ALBERT

Description:    Despite much progress over the past years in fundamental gas hydrate research, frontiers to the unknown are the early beginning and early decomposition of gas hydrates in their natural, submarine environment: gas bubbles meeting ocean water and forming hydrate, and gas starting to escape from the surface of a hydrate grain. In this paper we report on both of these topics, and present three-dimensional microstructure results obtained by synchrotron radiation X-ray cryo-tomographic microscopy (SRXCTM). Hydrates can precipitate when hydrate-forming molecules such as methane exceed solubility, and combine with water within the gas hydrate stability zone. Here we show hydrate formation on surfaces of bubbles from different gas mixtures and seawater, based on underwater robotic in situ experiments in the deep Monterey Canyon, offshore California. Hydrate begins to form from the surrounding water on the bubble surfaces, and subsequently grows inward into the bubble, evidenced by distinct edges. Over time, the bubbles become smaller while gas is being incorporated into newly formed hydrate. In contrast, current understanding has been that hydrate decomposition starts on the outer surface of hydrate aggregates and grains. It is shown that in an early stage of decomposition, newly found tube structures connect well-preserved gas hydrate patches to areas that are dissociating, demonstrating how dissociating areas in a hydrate grain are linked through hydrate that is still intact and will likely decompose at a later stage. Figure  The boundaries of a gas hydrate grain: excepting for the matrix (transparent, not shown), one can see tubular structures, pores from decomposition, and bubbles. Content Type Journal Article Category Original Pages 1-8 DOI 10.1007/s00367-012-0276-0 Authors Stephan A. Klapp, MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen, Germany Frieder Enzmann, Department of Geosciences, Johannes-Gutenberg-University of Mainz, Gutenberg, Germany Peter Walz, Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA Thomas Huthwelker, Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland Jürgen Tuckermann, Department of Geosciences, Johannes-Gutenberg-University of Mainz, Gutenberg, Germany J.-Oliver Schwarz, Department of Geosciences, Johannes-Gutenberg-University of Mainz, Gutenberg, Germany Thomas Pape, MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen, Germany Edward T. Peltzer, Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA Rajmund Mokso, Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland David Wangner, MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen, Germany Federica Marone, Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland Michael Kersten, Department of Geosciences, Johannes-Gutenberg-University of Mainz, Gutenberg, Germany Gerhard Bohrmann, MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen, Germany Werner F. Kuhs, GZG, Abt. Kristallographie, Universität Göttingen, Göttingen, Germany Marco Stampanoni, Swiss Light Source, Paul Scherrer Institute, Villigen, Switzerland Peter G. Brewer, Monterey Bay Aquarium Research Institute, Moss Landing, CA, USA Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    Multibeam echosounder data and TOPAS seismic reflection profiles collected during the AntPac 1997, Scan 2004, and Scan 2008 cruises aboard the RV Hespérides reveal a host of surficial geomorphological features as yet poorly investigated in the Scan Basin, south-central Scotia Sea. This area represents one of the deep gateways between the Weddell Sea and the Scotia Sea, since it enables the northward flow of a branch of the Weddell Sea Deep Water (WSDW). Analysis of the data identifies numerous elongated depressions interpreted as furrows in the southernmost sector of the basin. These furrows show two main trends, i.e., either N–NNW parallel to, or NE oblique to regional bathymetric contours. These trends plausibly reflect a tectonic influence on the bottom-flow distribution, conditioned by a set of recent, conjugate strike-slip faults that developed on the seafloor under dominant NNE–SSW compression and orthogonal extension. The furrows exhibit distinct geomorphological patterns at either side of the basin, which can be related to west–east asymmetry in the WSDW flow direction. Consistent with existing knowledge of regional WSDW dynamics, northward WSDW overflows would be channeled along the western part of the basin at higher bottom-current velocities, thereby generating more erosional-type furrows that are straighter, more elongated, and have more abrupt sidewalls than their eastern counterparts. In contrast, weaker southward WSDW would flow along the eastern part of the basin, resulting in more depositional-type furrows that are more curved, less elongated, and have gentler sidewalls. Content Type Journal Article Pages 1-14 DOI 10.1007/s00367-011-0240-4 Authors Francisco José Lobo, Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Facultad de Ciencias, Avenida