首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
In 1983 a combined SeaMARC I, Sea Beam swath mapping expedition traversed the East Pacific Rise from 13°20 N to 9°50 N, including most of the Clipperton Transform Fault at 10°15 N, and a chain of seamounts at 9°50 N which runs obliquely to both the ridge axis and transform fault trends. We collected temperature, salinity and magnetic data along the same track. These data, combined with Deep-Tow data and French hydrocasts, are used to construct a thermal section of the rise axis from 13°10 N to 8°20 N.Thermal data collected out to 25 km from the rise axis and along the Clipperton Transform Fault indicate that temperatures above the rise axis are uniformly warmer by 0.065°C than bottom water temperatures at equal depths off the axis. The rise axis thermal structure is punctuated by four distinct thermal fields with an average spacing of 155 km. All four of these fields are located on morphologic highs. Three fields are characterized by lenses of warmed water 20 km in length and 300 m thick. Additional clues to hydrothermal activity are provided in two cases by high concentrations of CH4, dissolved Mn and 3He in the water column and in another case by concentrations of benthic animals commonly associated with hydrothermal regions.We use three methods to estimate large-scale heat loss. Heat flow estimates range from 1250 MW to 5600 MW for one thermal field 25 km in length. Total convective heat loss for the four major fields is estimated to lie between 2100 MW and 9450 MW. If we add the amount of heat it takes to warm the rest of the rise axis (489 km in length) by 0.065.°C, then the calculated axial heat loss is from 12,275 to 38,525 MW (19–61% of the total heat theoretically emitted from crust between 0 and 1 m.y. in age).  相似文献   

2.
Sea Beam and Deep-Tow were used in a tectonic investigation of the fast-spreading (151 mm yr-1) East Pacific Rise (EPR) at 19°30 S. Detailed surveys were conducted at the EPR axis and at the Brunhes/Matuyama magnetic reversal boundary, while four long traverses (the longest 96 km) surveyed the rise flanks. Faulting accounts for the vast majority of the relief. Both inward and outward facing fault scarps appear in almost equal numbers, and they form the horsts and grabens which compose the abyssal hills. This mechanism for abyssal hill formation differs from that observed at slow and intermediate spreading rates where abyssal hills are formed by back-tilted inward facing normal faults or by volcanic bow-forms. At 19°30 S, systematic back tilting of fault blocks is not observed, and volcanic constructional relief is a short wavelength signal (less than a few hundred meters) superimposed upon the dominant faulted structure (wavelength 2–8 km). Active faulting is confined to within approximately 5–8 km of the rise axis. In terms of frequency, more faulting occurs at fast spreading rates than at slow. The half extension rate due to faulting is 4.1 mm yr-1 at 19°30 S versus 1.6 mm yr-1 in the FAMOUS area on the Mid-Atlantic Ridge (MAR). Both spreading and horizontal extension are asymmetric at 19°30 S, and both are greater on the east flank of the rise axis. The fault density observed at 19°30 S is not constant, and zones with very high fault density follow zones with very little faulting. Three mechanisms are proposed which might account for these observations. In the first, faults are buried episodically by massive eruptions which flow more than 5–8 km from the spreading axis, beyond the outer boundary of the active fault zone. This is the least favored mechanism as there is no evidence that lavas which flow that far off axis are sufficiently thick to bury 50–150 m high fault scarps. In the second mechanism, the rate of faulting is reduced during major episodes of volcanism due to changes in the near axis thermal structure associated with swelling of the axial magma chamber. Thus the variation in fault spacing is caused by alternate episodes of faulting and volcanism. In the third mechanism, the rate of faulting may be constant (down to a time scale of decades), but the locus of faulting shifts relative to the axis. A master fault forms near the axis and takes up most of the strain release until the fault or fault set is transported into lithosphere which is sufficiently thick so that the faults become locked. At this point, the locus of faulting shifts to the thinnest, weakest lithosphere near the axis, and the cycle repeats.  相似文献   

