ± 0.02 mg L−1, respectively). We assert that estuarine and deltaic processes require consideration in order to correctly understand OM dynamics throughout Arctic nearshore coastal zones and how these processes may evolve under future climate-driven change.

We discuss present and developing techniques for studying radiocarbon in marine organic carbon (C). Bulk DOC (dissolved organic C) Δ14C measurements reveal information about the cycling time and sources of DOC in the ocean, yet they are time consuming and need to be streamlined. To further elucidate the cycling of DOC, various fractions have been separated from bulk DOC, through solid phase extraction of DOC, and ultrafiltration of high and low molecular weight DOC. Research using 14C of DOC and particulate organic C separated into organic fractions revealed that the acid insoluble fraction is similar in 14C signature to that of the lipid fraction. Plans for utilizing this methodology are described. Studies using compound specific radiocarbon analyses to study the origin of biomarkers in the marine environment are reviewed and plans for the future are outlined. Development of ramped pyrolysis oxidation methods are discussed and scientific questions addressed. A modified elemental analysis (EA) combustion reactor is described that allows high particulate organic C sample throughput by direct coupling with the MIniCArbonDAtingSystem.

The changes in atmospheric pCO2 provide evidence for the release of large amounts of ancient carbon during the last deglaciation. However, the sources and mechanisms that contributed to this process remain unresolved. Here, we present evidence for substantial ancient terrestrial carbon remobilization in the Canadian Arctic following the Laurentide Ice Sheet retreat. Glacial-retreat-induced physical erosion of bedrock has mobilized petrogenic carbon, as revealed by sedimentary records of radiocarbon dates and thermal maturity of organic carbon from the Canadian Beaufort Sea. Additionally, coastal erosion during the meltwater pulses 1a and 1b has remobilized pre-aged carbon from permafrost. Assuming extensive petrogenic organic carbon oxidation during the glacial retreat, a model-based assessment suggests that the combined processes have contributed 12 ppm to the deglacial CO2 rise. Our findings suggest potentially positive climate feedback of ice-sheet retreat by accelerating terrestrial organic carbon remobilization and subsequent oxidation during the glacial-interglacial transition.

Recent research has challenged the traditional view of rock-derived or petrogenic organic carbon (OCpetro) as non-bio-available and bypassing the active carbon cycle when eroded and buried in marine sediments 1 and identified it as a potential source of fossil greenhouse gas emissions to the atmosphere2. Due to rising global temperatures, glacial OCpetro export rates are expected to increase3, thus, increasing the amount of OCpetro accessible to modern microbes in downstream depositional environments like the carbon burial “hot spots” of fjord sediments4. Using compound-specific radiocarbon analysis of fatty acids from intact polar lipids derived from live microbes, we were able to quantify the bio-availability of OCpetro in marine sediments in Hornsund Fjord, Svalbard. Our data indicate that local bacterial communities utilize between 5 ± 2% and 55 ± 6% of OCpetro (average of 25 ± 16%) for their biosynthesis, providing evidence for OCpetro bio-availability and its importance as substrate after redeposition. We hypothesize that the lack of sufficient recently synthesized organic carbon from primary production forces microbes into OCpetro utilization as an alternative energy source. The enhanced input of OCpetro and subsequent utilization by subsurface microbes represents an increasing natural source of fossil greenhouse gas emissions and a potential further positive feedback mechanism in a warming climate.

The radiocarbon analysis laboratory at Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) is equipped with an accelerator mass spectrometer (AMS) MICADAS (MIni CArbon Dating System). The laboratory provides routine 14C analyses on bulk organic matter, plant fragments, dissolved and particulate organic matter, individual molecular lipids, and carbonate (micro-) fossils with the aim to foster international research efforts in vulnerable high latitudes. The AWI MICADAS allows AMS 14C analysis on graphite targets as well as on CO2 samples via gas injection into the hybrid ion source. The laboratory thus provides reliable datasets even if only small amounts of sample material are available, a problem often encountered in polar research. Here we describe the standard operation procedures and sample preparation methods employed, and demonstrate the instrument performance and data quality based on repeat analysis of international reference materials.

