We investigate the geometry and ventilation of the water masses within bathyal depths (~1,500 to ~2,500 m) of the Southeast Pacific (SEP), inferring the lower depth limit variations of the Antarctic ...Intermediate Water (AAIW) since ~22 kyr cal. BP. We use three cores collected at the upper limit of the Pacific deep waters, between 41°S and 49°S, and one core at a greater depth within this same water mass, at 46°S. The benthic foraminiferal assemblages and carbon and oxygen isotopes are used to show strong linkages between the timing of the deglacial Southern Ocean upwelling events and changes in the vertical extension and ventilation of the AAIW. In accordance with local/sublocal oxygen reconstructions, we propose at least three states of ventilation‐AAIW vertical extension: (i) the late glacial and the Antarctic Cold Reversal (ACR): AAIW depth‐limit shoals, as its formation zone moves northward; (ii) the deglaciation (excluding the ACR): the O2 enrichment of the AAIW and the dominance of benthic species Trifarina angulosa indicate ventilated AAIW, along with a deepening of its lower limit; and (iii) the Holocene: enhanced influence of the Pacific deep water at bathyal depths (1,500–2,500 m) in the SEP north of ~46°S and the circumpolar deep water south of ~46°S.
Key Points
We reconstructed the AAIW and PDW ventilation and geometry using δ13C, δ18O, and benthic foraminifera assemblages
We observe a deepening of the AAIW during SO upwelling events during Termination I
This deepening is probably accompanied by a southern extension of the AAIW
A detailed tephrochronological study was undertaken in three deep-sea cores collected in the Tyrrhenian and Ionian Seas. The age and the origin of the marine tephra were inferred from oxygen isotope ...records of foraminifera and from major element compositions of glass-shards. Seventy-one eruptions were detected in the time interval 90,000–200,000 yrs during which the volcanoes of the Roman and Campanian regions and of the southern Italy were in activity. This is attested by the consistency of the geochemical compositions of both marine and terrestrial deposits. Most of the marine tephra consisted in trachytes and phonolites characterizing a Roman and Campanian origin. Several tephra were proposed as key-horizons for proximal and distal sediments. Among them, one tephra originating from Mount Etna (149,300 yrs) and five tephra from Pantelleria island (130,000 yrs, 163,600 yrs, 192,500 yrs, 197,400 yrs and 198,400 yrs) were northerly dispersed. Several other key horizons originated from the Campanian or Roman provinces were detected as far as 1000 km from the vents.
Sea surface reservoir ages must be known to establish a common chronological framework for marine, continental, and cryospheric paleoproxies, and are crucial for understanding ocean-continent ...climatic relationships and the paleoventilation of the ocean. Radiocarbon dates of planktonic foraminifera and tephra contemporaneously deposited over Mediterranean marine and terrestrial regions reveal that the reservoir ages were similar to the modern one (∼400 years) during most of the past 18,000 carbon-14 years. However, reservoir ages increased by a factor of 2 at the beginning of the last deglaciation. This is attributed to changes of the North Atlantic thermohaline circulation during the massive ice discharge event Heinrich 1.
Sea surface temperatures were reconstructed over the last 30,000 years from alkenone paleothermometry (SST‐alk) and planktonic foraminifera assemblages using the Modern Analog Technique (MAT) ...(SST‐foram) along two cores of the Mediterranean Sea: MD84‐632 (Levantine basin) and MD04‐2797 (Siculo‐Tunisian Strait). Oxygen isotope of planktonic foraminifera G. bulloides for core MD04‐2797 and G. ruber for core MD84‐632 were also determined. SST‐alk in the Levantine basin indicate colder values at the Last Glacial Maximum (LGM) (∼14°C) than earlier established from MAT, and a cooling amplitude of 6°–7°C, comparable to the central Mediterranean Sea. Climatic events such as the Younger Dryas (YD) and Heinrich events 1 and 2 (H1 and H2) were times of significant cooling in the two cores. In the Eastern basin, values of local seawater oxygen isotope, δw, indicate relatively saltier waters during the LGM and deglaciation than today, with increasing δw values (higher salinity) in the Eastern basin and decreasing ones (lower salinity) in the central Mediterranean Sea, during cold stadials. The observed alterations of surface water properties (T and δw) in the central and eastern Mediterranean at the LGM are consistent with model experiments showing slightly lower evaporation in the Mediterranean than today, except for the Eastern basin.
