C3-type Vegetation Research Articles

Isotope compositions of dinosaur eggs and associated depositional settings in the Upper Cretaceous Huizhou Formation from the Qiyunshan area, Anhui Province, China: implications for paleoenvironmental reconstruction

ABSTRACT We analysed the stable isotope compositions of dinosaur eggshells and their associated depositional settings of the egg-bearing rocks in the Upper Cretaceous of the Qiyunshan area, Anhui Province, China. Data show that δ13C values for Similifaveoloolithus qiyunshanensis and Umbellaoolithus xiuningensis range between −5.94‰ and −3.55‰; this suggests that C3-type vegetation was consumed by dinosaurs with relatively high atmospheric CO2. δ18O values vary between −8.45‰ and −4.95‰, indicative of high temperature and low humidity within nesting areas. The lithological characteristics of the egg-bearing section evaluated in this study are dominated by red-brown fine sandy siltstone, correlating with pebbly medium-fine grained and medium-fine grained lithic sandstones. Grain size parameters, histograms, and sample probability cumulative curves are also all characterised by fine-grained sediments and suspension populations, likely indicative of floodplain and point bar environments. Therefore, the paleoclimate of the dinosaur nesting habitat was semiarid-to-arid based on food types as well as the colour and high Fe content of sediments. We suggest that this fluvial environment provided the best nesting and egg laying area for drought-adapted dinosaurs in the Upper Cretaceous of the Qiyunshan area and that the excavated nesting could be concluded in view of the periodic flooding events.

Near-infrared spectroscopy: Alternative method for assessment of stable carbon isotopes in various soil profiles in Chile

The role of soil in the global carbon cycle and carbon–climate feedback mechanisms has attracted considerable interest in recent decades. Consequently, development of simple, rapid, and inexpensive methods to support the studies on carbon dynamics in soil is of interest. Near-infrared spectroscopy (NIRS) has emerged as a rapid and cost-effective method for measurements of soil properties. The aim of this study was to develop and validate a predictive model for δ13C values using NIRS in various soil profiles across Chile. Eleven sites were selected in the range of 30° to 50° S. These sites represent different soil moisture and soil temperature regimes, clay mineralogies, parent materials, and climates; in addition, they have prairie vegetation and contain C3-type vegetation. Air-dried soil samples were scanned in the NIR range at a resolution of 4 cm−1. The carbon isotopic composition, expressed as δ13C relative to the Vienna Pee Dee Belemnite standard, was analysed using an elemental analyser–isotope ratio mass spectrometer system. A prediction model for δ13C values based on NIRS data was developed through a partial least-squares regression (PLS) model using ten latent variables. A second model was generated using a random forest (RF) approach. The model performances were acceptable. The RF model provided the best results. The values of the root mean square error of prediction for the validation runs for δ13C obtained using the PLS and RF models were 1.38‰, and 1.15‰, respectively. These model performances indicate that NIRS can be used to predict δ13C for the selected dataset. The results of this study support the use of NIRS as a predictive method in soil analyses and as a nondestructive waste-free method for studies on carbon dynamics in soil.

A multiple-proxy stalagmite record reveals historical deforestation in central Shandong, northern China

Evaluating anthropogenic impacts on regional vegetation changes during historical time is not only important for a better understanding of the Anthropocene but also valuable in improving the vegetation-climate models. In this study, we analyzed stable isotopes (δ18O, δ13C) and trace elements (Mg/Ca, Sr/Ca) of a stalagmite from Huangchao Cave in central Shandong, northern China. 230Th and AMS14C dating results indicate the stalagmite deposited during 174BC and AD1810, with a hiatus between AD638 and 1102. Broad similarities of the δ18O and trace elements in the stalagmite suggest they are reliable precipitation indexes. The δ13C of the stalagmite, a proxy of vegetation change, was generally consistent with local precipitation and temperature variations on a centennial-scale before the 15th century. It typically varied from −9.6‰ to −6.3‰, indicating climate controlled C3 type vegetation during this period. However, a persistent and marked increasing trend in the δ13C record was observed since the 15th century, resulting in δ13C values from −7.7‰ to −1.6‰ in the next four centuries. This unprecedented δ13C change caused by vegetation deterioration cannot be explained by climate change but is fairly consistent with the dramatically increasing population and farmland in Shandong. We suggest that the increasing deforestation and reclamation in central Shandong began to affect vegetation in the mountain region of central Shandong since the 15th century and severely destroyed or even cleared the forest during the 16th–18th century.

