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| Tripati, Aradhna; Darby, Dennis. |
| Earth's modern climate is defined by the presence of ice at both poles, but that ice is now disappearing. Therefore understanding the origin and causes of polar ice stability is more critical than ever. Here we provide novel geochemical data that constrain past dynamics of glacial ice on Greenland and Arctic sea ice. Based on accurate source determinations of individual ice-rafted Fe-oxide grains, we find evidence for episodic glaciation of distinct source regions on Greenland as far-ranging as similar to 68 degrees N and similar to 80 degrees N synchronous with ice-rafting from circum-Arctic sources, beginning in the middle Eocene. Glacial intervals broadly coincide with reduced CO2, with a potential threshold for glacial ice stability near similar to 500... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00434/54587/55976.pdf |
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| Leutert, Thomas J.; Sexton, Philip F.; Tripati, Aradhna; Piasecki, Alison; Ling Ho, Sze; Nele Meckler, A.. |
| Applying the clumped isotope (Δ47) thermometer to foraminifer microfossils offers the potential to significantly improve paleoclimate reconstructions, owing to its insensitivity to the isotopic composition of seawater (unlike traditional oxygen isotope (δ18O) analyses). However, the extent to which primary Δ47 signatures of foraminiferal calcites can be overprinted during diagenesis is not well known. Here, we present Δ47 data as well as high-resolution (∼10 kyr) δ18O and δ13C middle Eocene time series, measured on benthic and planktic foraminifera from ODP/IODP Sites 1408, 1409, 1410, 1050, 1260 and 1263 in the Atlantic Ocean. The sites examined span various oceanographic regimes, including the western tropical to mid-latitude North Atlantic, and the... |
| Tipo: Text |
Palavras-chave: Clumped isotopes; Foraminifera; Diagenesis; Eocene; Stable-isotope geochemistry; Preservation. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00495/60683/64757.pdf |
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| Zarkogiannis, Stergios D.; Antonarakou, Assimina; Tripati, Aradhna; Kontakiotis, George; Mortyn, P. Graham; Drinia, Hara; Greaves, Mervyn. |
| This study provides evidence that ambient seawater density influences calcification and may account for the observed planktonic foraminifera shell mass increase during glacial times. Volumes of weighed fossil Globigerina bulloides shells were accurately determined using X-ray Computer Tomography and were combined with water density reconstructions from Mg/Ca and delta O-18 measurements to estimate the buoyancy force exerted on each shell. After assessment of dissolution effects, the resulting relationship between shell mass and buoyancy suggests that heavier shells would need to be precipitated in glacial climates in order for these organisms to remain at their optimum living depth, and counterbalance the increased buoyant force of a denser, glacial ocean.... |
| Tipo: Text |
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| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00481/59268/61983.pdf |
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| Guillermic, Maxence; Misra, Sambuddha; Eagle, Robert; Tripati, Aradhna. |
| Constraints on the evolution of atmospheric CO2 levels throughout Earth's history are foundational to our understanding of past variations in climate. Despite considerable effort, estimates of past CO2 levels do not always converge and therefore new records and proxies are valuable. Here we reconstruct atmospheric CO2 values across major climate transitions over the past 17 million years using the boron isotopic composition (δ11B) of planktic foraminifera from 89 samples obtained from two sites in the West Pacific Warm Pool, Ocean Drilling Program (ODP) Sites 806 and 807. These sites are in a region that today is in equilibrium with the atmosphere and are thought to have been in equilibrium with the atmosphere for the interval studied. We use... |
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| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00678/79045/81493.pdf |
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| Came, Rosemarie E.; Azmy, Karem; Tripati, Aradhna; Olanipekun, Babatunde-john. |
| Widespread application of the novel clumped isotope paleothermometer (Δ47) using dolomite samples from shallow crustal settings has been hindered by a lack of adequate constraints on clumped isotope systematics in dolomites that formed at temperatures greater than 50 °C. Consequently, many high-temperature applications involving diagenetic dolomites have required an assumption that the relationship between temperature and Δ47 in diagenetic dolomite resembles the theoretical temperature dependence for calcite. Here we present Δ47 results from dolomite cements for which precipitation temperatures were determined independently using fluid inclusion microthermometry. We compare a rock-based “calibration” for samples from the temperature range of ∼73 to 176 °C... |
| Tipo: Text |
Palavras-chave: Clumped isotopes; Dolomite; Calibration. |
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00357/46791/46657.pdf |
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| Guillermic, Maxence; Misra, Sambuddha; Eagle, Robert; Villa, Alexandra; Chang, Fengming; Tripati, Aradhna. |
| Boron isotope systematics of planktonic foraminifera from core-top sediments and culture experiments have been studied to investigate the sensitivity of delta B-11 of calcite tests to seawater pH. However, our knowledge of the relationship between delta B-11 and pH remains incomplete for many taxa. Thus, to expand the potential scope of application of this proxy, we report delta B-11 data for seven different species of planktonic foraminifera from sediment core tops. We utilize a method for the measurement of small samples of foraminifera and calculate the delta B-11-calcite sensitivity to pH for Globigerinoides ruber, Trilobus sacculifer (sacc or without sacc), Orbulina universa, Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globorotalia... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00687/79861/82712.pdf |
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| Li, Huashu; Liu, Xingqi; Tripati, Aradhna; Feng, Shengnan; Elliott, Ben; Whicker, Chloe; Arnold, Alexandrea; Kelley, Anne Marie. |
| In the carbonate-water system, at equilibrium, the oxygen isotopic composition of carbonate is dependent not only on the temperature but also on the isotopic composition of host water in which the carbonate is formed. In this study, lake surface sediment and water samples were collected from 33 terminal lakes in Western China to evaluate controls on the oxygen isotopic composition of lacustrine authigenic carbonates (ä18Ocarb) and its spatial distribution. Our results show that water oxygen isotopic composition (ä18Owater) rather than lake summer water temperature ( Twater), is the main determinant of ä18Ocarb, irrespective of whether oxygen isotope equilibrium is achieved. There are significant linear correlations between ä18Ocarb and elevation, as well... |
| Tipo: Text |
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| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00653/76549/77666.pdf |
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| Lee, Hung‐i; Mitchell, Jonathan L.; Tripati, Aradhna; Lora, Juan M.; Chen, Ge; Ding, Qinghua. |
| Using a global space‐time diagram of column water vapor (CWV) at 30° N latitude from daily reanalysis data, we find two quasi‐stationary parts of atmospheric rivers (QSARs) that feature locally enhanced CWV and evolve from the Eastern Pacific/Atlantic basins in the winter to the Western Pacific/Atlantic in the summer. East Asian Summer Monsoon onset coincides with the time CWV in the Pacific QSAR first exceeds 40 mm, which also typically occurs just before it makes landfall. QSARs exist in 39‐year (1979–2017) daily climatological CWV, demonstrating the seasonal cycles of these features are quasi‐stationary and potentially useful for monsoon onset prediction. East Asian Summer Monsoon onset is particularly predictable following El Niño‐Southern Oscillation,... |
| Tipo: Text |
Palavras-chave: Atmospheric rivers; Monsoon; Rossby wave breaking. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00592/70439/68539.pdf |
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