Discovery of ferromanganese hydrocarbon-related nodules associated with the Meknes mud volcano (Western Moroccan margin)

A suite of ferromanganese nodules were sampled during the MVSEIS-2008 cruise aboard of the R/V Hespérides in the flanks of Meknes mud volcano (Moroccan margin, NE Central Atlantic). The nodules were collected at water depths between 750-850 m within a seabed area characterized by high acoustic backscatter values. Debris of cold water corals and hydrocarbon-derived authigenic carbonate crusts were sampled at same time. The nodules show tabular morphology, up to 20 cm in maximum diameter and 2 kg of weight, brown-reddish external color and they are internally composed by a concentric to complex arrangement of laminae. The results of X-ray diffraction analysis show that these ferromanganese nodules are essentially composed of goethite and lepidocrocite, being Mn-oxides, silicates (quartz and clay minerals) and carbonates (calcite, dolomite and siderite) accessory to occasional minerals. All the samples display micritic to micro-sparitic mosaic under the petrographic microscope which forms massive, laminated or dendritic-mottled textures. The nodules show a high abundance of Fe, minor Mn and low contents of trace metals and REEs. Mature hydrocarbons, as n-alkanes derived from marine bacterial activity, and phenanthrene have been detected in all the ferromanganese nodules analyzed. These nodules display analogous characteristics (textural, mineralogical and geochemical) to the nodules studied by González et al (2009) in the carbonate mud-mounds in the Gulf of Cadiz, offshore Iberian margin. In this way, the same preliminary genetic model proposed for these nodules might be applicable to those find in the Meknes mud volcano. Therefore, the anaerobic oxidation of hydrocarbon-rich fluids within the mud-breccia sediments in the flanks of Meknes mud volcano would induce the formation of early diagenetic Fe-(Mn) carbonate nodules. Thus, the nodules were later exhumed by the erosive action of sea bottom currents generating the replacement of ferromanganese carbonates by Fe-Mn oxy-hydroxides. Thus, the hydrocarbon-rich fluid venting from deep seated reservoirs and erosive action of bottom currents must have been essential actors, as mineralization controls, for ferromanganese nodules generation and evolution. These findings imply that this type of nodules must be considered as new product as derived from the anaerobic/aerobic oxidation of hydrocarbons in areas of active seepages.

First Western Atlantic occurrence of the pigmy killer whale [by] Pauline James, Frank W. Judd, and Joseph Curtis Moore.

v.58:no.1(1970)

Stable oxygen isotope records of different benthic foraminiferal species of core GeoB3004-1 from the western Arabian Sea

The stable isotope composition of one epifaunal and three infaunal benthic foraminiferal species of a sediment core from 1800 m water depth of the western Arabian Sea was determined to evaluate deepwater oxygenation, organic matter remineralization, and early diagenetic processes during the past 190,000 years. The d18O records reveal species-specific metabolic effects, susceptibility to changes in carbonate ion concentration, and supralysoclinal calcite dissolution. The foraminiferal d13C records reveal changes in the stable carbon isotope gradients of pore water dissolved inorganic carbon (d13CDIC) and in the microhabitat depth of infaunal species. Maximum d13CDIC offsets between bottom and pore waters ranged between mean values of 0.8 and 1.2% corresponding to estimates of deepwater oxygen concentration between approximately 1 and 2.7 ml/l. Intervals of improved deepwater oxygenation coincided with high benthic foraminiferal diversity and indicate the admixture of well-oxygenated deepwater masses during interglacials. During interglacial maxima the d13C difference between epifauna and shallow infauna indicates highest organic matter remineralization rates at times of maximum organic matter fluxes.

