Physical properties of deep sea sediments

Erstmals quantitativ bearbeitete Rutschungen aus dem Tiefseebereich des äquatorialen Ostatlantiks liegen auf Hängen von 0,4 Grad und 0,7 Grad - das ist sehr viel flacher als die für statische Rutschungsauslösung benötigte kritische Hangneigung (14 Grad bis 16 Grad ). Im Gegensatz zu Flachwassergebieten kann bei Wassertiefen von über 4000 m natürlich der Einfluß von Wellenwirkung und Tidenhub auf die Hangstabilität vernachlässigt werden. Die Sedimentationsraten sind in diesem Bereich zur Bildung eines Porenwasserüberdruckes vielfach zu niedrig. Nach den Hangstabilitätsanalysen bilden hier Erdbeben den wirksamsten Auslösemechanismus für die Rutschungen. Dies gilt auch für Rutschungen an den Kontinentalrändern von Nordwest- und Westafrika sowie für das europäische Nordmeer und für Rutschungen im nördlichen Fidji-Becken. Das Alter der besonders gut datierten Rutschungen vom nordwestafrikanischen Kontinentalrand und der Tiefsee des äquatorialen Ostatlantiks schwankt zwischen 16,000 J.v.h. und 18,000 J.v.h. sowie etwa 130,000 J.v.h.. Es handelt sich dabei um Phasen des Beginns besonders starker Meeresspiegelschwankungen. Ein Vergleich der Meeresspiegelkurve mit dem Alter älterer Rutschungen zeigt ebenfalls eine Parallele mit Zeiten von Regressionen und Transgressionen. Durch die Meeresspiegelschwankungen werden isostatische Vertikalbewegungen des Tiefseebodens von bis zu 30 m bewirkt, die Spannungen in den Lithosphärenplatten erzeugen. Sie allein sind jedoch nicht groß genug, um Brüche in intakten Plattenbereichen zu verursachen. Entlang alter, ehemals aktiver Transform-Bruchzonen (Fracture Zones) können jedoch die aufgebauten Spannungen eher wieder abgebaut werden. Dabei entstehen kleinere Erdstösse und führen zur Auslösung von Rutschungen. Ein Vergleich der Verbreitung von Transform-Störungen und Rutschungen vor Norwegen, Nordwest- und Westafrika sowie vor dem südlichen Afrika zeigt, daß in diesen Gebieten Rutschmassen tatsächlich besonders häufig entlang und in der Verlängerung von Fracture Zones auftreten. Modellrechnungen, die mit typischen Werten für Hangwinkel (0,5 Grad bis 3 Grad) von Tiefseeböschungen und passive Kontinentalränder sowie für häufig ermittelte Scherfestigkeitsgradienten im Sediment (0,5 kPa/m bis 1,7 kPa/m) durchgeführt wurden, ergaben, daß in Gebieten mit normal konsolidierten Sedimenten (ohne Porenwasserüberdruck) nur Erdbeben Rutschungen ausgelöst haben können.

Stable carbon and oxygen isotope ratios of Planulina wuellerstorfi from sediments of the Sierra Leone Rise

Causes of change in deep water delta13C can be either global or local in extent. Global causes include (1) climatically-induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir (Shackleton, 1977), and (2) erosion and deposition of organic-rich, continental shelf sediments during sea level fluctuations which change the mean oceanic carbon: phosphorus ratio (Broecker, 1982 doi:10.1016/0079-6611(82)90007-6). Regional gradients of delta13C are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow. Changes in a single geological record of benthic foraminiferal delta13C can result from any combination of these global and abyssal circulation effects. By sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity. We can assume that each delta13C record was equally affected by global causes of delta13C variation. The differences seen between the delta13C records must, therefore, reflect changes in the distribution of delta13C in the deep ocean. We interpret these differences in distribution in terms of changes in the ocean's abyssal circulation. Benthic foraminiferal carbon isotopic evidence from a suite of Sierra Leone Rise cores indicates that the deeper parts of the eastern Atlantic basins underwent a reduction in [O2] during the maximum of the last glaciation. Reduced advection of O2-rich deep water through low-latitude fracture zones, associated with increased delivery of organic matter to the deep ocean, lowered the delta13C of deep water SumCO2 at all depths below the sill separating the eastern and western Atlantic basins (Metcalf et al., 1964 doi:10.1016/0011-7471(64)91078-2). This decreased advection into the eastern Atlantic Ocean coincides with the overall decrease in deep water production in the North Atlantic during the last glacial maximum (Curry and Lohmann, 1982 doi:10.1016/0033-5894(82)90071-0; Boyle and Keigwin, 1982 doi:10.1126/science.218.4574.784; Schnitker, 1979 doi:10.1016/0377-8398(79)90020-3; Streeter and Shackleton, 1979 doi:10.1126/science.203.4376.168).

