Climate change signal in the ocean circulation of the Tyrrhenian Sea

The Tyrrhenian Sea plays an important role in the winter deep water formation in the North Western Mediterranean through the water that enters the Ligurian Sea via the Corsica Channel. Therefore, the study of the impact of the changes in the future climate on the Tyrrhenian circulation and its consequences represents an important issue. Furthermore, the seasonally-dependent, rich in dynamical mesoscale structures, Tyrrhenian circulation is dominated by the interplay of local climate and the basin-wide Mediterranean circulation via the water transport across its major straits and an adequate representation of its features represents an important modeling challenge. In this work we examine with a regionally-coupled atmosphere-ocean model the changes in the Tyrrhenian circulation by the end of the 21st century under the RCP8.5 emission scenario, their driving mechanisms, as well as their possible impact on winter convection in the NW Mediterranean. Our model successfully reproduces the main features of the Mediterranean Sea and Tyrrhenian basin present-day circulation. We find that toward the end of the century the winter cyclonic, along-slope stream around the Tyrrhenian basin becomes weaker. This weakening increases the wind work transferred to the mesoscale structures, which become more intense than at present in winter and summer. We also find that, in the future, the northward water transport across the Corsica Channel towards the Liguro-Provençal basin becomes smaller than today. Also, water that flows through this channel presents a stronger stratification because of a generalized warming with a saltening of intermediate waters. Both factors may contribute to the interruption of deep water formation in the Gulf of Lions by the end of the century.

Kinematics of Deformable Blocks: Application to the Opening of the Tyrrhenian Basin and the Formation of the Apennine Chain

We describe the opening of back-arc basins and the associated formation of accretionary wedges through the application of techniques of deformable plate kinematics. These methods have proven to be suitable to describe complex tectonic processes, such as those that are observed along the Africa–Europe collision belt. In the central Mediterranean area, these processes result from the passive subduction of the lithosphere belonging to the Alpine Tethys and Ionian Ocean. In particular, we focus on the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain. We divide the area of the Apennine Chain and the Tyrrhenian basin into deformable polygons that are identified on the basis of sets of extensional structures that are coherent with unique Euler pole grids. The boundaries between these polygons coincide with large tectonic lineaments that characterize the Tyrrhenian–Apennine area. The tectonic style along these structures reflects the variability of relative velocity vectors between two adjacent blocks. The deformation of tectonic elements is accomplished, allowing different rotation velocities of lines that compose these blocks about the same stable stage poles. The angular velocities of extension are determined on the basis of the stratigraphic records of syn-rift sequences, while the rotation angles are obtained by crustal balancing.

Inverted Basins by Africa–Eurasia Convergence at the Southern Back-Arc Tyrrhenian Basin

The southern part of Tyrrhenian back-arc basin (NW Sicily), formed due to the rifting and spreading processes in back-arc setting, is currently undergoing contractional tectonics. The analysis of seismic reflection profiles integrated with bathymetry, magnetic data and seismicity allowed us to map a widespread contractional tectonics structures, such as positive flower structures, anticlines and inverted normal faults, which deform the sedimentary sequence of the intra-slope basins. Two main tectonic phases have been recognised: (i) a Pliocene extensional phase, active during the opening of the Vavilov Basin, which was responsible for the formation of elongated basins bounded by faulted continental blocks and controlled by the tear of subducting lithosphere; (ii) a contractional phase related to the Africa-Eurasia convergence coeval with the opening of the Marsili Basin during the Quaternary time. The lithospheric tear occurred along the Drepano paleo-STEP (Subduction-Transform-Edge-Propagator) fault, where the upwelling of mantle, intruding the continental crust, formed a ridge. Since Pliocene, most of the contractional deformation has been focused along this ridge, becoming a good candidate for a future subduction initiation zone.

Plate kinematic relationship between the Tyrrhenian basin and the Apennine chain (Central Mediterranean)

<p>The fragmentation of the Adriatic plate and the sinking of the remnant Alpine Tethys and Ionian lithosphere give rise to passive subduction processes that, together with the collision of the African and European plates, characterize the Central Mediterranean area.<br>Circum - Mediterranean mountain ranges and Alboran, Balearic, Tyrrhenian and Hellenic back-arc basins are formed in this complex deformation system.<br>The evolution of the geodynamic processes that guided the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain are described in this work using the plate kinematics technique.<br>The study area has been divided into polygons (crustal blocks of microplates) after careful observation of the regional structures. The polygons are distinguished on the basis of the direction of the Tyrrhenian extension and the boundaries between them coincide with the large structures that characterize the Tyrrhenian-Apennine area.<br>The Tyrrhenian extension directions are indicators of the Euler poles of the individual polygons, in the Sardo-Corso block reference frame. The velocity ratios were determined by the slip vectors of the structures (plate boundaries) that separates the polygons. The rotation time and angle are determined respectively: using the stratigraphic records of the syn-rift sequences and comparing the crustal balance with the speed ratios.<br>At the end including the new kinematic framework in the global rotation model we were able to reconstruct the tectonic evolution of the central Mediterranean during the opening of the Tyrrhenian basin.</p>