3.
Total magnetic intensity and bathymetric surveys were carried out in the northern Bay of Bengal between 6° to 11° 45 N latitudes and east of 84° to 93° 30 E longitudes. The hitherto known 85° E Ridge is characterised as a subsurface feature by a large amplitude, positive magnetic anomaly surrounded by Mesozoic crust. A newly identified NE to NNESSW trending magnetic anomaly between 7° N, 87° 30 E and 10° 30 N, 89–90° E may be one of the unidentified Mesozoic lineations in the northern Bay of Bengal. The Ninetyeast Ridge is not associated with any recognizable magnetic anomaly. The Sunda Trough to the east of the Ninetyeast Ridge is characterised by a positive magnetic anomaly. A combined interpretation, using Werner deconvolution and analytical signal methods, yields basement depths ~ 10 km below sea level. These depths are in agreement with the seismic results of Curray (1991).Deceased 24 December 1991  相似文献   

4.
The distribution of the colour index is considered in the region bounded by 8–11°N and 13°30–18°30W based on the results of measurements made on board vessels of the Marine Hydrophysical Institute of the Ukrainian SSR Academy of Sciences (MHI) in 1977–1985. Mean values and statistical characteristics are calculated for the colour index variability over one-degree squares. A map of its multi-yearly average distribution is plotted.Translated by M. M. Trufanov.  相似文献   

5.
A study of Sea Beam bathymetry and SeaMARC II side-scan sonar allows us to make quantitative measures of the contribution of faulting to the creation of abyssal hill topography on the East Pacific Rise (EPR) 9°15 N–9°50 N. We conclude that fault locations and throws can be confidently determined with just Sea Beam and SeaMARC II based on a number of in situ observations made from the ALVIN submersible. A compilation of 1026 fault scarp locations and scarp height measurements shows systematic variations both parallel and perpendicular to the ridge axis. Outward-facing fault scarps (facing away from the ridge axis), begin to develop within 2 km of the ridge and reach their final average height of 60 m at 5–7 km. Beyond these distances, outward-dipping faults appear to be locked, although there is some indication of continued lengthening of outward-facing fault scarps out to the edge of the survey area. Inward-facing fault scarps (facing toward the ridge axis), initiate 2 km off axis and increase in height and length out to the edge of our data at 30 km, where the average height of inward fault scarps is 60–70 m and the length is 30 km. Continued slip on inward faults at a greater distance off axis is probable, but based on fault lengths, 80% of the lengthening of inward fault scarps occurs within 30 km of the axis (>95% for outward faults). Along-strike propagation and linkage of these faults are common. Outward-dipping faults accommodate more apparent horizontal strain than inward ones within 10 km of the ridge. The net horizontal extension due to faulting at greater distances is estimated as 4.2–4.3%, and inward and outward faults contribute comparably. Both inward- and outward-facing fault scarps increase in height from north to south in our study area in the direction of decreasing inferred magma supply. Average fault spacing is 2 km for both inward-dipping and outward-dipping faults. The azimuths of fault scarps document the direction of ridge spreading, but they are sensitive to local changes in least compressive stress direction near discontinuities. Both the ridge trend and fault scarp azimuths show a clockwise change in trend of 3–5° from 9°50 N to 9°15 N approaching the 9° N overlapping spreading center.  相似文献   

6.
A surface buoy was moored from 20 April to 2 November 1988 at 28°48 N and 135°01 E where the water depth was 4900 m to measure temperature and velocity in the upper 150 m. The Typhoon 8824 passed at 0300 (JST) on 8 October about 50 km north to the mooring station with a maximum wind speed of 43.5 m s–1. The buoy was shifted about 30 km to southwest, and the instruments were damaged. The records of temperature at 0.5 m and velocity at 50 m were obtained. The inertial oscillation caused by the typhoon is described using the current record. The oscillation endured for about 20 days. Deep mixing and vertical, heart transport by the typhoon are discussed based on the data from the Ocean Data Buoy of the Japan Meteorological Agency moored at 29°N and 135°E.  相似文献   

