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Mixed (turbidite-contourite) depositional systems are formed by a complex interplay of deep-water processes. An evaluation of their morphological elements and their lateral and spatial distribution is crucial to better understand the interplay of transport and depositional processes, involving along-slope bottom currents and down-slope turbidity currents. This work investigates extensive and still active mixed depositional systems developed along the Pacific margin of the Antarctic Peninsula, which comprise large asymmetric mounded drifts, dendritic channel-complex systems and wide trunk channels. These systems offer a unique setting to investigate diverse morphological elements at a high-resolution spatial scale (10–100 m), using multibeam bathymetry and acoustic sub-bottom profiles. Four main seismic units define distinct evolutionary stages for the Pleistocene to present day record: a) 1.3–1 Ma, characterized by aggradational mounded drifts built by a dominant along-slope bottom current; b) 1–0.6 Ma, built by synchronous interactions between a SW-flowing bottom current and NW-directed turbidity currents; c) 0.6–0.2 Ma, characterized by deposition of thick gravitational deposits across the margin under a weak SW-flowing bottom current comprising modified Lower Circumpolar Deep Water (LCDW); and d) 0.2 Ma – present, when synchronous interactions between the bottom current, characterized by flow speed fluctuations, and ephemeral turbidity currents led to intercalations of turbidites, contourites, reworked turbidite deposits and hemipelagites. Alternations in the stratigraphic stacking pattern suggest cyclic spatial and temporal variations of gravity-driven down-slope processes and along-slope bottom currents, which were responsible for the construction of these modern mixed depositional systems and which themselves were controlled by glacial-interglacial changes. The new results are compared with similar mixed depositional systems to decode the main processes involved in their formation, explore their interactions at short- and long-term time scales, and propose a conceptual sedimentary model.

This is chapter 6 of the State of Environmental Science in Svalbard (SESS) report 2018 (https://sios-svalbard.org/SESS_Issue1). In the Fram Strait, a remarkable increase in the temperature and salinity of inflowing Atlantic Water has been observed since the 1990s. This is in part a natural trend, but recent temperature anomalies, ~1°C relative to the 1970s are related to anthropogenic causes. Air temperature increased by about 3°C in the 20th century and meteorological stations at Svalbard confirm this positive trend. At the West Spitsbergen margin, Atlantic and Arctic waters converge, mix and exchange, while air–sea interactions and shelf–slope dynamics trigger vertical mixing and formation of cold and salty water. This water is sufficiently dense to sink to greater depths and contribute to the global thermohaline circulation. The circulation process permits exchange of heat (i.e., energy) between low and high latitudes. Since the formation of dense water and its spreading at greater depths are strongly influenced by the properties of Atlantic Water, which have been changing in the last decades, we cannot exclude the possibility that the global thermohaline circulation may change in the near future. We analysed oceanographic data (obtained from shelf and deep-sea oceanographic moorings and hydrographic cruises) and meteorological data from the west Svalbard margin, comparing temperature and salinity variability in the deep ocean flow and the wind regime. Time-series revealed occasional intrusions of warm and salty waters at 1000 m depth, mainly during the period October – April, quasi-simultaneously at several locations more than 150 apart, along the continental slope west of Svalbard. The fact that the most energetic events, both in the deep flow and in the wind speed, occurred with similar periodicities (10-20 days) suggests atmospheric storms as the likely forcing mechanism underlying the observed deep sea variability. Others energetic events with periodicity of 12 and 24 hours, instead, could be related to internal tidal oscillations. The fact that the most energetic events, both in the deep flow and in the wind speed, had similar periodicities (10-20 days) suggests atmospheric storms as the likely forcing mechanism underlying the observed deep-sea variability. Other energetic events with periodicity of 12 and 24 hours could instead be related to tidal oscillations.

