Soils of the northern high latitudes store carbon over millennial timescales (thousands of years) and contain approximately double the carbon stock of the atmosphere. Warming and associated ...permafrost thaw can expose soil organic carbon and result in mineralization and carbon dioxide (CO2) release. However, some of this soil organic carbon may be eroded and transferred to rivers. If it escapes degradation during river transport and is buried in marine sediments, then it can contribute to a longer-term (more than ten thousand years), geological CO2 sink. Despite this recognition, the erosional flux and fate of particulate organic carbon (POC) in large rivers at high latitudes remains poorly constrained. Here, we quantify the source of POC in the Mackenzie River, the main sediment supplier to the Arctic Ocean, and assess its flux and fate. We combine measurements of radiocarbon, stable carbon isotopes and element ratios to correct for rock-derived POC. Our samples reveal that the eroded biospheric POC has resided in the basin for millennia, with a mean radiocarbon age of 5,800 ± 800 years, much older than the POC in large tropical rivers. From the measured biospheric POC content and variability in annual sediment yield, we calculate a biospheric POC flux of 2.2(+1.3)(-0.9) teragrams of carbon per year from the Mackenzie River, which is three times the CO2 drawdown by silicate weathering in this basin. Offshore, we find evidence for efficient terrestrial organic carbon burial over the Holocene period, suggesting that erosion of organic carbon-rich, high-latitude soils may result in an important geological CO2 sink.
Chemical weathering consumes atmospheric carbon dioxide through the breakdown of silicate minerals and is thought to stabilize Earth's long-term climate. However, the potential influence of silicate ...weathering on atmospheric pCO
levels on geologically short timescales (10
-10
years) remains poorly constrained. Here we focus on the record of a transient interval of severe climatic warming across the Toarcian Oceanic Anoxic Event or T-OAE from an open ocean sedimentary succession from western North America. Paired osmium isotope data and numerical modelling results suggest that weathering rates may have increased by 215% and potentially up to 530% compared to the pre-event baseline, which would have resulted in the sequestration of significant amounts of atmospheric CO
. This process would have also led to increased delivery of nutrients to the oceans and lakes stimulating bioproductivity and leading to the subsequent development of shallow-water anoxia, the hallmark of the T-OAE. This enhanced bioproductivity and anoxia would have resulted in elevated rates of organic matter burial that would have acted as an additional negative feedback on atmospheric pCO
levels. Therefore, the enhanced weathering modulated by initially increased pCO
levels would have operated as both a direct and indirect negative feedback to end the T-OAE.
During the Pliensbachian–Toarcian interval of the Early Jurassic, there is a well-known second order marine extinction that is observable at the species and genus levels. Ammonite diversity data from ...successions throughout Europe and parts of the Arctic suggest that this extinction may have been multi-phased with diversity declining over six separate intervals. The main-phase of decline begins at the Pliensbachian–Toarcian boundary and extends into the Lower Toarcian, to a level that is correlative with the Tenuicostatum/Serpentinum Zone boundary. To date, only the main-phase of extinction has been demonstrated as being global in extent and affecting multiple taxonomic groups. This multi-phased extinction has been attributed to regional and global controlling mechanisms that are associated with the Volcanic Greenhouse Scenario which links the eruption of the Karoo–Ferrar large igneous province (LIP) to global warming and mass extinction.
We compare stratigraphic ranges of ammonite and foraminiferal species in Pliensbachian–Toarcian successions of western North America to the record in Europe and parts of the Arctic in order to test the geographic extent of the multiple phases of extinction. Our results show six intervals of species level decline that correlate with those recognized in Europe: 1) middle of the Lower Pliensbachian (middle Whiteavesi–middle Freboldi Zones), 2) middle of the Upper Pliensbachian (upper Kunae–lower Carlottense Zone), 3) Pliensbachian/Toarcian boundary into the Lower Toarcian (upper Carlottense–middle Kanense Zones), 4) Middle Toarcian (upper Planulata–lower Crassicosta Zones), 5) upper Middle–lower Upper Toarcian (middle Crassicosta–Hillebrandti Zones) and 6) Upper Toarcian (lower Yakounensis Zone).