Large rivers discharge great amounts of terrigenous organic carbon (OCterr) to the ocean, 90% of which are trapped in the coastal areas. The OCterr processing during transport to and within the coastal oceans are not well known. The Pearl River is the second largest river in China in terms of annual runoff. Here, we studied OCterr delivered from the river in the Pearl River Estuary (PRE) and the northern South China Sea (SCS) shelf using stable and radioactive carbon isotope compositions (δ13C and F14C) of OC in surface sediments to (1) constrain sources of OC, (2) explore the role of hydrodynamic processes for OCterr transport, and (3) better understand the burial and degradation processes of OCterr. A three end-member mixing model based on δ13C and 1/(C/N) values of bulk OC was used to calculate relative contributions of OCterr, OC derived from marine (OCmar) and riverine primary production (OCRpp). Results showed that the PRE and its western coastal inshore mud deposit are dominated by OCterr (70 ± 3% and 54 ± 10%, respectively), but other areas receive increasing contributions from OCmar: the slope (49 ± 10%), the eastern coast (58 ± 2%) and the outer shelf (68 ± 3%). OCRpp accounted for substantial proportions in the PRE (14 ± 6%) and rapidly decreased in the offshore area (3–5%), likely due to extensive aerobic respiration of organic matter (OM). Subsequently, average F14C values of OCterr were calculated ranging from 0.271 to 0.639 using a Monte-Carlo simulation strategy and based on the assumption that F14C values of OCRpp and OCmar varied within narrow ranges. Together with OCterr contents and grain sizes of sediments, F14C values of OCterr were used to distinguish two regions of distinctive sedimentological characteristics in the study area. Region I, including the PRE and inner shelf, showed a decrease of OCterr content along the trajectory of westward along-shelf transport, reflecting resuspension-dominated conditions for OCterr transport. Region II, including the outer shelf and one site on the inner shelf (E701), exhibited relatively old OCterr (9180 ± 730 yr BP), which is attributed to preferential accumulation of coarser sediments by bedload movement. Finally, a first-order degradation rate constant was calculated from contents and 14C ages of OCterr, yielding a slow OCterr degradation rate of (2.88 ± 0.61) × 10–4 yr−1, indicating a more refractory nature and likely effective mineral protection of OCterr. The ΣCO2 efflux due to OCterr degradation was estimated to be 3.68 ± 1.39 Gg C yr−1 for the entire surface sediments in the Pearl River derived mud belt, equivalent to only 0.7 ± 0.3% of the total particulate OC flux of the Pearl River. This, hence, suggests that the OCterr is more persistent and the preservation of OCterr in the marine system is better than previously thought, but experiences substantial degradation on centennial to millennial timescales.

The rapid warming of the Arctic may affect the stability of coastal geomorphological systems. Prograded sequences of wave-built deposits, so-called beach-ridge systems, preserve a proxy record of the long-term variability in the drivers of coastal evolution. Information on relative sea level (RSL), climate forcing and sediment supply can be reconstructed from these archives. Buor Khaya Bay is one of the few places along the Siberian Arctic coast where wide beach-ridge systems exist. A previously undescribed field site was surveyed in order to obtain information on the geomorphological processes along the modern shoreline under the current environmental conditions, and the characteristics of the Holocene beach-ridge deposits (e.g., elevation, sediment and age). Our data show that the system formed under storm wave/surge conditions. The beach ridges prograded ca. 1100 m between 6200 and 2600 cal yr BP, with only minor variations in surface elevation. This suggests a continuous and high sediment supply and similar storm wave run-up heights during that time. This relationship is interpreted as indicating RSL stability at a similar-to-present elevation during the period of beach-ridge formation. The hiatus in coastal progradation is concurrent with a deteriorating climate (cooling) in the Laptev Sea area and our data hence suggest increased rates of coastal change during periods of warmer climate conditions. Our study illustrates the potential of coastal sedimentary archives to provide a more complete view of the forcing, resilience and long-term evolution of unconsolidated Arctic coasts in a changing environment.