Seismic radial anisotropy in Central-Western Mediterranean and Italian peninsula from ambient noise recordings

<p><span>The dynamics of crustal extension and the crust-mantle interaction i</span>n the Central-Western Mediterranean and Italian peninsula (i.e. Liguro-Provençal and Tyrrhenian Basin), and plate convergence (i.e. Alpine and Apennines chains) are key for the understating of the current geodynamics setting and its evolution<span> in the region</span>. However, open questions <span>such as the style, depth and extent of the deformation </span>still exist despite the wealth of seismological and non-seismological data acquired in the past decades. In this context, it is necessary to provide improved subsurface models in terms of seismic velocities, from which better constraints on the geodynamic models can be derived.</p><p>We use seismic ambient noise for retrieving phase velocities of Rayleigh and Love waves in the 4-35 s period range, using private (LiSard network<span> in Sardinia island</span>) and publicly available continuous recordings from more than 500 seismic stations. Considering the excellent coverage and the short period of recovered phase velocities, our study aims to provide an unprecedented, high-resolution image of the shallow crust and uppermost mantle.</p><p>We employ a Bayesian trans-<span>dimensional</span>, Monte Carlo Markov chain inversion approach that requires no a-priori model nor a fixed parametrization. In addition to the (isotropic) shear wave velocity structure, we also recover the values of radial anisotropy (ξ=(V<sub>SH</sub>/V<sub>SV</sub>)<sup>2</sup>) as a function of depth, thanks to the joint inversion of both Rayleigh and Love phase velocities.</p><p>Focusing on radial anisotropy, this appears clearly uncoupled with respect to the shear wave velocity structure. The largest negative anisotropy anomalies (V<sub>SH</sub><V<sub>SV</sub>, ξ<0.9) are found in the Liguro-Provençal and western Tyrrhenian basins in the top 10-15 km, suggesting a common structural imprint inherited during the extensional phases of such basins. Conversely, the eastern Tyrrhenian basin shows positive radial anisotropy (V<sub>SH</sub>>V<sub>SV</sub>, ξ>1.1) within the same depth range. This evidence, combined with the observed shear wave velocities typical of the uppermost mantle, corroborates the presence of a sub-horizontal asthenospheric flow driving the current extension and <span>oceanization </span>of the eastern Tyrrhenian basins.</p><p>Moving towards the Italian mainland, a strong anomaly of negative anisotropy appears in the eastern portion of the Apennines chain. We relate such an anisotropic signal with the ongoing compressive regime affecting the area. Here, the high-angle thrust faults and folds, that accommodates the horizontal shortening, obliterate the horizontal layering of the sedimentary deposits, currently constituting the flanks of the fold system.</p><p>Our results suggest that the combination of radial anisotropy and shear wave velocities can unravel key characteristics of the crust and uppermost mantle, such as inherited or currently active structures resulting from past or ongoing geodynamic processes.</p>

Interactions between salt tectonics and crustal tectonics on the Eastern Sardinian Margin (Western Tyrrhenian Sea)

<p>The METYSS project (Messinian Event in the Tyrrhenian from Seismic Study) is based on high-resolution seismic data acquired along the Eastern Sardinian margin. The main aim is to study the Messinian Salinity Crisis (MSC) in the Western Tyrrhenian Basin, but we also investigated the thinning processes of the continental crust and the timing of crustal vertical movements across this backarc domain. Our first results shown that rifting ended before the MSC, but that crustal activity persisted long after the end of the rifting. This has been particularly observed on the proximal margin, the East-Sardinia Basin, where the Mobile Unit (MU, mobile Messinian salt) is thin or absent. In this study, we examined the distal margin, the Cornaglia Terrace, where the MU accumulated during the MSC and acted as a décollement, thus potentially decoupling the basement from the sedimentary cover. Our observations provide evidence for lateral flow and gravity gliding of the salt and its brittle sedimentary overburden along local basement slopes generated by the post-MSC tilting of some basement blocks formerly generated during the rifting. We also investigated an intriguing wedge-shaped body of MU located in a narrow N-S half graben bounded to the west by a major, east-dipping, crustal normal fault. Classically, one could think that this salt wedge is related to the syn-tectonics deposition of the MU, but we propose an original scenario, in which the post-rift vertical motion of the major fault has been cushioned by lateral flow of an initially tabular salt layer, leaving the supra-salt series apparently unaffected by the crustal motions of the basement. We tested this scenario by comparing natural data and physical (analogue) modelling data. Our results reveal that salt tectonics provides a powerful tool to understand the deep crustal tectonics of the margin and to constrain the timing of vertical motions in the Western Tyrrhenian Basin, results that can be applied to rifted salt-bearing margins worldwide.</p>