7.
Possibilities of using the GLORIA system for manganese nodule assessment   总被引：1，自引：0，他引：1  
The I.O.S. long range side-scan sonar GLORIA has been widely used over a variety of seabed types, but until recently had not been used over an independently authenticated field of manganese nodules. In the Eastern Atlantic Ocean at approximately 31°25 N 25°15 W, a field of nodules approximately 3–6 cm in diameter covering up to 18% of the seafloor was observed using an underwater camera. The nodule field occurred over approximately 2.8 km of the 8.3 km camera run. The corresponding GLORIA image shows an area of medium intensity backscattering, approximately 3.7 km in diameter. Considering the likely contrast in acoustic reflectivity between manganese nodules and deep sea sediments, we propose a correlation between the nodules observed in the photographs and the medium intensity echo target revealed by the GLORIA system.  相似文献   

8.
About 106 of total bacteria (direct microscopic count) or heterotrophic bacteria (colony count with Medium 2216E) and about 104 of petroleumlytic bacteria (oil-oxidizing bacteria) were enumerated per square centimeter of the surface of petroleum globules suspended in the topmost 10 meters of water from a station (22°00.2N, 125°51.9E) in the western North Pacific central water, where about 107 of total bacteria, about 103 of heterotrophic bacteria and about 10 of petroleumlytic bacteria were enumerated per liter of seawater.  相似文献   

9.
The bacterial populations of mangrove swamps of Killai backwaters (11°21–11°29N, 79°46–79°50E, South India) were studied during August 1968 (Pre monsoon period) and December (post monsoon period). The presence of these groups such as agar digesters, algin digesters, cellulose digesters, sulphate reducers etc., bring about transformation of organic matter in the mangrove swamps. The presence of denitrifiers in mangrove swamps and in association with the molluscs may bring about the precipitation of calcium carbonate by removing the acid radicals such as sulphate and nitrite, increasing alkalinity. The luminiscent bacteria such asVibrio andAeromonas were also isolated in mangrove swamps of Killai backwaters. The iron bacteria likeLeptothrix sp. andGallionella sp. were also isolated from mangrove swamps of Killai backwaters.  相似文献   

10.
A detailed survey of a 1°×1°-square of seafloor 100 miles south-east of the Azores shows a strong correlation between directions of regional topographic and magnetic lineations. The area is dissected by the East Azores Fracture Zone at 36°55N, identified as the active Eurasian-African plate boundary, and by another large, non-active fracture zone at 36°10N. Both fracture zones strike 265° and are accompanied by large amplitude magnetic anomalies. The general strike in the area in between is 000°–015°. The skewing effect at this magnetic latitude is very sensitive to variations in strike of the magnetic contrasts. This effect was eliminated by a non-linear transformation which also gives the positions of magnetic contrasts. Some N-S contrasts were identified as sea floor spreading polarity contrasts (anomalies 31 and 32). Weak contrasts could be identified as topographic effects and gave a magnetization intensity of 5 A m-1. The identified sea floor spreading anomalies to both sides of the fracture zone at 36°10N agree very well, also quantatively, with a three-dimensional model for the fracture zone anomalies. This model describes the non-linear anomalies as end effects of the magnetic layer which is divided in blocks of alternating polarity.  相似文献   

