Consulta: subjectFacets:"Radiocarbon"
Registros recuperados: 16
Data/hora: 01/06/2024 17:43:02

Termination 1 timing in radiocarbon-dated regional benthic delta O-18 stacks
Provedor de dados: 5
Autores: Stern, Joseph V.; Lisiecki, Lorraine E.
Benthic O-18 changes are often assumed to be globally synchronous, but studies comparing 2-9 radiocarbon-dated records over the most recent deglaciation (Termination 1) have proposed differences in the timing of benthic O-18 change between the Atlantic and Pacific, intermediate and deep, and North and South Atlantic. Because of the relatively small number of records used in these previous studies, it has remained unclear whether these differences are local or regional in scale. Here we present seven regional benthic O-18 stacks for 0-40 kyr B.P. that include 252 records with independent regional age models constrained by 852 planktonic foraminiferal C-14 dates from 61 of these cores. We find a 4000 year difference between the earliest termination onset in...
Tipo: Text
Palavras-chave: Termination 1; Regional stacks; Benthic delta O-18; Radiocarbon.
Ano: 2014
URL: https://archimer.ifremer.fr/doc/00289/40039/38763.pdf

The glacial mid-depth radiocarbon bulge and its implications for the overturning circulation
Provedor de dados: 5
Autores: Burke, Andrea; Stewart, Andrew L.; Adkins, Jess F.; Ferrari, Raffaele; Jansen, Malte F.; Thompson, Andrew F.
Published reconstructions of radiocarbon in the Atlantic sector of the Southern Ocean indicate that there is amid-depth maximum in radiocarbon age during the Last Glacial Maximum (LGM). This is in contrast to the modern ocean where intense mixing between water masses results in a relatively homogenous radiocarbon profile. Ferrari et al. (2014) suggested that the extended Antarctic sea ice cover during the LGM necessitated a shallower boundary between the upper and lower branches of the meridional overturning circulation. This shoaled boundary lay above major topographic features associated with strong diapycnal mixing, isolating dense southern sourced water in the lower branch of the overturning circulation. This isolation would have allowed radiocarbon to...
Tipo: Text
Palavras-chave: Radiocarbon; Overturning circulation; Last Glacial Maximum.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00497/60855/64245.pdf

Glacial-to-deglacial 14C reservoir ages of surface and deep waters from the mid- and low-latitude Atlantic
Provedor de dados: 5
Autores: Blamer, Sven.
The 14C reservoir age of ocean surface waters shows small-scale spatial and temporal variations. Accordingly, correct estimates of reservoir ages are crucial for any reconstruction of a precise radiocarbon-based chronology of marine sediments. To meet this target in the mid- and low- latitude Atlantic we obtained both 14C reservoir ages and an absolute age model for the glacial-to-deglacial sections of four marine sediment cores by means of the ‘14C Plateau Tuning Technique’. This method is independent of any common conversion scheme of 14C ages. The resulting empiric reservoir ages were compared with reservoir age estimates based on model simulations.
Tipo: Text
Palavras-chave: Reservoir ages; Deep water ventilation ages; Atlantic; Radiocarbon.
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00493/60445/63890.pdf

A high-resolution record of Southern Ocean intermediate water radiocarbon over the past 30,000 years
Provedor de dados: 5
Autores: Hines, Sophia K. V.; Southon, John R.; Adkins, Jess F.
The circulation of intermediate waters plays an important role in global heat and carbon transport in the ocean and changes in their distribution are closely tied to glacial-interglacial climate change. Coupled radiocarbon and U/Th measurements on deep-sea Desmophyllum dianthus corals allow for the reconstruction of past intermediate water ventilation. We present a high-resolution time series of Antarctic Intermediate Water radiocarbon from 44 corals spanning 30 ka through the start of the Holocene, encompassing the transition into the Last Glacial Maximum (LGM) and the last deglaciation. Corals were collected south of Tasmania from water depths between 1430 and 1950 m with 80% of them between 1500 and 1700 m, giving us a continuous record from a narrow...
Tipo: Text
Palavras-chave: Southern Ocean; Radiocarbon; Glacial interglacial climate change; Meridional overturning circulation; Southern Ocean fronts; Intermediate water.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00497/60838/64466.pdf

