Percorrer por autor "Quivelli, Ornella"
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- Multiproxy record of suborbital-scale climate changes in the Algero-Balearic Basin during late MIS 20-Termination IXPublication . Quivelli, Ornella; Marino, Maria; Rodrigues, Teresa; Girone, Angela; Maiorano, Patrizia; Bertini, Adele; Niccolini, Gabriele; Trotta, Samanta; Bassinot, FranckHigh-resolution quantitative analyses have been carried out in samples from the Ocean Drilling Program (ODP) Site 975 in the Algero-Balearic basin through late Marine Isotope Stage (MIS 20)-Termination IX (800-784 ka). The multi-proxy study combines data of planktonic delta O-18, delta C-13, calcareous plankton (coccolithophores, foraminifera), palynomorphs, alkenone-based sea surface temperature (SST), % alkenone tetraunsatured (% C-37:4), and terrigenous biomarkers (C-23-C-31 n-alkanes, C-22-C-30 n-alkanols) with the aim to reconstruct climate-induced paleoenvironmental changes at orbital-submillennial scale, in a crucial time interval of the Early-Midde Pleistocene transition. The surface water delta O-18(sw) has been reconstructed from delta O-18(G.bulloides) and alkenone-based SST as a proxy for salinity changes. The late MIS 20 has been subdivided in several phases based on evidence of (i) meltwater events of polar origin or from surrounding mountain glaciers, (ii) changes in the production rate of Western Mediterranean Deep Water (WMDW) and in deep water ventilation, (iii) variation in terrestrial input and river discharge, and iv) variations in the strength of the north westerlies, and polar front shift. Following a glacial stadial (lasting ca 3 kyr) marked by the strongest WMDW production, coeval with a boreal summer insolation minimum and a marked low sea level, the latest MIS 20 is characterized by a terminal stadial event (lasting ca 3.5 kyr), which is traced by the occurrence of cold-low salinity water, pointing to meltwater advection at the site location. Short-term warm and cool events occurred through Termination IX during sea level rise and insolation increase, preceding the onset of full MIS 19c, characterized by an organic rich layer (ORL) associated with insolation cycle 74. The succession of these climate and oceanographic events has been compared to evidences from other Mediterranean sites, highlighting similar basin-wide patterns, which recall the climate evolution of Termination I. The comparison of our results with the climate proxies from the Integrated Ocean Drilling Program (IODP) Site U1385 located west of Iberian margin made it possible to point at the connection between Mediterranean oceanographic and atmospheric dynamics and the northern hemisphere ice-sheet instability, providing insight on the relationship with the Atlantic meridional overturning circulation and thermal front migration. (C) 2021 Elsevier Ltd. All rights reserved.
- Paleoproductivity proxies and alkenone precursors in the Western Mediterranean during the Early-Middle Pleistocene transitionPublication . Marino, Maria; Rodrigues, Teresa; Quivelli, Ornella; Girone, Angela; Maiorano, Patrizia; Bassinot, FranckMultidisciplinary analyses (taxonomic analysis of coccolithophore assemblages, stable oxygen isotopes, marine and terrestrial biomarkers) have been carried out on sediments from Ocean Drilling Program Site 975 in the Algero-Balearic basin, through late marine isotope stage (MIS) 20-19 (800-756 ka). The aim is to compare coccolithophore paleoproductivity proxies, such as C-37 alkenone concentration and nannofossil accumulation rate (NAR), and understand their relationship with paleoceanographic condition and paleoenvironmental changes, alkenone-producing precursors and unsaturated C-37 alkenone compounds. The patterns of C-37 alkenones and NAR provide reliable information on past paleoproductivity changes since coccolith dissolution and organic matter preservation were excluded as relevant processes at the site. This is testified by the high values of Nannofossil Dissolution Index and relation between C-37 alkenone concentration and Alcohol Preservation Index, the latter used as a proxy of sea bottom ventilation in the basin. A weak mismatching between NAR and C-37 alkenone concentration records has been observed and related to paleoenvironmental factors and ecological preferences of alkenone-producing species. Temperature variations mostly controlled the alternating interspecific abundance variations of these taxa through glacial-interglacial and stadial-interstadial climate phases. The percentage abundances of alkenone-producing species, Gephyrocapsa caribbeanica and Gephyrocapsa with open central area (mainly G. margerelii-G. muellerae) strongly co-varied with the percentages of C-37:2 and C-37:3, respectively during warm and cool-cold periods, suggesting their prominent role in producing these unsaturated C-37 alkenone compounds. Moreover, Gephyrocapsa spp. with open central area > 3 mu m were likely the main C-37:4 producers during the colder late MIS 20 stadial and stadial phases. Other factors in addition to temperature influenced the paleoproductivity proxy patterns. The oceanographic condition established during MIS 20-MIS 19 deglaciation and the more nutrient-rich surface waters during the orbitally-controlled organic-rich layer deposition in the early MIS 19 enhanced primary productivity leading to higher production and preservation of total C-37 alkenones.
- Surface and deep water variability in the Western Mediterranean (ODP Site 975) during insolation cycle 74: high-resolution calcareous plankton and molecular biomarker signalsPublication . Quivelli, Ornella; Marino, Maria; Rodrigues, Teresa; Girone, Angela; Maiorano, Patrizia; Abrantes, Fatima; Salgueiro, Emilia; Bassinot, FrankWe reconstructed changes in productivity and surface/subsurface and deep-water dynamics in the Western Mediterranean through a multi-proxy study of Ocean Drilling Program Site 975 between late Marine Isotope Stage (MIS) 20 and early interglacial MIS 19. Our high-resolution study (down to similar to 200-year resolution) combines calcareous plankton assemblages (coccolithophores and foraminifera), biomarkers (C-37-alkenones, n-alkanes, n-alcohols) and elemental proxies (total organic carbon, total nitrogen, calcium carbonate). Surface water conditions are derived (i) from high-resolution delta O-18 and delta C-13 records obtained from the planktonic foraminifer Globigerina bulloides, and (ii) from summer and winter, foraminifera-based sea surface temperature reconstructions (SSTJAS-foram, SSTJFM-foram) achieved through transfer function. The integration of the whole dataset makes it possible to identify in the Balearic Sea, and to accurately characterize for the first time, an Organic Rich Layer (ORL) during latest MIS 20-early MIS 19, close to i-cycle 74. Its presence is marked firstly by higher values of total nitrogen (TN) and an increase of total C-37-alkenone and total organic carbon (TOC) preserved in the sediments. The multi-proxy approach reveals that the deglacial phase played a prominent role for ORL formation that was characterized by centennial scale phases. The alcohol preservation index (API) suggests that the shoaling of the circulation, which boosted marine productivity, started in the deglaciation and, in combination with freshening by Atlantic water inflow/riverine input and surface water buoyancy during sea level rising, culminated during the ORL event. At this time calcareous plankton proliferated on subsurface-surface waters, benefiting from ameliorating conditions, which promoted maximum marine productivity and higher organic matter preservation on the seafloor.