11.
A total magnetic intensity, iso-magnetic map is presented and discussed. Between East London and Durban large east-west trending anomalies are known on land and can be traced onto the continental shelf but not beyond the slope. Elsewhere the continental shelf is characterized by a remarkably quiet magnetic field. A feature of the map is the linear anomaly, named the Cape Slope Anomaly, which is parallel to the continental margin and coincides approximately with the 68° small circle about the early pole of opening for the South Atlantic as given by Le Pichon and Hayes (1971). The anomaly is traced between 30°54S, 30°48E and 37°45S, 20°31E and is interpreted as occurring over the truncated edge of a semi-infinite, sub-horizontal, remanently magnetized plate in oceanic crust beyond the continental margin.Between 37°03S, 21°49E and 37°41S, 21°12E the Slope Anomaly occurs over a ridge named the Agulhas Ridge. A continuous seismic reflection profile over the ridge shows acoustic basement occurring under a cover of sediments. A two dimensional model study indicates that the basement materials may belong to the body causing the anomaly with the exception of the basement material that forms the landward peak of the ridge, which is non-magnetic.  相似文献   

12.
We report the results of a study of the magnetic properties of basalts recovered from the axis and from 0.7 m.y. old crust at 21° N and 19°30 S on the East Pacific Rise as well as from the 9°03 N overlapping spreading centers. The natural remanent magnetization of the samples from 21° N and 19°30 S decreases from the axis to 0.7 m.y. old crust as a result of low-temperature oxidation. In addition, the magnetic properties of the samples from the 21° N sites indicate that: (1) the magnetic susceptibility and the Koenigsberger ratio decrease with low-temperature alteration, (2) the Curie temperature, the median demagnetizing field and the remanent coercivity increase with maghemitization, (3) the saturation magnetization measured at room temperature does not change significantly with age. The magnetic properties of the basalt samples from the 9°03 N overlapping spreading centers indicate the presence of a high magnetization zone at the tip of the eastern spreading center. This high magnetization zone is the result of the high percentage of unaltered, fine-grained titanomagnetites present in the samples. These measurements are consistent with the results of the three-dimensional inversion of the magnetic field over the 9°03 N overlapping system [Sempere et al., 1984] as well as with detailed tectonic and geochemical investigations of overlapping spreading centers (Sempere and Macdonald, 1986a; Langmuir et al., 1986; Natland et al., 1986). The high magnetization zone appears to be the result of the eruption of highly fractionated basalts enriched in iron associated with the propagation of one of the limbs of the overlapping system into older lithosphere and not just to rapid decay, due to low-temperature oxidation, of the initially high magnetization of pillows extruded in the neovolcanic zone.  相似文献   

13.
Assessment was made of residual ratio of North Pacific Intermediate Water (NPIW) produced in subpolar region of the North Pacific using chlorofluorocarbons, CFC-11 and CFC-12 (CCl3F and CCl2F2), along 175°E. NPIW on density horizons less than 26.80 remained more than 80% north of 30°N. It was suggested that new NPIW laterally spreads over the northern North Pacific without hardly being diluted by the surroundings. For density horizons greater than 26.80 north of 30°N, NPIW remained less than 60%. The difference in the residual ratio between <26.80 and >26.80 north of 30°N suggests that NPIW is produced on density horizons less than 26.80, which contacts the atmosphere in the subpolar region, and that NPIW is diluted by upwelling deep water on density horizons greater than 26.80 in high latitude of the North Pacific. NPIW on a density horizon of 26.80 remained about 50% south of 30°N. The decrease in the horizontal distribution of the residual ratio of NPIW suggests that half the new NPIW produced in the subpolar region is laterally spread over the North Pacific with the southward movement of NPIW.  相似文献   