Late Quaternary sporadic development of Desmophyllum dianthus deep-coral populations in the southern Labrador Sea with specific attention to their 14C- and 230Th-dating
Provedor de dados: 5
Autores: Maccali, Jenny; Hillaire-marcel, Claude; Ghaleb, Bassam; Ménabréaz, Lucie; Blénet, Aurélien; Edinger, Evan; Hélie, Jean-françois; Preda, Michel.
About 70 fossil and live-collected specimens of Desmophyllum dianthus were collected from steep rocky surfaces and time-averaged assemblages at their base (“coral graveyards”) in the southern Labrador Sea at depths ranging from ~1700 m (Orphan Knoll) to ~2200 m (Flemish Cap). Aside from stable isotope and mineralogical analysis, U-series and 14C age determinations were performed on the samples. Fossil corals from the coral graveyards display two principal age clusters corresponding respectively to the Holocene and Marine Isotope Stage (MIS) 5c intervals. Three samples lay outside these clusters, at ~13.5 ka (Bølling-Allerød), ~ 64 ka (MIS 3) and at ~181 ka (MIS 7a). The clusters are thought to record intervals with both i) high food availability, either...
Tipo: Text
Palavras-chave: Deep-sea corals; Aragonite corals; Labrador Sea; Radiocarbon; U-series dating.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00623/73496/72790.pdf

A Synthesis of Deglacial Deep-Sea Radiocarbon Records and Their (In)Consistency With Modern Ocean Ventilation
Provedor de dados: 5
Autores: Zhao, Ning; Marchal, Olivier; Keigwin, Lloyd; Amrhein, Daniel; Gebbie, Geoffrey.
We present a synthesis of 1,361 deep-sea radiocarbon data spanning the past 40kyr and computed (for C-14-dated records) from the same calibration to atmospheric C-14. The most notable feature in our compilation is a long-term Delta C-14 decline in deep oceanic basins over the past 25kyr. The Delta C-14 decline mirrors the drop in reconstructed atmospheric Delta C-14, suggesting that it may reflect a decrease in global C-14 inventory rather than a redistribution of C-14 among different reservoirs. Motivated by this observation, we explore the extent to which the deep water C-14 data jointly require changes in basin-scale ventilation during the last deglaciation, based on the fit of a 16-box model of modern ocean ventilation to the deep water Delta C-14...
Tipo: Text
Palavras-chave: Last deglaciation; Ocean ventilation; Data synthesis; Radiocarbon; Inverse method.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00496/60790/64955.pdf

Radiocarbon Evidence for the Contribution of the Southern Indian Ocean to the Evolution of Atmospheric CO     2     over the last 32,000 years
Provedor de dados: 5
Autores: Ronge, Thomas A.; Prange, M.; Mollenhauer, Gesine; Ellinghausen, Maret; Kuhn, G.; Tiedemann, R.
It is widely assumed that the ventilation of the Southern Ocean played a crucial role in driving glacial‐interglacial atmospheric CO2‐levels. So far however, ventilation records from the Indian sector of the Southern Ocean, are widely missing. Here we present reconstructions of water residence times (depicted as ΔΔ14C and Δδ13C) for the last 32,000 years on sediment records from the Kerguelen Plateau and the Conrad Rise (~570‐2500 m water depth), along with simulated changes in ocean stratification from a transient climate model experiment. Our data indicate that Circumpolar Deep Waters in the Indian Ocean were part of the glacial carbon pool. At our sites, close to or bathed by upwelling deep‐waters, we find two pulses of decreasing ΔΔ14C and δ13C values...
Tipo: Text
Palavras-chave: Radiocarbon; Ventilation; Southern Ocean; Younger Dryas; Carbon cycle; Indian Ocean.
Ano: 2020
URL: https://archimer.ifremer.fr/doc/00611/72351/71258.pdf

Atlantic Meridional Overturning Circulation during the Last Glacial and Deglacial: Inferences from the Atlantic Tropical Thermocline Temperature and Seawater Radiocarbon Activity
Provedor de dados: 5
Autores: Huang, Enqing.
This thesis aims to investigate variations of the last glacial and deglacial Atlantic Ocean circulation, with emphasize on the Atlantic deepwater ventilation rate during the Last Glacial Maximum (LGM). The highlights of the thesis are as the followings: (1) the modern frontal zone between the North Atlantic and the South Atlantic central waters off NW Africa shifted to the south during the last glacial and deglacial time periods. (2) The radiocarbon-based circulation age of the deep Atlantic (&gt; 1500 m) was estimated to be less than 400 years during the LGM, which was equal to or less than its pre-bomb value. Therefore, the LGM deep Atlantic was inferred to be well ventilated. (3) The abyssal Atlantic (below 2500 m) prior to the LGM was more depleted in...
Tipo: Text
Palavras-chave: Climate change; Ocean circulation; Atlantic Ocean; Glacial; Deglacial; Thermocline; Radiocarbon; Global carbon cycle; Foraminifera; Carbonate; Trace elements; Deep ocean ventilation rates.
Ano: 2013
URL: https://archimer.ifremer.fr/doc/00493/60446/63891.pdf

