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901.
Palaeo-bottom current strength of the West Spitsbergen Current (WSC) and the influence of the Svalbard-Barents Sea Ice Sheet (SBIS) on the depositional environment along the northern Svalbard margins are poorly known. Two gravity cores from the southern Yermak Plateau and the upper slope north of Nordaustlandet, covering marine isotope stage (MIS) 1 to MIS 5, are investigated. Five lithofacies, based on grain size distribution, silt/clay ratio, content and mean of sortable silt (SS), are distinguished to characterise the contourite-dominated sedimentary environments. In addition, depositional environments are described using total organic carbon (TOC), total sulphur (TS) and calcium carbonate (CaCO3) contents of sediments. Facies A, containing coarse SS, suggests strong bottom current activity and good bottom water ventilation conditions as inferred from low TOC content. This facies was deposited during the glacial periods MIS 4, MIS 2 and during the late Holocene. Facies B is dominated by fine SS indicating weak bottom current and poor ventilation (cf. high TOC content of 1.2–1.6%), and correlates with the MIS 4/3 and MIS 2/1 transition periods. With an equal amount of clay and sand, fine SS and high content of TOC, facies C indicates reduced bottom current strength for intervals with sediment supply from proximal sources such as icebergs, sea ice or meltwater discharge. This facies was deposited during the last glacial maximum. Facies D represents mass-flow deposits on the northern Svalbard margin attributed to the SBIS advance at or near the shelf edge. Facies E sediments indicating moderate bottom current strength were deposited during MIS 5 and MIS 3, and during parts of MIS 2. This first late Quaternary proxy record of the WSC flow and sedimentation history from the northern Svalbard margin suggests that the oceanographic conditions and ice sheet processes have exerted first-order control on sediment properties. 相似文献
902.
Low calcification rates and calcium carbonate production in Porites panamensis at its northernmost geographic distribution 下载免费PDF全文
Carlos Orión Norzagaray‐López Luis Eduardo Calderon‐Aguilera José Martín Hernández‐Ayón Héctor Reyes‐Bonilla Juan P. Carricart‐Ganivet Rafael Andrés Cabral‐Tena Eduardo Francisco Balart 《Marine Ecology》2015,36(4):1244-1255
Porites panamensis is a hermatypic coral present in the eastern Pacific Ocean. Skeletal growth parameters have been reported, but studies of the relationship between annual calcification rates and environmental controls are scarce. In this study, we investigated three aspects of the annual calcification rates of P. panamensis: growth parameters among three P. panamensis populations; the sea surface temperature as a calcification rate control spanning a latitudinal gradient; and calcium carbonate production among three sites. Growth parameters varied among the sites due to the colony growth form. Massive colonies in the north showed a higher calcification rate than encrusting colonies in the south (mean: 1.22–0.49 g CaCO3 · cm?2 · yr?1), where variations in calcification rates were related to growth rate (0.91–0.38 cm · yr?1) rather than to skeletal density differences (overall mean ± SD, 1.31 ± 0.04 g CaCO3 · cm?3). Our results showed a positive linear relationship between annual calcification rates and sea surface temperatures within these P. panamensis populations. Differences were related to distinct oceanographic environments (within and at the entrance of the Gulf of California) with different sea surface temperature regimes and other chemical properties. Different populations calcified under different environmental conditions. Calcium carbonate production was dependent upon the calcification rate and coral cover and so carbonate production was higher in the north (coral cover 12%) than in the south (coral cover 3.5). Thus, the studied sites showed low calcium carbonate production (0.25–0.43 kg CaCO3 · m?2 · yr?1). Our results showed reduced calcification rates, regional temperature regime control over calcification rates, different growth forms, low coral cover and low calcium carbonate production rates in P. panamensis. 相似文献
903.
The influence of the sea surface temperature (SST) on the carbon dioxide (CO2) exchange with the atmosphere at different spatial and temporal scales, which has a multidirectional character, was studied. The initial data included the monthly averages of the CO2 flux during the period of 1982–2011 at grid nodes of 4° by latitude and 5° by longitude, as well as the SST satellite data from January 1, 1982 to December 31, 2012 at the geographical grid nodes of 0.25° × 0.25°. Statistical models of estimation of the resulting global CO2 flux were suggested on the basis of data on SST anomalies. It is demonstrated that the SST variations in the equatorial zone mostly control the interannual fluctuations of the resulting CO2 flux in the ocean-atmosphere system. 相似文献
904.
905.
906.
