Organic carbon and nitrogen isotopes in surface sediments from the western Arctic Ocean and their implications for sedimentary environments

Surface sediments from the Chukchi Sea and adjacent arctic deep sea were investigated for organic carbon and nitrogen isotopes （in δ13Corg and δ15Norg） as well as biogeni＇c silica （BSiO2）. δ13Corg and δ15Norg values of surface sediments in the study area fall between the end-member values of marine and terrestrial organic matter from the surrounding lands and seas, their variations reflect the changes of marine productivity and terrestrial supply in the study area. BSiO2 shows a similar distribution pattern with δ13Corg and δ15Norg, and can be used as an indicator of marine productivity. In the central-west Chukchi Sea and the Chukchi Rise, sediments have higher δ13Corg, δ15Norg and BSiO2 values, indicating the region has high marine productivity influenced by the nutrient-rich branches of the Pacific waters. In the coastal zone off northwestern Alaska, δ13Corg and δ15Norg values become lighter, indicating a weakening marine productivity and an increasing terrigenous supply due to the effects of the least nutrient-rich branch of the Pacific waters. In the north and the northeast of the study area （including the Chukchi Plateau, the Canada Basin and the Beaufort shelf）, δ13Corg, δ15Norg and BSiO2 have the lowest values, and the terrigenous organic matter becomes dominant in surface sediments because this region has the longest ice-covered duration, the least nutrient-rich seawater and the increasing supply of terrestrial materials from the Mackenzie River and the northern Alaska under the action of the clockwise Beaufort gyre. Because the subarctic Pacific waters are continuously discharged into the central basin of the Arctic Ocean through the study area, the nutrient pool in the Chukchi Sea can be considered as a typical open system, the ratio of δ15Norg to BSiO2 content show some tracers that the level of nutrient utilization is contrary to nutrient supply and marine productivity formed in seawater.

The subsistence patterns of the Shengedaliang site(-4,000 yr BP)revealed by stable carbon and nitrogen isotopes in northern Shaanxi,China

In order to explore subsistence patterns in northern Shaanxi Province around 4,000 yr BP,28 human and 24 animal bones from the Shengedaliang site were sampled for stable carbon and nitrogen isotope ratio analysis.The results show that most people primarily subsisted on C_4 resources,e.g.millet and millet-related animal products,despite the fact that there was some intake of C_3 plants by some individuals.Stable nitrogen isotope values indicate that there were differences in meat consumption between individuals at the site.Pigs were mainly foddered with millet and millet byproducts,as well as some cattle,according to their highδ^(13)C values.However,most cattle and the sheep/goats consumed wild C_3 plants at Shengedaliang.Our above findings indicates that subsistence patterns in northern Shaanxi around 4,000 yr BP were characterized by millet farming,while the grassland animal husbandry,e.g.cattle and sheep/goats raising,displayed very little contribution to local economy.The intensive millet farming in northern Shaanxi provided enough food for population growth,ensured the accumulation of wealth,and consequently accelerated social differentiation and complexity.

Spatial distributions of organic carbon and nitrogen and their isotopic compositions in sediments of the Changjiang Estuary and its adjacent sea area

The spatial distribution patterns of total organic carbon and total nitrogen show significant correlations with currents of the East China Sea Shelf. Corresponding to distributions of these currents, the study area could be divided into four different parts. Total organic carbon, total nitrogen, and organic carbon and nitrogen stable isotopes in sediments show linear correlations with mean grain size, respectively, thus ＂grain size effect＂ is an important factor that influences their distributions. C/N ratios can reflect source information of organic matter to a certain degree. In contrast, nitrogen stable isotope shows different spatial distribution patterns with C/N and organic carbon stable isotope, according to their relationships and regional distributions. The highest contribution （up to 50%） of terrestrial organic carbon appears near the Changjiang Estuary with isolines projecting towards northeast, indicating the influence of the Changjiang dilution water. Terrestrial particulate organic matter suffers from effects of diagenesis, benthos and incessant inputting of dead organic matter of plankton, after depositing in seabed. Therefore, the contribution of terrestrial organic carbon to particulate organic matter is obviously greater than that to organic matter in sediments in the same place.