(Table 1) Age determination of western North Atlantic sediment cores

Foraminiferal abundance, 14C ventilation ages, and stable isotope ratios in cores from high deposition rate locations in the western subtropical North Atlantic are used to infer changes in ocean and climate during the Younger Dryas (YD) and Last Glacial Maximum (LGM). The d18O of the surface dwelling planktonic foram Globigerinoides ruber records the present-day decrease in surface temperature (SST) of ~4°C from Gulf Stream waters to the northeastern Bermuda Rise. If during the LGM the modern d18O/salinity relationship was maintained, this SST contrast was reduced to 2°C. With LGM to interglacial d18O changes of at least 2.2 per mil, SSTs in the western subtropical gyre may have been as much as 5°C colder. Above ~2.3 km, glacial d13C was higher than today, consistent with nutrient-depleted (younger) bottom waters, as identified previously. Below that, d13C decreased continually to -0.5 per mil, about equal to the lowest LGM d13C in the North Pacific Ocean. Seven pairs of benthic and planktonic foraminiferal 14C dates from cores >2.5 km deep differ by 1100 ± 340 years, with a maximum apparent ventilation age of ~1500 years at 4250 m and at ~4700 m. Apparent ventilation ages are presently unavailable for the LGM < 2.5 km because of problems with reworking on the continental slope when sea level was low. Because LGM d13C is about the same in the deep North Atlantic and the deep North Pacific, and because the oldest apparent ventilation ages in the LGM North Atlantic are the same as the North Pacific today, it is possible that the same water mass, probably of southern origin, flowed deep within each basin during the LGM. Very early in the YD, dated here at 11.25 ± 0.25 (n = 10) conventional 14C kyr BP (equal to 12.9 calendar kyr BP), apparent ventilation ages <2.3 km water depth were about the same as North Atlantic Deep Water today. Below ~2.3 km, four YD pairs average 1030 ± 400 years. The oldest apparent ventilation age for the YD is 1600 years at 4250 m. This strong contrast in ventilation, which indicates a front between water masses of very different origin, is similar to glacial profiles of nutrient-like proxies. This suggests that the LGM and YD modes of ocean circulation were the same.

Chemical observations in the Red Sea and the inner Gulf of Aden during the International Indian Ocean Expedition 1964/65

The Red Sea has a special place among the adjacent seas of the world. High evaporation, exclusion of its deep water from contact with the Indian Ocean proper and complete absence of continental drainage may result special conditions of the chemistry of the Red Sea. This paper aims to describe and explain the peculiarity of the hydrochemical situation. The influence of the topography, of the inflow and outflow through the straights of Bab el Mandeb, of the evaporation, of the stability of the water layers, and of the circulation will be studied. An attempt is made to estimate the apparent oxygen ultilisation in order to obtain an indication of the biological activity. A further attempt is made toward the quantitative estimation of the circulation of the nutrients and also to obtain some information about transport, dissolution, and precipitation of calcium carbonate. The basis of these investigations are mainly observations of R. V. "Meteor" during the International Indian Ocean Expedition 1964/65. The determination of dissolved oxygen, dissolved inorganic phosphate, nitrate, nitrite, ammonia, pH, alkalinity, silicate as well as salinity and temperature forms the necessary basis for such an investigation of the chemical conditions. In the first chapter the methods and some modifications for the determination of the chemical properties as applied during the I.I.O.E. cruise of R. V. "Meteor" are described. The new methods, as worked out and tested under sea going conditions during several years by the author, are described in more detail. These are the methods for nitrate, silicate, the automatic determination of dissolved inorganic phosphate and silicate, the automated determination of total phosphorus, the in situ recording of the oxygen tension, and the modification for the determination of ammonia, calcium, and dissolved oxygen. With these revised methods more than 18,000 determinations have been carried out during the Indian Ocean cruise. The complete working up of the chemical data of the Indian Ocean Expedition of R. V. "Meteor" is devided into four sections: Contributions 1) to the Chemistry of the Red Sea and the Inner Gulf of Aden, 2) to the Gulf of Aden and the Somali Coast Region, 3) to the Western Indian Coast Region, and 4) to the Persian Gulf and the Straits of Oman. This paper presents the first contribution. The special hydrographical conditions are discussed. It can be shown, that the increase of salinity in the surface waters from the south to the north of the Red Sea is only to about 30 % due to evaporation. The remaining increase is presumed to be due to the admixture of deep water to the surface layers. A special rate for the consumption of oxygen (0.114 ml/ l/a) is derived for the deep water of the Red Sea at 1500 m. Based upon the distribution of the dissolved oxygen along the axii of the Red Sea, a chematic model for the longitudinal circulation of the Red Sea is constructed. This model should be considered as a first approximation and may explain the special distribution of phosphate, nitrate, and silicate. Based upon the evaluation of the residence time of the deep water a dissolution rate for silicate is estimated as 1 mygat/a. It seems possible to calculate residence times of water masses outside the Red Sea from the silicate content. The increase of silicate and the consumption of oxygen lead to residence times of the water below the thermocine of 30 to 48 years. The distribution of oxygen in the Straits of Bab el Mandeb is described and discussed. The rate of consumption of the oxygen in the outflowing Red Sea water is estimated to 8.5 ml/ l/a. This rather high rate is explained with reference to the special conditions in the outflowing water. The Red Sea water is characterized initially by a relative high content of oxygen and a low content of nutrients. The increase in nutrients and the decrease in the oxygen content is a secondary process of the Red Sea water on its way to the Arabian Sea. Based upon the vertical distribution of the dissolved inorganic phosphate vertical exchange coefficients of 1 - 4 g/cm/sec and vertical current speeds of 10**-5 to 10**-4 cm/sec are calculated for some stations in the Red Sea. The distribution of phosphate, silicate, nitrate, nitrite and ammonia for the Red Sea and the Straits of Bab el Mandeb are discussed. The special circulation is evaluated and the balance of the nutrients is estimated by means of the brutto transport. The nutrient deficit is assumed to be balanced by sporadic inflow of intermediate water from the Gulf of Aden. An example for such an inflow has been observed and is demonstrated. The silicate-salinity relationships are a suitable way for characterizing water masses in the Red Sea. Equations for the calculation of the different components from the carbonate system, the ion activities, and the calcium carbonate saturation are evaluated. The influence of temperature and pressure is taken into account. The carbonate saturation is calculated from the determined concentrations of calcium, alkalinity, and the hydrogen ion activity. Saturation values of 320 % are found for the surface layer and of 100% ± 1 for the deep water. The extraordinary equilibrium conditions may explain the constant Ca/Cl ratio and also the sedimentation of undissolved carbonate skelecons even in greater depths. A main sedimentation rate of 2 * 10**-3cm/year is evaluated from a total sedimentation of 10 * 106 to/a of calcium carbonate in the Red Sea. The appendix contains those data, which are not published in the data volume of the I.I.O.E. expedition of R. V. "Meteor".