Metamorphic processes in sediments at DSDP Leg 65 Holes

Sites 482, 483, and 485 were drilled during Leg 65 on young oceanic crust south of the Tamayo Transform Fault. The Leg 65 drilling program was part of a multinational effort to study the East Pacific Rise (EPR) and complements sea bottom surveys conducted both in this area (Lewis, 1979; Cyamex Scientific Team and Pastouret, 1981) and farther south at 21 °N (Larson, 1971; Normark, 1976; Cyamex Scientific Team; Rise Project Group, 1980). These studies, which included deep-tow, Angus and submersible surveys, were recently complemented by sea-beam surveys conducted by the Jean Charcot on the Tamayo Fracture Zone and farther south along the EPR. They have led to a better understanding of the magmatic, tectonic, and sedimentary processes occurring on the East Pacific Rise between the Tamayo and Rivera fracture zones. The purpose of this chapter is to describe the metamorphic processes affecting Pliocene through Quaternary sediments found in contact, or inter layered, with basaltic units drilled during Leg 65 at the mouth of the Gulf of California.

Dive depth and dive duration data of male southern elephant seals from Marion Island between 2004 and 2008 with links to datasets

We describe the habitat use of 22 male southern elephant seals (Mirounga leonina) satellite tagged at Marion Island between 2004 and 2008. While a few areas of increased utilization appeared to be associated with areas of shallower bathymetry (such as sea-floor ridges and fracture zones), seals in our study did not target other areas of shallow bathymetry within close proximity to Marion Island. Rather, most elephant seals foraged pelagically over very deep water where much variation was evident in diel vertical migration strategies. These strategies resulted in generally deeper and longer dives than what has been reported for male elephant seals from other colonies. No significant differences were recorded for dive durations or dive depths between adults and sub-adults. However, younger animals displayed a positive relationship between dive durations and age, as well as between dive depths and age, while these relationships became negative for older animals. Mixed model outputs suggested that seals increased their aerobic fitness as migrations progressed, enabling them to undertake longer dives. We conclude that Marion Island male elephant seals exhibit much variability in dive strategy and are seemingly capable of exploiting a range of different prey types occurring in various depth layers.

Benthic foraminifera of surface sediments from the continental slope off Sierra Leone, North-West Africa