Correlation between oxygen and carbon isotopes of speleothems from Tian’e Cave, central China: Insights into the phase relationship between Asian summer and winter monsoons

The correlation of East Asian summer and winter monsoons (EASM and EAWM) is believed to be variable at various timescales and under different climate backgrounds. In order to address this issue, high-resolution δ18O (depleted values indicating a strong EASM) and δ13C records (depleted values representing a weak EAWM) from three stalagmites, covering Marine Isotope Stages (MIS) 4 and 3, are reconstructed from an alpine cave in central China. During MIS 4, millennial-scale changes are clear in δ18O and δ13C records, while the δ13C is only characterized by centennial-scale variability across MIS 3. Changes in these speleothem δ13C records are supported by pollen records from the same area, which suggested millennial-scale alternations between conifer and deciduous broadleaf forests during MIS 4 and a stable C3-type vegetation in MIS 3. After detrended, δ18O changes are positively correlated with the δ13C record at a centennial scale, indicating an anti-phase of EASM and EAWM. In early MIS 4, however, an in-phase relationship of EASM and EAWM can be observed at a millennial scale. Thus, an anti-phased EASM/EAWM can be expected at a centennial scale, while a complicated correlation is seen at a millennial scale. These results imply a variable EASM/EAWM phase relationship under varying climatic conditions through the geological records and at different timescales.

Reconstruction of Late Quaternary Climate From a Paleo-Lacustrine Profile in the Central (Kumaun) Himalaya: Viewing the Results in a Regional Context

In this paper, we reconstruct the climatic changes starting from late Pleistocene to the early Holocene as recorded from a fluvio-lacustrine section located within the Kumaun Central Himalaya. The results suggest two major climatic events corresponding with the Last Glacial Maximum (LGM) and Older Dryas (OD). The values of carbon isotopes vary between -23‰ to -14‰, along with a shift in vegetation pattern. The lower part of the section shows prevalence of C3 type vegetation, indicating warm and moist conditions at around 25,000 yr BP, possibly coinciding with the intensification of the Indian Summer Monsoon. The onset of cold and arid phase is evident in the gradual shift in vegetation pattern from C3 to C4 plants, which is prominently observed in the middle part of the paleolake profile. Eventually, as the value of δ13C during this time interval confirms, a prolonged phase of cold and arid climate sets in, coinciding with the strengthening of winter westerlies. This cold phase is dated at ~19,000 yr BP and the extended phase of cold interval observed at Dwarahat profile correlates well with previous results elsewhere from the Himalaya. The profile also shows that the LGM phase gradually transforms into a warm and moist climate. This transition registered at 200 cm above the base of the profile, marks the end of glacial period. The short, yet a clear warm spike could be related to the oscillation of Bolling-Allerod interstadial at ~15,000 yr BP. A significant negative excursion marked by an abrupt increase in δ13C values from -20‰ to -14‰ observed towards the top part of the profile, however, is reflective of the reduced monsoon precipitation, corresponding possibly with Older Dryas (OD). The topmost part of the profile that registers a depleted trend in δ13C values with dominance of C3 vegetation marks the return of the warm and moist climate.

Middle Pleistocene (MIS 14) environmental conditions in the central Mediterranean derived from terrestrial molluscs and carbonate stable isotopes from Sulmona Basin (Italy)

