Changes In δ13C Research Articles

Functional changes in the gut microbiota across the hibernation cycle examined by stable isotope‐assisted labeling

Hibernation in ground squirrels is a complex annual cycle of physiological adaptations characterized by high metabolic rate and body temperature (Tb) in summer, and bouts of depressed metabolism (torpor) with periodic returns to high metabolic rate and Tb (interbout arousal) in winter. Our previous results showed that the dynamic nature of the hibernation cycle in 13‐lined ground squirrels drives changes in the taxonomic composition of the gut microbial community (microbiota). These taxonomic shifts are likely due to changes in host diet, particularly the lack of ingested food during the hibernation season. Relative abundances of taxa that degrade plant‐derived glycans decrease during hibernation, while taxa that thrive on host‐derived substrates such as mucin increase. However, the functional significance of these shifts in microbiota composition is unknown due to a paucity of tools to measure such changes directly in hosts. To address this, we utilized cavity ring‐down spectroscopy (CRDS) to trace changes in 13CO2/ 12CO2 ratio (δ13C) in exhaled breath from ground squirrels as a real time functional output for microbial activities. Ground squirrels were orally gavaged with 13C‐labeled substrates that can only be metabolized by bacterial and not mammalian enzymes. These include inulin, a complex plant glycan, and mannitol, a simple sugar alcohol. Changes in breath δ13C reflect changes in bacterial metabolism of a labeled substrate. Baseline δ13C (δ13Cbase) before substrate gavage in all squirrels was −20 ± 2 ‰ (N=17). Administration of 13C‐labeled mannitol (150 mg/kg) in summer squirrels produced a δ13C peak of 897 ± 601 ‰ (mean±SD, N=5), a 178‐fold increase over δ13Cbase, reached ~2 h after gavage. Summer squirrels gavaged with 13C‐labeled inulin (500 mg/kg) had a δ13C peak of 2201 ± 913 ‰ (N=5), a 463‐fold increase over δ13Cbase, reached between 3–4 h after gavage. Further validation was provided when squirrel microbiotas were depleted using an orally administered antibiotic cocktail (ABX). Relative to untreated squirrels, peak δ13C values were lower after gavage of mannitol (−17 ± 0.9 ‰, 0.9‐fold increase over δ13Cbase, N=4, P<0.05) and inulin (258 ± 105 ‰, 86‐fold increase over δ13Cbase, N=3, P<0.01) administration. These results demonstrate that stable isotope‐assisted labeling with CRDS is a powerful technique to assess the functional capacities of ground squirrel gut microbiotas to metabolize different substrates in vivo, in real time. The reduced δ13C peaks of ABX‐treated squirrels (whose cecal contents had reduced bacterial DNA yield) confirm that the breath responses are attributable to gut microbes. To test whether seasonal changes in squirrel microbiotas produce parallel changes in microbiota functional activity, the results from summer squirrels will be compared to interbout arousal hibernating squirrels and to spring squirrels two weeks after refeeding.Support or Funding InformationThis study was supported by funds from UW‐Madison Hilldale Undergraduate/Faculty Research Fellowship and NSF award IOS1558044.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Climate stability in central Anatolia during the Messinian Salinity Crisis

Deposition of large amounts of evaporites and erosion of deep canyons within the Mediterranean Basin as a result of reduced basin connectivity with the Atlantic Ocean and the epicontinental Paratethys Sea characterized the Messinian Salinity Crisis (MSC, 5.97–5.33 Ma). The influence of the MSC on Mediterranean environmental conditions within the basin itself has been intensely studied from marine records, but reconstructing the impact of the MSC on circum-Mediterranean continental climate has been hampered by the absence of continuous sedimentary archives that span the duration of the event.Here, we report results of a continental record of carbon (δ13C) and oxygen (δ18O) isotopes from lake carbonates framed by new magnetostratigraphic and 40Ar/39Ar dating, as well as by existing mammal stratigraphy (Kangal Basin, central Anatolia). The sampled section records continuous fluvio-lacustrine sedimentation from ~6.6 Ma to 4.9 Ma, which spans the MSC and the Miocene-Pliocene boundary. This dataset so far represents the only continuous continental paleoenvironmental record of the MSC in the circum-Mediterranean realm.The Kangal Basin isotope record indicates a low degree of evaporation. Furthermore, covariance between δ13C and δ18O suggests a coupling between lake water balance and biologic productivity. Variations in δ13C and δ18O therefore likely reflect changes in the amount of incoming precipitation, rather than changes in δ18O values of incoming precipitation. The most prominent spike in δ13C and δ18O occurs during the acme of the MSC and is therefore interpreted to have resulted from a decrease in the amount of incoming moisture correlative to a period of vigorous erosion and sea level lowering in the Mediterranean Basin. Major sea level lowering of Mediterranean basin waters during the acme of the MSC could have therefore led to slightly dryer conditions over Anatolia, which is also suggested by modeling studies. Overall, changes in δ13C and δ18O values are small. Therefore, we surmise that the MSC had limited effects on the paleoenvironmental and paleoclimatic conditions in the Anatolian interior.