Initial assessment of time of travel and mixing through Gulf Island Pond and the lower Androscoggin River, Maine /

Bibliography: p. 29.

Age determination and paleotemperatures of western Mediterranean Sea sediments

Sea surface temperature (SST) profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a W-E latitudinal transect encompassing the Gulf of Cadiz (Atlantic Ocean), the Alboran Sea, and the southern Tyrrhenian Sea (western Mediterranean). The results document the sensitivity of the Mediterranean region to the short climatic changes of the North Atlantic Ocean, particularly those involving the latitudinal position of the polar front. The amplitude of the SST oscillations increases toward the Tyrrhenian Sea, indicating an amplification effect of the Atlantic signal by the climatic regime of the Mediterranean region. All studied cores show a shorter cooling phase (700 years) for the Younger Dryas (YD) than that observed in the North Atlantic region (1200 years). This time diachroneity is related to an intra-YD climatic change documented in the European continent. Minor oscillations in the southward displacement of the North Atlantic polar front may also have driven this early warming in the studied area. During the Holocene a regional diachroneity propagating west to east is observed for the SST maxima, 11.5-10.2 kyr B.P. in the Gulf of Cadiz, 10-9 kyr B.P. in the Alboran Sea, and 8.9-8.4 kyr B.P. in the Thyrrenian Sea. A general cooling trend from these SST maxima to present day is observed during this stage, which is marked by short cooling oscillations with a periodicity of 730±40 years and its harmonics.

