Sampling and Precise Dating Requirements for Extracting Isotopic Records from Three Rings

1982 ◽  
pp. 225-232
Author(s):  
CHARLES W. STOCKTON ◽  
WILLIAM R. BOGGESS
Keyword(s):  
Isotopic Records

STEPWISE ONSET OF CARBONIFEROUS GLACIATION CAPTURED IN C AND SR ISOTOPIC RECORDS OF PLATFORM CARBONATES

2016 ◽  
Author(s):  
Jitao Chen ◽  
◽  
Isabel P. Montanez ◽  
Isabel P. Montanez ◽  
Xiangdong Wang ◽  
...  
Keyword(s):  
Platform Carbonates ◽  
Isotopic Records

The Neogene transition from C3 to C4 grasslands in North America: assemblage analysis of fossil phytoliths

Paleobiology ◽  
2011 ◽  
Vol 37 (1) ◽  
pp. 50-71 ◽  
Author(s):  
Caroline A. E. Strömberg ◽  
Francesca A. McInerney
Keyword(s):  
North America ◽  
Great Plains ◽  
Late Miocene ◽  
Vegetation Change ◽  
Stable Carbon Isotopes ◽  
Fire Regime ◽  
Tooth Enamel ◽  
Regional Scale ◽  
Grassland Ecosystems ◽  
Isotopic Records

The rapid ecological expansion of grasses with C4 photosynthesis at the end of the Neogene (8–2 Ma) is well documented in the fossil record of stable carbon isotopes. As one of the most profound vegetation changes to occur in recent geologic time, it paved the way for modern tropical grassland ecosystems. Changes in CO2 levels, seasonality, aridity, herbivory, and fire regime have all been suggested as potential triggers for this broadly synchronous change, long after the evolutionary origin of the C4 pathway in grasses. To date, these hypotheses have suffered from a lack of direct evidence for floral composition and structure during this important transition. This study aimed to remedy the problem by providing the first direct, relatively continuous record of vegetation change for the Great Plains of North America for the critical interval (ca. 12–2 Ma) using plant silica (phytolith) assemblages.Phytoliths were extracted from late Miocene-Pliocene paleosols in Nebraska and Kansas. Quantitative phytolith analysis of the 14 best-preserved assemblages indicates that habitats varied substantially in openness during the middle to late Miocene but became more uniformly open, corresponding to relatively open grassland or savanna, during the late Miocene and early Pliocene. Phytolith data also point to a marked increase of grass short cells typical of chloridoid and other potentially C4 grasses of the PACMAD clade between 8 and 5 Ma; these data suggest that the proportion of these grasses reached up to ∼50–60% of grasses, resulting in mixed C3-C4 and highly heterogeneous grassland communities by 5.5 Ma. This scenario is consistent with interpretations of isotopic records from paleosol carbonates and ungulate tooth enamel. The rise in abundance of chloridoids, which were present in the central Great Plains since the early Miocene, demonstrates that the “globally” observed lag between C4 grass evolution/taxonomic diversification and ecological expansion occurred at the regional scale. These patterns of vegetation alteration imply that environmental change during the late Miocene-Pliocene played a major role in the C3-C4 shift in the Great Plains. Specifically, the importance of chloridoids as well as a decline in the relative abundance of forest indicator taxa, including palms, point to climatic drying as a key trigger for C4 dominance.

scholarly journals Spatiotemporal variations of nitrogen isotopic records in the Arabian Sea

2015 ◽  
Vol 12 (1) ◽  
pp. 1-14 ◽  
Author(s):  
S.-J. Kao ◽  
B.-Y. Wang ◽  
L.-W. Zheng ◽  
K. Selvaraj ◽  
S.-C. Hsu ◽  
...  
Keyword(s):  
Dissolved Oxygen ◽  
Arabian Sea ◽  
Euphotic Zone ◽  
Southeastern Part ◽  
Data Set ◽  
Global Coherence ◽  
One Step ◽  
Isotopic Records ◽  
Bottom Depth ◽  
Reported Data

Abstract. Available reports of dissolved oxygen, δ15N of nitrate (δ 15NNO3) and δ15N of total nitrogen (δ15Nbulk) for trap material and surface/downcore sediments from the Arabian Sea (AS) were synthesized to explore the AS' past nitrogen dynamics. Based on 25 μmol kg−1 dissolved oxygen isopleth at a depth of 150 m, we classified all reported data into northern and southern groups. By using δ15Nbulk of the sediments, we obtained geographically distinctive bottom-depth effects for the northern and southern AS at different climate stages. After eliminating the bias caused by bottom depth, the modern-day sedimentary δ15Nbulk values largely reflect the δ15NNO3 supply from the bottom of the euphotic zone. Additionally to the data set, nitrogen and carbon contents vs. their isotopic compositions of a sediment core (SK177/11) collected from the most southeastern part of the AS were measured for comparison. We found a one-step increase in δ15Nbulk starting at the deglaciation with a corresponding decrease in δ13CTOC similar to reports elsewhere revealing a global coherence. By synthesizing and reanalyzing all reported down core δ15Nbulk, we derived bottom-depth correction factors at different climate stages, respectively, for the northern and southern AS. The diffusive sedimentary δ15Nbulk values in compiled cores became confined after bias correction revealing a more consistent pattern except recent 6 ka. Such high similarity to the global temporal pattern indicates that the nitrogen cycle in the entire AS had responded to open-ocean changes until 6 ka BP. Since 6 ka BP, further enhanced denitrification (i.e., increase in δ15Nbulk) in the northern AS had occurred and was likely driven by monsoon, while, in the southern AS, we observed a synchronous reduction in δ15Nbulk, implying that nitrogen fixation was promoted correspondingly as the intensification of local denitrification at the northern AS basin.