Structure of the crust and uppermost mantle beneath the Sicily channel from ambient noise and earthquake tomography

• In this work, we study the crust and the uppermost mantle structure beneath the Sicily Channel, by applying the ambient noise and earthquake tomography method. After computing cross-correlation of the continuous ambient noise signals and processing the earthquake data, we extracted 104 group velocity and 68 phase velocity dispersion curves corresponding to the fundamental mode of the Rayleigh waves. We computed the average velocity of those dispersion curves to obtain tomographic maps at periods ranging from 5 s to 40 s for the group velocities and from 10 s to 70 for the phase velocities. We inverted group and phase speeds to get the shear-wave velocity structure from the surface down to 100 km depth with a lateral resolution of about 200 km. The resulted velocity models reveal a thin crust with thickness value of 15 km beneath the southern part of the Tyrrhenian basin and a thickness value of 20 km beneath Mount Etna. The obtained thickness values are well correlated with the reported extension of the Tyrrhenian lithosphere due to the past earthquake tomography subduction and rollback of the Ionian slab beneath the Calabrian Arc. The crustal thickness increases and reaches values between 28 and 30 km beneath the Tunisian coasts and Sicily Channel. The S-wave models reveal also the presence of high velocity body beneath the island of Sicily. This finding can be interpreted as the presence of the Ionian slab subducting beneath the Calabrian Arc. Another high velocity body is observed beneath the southern part of the Tyrrhenian basin, it might be interpreted as the presence of fragments of the African continental lithosphere beneath the Tyrrhenian basin.

Structure and functioning of epipelagic mesozooplankton and response to dust events during the spring PEACETIME cruisein the Mediterranean Sea

The PEACETIME cruise (May–June 2017) was a basin scale study mainly dedicated to the study of different planktonic trophic regimes in the Algerian, Tyrrhenian and Ionian basins and, in particular, focusing on areas impacted by Saharan dust deposition. This paper presents the structural and functioning patterns of the zooplankton component during this survey, including their responses to two major dust events in the Algerian and Tyrrhenian basins. The mesozooplankon was sampled at 12 stations by combining nets with 2 mesh sizes (100 and 200 µm) mounted on a bongo frame for vertical hauls within the upper 300 meter layer. In this general post-bloom situation, total mesozooplankton showed reduced variations in abundance and biomass over the whole area, with a noticeable contribution of the small size fraction (< 500 µm) of up to 50 % in abundance and 25 % in biomass. The taxonomic structure was dominated by copepods, mainly cyclopoids and calanoids, and completed by appendicularians, ostracods and chaetognaths. Distinct zooplankton taxa assemblages in the three main regions were in agreement with recently proposed regional patterns for the Mediterranean Basin, although the assemblages found in the western Ionian stations presented a closer analogy with those of the Tyrrhenian basin than with those of the Ionian basin., probably due to Atlantic water influence. Zooplankton carbon demand, grazing pressure, respiration and excretion rates were estimated using allometric relationships to the mesozooplankton size-spectrum. On average, the daily zooplankton consumption potentially represents 15 % of the phytoplankton stock, almost the whole of the primary production, with a narrow range of variations, and its excretion contributes roughly one quarter of the N and P requirements of phytoplankton production. The small size fractions make a significant contribution to these mesozooplankton estimated fluxes. Whereas in the Algerian basin (long station FAST), the initial impact on the pelagic ecosystem of a tracked dust deposition was studied, the survey of the southern Tyrrhenian basin occurred almost a week after another dust event. The changes in mesozooplankton taxonomic structure appear to be a relevant indicator to study this response, with an initial phase with no real dominance of taxa, then a disturbed state of the community with strong dominance of certain herbivorous taxa and the appearance of carnivorous species, and finally a recovery state towards a more stable system with diversification of the community. To our knowledge, PEACETIME is the first in situ study allowing observation of mesozooplankton responses before and soon after natural Saharan dust depositions. The changes in rank-frequency diagrams of the zooplankton taxonomic structure are an interesting index to highlight short-term responses of zooplankton to episodic dust deposition events.

