δ13C Data Research Articles

Radio- and stable carbon isotope analysis reveals minimal assimilation of petrogenic carbon into an oligotrophic freshwater food web after experimental spills of diluted bitumen

Following an oil spill into water, bacteria can biodegrade petroleum hydrocarbons which could lead to petrogenic carbon assimilation by aquatic biota. We used changes in the isotope ratios of radio- (Δ14C) and stable (δ13C) carbon to examine the potential for assimilation of petrogenic carbon into a freshwater food web following experimental spills of diluted bitumen (dilbit) into a boreal lake in northwestern Ontario, Canada. Different volumes (1.5, 2.9, 5.5, 18, 42, 82, and 180 L) of Cold Lake Winter Blend (a heavy crude blend of bitumen and condensate) dilbit were applied to seven 10-m diameter littoral limnocorrals (approximate volume of 100 m3), and two additional limnocorrals had no added dilbit to serve as controls. Particulate organic matter (POM) and periphyton from oil-treated limnocorrals had lower δ13C (up to 3.2‰ and 2.1‰ for POM and periphyton, respectively) than the control at every sampled interval (3, 6 and 10 weeks for POM and 6, 8 and 10 weeks for periphyton). Dissolved organic and inorganic carbon (DOC and DIC, respectively) had lower Δ14C in the oil-treated limnocorrals relative to the control (up to 122‰ and 440‰ lower, respectively). Giant floater mussel (Pyganodon grandis) housed for 25 days in aquaria containing oil-contaminated water from the limnocorrals did not show significant changes in δ13C values of muscle tissue compared to mussels housed in control water. Overall, the changes in δ13C and Δ14C observed indicated small amounts (up to 11% in DIC) of oil carbon incorporation into the food web. The combined δ13C and Δ14C data provide evidence for minimal incorporation of dilbit into the food web of this oligotrophic lake, suggesting that microbial degradation and subsequent incorporation of oil C into the food web may play a relatively small role in the ultimate fate of oil in this type of ecosystem.

Evaluation of the non-climatic (age-related) trends of stable oxygen and carbon isotopes in Swiss stone pine (Pinus cembra L.) tree rings from the Eastern Carpathians, Romania

The presence, magnitude, and duration of age and/or size-related trends in the stable isotopes in tree-ring cellulose time series has been a subject of scientific debate. Where present, their evaluation and removal are key to the development of robust climate calibrations and reconstructions, especially in the low-frequency domain and where sample replication levels are low. Where reported, results suggest that the age/size/height-related trend of stable oxygen (δ18O) and carbon (δ13C) isotope compositions in tree-ring cellulose may vary according to the tree species and the individual tree location. For this reason, it is important when developing long palaeoclimate reconstructions for a new species, geographical region or ecological setting to perform studies to investigate non-climatic (age-related) trends. This study evaluates the ontogenetic pattern in the δ18O and δ13C data in Swiss stone pine trees from the Eastern Carpathians, Romania. For this, we used a new multi-centennial dataset consisting of 5 living and 10 relict Swiss stone pine samples collected from the Eastern Carpathians, which were annually resolved for δ18O and δ13C composition. Age-related trends were evaluated using the conventional “slope of the mean” approach as well as the “mean of the slope” method. The results suggest that neither the traditional “slope-of-the mean” nor the “mean-of-the-slope” approach indicates a persistent linear trend in the Swiss stone pine δ18O data, while for the δ13C data a systematic enrichment in 13C was observed over a < 40 year-long period after germination. Despite the limited sample size of this developing dataset these findings help to inform more detailed analyses and future sampling strategies in the Eastern Carpathian Swiss stone pine stands.

The use of radiocarbon to evaluate the trophic role of geothermal bacteria in shallow hydrothermal water ecosystem

Stable isotopes such as δ13C and δ15N are routinely used in trophic ecology as isotope values are derived from diet and recorded subsequent fractionation in consumer tissue. However, this approach necessitates to estimate a priori the fractionation between food source and consumer leading to potential uncertainties. In this context, the development of additional biomarkers enables to have better resolution on feeding habits. Dissolved Inorganic Carbon (DIC) from volcanic activity and bacteria using this DIC presents a strongly depleted natural radiocarbon abundances (Δ14C). Through its activity, the geothermal plant of Bouillante in Guadeloupe (French West Indies) releases sulfur bacteria in shallow environment of the Bay. A previous study reveals ingestion of those bacteria by opportunist species (sea urchin and fish species). In the present study, ten species with different diet and feeding mode were sampled close to the release channel of the geothermal plant and in a control station in order to simultaneously determine their stable isotopes (δ13C and δ15N) and radiocarbon compositions. Compared to models using Δ14C data, models using δ13C and δ15N data underestimate the role of bacteria in diet of urchin and fish species whereas this role is overestimated for all other species. Compared to previous models, radiocarbon would give more realistic and reliable results than the classical use of stable isotope. This study confirms the utility of radiocarbon in food web ecology, particularly at the ecosystems having food sources with contrasting Δ14C values.