Nitrogen isotopes suggest a change in nitrogen dynamics between the Late Pleistocene and modern time in Yukon, Canada.

A magnificent repository of Late Pleistocene terrestrial megafauna fossils is contained in ice-rich loess deposits of Alaska and Yukon, collectively eastern Beringia. The stable carbon (δ13C) and nitrogen (δ15N) isotope compositions of bone collagen from these fossils are routinely used to determine paleodiet and reconstruct the paleoecosystem. This approach requires consideration of changes in C- and N-isotope dynamics over time and their effects on the terrestrial vegetation isotopic baseline. To test for such changes between the Late Pleistocene and modern time, we compared δ13C and δ15N for vegetation and bone collagen and structural carbonate of some modern, Yukon, arctic ground squirrels with vegetation and bones from Late Pleistocene fossil arctic ground squirrel nests preserved in Yukon loess deposits. The isotopic discrimination between arctic ground squirrel bone collagen and their diet was measured using modern samples, as were isotopic changes during plant decomposition; Over-wintering decomposition of typical vegetation following senescence resulted in a minor change (~0–1 ‰) in δ13C of modern Yukon grasses. A major change (~2–10 ‰) in δ15N was measured for decomposing Yukon grasses thinly covered by loess. As expected, the collagen-diet C-isotope discrimination measured for modern samples confirms that modern vegetation δ13C is a suitable proxy for the Late Pleistocene vegetation in Yukon Territory, after correction for the Suess effect. The N-isotope composition of vegetation from the fossil arctic ground squirrel nests, however, is determined to be ~2.8 ‰ higher than modern grasslands in the region, after correction for decomposition effects. This result suggests a change in N dynamics in this region between the Late Pleistocene and modern time.

Carbon stable isotope record in the coral species Siderastrea stellata: A link to the Suess Effect in the tropical South Atlantic Ocean

Coral skeletons are natural archives whose geochemical signatures provide insights into the tropical ocean history beyond the instrumental record. Carbon stable isotopes from coral skeletons (δ13Ccoral) have been used as a proxy for multiple variables on a seasonal basis. Long-term changes in coral δ13C could be related to the changing isotopic composition of the dissolved inorganic carbon (δ13CDIC). δ13CDIC in turn reflects changes in the δ13C of atmospheric CO2, which in the modern Earth system is governed primarily by anthropogenic injection of CO2 into the atmosphere – a process known as the Suess Effect. Here we report three δ13C coral-based records of Siderastrea stellata from the tropical South Atlantic. U-series dating for the colonies 12SFB-1, 13SS-1 and 13SS-2 suggests these corals lived 13, 57 and 65 years, respectively. Short-term δ13C variations in their skeletal aragonite are dominated by interannual variation. All three δ13C records additionally exhibit an overall decreasing trend, with a depletion of about −0.0243 ± 0.0057‰·yr−1 (12SFB-1), −0.0208 ± 0.0007‰·yr−1 (13SS-1) and −0.0214 ± 0.0013‰·yr−1 (13SS-2). These rates of the coral records from Rocas Atoll are similar to the reported trend for the δ13C of atmospheric CO2 over the years 1960–1990 (−0.023 to −0.029‰·yr−1), and to the decreasing rates of global δ13CDIC. Our findings suggest that multiple δ13C coral-based records are required for confidently identifying local changes in the δ13CDIC of the ocean. This information, in turn, can be used to infer changes in the δ13C of the atmospheric CO2 composition and provide valuable information about recent changes on the carbon biogeochemical cycle during the Anthropocene epoch.