The Paleogene carbonate megabreccias of the Eastern Friuli, South-Eastern Alps of Italy, are thick, up to 260 m, and laterally extensive, up to 100 km, bodies attributed to catastrophic submarine landslides, which occurred in a deep-water, turbidite-filled foredeep basin (Julian Basin or Slovenian Basin of the Slovene geologists). The Grivo Flysch succession (late Paleocene-early Eocene) contains several of these mass-transport deposits (MTD) intercalated within carbonate, siliciclastic and mixed turbidites. Megabreccias are mainly composed by shallow-marine detritus from the Friuli Carbonate Platform. The latter, placed at the southern boundary of the basin, was a passive, distal margin at the time of deposition of these units, far from the deformational front of the Southern Alps. The type and the scale of the processes interred for the largest MTDs, as well as the size of the individual component slide blocks (olistoliths), are comparable with the well-studied Eocene carbonate megabreccias of the Southern Pyrenean Foreland Basin. Notwithstanding such impressive characteristics, the MTDs of the Julian Basin have attracted the attention of a limited number of researchers with only few local scientific productions, not easily available to the international community. Therefore, these bodies are still relatively poorly understood especially in terms of sedimentary processes and emplacement mechanism. Previous studies mainly addressed the litostratigraphy of the Julian Basin succession and the sedimentological characteristics of the internal organization of the MTDs. Other aspects such as the number and the ages of these bodies, thicknesses and variation of internal divisions, the provenance of the material and the triggering mechanisms have been also considered. On the other hand, many crucial issues concerning the Julian Basin MTDs have not been discussed or remain unsolved, especially in light of a modern approach that takes into account the recent progressions in marine geology regarding large-scale mass transport deposits. In particular, detailed studies on the internal kinematics and the down-slope evolution of the mass-transport have not been performed systematically, although the excellent and continuous exposures and the high basin-wide correlation potential of each bed, due to the lack of intense tectonic deformation. This favorable context allows studies on the relationships between the transport-emplacement of the MTDs and the deformation of the substratum, which have not been investigated so far. Our communication addresses these aspects, as well as the overall distribution, architecture and physiographic setting of these deposits in the framework of the Julian Basin. A general synthesis of the emplacement mechanism of the largest of these beds (ie. Vernasso unit or MB 11) will be advanced, in comparison with other fossil examples known in the literature.

The Paleogene carbonate “megabreccias” of the Eastern Friuli, South-Eastern Alps of Italy, are thick, up to 260 m, and laterally extensive, up to 100 km, bodies attributed to catastrophic submarine landslides, which occurred in a deep-water, turbidite-filled foredeep basin (Julian Basin or Slovenian Basin of the Slovene geologists). The Grivo Flysch succession (late Paleocene-early Eocene) contains several of these mass-transport deposits (MTD) intercalated within carbonate, siliciclastic and mixed turbidites. Megabreccias are mainly composed by shallow-marine detritus from the Friuli Carbonate Platform. The latter, placed at the southern boundary of the basin, was a passive, distal margin at the time of deposition of these units, far from the deformational front of the Southern Alps. The type and the scale of the processes inferred for the largest MTDs, as well as the size of the individual component slide blocks (olistoliths), are comparable with the well-studied Eocene carbonate megabreccias of the Southern Pyrenean Foreland Basin. Notwithstanding such impressive characteristics, the MTDs of the Julian Basin have attracted the attention of a limited number of researchers with only few local scientific productions, not easily available to the international community. Therefore, these bodies are still relatively poorly understood especially in terms of sedimentary processes and emplacement mechanism. Previous studies mainly addressed the litostratigraphy of the Julian Basin succession and the sedimentological characteristics of the internal organization of the MTDs. Other aspects such as the number and the ages of these bodies, thicknesses and variation of internal divisions, the provenance of the material and the triggering mechanisms have been also considered. On the other hand, many crucial issues concerning the Julian Basin MTDs have not been discussed or remain unsolved, especially in light of a modern approach that takes into account the recent progressions in marine geology regarding large-scale mass transport deposits. In particular, detailed studies on the internal kinematics and the down-slope evolution of the mass-transport have not been performed systematically, although the excellent and continuous exposures and the high basin-wide correlation potential of each bed, due to the lack of intense tectonic deformation. This favorable context allows studies on the relationships between the transport-emplacement of the MTDs and the deformation of the substratum, which have not been investigated so far. Our communication addresses these aspects, as well as the overall distribution, architecture and physiographic setting of these deposits in the framework of the Julian Basin. A general synthesis of the emplacement mechanism of the largest of these beds (i.e. Vernasso unit or MB 11) will be advanced, in comparison with other fossil examples known in the literature.