On "Meteor" cruise 30 (1973) 22 piston-cores were collected off Sierra Leone from water-depths between about 5000 m (Sierra Leone Basin) and 500 m (upper continental slope) with the objective to study the sediment composition and age as well as processes of sedimentation on the continental slope in a tropical humid region. Granulometric analysis and determinations of the carbonate contents of the sediment samples were carried out, as well as qualitative and quantitative analysis of the components of the grain size fractions > 63 µm and of the planktonic and benthonic foraminifera > 160 µm. Presently, the cold Canary Current influences the composition of the planktonic foraminifera within the northwestern area of investigation (profile A), whereas the planktonic fauna of the eastern area (profile C) seems to be truly tropical. In all Quaternary sediments from the continental slope off Sierra Leone, species of Globorotalia are less abundant than in truly pelagic sediments. For that reason, the zonation of the Pleistocene sediments based on the presence or absence of Globorotalia cultrata does not always agree with the climatic changes reflected in the sediments. Concerning past climates better results can be obtained by using the changes in percentage abundances of Globigerina sp. sp. and Globigerinoides sp. sp. as indicators for cool and warm temperatures. The Tertiary sediments contain a pelagic foraminiferal assemblage. In the Holocene sediments the benthonic foraminifera do not only serve as good paleodepth indicators, but their communities are also restricted to defined water masses, which change their positions in accordance with climatic changes. Thus, Cassidulina carinata in the area of investigation is an excellent indicator for sediments deposited during times, which were cooler than today; this is true for all cores from the continental slope off Sierra Leone independent of water-depth although this species presently abounds at water-depths around 600 m. The cores from the continental rise and from the Sierra Leone Basin (M30-261, M30-146, M30-147) were deposited below the calcium carbonate compensation depth. Only small sections of the cores consist of the original carbonate-free sediments, whereas the main part of the sediment column is redeposited material, rich in foraminifera, which normally live on the upper continental slope, or even on the shelf. From these cores only M30-261 can be subdivided into biostratigraphic zones ranging from zone V to zone Y. In all cores from the middle and upper continental slope of the eastern area of investigation (profile C; KL 230, 209-204) and in cores KL 183 and KL 184 from the northwestern area (profile A) we observed an undisturbed succession of sediments from the biostratigraphic zones X (partly), Y and Z. All cores from the central area (M30-181, M30-182, M30-262 to 264) and M30-187 from the upper slope of profile A show variable hiatuses in the sedimentary record. Locally, high velocity bottom currents were probably responsible for erosion, nondeposition or minimal sedimentation rates. These currents might have been initiated partly by the somewhat exposed position of this part of the continental slope, where the shelf edge bends from a northwest towards an eastern direction, and partly by very young tectonic movements. Fracture zones with vertically displaced fault blocs are frequent at Sierra Leone continental margin. According to seismic measurements by McMaster et al. (1975) the sites of the central area are located on an uplifted fault bloc explaining the reduced sediment rates or erosion. Unlike the central area, the eastern area (profile C) is situated on a downfaulted bloc with high sediment rates. The sediments from the cores of profile B as well as the turbiditic deep-sea sediments were deposited under a higher flow regime; therefore they are coarser than the extremely fine-grained sediments of the cores from profile C. Since the sand fraction (> 63 µm) is mainly composed of foraminifera, besides pteropods and light-colored fecal pellets, the carbonate content increases with the increasing percentage of the coarse grain fraction. Higher concentrations of quartz were only observed in core sections with considerable carbonate dissolution (mainly in the X-Zone), and, in general, in all sediments from the eastern area with higher terrigenous input including larger concentration of mica. Especially during times transitional between glacials and interglacials (or interstadials) the bottom currents were intensified. The percentages of coarse fraction and carbonate increase with increasing current velocities. Calcium carbonate dissolution becomes important in water depths > 3500 m. During cooler times the lysokline is depressed. Light-colored fecal pellets were redeposited from Late Neogene sediments (M30-187, M30-181). In the area of investigation they occur in the Holocene and mainly the Pleistocene sediments of the cores from the northwestern and central area because only here Tertiary sediments have been eroded at the uppermost continental slope. In the central area there are at least two periods of non-sedimentation and/or erosion which can be confined as being (1) not older than middle Pliocene and not younger than zone V and (2) younger than zone W. The local character of the erosion is documented by the fact that a complete Late Quaternary section is present in the cores of the northwestern and eastern area, each within less than 100 km from incomplete cores from the central area.

Geochemistry and isotopes at DSDP Hole 79-546

At Site 546, below the Mazagan Escarpment at a water depth of 4 km, 36 m of salt rock was cored from the top of one of a field of salt domes. The core was studied by thin section and a variety of geochemical procedures. The salt rock contains 0.1 to 3% carnallite and lesser amounts of sylvite and polyhalite, which with the corresponding high level of bromide place it within the potash evaporite facies. The bromide profile is of a dominantly marine evaporite deposited in moderately shallow brine which, however, was not repeatedly desiccated. A mineralogical argument suggests that the brine surface was not below sea level. An average of about 5% elastics, with dispersed anhydrite, darken the salt rock to deep shades of red, brown, and gray green. Most of the included materials are in highly deformed boudins or dispersions in the salt rock that has also undergone cataclasis in a subsequent, probably tectonic, deformation. The salt rock is slightly deficient in anhydrite, and the usual separate beds and laminae of anhydrite are virtually absent. Stable isotope ratios of sulfur and oxygen in the sulfate are clearly derived from sea water of Permian to Scythian age, in contrast to the late Triassic or Early Jurassic age of evaporites onshore in Morocco and Portugal and the corresponding evaporites offshore Maritime Canada. In contrast to those evaporites off the axis of Atlantic rifting, the salt at Site 546 may have been deposited in a very early central rift fed by marine waters from Tethys through the Gibraltar or South Atlas fracture zones.