14.
Hekinian  R.  Juteau  T.  Gràcia  E.  Sichler  B.  Sichel  S.  Udintsev  G.  Apprioual  R.  Ligi  M. 《Marine Geophysical Researches》2000,21(6):529-560
The St. Paul F.Z. is a large structural domain made up of multiple transform faults interrupted by several Intra-Transform Ridge (ITR) spreading segments. Two regions were studied in details by submersible: (1) The ITR short (<20 km in length) segment near 0° 37N–25° 27W and 1° N–27° 42W and (2) The St. Peter and St. Paul's Rocks (SPPR) massif located at 29° 25W (¡3700 m depth). (1) The short ITR segments consist of a magma starved rift valley with recent volcanic activities at 4700 m depth. A geological profile made along the rift valley wall showed localized volcanics (basalts and dykes) which are believed to overlay and intrude the ultramafics. The geological setting and the high ultramafic/volcanic ratio suggest an extremely low magmatic supply and crustal-mantle uplift during lithospheric stretching and denudation. (2) The St. Peter and St. Paul's Rocks (SPPR) massif consists of a sigmoidal ridge within the active transform zone. The SPPR is divided into two different geological domains called the North and the South Ridges. The North Ridge consists of strongly tectonized fault scarps composed of banded and mylonitized peridotite, sporadic gabbros (3900–2500 m) and metabasalts (2700–1700 m). The South Ridge is less tectonized with undeformed, serpentinized spinel lherzolite (2000–1400 m) and basalts. Extensional motion and denudation accompanied by diapirism affected the South Ridge within a transform domain. Instead, the North Ridge was formed during an important strike-slip and faulting motion resulting in the uplifted portion of the St. Paul F.Z. transverse ridge. There is a regional compositional variation of the volcanics where E-MORBs and alkali basalts are produced on the SPPR massif and are comparable to the adjacent northern segments of the Mid-Atlantic Ridge. On the other hand, N and T- MORBs collected from the eastern part of the St. Paul F.Z. (25° 27W IRT) are similar to the volcanics from the southern segments of the MAR. The peridotites exposed in these provinces (SPPR and ITR) are similar in their REE and trace element distribution. Different degrees (3–15%) of partial melting of a mixed composite mantle consisting of spinel and amphibole bearing lherzolite veined with 5–40% clinopyroxenite gave rise to the observed MORBs and alkali basalts.  相似文献   

15.
The junction between oceanic crust generated, within the Antarctic plate, at the Southeast Indian Ridge and the Southwest Indian Ridge has been studied using a SEABEAM swathe bathymetry mapping system and other geophysical techniques between the Indian Ocean Triple Junction (approximately 25°S, 70° E), and a point some 500 km to the southwest (at 28°25 S, 66°35 E). The morphotectonic boundary which marks this trace of the ridge-ridge-ridge triple junction is complex and varies with age. Recent theories proposing a cyclicity of volcanic and tectonic processes at this mode of triple junctions appear to be supported by a series of regularly spaced, en echelon escarpments facing the slowly spreading (0.6 to 0.8 cm a-1, half rate) Southwest Indian Ridge axis. The en echelon escarpments intersect at approximately right angles with the regularly spaced oceanic spreading fabric formed on the Antarctic plate at the Southeast Indian Ridge and together locally flank uplifted northward-pointing corner sections of ocean floor. The origins for the localised elevations are unclear, but may relate to intermittent and/or alternating rifting and volcanic episodes. Variations of degree of asymmetry and/or obliquity in spreading on the Central Indian Ridge and the Southwest Indian Ridge are suggested to explain detailed structural changes along the triple junction trace. It is suggested that discontinuities of the trace may be related to an intermittent development of new spreading centres beneath the most easterly part of the Southwest Indian Ridge, coupled with a more continuous process beneath the faster spreading Central Indian Ridge (2 to 2.5 cm a-1) and the Southeast Indian Ridge (2.5 to 3 cm a-1). A detailed history of triple junction evolution may be thus inferred from basic morphological and structural mapping along the three triple junction traces.  相似文献   

