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991.
O. Algan N. Çağatay A. Tchepalyga D. Ongan C. Eastoe E. Gökaşan 《Geo-Marine Letters》2001,20(4):209-218
The sediment infill over the Paleozoic bedrock in the Bosphorus Strait consists of four sedimentary units which were deposited in the last 26,000 14C years B.P. The stratigraphy of these units suggests that this part of the Bosphorus was a freshwater lake between 26,000 and 5,300 14C years B.P., depositing sands with a freshwater mollusc fauna of Black Sea neo-euxinian affinity (Dreissena rostriformis, Dreissena polymorpha, and Monodacna pontica). The first appearance of euryhaline Mediterranean molluscs (e.g., Ostrea edulis, Mytilus edulis) was observed at 5,300 14C years B.P. in this part of the Bosphorus. Deposition of coarse Mytilus-bank and Ostrea-bank units suggests that the establishment of the present dual-flow regime in the Bosphorus took place at about 4,400 14C years B.P. 相似文献
992.
993.
C. Rabouille H. Stahl F. Bassinot A. Tengberg J. Brunnegard P. Hall K. Kiriakoulakis J. -L. Reyss L. Dezileau P. Crassous P. Roos R. S. Lampitt 《Progress in Oceanography》2001,50(1-4)
Fluxes contributing to the particulate carbonate system in deep-sea sediments were investigated at the BENGAL site in the Porcupine Abyssal Plain (Northeast Atlantic). Deposition fluxes were estimated using sediment traps at a nominal depth of 3000 m and amounted to 0.37±0.1 mmol C m−2 d−1. Dissolution of carbonate was determined using flux of total alkalinity from in situ benthic chambers, is 0.4±0.1 mmol C m−2 d−1. Burial of carbonate was calculated from data on the carbonate content of the sediment and sedimentation rates from a model age based on 14C dating on foraminifera (0.66±0.1 mmol C m−2 d−1). Burial plus dissolution was three times larger than particle deposition flux which indicates that steady-state is not achieved in these sediments. Mass balances for other components (BSi, 210Pb), and calculations of the focusing factor using 230Th, show that lateral inputs play only a minor role in this imbalance. Decadal variations of annual particle fluxes are also within the uncertainty of our average. Long-term change in dissolution may contribute to the imbalance, but can not be the main reason because burial alone is greater than the input flux. The observed imbalance is thus the consequence of a large change of carbonate input flux which has occured in the recent past. A box model is used to check the response time of the solid carbonate system in these sediments and the time to reach a new steady-state is in the order of 3 kyr. Thus it is likely that the system has been perturbed recently and that large dissolution and burial rates reflect the previously larger particulate carbonate deposition rates. We estimate that particulate carbonate fluxes have certainly decreased by a factor of at least 3 and that this change has occurred during the last few centuries. 相似文献
994.
A New Methodology for Incorporating Tide Gauge Data in Sea Surface Topography Models 总被引:1,自引:0,他引:1
As part of the Vertical Offshore Reference Frames (VORF) project sponsored by the U. K. Hydrographic Office, a new model for Sea Surface Topography (SST) around the British Isles has been developed. For offshore areas (greater than 30 km from the coast), this model is largely derived from satellite altimetry. However, its accuracy and level of detail have been enhanced in coastal areas by the inclusion of not only the 60 PSMSL tide gauges with long-term records around the coasts of the United Kingdom and Ireland but also some 385 gauges established at different epochs and for different observation spans by the U. K. Admiralty. All tide gauge data were brought into a common reference frame by a combination of datum models and direct GPS observations, but a more significant challenge was to bring all short-term sea level observations to an unbiased value at a common epoch. This was achieved through developing a spatial-temporal correlation model for the variations in mean sea level around the British Isles, which in turn meant that gauges with long-term observation spans could be used as control points to improve the accuracy of Admiralty gauges. It is demonstrated that the latter can contribute point observations of mean sea level (MSL) with a precision of 0.078 m. A combination of least squares collocation and interpolation was developed to merge the coastal point and offshore gridded data sets, with particular algorithms having to be developed for different configurations of coastal topology. The resulting model of sea surface topography is shown to present a smooth transition from inshore coastal areas to offshore zones. Further benefits of the techniques developed include an enhanced methodology for detecting datum discontinuities at permanent tide gauges. 相似文献
995.