de Fuentenueva s/n, 18002 Granada, Spain Francisco Javier Hernández-Molina, Departamento de Geociencias Marinas y Ordenación del Territorio, Universidad de Vigo, 36200 Vigo, Pontevedra, Spain Fernando Bohoyo, Instituto Geológico y Minero de España, Ríos Rosas 23, 28003 Madrid, Spain Jesús Galindo-Zaldívar, Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Facultad de Ciencias, Avenida de Fuentenueva s/n, 18002 Granada, Spain Andrés Maldonado, Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Facultad de Ciencias, Avenida de Fuentenueva s/n, 18002 Granada, Spain Yasmina Martos, Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Facultad de Ciencias, Avenida de Fuentenueva s/n, 18002 Granada, Spain José Rodríguez-Fernández, Instituto Andaluz de Ciencias de la Tierra, CSIC-Universidad de Granada, Facultad de Ciencias, Avenida de Fuentenueva s/n, 18002 Granada, Spain Luis Somoza, Instituto Geológico y Minero de España, Ríos Rosas 23, 28003 Madrid, Spain Juan Tomás Vázquez, Centro Oceanográfico de Málaga, Instituto Español de Oceanografía, Puerto Pesquero s/n, 29640 Fuengirola, Málaga, Spain Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    One important handicap when working with stratigraphic sequences is the discontinuous character of the sedimentary record, especially relevant in cyclostratigraphic analysis. Uneven palaeoclimatic/palaeoceanographic time series are common, their cyclostratigraphic analysis being comparatively difficult because most spectral methodologies are appropriate only when working with even sampling. As a means to solve this problem, a program for calculating the smoothed Lomb-Scargle periodogram and cross-periodogram, which additionally evaluates the statistical confidence of the estimated power spectrum through a Monte Carlo procedure (the permutation test), has been developed. The spectral analysis of a short uneven time series calls for assessment of the statistical significance of the spectral peaks, since a periodogram can always be calculated but the main challenge resides in identifying true spectral features. To demonstrate the effectiveness of this program, two case studies are presented: the one deals with synthetic data and the other with paleoceanographic/palaeoclimatic proxies. On a simulated time series of 500 data, two uneven time series (with 100 and 25 data) were generated by selecting data at random. Comparative analysis between the power spectra from the simulated series and from the two uneven time series demonstrates the usefulness of the smoothed Lomb-Scargle periodogram for uneven sequences, making it possible to distinguish between statistically significant and spurious spectral peaks. Fragmentary time series of Cd/Ca ratios and δ 18 O from core AII107-131 of SPECMAP were analysed as a real case study. The efficiency of the direct and cross Lomb-Scargle periodogram in recognizing Milankovitch and sub-Milankovitch signals related to palaeoclimatic/palaeoceanographic changes is demonstrated. As implemented, the Lomb-Scargle periodogram may be applied to any palaeoclimatic/palaeoceanographic proxies, including those usually recovered from contourites, and it holds special interest in the context of centennial- to millennial-scale climatic changes affecting contouritic currents. Content Type Journal Article Pages 1-9 DOI 10.1007/s00367-011-0247-x Authors Eulogio Pardo-Iguzquiza, Instituto Geológico y Minero de España (IGME), 28003 Madrid, Spain Francisco J. Rodríguez-Tovar, Dpto de Estratigrafía y Paleontología, Fac. de Ciencias, Universidad de Granada, 18002 Granada, Spain Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    The Argentine continental margin is characterised by a large contourite depositional system driven by southern-sourced water masses flowing at different water depths. Interest in contourite deposits is increasing in geoscience and related fields, though knowledge of the Argentine contourite system is still limited. In particular, studies based on core data providing detailed descriptions of sedimentary facies are lacking, as are investigations of principal sediment source areas and of key factors controlling sedimentary processes. This study combines visual core description and downcore grain-size analyses as well as petrographic thin-section and magnetic susceptibility analyses of 14 cores from intermediate water depths of 616–1,208 m to characterise contourite deposits on the north-eastern Argentinean slope. Gravel-rich, sandy–silty and muddy contourites as well as hemipelagic facies were identified. The deposition of these contourites was presumably controlled by sea level, the depth range of the Antarctic water mass, climate conditions and windborne terrigenous supply. It is proposed that, during glacial lowstands, muddy contourites were deposited at depths 〈900 m, whereas sandy–silty sequences dominated at deeper depths. During the late Pleistocene–Holocene transition, sandy–silty contourites covered the entire middle slope. Hemipelagic facies draped limited