Long-term Aptian marine osmium isotopic record of Ontong Java Nui activity

Geology ◽  
2021 ◽  
Author(s):  
Hironao Matsumoto ◽  
Rodolfo Coccioni ◽  
Fabrizio Frontalini ◽  
Kotaro Shirai ◽  
Luigi Jovane ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Volcanic Eruptions ◽  
Hydrothermal Activity ◽  
Published Data ◽  
Isotopic Data ◽  
Oceanic Plateaus ◽  
Carbon Burial ◽  
Organic Carbon Burial ◽  
Isotopic Records

The early to mid-Aptian was punctuated by episodic phases of organic-carbon burial in various oceanographic settings, which are possibly related to massive volcanism associated with the emplacement of the Ontong Java, Manihiki, and Hikurangi oceanic plateaus in the southwestern Pacific Ocean, inferred to have formed a single plateau called Ontong Java Nui. Sedimentary osmium (Os) isotopic compositions are one of the best proxies for determining the timing of voluminous submarine volcanic episodes. However, available Os isotopic records during the age are limited to a narrow interval in the earliest Aptian, which is insufficient for the reconstruction of long-term hydrothermal activity. We document the early to mid-Aptian Os isotopic record using pelagic Tethyan sediments deposited in the Poggio le Guaine (Umbria-Marche Basin, Italy) to precisely constrain the timing of massive volcanic episodes and to assess their impact on the marine environment. Our new Os isotopic data reveal three shifts to unradiogenic values, two of which correspond to black shale horizons in the lower to mid-Aptian, namely the Wezel (herein named) and Fallot Levels. These Os isotopic excursions are ascribed to massive inputs of unradiogenic Os to the ocean through hydrothermal activity. Combining the new Os isotopic record with published data from the lowermost Aptian organic-rich interval in the Gorgo a Cerbara section of the Umbria-Marche Basin, it can be inferred that Ontong Java Nui volcanic eruptions persisted for ~5 m.y. during the early to mid-Aptian.

scholarly journals What controls the stable isotope composition of precipitation in the Asian monsoon region?

2017 ◽  
Author(s):  
Le Duy Nguyen ◽  
Ingo Heidbüchel ◽  
Hanno Meyer ◽  
Bruno Merz ◽  
Heiko Apel
Keyword(s):  
Isotopic Composition ◽  
Asian Monsoon ◽  
Precipitation Amount ◽  
Climatic Conditions ◽  
Monsoon Region ◽  
Asian Monsoon Region ◽  
Air Mass ◽  
Local Factors ◽  
Regional Factors ◽  
Isotopic Records

Abstract. This study analyzes the influence of local and regional climatic factors on the stable isotopic composition of rainfall in the Vietnamese Mekong Delta as part of the Asian monsoon region. It is based on 1.5 years of weekly rainfall samples. Their isotopic content is analyzed by Local Meteoric Water Lines (LMWL) and single-factor regressions. Additionally, the contribution of several regional and local factors is quantified by multiple linear regressions (MLR) of all possible factor combinations and by relative importance analysis, a novel approach for the interpretation of isotopic records. The local factors are extracted from local climate records, while the regional factors are derived from atmospheric backward trajectories of water particles. The regional factors, i.e. precipitation, temperature, relative humidity and moving distance of the backward trajectories, are combined with equivalent local climatic parameters to predict the response variables δ18O, δ2H, and d-excess of precipitation at the station of measurement. The results indicate that (i) MLR can much better explain the isotopic variation of precipitation (R2 = 0.8) compared to single-factor linear regression (R2 = 0.3); (ii) the isotopic variation in precipitation is controlled dominantly by regional moisture regimes (~ 70 %) compared to local climatic conditions (~ 30 %); (iii) the most important climatic parameter during the early rainy season is the precipitation amount along the trajectories of air mass movements; (iv) the influence of local precipitation amount and temperature is not significant during the early rainy season, unlike the regional precipitation amount effect; (v) secondary fractionation processes (e.g. sub-cloud evaporation) take place mainly in the dry season, either locally for δ18O and δ2H, or along the air mass trajectories for d-excess. The analysis shows that regional and local factors vary in importance over the seasons, and that the source regions and transport pathways, and in particular the climatic conditions along the pathways, have a large influence on the isotopic composition of rainfall. The proposed methods thus proved to be valuable for the interpretation of the isotopic records in rainfall and the factors controlling it. The results illustrate that the interpretation of the isotopic composition in precipitation as a recorder of local climatic conditions, as for example performed for paleo records of water isotopes, may not be adequate in the Southern part of the Indochinese Peninsula, and likely also not in other regions affected by monsoon processes. However, the presented approach could open a pathway towards better and seasonally differentiated reconstruction of paleoclimates based on isotopic records.

scholarly journals Paleoenvironmental Interpretations on Organic Carbon Isotopic Records from Lake Sediments:A Critique

2001 ◽  
Vol 13 (1) ◽  
pp. 72-78 ◽  
Author(s):  
YU Junqing ◽  
◽  
WANG Xiaoy an ◽  
LI Jun ◽  
AN Zhisheng
Keyword(s):  
Organic Carbon ◽  
Carbon Isotopic ◽  
Isotopic Records
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