Recognition of this multi-phased event in three separate ocean basins (paleo Pacific, paleo Arctic, and Tethys Oceans), in at least two taxonomic groups, greatly expands the known geographic extent of this multi-phased event and argues for a controlling mechanism that is global in its reach. In relation to the Volcanic Greenhouse Scenario, our study shows that four of the six pulses of extinction occur within the main-phase of Karoo magmatism. The decline in the Early Pliensbachian, previously thought to be separate from this event, occurs within error range of the onset of Karoo magmatism and the decline in the Late Toarcian coincides with the later stages of magmatism. These observations extend the known duration of this multi-phased extinction event to the Early Pliensbachian and support the Volcanic Greenhouse Scenario, specifically the eruption of the Karoo–Ferrar LIP, as a preeminent factor driving the multi-phased extinction of the Pliensbachian–Toarcian.
•Duration of Pliensbachian–Toarcian extinction is analyzed in western North America.•Species-level diversity data includes ammonoid and foraminiferal occurrences.•Data shows six correlative phases of diversity decline in three ocean basins.•Multiple correlative declines argue for global controls for all phases.•Correlation in timing between multi-phased event and Karoo magmatism.
Rationale
Stable nitrogen isotope ratios (δ15N) can be used to discern sources of excess nitrogen pollution in water. The δ15N values of nitrate in water often do not reflect the true δ15N source ...value owing to high temporal variation, and there are high analytical costs associated with obtaining δ15N values from water nitrate. To find alternative solutions, we isotopically labelled macroalgae (i.e. seaweed) beyond natural variation as a new method for determining sources of excess nitrogen pollution in seawater.
Methods
Fucus vesiculosus (bladder wrack) non‐fertile tips were collected from Easington Colliery, County Durham, UK, and cultured in two isotopically enriched solutions containing ammonium sulphate with δ15N values of 170 ± 5‰ and –60 ± 3‰ for a period of 19 days. The macroalgae were cultured in separate opened glass jars in an incubator with set temperature (11°C) and light (125 μmol photons m−2 s−2 on a light/dark rhythm of 16 h/8 h). The oven‐dried tips were analysed for δ15N over the 19‐day experiment.
Results
The macroalgal tips incorporated the isotopically enriched solutions rapidly, reaching 50% of the isotopically enriched seawater after ca 11 days for the 15N‐enriched solution and ca 15 days for the 14N‐enriched solution. δ15N values were incorporated more into the torn base of the macroalgal tips than into the middle and apex regions.
Conclusions
F. vesiculosus rapidly incorporates the isotopic ratio of the artificial seawater solution to which it is translocated. The laboratory‐developed isotopically labelled macroalgae can be manufactured to generate ‘unnatural’ δ15N values for translocation into coastal environments. This approach can provide an efficient, low‐cost alternative to current analytical methods for determining and monitoring nitrogen pollution.
During the Early Toarcian there was a significant disruption in the short-term active carbon reservoir as revealed by carbon-isotope records, which show a broad positive shift that is interrupted by ...a large 5–7‰ negative excursion (δ
13C
org). Carbon-isotope excursion co-occurs with the deposition of organic-rich shales in many areas. This perturbation in carbon isotopes is thought to be indicative of severe climate change and marine anoxia. The two leading hypotheses as to the cause of this event invoke either global or regional controls. Here we present carbon-isotope data from Haida Gwaii, British Columbia, Canada showing a significant perturbation within a temporally constrained Early Toarcian succession that was deposited in the northeastern paleo-Pacific Ocean. These data reinforce the concept that the short-term active carbon reservoir was affected globally, and assist with the correlation of ammonite zonal schemes between western North America and Europe. The δ
13C
org data show a broad positive shift that is interrupted by a sharp and pronounced negative excursion of 7‰ (8.5‰ in δ
13C
wood) in the Early Toarcian Kanense Zone. This negative excursion also coincides with increasing total organic carbon (TOC) from ~
0.4% to ~
1.2%. These data suggest that the Early Toarcian carbon-isotope perturbation was indeed global and imprinted itself on all active global reservoirs of the exchangeable carbon cycle (deep marine, shallow marine, atmospheric).
► We present new Early Toarcian carbon-isotope data from the northeastern paleo-Pacific Ocean. ► A negative CIE of 7‰ δ
13C
org and 8.5‰ δ
13C
wood average −
31‰ for 11
m in the Early Toarcian Kanense Zone. ► Negative CIE also coincides with increasing total organic carbon (TOC) from ~
0.4% to 1.2%. ► Data show a global control mechanism and a correlation of ammonite zonal schemes.