A detailed tephrostratigraphic study supported by stable isotope (δ18O) analyses and AMS 14C dating was carried out on a high sedimentation rate deep-sea core recovered in the northern Ionian Sea. ...Eight tephra layers were recognised, all originated from explosive eruptions of southern Italian volcanoes. These tephra layers are correlated with terrestrial proximal counterparts and with both marine and lacustrine tephra already known in the central Mediterranean area. The oldest tephra (dated at ca. 19.4ka cal BP) is tentatively correlated to the Monte Guardia eruption from Lipari Island. Two other rhyolitic tephra layers were correlated with the explosive volcanic activity of Lipari Island: Gabellotto-Fiumebianco/E-1 (8.3ka cal BP) located close to the interruption of Sapropel S1 deposit, and Monte Pilato (ca. AD 1335) in the uppermost part of the core. The Na-phonolitic composition of the other five recognised tephra layers indicates the Somma-Vesuvius as the source. The composition is quite homogeneous among the five tephra layers, and fits that of the Mercato proximal deposits. Beyond the striking chemical similarity with the Mercato eruption, these tephra layers span over ca. 2000years, preventing correlation with the single well known Plinian eruption of the Somma-Vesuvius. Therefore, at least two of these tephra layers were assigned to an interplinian activity of the Somma-Vesuvius between the eruptions of Mercato and Avellino, even though these eruptions remains poorly constrained in the proximal area. By contrast, the most prominent tephra layer (2mm white tephra visible at naked eyes) was found within the S1a Sapropel interval. Despite the possible complication for the presence of similar eruption with different ages we argue that Mercato is probably a very good marker for the onset of sapropelic condition in the Ionian Sea and can be used for land-sea correlations for this important climatic event. More in general, these data allow a significant update of the knowledge of the volcanic ash dispersal from Lipari and Somma-Vesuvius volcanoes.
► 8 Tephra layers are present across the last 20ka in the marine core MD90-918. ► Most of these tephra are derived from Somma-Vesuvius and Aeolian Islands. ► We provide new clues about the volcanic activity from Lipari and Somma-Vesuvius. ► Results provide new data of ash dispersal from Lipari and Somma-Vesuvius volcanoes. ► Mercato tephra layer is a powerful time marker for the onset of Sapropel S1a interval.
We have measured the diffusion coefficients, D, of aqueous micelles formed by cetyltriethyl-, cetyltripropyl- and cetyltributyl-ammonium bromides (CTEABr, CTPABr and CTBABr, respectively) and ...cetyltriethyl- and cetyltripropyl-ammonium hydroxides (CTEAOH and CTPAOH, respectively) by dynamic light scattering (DLS) at several temperatures from 15 to 55 °C and a range of surfactant (0.01–0.05 M) and salt (0.02–0.06 M NaBr; 0.05–0.3 M NaOH) concentrations. From values of D, we derived the respective fractional ionization values of micellar surfaces. For surfactants with bromide counterion we obtained fits of the diffusivity data using the linear interaction/DLVO approach, thus yielding estimates of the micellar hydrodynamic radius, Rh, and the micellar fractional ionization, α, which ranged from 0.26 to 0.35. For CTEAOH and CTPAOH, the fits appeared to be poorly sensitive to changes in the London-Van der Waals interactions, as expressed by the Hamaker constant, and only a large fractional ionization could account for the observed diffusivities.
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•Cetyltrialkylammonium bromide and hydroxide micelles were investigated by dynamic light scattering.•Linear inteaction-DLVO theory was adopted as a simple approach to evaluate interaction behavior of micelles.•Micelles remained essentially spherical throughout the temperature and ionic strength ranges.•Fractional ionization, α, for Br- micelles ranged from 0.26 to 0.35, with Hamaker parameters increasing with the head group bulk.•Fractional ionization for OH- micelles is much higher (0.58 to 0.65); fits are rather insensitive to the Hamaker parameter.
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