996.
Several coeval volcanogenic complexes indicating synchronous volcanic events in the Sea of Japan and the Sea of Okhotsk are defined. Volcanics from different-age complexes of the Sea of Okhotsk show many features in common and are attributed to the Pacific type of calc-alkaline series. They were formed in geodynamic settings of the active continental margin and point to its origination on the continental crust of the fragmented Asian continent margin. The volcanic rocks developed in the Sea of Japan reflect different rifting stages. The initial stage was marked by an eruption of calc-alkaline lavas (Paleocene-Eocene complex). At the stage of the marginal-sea spreading, erupted volcanics of the middle Miocene-Pliocene complex were melted from the depleted mantle and magmatism terminated by an eruption of postspreading Pliocene-Holocene volcanics melted from the enriched mantle EM I. Along with the differences, the magmatism in the Sea of Japan and Sea of Okhotsk has some features in common. In both cases, the sialic component of the lithosphere substantially influenced the magma generation. 相似文献
997.
The Blake Outer Ridge is a 480–kilometer long linear sedimentary drift ridge striking perpendicular to the North American
coastline. By modeling free-air gravity anomalies we tested for the presence of a crustal feature that may control the location
and orientation of the Blake Outer Ridge. Most of our crustal density models that match observed gravity anomalies require
an increase in oceanic crustal thickness of 1–3 km on the southwest side of the Blake Outer Ridge relative to the northeast
side. Most of these models also require 1–4 km of crustal thinning in zone 20–30 km southwest of the crest of the Blake Outer
Ridge. Although these features are consistent with the structure of oceanic fracture zones, the Blake Outer Ridge is not parallel
to adjacent known fracture zones. Magnetic anomalies suggest that the ocean crust beneath this feature formed during a period
of mid-ocean ridge reorganization, and that the Blake Outer Ridge may be built upon the bathymetric expression of an oblique
extensional feature associated with ridge propagation. It is likely that the orientation of this trough acted as a catalyst
for sediment deposition with the start of the Western Boundary Undercurrent in the mid-Oligocene. 相似文献
998.
999.
Macro-ecological theories relating species richness, abundance, range size, biological traits and environmental tolerance have rarely been tested in marine soft-sediments, despite the spatial extent of these habitats and the inherent richness of resident communities. This study examines the contribution of rare species to marine soft-sediment communities from New Zealand, focussing on the relationships of range size with abundance, environment, habitat diversity and life history traits. 54% of the 351 species sampled exhibited restricted ranges (found at ≤ 2 sites). In contrast to many terrestrial systems, we observed only a weak positive relationship between abundance and frequency of occurrence. Restricted-range species were not randomly distributed, with their distribution related to habitat characteristics, suggesting an important link between habitat diversity and rarity. They exhibited a similar range of traits to the total observed species pool, suggesting that they are not only important to biodiversity but could play a role in stability. Restricted range species were generally not small and this, together with the number of different biological traits represented, suggests that rare species are important to the functioning of marine systems. Thus, our results highlight the importance of considering rare species in habitat-based approaches to conservation. 相似文献
1000.
D. S. Drozdov F. M. Rivkin V. Rachold G. V. Ananjeva-Malkova N. V. Ivanova I. V. Chehina M. M. Koreisha Yu. V. Korostelev E. S. Melnikov 《Geo-Marine Letters》2005,25(2-3):81-88
A set of digital maps including geology, Quaternary sediments, landscapes, engineering-geological, vegetation, geocryological and the series of regional sources have been selected to characterize the Russian Arctic coast. Based on this data, new maps of engineering geocryological zoning and zoning of the coast with respect to the intensity of exogenous geological processes and risk of technogenic impacts have been generated at the scales of 1:4,000,000–1:8,000,000. These maps are a tool to assess the impact of industry on the Arctic coast of the country. 相似文献