Despite the extensive use of sulphur isotope ratios (δ
S) for understanding ancient biogeochemical cycles, many studies focus on specific time-points of interest, such as the end-Permian mass ...extinction (EPME). We have generated an 80 million-year Permian-Triassic δ
S
curve from the Staithes S-20 borehole, Yorkshire, England. The Staithes δ
S
record replicates the major features of the global curve, while confirming a new excursion at the Olenekian/Anisian boundary at ~ 247 million years ago. We incorporate the resultant δ
S
curve into a sulphur isotope box model. Our modelling approach reveals three significant pyrite burial events (i.e. PBEs) in the Triassic. In particular, it predicts a significant biogeochemical response across the EPME, resulting in a substantial increase in pyrite burial, possibly driven by Siberian Traps volcanism. Our model suggests that after ~ 10 million years pyrite burial achieves relative long-term stability until the latest Triassic.
For this study, we generated thallium (Tl) isotope records from two anoxic basins to track the earliest changes in global bottom water oxygen contents over the Toarcian Oceanic Anoxic Event (T-OAE; ...∼183 Ma) of the Early Jurassic. The T-OAE, like other Mesozoic OAEs, has been interpreted as an expansion of marine oxygen depletion based on indirect methods such as organic-rich facies, carbon isotope excursions, and biological turnover. Our Tl isotope data, however, reveal explicit evidence for earlier global marine deoxygenation of ocean water, some 600 ka before the classically defined T-OAE. This antecedent deoxygenation occurs at the Pliensbachian/Toarcian boundary and is coeval with the onset of initial large igneous province (LIP) volcanism and the initiation of a marine mass extinction. Thallium isotopes are also perturbed during the T-OAE interval, as defined by carbon isotopes, reflecting a second deoxygenation event that coincides with the acme of elevated marine mass extinctions and the main phase of LIP volcanism. This suggests that the duration of widespread anoxic bottom waters was at least 1 million years in duration and spanned early to middle Toarcian time. Thus, the Tl data reveal a more nuanced record of marine oxygen depletion and its links to biological change during a period of climatic warming in Earth’s past and highlight the role of oxygen depletion on past biological evolution.
The lethally maltreated body of Vittrup Man was deposited in a Danish bog, probably as part of a ritualised sacrifice. It happened between c. 3300 and 3100 cal years BC, i.e., during the period of ...the local farming-based Funnel Beaker Culture. In terms of skull morphological features, he differs from the majority of the contemporaneous farmers found in Denmark, and associates with hunter-gatherers, who inhabited Scandinavia during the previous millennia. His skeletal remains were selected for transdisciplinary analysis to reveal his life-history in terms of a population historical perspective. We report the combined results of an integrated set of genetic, isotopic, physical anthropological and archaeological analytical approaches. Strontium signature suggests a foreign birthplace that could be in Norway or Sweden. In addition, enamel oxygen isotope values indicate that as a child he lived in a colder climate, i.e., to the north of the regions inhabited by farmers. Genomic data in fact demonstrates that he is closely related to Mesolithic humans known from Norway and Sweden. Moreover, dietary stable isotope analyses on enamel and bone collagen demonstrate a fisher-hunter way of life in his childhood and a diet typical of farmers later on. Such a variable life-history is also reflected by proteomic analysis of hardened organic deposits on his teeth, indicating the consumption of forager food (seal, whale and marine fish) as well as farmer food (sheep/goat). From a dietary isotopic transect of one of his teeth it is shown that his transfer between societies of foragers and farmers took place near to the end of his teenage years.
In the Jurassic period, the Early Toarcian oceanic anoxic event (about
183 million years ago) is associated with exceptionally high rates of organic-carbon
burial, high palaeotemperatures and ...significant mass extinction.
Heavy carbon-isotope compositions in rocks and fossils of this age have been
linked to the global burial of organic carbon, which is isotopically light.
In contrast, examples of light carbon-isotope values from marine organic matter
of Early Toarcian age have been explained principally in terms of localized
upwelling of bottom water enriched in 12C versus 13
C (refs 1,2,5,6). Here, however, we report
carbon-isotope analyses of fossil wood which demonstrate that isotopically
light carbon dominated all the upper oceanic, biospheric and atmospheric carbon
reservoirs, and that this occurred despite the enhanced burial of organic
carbon. We propose that-as has been suggested for the Late Palaeocene
thermal maximum, some 55 million years ago-the observed
patterns were produced by voluminous and extremely rapid release of methane
from gas hydrate contained in marine continental-margin sediments.
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