965 resultados para Inflection points


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Variability of total alkalinity in sea ice of the high-latitudinal Arctic from November 2005 to May 2006 is considered. For the bulk of one- and two-year sea ice, alkalinity dependence on salinity is described as TA = k x Sal, where k is salinity/alkalinity ratio in under-ice water. The given relationship is valid within a wide range of salinity from 0.1 psu in desalinated fraction of two-year ice to 36 psu in snow on the young ice surface. Geochemically significant deviations from the relationship noted were observed exclusively in snow and the upper layer of one-year ice. In the upper layer of one-year ice, deficiency of alkalinity is observed ( delta TA ~= -0.07 mEq/kg, or -15%). In snow on the surface of the one-year ice, alkalinity excess is formed under desalination ( delta TA is as high as 1.3 mEq/kg, or 380%). Deviations registered are caused by possibility of carbonate precipitation in form of CaCO3 x 6H2O under seawater freezing. It is shown that ice formation and the following melting might cause losses of atmospheric CO2 of up to 3 x 10**12 gC/year.

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Multiple copies of Cretaceous black shales extending from the early Cenomanian to the end of the Santonian were recovered at five sites on Demerara Rise during Leg 207 of the Ocean Drilling Program. These sediments are primarily composed of laminated organic-rich claystones interbedded with coarser, lightly laminated foraminferal-bearing packstones and wackestones. The black shales represent the local expression of widespread organic-rich sedimentation in the Atlantic during the mid-Cretaceous. However, incomplete recovery prevented construction of continuous composite sections, resulting in uncertainties concerning the correct stratigraphic placement of individual cores. By combining high-resolution measurements of bulk density collected shipboard on the multisensor track with continuous downhole measurements of formation resistivity using the Formation MicroScanner, an equivalent logging depth scale was constructed for black shales recovered from Sites 1258, 1260, and 1261. The integrated depths approach centimeter-scale resolution and are supported by comparisons of coarser resolution natural gamma ray emissions collected on cores and through downhole logging operations. The new depths highlight the extent of both intra- and intercore gaps and provide an opportunity to further constrain temporal and spatial paleoceanographic changes captured in proxy records from these sediments.

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Monitoring the impact of sea storms on coastal areas is fundamental to study beach evolution and the vulnerability of low-lying coasts to erosion and flooding. Modelling wave runup on a beach is possible, but it requires accurate topographic data and model tuning, that can be done comparing observed and modeled runup. In this study we collected aerial photos using an Unmanned Aerial Vehicle after two different swells on the same study area. We merged the point cloud obtained with photogrammetry with multibeam data, in order to obtain a complete beach topography. Then, on each set of rectified and georeferenced UAV orthophotos, we identified the maximum wave runup for both events recognizing the wet area left by the waves. We then used our topography and numerical models to simulate the wave runup and compare the model results to observed values during the two events. Our results highlight the potential of the methodology presented, which integrates UAV platforms, photogrammetry and Geographic Information Systems to provide faster and cheaper information on beach topography and geomorphology compared with traditional techniques without losing in accuracy. We use the results obtained from this technique as a topographic base for a model that calculates runup for the two swells. The observed and modeled runups are consistent, and open new directions for future research.

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Fluids in subduction zones can influence seismogenic behaviour and prism morphology. The Eastern Makran subduction zone, offshore Pakistan, has a very thick incoming sediment section of up to 7.5 km, providing a large potential fluid source to the accretionary prism. A hydrate-related bottom simulating reflector (BSR), zones of high amplitude reflectivity, seafloor seep sites and reflective thrust faults are present across the accretionary prism, indicating the presence of fluids and suggesting active fluid migration. High amplitude free gas zones and seep sites are primarily associated with anticlinal hinge traps, and fluids here appear to be sourced from shallow biogenic sources and migrate to the seafloor along minor normal faults. There are no observed seep sites associated with the surface expression of the wedge thrust faults, potentially due to burial of the surface trace by failure of the steep thrust ridge slopes. Thrust fault reflectivity is restricted to the upper 3 km of sediment and the deeper décollement is non-reflective. We interpret that fluids and overpressure are not common in the deeper stratigraphic section. Thermal modelling of sediments at the deformation front suggests that the deeper sediment section is relatively dewatered and not currently contributing to fluid expulsion in the Makran accretionary prism.

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Barents cod spawn in the Motovsky Bay during the periods of warming in the Arctic when proportion of mature fish in the population is high enough. Cod spawning is most likely to occur in the Motovsky Bay when large cod forage in southeastern waters, and prespawning fish migrate close by the Murmansk coast. Under such conditions cod spawn in the Motovsky Bay, but low water temperature and slow egg drift toward Murmansk coastal waters delay development of cod eggs. As a result the eggs remain at the first stage for a long time; this causes high egg mortality before hatching. Larvae that survive and become pelagic and then bottom juveniles nevertheless have little chance to survive in winter because they are not biologically ready for overwintering. Thus, delay in egg development at the first stage delays subsequent stages of fish ontogeny, and strongly impairs survival of cod juveniles from the Motovsky Bay.

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These data are provided to allow users for reproducibility of an open source tool entitled 'automated Accumulation Threshold computation and RIparian Corridor delineation (ATRIC)'

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We present composite depth scales for the multiply cored intervals from Sites 1150 and 1151. These new depth scales place coeval strata recovered in cores from different holes at a single site into a common stratigraphic framework. At Site 1150, double coring between Holes 1150A and 1150B occurred over only a short interval between ~703 and 713 meters below seafloor (mbsf), but this is sufficient to tie the upper portion of the stratigraphic section cored in Hole 1150A to the lower portion cored in Hole 1150B. The upper ~100 m of the sedimentary section at Site 1151 was double cored with the advanced piston corer and partially cored with the rotary core barrel, resulting in the complete recovery of this interval. The composite depth scales were constructed using Splicer software to vertically adjust the relative depths of various cores from one hole to the depths from another hole so as to align distinct physical properties measured on cores. The magnetic susceptibility data was the physical property most easily correlated between holes, and therefore primarily used to create a composite depth scale and spliced stratigraphic section. The spliced section is a continuous stratigraphic section constructed from representative cored intervals from the holes at a site. Both the splice and the composite depth scale can be applied to other data sets from Site 1151 to provide a stratigraphically continuous and laterally consistent basis for interpreting lithologic features or data sets. The resulting composite scale showed a 30% improvement in correlation of the magnetic susceptibility data relative to the original mbsf depth scale, and comparable improvement when applied to the other data sets.