Daily pan-Arctic sea-ice lead maps for 2003-2015, with links to maps in netCDF format

The presence of sea-ice leads represents a key feature of the Arctic sea ice cover. Leads promote the flux of sensible and latent heat from the ocean to the cold winter atmosphere and are thereby crucial for air-sea-ice-ocean interactions. We here apply a binary segmentation procedure to identify leads from MODIS thermal infrared imagery on a daily time scale. The method separates identified leads into two uncertainty categories, with the high uncertainty being attributed to artifacts that arise from warm signatures of unrecognized clouds. Based on the obtained lead detections, we compute quasi-daily pan-Arctic lead maps for the months of January to April, 2003-2015. Our results highlight the marginal ice zone in the Fram Strait and Barents Sea as the primary region for lead activity. The spatial distribution of the average pan-Arctic lead frequencies reveals, moreover, distinct patterns of predominant fracture zones in the Beaufort Sea and along the shelf-breaks, mainly in the Siberian sector of the Arctic Ocean as well as the well-known polynya and fast-ice locations. Additionally, a substantial inter-annual variability of lead occurrences in the Arctic is indicated.

Petrology and origin of basalts at DSDP Hole 66-487

The volcanism of Central America, according to current theory (Pichler and Weyl, 1973; Stoiber and Carr, 1974; Hey, 1977), is related to the subduction of the Cocos Plate under the North American lithospheric plate and the melting of ocean crust material in the subduction zone (Green and Ringwood, 1968; Dickinson, 1970, Fitton, 1971). Since Cocos Plate subduction occurs at the rate of more than 7 cm/y. (Hey et al., 1977), basalts underlying upper Miocene sediments of the Middle America Trench outer slope, penetrated in Hole 487 (Fig. 1) during Leg 66 (Moore et al., 1979), should have formed far from their present position if current theory is accurate. Present manifestations of basaltic magmatism in adjacent areas of the Pacific derive from the axial part of the East Pacific Rise, the Galapagos spreading center, and transform fracture zones. The question arises: Are there analogs of the Middle America Trench basalts among magmatic cock associated with these modern features, or do the trench basalts have some other origin?

Properties, sedimentation and accumulation rates, and chemical composition of bottom sediments from the Deryugin Basin, Sea of Okhotsk

Results of a study of contents and accumulation rates of Fe, Mn, and some trace elements in Upper Quaternary sediments of the Deryugin Basin are presented. Maps of average contents and accumulation rates of excessive Fe, Mn, Zn, Ba, Ni, Pb, Cu, and Mo in sediments of the first oxygen isotope stage (OIS) have been plotted. Anomalous contents and accumulation rates are confined to peripheral zones of the Deryugin sedimentary basin and large fracture zones. Different mechanisms of influence of fluid-dynamic processes on rate of hydrogenic and biogenic accumulation of ore elements are assumed.

Swath sonar bathymetry during POLARSTERN cruise ANT-XXVI/2 (PS75) with links to multibeam raw data files

Multibeam data were collected during R/V Polarstern cruise ANT-XXVI/2 along track lines of about 9,270 NM total length along transits, survey profiles and during stationary work. Departing in Punta Arenas the ship headed for its first main working area, the Eltanin Impact Area. In the following the ship's track crosses Pacific Antarctic Ridge and the corresponding fracture zones several times before arriving in Wellington. The refraction correction was achieved utilizing CTD profiles or by the system's own cross fan calibration. The quality of data might be reduced during bad weather periods or adverse sea ice conditions. The dataset contains raw data that are not processed and thus may contain errors and blunders in depth and position.

(Table 1) Magnetic viscosity coefficient, VRM and NRM of DSDP Hole 6-57

THE magnetic properties of the basalts which form layer 2 of the oceanic lithosphere are important because of their relevance to the hypothesis (Vine and Matthews, 1963, doi:10.1038/199947a0) of seafloor spreading. Most studies of these magnetic properties have been carried out on basalts obtained from dredge hauls taken predominantly from ocean ridge systems and fracture zones. These constitute special areas of the oceanic crust where the sediment cover is negligible. It is of interest to compare the magnetic properties of the dredged basalts with samples recovered from holes drilled through the overlying sediments into the basaltic layer at places distant from ridge axes. Samples obtained from the abandoned Mohole project and, more recently, from the Deep Sea Drilling Project (DSDP) possessed magnetic properties similar to those of dredged basalts (Cox and Doell, 1962, doi:10.1029/JZ067i010p03997; Lowrie et al., 1973, doi:10.1016/0012-821X(73)90198-2). Here I describe highly unstable magnetic characteristics found in basalts from DSDP hole 57.

