Response of deep-sea ostracod assemblages to Late Cretaceous palaeoceanographical changes: ODP Site 689 in the Southern Ocean

Twenty-six deep-sea ostracod species are described from the late Campanian to late Maastrichtian of ODP Site 689 in the Southern Ocean. Three are described as new:Cytherelloidea megaspirocostata,Agulhasina sudoceanicaandPennyella foveolata. Correspondence analysis identified three faunal sample groups. The first is mainly characterised byA. sudoceanica,Kirthesp. andCytherellasp. This is replaced, first temporarily (betweenc. 71 and 69 Ma) by a group mainly characterised byArgilloeciaspp. andC. megaspirocostata, possibly a consequence of a short-lived global palaeoceanographic event marked by increased ventilation and cooling of intermediate waters at site 689. It then reappears before finally being replaced by a third group largely characterised byEucytherecf.circumcostata,P. foveolataandDutoitella mimicaDingle. This final change is coeval with a marked increase in the faunal density of ostracods, probably owing to an increase in food supply. However, the oxygen isotopic records of benthonic foraminifera suggests that the replacement of the first ostracod group by the third is a result of the long term Maastrichtian cooling of intermediate waters at high latitudes. This replacement is also coeval with a gradual change in benthonic foraminiferal assemblages at site 689. It is suggested, therefore, thatPennyellaandDutoitellahad a greater potential of adapting to successively colder palaeoceanographical conditions thanAgulhasina. The former genera have a cosmopolitan deep-sea distribution today.     

Temporal and three-dimensional spatial analyses of the frequency–magnitude distribution near Long Valley Caldera, California

The 3-D distribution of the b value of the frequency–magnitude distribution is analysed in the seismically active parts of the crust near Long Valley Caldera, California. The seismicity is sampled in spherical volumes, containing N =150 earthquakes and centred at nodes of a grid separated by 0.3  km. Significant variations in the b value are detected, with b ranging from b ≈0.6 to b ≈2.0. High b -value volumes are located near the resurgent dome, and at depths below 5  km at Mammoth Mountain. b values are found to be much lower south of the Long Valley Caldera. We interpret this to indicate that an active magma body has advanced from depths below 8  km to depths of 4 to 5  km beneath Mammoth Mountain in 1989, and that anomalous crust, either highly fractured or containing unusually high pore pressure, such as is the case in the vicinity of active magma bodies, exists north of the seismically active area beneath the resurgent dome at all depths. We also investigate the spatial distribution of temporal variations of the frequency–magnitude distribution by introducing differential b -value maps. b values increased from b ≈0.8 to b ≈1.5 underneath Mammoth Mountain at the onset of the 1989 earthquake swarm and remained high thereafter. This suggests that an intrusion permanently altered the average distribution of cracks at 5–10  km depth, or that the pore pressure permanently increased. We propose that high b values are a necessary (but not sufficient) condition near a magmatic body, and therefore spatial b -value mapping can be used to aid in the identification of active magma bodies.     

Nannofossils and biostratigraphy: An overview

Intensive biostratigraphic studies of calcareous nannofossils have been carried out for only about a decade, even though nannofossils have been known for over a century. Although coccoliths have been reported from various Paleozoic deposits, datable assemblages are known only from Liassic (early Jurassic) and younger strata. Today nannofossils are one of the best correlation tools available to the biostratigrapher in marine sediments that contain pelagic constituents. Precise age determinations and correlations can be made in Cretaceous and Cenozoic strata for which numerous reference sections have been studied. The Jurassic nannofossil succession is less completely known mainly because of a lack of good reference material.The very large number of specimens per sample and the minute size of calcareous nannofossils create both advantages and disadvantages in their utilization. Variability of synchronous assemblages may occur latitudinally as well as from the oceanic to the hemipelagic realms.     

Including the Urban Canopy Layer in a Lagrangian Particle Dispersion Model

Boundary-Layer Meteorology - When wind blows over the ocean, short wind-waves (of wavelength smaller than 10 m) are generated, rapidly reaching an equilibrium with the overlying turbulence (at...     

