1,721,845 research outputs found
Présentation de la datation 14C en spectrométrie de masse par accélérateur
No full textArnold Maurice, Bard Edouard, Duplessy Jean-Claude, Valladas Hélène. Présentation de la datation 14C en spectrométrie de masse par accélérateur. In: Les Nouvelles de l'archéologie, n°27, printemps 1987. pp. 68-69
Biomarker indices and concentrations and biomarker-based temperature estimates from the Iberian Margin core MD95-2042
No full textThis dataset provides the following information for core MD95-2042: depth, age, summed OH-GDGT, iGDGT, and di-unsaturated and tri-unsaturated C37 alkenone concentrations, OH-GDGT-based, iGDGT-based, and alkenone-based paleothermometric indices, GDGT-2/GDGT-3 ratio, and biomarker-based sea surface temperature (SST) and 0‐ to 200‐m sea temperature (subT; gamma function probability distribution for target temperatures with a = 4.5 and b = 15) estimates. Sediment samples were taken every 5 cm from core MD95-2042 and homogenized before lipid extraction. The lipid extracts were splitted into two fractions: one for alkenone analysis by gas chromatography coupled to a flame ionization detector, and the other for GDGT analysis by high-performance liquid chromatography coupled to mass spectrometry. All GDGT analyses were done in duplicate. The 1σ analytical uncertainties from 37 replicate analyses of the core catcher sample from core MD95-2042 are 0.007 (0.4 °C) for RI-OH, 0.008 (0.2 °C) for RI-OH′, 0.003 (0.2 °C) for TEX86, 0.238 for GDGT-2/GDGT-3, and 0.010 (0.26 °C) for UK′37. RI-OH′-SST estimates are from the following global calibration: SST = (RI-OH′ + 0.029)/0.0422 (Fietz et al., 2020). RI-OH-SST estimates are from the following global calibration: SST = (RI-OH − 1.11)/0.018 (Lü et al., 2015). TEX86H-SST estimates are from the following regional paleocalibration: SST = 68.4 × TEX86H + 33.0 (Darfeuil et al., 2016). UK′37-SST estimates are from the following global calibration: SST = 29.876 × UK′37 − 1.334 (Conte et al., 2006). Bayesian calibrations were also used for TEX86-SST and TEX86-subT estimates (BAYSPAR; Tierney & Tingley, 2014, 2015) and for UK′37-SST estimates (BAYSPLINE; Tierney & Tingley, 2018). Alkenone data covering the 160–70 and 70–0 ka BP periods are from Davtian et al. (2021) and Darfeuil et al. (2016), respectively. GDGT data covering the 160–45 ka BP period are from Davtian et al. (2021). The age model of core MD95-2042 for the 160–43 and 43–0 ka BP periods was obtained by tuning to Chinese speleothems (Cheng et al., 2016) and by recalibrating existing 14C ages with the Marine20 calibration curve (Heaton et al., 2020), respectively. MIS, Marine Isotope Stage; GDGT, glycerol dialkyl glycerol tetraether; and N/A, not available
Planktonic foraminifera δ18O, Mg/Ca and UK37 ratios and benthic foraminifera δ18O of sediment core MD97-2125
No full textTo derive and age-depth model radiocarbon ages were measured on the planktonic foraminifera species Globigerinoides ruber alba. Stable oxygen isotope ratios were measured on planktonic and benthic foraminifera. For benthic d18O measurements were done on 5-7 specimens of Cibicides wuellerstorfi from the 250-355 micrometer size fraction. Two species of planktonic foraminifera were analysed: Globigerinoides ruber alba and Trilobatus sacculifer. 5-7 shells from the 250-355 micrometer size fraction were analysed. Mg/Ca ratios were measured on the same two planktonic foraminifera species. For the Mg/Ca measurements 30 specimens were used that were cleaned using an oxidative cleaning procedure. Seawater temperatures were calculated using T = ln(Mg/Ca/0.102)/0.31 (doi:10.1029/2002PA000846) for G. ruber alba and T = ln(Mg/Ca/0.09)/0.37 (doi:10.1029/2001GC000200) for T. sacculifer. Since the latter calibration was established using the Cd cleaning, a correction of -8 % was applied prior to Mg/Ca-SST conversion. Additional seawater temperature estimates were calculated from UK37' ratios which were converted to SST using T (°C) = -0.957 (54.293 * Uk'37) - (52.894 (Uk'37)^2) (28.321 (Uk'37)^3) (doi:10.1029/2005GC001054)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Radiocarbon ages of sediment core MD97-2125
No full textTo derive and age-depth model radiocarbon ages were measured on the planktonic foraminifera species Globigerinoides ruber alba. Stable oxygen isotope ratios were measured on planktonic and benthic foraminifera. For benthic d18O measurements were done on 5-7 specimens of Cibicides wuellerstorfi from the 250-355 micrometer size fraction. Two species of planktonic foraminifera were analysed: Globigerinoides ruber alba and Trilobatus sacculifer. 5-7 shells from the 250-355 micrometer size fraction were analysed. Mg/Ca ratios were measured on the same two planktonic foraminifera species. For the Mg/Ca measurements 30 specimens were used that were cleaned using an oxidative cleaning procedure. Seawater temperatures were calculated using T = ln(Mg/Ca/0.102)/0.31 (doi:10.1029/2002PA000846) for G. ruber alba and T = ln(Mg/Ca/0.09)/0.37 (doi:10.1029/2001GC000200) for T. sacculifer. Since the latter calibration was established using the Cd cleaning, a correction of -8 % was applied prior to Mg/Ca-SST conversion. Additional seawater temperature estimates were calculated from UK37' ratios which were converted to SST using T (°C) = -0.957 (54.293 * Uk'37) - (52.894 (Uk'37)^2) (28.321 (Uk'37)^3) (doi:10.1029/2005GC001054)
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