Hydrogeochemical investigation of shallow aquifers before and after the 2012 Emilia seismic sequence (northern Italy)

Soon after the MW = 6.0 main event of May 20, 2012 that struck the central part of the Emilia-Romagna region (Italy), several geochemical surveys were carried out on groundwater within the epicentral area. A total of 20 water samples were periodically collected, from May 2012 to July 2014, from shallow (up to 6 m depth) to deep (down to 175 m depth) wells within both unconfined and confined aquifers and analyzed for major ions, trace elements, dissolved gases and stable isotopes (δ2H–H2O, δ18O–H2O and δ13C-TDIC). Geochemical data were compared with previous data collected and analyzed in 2006 in a phase of absence of significant seismic activity.Monitored waters showed concentration variations in post-earthquake sampling on a large number of geochemical parameters. Many of these variations were recorded during the co-seismic phase and were transient as the geochemical parameters returned towards pre-earthquake values over time.The most significant transient variations involved trace elements, which generally show high sensitivity even to small variations in the surrounding environment due to their usually low concentrations in groundwater. Physical-chemical parameters (water temperature, pH, TDS) and major ions provided less unambiguous indications, whereas among dissolved gases CH4 and CO2 showed a general post-seismic increase within the unconfined aquifer. Increased contents of such gas species in both aquifers (this study) and soils (previous studies) suggest that the seismic-induced overpressure on the ground had enhancing effects on soil permeability and porosity and triggered their co-seismic migration upwards from deeper reservoirs. Water isotopes showed the systematic post-seismic change in δ2H toward heavier compositions with no significant changes in the δ18O, which was interpreted as due to isotopic exchange between water and a H2-bearing gas phase (e.g., H2S, CH4, H2) entering the system. Calculated δ13C data of CO2 suggested a relatively shallow production from both plant-root respiration and microbial-driven degradation of organic matter while the almost pure crustal origin of He (R/Ra values = 0.04–0.16 from the bubbling gas phase emitted by one of the monitored wells) reasonably excludes any evidence of both primary mantle 3He degassing and ascent of heavier CO2 from deep (mantle, decarbonation) inorganic sources.Monitored waters which showed the most significant transient variations are aligned in the same E-W direction along which the seismicity and soil gas anomalies were distributed, at about 5 km S from the epicenter of the May 20th seismic event and along the main direction of the May 29th (MW = 5.8) event. This confirms that the transient variations have been activated by the seismic sequence in a sector of the crust where the presence of a fault/fracture system favors the intensification of processes affecting sediments and groundwater (variations of porosity/permeability of soils, the groundwater level, redox state, etc.) and which are able to explain the observed geochemical variations.Only one sample monitored, the one closest to the epicenter of the May 20th event, showed clear geochemical evidence suggesting the hypothesis of mixing between superimposed water bodies.

Multi-taxa marine isoscapes provide insight into large-scale trophic dynamics in the North Pacific