The Asymmetric Connection of SST in the Tasman Sea with Respect to the Opposite Phases of ENSO in Austral Summer

This study uses linear regression and composite analyses to identify a pronounced asymmetric connection of sea surface temperature (SST) in the Tasman Sea with the two opposite phases of El Ni?o-Southern Oscillation (ENSO) during austral summer. In El Ni?o years, the SST anomalies (SSTAs) in the Tasman Sea exhibit a dipolar pattern with weak warmth in the northwest and modest cooling in the southeast, while during La Ni?a years the SSTAs exhibit a basin-scale warmth with greater amplitude. Investigations into the underlying mechanism suggest that this asymmetry arises from a mechanism related to oceanic heat transport, specifically the anomalous Ekman meridional heat transport induced by the zonal wind stress anomalies, rather than the surface heat fluxes on the air-sea interface. Further analysis reveals that the asymmetry of oceanic heat transport between El Ni?o and La Ni?a years is driven by the asymmetric atmospheric circulation over the Tasman Sea stimulated by the asymmetric diabatic heating in the tropical Pacific between the two opposite ENSO phases.     

Identification and quantification of pesticides, industrial chemicals, and organobromine compounds of medium to high polarity in the North Sea

Solid-phase extraction of 20 L seawater samples enabled the enrichment and determination of a wide array of organic substances, including compounds of medium to high polarity, in the pg/L-range. A number of contaminants was detected and quantified throughout the North Sea, among them the pesticides dichlobenil (2,6-dichlorobenzonitrile), metolachlor and terbuthylazine as well as the industrial chemicals dichloropyridines (DCPy, 4 isomers) and nitrobenzene. Concentrations attained values up to 1.4 ng/L for dichlobenil, 0.83 ng/L for terbuthylazine, 0.61 ng/L for metolachlor, 0.13 ng/L for 2,6-DCPy, 4.37 ng/L for nitrobenzene and 1-8 ng/L for tris(chloropropyl)phosphates (TCPP). A number of North Sea water samples was screened for non-target compounds, revealing the presence of further contaminants, e.g., lindane and TCPP, as well as several biogenic and/or anthropogenic organobromine substances, among which bromoindols, -phenols and -anisoles were identified.     

An assessment of the risk associated with urban development in the Thiaroye area (Senegal)

Water quality data from 56 wells, aquifer characteristics, soil types and land use in the city suburb of Dakar were compared to assess the effects of land use on the Thiaroye groundwater quality. The study area encompassed an unsewered densely populated zone, agricultural land, low density villages, and undeveloped land located in the sand dunes. A method similar to GIS technologies was applied to evaluate the degree of vulnerability of the different parts of the aquifer in relation to urban development, land use and aquifer characteristics. The aquifer parameters (hydraulic conductivity, groundwater level depth, recharge, soil type) were re-evaluated qualitatively into three class rankings (high, moderate and low), depending on the likelihood for contaminants reaching the water table, then combined using the two matrix Boolean logic based approaches to identify the nine classes of vulnerability assessed in the aquifer domain. An attempt was made to explain the distribution of nitrate concentration with the assessed vulnerability. In the area assessed, in the densely populated zone running from Pikine, to Thiaroye and Yeumbeul, very high nitrate concentrations correspond with the highest vulnerability index (H1). Nitrate contamination in this area is a consequence of point-source seepage from individual septic systems improperly built in this area. In the eastern part of the aquifer, high nitrate concentrations at Deni B. Ndao, Mbawane and Golam localities coincide with a moderate vulnerability assessment. The major source of nitrate in these areas is induced by agricultural activities.     

Vesteris Seamount: An enigma in the Greenland Basin

Vesteris Seamount is a solitary submarine volcano located at 73°30 N, 9°10W in the Greenland Basin. Steeply rising from a base depth of 3100 m to a minimum depth of ~ 130 m and striking 030°/210°, the feature lies ~ 300 km east of the east Greenland margin on an otherwise nearly flat and featureless seafloor. The main body of the seamount appears to have been formed episodically, the last of which culminated about 110 000 years ago. Subsequent, lower intensity volcanic activity continued sporadically until about 25 000 years ago, as evidenced by ash layers found in cores near the base of the feature. The smoothed surfaces at the summit make it likely that the seamount actually broached the surface during the Weichselian glacial period, between 8000 and 13 000 years ago. Two multibeam bathymetric investigations aboardPFS Polarstern during ARKTIS II/4 (1984) and ARKTIS VII/1 (1990), combined with geologic sampling, single-channel seismic profiling and underwater television coverage, have resulted in a new interpretation of both the morphology and origins of the seamount. Data collected aboardPolarstern from ARKTIS II/4 (1984) have been previously reported by Hempelet al. (1991), however, when combined with the ARKTIS VII/1 (1990) data set, a more detailed interpretation of the morphology and structure was feasible. This included the elongated shape of the feature and showed the existence of several small volcanic cones on the seamount flanks.The U.S. Government right to retain a non-exclusive, royalty free licence in and to any copyright is acknowledged.