Assessing the effects of sediment inhomogeneity on the core stratigraphy and on proxy records is essential to perform reliable climate reconstructions from marine sediments. Inhomogeneities can stem from sediment mixing (e.g., bioturbation) which destroys the temporally layered climatic information stored in proxy carrier. Thus, in addition to the measurement error, the time-uncertainty in radiocarbon-dated sediments must be taken into account for depth-age modelling in order to obtain an unambiguous time scale. Here, we present a case-study based on a boxcore (OR1-1218-C2-BC) from the South China Sea (2208 m water depth) covering the last 20 kyr. The boxcore was divided into nine sub-cores by a grid of 3 x 3 (each sub-core is 8 x 8 cm with a length of 34 cm), yielding a total surface area of 576 cm2. This sampling scheme offers the possibility for detailed, three-dimensional analyses on small spatial scales. Radiocarbon measurements were performed in every sub-core for seven depth layers, each with a fraction of 200 crushed and well mixed foraminifera (Trilobatus sacculifer, 250 – 350 µm) to study the horizontal sediment heterogeneity. In addition, small sample (5 specimen) replicate radiocarbon measurements from a single sediment sample allow to estimate the age heterogeneity within a 1 cm sediment slice and thus the vertical mixing from bioturbation. The replicate radiocarbon dates suggest a bioturbation depth of around 12 cm; however, the downcore radiocarbon dates show no clear sign of a well-mixed bioturbation layer. Using statistical analysis (e.g., spatial correlation measures and variance analyses), we separate the errors from the radiocarbon measurements, the finite sample size and both the vertical and horizontal heterogeneity. Comparing the radiocarbon dates in the sub-cores indicates a small horizontal heterogeneity compared to the vertical mixing. The three-dimensional data set allows us to quantify the effect introduced by (post-depositional) sediment mixing on the age-estimate as well as on the proxy signal and to discuss the effects on low-sedimentation climate records. This will provide a better quantification of uncertainties within proxy time series.

Rapid climate warming in the Arctic intensifies permafrost thaw, increases active layer depth in summer and enhances riverbank and coastal erosion. All of these cause additional release of organic matter (OM) into streams and rivers. OM will be (1) transformed and modified during transport and subsequently discharged into the Arctic Ocean, or (2) removed from the active cycling by sedimentation. Here, the nearshore zone (which includes deltas, estuaries and coasts) is of great importance, where the major transformation processes of terrestrial material take place. Despite the importance of deltas for the biogeochemical cycle, their functioning is poorly understood. For our study we examined the Lena River nearshore, which represents the world’s third largest delta and supplies the second highest annual water and sediment discharge into the Arctic Ocean. Running through almost the entirety of East Siberia from Lake Baikal to the Laptev Sea, the Lena River drains an area of ∼2,61×106 km2 with approximately 90% underlain by permafrost. Our aims were to investigate the spatial variation of OM concentration and isotopic composition during transit from terrestrial permafrost source to the ocean interface, and to compare riverine and deltaic OM composition. We measured particulate and dissolved organic carbon (POC and DOC) concentrations and their associated δ13C and ∆14C values in water samples collected along a ∼1500 km long Lena River transect from Yakutsk downstream to the river outlet into the Laptev Sea.We find significant qualitative and quantitative differences between the OM composition in the Lena River main channel and its delta. Further, we found suspended matter and POC concentrations decreased during transit from river to the Arctic Ocean. DOC concentrations in the Lena delta were almost 50% lower than OM from the main channel. We found that deltaic POC is depleted in 13C relative to fluvial POC, and that its 14C signature suggests a modern composition indicating phytoplankton origin. This observation likely reflects the difference in hydrological conditions between the delta and the river main channel, caused by lower flow velocity and average water depth. We propose that deltaic environments provide favorable growth conditions for riverine primary producers such as algae and aquatic plants. Deltaic DOC is depleted in 14C compared to riverine, especially in samples taken from the water surface, which indicates contributions from an additional old carbon stock source, specific for the Lena Delta. We suggest that this C is released from deltaic bank erosion and partly stays floating on the surface. In conclusion, we found a strong impact of deltaic processes on the fate and dominant signatures of OM discharged into the Arctic Ocean.