The impact of rapid heating by intrusion on the geochemistry and petrography of coals and organic-rich shales in the Illinois Basin

Igneous intrusion into organic-rich sedimentary rocks and coals has been suggested as a factor in the large-scale release of 13C–depleted thermogenic CH4, which may have led to global warming and mass extinction events in the geologic past. If a significant release of 13C–depleted thermogenic CH4 results from the intrusion of coal or organic-rich rocks, then it should produce 13C–enriched residual coal and dispersed organics in rocks adjacent to the intrusion due to the release of isotopically lighter CH4 gas. A review of the literature suggests only minor changes in the δ13Corg of coals adjacent to intrusions; however, a few studies have shown that changes in δ13Corg in intruded shales may be slightly more pronounced. The current study further evaluates the geochemical, isotopic, and petrographic changes that result from contact metamorphism and specifically compares the intrusion of coal to that of an organic-rich shale collected from the same general vicinity. Data for two different transects of intruded Pennsylvanian coal (Danville (No. 7) Coal) and an intruded organic-rich shale in the southern part of the Illinois Basin are presented.Both transects show similar increases in mean vitrinite reflectance (Rr); reflectance increases from background levels of 0.66% to 4.40% in the Danville (No. 7) Coal and 0.71% to 4.78% in the organic-rich shale. In addition, both transects show the formation of isotropic coke, and even development of fine circular mosaic anisotropic coke structure at and near the contact with the intrusion, along with the visual loss of liptinites at higher reflectances. In the Danville Coal transect, volatile matter, N, H, S, and O decrease whereas fixed carbon, C, and ash increase approaching the intrusion. The coal shows a marked decrease in remaining hydrocarbon potential (S2) and hydrogen index (HI) and an increase in Tmax (°C). Trends in most of the Rock-Eval parameters for the organic-rich shale are less clear due to variations in the amount of organic matter present, but a significant increase in thermal maturity (Tmax, 0C) is observed.No systematic changes in δ13C occur in the No. 7 Coal transect as the intrusion is approached, with δ13C varying between −25.4‰ and −24.8‰. The organic-rich shale transect shows a minor 1.2‰ enrichment in δ13C (from −25.2‰ to −24.0‰) within 2m of the intrusion. These isotopic shifts are not of a magnitude that would be expected if associated with a large-scale release of thermogenic CH4. In addition, no evidence exists in either transect for 13C–depleted condensed gas or pyrolytic carbon at the intrusion contact that could have moderated the isotopic signature. These data agree with those reported previously that indicate no clear isotopic evidence for large-scale CH4 generation due to rapid heating by igneous intrusion into coals or sedimentary rocks.

Isotopic composition of sinking particles: Oil effects, recovery and baselines in the Gulf of Mexico, 2010–2015

The extensive release of oil during the 2010 Deepwater Horizon spill in the northern Gulf of Mexico perturbed the pelagic ecosystem and associated sinking material. To gauge the recovery and post-spill baseline sources, we measured Δ14C, δ13C and δ34S of sinking particles near the spill site and at a reference site and natural seep site. Particulates were collected August 2010–April 2016 in sediment traps moored at sites with depths of 1160–1660 m. Near the spill site, changes in Δ14C indicated a 3-year recovery period, while δ34S indicated 1–2 years, which agreed with estimates of 1–2 years based on hydrocarbon composition. Under post-spill baseline conditions, carbon inputs to sinking particulates in the northern Gulf were dominated by surface marine production (80–85%) and riverine inputs (15–20%). Near the spill site, Δ14C values were depleted in October 2010 (–140 to –80‰), increasing systematically by 0.07 ± 0.02‰ day–1 until July 2013 when values reached –3.2 ± 31.0‰. This Δ14C baseline was similar to particulates at the reference site (3.8 ± 31.1‰). At both sites, δ13C values stayed constant throughout the study period (–21.9 ± 0.5‰ and –21.9 ± 0.9‰, respectively). δ34S near the spill site was depleted (7.4 ± 3.1‰) during October 2010–September 2011, but enriched (16.9 ± 2.0‰) and similar to the reference site (16.2 ± 3.1‰) during November 2012–April 2015. At the seep site, Δ14C values were –21.7 ± 45.7‰ except during August 2012–January 2013 when a significant Δ14C depletion of –109.0 ± 29.1‰ was observed. We interpret this depletion period, also observed in δ13C data, as caused by the incorporation of naturally seeped oil into sinking particles. Determination of post-spill baselines for these isotopic signatures allows for evaluation of anthropogenic inputs in future.