Sedimentology and geochemistry of surface sediments from the Pagassitikos Gulf

Volos city and its port are situated in the northern part of Pagassitikos Gulf, a shallow, semi-enclosed marine area in central Greece. A wastewater treatment plant (WWTP) and pipeline operate in the same area. Muddy sediments with low carbonate contents cover most of the seabed, except for the Volos embayment and the western part of the gulf where sandy carbonates prevail. Bulk organic carbon contents and the organic carbon contents of the clay fractions are high in the vicinity of Volos embayment. High element (Pb, Cu, and Zn) contents and Igeo (geoaccumulation index) values were found for the clay fractions in the northern part of Pagassitikos Gulf. This enrichment is attributed to the discharge of raw domestic and industrial effluents of Volos city and port before the WWTP was installed. The dispersal of pollutants is essentially controlled by diffusion from point sources (city, port and WWTP) and is limited to Volos Bay. Relatively high Mn levels are ascribed to diagenetic formation of manganese carbonates (authigenic phase), whereas Cr and Ni are elevated due to weathering of ultrabasic formations on land.

Mineralogical, geochemical and magnetic signatures of surface sediments from the Canadian Beaufort Shelf and Amundsen Gulf (Canadian Arctic)

Mineralogical, geochemical, magnetic, and siliciclastic grain-size signatures of 34 surface sediment samples from the Mackenzie-Beaufort Sea Slope and Amundsen Gulf were studied in order to better constrain the redox status, detrital particle provenance, and sediment dynamics in the western Canadian Arctic. Redox-sensitive elements (Mn, Fe, V, Cr, Zn) indicate that modern sedimentary deposition within the Mackenzie-Beaufort Sea Slope and Amundsen Gulf took place under oxic bottom-water conditions, with more turbulent mixing conditions and thus a well-oxygenated water column prevailing within the Amundsen Gulf. The analytical data obtained, combined with multivariate statistical (notably, principal component and fuzzy c-means clustering analyses) and spatial analyses, allowed the division of the study area into four provinces with distinct sedimentary compositions: (1) the Mackenzie Trough-Canadian Beaufort Shelf with high phyllosilicate-Fe oxide-magnetite and Al-K-Ti-Fe-Cr-V-Zn-P contents; (2) Southwestern Banks Island, characterized by high dolomite-K-feldspar and Ca-Mg-LOI contents; (3) the Central Amundsen Gulf, a transitional zone typified by intermediate phyllosilicate-magnetite-K-feldspar-dolomite and Al-K-Ti-Fe-Mn-V-Zn-Sr-Ca-Mg-LOI contents; and (4) mud volcanoes on the Canadian Beaufort Shelf distinguished by poorly sorted coarse-silt with high quartz-plagioclase-authigenic carbonate and Si-Zr contents, as well as high magnetic susceptibility. Our results also confirm that the present-day sedimentary dynamics on the Canadian Beaufort Shelf is mainly controlled by sediment supply from the Mackenzie River. Overall, these insights provide a basis for future studies using mineralogical, geochemical, and magnetic signatures of Canadian Arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late Quaternary climate and oceanographic changes.

On the sound waves propagation in the Persian Gulf

In this research I focused on the propagation of acoustic rays in shallow water areas then I selected the Persian Gulf and described sound transmission in this region with emphasize on physical properties of water masses and of sediments. Finally I studied on the sound speed variations and sound attention with data collected from this area (NE of Farsi Island & 50 kilometers south of Delware). Sound speed deviation in western part of Strait of Hormuz in winter is between 20-30 m/s and it is between 5-20 m/s in the Oman Sea. Minimum sound speed deviation is at 23-24 degree north & 60-62 degree east. In spring, this deviation varies from 25-35 m/s, which is greater than in winter. In winter, at east of 56 degree east, greater speed are in shallow water coastal areas. In summer, sound speeds are greater than in spring and vary from 35 to 55 m/s at western part of Strait of Hormuz and 20 to 40 m/s in Oman Sea. Finally in autumn, sound speed deviation is 30-45 m/s west of 56 degree east and in Oman Sea is the same. The greatest attenuation rate caused by absorption in Bandar Dayer is between 17 to 27 meters depth, which is from water masses with different densities.

