Submarine emissions on the seafloor: from cold sepes to hot vents

The main types of submarine geological emissions are classified as cold seeps (hydrocarbons and brines) and hot vents. These processes result in the emission of geological fluids: brine, gases (mainly hydrocarbons), sediments and rocks. Submarine emissions are associated with an intensive geological, geochemical, thermal and biological activity (Judd and Hovland, 2007), and constitute a key process in the dynamics of the global cycles of the planet Earth. These systems play a major role in the exchange of matter and energy between the Geosphere and Hydrosphere, contributing to the greenhouse gases and affecting the ocean chemistry (Dimitrov, 2002; Alt, 2003). They also control the evolution of continental margins and oceanic basins (Paull y Dillon, 2001), and can produce the formation of significant and strategic mineralizations, as well as focus the development of specific habitats (Boetius et al., 2000) and provide an insight of deeper parts of the crust.LIFE+ INDEMARES/CHICA (LIFE07/NAT/E/000732), CADHYS (P08-RNM-03581), MONTERA (CTM2009-14157-C02), VULCANO (CTM2012-36317) and SUBVENT (CGL2012-39524-C02)

Morphological characterization of contourite and mass-wasting recent processes at the Guadalquivir Bank Margin uplift, Gulf of Cádiz

The Gulf of Cadiz records the interplay of a variety of sedimentary processes related to the circulation of water masses. The most important one is the Mediterranean Outflow Water (MOW) that exits the Mediterranean Sea, but other water masses also affect the seafloor, with complex variations along time and space. This work studies the interplay between oceanographic and gravitational sedimentary processes on the Guadalquivir Ridge, based on bathymetry and high-resolution seismic profiles. A series of morphological features including flat terraces, circular/elliptical depressions, semicircular scarps and valley-shaped features are analysed in order to better understand the interaction between water masses circulation and mass-wasting processes of the Gulf of Cadiz.Versión del edito

Seabed morphology and bottom water masses related to benthic habitats at the Cristóbal Colón diapir (NW of the Guadalquivir ridge, Gulf of Cádiz)

The seabed morphology and the sub-superficial characteristics of the Cristóbal Colón diapir located on the continental slope of the Gulf of Cadiz have been analysed from data obtained in the framework of the LIFE+INDEMARES/CHICA project. The aim of this study is to recognize the morphological features and the geological processes generated by the bottom water masses and their influence on the habitats and associated benthic communities. The NACW affects the generation of morphological features on the summit, revealing that different oceanographic conditions favoured the carbonate mound growth in the past. The interface between the NACW and the MOW sweeps the bottom from the SE to the NW and the presence of benthic communities dominated by filter feeders on the contouritic drift indicates that this current is strong enough to favour the availability of nutrients and organic particles and to develop both the contouritic deposits on the SE flank and the moats on the N and W flanks.Versión del edito

Seafloor geomorphology of the Passage of Lanzarote (West Africa Margin): Influences of the oceanographic processes

The seafloor morphology of the Passage of Lanzarote has been analysed with the aim to know the active processes on the bottom surface related to the oceanographic context. Multibeam bathymetric data and high and very high resolution seismic profiles obtained in the SUBVENT2 cruise have been used. Five main morphological groups have been analysed: (a) Volcanic or diapiric submarine hills; (b) Tectonic features on the continental slope (linear scarps and a rhombohedral depression) related to normal faults; (c) Submarine venting at top of diapirs initially triggered circular depressions; (d) Sedimentary instabilities (gullies, canyons, mass transport deposits) are present specially on the Fuerteventura-Lanzarote ridge; and (e) Contouritic bottom features both erosive (central valley, marginal valleys) and depositional (plastered drifts) are on the central part of the passage, and are generated by the interaction of MW and the interface MW-AAIW with seafloor.Versión del edito

Djibouti Ville Drift (SW Mediterranean): Sedimentation and record of bottom-current fluctuations during the Pleistocene and Holocene