Facies-dependent δ13C variation and diagenetic overprinting at the onset of the Sturtian glaciation in North-East Greenland

Time-significant surfaces are used to construct a stratigraphic test of the intrabasinal reproducibility of a 16‰ Neoproterozoic carbon-isotope (δ13C) anomaly in the NE Greenland Caledonides. The δ13C excursion from +6‰ to −10‰ occurs in the carbonate-dominated Andrée Land Group and lies below glacial diamictites of the Tillite Group commonly correlated as Sturtian in age (∼720 Ma) and has been widely interpreted to record a global isotopic event reflecting a perturbation in the carbon cycle preceding the initiation of the snowball ice age. δ13C stratigraphic patterns were determined in two strike sections with relatively shallow platform deposits at Kap Weber and slope deposits on Ella Ø preserved directly below the first evidence for glaciation. The top and bottom of the δ13C profile was bounded by contiguous chronostratigraphic surfaces including an unconformity (sequence boundary) at the base recognisable in both sections and a subaerial exposure surface with a basinal correlative conformity at the top. The δ13C profile at Kap Weber shows δ13C values of +6‰ that drop to −8‰ in fine-grained slope deposits before returning to +6‰ in platform carbonates at the base of the glacial diamictite. The slope section on Ella Ø shows similar values for platformal carbonates of +6‰ with a similar drop to ∼−10‰ in slope deposits, but this section lacks the return to platform deposits evident at Kap Weber beneath the diamictite as well as a return to positive δ13C values. The absence of the platformal sediments and positive δ13C values on Ella Ø cannot be attributed to erosional truncation because the contact in this section shows a conformable, interbedded transition into the glacial deposits indicating that a continuous record is preserved. This disparity in δ13C values below the base of the Tillite Group suggests that the most negative δ13C values recorded in slope mudstone facies (−10‰) occur near synchronously with values of +6‰ on the platform. Elemental mapping of the mudstone facies indicates that carbonate is largely pore-filling and authigenic, representing a secondary phase that is unlikely to record a seawater value. Elevated δ13C values in shallow inner-ramp carbonate intervals may record locally modified seawater enriched in 13C by photosynthesis and evaporation. The excursion in δ13C values in the upper Andrée Land Group is therefore interpreted to result from a shift in facies from platform carbonates to carbonate cemented and diagenetically overprinted mudstone and does not record the secular change in seawater δ13C used for correlation or interpretation of biogeochemical events preceding the snowball ice age.

Origin of carbonatites of the Matcha alkaline pluton from Turkestan-Alai ridge, Kyrgyz Southern Tien Shan

Postorogenic alkaline intrusions in the Turkestan-Alai segment of the Southern Tien Shan coexist with dikes and veins of carbonatites dated at ∼220 Ma. They are primarily composed of calcite and dolomite (60–85 %), as well as sodic amphibole, phlogopite, clinopyroxene, microcline, albite, apatite, and magnetite, with accessory niobate, ilmenite, Nb-rutile, titanite, zircon, baddeleyite, monazite-(Ce), barite, and sulfides. The rocks share mineralogical and geochemical similarity with carbonatites that originated by liquid immiscibility at high temperatures above 500°C. Silicate and salt-carbonate melts are derived from sources with mainly negative bulk εND(t) ∼ from −11 to 0 and high initial 87Sr/86Sr ratios (∼ 0.7061-0.7095) which may be due to mixing of PREMA and EM-type mantle material. Pb isotopic ratios in accessory pyrrhotite (206Pb/204Pb = 18.38; 207Pb/204Pb = 15.64; 208Pb/204Pb = 38.41) exhibit an EM 2 trend. The intrusions bear signatures of significant crustal contamination as a result of magma genesis by syntexis and hybridism. Concordant isotope composition changes of δ13C (−6.5 to −1.9 ‰), δ18O (9.2-23 %„), δD (−58 to −41 %„), and δ34S (12.6-12.8 ‰) in minerals and rocks indicate inputs of crustal material at the stage of melting and effect of hot fluids released during dehydration of metamorphosed oceanic basalts or sediments. The observed HFSE patterns of the oldest alkaline gabbro may be due to interaction of the primary mafic magma with IAB-type material. The isotope similarity of alkaline rocks with spatially proximal basalts of the Tarim large igneous province does not contradict the evolution of the Turkestan-Alai Triassic magmatism as the «last echo» of the Tarim mantle plume.