Trophic niche overlap of sprat and commercial small pelagic teleosts in the Gulf of Lions (NW Mediterranean Sea)

Increasing abundance of non-commercial sprats and decreasing biomass and landings of commercial anchovies and sardines justify the need to study the feeding ecology and trophic niche overlap of these planktivorous species in the Gulf of Lions. Their diet has been investigated on the basis of stomach content and stable isotope analyses in 2011 and 2012 according to different depths and regions in the study area. The main prey were Corycaeidae copepods, Clauso/Paracalanus, Euterpina acutifrons and Microsetella, for sprats and small copepods, such as Microsetella, Oncaea and Corycaeidae, for anchovies and sardines. This is the first time that the diet of sprats is described in the Gulf of Lions. Sprats fed on a larger size spectrum of prey and seem to be more generalist feeders compared to anchovies and sardines. Ontogenetic changes as well as spatial and temporal variations of the diet occurred in the three species. Stable isotope analysis revealed mobility of sardines and sprats among feeding areas while anchovies exhibited preferred feeding areas. Sprats showed a higher relative condition assessed by C/N ratios than sardines and anchovies. Our results showed an overlap of the trophic niches for the three species, indicating a potential trophic competition in the Gulf of Lions.

Influence of environmental variability and age on the body condition of small pelagic fish in the Gulf of Lions

Endogenous and environmental variables are fundamental in explaining variations in fish condition. Based on more than 20 yr of fish weight and length data, relative condition indices were computed for anchovy and sardine caught in the Gulf of Lions. Classification and regression trees (CART) were used to identify endogenous factors affecting fish condition, and to group years of similar condition. Both species showed a similar annual cycle with condition being minimal in February and maximal in July. CART identified 3 groups of years where the fish populations generally showed poor, average and good condition and within which condition differed between age classes but not according to sex. In particular, during the period of poor condition (mostly recent years), sardines older than 1 yr appeared to be more strongly affected than younger individuals. Time-series were analyzed using generalized linear models (GLMs) to examine the effects of oceanographic abiotic (temperature, Western Mediterranean Oscillation [WeMO] and Rhone outflow) and biotic (chlorophyll a and 6 plankton classes) factors on fish condition. The selected models explained 48 and 35% of the variance of anchovy and sardine condition, respectively. Sardine condition was negatively related to temperature but positively related to the WeMO and mesozooplankton and diatom concentrations. A positive effect of mesozooplankton and Rhone runoff on anchovy condition was detected. The importance of increasing temperatures and reduced water mixing in the NW Mediterranean Sea, affecting planktonic productivity and thus fish condition by bottom-up control processes, was highlighted by these results. Changes in plankton quality, quantity and phenology could lead to insufficient or inadequate food supply for both species.

Post-rift evolution of the Gulf of Lion margin tested by stratigraphic modelling

The sedimentary architecture of basins and passive margins is determined by a complex interaction of parameters, including subsidence, eustasy, and sediment supply. A quantification of the post-rift (20 Ma-0 Ma) vertical movements of the Gulf of Lion (West Mediterranean) is proposed here based on the stratigraphic study of sedimentary paleomarkers using a large 3D grid of reflection seismic data, correlations with existing drillings, and refraction data. Post-rift subsidence was measured by the direct use of sedimentary geometries analysed in 3D and validated by numerical stratigraphic modelling. Three domains of subsidence were found: on the continental shelf and slope, subsidence corresponds to a seaward tilting with different amplitudes, whereas the deep basin subsides purely vertically. We show that these domains fit with the deeper crustal domains highlighted by previous geophysical data, and that post-break-up subsidence follows the initial hinge lines of the rifting phase. Subsidence rates are quantified on each domain for each stratigraphic interval. At a constant distance from the rotational hinge line, the Plio-Quaternary subsidence rate is constant on the shelf overall. Conversely, Miocene subsidence rates are very different on the eastern and western shelves. Stratigraphic simulations focused on the Messinian salinity crisis (MSC) were also performed. Their results are discussed together with our post-rift subsidence estimates in order to provide ideas and hypotheses for future detailed quantifications of Miocene subsidence, including isostatic readjustments linked to the MSC.

