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《Marine Geology》2005,216(3):107-126
We report on the spatial distribution of isotopic compositions of the two planktic foraminifera species Globigerina bulloides and Neogloboquadrina pachyderma (dex.), and the faunal assemblages of planktic foraminifera in 91 surface sediment samples along the Chilean continental slope between 23°S and 44°S. Both δ13C and δ18O data of N. pachyderma (dex.) show little variability in the study area. North of 39°S, the isotopic values of N. pachyderma (dex.) are heavier than those of G. bulloides, whereas south of 39°S, this relation inverses. This is indicative for a change from a well-mixed, deep thermocline caused by coastal upwelling north of 39°S to well-stratified water masses in a non-upwelling environment south of 39°S. In addition, the faunal composition of planktic foraminifera marks this change by transition from an upwelling assemblage north of 39°S to a high-nutrient-non-upwelling assemblage south of 39°S, which is characterized by decreased contributions of upwelling indicators such as G. bulloides, N. pachyderma (sin.), and Globigerinita glutinata. In general, we can conclude that food and light rather than temperature are the primary control of the planktic foraminiferal assemblage between 23°S and 44°S off Chile. Our data point to higher marine productivity at upwelling centers north of 25°S and at 30–33°S. South of 39°S, significant supply of nutrients by fluvial input most likely boosts the productivity. 相似文献
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R K Sarangi Prakash Chauhan Shailesh Nayak 《Journal of the Indian Society of Remote Sensing》2001,29(4):197-201
Remote sensing of ocean colour yields information on the constituents of sea water, such as the concentration of phytoplankton
pigments, suspended sediments and yellow substances. It is well understood that the study of ocean colour is significantly
related with the primary production and zonation of potential fishing sites in coastal and oceanic waters. The major pigment
constituent is predominated by chlorophyll-a (ocean colour pigment of phytoplankton). The chlorophyll mapping on regular basis
plays a major role in assessing water quality and classifying different water types. IRS P-3 MOS-B satellite data for three
consecutive passes of path 94, during the period of January-February 1997 have been used to derive chlorophyll-a concentration.
The present study emphasizes on the chlorophyll mapping using IRS-P3 MOS-B data for the coastal and offshore water of Maharashtra
coast, India. 相似文献
4.
《Polar Science》2014,8(4):370-384
An anomalous phytoplankton bloom was recorded in the Indian Ocean sector of the Antarctic Zone (AZ) of the Southern Ocean (SO) during the austral summer, 2011. Possible mechanisms for the triggering of such a large bloom were analyzed with the help of in situ and satellite data. The bloom, which formed in January 2011, intensified during February and weakened by March. High surface chlorophyll (Chl) concentrations (0.76 mg m−3) were observed in the area of the bloom (60°S, 47°E) with a Deep Chlorophyll Maximum (DCM) of 1.15 mg m−3 at a depth of 40–60 m. During 2011, both the concentration and spatial extent of sea ice were high on the western side of the bloom, between 0°E and 40°E, and enhanced freshwater influx was observed in the study area as a result of melting ice. A positive Southern Annular Mode (SAM) (with a resultant northward horizontal advection) and an intense La Niña during 2010–2011 are possible reasons for the high sea-ice concentrations. The enhanced Chl a observed in the study region, which can be attributed to the phytoplankton bloom, likely resulted from the influx of nutrient-laden freshwater derived from melting sea ice. 相似文献
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Raj esh Asthana Prakash Kumar Shrivastav Hari Bahadur Srivastava Mirza Javed Beg Pradeep Kumar 《极地研究(英文版)》2013,(4):281-295
Fisher Island and Broknes Peninsula in the Larsemann Hills constitute part of a polar lowland periglacial environment between marine and glacial ecosystems. The landscape is characterized by gently rolling hills and broad valleys interspersed with lakes formed in glacially scoured basins. We analyzed the physieochemical parameters and the ionic constituents of water samples from 10 lakes in each of these two locations. Our results showed considerable differences between the two regions and demon- strated the influence of lithology and processes including weathering, evaporation, and atmospheric precipitation. All major cations and anions in the lake waters showed positive correlations indicating balanced ionic concentrations. Unconsolidated sediments were sparsely distributed and scattered over glacial deposits, valley fills, and occasional moraine ridges. The type and rate of sedi- mentation was mainly controlled by surface run-off and aeolian influx. The sediment samples from lake beds and the catchment area on Fisher Island were immature and poorly to very poorly sorted, consisting of gravelly sand with negligible silt and finer fractions. Sediments had a polymodal grain size distribution with the two major populations lying between -2 and 1 phi and be- tween 0 and 1.5 phi. The sediments were lithic arenite to arkosic in composition and the microtextures imprinted over quartz grains were dominated by mechanical textures resulting from several stages of glacial crushing and grinding. The presence of deep disso- lution cavities, cryptocrystalline precipitation, and euhedral crystal growth signified the effect of chemical activity after the deposition of grains in the lacustrine environment. 相似文献