A paleosol from the Middle Pleistocene lacustrine-fluvial succession of Sulmona Basin, central Italy, was analysed for the land snail shell content, and the stable isotope composition of the shells and associated pedogenic carbonates. The paleosol – known as Fiorata Paleosol – is covered by a thick tephra layer dated to ca. 527ka allowing the pedogenetic horizons to be correlated to the marine isotope stage (MIS) 14-early MIS 13 interval. The terrestrial mollusc assemblage contained few individuals and was characterized by a low number of species which predominantly indicate open and dry habitats, thus suggesting that Fiorata Paleosol likely developed during glacial conditions of the MIS 14. The δ13C values of pedogenic carbonates and terrestrial shells indicate prevailing C3-type vegetation, probably marked by some degree of water stress. Calculation of the δ18O precipitation values, derived from pedogenic carbonates and shell δ18O values, indicate that the average temperature was 3–5°C lower than present day. This study highlights how paleosols, despite offering only snapshots of past climate and environments, provide valuable complementary information to paleoclimatic data obtained in the adjacent lacustrine intervals, specifically for the Sulmona successions.

Effect of conventional versus mechanized sugarcane cropping systems on soil organic carbon stocks and labile carbon pools in Mauritius as revealed by 13C natural abundance

Maintenance of adequate levels of soil organic carbon (SOC) is crucial for the biological, chemical and physical functioning of soils. This study was conducted (i) to determine the impact of long-term sugarcane monoculture on total SOC stocks and on its labile fractions and (ii) to quantify the loss of original SOC and the accretion of sugarcane-derived C following the adoption of new management practices namely de-rocking/land grading and mechanized harvesting. Five study sites representing the five major soil groups under sugarcane in Mauritius were selected with a classical “paired-plot” design adopted. In this design, two sites with similar initial conditions were developed in different ways over time. One represents the reference soil (virgin land with predominantly C3 type vegetation) and the other represents one of the following cropping treatments: (i) fields continuously cultivated with sugarcane for more than 25 or 50 years without de-rocking or land grading, (ii) fields under long-term sugarcane but having undergone de-rocking and land grading for mechanized harvesting in the last 3 years. Soil samples were taken to a depth of 50 cm and analysed for total organic C, labile C, 13C natural abundance, bulk density and stone content. Changes in SOC stock in the 0–50 cm profile following >50 years of cane cropping were not significant (P > 0.05) compared to virgin land at any site. Soil δ13C values revealed that long-term sugarcane cultivation resulted in a depletion of original SOC by 34 to 70 %. However, this loss was fully compensated by C input from sugarcane residues at all sites studied resulting in no net change in SOC stock. Adoption of mechanized harvest did not have any detrimental effect on SOC stocks due to C inputs from crop residues. However, long-term sugarcane cultivation resulted in significant decline in a labile C (KMnO4-oxidizable) fraction. Despite the large losses of original C following conversion from forest to sugarcane, long-term sugarcane cultivation resulted in sequestration of sugarcane-derived C which adequately compensated these losses. Moreover, intensive de-rocking and land grading preceding mechanized harvesting did not have any detrimental effect on SOC stocks. However, the quality of sugarcane soils, as indicated by a decline in labile C, could be degraded.

Diversity and abundance of earthworms in land use systems in central-western Colombia

The neotropical landscapes of Colombia's Andean region are characterized by a mosaic of agroecosystems presenting a range of vegetational cover for which soil fauna adaptation is still unknown. To analyze the diversity and abundance of earthworm species in relation to changes in selected soil physical and chemical parameters (bulk density, C stock, N stock, %C, %N, 13C, 15N, C:N ratio), these systems were classified into five categories according to land use intensity: non-intensive (NI), low intensity (LI), medium intensity (MI), high intensity (HI), and maximum intensity (IN). The influence of livestock production was confirmed in the significant differences observed in bulk density and 15N between NI, HI, and IN (P < 0.05). The C and N contents of IN systems (pastures) differed significantly (P < 0.05) in comparison with the other categories. Average δ 13C at the three soil depths evaluated (0–10, 10–20, and 20–30 cm) ranged between −24.9 for LI and −22.87 for IN, indicating that soil organic carbon was related to C3-type vegetation for all land uses and vegetation covers. Overall, 26 earthworm species were recorded, of which 16 showed a high capacity to adapt to natural, NI, LI, and MI systems. Depending on land use intensity, significant differences were also observed (P < 0.05) in the origin and ecological category of earthworms, mainly in terms of the following variables: diversity of native species, diversity of endogeic species, abundance of native species, biomass of native species, and abundance of exotic species. Based on the results obtained, the most favorable mosaic systems for agrobiodiversity conservation were identified as well as those subsystems that require special management to solve problems of habitat degradation.