Stable carbon and oxygen isotope ratios of benthic foraminifera

Carbon isotopic measurements on the benthic foraminiferal genus Cibicidoides document that mean deep ocean delta13C values were 0.46 per mil lower during the last glacial maximum than during the Late Holocene. The geographic distribution of delta13C was altered by changes in the production rate of nutrient-depleted deep water in the North Atlantic. During the Late Holocene, North Atlantic Deep Water, with high delta13C values and low nutrient values, can be found throughout the Atlantic Ocean, and its effects can be traced into the southern ocean where it mixes with recirculated Pacific deep water. During the glaciation, decreased production of North Atlantic Deep Water allowed southern ocean deep water to penetrate farther into the North Atlantic and across low-latitude fracture zones into the eastern Atlantic. Mean southern ocean delta13C values during the glaciation are lower than both North Atlantic and Pacific delta13C values, suggesting that production of nutrient-depleted water occurred in both oceans during the glaciation. Enriched 13C values in shallow cores within the Atlantic Ocean indicate the existence of a nutrient-depleted water mass above 2000 m in this ocean.

Benthic foraminifera in Southwest Indian Ocean surface sediments

The distribution of deep-sea benthonic foraminifera in core top samples from the southwest Indian Ocean is examined. Principal component analysis reveals two major assemblages. One assemblages between 3600 and 4800-m water depth is dominated by Episominella umbonifera and is associated with cold (Theta = -0.3 to 0.8°C), low salinity (34.66 to 34.72 * 10**-3) Antarctic Bottom Water in the Crozet Basin, in fracture zones, and on the flanks of the Southwest Indian Ridge. A second assemblage, dominated by Planulina wuellerstorfi, Globocassidulina subglobasa, Astrononion echolsi and Pullenia bulloides, is between 1600 and 3800 m on the Crozet Plateau, Madagascar Ridge, Central Indian Ridge, and Southwest Indian Ridge and is associated with relatively warm (Theta = 0.8 to 2.6°C), high salinity (34.72 to 34.76 * 10**-3) North Atlantic Deep Water. The third principal component divides the P. wuellerstorfi assemblage into two subgroups. One is dominated by Epistominella exigua, P. bulloides, P. wuellerstorfi, and A. echolsi and a second is dominated by G. subglobosa. The distribution of the E. umbonifera assemblage and previous hydrographic studies suggest that AABW flows as a western boundary contour current in the Crozet Basin and penetrates fracture zones in the Southwest Indian Ridge between 55 and 57°E and near 66°E as it travels northward into the Madagascar and Mascarene basins. The faunal-water mass associations from the southeast Indian Ocean are compared; the most notable faunal difference is the absence of Uvigerina as a dominant taxon in the southwest Indian Ocean. A comparison of dissolved oxygen and Uvigerina data shows that oxygen is not a major influence upon the distribution of Uvigerina. A correlation analysis of the faunal data and water depth, potential temperature, in situ temperature, salinity, dissolved oxygen, and 1 - Omega, an index of calcium carbonate undersaturation, was carried out to determine the relationships between fauna and hydrography. The second principal component has a significant positive correlation at the 99.9% level with temperature and negative correlations with water depth and 1 - Omega. A general faunal-water mass correlation exists, but it is not possible to determine which variable controls the faunal distributions.

PIES time series in the North Atlantic at the Mid-Atlantic Ridge (2006-2010)

In the western North Atlantic, warm and saline water is brought by the North Atlantic Current (NAC) from the subtropics into the subpolar gyre. Four inverted echo sounders with high precision pressure sensors (PIES) were moored between 47°40' N and 52°30' N to study the main pathways of the NAC from the western into the eastern basin. The array configuration that forms three segments (northern, central, and southern) allows partitioning of the NAC and some assessment of NAC flow paths through the different Mid-Atlantic Ridge fracture zones. We exploit the correlation between the NAC transport measured between 2006 and 2010 and the geostrophic velocity from altimeter data to extend the time series of NAC transports to the period from 1992 to 2013. The mean NAC transport over the entire 21 years is 27 ± 5 Sv, consisting of 60% warm water of subtropical origin and 40% subpolar water. We did not find a significant trend in the total transport time series, but individual segments had opposing trends, leading to a more focused NAC in the central subsection and decreasing transports in the southern and northern segments. The spectral analysis exhibits several significant peaks. The two most prominent are around 120 days, identified as the time scale of meanders and eddies, and at 4-9 years, most likely related to the NAO. Transport composites for the years of highest and lowest NAO indices showed a significantly higher transport (+2.9 Sv) during strong NAO years, mainly in the southern segment.