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- Data report: IODP Site U1387: the revised splice between Sections U1387B-18X-3 and U1387C-8R-3 (>171.6 mcd)Publication . Voelker, Antje; Jimenez-Espejo, F. J.; Bahr, A.; Rebotim, Andreia; Cavaleiro, Catarina; Salgueiro, Emilia; Röhl, U.; Stow, Dorrik A. V.; Hernández-Molina, F. J.; Alvarez Zarikian, Carlos A.; Expedition 339 ScientistsThe Expedition 339 shipboard splice of Integrated Ocean Drilling Program (IODP) Site U1387 deeper than ~155 meters composite depth (mcd) is based on a composite of the magnetic susceptibility and natural gamma radiation data. When generating high-resolution paleoceanographic reconstructions for the Mid-Pleistocene Transition and early Pleistocene sections of Site U1387, it quickly became obvious that proxy data misfits existed at several splice transitions. Thus, a revised splice was generated for Site U1387 below Core 339-U1387B-18X based on X-ray fluorescence– derived element records (e.g., ln[Fe/Ca]) and the stable isotope records obtained for planktonic and benthic foraminifers. Corrections were needed at most of the splice transitions below Core 339-U1387A-19X, with adjustments ranging from a few centimeters to several meters. In addition, Core 339-U1387A-33X and sections of Core 36X were integrated into the revised splice to replace Core 339-U1387C-2R and sections of Core 5R, respectively. The replacement of Core 339-U1387C-2R with Core 339-U1387A33X is an option for the intended paleoceanographic research and not essential for lower resolution studies. The splice tie point table, therefore, also includes an option for a splice that retains Core 339-U1387C-2R. The extensive revision of the shipboard splice reveals that making a splice for sediment sequences rich in contourite layers and coring disturbances (biscuiting in the extended core barrel cores) can be tricky and that data misfits at splice transitions are not necessarily a data problem but could indicate a splice problem.
- Assessment of sea surface temperature changes in the Gulf of Cadiz during the last 30 ka: Implications for glacial changes in the regional hydrographyPublication . Penaud, A.; Eynaud, F.; Voelker, Antje; Kageyama, M.; Marret, F.; Turon, J.L.; Blamart, D.; Mulder, T.; Rossignol, L.New dinocyst analyses were conducted on core MD99-2339 retrieved from the central Gulf of Cadiz. Dinocyst and foraminiferal assemblages from this core are combined with existing data off SW Portugal and NW Morocco to investigate past hydrological and primary productivity regimes in the subtropical NE Atlantic Ocean over the last 30 ka. Our results have revealed highest upwelling intensity during Heinrich Stadial 1 (HS 1) and the Younger Dryas and weaker upwelling cells during the Last Glacial Maximum (LGM) and HS 2, off the SW Iberian and NW Moroccan margins. Similar assemblages between the Gulf of Cadiz and the NW Moroccan margin, and distinct species off Portugal, were observed during the cold climatic extremes that punctuated the last 30 ka. This pattern has been linked to the occurrence of a hydrological structure between SW Iberia and Cadiz during the last glacial period, perhaps similar to the modern Azores Front. This front was probably responsible locally for heterotrophic dinocysts found in the Gulf of Cadiz during the last glacial period, even if this sector is not conductive to upwelling phenomena by Ekman transport. Regional reconstructions of paleo-sea-surface temperatures (SSTs) using dinocyst and foraminiferal transfer functions, as well as alkenones, are also discussed and depict coherent scenarios over the last 30 ka. Seasonal reconstructions Correspondence to: A. Penaud (aurelie.penaud@univ-brest.fr.) of LGM SSTs obtained with this multi-proxy panel are discussed jointly with model outputs in order to contribute to ongoing efforts in model-data comparison
- Mediterranean outflow conditions during the early to middle Pleistocene linked to precession forcingPublication . Voelker, Antje; Salgueiro, Emilia; Henning, KuhnertThe Mediterranean Outflow Water (MOW) is an important intermediate depth water mass in the North Atlantic. Here we reconstruct changes in the MOW during the early Pleistocene interval from 630 to 1760 ky, encompassing the Mid-Pleistocene Transition (MPT), which marks an important change in orbital climate forcing. Neither MOW ventilation nor MOW flow strength reveal changes related to the MPT, but incorporate variations related to precession (insolation) forcing. The MPT related change to higher glacial benthic δ O values occurs earlier at Site U1387 than in most deep-sea records, i.e. with MIS 26 instead of the MIS 24 to MIS 22 interval