Carbon isotopic composition of branched tetraether membrane lipids in soils suggest a rapid turnover and a heterotrophic life style of their source organism(s)

Abstract. Branched Glycerol Dialkyl Glycerol Tetraethers (GDGTs) are membrane spanning lipids synthesised by as yet unknown bacteria that thrive in soils and peat. In order to obtain more information on their ecological niche, the stable carbon isotopic composition of branched GDGT-derived alkanes, obtained upon ether bond cleavage, has been determined in a peat and various soils, i.e. forest, grassland and cropland, covered by various vegetation types, i.e., C3- vs. C4-plant type. These δ13C values are compared with those of bulk organic matter and higher plant derived n-alkanes from the same soils. With average δ13C values of −28‰, branched GDGTs in C3 soils are only slightly depleted (ca. 1‰) relative to bulk organic carbon and on average 8.5‰ enriched relative to plant wax-derived long-chain n-alkanes ( nC29–nC33). In an Australian soil dominantly covered with C4 type vegetation, the branched GDGTs have a δ13C value of −18‰, clearly higher than observed in soils with C3 type vegetation. As with C3 vegetated soils, branched GDGT δ13C values are slightly depleted (1‰) relative to bulk organic carbon and enriched (ca. 5‰) relative to n-alkanes in this soil. The δ13C values of branched GDGT lipids being similar to bulk organic carbon and their co-variation with those of bulk organic carbon and plant waxes, suggest a heterotrophic life style and assimilation of relatively heavy and likely labile substrates for the as yet unknown soil bacteria that synthesise the branched GDGT lipids. However, a chemoautotrophic lifestyle, i.e. consuming respired CO2, could not be fully excluded based on these data alone. Based on a natural labelling experiment of a C3/C4 crop change introduced on one of the soils 23 years before sampling and based on a free-air CO2 enrichment experiment with labelled CO2 on another soil, a turnover time of ca. 18 years has been estimated for branched GDGTs in these arable soils.

Recent Sediment Accumulation in a Mangrove Forest and Its Relevance to Local Sea-Level Rise (Ilha Grande, Brazil)

An accumulation rate in a well-developed mangrove forest has been associated with relative sea-level rise on an island off the coast of Rio de Janeiro State. This rate was calculated by 210Pb dating models from a single sediment core. Results indicate an accumulation rate of approximately 1.7 mm/y for the past approximately 100 years. This rate is almost identical to the ongoing eustatic mean rise in global sea level, indicating a tectonically stable mangrove habitat. Organic C (OC), total N, δ13C(OC), and δ15N values from selected core intervals suggest a constant source of accumulating vegetal debris, dominated by C3-type vegetation with insignificant input of marine-derived organic matter, and a stable subaerial mangal habitat.

Occurrence of sombric-like subsurface A horizons in some andic soils of the Nilgiri Hills (Southern India) and their palaeoecological significance

This paper deals with four pedons (three Fulvudands and one Andic Haplorthox) located at high elevations (2000–2400 m a.s.l.) in the Nilgiri Hills on an old laterized surface of South India, and characterized by thick (50–100 cm) epipedons whose colour tends to darken with depth. In two of them, the colour contrast between the top and the bottom A horizons was so well expressed that they were morphologically very similar to the African Oxisols reported to have sombric subsurface horizons. Soil organic matter (SOM) of the different selected A horizons was characterized by its mean residence time (MRT) and its δ 13C value, whereas their humic acids (HAs) were examined by techniques that made it possible to determine their chemical composition and their chromatic properties. It was found that the darker colour of the subsurface A horizons of these soils was related to three joined characteristics: a SOM δ 13C signature indicating a C4-type vegetation (i.e. a grassland-type) origin, the presence of humic acids belonging to the A-type (i.e. melanic) category of Kumada (Kumada, K., 1987. Chemistry of soil organic matter. Developments in Soil Science, Elsevier, Tokyo), and large mean residence time values. In contrast, the top A horizons had a more recent SOM, mainly inherited from a C3-type vegetation, and humic acids (HAs) that were less condensed than the A-type HAs. It was also found that where the presence of sombric-like subsurface A horizons was the most evident, the vegetation change recorded by the soils (i.e. the change from a grassland-type vegetation towards a C3-type vegetation) was expressed on the thickest part of their epipedon. These observations led us to propose that the occurrence of sombric-like subsurface A horizons resulted from the following sequence of events: (i) an exceptionally thick accumulation of organic matter deriving from grassland followed by (ii) its progressive replacement by less dark organic matter derived from a C3-type vegetation. This proposal was found to be in reasonable agreement with the history of the vegetation changes experienced by the Nilgiri Hills since the end of the Pleistocene. On the other hand, it is also very similar to one of the hypotheses proposed by Van Wambeke (Van Wambeke, A., 1992. Soils of the Tropics—Properties and Appraisal. McGraw-Hill, New York) to explain the frequent occurrence of sombric horizons in the Oxisols and Ultisols of the high-altitude areas of Central Africa.

