1000 resultados para Globigerinoides tenellus


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The oxygen isotopic composition of pore waters squeezed from sediments in Hole 817C co-varies with the oxygen isotopic composition of Globigerinoides ruber below 8 mbsf. The magnitude of the variation in the pore water d18O is approximately 30% of the variation in the foraminifers. Overall, the d18O of the pore waters increases down the core, a trend that is also present in the Cl- concentrations. The variations in the d18O of pore waters may be the result of either of two phenomena. First, these may reflect original variations in the waters, the magnitude of which has been subsequently reduced by process of diffusion. Second, these may reflect recrystallization of the precursor sediment and isotopic exchange between the fluids and the recrystallized sediment. At the moment data are not available to ascertain which process is responsible although the correlation between the Cl- and the d18O data suggests that these values reflect the original composition modified by diffusion.

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The delta18O values of planktonic foraminifera increased in the Caribbean by about 0.5? relative to the equatorial East Pacific values between 4.6 and 4.2 Ma as a consequence of the closure of the Central American Gateway (CAG). This increase in delta18O can be interpreted either as an increase in Caribbean sea surface (mixed layer) salinity (SSS) or as a decrease in sea surface temperatures (SST). This problem represents an ideal situation to apply the recently developed paleotemperature proxy delta44/40Ca together with Mg/Ca and d18O on the planktic foraminifer Globigerinoides sacculifer from ODP Site 999. Although differences in absolute temperature calibration of delta44/40Ca and Mg/Ca exist, the general pattern is similar indicating a SST decrease of about 2-3 8C between 4.4 and 4.3 Ma followed by an increase in the same order of magnitude between 4.3 and 4.0 Ma. Correcting the delta18O record for this temperature change and assuming that changes in global ice volume are negligible, the salinity-induced planktonic delta18O signal decreased by about 0.4? between 4.4 and 4.3 Ma and increased by about 0.9? between 4.3 and 4.0 Ma in the Caribbean. The observed temperature and salinity trends are interpreted to reflect the restricted exchange of surface water between the Caribbean and the Pacific in response to the shoaling of the Panamanian Seaway, possibly accompanied by a southward shift of the Intertropical Convergence Zone (ITCZ) between 4.4 and 4.3 Ma. Differences in Mg/Ca- and delta44/40Ca-derived temperatures can be reconciled by corrections for secular variations of the marine Mg/Ca[sw] and delta44/40Ca, a salinity effect on the Mg/Ca ratio and a constant temperature offset of ~2.5 C between both SST proxy calibrations.

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Variations in sea surface temperature (SST), d18O of sea water (?18Ow), and salinity were reconstructed for the past 68 ka using a sediment core (AAS9/21) from the eastern Arabian Sea (EAS) in order to understand the changes in evaporation and precipitation associated with the monsoon system. The Mg/Ca-derived SST record varies by ~4C; it shows that marine isotope stage (MIS) 4 was warmer than MIS 3, that the Last Glacial Maximum was 4C cooler than the present, and that there was a 2C increase within the Holocene. MIS 4 records higher d18Ow and salinity values than MIS 2, suggesting variable flow of low-salinity Bay of Bengal flow into the EAS during glacial periods. The transition from MIS 4 to MIS 3 was marked with a conspicuous shift from higher to lower d18Ow values, which reflects a decrease in the evaporation-precipitation budget in the EAS, perhaps due to the strengthening of southwest monsoon. Monsoon reconstructions based on d18Ow reveal that monsoon-driven precipitation was higher during MIS 3 and MIS 1 and was lower during MIS 2 and MIS 4. This is consistent with earlier monsoon reconstructions based on upwelling indices from the western Arabian Sea. However, the amplitude of monsoon fluctuations derived through upwelling indices and d18Ow varies significantly, which may indicate spatial variability of monsoon rainfall.

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Nine new species of smut fungi, belonging to eight genera, are described from Australia: Dermatosorus schoenoplecti Vnky & R.G. Shivas, on Schoenoplectus mucronatus, Entyloma grampiansis Vnky & R.G. Shivas, on Hydrocotyle laxiflora, Macalpinomyces brachiariae Vnky, C. Vnky & R.G. Shivas, on Brachiaria holosericea, M. digitariae Vnky & R.G. Shivas, on Digitaria gibbosa, Restiosporium baloskionis Vnky & R.G. Shivas, on Baloskion tetraphyllum, Thecaphora maireanae R.G. Shivas & Vnky, on Maireana pentagona, Tilletia cape yorkensis Vnky & R.G. Shivas, on Whiteochloa airoides, Urocystis chorizandrae J. Cunnington, R.G. Shivas & Vnky, on Chorizandra enodis, and Ustanciosporium tenellum R.G . Shivas & Vnky, on Cyperus tenellus. New combinations are: Macalpinomyces ordensis(R.G. Shivas & Vnky) Vnky & R.G. Shivas (based on Sporisorium ordense, type on Brachiaria pubigera, Australia), and Sporisorium setariae (McAlpine) Vnky & R.G. Shivas (based on Sorosporium setariae, type on Setaria glauca, Australia).

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(Philodromus)(Tibellus)1:(1)P. xinjiangensis sp. nov.,P. mysticus,(2)T. zhui sp. nov.,,T. tenellus(1),(2)72

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C-37 unsaturated alkenones were analyzed on a core retrieved from the middle Okinawa Trough. The calculated U-37(K') displays a trend generally parallel with those of the oxygen isotopic compositions of two planktonic foraminiferal species, Neogloboquadrina dutertrei and Globigerinoides sacculifer, suggesting that in this region, SST has varied in phase with global ice volume change since the last glacial -interglacial cycle. The U-37(K')-derived SST ranged from ca. 24.0 to 27.5 degrees C, with the highest value 27.5 degrees C occurring in marine isotope stage 5 and the lowest similar to 24.0 degrees C in marine isotope stage 2. This trend is consistent with the continental records from the East Asian monsoon domain and the marine records from the Equatorial Pacific. The deglacial increase of the U-37(K')-derived SST is similar to 2.4 degrees C from the Last Glacial Maximum to the Holocene. (c) 2007 Elsevier B.V. All rights reserved.

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SSTMg/CaSSTSSTICP-OESMg/Ca 53(N1840.23E13537.113225m)Globigerinoides ruberMg/CaMg/CaMg(30%H2O20.1M NaOH90)(250l 0.001N HNO3 10S)(ICP-OES)Mg/CaAr0.5L/min0.5L/min-1.5L/min0.2Mpa0-0.4Mpa20rpm0-125rpmRF1150W750W-1500W15.5mm8-21mmMg/Ca=3.333mmol/molMg/Ca<0.5%,1%53Mg/CaRSD2.7%Lea(2000)G. ruber()Mg/CaSST:Mg/Ca(mmol/mol) 0.30exp[0.089SST()]SST280.3