Foraminifera isolated from deep-sea sediments are among the most common materials in AMS radiocarbon analysis. These results are used to determine accurate age models for sediment sequences as well as to detect changes in deep-sea ventilation. Often, only small numbers of (monospecific) foraminifera shells can be isolated, in particular when studying benthic species in sediments from the polar regions. Therefore, these samples are often analyzed as CO2 gas using MICADAS instruments, and the method can typically be used for samples of up to around 40 ka in age. For reliable results, an accurate determination and minimization of processing blanks is required.Processing blanks for foraminifera samples may in part derive from acid hydrolysis of the carbonates. It has, however, been shown that contamination of the carbonate fossils, mainly from atmospheric CO2 adsorbed on the porous surfaces of foraminifera, is the largest source of blank found in foraminifera samples. The removal of such contamination has been attempted by various leaching methods, which come at the risk of introducing additional contaminations. Alternatively, blank correction of AMS results may be achieved using fossil foraminifera from ancient deposits much beyond the range of the radiocarbon method.Here we report results of a systematic test comparing the F14C levels obtained for fossil (>130 ka) and sub-modern monospecific planktic and benthic foraminifera samples using different blank correction approaches. Specifically, we compare leaching with dilute hydrochloric acid, blank correction relative to a leached and an un-leached fossil foraminifera standard, and blank correction relative to the IAEA-C1 certified carbonate standard.

It is consensus that the deglacial changes in ocean carbon storage and circulation play a role in regulating atmospheric CO2. However, emerging evidence suggests that the rapid deglacial CO2 rises can in part be attributed to large quantities of pre-aged carbon being released from degrading permafrost. In this study, we apply a radiocarbon approach on both terrestrial compounds (high molecular weight fatty acids; HWM-FA) and bulk organic carbon from a well-studied core ARA04C/37 from the Canadian Beaufort Sea. Based on our records, substantial amounts of ancient carbon were supplied from land to the ocean during the mid-late deglaciation (14.5-10 cal. kyr BP) by frequent high sediment flux events. Because the core location is strongly influenced by the Mackenzie River discharge, sediments only contain minor contributions from marine organic matter, allowing to consider mainly two terrestrial sources to explain the characteristics of bulk sedimentary organic matter. The terrestrial HMW-FA are taken to represent the biospheric carbon, and their age differences from the bulk organic carbon are explained by petrogenic carbon input. During the Younger Dryas, ice-sheet melting and meltwater outbursts enhanced petrogenic carbon contributions, suggesting a major source in the hinterland drainage system. During the rapid sea-level rise (meltwater pulses 1a and 1b), the very old organic carbon and comparable ages between biospheric carbon and bulk organic carbon indicate the occurrence of permafrost carbon remobilization primarily via coastal erosion while petrogenic carbon from the drainage system was found negligible. Remobilized ancient permafrost carbon is commonly regarded to be highly bioavailable, while petrogenic carbon is likely more recalcitrant to biological degradation. Our records thus suggest that the release of ancient carbon to the Beaufort Sea had the strongest impact on the atmospheric CO2 level and contributed to its rapid increases during the B/A and Pre-Boreal when permafrost deposits along the coast were eroded.

The thawing of permafrost in the polar regions has important implications for climate on Earth. Indeed, permafrost degradation results in a positive climate feedback which is currently aggravated by human action. The dynamic character of Earth’s climate means that past trends and variability can be examined to improve future projections of this effect. Notably, the permafrost zone that covered parts of Europe during the Last Glacial Maximum (LGM) is currently absent, indicating that this region is a crucial area for the study of permafrost carbon remobilization during the last deglacial warming. Here, we investigate the mobilization of permafrost material to the Bay of Biscay, off the English Channel. Although this location has been shown to have experienced an enhanced deposition of terrigenous material during the last deglaciation, the contribution of permafrost thaw is unknown. We have established an accurate and robust chronological framework for this deposition, showing enhanced rates of sediment accumulation from approximately 20.2 to 15.8 kcal BP. Biomarker analysis has revealed periods of marked increases in terrigenous input, namely from approximately 20.5 to 19 and from 19 to 16.5 kcal BP. Moreover, by performing compound specific radiocarbon dating on n-alkanoic acids isolated from the sedimentary archive, we have been able to determine the origin of organic matter deposited at the core location. Our results will help researchers to assess to what extent permafrost thaw contributed to the peak of organic matter deposition present in the marine sediment, allowing us to sharpen our understanding of the mechanisms of permafrost carbon mobilization.

Summary Here we report on the radiocarbon composition of particulate organic matter (POC) collected on four shelf (∼100 m water depth) to open ocean (∼2700 m water depth) transects in the northwest African upwelling system off Cape Blanc. Data show complex, seasonaly variable features of highly depleated POC in the water column sugguesting remobilization of pre-aged sediments.