Late Quaternary Paleoclimate in the Eastern Mediterranean Region from Stable Isotope Analysis of Speleothems at Soreq Cave, Israel

The eastern Mediterranean continental paleoclimate during the past 25,000 years was determined by a high-resolution petrographic, stable isotopic, and age study of speleothems from Soreq Cave, Israel. δ18O–δ13C trends indicate that all speleothems older than 7000 yr formed under conditions that differ from those of today. The period from 25,000 to 17,000 yr B.P. was characterized by the highest δ18O and δ13C values, which indicate deposition at temperatures of 12°–16°C, annual rainfall of 300–450 mm, and vegetation typical of a mixed C3–C4type. From 17,000 to 10,000 yr B.P. (deglaciation in northern Europe) δ18O values dropped progressively, correlative with warming (2°–3°C) and a gradual increase in precipitation. A simultaneous decrease in δ13C gives a range expected for C3-type vegetation. This period also shows significant δ18O and δ13C “spikes” which are correlatable with global events (e.g., Heinrich events and the Younger Dryas Stade). The speleothems that grew between 10,000 and 7000 yr B.P. have a unique petrography showing irregular thin laminae of various colors and much detritus. They have the lowest δ18O (corresponding to ∼1000 mm rain) coupled with the highest δ13C (caused by flooding events which stripped the soil cover). From 7000 to 1000 yr B.P. conditions became closer to those of today. This study demonstrates that global events which were recognized in Northern Europe and North Africa are also evident in the eastern Mediterranean and are reflected principally by large changes in the rainfall rate.

Chronology of the Baxie Loess Profile and the History of Monsoon Climates in China Between 17,000 and 6000 Years BP

The valley of the Baxie River, situated in the western region of the Loess Plateau in central China, contains a loess profile 15 m thick, which can be considered representative of loess-paleosol sequences formed over the last 17 ka. Both thermoluminescence (TL) determinations on fine-grained sediment (4–11 μm) and 14C determinations on various organic fractions of paleosols from the profile have provided an extremely useful chronological framework for these sequences. These sequences indicate a weakened summer monsoon during the last glacial maximum followed by a strengthening of the summer monsoon, beginning ca. 13 ka cal bp. An abrupt change to a weakened summer monsoon regime lasted from ca. 10.9 to 10.2 ka cal bp. The Asian summer monsoon circulation, recording the Holocene optimum, then increased and lasted from ca. 10.2 to 6 ka cal bp. The organic component of samples taken down the profile has δ13C values ranging from −21 to −24‰ with respect to the PDB standard. The more positive δ13C values suggest that the proportion of C4-type plants in river valleys of the Loess Plateau increased as Asian summer monsoon influence weakened, and C3-type vegetation increased as the summer monsoon influence strengthened. Magnetic susceptibility and organic content were low during loess deposition, also reflecting weakening of summer monsoon. Two 14C determinations on the humin fraction of the organic component near the top of the lower paleosol and the base of the upper paleosol complex gave ages of 10.2 and 10.9 ka cal BP, respectively. These ages mark the beginning and termination of a brief event involving increased dust influx under weakened summer monsoon conditions.