- Data report: diatom and silicoflagellate records of marine isotope Stages 25-27 at IODP Site U1387, Faro DriftPublication . Ventura, C.; Abrantes, Fatima; Loureiro, I.; Voelker, Antje; Stow, Dorrik A. V.; Hernandez-Molina, F. Javier; Alvarez Zarikian, Carlos A.; Expedition 339 ScientistsDuring Integrated Ocean Drilling Program Expedition 339, the shipboard micropaleontological studies of Site U1387 core catcher samples revealed the preservation of diatoms and radiolarians in specific depths from early Pleistocene age (900–1000 ka). To evaluate the ecological significance of those diatoms, we analyzed 98 samples from the intervals of 244 to 274 m along the corrected splice, corresponding to marine isotope Stage (MIS) 25 to MIS 29, for the abundance of diatoms and silicoflagellates. In 6 samples, the composition of the diatom assemblage was determined as well. Although most samples were barren of siliceous microfossils, the downcore record revealed two intervals, 249–252 corrected meters composite depth (cmcd) and 263–265 cmcd, where diatoms and silicoflagellates reach their maximum values. These maxima occurred from the MIS 26/25 transition to interglacial MIS 25, and again during early MIS 27. The diatom assemblage includes 27 identified taxa with Chaetoceros (Hyalochaete) resting spores being dominant and Thalassionema nitzschioides and Paralia sulcata significant. The Chaetoceros spores clearly indicate strong influence of seasonal upwelling and associated high primary productivity. Special to the diatom record is, however, the occurrence of the large-diameter (>125 µm) centric diatoms Coscinodiscus asteromphalus, Coscinodiscus apiculatus, and Coscinodiscus cf. gigas that imply incursions of low-nutrient, open-ocean water into the southern Portuguese coast during MIS 25.
- Planktonic foraminifera evidence for surface-water conditions off Southern Portugal during Mid-Pleistocene marine isotope stages 20 to 24 (790 – 940 ky)Publication . Mega, Aline; Salgueiro, Emilia; Voelker, AntjeCharacterized by a drastic change in the deep thermohaline circulation, the Mid Pleistocene Transition (MPT) was a global climatic event resulted in more intense and longer lasting glacial periods and cooler sea -surface temperatures. The present study's objective is characterized surface -water variations during the MPT interval at the mid -latitude southern Portuguese margin using planktonic foraminifera faunal data from Site U1387. Stratigraphy records reveals dominantly tropical and subtropical species interrupted by incursions of subpolar waters when the North Atlantic's subarctic front moved to southernmost position during the MPT.
- Data report: early Pleistocene calcareous nannofossils, IODP Expedition 339, Site U1387Publication . Balestra, B.; Voelker, Antje; Flores, J.A.; Stow, D. A. V.; Hernandez-Molina, F. Javier; Alvarez Zarikian, Carlos A.; Expedition 339 ScientistsWe present a revision and refinement of semiquantitative analyses of calcareous nannofossil assemblages in early Pleistocene samples from Holes U1387A and U1387C recovered toward the eastern end of the Faro Drift (36°48.3210N, 7°43.1321W) during Integrated Ocean Drilling Program Expedition 339, Mediterranean Outflow (November 2011–January 2012). The record is characterized by intervals very rich in calcareous nannofossils that are in general moderately to well preserved. On the other hand, the record contains an interval directly above the youngest dolomite layer in Section 339-U1387C-19R-4 (~0.7 m) where no coccoliths were preserved. The new stratigraphic constraints of events such as the lowest occurrence (LO) of large Gephyrocapsa, the highest occurrence (HO) of Calcidiscus macintyrei (1.66 Ma), the LO of medium-sized Gephyrocapsa group, and the HO of Discoaster brouweri (1.95 Ma) allow better interpretation of the isotope stratigraphy applied to this interval.