16.
The Central Spreading Ridge (CSR) is located in the central part of the North Fiji Basin, a complex back-arc basin created 12 Ma ago between the Pacific and Indo-Australian plates. The 3.5 Ma old CSR is the best developed, for both structure and magmatism, of all the spreading centers identified in the basin, and may be one of the largest spreading systems of the west Pacific back-arc basins. It is more than 800 km long and 50–60 km wide, and has been intensively explored during the French-Japanese STARMER project (1987–1991).The CSR is segmented into three first order segments named, from north to south, N160°, N15° and N-S according to their orientation. This segmentation pattern is similar to that found at mid-ocean ridges. The calculated spreading rate is intermediate and ranges from 83 mm/yr at 20°30 S to 50 mm/yr at 17°S. In addition, there is a change in the axial ridge morphology and gravity structure between the northern and southern sections of the CSR. The axial morphology changes from a deep rift valley (N160° segment), to a dome split by an axial graben (N15° segment) and to a rectangular flat top high (N-S segment). The Mantle Bouguer Anomalies obtained on the northern part of the CSR (N160°/N15° segments) show bull's eye structures associated with mantle upwelling at the 16°50S triple junction and also in the middle of the segments. The Mantle Bouguer Anomalies of the southern part of the ridge (N-S segment) are more homogeneous and consistent with the observed smooth topography associated with axial isostatic compensation.At these intermediate spreading rates the contrast in bathymetry and gravity structure between the segments may reflect differences in heat supply. We suggest that the N160° and N15° segments are cold with respect to the hot N-S segment. We use a non-steady-state thermal model to test this hypothesis. In this model, the accretion is simulated as a nearly steady-state seafloor spreading upon which are superimposed periodic thermal inputs. With the measured spreading rate of 50 mm/yr, a cooling cycle of 200,000 yr develops a thermal state that permits to explain the axial morphology and gravity structure observed on the N160° segment. A spreading rate of 83 mm/yr and a cooling cycle of 120,000 yr would generate the optimal thermal structure to explain the characteristics of the N-S segment. The boundaries between the hot N-S segment and its cold bounding segments are the 18°10 S and 20°30 S propagating rifts. A heat propagation event along the N-S segment at the expense of the adjacent colder failing segments, can explain the sharp changes in the observed morphology and structure between the segments.  相似文献   

17.
The analysis of multibeam bathymetric data of the Southwest Indian Ridge(SWIR) domain between the triple junction traces from 68° E to theRodrigues Triple Junction (RTJ; 70° E) reveals the evolution of thisridge since magnetic anomaly 4 (8 Ma). Image processing has been used toshow that the horizontal component of strain due to a network of normal stepfaults increases dramatically between 69°30 E and the RTJ. Thisarea close to the RTJ is characterized by a deep graben at the foot of thetriple junction trace on the African plate and by a narrow fault-boundedridge that joins an offset of the trace on the Antarctic plate. In thatarea, spreading is primarily amagmatic and dominated by tectonic extensionprocesses. To the west of 69°30 E, some lobate bathymetricfeatures atop of a large topographic high suggest volcanic constructions.Between 68°10 E and 69°25 E the southern flank of theSWIR domain is wider than the northern one and is characterized by a series of 7 en echelon bathymetric highs similar in size,shape and orientation to the one centred at 69°30E near the present-day triple junction. Their en echelon organization along the triple junction trace on the Antarctic plate and the typical lack of conjugated parts on the northern flank show that these bathymetric highs have been shifted to the south by successive northward relocalisations of the SWIR rifting zone. This evolution results in the asymmetric spreading of the SWIR in the survey area. The off-axis bathymetric highs connect to the offsets of the triple junction trace on the Antarctic plate when the Southeast Indian Ridges lightly lengthenstoward the northwest and the triple junction is relocated to the north. We propose that the SWIR lengthens toward the northeast with two propagation modes: 1) a continuous and progressive propagation with distributed deformation in preexisting crust of the Central Indian Ridge, 2) a discontinuous propagation with focusing of the deformation in a rift zone when the triple junction migrates rapidly to the north. The modes of propagation of the SWIR are related to different localisation and distribution of strain which are in turn controlled by changes of the triple junction configurations due to propagation, recession or a symmetric spreading on the Central and Southeast Indian Ridges.  相似文献   