Quantifying large scale trophic dynamics and interactions in marine systems remains a key challenge in ecological research and conservation, particularly in remote habitats which are difficult and costly to access. Stable isotope (SI) analysis has emerged as an effective tool for studying ecosystem interactions, especially when used to construct isotopic landscapes, or “isoscapes”. We used a combination of empirical SI data, global modeled phytoplankton isoscapes, and oceanographic data to investigate how large SI datasets might be harnessed to describe and predict patterns of regional food web dynamics and trophic structuring. We collated data from 99 published and author-contributed datasets of carbon and nitrogen SI data for open-ocean and neritic nektonic fish and invertebrates in the North Pacific Ocean to estimate mean SI values for successive trophic level groups within Longhurst biogeographic provinces. We found that these estimates reflected geographic patterns predicted by modeled phytoplankton isoscapes, suggesting that baseline SI ratios are consistently propagated up through regional food webs. This was further corroborated by significant correlations between our estimated SI values with the same oceanographic and geographic variables known to influence phytoplankton SI ratios. However, we observed variable amounts of isotopic offset between successive trophic level groups within and across provinces, indicating that the underlying drivers of trophic dynamics differ across regions. We found evidence of decreased isotopic differences between higher level trophic groups, suggesting the possibility of trophic compression and highlighting the importance of using taxa- and tissue-specific trophic discrimination factors (TDFs) when comparing or predicting consumer SI ratios. We used stable isotopic niche analyses to demonstrate that coupled use of δ13C and δ15N data increased capacity to differentiate province-specific consumer groups, particularly where adjacent provinces had similar ranges of values for a single SI. We also found that baseline isoscapes may be a viable tool for predicting broad trends of consumer SI ratios by calculating ‘predicted’ δ13C and δ15N values for successive trophic groups across provinces using modeled phytoplankton data and diet-dependent discrimination factors. These predicted values were significantly correlated with our estimates based on empirical data, with similarity of predicted δ13C values increasing for higher trophic level groups. We conclude that regional SI patterns remain consistent across diverse ecosystems. With increased spatiotemporal resolution of SI data across ocean basins and increased availability of species-specific life history traits and physiologies, multi-taxa isoscapes hold great potential for studying large scale marine trophodynamics and movement patterns of highly mobile marine species.

Radiocarbon Constraints on Carbon Release From the Antarctic Ice Sheet Into the Amundsen Sea Embayment

AbstractThe Amundsen Sea Embayment in West Antarctica is experiencing rapid ice mass loss, resulting in biogeochemical changes via altered nutrient and organic matter supply. However, organic carbon released from melting ice has not yet been accurately quantified. In this paper, we have integrated new dissolved organic carbon (DOC) data obtained close to the melting Dotson Ice Shelf (DIS) with published radiocarbon (Δ14C) data on sinking and suspended particulate organic carbon (POC), sedimentary OC, DOC and dissolved inorganic carbon to quantify the effect of ice melt to the carbon cycle. Elevated DOC concentrations in deep water near the DIS indicate the transport of carbon sources from the ice shelf to the water column at a rate of 4.6 ± 2.0 × 1010 g C yr−1. Furthermore, Δ14C‐DOC measurements suggest there is a possible dark chemoautotrophic production under the influence of meltwater input. The vertical profile of Δ14C in the sedimentary OC from the Sea Ice Zone and the edge of the DIS demonstrates the presence of aged organic carbon sources during warm episodes at ∼11.5 and 15.9 ka BP. Our study indicates that deep water is not only affected by OC discharge from meltwater but also by biological processes due to altered nutrient inputs. Limited data hampers a precise assessment of the influence of meltwater on the carbon cycle. Further sampling in front of the DIS will be beneficial to enhance our understanding of the role of Antarctic Ice Sheet melting in the downstream ecosystem.

A monthly resolved coral δ13C and δ18O record of changes in the Kuroshio Current into the South China Sea via the Luzon Strait

The Kuroshio Current enters the South China Sea (SCS) via the Luzon Strait and exerts significant effects on circulation and water mass properties of this marine basin. However, because of a lack of continuous oceanographic observations, multi-decadal variations in Luzon Strait Transport (LST) remain uncertain. In this study, monthly resolved coral δ13C and δ18O data from Xiaoliuqiu Island, located offshore of southwestern Taiwan and along the Kuroshio Current intrusion route, are used to reconstruct LST from 1977 to 2003 and investigate interannual and decadal variability. On an interannual timescale, greater LST leads to stronger upwelling, which brings deep low-temperature and high-salinity sub-surface waters containing 13C-depleted dissolved inorganic carbon to the surface; this is reflected in lower coral δ13C and higher coral δ18O values. The interannual variability in the upper (0–745 m) and surface (0–1 m) layers of LST during 1977–2003 is also reconstructed using the coral δ18O record. Coral δ18O data indicate that LST has weakened since the 1990s. The upper layer of LST has decreased by nearly 25%, and the surface layer of LST has decreased by 60% over the 27 years of observation. Our results show that coral δ13C and δ18O data can be used to reconstruct interannual variations in LST.