sectors of the middle slope when the sea level reached the present-day position and gravel-rich contourites became restricted to contouritic channels and moats. Northern Patagonia and the southern Pampa are the most plausible sources for sediments deposited via along-slope processes, whereas the Tandilia Range is the best candidate for sediments deposited via down-slope processes. Content Type Journal Article Pages 1-13 DOI 10.1007/s00367-011-0239-x Authors Graziella Bozzano, Sección Geología Marina, Servicio de Hidrografía Naval, Av. Montes de Oca 2124, C1270ABV Buenos Aires, Argentina Roberto A. Violante, Sección Geología Marina, Servicio de Hidrografía Naval, Av. Montes de Oca 2124, C1270ABV Buenos Aires, Argentina Maria Elena Cerredo, Departamento Cs Geológicas, FCEyN, Universidad de Buenos Aires, Ciudad Universitaria, Argentina Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    This study reports the first in situ measurements of tensile fracture toughness, K IC , of soft, surficial, cohesive marine sediments. A newly developed probe continuously measures the stress required to cause tensile failure in sediments to depths of up to 1 m. Probe measurements are in agreement with standard laboratory methods of K IC measurements in both potter’s clay and natural sediments. The data comprise in situ depth profiles from three field sites in Nova Scotia, Canada. Measured K IC at two muddy sites (median grain size of 23–50 μm) range from near zero at the sediment surface to 〉1,800 Pa m 1/2 at 0.2 m depth. These profiles also appear to identify the bioturbated/mixed depth. K IC for a sandy site (〉90% sand) is an order of magnitude lower than for the muddy sediments, and reflects the lack of cohesion/adhesion. A comparison of K IC , median grain size, and porosity in muddy sediments indicates that consolidation increases fracture strength, whereas inclusion of sand causes weakening; thus, sand-bearing layers can be easily identified in K IC profiles. K IC and vane-measured shear strength correlate strongly, which suggests that the vane measurements should perhaps be interpreted as shear fracture toughness, rather than shear strength. Comparison of in situ probe-measured values with K IC of soils and gelatin shows that sediments have a K IC range intermediate between denser compacted soils and softer, elastic gelatin. Content Type Journal Article Pages 1-10 DOI 10.1007/s00367-011-0243-1 Authors Bruce D. Johnson, Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada Mark A. Barry, Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada Bernard P. Boudreau, Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada Peter A. Jumars, Darling Marine Center, University of Maine, Walpole, ME 04573-3307, USA Kelly M. Dorgan, Scripps Institution of Oceanography, UCSD, 9500 Gilman Drive, La Jolla, CA 92093-0202, USA Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    Major plastered drift sequences were imaged using high-resolution multichannel seismics during R/V Meteor cruises M63/1 and M75/3 south of the Mozambique Channel along the continental margin of Mozambique off the Limpopo River. Detailed seismic-stratigraphic analyses enabled the reconstruction of the onset and development of the modern, discontinuous, eddy-dominated Mozambique Current. Major drift sequences can first be identified during the Early Miocene. Consistent with earlier findings, a progressive northward shift of the depocenter indicates that, on a geological timescale, a steady but variable Mozambique Current existed from this time onward. It can furthermore be shown that, during the Early/Middle Miocene, a coast-parallel current was established off the Limpopo River as part of a lee eddy system driven by the Mozambique Current. Modern sedimentation is controlled by the interplay between slope morphology and the lee eddy system, resulting in upwelling of Antarctic Intermediate Water. Drift accumulations at larger depths are related to the reworking of sediment by deep-reaching eddies that migrate southward, forming the Mozambique Current and eventually merging with the Agulhas Current. Content Type Journal Article Pages 1-9 DOI 10.1007/s00367-011-0238-y Authors Benedict Preu, MARUM—Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany Volkhard Spieß, MARUM—Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany Tilmann Schwenk, MARUM—Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany Ralph Schneider, Department of Geosciences, Christian-Albrecht University Kiel, 24118 Kiel, Germany Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    This study reports novel findings on the Pliocene–Quaternary history of the northern Gulf of Cadiz margin and the spatiotemporal evolution of the associated contourite depositional system. Four major seismic units (P1, P2, QI and QII) were identified in the Pliocene–Quaternary sedimentary record based on multichannel seismic profiles. These are bounded by five major discontinuities which, from older to younger, are the M (Messinian), LPR (lower Pliocene revolution), BQD (base Quaternary discontinuity), MPR (mid-Pleistocene revolution) and the actual seafloor. Unit P1 represents pre-contourite hemipelagic/pelagic deposition along the northern Gulf of Cadiz margin. Unit P2 reflects a significant change in margin sedimentation when contourite deposition started after the Early Pliocene. Mounded elongated and separated drifts were generated during unit QI deposition, accompanied by a general upslope progradation of drifts and the migration of main depocentres towards the north and northwest during both the Pliocene and Quaternary. This progradation became particularly marked during QII deposition after the mid-Pleistocene (MPR). Based on the spatial distribution of the main contourite depocentres and their thickness, three structural zones have been identified: (1) an eastern zone, where NE–SW diapiric ridges have controlled the development of two internal sedimentary basins; (2) a central zone, which shows important direct control by the Guadalquivir Bank in the south and an E–W Miocene palaeorelief structure in the north, both of which have significantly conditioned the basin-infill geometry; and (3) a western zone, affected in the north by the Miocene palaeorelief which favours deposition in the southern part of the basin. Pliocene tectonic activity has been an important factor in controlling slope morphology and, hence, influencing Mediterranean Outflow Water pathways. Since the mid-Pleistocene (MPR), the sedimentary stacking pattern of contourite drifts has been less affected by tectonics and more directly by climatic and sea-level changes. Content Type Journal Article Pages 1-14 DOI 10.1007/s00367-011-0241-3 Authors Estefanía Llave, Instituto Geológico y Minero de España (IGME), c/ Ríos Rosas 23, 28003 Madrid, Spain Hugo Matias, REPSOL, Exploration Spain, Paseo de la Castellana 280, 28046 Madrid, Spain F. Javier Hernández-Molina, Facultad de Ciencias del Mar, Universidad de Vigo, 36200 Vigo, Spain Gemma Ercilla, Dpto. de Geología Marina y Oceanografía Física, Instituto de Ciencias del Mar, CMIMA-CSIC, Paseo Marítimo de la Barceloneta, 08003 Barcelona, Spain Dorrik A. V. Stow, IPE-ECOSSE, Heriot-Watt University, Edinburgh, EH14 4AS UK Teresa Medialdea, Instituto Geológico y Minero de España (IGME), c/ Ríos Rosas 23, 28003 Madrid, Spain Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    The seabed morphology in the vicinity of the seamounts on the Motril Marginal Plateau (northern Alboran Sea) was investigated using high-resolution (sparker) and very high-resolution (TOPAS) seismic reflection profiles and multibeam bathymetry. The aim of the study was to determine the recent geological processes, and in particular those that control the contourite depositional system associated with the intermediate and deep Mediterranean water masses. Six groups of morphological features were identified: structural features (seamount tops, tectonic depressions), fluid escape-related features (pockmarks), mass-movement features (gullies, slides), bottom-current features (moats, scour marks, terraces, elongated and separated drifts, plastered drifts, confined drifts, sheeted drifts), mixed features (ridges) and biogenic features (including evidence of (dead) cold water corals such as Lophelia pertusa and Madrepora oculata ). The main processes controlling the formation of these features are recent tectonic activity and the interaction of Mediterranean water masses with the seafloor topography. Seamounts act as topographic barriers that affect the pathway and velocity of the deep Mediterranean water masses, which are divided into strands that interact with the surrounding seafloor. The influence of the intermediate Mediterranean water mass, by contrast, is restricted mainly to the tops of the seamounts. Sediment instability and fluid-escape processes play a minor role, their occurrence being probably related to seismicity. Content Type Journal Article Pages 1-15 DOI 10.1007/s00367-011-0246-y Authors Desirée Palomino, Instituto Español de Oceanografía, Centro Oceanográfico de Málaga, Puerto Pesquero s/n, 29640 Fuengirola, Málaga, Spain Juan-Tomás Vázquez, Instituto Español de Oceanografía, Centro Oceanográfico de Málaga, Puerto Pesquero s/n, 29640 Fuengirola, Málaga, Spain Gemma Ercilla, Instituto de Ciencias del Mar-CSIC, Paseo Marítimo de la Barceloneta 37–49, 08003 Barcelona, Spain Belén Alonso, Instituto de Ciencias del Mar-CSIC, Paseo Marítimo de la Barceloneta 37–49, 08003 Barcelona, Spain Nieves López-González, Instituto Español de Oceanografía, Centro Oceanográfico de Málaga, Puerto Pesquero s/n, 29640 Fuengirola, Málaga, Spain Víctor Díaz-del-Río, Instituto Español de Oceanografía, Centro Oceanográfico de Málaga, Puerto Pesquero s/n, 29640 Fuengirola, Málaga, Spain Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    This paper presents evidence for the presence of shallow-water contourite drifts on the south-western shelf and shelf edge off Mallorca in water depths between 