Increasing air and sea surface temperatures at high latitudes lead to accelerated thaw, destabilization, and erosion of perennially frozen soils (i.e., permafrost), which are often rich in organic carbon. Coastal erosion leads to an increased mobilization of organic carbon into the Arctic Ocean that can be converted into greenhouse gases and may therefore contribute to further warming. Carbon decomposition can be limited if organic matter is efficiently deposited on the seafloor, buried in marine sediments and thus removed from the short-term carbon cycle. Basins, canyons and troughs near the coastline can serve as sediment traps and potentially accommodate large quantities of organic carbon along the Arctic coast. Here we use biomarkers (source-specific molecules), stable carbon isotopes (δ13C) and radiocarbon (Δ14C) to identify the sources of organic carbon in the nearshore zone of the southern Canadian Beaufort Sea. We use an end-member model based on the carbon isotopic composition of bulk organic matter to identify sources of organic carbon. Monte Carlo simulations are applied to quantify the contribution of coastal permafrost erosion to the sedimentary carbon budget. The models suggest that 40% of all carbon released by coastal erosion is efficiently trapped and sequestered in the nearshore zone. We conclude that permafrost coastal erosion releases huge amounts of sediment and organic matter into the nearshore zone. Rapid burial removes large quantities of carbon from the carbon cycle in depositional settings.

Late Devonian mass extinctions attributed to extensive anoxia and/or euxinia of the oceans are associated with widespread deposition of organic-rich shales. Also in the epeiric waters of the Canning Basin (Western Australia), photic zone euxinia (PZE) prevailed during the Givetian–Frasnian, with geochemical evidence for PZE on the northern (Lennard Shelf)–, and southern (Barbwire Terrace) margins of the Fitzroy Trough. On the Lennard Shelf, shales record episodic pulses of PZE associated with high algal activity due to enhanced nutrient supply, whereas a restricted marine setting on the Barbwire Terrace is thought to be the main driver for the development of persistent PZE and associated bacterial predominance. Structural evidence indicates that the Fitzroy Trough was a confined basin during the Late Devonian with the possibility of limited ocean circulation. Widespread PZE is expected to have developed in the poorly mixed water column, if the basin received sufficient nutrient supply for enhanced primary production. Notwithstanding the presence of anoxia during deposition of potential source rocks, only two small Devonian-sourced oil fields and numerous oil shows have been found in the Canning Basin. Biomarker assemblages show that the oils produced from the Lennard Shelf fields (i.e. Blina-1, Blina-4 and Janpam North-1) have substantially different molecular compositions to the minor oil recovered from Mirbelia-1 on the Barbwire Terrace. A correlation was established between the Lennard Shelf oils and rock extracts from the Gogo Formation at Blina-1 and McWhae Ridge-1 based on their hopane, sterane and carotenoids abundances. A definitive source correlation was not obtained for the Mirbelia-1 oil, but it did show some genetic affinity to the Givetian–Frasnian extracts from the Barbwire Terrace, suggesting that local source rocks are developed in the region.

Hydropyrolysis (HyPy) of S-containing oil mature rock samples from two geologic settings each produced much higher concentrations of organosulfur compounds (OSCs) compared to their free occurrence in the bitumen. The δ 34 S values of the most abundant OSCs from the kerogen and in the bitumen, were measured by gas chromatography inductively coupled plasma mass spectrometry (GC-ICP-MS). DBT and mDBTs from the HyPy processed kerogen fractions showed a distinct 34 S depletion, with δ 34 S values up to 12‰ lighter than their bitumen occurrence. The different δ 34 S values of OSCs from the kerogen and bitumen fractions is likely reflective of differences in timing of production, reduced sulfur sources or organic sulfurisation mechanism.