A multi-isotope approach reveals seasonal variation in the reliance on marine resources, production of metabolic water, and ingestion of seawater by two species of coastal passerine to maintain water balance

Tracing how free-ranging organisms interact with their environment to maintain water balance is a difficult topic to study for logistical and methodological reasons. We use a novel combination of triple-oxygen stable isotope analyses of water extracted from plasma (δ16O, δ17O, δ18O) and bulk tissue carbon (δ13C) and nitrogen (δ15N) isotopes of feathers and blood to estimate the proportional contribution of marine resources, seawater, and metabolic water used by two species of unique songbirds (genus Cinclodes) to maintain their water balance in a seasonal coastal environment. We also assessed the physiological adjustments that these birds use to maintain their water balance. In agreement with previous work on these species, δ13C and δ15N data show that the coastal resident and invertivore C. nigrofumosus consumes a diet rich in marine resources, while the diet of migratory C. oustaleti shifts seasonally between marine (winter) to freshwater aquatic resources (summer). Triple-oxygen isotope analysis (Δ17O) of blood plasma, basal metabolic rate (BMR), and total evaporative water loss (TEWL) revealed that ~25% of the body water pool of both species originated from metabolic water, while the rest originated from a mix of seawater and fresh water. Δ17O measurements suggest that the contribution of metabolic water tends to increase in summer in C. nigrofumosus, which is coupled with a significant increase in BMR and TEWL. The two species had similar BMR and TEWL during the austral winter when they occur sympatrically in coastal environments. We also found a positive and significant association between the use of marine resources as measured by δ13C and δ15N values and the estimated δ18O values of ingested (pre-formed) water in both species, which indicates that Cinclodes do not directly drink seawater but rather passively ingest when consuming marine invertebrates. Finally, results obtained from physiological parameters and the isotope-based estimates of marine (food and water) resource use are consistent, supporting the use of the triple-oxygen isotopes to quantify the contribution of water sources to the total water balance of free-ranging birds.

Coupled biostratigraphy and chemostratigraphy at Lanna, Sweden: A key section for the Floian–lower Darriwilian interval (Lower–Middle Ordovician)

The Lanna area in the province of Närke, south-central Sweden, hosts a succession of cool-water carbonate strata that are largely devoid of tectonic and diagenetic alteration, and span the Floian through lower Darriwilian Global stages (Ottenbyan–Kundan Regional stages). In this study we assess the integrated biostratigraphic and chemostratigraphic framework for the Ordovician sequence at Lanna, utilizing trilobites and conodonts coupled with bulk-rock carbon and oxygen isotopes (δ13Ccarb and δ18Ocarb). The local succession is thin but relatively complete; biostratigraphic details are similar to coeval successions in Baltoscandia. The new high-resolution δ13C and δ18O data are broadly consistent with other chemostratigraphic records at the regional scale, but notable differences in δ13C are obvious compared to global records. δ13C trends diverge markedly in the Dapingian and intra- and inter-regional differences become increasingly pronounced through younger strata. This may largely be explained by an overall low eustatic sea level, which led to more widespread oceanic restriction of epeiric seas. As a result, δ13C records became more influenced by local variables, muddling the global δ13C signal. This, in turn, suggests that sea level played a larger role than long-term changes within the global carbon cycle for regulating local–regional δ13C gradients in the Middle Ordovician. Regardless of the underlying cause(s), the documented variability poses significant challenges for using δ13C as a tool for detailed stratigraphic correlations. The limited expression of many named ‘carbon isotope excursions’ (CIEs) in the studied interval indicate that they are artefacts of local overprinting rather than reflective of changes to the global carbon cycle. Thus, these CIEs are of questionable correlative importance and validity. Although the scatter in numeric values is relatively large, long-term δ18O trends are overall consistent at the global scale, tentatively supporting the notion that climate cooled during the studied time interval.

Karst-ecological changes during the middle and late Holocene in Southwest China revealed by δ18O and δ13C records in a stalagmite

Rocky desertification is a major environmental problem in the karst regions of Southwest China and seriously impacts ecological and socioeconomic development. Human activities and climate change have been proposed as the main factors responsible for the development and expansion of rocky desertification, but more evidence is needed to support this hypothesis. In this study, the history of the Asian summer monsoon (ASM) since 6200 yr BP is reconstructed based on 230Th dating and δ18O and δ13C data of a stalagmite from Feilong Cave in Guizhou Province of Southwest China. Positive δ18O and δ13C excursions record eleven interdecadal–centennial weak summer monsoon events at 1000–870, 1660–1460, 2040–1900, 2780–2460, 3020–2860, 3250–3120, 3650–3370, 4273–3980, 4820–4480, 5370–5180, and 5840–5560 yr BP. These weak ASM events were controlled by a southward shift of the Intertropical Convergence Zone and frequent El Niño events. Changes in the δ13C values of this stalagmite were mainly driven by changes in vegetation coverage and type, soil microbial activity, and regional hydrogeological conditions. The simultaneous positive excursions of δ18O and δ13C at ∼5500, 4200, and 2800 yr BP indicate a degradation of the karst ecological environment in response to the weak summer monsoon. In addition, frequent dynasty changes in China since 3000 yr BP profoundly influenced the karst ecological environment. During the Medieval Warm Period, the Jing-Kang event (JK event) resulted in the fall of the Northern Song Dynasty and led to a large-scale migration into southern China. As a consequence, the population increase in the Yangtze River basin enhanced land use, accelerated the disappearance of forests, and finally resulted in the deterioration of the regional environment. We conclude that climate change and anthropogenic activity may have jointly triggered and/or exacerbated rocky desertification in Southwest China.