Reduced ventilation and enhanced magnitude of the deep Pacific carbon pool during the last glacial period
Provedor de dados: 5
Autores: Skinner, L.; Mccave, I. N.; Carter, L.; Fallon, S.; Scrivner, A. E.; Primeau, F.
It has been proposed that the ventilation of the deep Pacific carbon pool was not significantly reduced during the last glacial period, posing a problem for canonical theories of glacial-interglacial CO2 change. However, using radiocarbon dates of marine tephra deposited off New Zealand, we show that deep(&gt;2000 m) and shallow sub-surface ocean-atmosphere C-14 age offsets (i.e. 'reservoir-' or 'ventilation' ages) in the southwest Pacific increased by similar to 1089 and 337 yrs respectively, reaching similar to 2689 and similar to 1037 yrs during the late glacial. A comparison with other radiocarbon data from the southern high-latitudes suggests that broadly similar changes were experienced right across the Southern Ocean. If, like today, the Southern...
Tipo: Text
Palavras-chave: Radiocarbon; Ocean ventilation; Carbon cycling; Palaeoceanography.
Ano: 2015
URL: https://archimer.ifremer.fr/doc/00352/46279/46041.pdf

An improved method for estimating water-mass ventilation age from radiocarbon data
Provedor de dados: 5
Autores: Devries, Tim; Primeau, Francois.
Existing methods for inferring the ventilation age of water masses in the ocean using radiocarbon data neglect the effects of diffusive mixing. in the presence of varying atmospheric Delta(14)C, this neglect produces spurious time dependence in the estimated ventilation ages. To correct this deficiency we propose a new method for estimating the ventilation age from sediment core radiocarbon data. The new method is formulated in terms of parameterized age distributions that account for the effects of advective and diffusive transport in the ocean. When applied to simulated radiocarbon data from an OGCM, the method is able to closely reproduce the modeled ventilation age, whereas other methods are not. We also applied the method to sediment-core radiocarbon...
Tipo: Text
Palavras-chave: Ocean Drilling Program; Site 887; Ventilation age; Radiocarbon; Transit-time distribution; Glacial-interglacial.
Ano: 2010
URL: https://archimer.ifremer.fr/doc/00231/34197/32870.pdf

New constraints on deglacial marine radiocarbon anomalies from a depth transect near Baja California
Provedor de dados: 5
Autores: Lindsay, Colin M.; Lehman, Scott J.; Marchitto, Thomas M.; Carriquiry, Jose D.; Ortiz, Joseph D.
Previous studies have shown that radiocarbon activities (C-14) in the low-latitude, middepth Pacific and Indian Oceans were anomalously low during Heinrich Stadial 1 (HS1, similar to 17.8-14.6ka) and the Younger Dryas (YD, similar to 12.8-11.5ka), coincident with intervals of rising atmospheric CO2 concentration and declining atmospheric C-14. However, a full explanation of these events remains elusive due to sparse and sometimes conflicting data. Here we present new C-14 measurements on benthic and planktic foraminifera that, in combination with previously published measurements, enable us to reconstruct the C-14 depth gradient near Baja California. Vertical profiles were similar to present during the Last Glacial Maximum and BOlling/Allerod (14.6-12.8ka)...
Tipo: Text
Palavras-chave: Radiocarbon; Deglaciation; Heinrich Stadial 1; Baja California; Benthic foraminifera.
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00496/60797/64925.pdf

Atlantic Ocean ventilation changes across the last deglaciation and their carbon cycle implications
Provedor de dados: 5
Autores: Skinner, L. C.; Freeman, E.; Hodell, D.; Waelbroeck, C.; Vazquez Riveiros, Natalia; Scrivner, A.e.
Changes in ocean ventilation, controlled by both overturning rates and air‐sea gas exchange, are thought to have played a central role in atmospheric CO2 rise across the last deglaciation. Here we constrain the nature of Atlantic Ocean ventilation changes over the last deglaciation using radiocarbon and stable carbon isotopes from two depth transects in the Atlantic basin. Our findings broadly cohere with the established pattern of deglacial Atlantic overturning change, and underline the existence of active northern sourced deep‐water export at the Last Glacial Maximum (LGM). We find that the western Atlantic was less affected by incursions of southern‐sourced deep water, as compared to the eastern Atlantic, despite both sides of the basin being strongly...
Tipo: Text
Palavras-chave: Air&amp;#8208; Sea exchange; AMOC; Carbon cycle; Deglaciation; Radiocarbon; Ventilation.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00665/77717/79810.pdf