Origin of the Diamonds within Chromitite from the Mirdita Ophiolite(Albania) and its Geological Significance

Geophysical investigations and laboratory experiments show evidence for possible subduction of ancient oceanic crust.Geological and mineralogical observations suggest that subducted oceanic crust is recycled into the upper mantle.The subduction is supported by the recovery of superdeep diamonds from kimberlites and the presence of crustal materials in ophiolitic chromitites and their host peridotites.What is the mechanism?Here we report the new discovery of ophiolite-hosted diamonds in the podiform chromitites within the Skenderbeu massif from the Mirdita ophiolite in the western part of Neo-Tethys(Fig.1).The diamonds are characterized by exceedingly light C isotopes(δ13CPDB^-25‰),which can be interpreted as evidence for subduction of organic carbon from Earth’s surface.The diamonds are also characterized by an exceptionally large range inδ15Nair(-12.9‰to+25.5‰),accompanied by a low N aggregation state(Fig.2).On the other hand,materials sparsely included in diamonds include amorphous material,Ni-Mn-Co alloy,nanocrystals(20 nm×20 nm)of calcium silicate with an orthorhombic perovskite structure(Ca-Pv),and fluids(Fig.3).We consider that the Skenderbeu diamonds nucleated and grew from a C-saturated,NiMnCo-rich melt derived from a subducted slab of ocean crust and lithosphere in the deep mantle environment.The environment is in the diamond stability field or near the top of the mantle transition zone.The new discovery of diamonds from the Mirdita ophiolite provides a valuable opportunity to understand deep cycling of subducted oceanic crust and mantle(i.e.,composition and process).

The influence of agriculture in the process of population integration and cultural interaction during the Eastern Zhou Period in central-south, Inner Mongolia: Carbon and nitrogen stable isotope analysis of human bones from the Dabaoshan cemetery, Helingee

Central-south Inner Mongolia, China, is highly sensitive to the cultural interactions between sedentary agriculturalists and nomadic pastoralists during the Eastern Zhou Period(770–256 BC). The previous pattern of multiple cultures and diverse ethnic groups has been transformed to the increasingly dominated cultural system of Central Plain since the middle and late Warring States Period, when the states of Zhao and Qin have conquered the most parts of central-south Inner Mongolia.However, the variation of subsistence strategies during this historical process has never been evaluated. Particularly, as the typical representative of Central Plain cultures, the effect of intensive millet agriculture is still unknown in the process of population integration and culture interaction. Thus, to explore the shift of subsistence pattern, carbon and nitrogen stable isotope analysis of bone collagen from Dabaoshan site(410–180 BC) have been performed. The isotopic result indicates a large amount of C_4-based animal protein consumed by Dabaoshan humans. According to the archaeological backgrounds, we propose the Dabaoshan persons intensively relied on the millet agriculture and developed the agro-pastoral economy, which hinted the comprehensive influences from Central plain civilizations in late Warring States Period. Further compared with other published isotopic data in the same region during different periods, we suggest the millet agriculture has played the positive role in the process of population integration and culture fusion in central-south Inner Mongolia during the Eastern Zhou Period.

Divergent patterns of foliar δ^(13)C and δ^(15)N in Quercus aquifolioides with an altitudinal transect on the Tibetan Plateau: an integrated study based on multiple key leaf functional traits

Aims With a close association with plant water availability,foliar δ^(13)C had been investigated extensively in alpine regions;however,foliar δ^(15)N has rarely been concurrently used as an indicator of plant nitrogen availability.Due to the positive correlations between leaf nitrogen con-tent and foliar δ^(13)C andδ15N found in previous studies,we expected that they should show consistent patterns along an altitudinal gradient.Methods To test our hypothesis,we measured foliar δ^(13)C andδ15N in conjunc-tion with multiple key leaf functional traits of Quercus aquifolioides,a dominant species of alpine forest on the eastern slopes of the sygera mountains,southeastern Tibetan Plateau from 2500 to 3800 m.Important findings(i)Contrary to our hypothesis,foliar δ^(13)C exhibited a significant pos-itive linear relationship with altitude;in contrast,foliarδ15N initially increased and subsequently decreased with altitude,the change in trend occurring around 3300 m.(ii)our analyses indicated that leaf internal resistance and stomatal conductance,rather than photosynthetic capacity indicated by leaf N concentration,appar-ently explained the altitudinal variation in foliar δ^(13)C,while differ-ences in foliar δ^(15)N were likely the result of soil N availability.(iii)Principal component analysis revealed a clear association between δ^(13)C and a tradeoff between water loss and carbon gain,indicated by traits related to gas exchange such as leaf thickness,density,sto-matal properties.In contrast,the second axis was associated withδ15N and nitrogen acquisition strategy in Q.aquifolioides across its altitudinal distribution,represented by traits related to nitrogen concentration and stomata per gram of leaf nitrogen.