Mineralogy and geochemistry of triassic carbonatites in the Matcha alkaline intrusive complex (Turkestan-Alai Ridge, Kyrgyz Southern Tien Shan), SW Central Asian orogenic belt

Postorogenic intrusions of essexites and alkaline and nepheline syenites in the Turkestan-Alai segment of the Kyrgyz Southern Tien Shan coexist with dikes and veins of carbonatites dated at ∼220 Ma by the Ar–Ar and Rb–Sr age methods. They are mainly composed of calcite and dolomite (60–85%), as well as sodic amphibole, phlogopite, clinopyroxene, microcline, albite, apatite, and magnetite, with accessory niobate, ilmenite, Nb-rutile, titanite, zircon, baddeleyite, monazite-(Ce), barite, and sulfides. The rocks share mineralogical and geochemical similarity with carbonatites that originated by liquid immiscibility at high temperatures above 500 °C. Alkaline silicate and salt-carbonate melts are derived from sources with mainly negative bulk εNd(t) ∼ from −11 to 0 and high initial 87Sr/86Sr ratios (∼0.7061–0.7095) which may be due to mixing of PREMA and EM−type mantle material. Pb isotopic ratios in accessory pyrrhotite (206Pb/204Pb = 18.38; 207Pb/204Pb = 15.64; 208Pb/204Pb = 38.41) exhibit an EM2 trend. The intrusions bear signatures of significant crustal contamination as a result of magma genesis by syntexis and hybridism. Concordant isotope composition changes of δ13C (−6.5 to −1.9‰), δ18O (9.2–23‰), δD (−58 to −41‰), and δ34S (12.6–12.8‰) in minerals and rocks indicate inputs of crustal material at the stage of melting and effect of hot fluids released during dehydration of metamorphosed oceanic basalts or sediments. The observed HFSE patterns of the oldest alkaline gabbro may be due to interaction of the primary mafic magma with IAB-type material. The isotope similarity of alkaline rocks with spatially proximal basalts of the Tarim large igneous province does not contradict the evolution of the Turkestan-Alai Triassic magmatism as the “last echo” of the Tarim mantle plume.

Validating fin tissue as a non-lethal proxy to liver and muscle tissue for stable isotope analysis of yellow perch (Perca flavescens)

ABSTRACTStable isotope ecology typically involves sacrificing the animal to obtain tissues. However, with threatened species or in long-term longitudinal studies, non-lethal sampling techniques should be used. The objectives of this study were to (1) determine if caudal fin tissue could be used as a non-lethal proxy to liver and muscle for stable isotope analysis, and (2) assess the effects of ethanol preservation on δ15N and δ13C in fin tissue of juvenile yellow perch Perca flavescens. The δ13C of caudal fin was not significantly different from liver (t23 = −0.58; p = 0.57), and was more correlated with δ15N in liver (r2 = 0.78) than muscle (r2 = 0.56). Ethanol preservation enriched 15N and 13C for caudal fins, but by using our developed regression models, these changes in δ15N and δ13C can now be corrected. Overall, caudal fin tissue is a more reliable proxy to liver than muscle for δ15N and δ13C in yellow perch.

Species-specific tree growth and intrinsic water-use efficiency of Dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var. mongolica) growing in a boreal permafrost region of the Greater Hinggan Mountains, Northeastern China

Increasing air temperature and atmospheric CO2 concentrations (Ca) can profoundly affect photosynthesis and intrinsic water-use efficiency (iWUE). However, the response of trees in boreal permafrost regions to rapid warming and Ca increases is poorly constrained by prior research. Here, we evaluated long-term changes in growth (using regional curve standardization [RCS]) and iWUE of Dahurian larch (Larix gmelinii) and Mongolian pine (Pinus sylvestris var. mongolica) in the boreal permafrost region of northeastern China and species-specific responses to increasing Ca and temperature. From 1930–2010, RCS growth of Dahurian larch and Mongolian pine decreased, while iWUE increased by 25.5 and 21.1%, respectively. RCS growth of both species was negatively correlated with winter temperatures, but Mongolian pine depended most strongly on previous December to current February temperatures and Dahurian larch depended most strongly on March temperatures. Moisture conditions only weakly influenced growth.We found similar long-term changes of tree-ring δ13C in the two species. Carbon isotopic discrimination of Dahurian larch and Mongolian pine was determined mainly by growing season temperature (positive) and moisture (negative), but with different signal strengths, suggesting that stomatal conductance influenced tree-ring δ13C. Commonality analysis showed that RCS growth was affected mainly by temperature, but also by the combined effect (interaction) of iWUE and temperature. However, the contribution of iWUE alone was lower for Mongolian pine. Our results suggest that the increased iWUE caused by increasing Ca will not improve tree growth sufficiently to compensate for temperature-induced water stress. The rate of temperature increase has slowed around 1990, which would have stabilized the degree of temperature-induced water stress, and this could be helpful to tree growth recovery in the permafrost region of northeastern China.