Carbon isotope values for grasses in Madagascar's Central Highlands establish baselines for historical and paleoecological research

Societal Impact StatementGrasses are significant drivers of fires and are the primary food source for cattle in Madagascar's Central Highlands. However, their extent and importance to animals and people in the past remain poorly understood. Clarifying the history of Malagasy grasslands is necessary for building climate resilient food systems and supporting carbon stores that also conserve biodiversity. We generated chemical data for grasses that grow in open habitats in central Madagascar, which will help improve our understanding of the ecological and economic importance of modern grassy ecosystems, reconstruct the regional history of grasses, and anticipate how vegetation may respond to changing climate and rising atmospheric carbon dioxide levels.Summary Stable carbon isotope (δ13C) data for Malagasy grasses are needed to establish expected values for C3 and C4 grasses from particular regions in Madagascar, and possible differences among different grass lineages, or species with different distributions or adaptations. These data, in turn, may help inform how widespread grasses were in the past, and the importance of grasses to endemic and domesticated animals as well as people over time. We analysed both δ13C and weight %C:N from 63 Poaceae species that grow in open grassy biomes in Madagascar's Central Highlands and explored how these values relate to multiple variables, including encounter frequency, distribution, lineage, adaptations to grazing and fire and the typical floral assemblage in which each species occurs. Of the species sampled, 56 are C4 and seven are C3. There are no differences in δ13C or weight %C:N among either C3 or C4 species with different distributions or adaptations, from different assemblages, or that are frequently or infrequently encountered. However, there are differences in both δ13C and weight %C:N among C4 lineages, and the single C3 arundinoid (Styppeiochloa hitchcockii) has larger weight %C:N than C3 Paniceae. Our results provide a foundation for evaluating reliance on C4 resources by people, as well as domesticated and endemic animals both today and in the past. We encourage gathering additional comparative data for co‐occurring individual plants from the same open grassy biome localities, as well as other species, habitats and regions in Madagascar.

Neogene aridification and lake development in the Issyk‐Kul basin, Kyrgyzstan

AbstractUplift of the Tian Shan range modified regional climate during Cenozoic aridification in Central Asia. This study presents facies analyses and Neogene oxygen and carbon isotopic records from magnetostratigraphically dated terrestrial sedimentary sections on the southern side of the intermontane Issyk‐Kul basin in the Kyrgyz Tian Shan and 26Al/10Be isochron burial ages from the southern and eastern sides of the basin. The δ18O and δ13C data show a positive ca. 2‰ shift in values between ca. 8 and 7 Ma and a change from a negative to a positive trend. This change is attributed to the upwind growth of the Kyrgyz, Kungey and Trans Ili (Zaili) ranges, which diverted the westerlies, thereby changing the Issyk‐Kul basin from a windward to a leeward position, enhancing aridification and establishing the modern‐day spring and summer precipitation regime within the basin. Two 4 to 5 Ma 26Al/10Be isochron burial ages constrain the onset of Sharpyl Dak deposition on the eastern side of the basin; southward paleocurrent directions there suggest the eastward growth of the Kungey range in the Pliocene. Increased subsidence on the southern side of the basin and local tectonically induced river system reorganization led to the commencement of lake formation at ca. 5 Ma, followed by a ca. 2 Ma local depositional hiatus. The transition from sandstones of the Chu sedimentary group to conglomerates of the Sharpyl Dak group, marking a change from fluvial‐alluvial deposits to a proximal alluvial fan, is dated at 2.6–2.8 Ma by 26Al/10Be isochron burial dating on the southern side of the basin, driven either by tectonics or Northern Hemisphere glaciation. This study concludes that the late Miocene–Pliocene northward growth of Tian Shan significantly altered environmental conditions within the range, preventing the moisture‐bearing westerlies from reaching the intermontane Issyk‐Kul basin and promoting lake formation and expansion.