150 and 275 m. These are called the Mallorca contourite depositional system (CDS). The elongate-mounded shallow-water CDS in this area is ascribed to an offshoot of the Balearic Current, which flows north to south through the Mallorca Channel as part of the overall thermohaline circulation in the Mediterranean Sea. Drift geometry suggests that the north–south current is deflected into an east–west flow pattern by interaction with a marked seafloor bathymetry, associated with major fault displacement. Four seismic units separated by three prominent discontinuities can be identified. The three internal discontinuities are correlated to large-scale basin-wide events: the lower Pliocene revolution (4.2 Ma), the upper Pliocene revolution (2.4 Ma) and the mid-Pleistocene revolution (0.9 Ma). The Plio-Quaternary succession has been deposited on top of a Miocene reef, which serves as an acoustic basement and is affected by a large fault, offsetting the basement on average by 150 m. Marked erosional features throughout and further incision of the Sant Jordi Channel along the basement fault in the Pleistocene deposits indicate stronger currents in this period. The Pleistocene deposits also show a pronounced cyclicity, which is tentatively ascribed to climatic variations and the effects of eustatic sea-level fluctuation over the south-western Mallorca shelf at that time. Content Type Journal Article Pages 1-13 DOI 10.1007/s00367-011-0248-9 Authors Thomas Philippe Vandorpe, Renard Centre of Marine Geology, Department of Geology & Soil Science, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium David Van Rooij, Renard Centre of Marine Geology, Department of Geology & Soil Science, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium Dorrik A. V. Stow, Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh, EH14 4AS UK Jean-Pierre Henriet, Renard Centre of Marine Geology, Department of Geology & Soil Science, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460

Description:    This contribution to this special volume represents the first attempt to comprehensively describe regional contourite (along-slope) processes and their sedimentary impacts around the Iberian margin, combining numerically simulated bottom currents with existing knowledge of contourite depositional and erosional features. The circulation of water masses is correlated with major contourite depositional systems (CDSs), and potential areas where new CDSs could be found are identified. Water-mass circulation leads to the development of along-slope currents which, in turn, generate contourite features comprising individual contourite drifts and erosional elements forming extensive, complex CDSs of considerable thickness in various geological settings. The regionally simulated bottom-current velocities reveal the strong impact of these water masses on the seafloor, especially in two principal areas: (1) the continental slopes of the Alboran Sea and the Atlantic Iberian margins, and (2) the abyssal plains in the Western Mediterranean and eastern Atlantic. Contourite processes at this scale are associated mainly with the Western Mediterranean Deep Water and the Levantine Intermediate Water in the Alboran Sea, and with both the Mediterranean Outflow Water and the Lower Deep Water in the Atlantic. Deep gateways are essential in controlling water-mass exchange between the abyssal plains, and thereby bottom-current velocities and pathways. Seamounts represent important obstacles for water-mass circulation, and high bottom-current velocities are predicted around their flanks, too. Based on these findings and those of a selected literature review, including less easily accessible “grey literature” such as theses and internal reports, it is clear that the role of bottom currents in shaping continental margins and abyssal plains has to date been generally underestimated, and that many may harbour contourite systems which still remain unexplored today. CDSs incorporate valuable sedimentary records of Iberian margin geological evolution, and further study seems promising in terms of not only stratigraphic, sedimentological, palaeoceanographic and palaeoclimatological research but also possible deep marine geohabitats and/or mineral and energy resources. Content Type Journal Article Pages 1-27 DOI 10.1007/s00367-011-0242-2 Authors Francisco Javier Hernández-Molina, Facultad de Ciencias del Mar, Universidad de Vigo, 36200 Vigo, Spain Nuno Serra, Institute of Oceanography, University of Hamburg, Bundesstr. 53, 20146 Hamburg, Germany Dorik A. V. Stow, IPE-ECOSSE, Heriot-Watt University, Edinburgh, EH14 4AS UK Estefanía Llave, Instituto Geológico y Minero de España, Ríos Rosas 23, 28003 Madrid, Spain Gemma Ercilla, Instituto de Ciencias del Mar, CMIMA-CSIC, Paseo Marítimo de la Barcelonesa 37–49, 08003 Barcelona, Spain David Van Rooij, Renard Centre of Marine Geology (RCMG), Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium Journal Geo-Marine Letters Online ISSN 1432-1157 Print ISSN 0276-0460