Seasonal dynamics in a nearshore isotopic niche and spatial subsidies from multi-trophic aquaculture

A poorly understood food web dynamic concerns possible seasonal variation in spatial subsidies associated with multi-trophic aquaculture and their effects on extractive and naturally occurring organisms. We used the stable isotopes δ13C and δ15N and circular statistics to investigate niche overlap across a year-long period at an experimental multi-trophic aquaculture facility in British Columbia, Canada. A two-source mixing model revealed that particulate organic matter was the most important food source for all sample invertebrates (mean range 40%–98%) compared with farm effluent (mean range 3%–35%). There were significant month-to-month changes in δ13C and δ15N for all species except for the brooding transparent tunicate (Corella inflata). We did not detect any directionality for the entire community, but did identify variable directional shifts for each species, suggesting resource partitioning driven by competition and (or) morphology-based differences in feeding strategies. This was further supported by seasonal variation in inter- and intraspecific isotopic niche widths. Isotopic niche overlap among co-occurring invertebrates appeared to be stronger during winter and summer than autumn months. Our study provides valuable insights on the role of multi-trophic derived effluent on a nearshore marine community composed of both natural and cultured species within the same feeding guild.

Integrated record of Ludlow (Upper Silurian) oceanic geobioevents – Coordination of changes in conodont, and brachiopod faunas, and stable isotopes

The Ludlow Epoch (Silurian) was marked by several globally recognized but mechanistically poorly understood biotic events. The most pronounced of them was the Lau Event, which strongly decimated conodont, graptolite, and brachiopod faunas. Additionally, this event coincides with the largest positive stable carbon isotopic anomaly in the whole Phanerozoic, as well as the resurgence of the so-called “anachronistic” microbial facies that were frequently encountered during survival episodes of the major mass extinction events. In this contribution, based on the analysis of the outer shelf facies succession (Milaičiai-103 core), from the Lithuanian part of the Silurian Baltic Basin, as integrated quantitative record of conodont, brachiopod and δ13C changes across most of the Ludlow is presented. The succession was subdivided into four conodont zones that served as a stratigraphic framework for analyzing the δ13C and palaeoecological trends. The depth constrained cluster analysis revealed successions of three statistically distinct conodont and six statistically distinct brachiopod assemblages that replace each other near the change points in the stable carbon isotopic curve. The application of a newly developed mathematical technique based on the analysis of recurrence patterns of the fossil assemblages revealed that both conodonts and brachiopods are represented by highly time specific assemblages in the aftermath of the Lau event (O. snajdri Interval Zone). The anomalous interval is confined to the transgressive and highstand phases of the 3rd order post-Lau transgression. The discussed interval is coeval with the extensive development of stromatolitic communities in the nearshore environments around the world. The results allow for the first time to quantify the profound ecosystem-wide geobiological impact of the mid-Ludfordian event that lasted up to the latest Ludfordian.

Rapid speleothem δ13C change in southwestern North America coincident with Greenland stadial 20 and the Toba (Indonesia) supereruption

Rapid speleothem δ13C change in southwestern North America coincident with Greenland stadial 20 and the Toba (Indonesia) supereruption

Stable isotopes reveal the effect of trawl fisheries on the diet of commercially exploited species

Bottom trawling can change food availability for benthivorous demersal species by (i) changing benthic prey composition through physical seabed impacts and (ii) by removing overall benthic consumer biomass increasing the net availability of benthic prey for remaining individuals. Thus trawling may both negatively and positively influence the quantity and quality of food available. Using δ13C and δ15N we investigated potential diet changes of three commercially exploited species across trawling gradients in the Kattegat (plaice, dab and Norway lobster (Nephrops)) and the Irish Sea (Nephrops). In the Kattegat, trawling affected primarily the biomass of benthic consumers, lowering competition. Nephrops showed significant positive relationships for δ13C and a domed relationship for δ15N with trawling. In the Irish Sea, intense trawling had a negative effect on benthic prey. δ13C and δ15N thus showed the inverse relationships to those observed in the Kattegat. Plaice from the Kattegat, showed a significant relationship with trawling intensity for δ13C, but not for δ15N. No relationship was found for dab. Changes of δ13C and δ15N correlated with changes in condition of species. The results show that the removal of demersal competitors and benthos by trawling can change the diets of commercial species, ultimately affecting their body condition.