Dietary strategies of Pleistocene Pongo sp. and Homo erectus on Java (Indonesia).

During the Early to Middle Pleistocene, Java was inhabited by hominid taxa of great diversity. However, their seasonal dietary strategies have never been explored. We undertook geochemical analyses of orangutan (Pongo sp.), Homo erectus and other mammalian Pleistocene teeth from Sangiran. We reconstructed past dietary strategies at subweekly resolution and inferred seasonal ecological patterns. Histologically controlled spatially resolved elemental analyses by laser-based plasma mass spectrometry confirmed the preservation of authentic biogenic signals despite the effect of spatially restricted diagenetic overprint. The Sr/Ca record of faunal remains is in line with expected trophic positions, contextualizing fossil hominid diet. Pongo sp. displays marked seasonal cycles with ~3 month-long strongly elevated Sr/Ca peaks, reflecting contrasting plant food consumption presumably during the monsoon season, while lower Sr/Ca ratios suggest different food availability during the dry season. In contrast, omnivorous H. erectus shows low and less accentuated intra-annual Sr/Ca variability compared to Pongo sp., with δ13C data of one individual indicating a dietary shift from C4 to a mix of C3 and C4 plants. Our data suggest that H. erectus on Java was maximizing the resources available in more open mosaic habitats and was less dependent on variations in seasonal resource availability. While still influenced by seasonal food availability, we infer that H. erectus was affected to a lesser degree than Pongo sp., which inhabited monsoonal rain forests on Java. We suggest that H. erectus maintained a greater degree of nutritional independence by exploiting the regional diversity of food resources across the seasons.

Sources and sequestration rate of organic carbon in sediments of the bare tidal flat ecosystems: A model approach

Humans have been contributing adversely to greenhouse gas emissions by generating a vast amount of CO2, primarily causing climate change. Nature-based climate solutions, consisting of both terrestrial and marine ecosystems, are tremendous potential for sequestering and storing significant amounts of carbon, which can help to slow the progression of climate change. In this study, we use a carbon balance model to simulate the carbon sequestration rate and carbon stored in bare tidal flat (BTF) areas along Korea's west and south coasts from 2018 to 2050. Furthermore, the percentage of potential carbon sources deposited at BTF sites was calculated using a two-terminal mixing model and δ13C data. The carbon deposited on the BTF areas is the result of lateral carbon transport from upslope terrestrial regions as well as marine sources. Based on the δ13C isotope, this study classified potential carbon sources in BTFs sediment into two categories: terrestrial and marine. The results indicate that the proportion of organic carbon contribution from terrestrial sources ranged from 7.63% to 49% in the BTF studied areas. We discuss the validity of projection which was investigated over three years, from 2018 to 2020. A preliminary conclusion is that future carbon storage at BTF sites will increase significantly. Carbon accumulation increases linearly over time in nearly all areas studied, with carbon sequestration rates ranging from 0.053 to 0.623 (MgC ha−1 yr−1). This study found that a significant amount of carbon is sequestered for a long time in the BTF regions based on model simulation results. In addition, it also contributes to projects that seek to promote and conserve these climate benefits by providing estimates of carbon storage in coastal BTFs that can be included in NDCs for the Paris Agreement.

Reconstruction of landscape and climate of the largest drainage basin in the Ladakh Range, NW Trans Himalaya during the last 7000 years

Landform geomorphology and glacial lake deposits in the largest drainage basin of the Ladakh Range i.e. Chang La-Tangtse basin were studied to infer their palaeoclimatic significance. The grain size, mineral magnetism, percentage loss on ignition (%LOI) and organic carbon stable isotope (δ13C) data in combination with total organic carbon (TOC) supported by AMS 14C (calibrated) dates of a 190 cm long section from the Chang La-Tsoltak palaeolake provides a climatic record since the last ∼ 7075 cal yr BP. The χlf, χARM, and SIRM values suggest that the catchment-derived palaeolake sediments predominantly contain magnetically “soft” minerals like magnetite and maghemite. The δ13C values range between −21 and −24 ‰ with an average of –22 ‰ which suggests a mixed C3-C4 plant signature and water stressed ecosystem. The relatively small variations in the δ13C values of organic matter in the entire lake profile suggest a stable climatic condition. The prominent effect of westerlies is seen between 7075 and 6040 cal yr BP with huge detrital influx at the lake bottom indicating a glacial advancement in the region. The affect of Mid-Holocene warm period is evident at 6040 cal yr BP with the advent of ISM. Paradigm shifts in the proxy values are observed at 5710, 4890, 3435, and 2800 cal yr BP. The influence of westerlies gradually reduces at 2800 cal yr BP. The landscape evolution and the climatic variations in the Trans-Himalaya are primarily governed by westerlies and do not correspond to the Indian monsoon variability records, particularly during the Mid-Holocene Thermal Maxima. Several other regions of the Ladakh Range also record similar climatic variations, indicating that the palaeolake sediments also reflect regional climate variations.