Three dimensional numerical simulation of thermohaline currents of the Persian Gulf

Observational data and a three dimensional numerical model (POM) are used to investigate the Persian Gulf outflow structure and its spreading pathway into the Oman Sea. The model is based on orthogonal curvilinear coordinate system in horizontal and train following coordinate (sigma coordinate) system in vertical. In the simulation, the horizontal diffusivity coefficients are calculated form Smogorinsky diffusivity formula and the eddy vertical diffusivities are obtained from a second turbulence closure model (namely Mellor-Yamada level 2.5 model of turbulence). The modeling area includes the east of the Persian Gulf, the Oman Sea and a part of the north-east of the Indian Ocean. In the model, the horizontal grid spacing was assumed to be about 3.5 km and the number of vertical levels was set to 32. The simulations show that the mean salinity of the PG outflow does not change substantially during the year and is about 39 psu, while its temperature exhibits seasonal variations. These lead to variations in outflow density in a way that is has its maximum density in late winter (March) and its minimum in mid-summer (August). At the entrance to the Oman Sea, the PG outflow turns to the right due to Coriolis Effect and falls down on the continental slope until it gains its equilibrium depth. The highest density of the outflow during March causes it to sink more into the deeper depths in contrast to that of August which the density is the lowest one. Hence, the neutral buoyancy depths of the outflow are about 500 m and 250 m for March and August respectively. Then, the outflow spreads in its equilibrium depths in the Oman Sea in vicinity of western and southern boundaries until it approach the Ras al Hamra Cape where the water depth suddenly begins to increase. Therefore, during March, the outflow that is deeper and wider relative to August, is more affected by the steep slope topography and as a result of vortex stretching mechanism and conservation of potential vorticity it separates from the lateral boundaries and finally forms an anti-cyclonic eddy in the Oman Sea. But during August the outflow moves as before in vicinity of lateral boundaries. In addition, the interaction of the PG outflow with tide in the Strait of Hormuz leads to intermittency in outflow movement into the Oman Sea and it could be the major reason for generations of Peddy (Peddies) in the Oman Sea.

Characterizing, modelling and understanding the climate variability of the deep water formation in the North-Western Mediterranean Sea

Observing, modelling and understanding the climate-scale variability of the deep water formation (DWF) in the North-Western Mediterranean Sea remains today very challenging. In this study, we first characterize the interannual variability of this phenomenon by a thorough reanalysis of observations in order to establish reference time series. These quantitative indicators include 31 observed years for the yearly maximum mixed layer depth over the period 1980–2013 and a detailed multi-indicator description of the period 2007–2013. Then a 1980–2013 hindcast simulation is performed with a fully-coupled regional climate system model including the high-resolution representation of the regional atmosphere, ocean, land-surface and rivers. The simulation reproduces quantitatively well the mean behaviour and the large interannual variability of the DWF phenomenon. The model shows convection deeper than 1000 m in 2/3 of the modelled winters, a mean DWF rate equal to 0.35 Sv with maximum values of 1.7 (resp. 1.6) Sv in 2013 (resp. 2005). Using the model results, the winter-integrated buoyancy loss over the Gulf of Lions is identified as the primary driving factor of the DWF interannual variability and explains, alone, around 50 % of its variance. It is itself explained by the occurrence of few stormy days during winter. At daily scale, the Atlantic ridge weather regime is identified as favourable to strong buoyancy losses and therefore DWF, whereas the positive phase of the North Atlantic oscillation is unfavourable. The driving role of the vertical stratification in autumn, a measure of the water column inhibition to mixing, has also been analyzed. Combining both driving factors allows to explain more than 70 % of the interannual variance of the phenomenon and in particular the occurrence of the five strongest convective years of the model (1981, 1999, 2005, 2009, 2013). The model simulates qualitatively well the trends in the deep waters (warming, saltening, increase in the dense water volume, increase in the bottom water density) despite an underestimation of the salinity and density trends. These deep trends come from a heat and salt accumulation during the 1980s and the 1990s in the surface and intermediate layers of the Gulf of Lions before being transferred stepwise towards the deep layers when very convective years occur in 1999 and later. The salinity increase in the near Atlantic Ocean surface layers seems to be the external forcing that finally leads to these deep trends. In the future, our results may allow to better understand the behaviour of the DWF phenomenon in Mediterranean Sea simulations in hindcast, forecast, reanalysis or future climate change scenario modes. The robustness of the obtained results must be however confirmed in multi-model studies.