Study of isotopes of carbon, thorium, and uranium in travertine and thermal spring samples: implications for effects of changes in geochemical environment and processes

ABSTRACTData on modern radiocarbon activity in the old travertine formations of the Pymvashor hydrothermal system were used, in combination with 230Th/U dating of the travertine, to estimate the 14C contents of the total dissolved inorganic carbon in the ancient thermal water at the time of precipitation of the travertine (14Ccalc). With the known values of 14Ccalc and average age of the thermal water, and under the assumption that the residence time of the water in aquifer was constant over the last 13.9 ± 1.5 ka, the initial 14C contents (14C0) in the ancient thermal water were estimated. The findings in this study are that (1) both 14C0 and δ13С have decreased in young waters compared to the ancient waters; (2) although atmospheric 14C activity (14Catm) has also decreased in the same time, the decrease in 14C0 is faster than the decrease in 14Catm. Under certain assumptions, one could link changes in 14C0 and δ13C to climate change. Decrease in δ13С of soil CO2 and decrease in 14C0 was caused predominantly by warmer and wetter climate, decomposition of fossil organic matter, and decrease in 14Catm. There could be also increased dissolution of solid carbonate and increased carbon exchange between DIC and soil CO2, caused by thawing permafrost.

Temporal effects of prescribed burning on terpene production in Mediterranean pines.

Prescribed burning is used to reduce fuel hazard but underburning can damage standing trees. The effect of burning on needle terpene storage, a proxy for secondary metabolism, in fire-damaged pines is poorly understood despite the protection terpenes confer against biotic and abiotic stressors. We investigated variation in needle terpene storage after burning in three Mediterranean pine species featuring different adaptations to fire regimes. In two pure-stands of Pinus halepensis Mill. and two mixed-stands of Pinus sylvestris L. and Pinus nigra ssp. salzmanni (Dunal) Franco, we compared 24 h and 1 year post-burning concentrations with pre-burning concentrations in 20 trees per species, and evaluated the relative contribution of tree fire severity and physiological condition (δ13C and N concentration) on temporal terpene dynamics (for mono- sesqui- and diterpenes). Twenty-four hours post-burning, monoterpene concentrations were slightly higher in P. halepensis than at pre-burning, while values were similar in P. sylvestris. Differently, in the more fire-resistant P. nigra monoterpene concentrations were lower at 24 h, compared with pre-burning. One year post-burning, concentrations were always lower compared with pre- or 24 h post-burning, regardless of the terpene group. Mono- and sesquiterpene variations were negatively related to pre-burning δ13C, while diterpene variations were associated with fire-induced changes in needle δ13C and N concentration. At both post-burning times, mono- and diterpene concentrations increased significantly with crown scorch volume in all species. Differences in post-burning terpene contents as a function of the pine species' sensitivity to fire suggest that terpenic metabolites could have adaptive importance in fire-prone ecosystems in terms of flammability or defence against biotic agents post-burning. One year post-burning, our results suggest that in a context of fire-induced resource availability, pines likely prioritize primary rather than secondary metabolism. Overall, this study contributes to the assessment of the direct and indirect effects of fire on pine terpene storage, providing valuable information about their vulnerability to biotic and abiotic stressors throughout time.

Dynamics of physically- separated soil organic carbon pools assessed from δ13C changes under 25 years of cropping systems

Quantification of the dynamics of soil organic carbon (SOC) pools under the influence of different cropping systems is essential for predicting carbon (C) sequestration. We combined soil fractionation with C isotope analyses to investigate the SOC dynamics of the various soil fractions in a black soil of Northeast China after 25 years of tillage. Soil samples from the initial condition (CK) and 2 cropping treatments including continuous maize cropping (MM), maize–soybean rotation (MS) were separated into 4 aggregate sizes (<53μm, 250–53μm, 2000–250μm, and >2000μm) and 3 density fractions: free light fraction (LF), intra-aggregate particulate organic matter (iPOM), and mineral-associated organic matter (mSOM). The 25 years of cropping with manure application significantly increased the SOC storage, mainly by enhancing the soil C of the macroaggregates (2000–250μm), with most of the C stored in the iPOM (62.01–90.32%). The MS system was more beneficial for the SOC accumulation in macroaggregates (>250μm) than the MM system because of enhanced SOC in heavier fractions (iPOM and mSOM); this was probably induced by the differentiation of the belowground humification rate between soybean and maize roots, while the MM system may be a more effective measure for future soil C sequestration because most of the stable C is stored in the small size fraction (<53μm). The δ13C values indicated that, among aggregate sizes, the fastest soil C turnover occurred in microaggregates (250–53μm). Moreover, C in the MS soils had a faster turnover rate than in the MM soils.