Unravelling δ13C signal in Scots pine trees for climate change and tree physiology studies

Stable carbon isotope composition (δ13C) recorded in trees responds sensitively to the changing environmental conditions and thus provides a powerful tool for paleoenvironmental reconstructions. The retrospective interpretation of tree δ13C signal depends on comprehensive understanding of how environmental and physiological signals are recorded in δ13C during photosynthesis and how the δ13C signal is modified after photosynthesis. This thesis aims to improve the understanding of photosynthetic and post-photosynthetic isotope fractionation processes, and to examine the suitability of tree ring δ13C for intra-seasonal reconstructions of intrinsic water use efficiency (iWUE). The former goal was studied by combining compound-specific isotope analysis of organic matter with isotope discrimination models and online δ13C measurements of leaf CO2 fluxes for field-grown mature Scots pine (Pinus sylvestris L.). The latter was achieved via comparing 18-year-long intra-seasonal iWUE chronologies estimated from laser ablation derived tree ring δ13C, gas exchange and eddy covariance data. Mesophyll conductance and time-integral effect of leaf assimilates had a clear impact on the intra-seasonal dynamics of leaf sugar δ13C. No significant use of reserves was observed for biomass growth of needles, stem or roots of Scots pine. Unlike sucrose, leaf bulk matters had a significant δ13C offset from new assimilates, leading to a distorted environmental signal documented in their δ13C. The reliability of tree ring δ13C data for intra-seasonal iWUE reconstructions was supported by an agreement of intra-seasonal patterns across the iWUE estimation methods. These results broaden our knowledge of the less well-known photosynthetic and post-photosynthetic isotopic fractionation processes, demonstrate the benefits of analysing sucrose δ13C for understanding plant physiological responses, and show that the tree ring δ13C based iWUE reconstructions can be extended to intra-seasonal scale. This information not only helps to better unravel δ13C signal in trees, but also improves reliable reconstructions of environmental and physiological signals from tree ring δ13C.

Pre-industrial ecology and foraging behavior of swordfish Xiphias gladius in the eastern North Pacific

The historical ecology and foraging behavior of many apex marine predators are poorly known. This includes highly mobile pelagic species such as billfish (Xiphiidae and Istiophoridae), which have long held cultural significance for coastal peoples. In California’s Santa Barbara Channel Region, Chumash people have hunted billfish for &gt;2000 yr, providing a deep historical record of these species. We present bulk tissue δ13C and δ15N data for 15 Late Holocene archaeological swordfish Xiphias gladius and 1 striped marlin Kajikia audax previously identified to species through collagen fingerprinting. When compared to data sets of modern northeastern Pacific and archaeological Gulf of Maine swordfish, we identified significant overlap in the isotopic values of modern and archaeological swordfish from the Pacific, indicating that pre-industrial swordfish were reliant on food webs of the North Pacific Subtropical Gyre and the California Current System. We also identified differences in the isotopic composition of swordfish captured by island vs. mainland communities, with swordfish remains from mainland sites having lower and more variable δ13C values, potentially indicating different source populations. The isotopic range of swordfish from California archaeological sites was much broader than those from the Gulf of Maine, suggesting a wider range of habitats used by Pacific swordfish. Our results provide important pre-industrial data for an apex marine predator.

TDFCAM: A method for estimating stable isotope trophic discrimination in wild populations.