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Astrid Lampert Johan Ström Christoph Ritter Roland Neuber Young Jun Yoon Nam Yi Chae Masataka Shiobara 《Acta Geophysica》2012,60(5):1287-1307
An inclined lidar with vertical resolution of 0.4 m was used for detailed boundary layer studies and to link observations at Zeppelin Mountain (474 m) and Ny-Ålesund, Svalbard. We report on the observation of aerosol layers directly above the Kongsfjord. On 29 April 2007, a layer of enhanced backscatter was observed in the lowest 25 m above the open water surface. The low depolarization ratio indicated spherical particles. In the afternoon, this layer disappeared. The ultrafine particle concentration at Zeppelin and Corbel station (close to the Kongsfjord) was low. On 1 May 2007, a drying process in the boundary layer was observed. In the morning, the atmosphere up to Zeppelin Mountain showed enhanced values of the backscatter coefficient. Around noon, the top of the highly reflecting boundary layer decreased from 350 to 250 m. The top of the boundary layer observed by lidar was confirmed by radiosonde data. 相似文献
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Significance of Dar-Zarrouk parameters in the exploration of quality affected coastal aquifer systems 总被引：1，自引：0，他引：1
The interpreted Earth subsurface resistivity layer parameters of 55 vertical geoelectrical soundings are analyzed over a fan shaped area of 1,700 km2 from Pipli-Astrang-Bhramgiri, Orissa, India. In this study, Dar-Zarrouk (D-Z) parameters, namely the longitudinal conductance (S), transverse resistance (T) and longitudinal resistivity (R
s
) are analyzed and we encountered the resistivity regime of the clay layers, saline and fresh water bearing formations. The significance of these parameters in establishing an easily decipherable vision about the occurrence and distribution of fresh and saline water aquifers, while dealing with complicated situations of intermixing of the resistivity ranges of saline and fresh water aquifers has been illustrated. The results show that the Dar-Zarrouk (D-Z) parameters provide a useful and confident solution in delineating the saline and fresh water aquifers. The behavior of the D-Z parameters S, T and R
s
, and its patterns in space over large areas with respect to the occurrence of saline water and fresh water aquifer systems in the deltaic coastal aquifer system has been demonstrated. 相似文献
9.
《Earth and Planetary Science Letters》2006,241(1-2):119-137
Detailed rock magnetic and electron microscope analyses indicate that the magnetic signature of Neogene marine sediments from the east coast of New Zealand is dominated by the authigenic iron sulphide greigite. The greigite is present as a mixed population of stable single domain and superparamagnetic grains, which is consistent with authigenic growth from solution. This growth can result from pyritization reactions soon after deposition, which also leads to dissolution of most detrital magnetite; however, where constrained by field tests, our data suggest that remanence acquisition can occur > 1 Myr after deposition, and can vary in timing at the outcrop scale. Strong viscous overprints result from oxidation of the iron sulphides, probably during percolation of oxic ground water. This process can sometimes destroy any ancient remanent magnetization. This complex magnetic behaviour, particularly the presence of late-forming magnetizations carried by greigite, means that the remanence in New Zealand Cenozoic sediments, and in similar sediments elsewhere, cannot be assumed to be primary without confirmation by field tests. The reversals test should be employed with caution in such sediments, as patchy remagnetizations can lead to false polarity stratigraphies. 相似文献
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《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(5):479-487
The 1766 ± 5 Ma Deschambault pegmatites are anorogenic intrusions emplaced into the Glennie domain at the end of the Trans-Hudson Orogeny (THO) in north-central Saskatchewan. They are composed mainly of orthoclase and quartz with minor biotite, muscovite, tourmaline and beryl. A coherent primary characteristic remanence is retained in all 18 sites (170 specimens) that resides in magnetite, hematite and minor pyrrhotite, giving a direction of Dec. = 28.3°, Inc. = 82.1°, α95 = 4.0°, and k = 77.5 based on alternating field and thermal step demagnetization and saturation remanence analyses. The pegmatites' pole position, along with recently published ∼1810 ± 10 Ma and ∼1795 ± 15 Ma poles for the THO, define a stillstand and hairpin in the apparent polar wander path for the THO that marks continent-continent collision of the Archean Superior, Sask and Hearne (?) cratons. 相似文献