Tropical and subtropical rivers deliver large quantities of terrestrial organic carbon (OCterr) to the ocean, acting as a crucial part of the global carbon cycle, but little is known about the timescale and efficiency of its transport to and in the adjacent coastal sea. Here we examined source-specific biomarker (fatty acids, FAs) contents and isotope compositions in surface sediments in an alongshore transect southwestward from the Pearl River mouth. The C28+30, rather than other long-chain saturated FAs, were found to be the most representative for OCterr, and a plant wax mean age of 3060 ± 90 yr (resulting from protracted storage) was estimated in the Pearl River watershed from the 14C age of C28+30 FA in a river mouth sample. A compilation of plant wax mean ages in global (sub)tropical river systems including this study suggests that regional differences in climate and morphology may have a limited impact on plant wax mean ages in (sub)tropical regions. A four-source mixing model based on bulk OC and biomarker isotope compositions demonstrated that surface sediments in the Pearl River-derived mudbelt consist of 0.15–0.36 wt.% marine OC, 0.03–0.13 wt.% riverine primary production-derived OC, 0.18–0.49 wt.% soil OC, and 0.07–0.16 wt.% fossil OC. The mean burial efficiency of fossil and soil OC is ∼85% and 49%, respectively, indicating the refractory nature of fossil OC but a significant loss of soil OC due to remineralization during transport in the marine environment before final burial. Over longer timescales, the OCterr loss experienced during transport may, thus, to some extent reduces the capacity of terrestrial ecosystems (particularly soils) as CO2 sinks.

An innovative experimental approach has been applied to a metamorphosed (> 550 °C) kerogen associated with orogenic Au mineralisation. The novel application of catalytic Hydropyrolysis (HyPy) to mineralised sediments associated with Au-mineralisation successfully liberated GC–MS-detectable hydrocarbons interpreted as indigenous to the high maturity organic matter (OM), and previously proven unamenable to more traditional methods of organic geochemical analyses. These organic compounds were likely sequestered within condensed polyaromatic structures of the high maturity kerogen that exhibited an intimate relationship to the mineral matrix as documented using high resolution in-situ microscopy. The major pyrolysis products were the polycyclic aromatic hydrocarbons (PAHs) pyrene (detected in particularly high abundance), coronene and hydrogenated analogues of these 4- and 7-ringed systems. To help distinguish the importance of specific organic–mineral relationships, each sample was subjected to a sequential demineralisation process using three increasingly stronger acids (i.e. 3 M HCl, 12 M HCl, HF). The kerogen isolated following each demineralisation step was subject to HyPy and then GC–MS analysis. Pyrene and hydrogenated analogues were again the major HyPy products of all demineralised kerogens (similar to the parent kerogen result). Other 2–7 ringed hydrocarbons and a homologous series of n -alkanes also were detected. Subtle differences in the distributions of compounds released and a pronounced increase in the abundance of most HyPy products at each demineralisation step (TOC also showed a general increase) were observed. These observations could be attributed to the increasing release of mineral-bound hydrocarbons, indicating the strong organic affinity for a wide variety of mineral types. The intimate association of the kerogen and minerals was clearly evident in the SEM–EDS photomicrographs of several freshly fractured surfaces that showed OM along mineral boundaries as inclusions, and as continuous infill in mineral grains. Most of the OM is intricately embedded in the clay structures. These mineral–kerogen relationships are retained even when the samples were finely powdered. Laser Raman analysis identified highly ordered and aromatic graphitic like carbonaceous material (CM-1) associated with the sedimentary matrix, although a distinct type of less ordered CM (CM-2) was also identified in proximity to sulphide veins — reflecting a separate organic origin of preservation pathway. The sequestration and protection of these hydrocarbons from thermal destruction likely result from an intimate structural relationship between the minerals and OM. This pioneering analytical approach represents a major breakthrough to the organic characterisation of sediments metamorphosed by high temperature mineralisation processes.

Ice wedges in the Yana Highlands of interior Yakutia – the most continental region of the Northern Hemisphere – were investigated to elucidate the winter climate and continentality during the Middle to Late Pleistocene. The Batagay megaslump exposes ice wedges and composite wedges that were sampled from three cryostratigraphic units: the lower sand unit of Marine Isotope Stage (MIS) 6 age, the upper Ice Complex (Yedoma) and the upper sand unit (both MIS3 to MIS2). A terrace of the nearby Adycha River provides a Late Holocene (MIS1) ice wedge that serves as a modern endmember for analysis. Stable-isotope values of ice wedges in the MIS3 upper Yedoma Ice Complex at Batagay are more depleted (mean δ18O about −35 ‰) than those from 17 other ice-wedge sites across coastal and central Yakutia. This observation points to lower winter temperatures and, therefore, higher continentality in the Yana Highlands during MIS3. Likewise, more depleted isotope values compared to other sites in Yakutia are found in Holocene wedge ice (mean δ18O about −29 ‰). Ice-wedge isotopic signatures of the MIS6 lower sand unit (mean δ18O about −33 ‰) and of the MIS3-2 upper sand unit (mean δ18O from about −33 to −30 ‰) are less distinctive regionally and preserve traces of fast formation in rapidly accumulating sand sheets and of post-depositional fractionation.