Stable isotope mixing models (SIMMs) are widely used for characterizing wild animal diets. Such models rely upon using accurate trophic discrimination factors (TDFs) to account for the digestion, incorporation, and assimilation of food. Existing methods to calculate TDFs rely on controlled feeding trials that are time-consuming, often impractical for the study taxon, and may not reflect natural variability of TDFs present in wild populations.We present TDFCAM as an alternative approach to estimating TDFs in wild populations, by using high-precision diet estimates from a secondary methodological source-in this case nest cameras-in lieu of controlled feeding trials, and provide a framework for how and when it should be applied.In this study, we evaluate the TDFCAM approach in three datasets gathered on wild raptor nestlings (gyrfalcons Falco rusticolus; peregrine falcons Falco perigrinus; common buzzards Buteo buteo) comprising contemporaneous δ13C & δ15N stable isotope data and high-quality nest camera dietary data. We formulate Bayesian SIMMs (BSIMMs) incorporating TDFs from TDFCAM and analyze their agreement with nest camera data, comparing model performance with those based on other relevant TDFs. Additionally, we perform sensitivity analyses to characterize TDFCAM variability, and identify ecological and physiological factors contributing to that variability in wild populations.Across species and tissue types, BSIMMs incorporating a TDFCAM outperformed any other TDF tested, producing reliable population-level estimates of diet composition. We demonstrate that applying this approach even with a relatively low sample size (n < 10 individuals) produced more accurate estimates of trophic discrimination than a controlled feeding study conducted on the same species. Between-individual variability in TDFCAM estimates for ∆13C & ∆15 N increased with analytical imprecision in the source dietary data (nest cameras) but was also explained by natural variables in the study population (e.g., nestling nutritional/growth status and dietary composition).TDFCAM is an effective method of estimating trophic discrimination in wild animal populations. Here, we use nest cameras as source dietary data, but this approach is applicable to any high-accuracy method of measuring diet, so long as diet can be monitored over an interval contemporaneous with a tissue's isotopic turnover rate.

Vėlyvojo bronzos amžiaus ekonomika rytų Baltijos regione: naujo modelio link

In this paper, we present the main results of interdisciplinary project that allowed us to formulate a new perspective on the economy of the Late Bronze Age in the Eastern Baltic region. New excavations at the Late Bronze Age fortified settlements of Garniai 1 (Utena district municipality) and Mineikiškės (Zarasai district municipality) lead us to analyse the economy of the communities in much greater detail and to formulate a more reliable economical model than before. This paper reviews the new results of archaeobotanical investigations of these fortified settlements, as well as δ13C and δ15N data of food remains in Late Bronze Age pottery, grains and animal bone collagen samples. These analyses allowed us to refine and clarify the likely dietary practices of consumers of certain products in the Eastern Baltic region. The paper also publishes new data on the elemental composition and lead isotopes of metalware, thereby adding to our earlier findings These studies show that metallurgy as a specialized activity did not play a significant role in the Late Bronze Age economy, but its emergence was driven by the economic changes of the period. In contrast, the production of high-level bone-antler artifacts reflects the activity of specialized craftsmen in Late Bronze Age settlements. The collection of a new large and varied dataset allows us to determine the lifestyle and dietary habits of the people living in these settlements. By developing a new model of the Late Bronze Age, we present a picture of the interwoven economies of agriculture, animal husbandry, hunting, fishing, gathering, metallurgy and bone craftsmanship as a whole, asking what might have influenced the distinctive development of the economy of the eastern Baltic Sea region during the Late Bronze Age.

Marine osmium‑uranium‑sulfur isotope evidence for the interaction of volcanism and ocean anoxia during the Middle Pleistocene in the tropical Western Pacific

Before the Quaternary, the Earth experienced a series of environmental perturbations. The causal links between large volcanic events, extreme climatic change, and ocean anoxia have been examined in the context of these perturbations. However, to date, the correlation between oceanic anoxia and large volcanic activity in the Pleistocene remains poorly constrained. Identifying the physical processes that can control changes to the marine osmium, uranium, and sulfur isotope ratios is critical to understanding how volcanic activity, climate changes, and ocean anoxia have coevolved throughout the Quaternary. In this study, we provide a continuous high-resolution marine record of 187Os/188Os from 1.31 Ma to 0.59 Ma, as well as uranium, sulfur and carbon isotope (δ238UCarb, δ34SCAS, and δ13C) data from carbonates collected from the International Ocean Discovery Program (IODP) site 363 to characterize the relationship between volcanic eruptions and the variations in the redox state of the oceans. The marine sediments in the studied core exhibited numerous prominent negative shifts in the isotopic ratios of osmium, implying that they were triggered by large volcanic events. Our δ238UCarb and δ34SCAS records also exhibit multiple negative shifts, suggesting a mantle-derived input during this period. Enhanced volcanic episodes can release large quantities of CO2, which can cause enhanced oceanic anoxia; hence, this study demonstrates that multiple oscillations in oceanic anoxia were driven by large volcanic eruptions during this stage.