GPS Imaging of Mantle Driven Uplift of the Apennines, Italy

&lt;p&gt;One way for the continental lithosphere to extend is to increase its regional elevation, yet the mechanism for the formation of high-topography in actively extending continental settings (e.g., Tibet, Basin and Range, southwestern Balkans, Apennines) is still uncertain.&amp;#160;It has been suggested that active extension in the Apennines Mountain chain in Italy is intimately related with regional topographic elevation. We use a newly updated GPS dataset and the GPS Imaging technique to show that the dynamic relief of the Apennines is currently increasing along its entire length by ~1 mm/yr. We image positive uplift along the entire length of the Apennine crest including the northern Apennines, Calabria and northern Sicily. The maximum rate is geographically aligned with the highest elevations and the topographic drainage divide. Relief is increasing in a ~120 km wide zone with a profile similar to the long wavelength topography, but not similar to the shorter wavelength topography generated by active faulting and erosion. A zone of minor active uplift is aligned with areas having restive volcanic fields and high geothermal potential west of the Apennines: e.g., Campi Flegrei, Alban Hills, and Lago Bolsena. However, the primary uplift axis aligns with the topography and zone of extension accommodating east-northeast translation of the Adriatic microplate relative to the Tyrrhenian Basin. Broad uplift occurs despite that the expected consequence of extension is crustal thinning and subsidence.&amp;#160;&amp;#160; Anomalies in free-air gravity and deep seismic wavespeed suggest that elevation gain is driven by forces originating in the mantle. We use these results to address the hypothesis that these forces result from upward flow of asthenospheric mantle beneath the Apennines, possibly related to a sinking and detached slab previously attached to the Adriatic microplate, or from extensional flank flexure across the axis of the Apennine rift.&lt;/p&gt;

Extensional tectonics during the Tyrrhenian back-arc basin formation synthetized in a new morpho-tectonic map

&lt;p&gt;A new tectonic map is presented focused upon the extensional style accompanying the formation of the Tyrrhenian back-arc basin. Our basin-wide analysis synthetizes the interpretation of vintage multichannel and single channel seismic profiles integrated with modern seismic images and P-wave velocity models, and with a new morpho-tectonic map of the Tyrrhenian (Palmiotto &amp; Loreto, 2019). Four distinct evolutionary opening stages have been constrained: 1) the initial Langhian(?)/Serravallian opening phase actives offshore central/southern Sardinia and offshore western Calabria; 2) the Tortonian/Messinian phase dominated by extension offshore North Sardinia-Corsica, and by oceanic accretion in the Cornaglia and Campania Terraces; 3) the Pliocene phase, dominated by mantle exhumation which was active mainly in the central Tyrrhenian and led to the full opening of Vavilov Basin; and 4) the Quaternary phase characterized by the opening of the Marsili back-arc basin. Listric and planar normal faults and their conjugates bound a series of horst and graben, half-graben and triangular basins. Distribution of extensional faults, active since Middle Miocene, throughout the basin allowed us to define a faults arrangement in the northern / central Tyrrhenian mainly related to in a pure shear which evolved a simple shear opening of continental margins. At depth, faults accommodate over a Ductile-Brittle Transitional zone cut by a low-angle detachment fault possibly responsible for mantle exhumation in the Vavilov and Magnaghi abyssal plains. In the southern Tyrrhenian, normal, inverse and transcurrent faults appear to be related to a large shear zone located along the continental margin of the northern Sicily. Extensional style variationthroughout the back-arc basin combined with wide-angle seismic velocity models, from Prada et al. (2014; 2015), allow to explore the relationship between shallow deformation, represented by faults distribution throughout the basin, and crustal-scale processes, subduction of Ionian slab and exhumation.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;REFERENCES&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Palmiotto, C., &amp; Loreto, M. F., (2019). Regional scale morphological pattern of the Tyrrhenian Sea: New insights from EMODnet bathymetry. Geomorphology, 332, 88-99.&lt;/p&gt;&lt;p&gt;Prada, M., Sallar&amp;#232;s, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. &amp; De Franco, R., 2014. Seismic structure of the Central Tyrrhenian basin: Geophysical constraints on the nature of the main crustal domains. J. Geophys. Res.: Solid Earth, 119(1), 52-70.&lt;/p&gt;&lt;p&gt;Prada, M., Sallar&amp;#232;s, V., Ranero, C.R., Vendrell, M.G., Grevemeyer, I., Zitellini, N. &amp; De Franco, R., 2015. The complex 3-D transition from continental crust to backarc magmatism and exhumed mantle in the Central Tyrrhenian basin. Geophys. J. Int., 203(1), 63-78.&lt;/p&gt;