Seismic profiles and sedimentological data (bulk fraction) of two sediment cores recovered from the Djibouti Ville Drift (SW Mediterranean Sea) indicate that bottom currents have played a fundamental role in shaping the sediment drift. The deposits are composed of biogenous to mixed muddy and silty contourites. A grain size analysis of the terrigenous fraction together with mineralogical, magnetic susceptibility, 14C-AMS dating and stable oxygen isotope data have been analysed to reconstruct glacial and interglacial changes in the bottom currents during the last 133kyr. The sharp vertical grain size changes in the moat and drift indicate that there were substantial bottom current acceleration and deceleration events with faster flow speeds being registered in the moat environment. In sediments from glacial periods (MIS2, MIS3, and MIS6) and stadials 5b and 5d, there is a low carbonate content, high levels of terrigenous elements and paleocurrent proxy values suggest faster flows with the exception of MIS4. Deposits from the interglacial period (MIS1) and interstadials 5a, 5c and 5e, have a high carbonate content, low levels of terrigenous elements, and the paleocurrent proxy values indicate slower flows.Versión del edito

(Paleo)circulation models in the Alboran seas during the Pliocene and Quaternary

A multiple Contourite Depositional System has been defined in the Plio-Quaternary sedimentary register in the Alboran Sea. This multiple system formed by the Atlantic and the low density and high density Mediterranean Waters, which shaped the margins and basins since the opening of the Gibraltar Strait. Three different (paleo)circulation scenarios are proposed since then: the Atlantic water Flooding;the Pliocene circulation, characterized by immature low and high density Mediterranean waters and a strong countercurrent in the Western Basin; and the Quaternary circulation, characterized by tabular Mediterranean water masses with multiple current dynamics,an increasing influence of density contrasts, and climate shifts causing major vertical and horizontal displacements of their interfaces.Versión del edito

Depositional processes and growth patterns of isolated oceanic basins: the Protector and the Pirie basins ofthe Southern Scotia Sea (Antarctica)

Sedimentary processes in small, isolated oceanic basins that form adjacent to continental margins but detached from continents remain poorly understood. This work describes two such basins located in the southern Scotia Sea, the Protector and Pirie basins. We analysed multichannel seismic profiles to interpret morphostructural features and stratigraphy of these basins. Sedimentary stacking patterns and depocentre distribution illustrate basin development patterns. Basal units infill basement depressions formed by the submerged banks of thinned continental crust that abut the basin plains. These lower and middle deposits of the sedimentary record are interpreted as pre- and syn-rift deposits. The laterally extensive upper deposits are interpreted as post-rift deposits. These include five discrete units evident in seismic profiles. A prominent regional reflection referred to as Reflector-c, separates in these upper deposits two sets of seismic units that have recorded major shifts in the dominant sedimentary processes, stacking patterns and paleo-environmental conditions. The most important processes controlling deposition of the older units (those beneath Reflector-c), include down-slope gravity processes that infill depressions created by crustal thinning and seafloor spreading. These occurred under the coeval influence of Circumpolar Deep Water circulation. The major processes influencing younger units (those above Reflector-c) include bottom water circulation of the Circumpolar Deep Water and Weddell Sea Deep Water water masses,which coursed along bathymetric contours of the seafloor. The Reflector-c discontinuity developed concurrently with middle Miocene tectonic changes, which led to the opening and deepening of deep gateways in the South Scotia Ridge. These facilitated overflow of Weddell Sea Deep Water from the Weddell Gyre into the Scotia Sea. This overflow in turn forced the Circumpolar Deep Water northwards. Analysis of the Protector and Pirie basins shows that their tectonic evolution influenced regional deepwater circulation patterns in an area that makes a significant coldwater contribution to the global conveyor belt system. As a long-termfactor controlling basin evolution and sedimentary processes, tectonics events in this region therefore influenced the present day climate system. These results further clarify our understanding of deep, isolated oceanic basins in terms their sedimentologic, climatologic and oceanographic significance.Postprint2,517