Black Sea "Lake" reservoir age evolution since the Last Glacial - Hydrologic and climatic implications
Provedor de dados: 5
Autores: Soulet, Guillaume; Menot, Guillemette; Garreta, Vincent; Rostek, Frauke; Zaragosi, Sebastien; Lericolais, Gilles; Bard, Edouard.
Chronologies of sediments that document the last glacial history of the Black Sea "Lake" are hampered by issues relating to reservoir age. Regulated by basin hydrology, reservoir ages represent a tool that could potentially be used to better understand the response of Black Sea "Lake" hydrology to climate change. Therefore, deciphering reservoir age evolution is crucial both for better constraining the basin chronological framework and for providing new insights into our understanding of Black Sea "Lake" hydrology. By tuning a meaningful new high-resolution geochemical dataset (obtained from core MD04-2790) to a climate reference record, here, we propose a reliable chronology spanning the last 32 kyr BP. The chronology is compared to a large AMS...
Tipo: Text
Palavras-chave: Black Sea; Reservoir age; Radiocarbon; Last Glacial; Last Deglaciation; Paleoclimate.
Ano: 2011
URL: http://archimer.ifremer.fr/doc/00043/15379/12817.pdf

Estimated reservoir ages of the Black Sea since the last glacial
Provedor de dados: 5
Autores: Kwiecien, O.; Arz, H. W.; Lamy, F.; Wulf, S.; Bahr, A.; Roehl, U.; Haug, G. H.
Accelerator mass spectrometry (AMS) radiocarbon dating of ostracod and gastropod shells from the southwestern Black Sea cores combined with tephrochronology provides the basis for studying reservoir age changes in the late-glacial Black Sea. The comparison of our data with records from the northwestern Black Sea shows that an apparent reservoir age of similar to 1450 C-14 yr found in the glacial is characteristic of a homogenized water column. This apparent reservoir age is most likely due to the hardwater effect. Though data indicate that a reservoir age of similar to 1450 C-14 yr may have persisted until the Bolling-Allerod warm period, a comparison with the GISP2 ice-core record suggests a gradual reduction of the reservoir age to similar to 1000 C-14...
Tipo: Text
Palavras-chave: Mediterranean abyssal sediments; Minoan eruption; Tephra layers; Radiocarbon; Santorini; Deglaciation; History; Variability; Calibration; Resolution.
Ano: 2008
URL: https://archimer.ifremer.fr/doc/00209/31990/30430.pdf

Biochar effect on the mineralization of soil organic matter
Provedor de dados: 86
Autores: Bruun,Sander; EL-Zehery,Tarek.
The objective of this work was to verify whether the addition of biochar to the soil affects the degradation of litter and of soil organic matter (SOM). In order to investigate the effect of biochar on the mineralization of barley straw, soil was incubated with 14C-labelled barley straw with or without unlabelled biochar. To investigate the effect of straw on the mineralization of biochar, soil was incubated with 14C-labelled biochar with or without straw. In addition, to investigate the effect of biochar on old SOM, a soil labelled by applying labelled straw 40 years ago was incubated with different levels of biochar. All experiments had a control treatment, without any soil amendment. The effect of biochar on the straw mineralization was small and...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Anthropogenic dark earth; Organic matter stability; Priming effect; Radiocarbon.
Ano: 2012
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-204X2012000500005

Radiocarbon geochronology of the sediments of the São Paulo Bight (southern Brazilian upper margin)
Provedor de dados: 42
Autores: Mahiques,Michel M.; Sousa,Silvia H.M.; Burone,Leticia; Nagai,Renata H.; Silveira,Ilson C.A.; Figueira,Rubens C.L.; Soutelino,Rafael G.; Ponsoni,Leandro; Klein,Daniel A.
The aim of this work was to generate an inventory of the data on radiocarbon datings obtained from sediments of the São Paulo Bight (southern Brazilian upper margin) and to analyze the data in terms of Late Quaternary sedimentary processes and sedimentation rates. A total of 238 radiocarbon datings from materials collected using differents ampling procedures was considered for this work. The sedimentation rates varied from less than 2 to 68 cm.kyr-1. The highest sedimentation rate values were found in a low-energy (ría type) coastal system as well as in the upwelling zones of Santa Catarina and Cabo Frio. The lowest rates were found on the outer shelf and upper slopes. Our results confirm the strong dependency of the shelf currents, with an emphasis to the...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Continental margin; Quaternary; Radiocarbon; Sea-level; Sedimentation.
Ano: 2011
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652011000300006