A series of hydropyrolysis (HyPy) experiments have been conducted on a small suite of authentic polycyclic aromatic hydrocarbons (PAHs: coronene, pyrene and perylene) to investigate the HyPy behaviour of these PAHs. This information may help in the interpretation of the structural significance of aromatic HyPy products, often detected in high abundance, from high maturity kerogens. The PAHs were separately treated by HyPy and were all susceptible to some extent of hydrogenation. Perylene also decomposed into low molecular weight aromatics (e.g. methylbiphenyls). Structurally, perylene is much less stable than the more condensed PAHs coronene and pyrene. The total product concentrations (wt% of starting PAH) from all HyPy experiments were consistently less than 100 wt%, probably due to either the condensation of semi-volatile products on walls of the transfer line prior to reaching the HyPy trap or the inefficient cold trapping of highly volatile products. Hydrogenation of PAHs was prevalent and was found to be significantly influenced by the addition of a Mo-S based catalyst and potentially the C/Mo ratio, but largely independent of the two final temperatures used (520 °C and 550 °C). The fully aromatised and hydrogenated products for any stable ring system may provide a general indication of the size distribution of aromatic units within the kerogen structure.

Carbonaceous material (CM) is thought to be a key reductant contributing to the formation of large Au deposits, but there has been much speculation about its source, molecular composition and reactivity. The first successful analytical retrieval of organic compounds from a thermally over-mature (>550 °C) Paleoproterozoic Cosmo-Howley Orogenic Au deposit was recently achieved by Robert et al. (2016). Here, we have evaluated the nature of the CM associated with this high temperature Au mineralisation via an integrated analytical approach which combined high-resolution in situ laser Raman spectroscopy, micro to nano-scale imaging (e.g., EELS, HAADF-STEM, and HRTEM) and molecular and isotopic geochemistry. We identified two distinct CM types: CMker – an ubiquitous highly graphitic kerogen typical of high-grade metamorphic conditions formed by regional metamorphism; and CMfd – small sub-microscopic inclusion-like nodules of highly disordered carbon rich in polycyclic aromatic hydrocarbons (PAHs), coincident within the Au-bearing sulfide minerals in hydrothermal vein regions. The paragenetic emplacement and molecular characteristics of CMfd suggests a formation by metasomatic processes and introduction by a hydrothermal fluid which might also have co-transported Au. CMker and CMfd gave different Raman spectra indicative of their contrasting origin and structural response to regional and contact metamorphic history and subsequent metasomatism of the Cosmo-Howley deposit. Raman signals indicated CMker had a graphitic like structure whereas CMfd comprised high concentrations or clusters of PAHs. The broad range of Raman spectra detected here (and by others in similar studies) was likely due to the mixed signals of these two types of CM. The δ13C values of PAH products released via the HyPy treatment of the parent and sequentially demineralised kerogen fractions were measured to be in the range of −20 to −30‰, indicative of an organic biopolymeric origin. The δ13C values of PAHs products decreased with demineralisation, concomitant with an increase in their concentrations and affinity to the sulfide-minerals (and associated CMfd) suggesting a close relationship. The localised (within 20 mm) co-occurrence of different CM types and apparent abundance correlation of CMfd with Au and sulfides suggests Au mineralisation might be supported by specific CM types, and these relationships should be evaluated further including on a wider Au deposit scale.

Phytanyl benzene and phytanyl toluene occur in mudstones from several key Permian-Triassic Boundary (PTB) sections from mid-northern palaeolatitudes (Spitsbergen and Eastern Greenland), as well as mid-southern palaeolatitudes (Western Australia). The occurrence of these compounds through the different PTB sections is related to the occurrence of the previously identified C33 n-alkyl cyclohexane, suggesting their parent organism shared a similar unique ecological niche and was associated with the extinction horizon. Further, the lack of these compounds in the carbonate-dominated palaeoequatorial, Global Stratotype Section and Point (GSSP), Meishan-1 (South China) section possibly points to their source being temperature and climate controlled.