Transient sediment supply in a high‐altitude Alpine environment evidenced through a 10Be budget of the Etages catchment (French Western Alps) 下载免费PDF全文
Romain Delunel Peter A. van der Beek Didier L. Bourlès Julien Carcaillet Fritz Schlunegger 《地球表面变化过程与地形》2014,39(7):890-899
Although beryllium‐10 (10Be) concentrations in stream sediments provide useful synoptic views of catchment‐wide erosion rates, little is known on the relative contributions of different sediment supply mechanisms to the acquisition of their initial signature in the headwaters. Here we address this issue by conducting a 10Be‐budget of detrital materials that characterize the morphogenetic domains representative of high‐altitude environments of the European Alps. We focus on the Etages catchment, located in the Ecrins‐Pelvoux massif (southeast France), and illustrate how in situ 10Be concentrations can be used for tracing the origin of the sand fraction from the bedload in the trunk stream. The landscape of the Etages catchment is characterized by a geomorphic transient state, high topographic gradients, and a large variety of modern geomorphic domains ranging from glacial environments to scarcely vegetated alluvial plains. Beryllium‐10 concentrations measured in the Etages catchment vary from ~1 × 104 to 4.5 × 105 atoms per gram quartz, while displaying consistent 10Be signatures within each representative morphogenetic unit. We show that the basic requirements for inferring catchment‐wide denudation from 10Be concentration measurements are not satisfied in this small, dynamic catchment. However, the distinct 10Be signature observed for the geomorphic domains can be used as a tracer. We suggest that a terrestrial cosmogenic nuclide (TCN) budget approach provides a valuable tool for the tracing of material origin in basins where the ‘let nature do the averaging’ principles may be violated. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
907.
David R. Geist Mark C. Joy David R. Lee Tom Gonser 《Ground Water Monitoring & Remediation》1998,18(1):78-82
An impact drive point method is described for emplacing piezometers in a cobble river bottom where this has previously been difficult without the use of drilling rigs. To force the drive point piezometers through coble, the vibrational impact of an air-powered hammer was carried directly to the drive point by the use of an internal drive rod. After insertion to depth, the drive rod was removed from the lower portion of the piezometer and a standpipe was added to extend the piezometer above the river level. Piezometers installed in this way have permitted water quality analysis and dynamic measurement of vertical potentials in cobble sediments ranging in size from 2.5 to >30 cm and the method has been successfully used in the Columbia River, USA, and Töss River, Switzerland. This innovative method provides information on the hydrodynamics of pore water in highly permeable, cobble deposits that are common in high-energy river and lake bottoms. Piezometers installed using the internal drive rod method facilitate the assessment of the temporal and spatial dynamics of recharge and discharge at the ground water/surface water interface and analyses of the ecological connectivity between the hyporheic zone and surface water of rivers and streams. This information will lead to improved management decisions related to our nation's ground water and surface water supplies. 相似文献
908.
The in situ uptake of mercury in tissues of Mytilus californianus was studied by exposing control specimens to waters at four depths near a submarine wastewater discharge for a period of 24 weeks. The response patterns observed for digestive gland, adductor muscle and gonadal tissues were strikingly different. Digestive gland concentrations increased rapidly to the heightened levels found for indigenous specimens. On the other hand, changes in the mercury content of adductor muscle were not statistically significant, and gonadal tissues generally exhibited a low rate of increase. No correlation with depth was observed. 相似文献
909.
W. M. Rizzo S. K. Dailey G. J. Lackey R. R. Christian B. E. Berry R. L. Wetzel 《Estuaries and Coasts》1996,19(2):247-256
We determined fluxes of oxygen and nutrients between water and sediments at 21 sites primarily in Virginia and North Carolina estuaries, over the past 15 yr. These sites represented broad ranges in salinity, tidal amplitude, hydrology, nutrient availability, turbidity, light availability, depth, sediment grain size, and anthropogenic disturbance. In general, we found that heterotrophically dominated sediments had the potential to degrade water quality, whereas photoautotrophy in the sediments ameliorated this impact. We propose a benthic trophic state index as a management tool to make general assessments of the degree to which sediments support ecological processes related to photoautotrophy. The index can be based on simple measurements of metabolic parameters. We also evaluated the relative significance of variability in the index across a number of spatial and temporal scales. Reduced photoautotrophy and/or enhanced heterotrophy tended to be associated with finer-grained, organic-rich sediments. This sediment type was common in oligohaline areas at water depths exceeding 2 m. Temporally, autotrophy declined from winter to spring particularly at sandy sites, while interannual variability was more pronounced for mud sites. *** DIRECT SUPPORT *** A01BY074 00011 相似文献
910.
Lobkovsky L. I. Vladimirova I. S. Gabsatarov Yu. V. Baranov B. V. Garagash I. A. Steblov G. M. 《Doklady Earth Sciences》2017,477(2):1498-1503
Doklady Earth Sciences - The interpretation of multiannual satellite geodetic observations after the 2010 Maule earthquake is given on the basis of the keyboard concept of the subduction region... 相似文献