1,721,048 research outputs found
Recent agglutinated foraminifera from the North Adriatic Sea: What the agglutinated tests can tell
No full textAgglutinated foraminifera from surface sediments of two sites (S1 and E1) in the North Adriatic Sea were investigated in order to detect their test composition and to explore possible links with the surrounding environment. Chemical-mineralogical analyses of the agglutinated tests by scanning Electron Microscopy and Energy Dispersive Spectroscopy, suggest that the chemical composition of the test surfaces generally mirrors the one of the sea-floor sediment. Only some species, as Reophax nana and Leptohalysis scottii exhibit a clear selectivity of the agglutinated grains. In detail, specimens of R. nana from site E1, which is mainly characterized by high hydrodynamic conditions at the sea-floor, show a preferential selection of mineral grains containing high concentrations
of Zircon (Zr) and Titanium (Ti) even if these elements occur in very low concentrations in the surrounding sediment. L. scottii exclusively picks mica flakes to build the test. We suggest that the compositional differences recorded in the considered agglutinated foraminiferal tests represent distinctive life strategies in order to live successfully in different environments
Benthic foraminifera as indicators of hydrologic and environmental conditions in the Ross Sea (Antarctica)
No full textThis study, present data on benthic foraminiferal assemblages from four box cores collected in different areas of the Ross Sea during the 2005 oceanographic cruise in the framework of the Italian Antarctic Research National Programme (PNRA)
Editorial
Full text linkThe present Special Issue entitled “Italian Long-Term Ecological Research for understanding ecosystem diversity and functioning. Case studies from aquatic, terrestrial and transitional domains” is the first published collection of studies performed at LTER-Italy sites which address the diversity and dynamics of ecosystems in different domains in responses to natural and anthropogenic forcing
Planktonic foraminifera response to the azores high and industrial-era global warming in the central-western Mediterranean Sea
Full text linkThe Mediterranean Sea is warming about 20 % more rapidly than global ocean and this phenomenon is
impacting ecosystems and biodiversity. Planktonic foraminifera are an important component of surface and
subsurface water ecosystems and food chains. Their species communities have been altering across the oceans
since the Industrial Era, in response to the ongoing climate change, especially in the western Mediterranean Sea,
where a significant productivity decrease has been recently reported.
Here we show planktonic foraminifera and multispecies stable isotopes from three short sediment cores,
recovered on the eastern flank of the Sicily Channel, central Mediterranean Sea. Results fully confirm the
planktonic foraminifera productivity decrease in the Industrial Era, which is especially relevant for the second
half of the 20th century. The planktonic foraminifera productivity decrease matches with a higher number of
Large Azores High events, i.e., the establishment of an exceptional and persistent winter atmospheric highpressure ridge over the western-central Mediterranean Sea. This is an unprecedented atmospheric phenomenon for the last millennia Mediterranean Sea history, as a direct response of the global warming. Surface productivity and DCM species are especially declining since ~1960 CE, at expenses of winter mixed layer taxa,
suggesting that the Azores High activity prevents a sustained water column vertical mixing and surface water
nutrient fuelling. Our results document and confirm that the climate change has already been affecting Mediterranean marine ecosystems and the basic level of the trophic chain, by extending the surface water stratification period
Globorotalia truncatulinoides in the Mediterranean Basin during the Middle–Late Holocene: Bio-Chronological and Oceanographic Indicator
No full textThe planktonic foraminiferal species Globorotalia truncatulinoides is widely used as a biostratigraphic proxy for the Quaternary in the Mediterranean region. High-resolution quantitative studies performed on sediment cores collected in the central and western Mediterranean Sea evidence a significant abundance of G. truncatulinoides during the Middle Holocene. The robust chronological frame allows us to date this bio-event to 4.8–4.4 ka Before Present (BP), very close to the base of the Meghalayan stage (4.2 ka BP). As a consequence, we propose that G. truncatulinoides can be considered a potential marker for the Middle–Late Holocene chronological subdivision. G. truncatulinoides is a deep-dwelling planktonic foraminifer and their distributional pattern in the central and western Mediterranean Sea provides a tool to monitor the onset of the regional deep vertical mixing of the water column. During the Holocene, the significant increase in the abundance of this species is in phase with the end of African Humid Period, which marks the transition from a more humid climate to the present-day semi-arid climate
Paleoceanographic reconstructions from geochemistry and ecology of planktonic foraminifera. Investigations in two key areas: the Southern ocean and the Mediterranean sea
No full textLa studio della distribuzione spaziale e temporale della associazioni a foraminiferi planctonici, campionati in zone con differente regime idrografico, ha permesso di comprendere che molte specie possono essere diagnostiche della presenza di diverse masse d’acqua superficiali e sottosuperficiali e di diversi regimi di nutrienti nelle acque oceaniche.
Parte di questo lavoro di tesi si basa sullo studio delle associazioni a foraminiferi planctonici attualmente viventi nel Settore Pacifico dell’Oceano Meridionale (Mare di Ross e Zona del Fronte Polare) e nel Mare Mediterraneo (Mar Tirreno Meridionale).