Stalagmite carbon isotopes and dead carbon proportion (DCP) in a near-closed-system situation: An interplay between sulphuric and carbonic acid dissolution

In this study, the ‘dead carbon proportion’ (DCP) calculated from combined U-Th and radiocarbon analyses was used to explore the carbon isotope systematics in Corchia Cave (Italy) speleothems, using the example of stalagmite CC26 which grew during the last ∼12ka. The DCP values in CC26 are among the highest ever recorded in a stalagmite, spanning the range 44.8–68.8%. A combination of almost closed-system conditions and sulphuric acid dissolution (SAD) are proposed as major drivers in producing such a high DCP with minor contribution from old organic matter from the deep vadose zone. The long-term decrease in both DCP and δ13C most likely reflects post-glacial soil recovery above the cave, with a progressive increase of soil CO2 contribution to the total dissolved inorganic carbon (DIC). Pronounced millennial-scale shifts in DCP and relatively small coeval but antipathetic changes in δ13C are modulated by the effects of hydrological variability on open and closed-system dissolution, SAD and prior calcite precipitation. Hence, the DCP in Corchia Cave speleothems represents an additional proxy for rainfall amount.

The impact of organic fluids on the carbon isotopic compositions of carbonate-rich reservoirs: Case study of the Lucaogou Formation in the Jimusaer Sag, Junggar Basin, NW China

The processes involved in the interaction between organic fluids and carbonates, and the resulting effect on reservoir quality during the evolution and maturation of organic matter remain unclear despite the fact that these processes influence the carbon and oxygen isotopic compositions of carbonates. Here, we provide new insights into these processes using data obtained from a detailed analysis of a mixed dolomitic–clastic and organic-rich sedimentary sequence within the middle Permian Lucaogou Formation in the Junggar Basin of NW China. The techniques used during this study include drillcore observations, thin section petrography, scanning electron microscopy (SEM) and electron probe microanalysis, and carbon and oxygen isotope analyses. Oil grades and total organic carbon (TOC) contents represent the amount of oil charging and the abundance of organic fluids within a reservoir, respectively, and both negatively correlate with the whole-rock δ13C and δ18O of the carbonates in the study area, indicating that organic fluids have affected the reservoir rocks. Secondary carbonates, including sparry calcite and dolomite overgrowths and cements, are common within the Lucaogou Formation. Well-developed sparry calcite is present within dark mudstone whereas the other two forms of secondary carbonates are present within the dolomite-rich reservoir rocks in this formation. Comparing thin section petrology with δ13C compositions suggests that the carbon isotopic composition of matrix carbonates varies little over small distances within a given horizon but varies significantly with stratigraphic height as a result of the development of secondary carbonates. The net change in whole-rock δ13C as a result of these secondary carbonates ranges from 1.8‰ to 4.6‰, with the secondary carbonates having calculated δ13C compositions from −18.6‰ to −8.5‰ that are indicative of an organic origin. The positive correlation between the concentration of Fe within matrix and secondary carbonates within one of the samples suggests that the diagenetic system within the Lucaogou Formation was relatively closed. The correlation between δ13C and δ18O in carbonates is commonly thought to be strengthened by the influence of meteoric water as well as organic fluids. However, good initial correlation between δ13C and δ18O of whole rock carbonates within the Lucaogou Formation (resulted from the evaporitic sedimentary environment) was reduced by organic fluids to some extent. Consequently, the δ13C–δ18O covariations within these sediments are not always reliable indicators of diagenetic alteration by organic fluids or meteoric water.The characteristics and δ13C compositions of the sparry calcite within the formation is indicative of a genetic relationship with organic acids as a result of the addition of organic CO2 to the reservoir. Further analysis suggests that both carbonate and feldspar were dissolved by interaction with organic CO2. However, dissolved carbonate reprecipitated as secondary carbonates, meaning that the interaction between organic fluids and dolomites did not directly improve reservoir quality, although this process did enhance the dissolution of feldspar and increase porosity. This indicates that the δ13C and δ18O of secondary carbonates and their influence on whole-rock carbonate isotopic values can be used to geochemically identify the effect of organic fluids on closed carbonate-rich reservoir systems.