18.
The heat balance of the upper ocean under a land and sea breeze was investigated based on observations of sea water temperature in the upper 300 m layer and heat flux across the sea surface at a fixed station in Sagami Bay (3510N, 13925E) during two periods of two days in August 1980 and three days in August 1981. During both periods, a typical land and sea breeze of 4–6 m sec–1 at maximum prevailed in the observation area. Large diurnal variation of sea surface temperature with a maximum peak around noon LST was observed during both periods (the daily value of the range was 0.9C and 2.5C in 1980, and 1.2C, 1.5C and 1.7C in 1981). It was found that these large temperature variations were caused by diurnal variation of the wind speed which dropped to 0–3 m sec–1 at noon when the strongest insolation (–270 Wm–2) penetrated the sea and at midnight in association with alternations of the land breeze and the sea breeze. On the other hand, vertical mixing of the sea water caused by the wind stress and/or convection due to cooling at night extended down only to the surface 10 m layer. Horizontal heat advection was negligibly small. Therefore the local time change of the heat content in the upper 10 m water column was affected mainly by the heat flux across the air-sea interface which was estimated from data on radiation fluxes measured directly on board and latent and sensible heat fluxes calculated by the aerodynamic bulk method. The water temperature below the 10 m layer also varied with time and the temperature variation in the thermocline (20–50 m depth) was frequently larger than that of the sea surface temperature. However, the variation in the upper 10 m layer was little influenced by that below the layer.  相似文献   

19.
A downwardf-looking acoustic Doppler current profiler (ADCP), suspended by a series of surface and subsurface floats and connecte to an anchroed ship, proided a quite stable platform to measure the, vertical profiles of backscatter strenght *BS) and three components of the velocith from 12 to 22 November 1992 at 1°30S and 156°15E, in the Intensive Flux Array (IFA) of TOGA/COARE. While the variability of the horizontal velocity was controlled by the semi-diurnal tide, BS and vertifal velocity were dominated by diurnal variability probably caused by the diel migration of zooplakton. The downward migration occurred early in the moring (0500–0700 in local time) and the upward one late in the afternoon (1700–1900). The average values of about 4 cm s–1 for the sinking and rising speed were estimated from Doppler shift and BS isopleth displacement. The subsurface chlorophyll maximum (SCM) coincident with the top of the thermocline at 80–100 m was also detectable in the BS data during daytime when almost no migrating zooplankton remained in the upper 300 m. Backscatter signals from the SCM and thermocline were separated by corrlating the BS data with the chlorophylla and temperature data. The maximum contribution of the migrating zooplanktion, passively drifting phytoplankton and temperature gradient on BS was estimated to be 14.8, 7.0, 5.1 dB, respectively.  相似文献   

20.
Six Deep-Tow magnetic profiles across the axis of the East Pacific Rise [EPR] in two small areas between 19°25 and 20°10S were collected during the 1983 Protea 1 cruise of the R/V Melville. These near-bottom profiles are of extremely high resolution allowing the interpretation of very short wavelength features. We have inverted the magnetic field data to determine the rock magnetization distribution near the axis of this ultrafast speading center (162 mm yr-1). The solutions reveal large amplitude (up to 35 A m-1) short wavelength (1–3 km) variations in magnetization. Specifically all crossings show a narrow (0.5 to 1.5 km) low in magnetization superimposed on a broader (2.5 to 4 km) high directly over the ridge axis. Four profiles in the northern area (19°25 to 19°33S) also show symmetrical near-axis (within 4 km) lows which are remarkably continuous along strike. Explanations for the short-wavelength variations are discussed which fall into the following categories: (1) variations in the thickness of the magnetized layer, (2) variations in rock chemistry (e.g. alteration due to hydrothermal activity), and (3) paleofield intensity variations. None of the mechanisms discussed alone adequately explain the observed phenomena in the study area or on a world-wide scale. Further sampling and high resolution surveying will be required in order to accurately determine the relative importance of the mechanisms discussed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号