L’obiettivo di questo studio è quello di comprendere i fattori (temperatura, salinità, nutrienti etc.) che determinano la distribuzione attuale delle diverse specie al fine di valutarne il valore di “indicatori” (proxies) utili alla ricostruzione degli scenari paleoclimatici e paleoceanografici succedutisi in queste aree.
I risultati documentano che la distribuzione delle diverse specie, il numero di individui e le variazioni nella morfologia di alcuni taxa sono correlate alle caratteristiche chimico-fisiche della colonna e alla disponibilità di nutrienti e di clorofilla.
La seconda parte del lavoro di tesi ha previsto l’analisi degli isotopi stabili dell’ossigeno e del rapporto Mg/Ca in gusci di N. pachyderma (sin) prelevati da pescate di micro zooplancton (per tarare l’equazione di paleo temperatura) da un box core e da una carota provenienti dalla zona del Fronte Polare (Oceano Pacifico meridionale), al fine di ricostruire le variazioni di temperatura negli ultimi 13 ka e durante la Mid-Pleistocene Revolution. Le temperature, dedotte tramite i valori degli isotopi stabili dell’ossigeno, sono coerenti con le temperature attuali documentate in questa zona e il trend di temperatura è paragonabile a quelli riportati in letteratura anche per eventi climatici come lo Younger Dryas e il mid-Holocene Optimum.
I valori del rapporto Mg/Ca misurato tramite due diverse tecniche di analisi (laser ablation e analisi in soluzione) sono risultati sempre molto più alti dei valori riportati in letteratura per la stessa specie. La laser ablation sembra carente dal punto di vista del cleaning del campione e da questo studio emerge che le due tecniche non sono comparabili e che non possono essere usate indifferentemente sullo stesso campione. Per quanto riguarda l’analisi dei campioni in soluzione è stato migliorato il protocollo di cleaning per il trattamento di campioni antartici, che ha permesso di ottenere valori veritieri e utili ai fini delle ricostruzioni di paleotemperatura. Tuttavia, rimane verosimile l’ipotesi che in ambienti particolari come questo, con salinità e temperature molto basse, l’incorporazione del Mg all’interno del guscio risenta delle condizioni particolari e che non segua quindi la relazione esponenziale con la temperatura ampiamente dimostrata ad altre latitudini.Spatial and temporal distribution of modern planktonic foraminifera collected in different oceanographic regimes document that some species are reliable tracers of oceanographic change in surface and subsurface water.
In order to determine the factors controlling the distribution of planktonic foraminifera as a proxy for reconstruction of palaeoenvironments, we present data on live assemblages collected in the Southern Ocean (Ross Sea and Polar Front Zone) and in the Mediterranean Sea (Tyrrhenian Sea).
Results document that diversity of planktonic foraminifera, number of specimens and variations in test morphology are related to nutrient contents and to regional differences in water properties.
Oxygen isotopic composition and Mg/Ca ratios were measured in the planktonic foraminifer Neogloboquadrina pachyderma (sin) from plankton tows (in order to select the paleotemperature equation) from a box core and a core collected in the Southern Ocean in order to reconstruct the temperature variation during the last 13 kyr and during the Mid-Pleistocene Revolution. Temperature estimates from δ18O of Neogloboquadrina pachyderma (sin) are consistent with today’s temperature and record the same trend evidenced in literature.
Mg/Ca ratios have been investigated using LA-ICPMS and ultracleaning procedures on ‘bulk’ foraminifera followed by ICP-MS/ICP-AES analysis. Mg/Ca ratios are particularly high for all samples measured by both techniques and correlation of Mg/Ca with calcification temperature are not statistically significant. Laser ablation technique seems to be unsuitable for this kind of samples and in this area. Ultracleaning procedures were improved for polar samples in order to reconstruct paleotemperatures in this area. One more potential hypothesis for anomalous values is that foraminiferal Mg/Ca ratios at the PF of the Pacific Ocean may be significantly influenced by seawater carbonate chemistry, mainly in water masses with polar characteristics, including lower salinity
Climatic and environmental changes during the last glacial-interglacial transition in the joides basin and the connected slope-basin system (Western Ross Sea, Antarctica).
No full textClimatic and environmental changes during the last glacial-interglacial transition in the Ross Sea, Antarctica.
No full textFour sediment cores (ANTA99-cJ3, ANTA95-98C, KI13-C1 and KI13-C2) and two box cores (KI13-bc2 and KI13-bc4), collected in the different geological settings of the Joides Basin-Central Basin area (Ross Sea, Southern Ocean), were studied in the framework of the Italian Antarctic Project ROSSLOPE (Past and present sedimentary dynamic in the ROSS Sea: a multidisciplinary approach to study the continental SLOPE). In this work we consider only the time interval spanning from the Last Glacial Maximum (LGM) to the Present in order to investigate the palaeoclimatic and palaeoceanographic evolution of the western Ross Sea during the last deglaciation phase. Based on the abundance pattern of diatom and foraminiferal assemblages as well as different geochemical and sedimentological properties (organic carbon, grain size, biogenic silica and CaCO3 content), we propose a climatic and environmental reconstruction of the last glacial/interglacial transition in this regions of the Southern Ocean
GEOLOGIA/ Risolto il giallo dei Trilobiti scomparsi: si era inceppata la pompa biologica oceanica
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