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1.
Seismoacoustic investigations with a high-resolution parametric echo-sounder “SES 2000 deep” carried out on cruises 33, 35, and 37 of the R/V Akademik Ioffe revealed several erosional-depositional contourite systems on the São Paulo Plateau escarpment and its toe in the South Atlantic. Two contourite terraces related to interfaces between different water masses are observable on the escarpment. These terraces presumably reflect the activity of internal waves and turbulent eddies. The São Paulo contourite channel and genetically related drift are traceable along the escarpment toe. Changes in planktonic foraminiferal assemblages in Core AI-2563 retrieved from the summit of the São Paulo contourite drift suggest a shallowing of the Weddell Sea Deep Water mass during glacial times. It is established that the contour current of the Weddell Sea Deep Water and Lower Circumpolar Water considerably affect the formation of contourite depositional systems on the escarpment and its toe.  相似文献   

2.
A study on the public׳s perceptions and conceptions of global environmental changes (GECs) is relevant to guide future educational strategies and management actions. The present study aimed to: (1) evaluate coastal tourists׳ conceptions and perceptions of GECs; (2) correlate the conceptions presented by tourists about GECs and their self-declared knowledge; (3) evaluate how these tourists perceive their personal contribution to GECs; and (4) verify the frequency at which the media exposed the tourists to information about the influence of GECs on coastal and marine environments. A structured questionnaire was applied to 183 coastal tourists. There was a weak but significant positive correlation (r2=0.152, p<0.001) between self-declared knowledge and the actual conceptions of tourists about GECs and about the sea. Tourists underestimate their role in GECs, pointing out fewer individual actions that contributed to GECs in the questionnaire than expected. Many tourists declared they had never heard of some subjects related to GECs and coastal environments. This study revealed that coastal tourists are still not well informed about their role in GECs and also on their consequences to the society, thus emphasizing the need of more intensive and effective coastal and marine environmental education strategies.  相似文献   

3.
Settling particles collected at 1550 m water depth off the São Francisco River, Brazil, between January and May 1995 showed peak fluxes of amino acids, hexosamines, and carbohydrates, which formed the onset of a three-week period of high organic matter (OM) flux, coinciding with the high discharge period of the river. Two phases of OM deposition exist: (1) the fluvial input of nutrients triggering a bloom of non biomineralizing plankton, and (2) suspended sediment mainly derived from shelf erosion increasing the fluxes of refractory OM. This indicates the importance of seasonally varying hydrodynamic conditions and nutrient input from the continent for the production and sedimentation of OM to the continental margin of eastern Brazil.  相似文献   

4.
The relationship between El-Ni?o/Southern Oscillation (ENSO) and the Indian monsoon is analyzed using cross-wavelet analysis and Granger causality estimation from empirical data for the period 1871-2003. In addition to the previously known negative correlation between the processes analyzed, their bidirectional coupling is detected and characteristics of its inertia and nonlinearity are estimated. The results from an analysis of variations in coupling characteristics in a moving window with a width ranging from 10 to 100 years demonstrate an alternation of different regimes of processes interaction, including intervals of almost unidirectional coupling.  相似文献   

5.
Phytoplankton samples were collected from the equatorial Pacific (10°S to 10°N along 155°E) in June 1992 as part of the Australian contribution to the JGOFS program. Chlorophyll and carotenoid pigments were measured by HPLC, and a PC-based computer program (CHEMTAX) was used to estimate the contribution of 9 algal classes to the total chlorophyll a concentration in 9 separate depth bands at each location. This cruise occurred in the middle of the prolonged 1991/1993 El Niño, and the results are compared with similar data from a cruise in October 1990 which occurred before this El Niño but after the 1988/1989 La Niña.Changes in the pigment : chlorophyll a ratios appeared consistent across algal classes and, apart from some minor exceptions, consistent between cruises. Pigments involved in light-harvesting generally increased relative to chlorophyll a with increasing depth, whereas the ratio for photoprotective pigments (e.g. diadinoxanthin) usually decreased with depth. The zeaxanthin concentration per cell for cyanobacteria decreased with depth in the surface 75 m during 1992 as would be expected for a photoprotective pigment.Based on their contribution to the total chlorophyll a concentration, haptophytes, prochlorophytes, cyanobacteria (Synechococcus) and chlorophytes were the dominant algal classes in 1992. The chlorophyte contribution to chlorophyll a in 1992 (14.8%) was almost double that in 1990 (7.8%). This increase was largely at the expense of the cyanobacteria and haptophytes, which both decreased significantly. The increase in chlorophytes in 1992 was particularly noticeable in the surface waters south of the equator at about 4°S, where there was evidence of upwelling.  相似文献   

6.
The Nazaré Canyon on the Portuguese Margin (NE Atlantic) was sampled during spring-summer for three consecutive years (2005–2007), permitting the first inter-annual study of the meiofaunal communities at the Iberian Margin at two abyssal depths (~3500 m and ~4400 m). Using new and already published data, the meiofauna standing stocks (abundance and biomass) and nematode structural and functional diversity were investigated in relation to the sediment biogeochemistry (e.g. organic carbon, nitrogen, chlorophyll a, phaeopigments) and grain size. A conspicuous increase in sand content from 2005 to 2006 and decrease of phytodetritus at both sites, suggested the occurrence of one or more physical disturbance events. Nematode standing stocks and trophic diversity decreased after these events, seemingly followed by a recovery/recolonisation period in 2007, which was strongly correlated with an increase in the quantity and bioavailability of phytodetrital organic matter supplied. Changes in meiofauna assemblages, however, also differed between stations, likely because of the contrasting hydrodynamic and food supply conditions. Higher meiofauna and nematode abundances, biomass and trophic complexity were found at the shallowest canyon station, where the quantity, quality and bioavailability of food material were higher than at the deeper site. The present results suggest that even though inter-annual variations in the sedimentary environment can regulate the meiofauna in the abyssal Nazaré Canyon, heterogeneity between sampling locations in the canyon were more pronounced.  相似文献   

7.
The morphotectonic setting of the East Pacific Rise (EPR) between21°12 and 22°40 S and its recent and past hydrothermalactivity were the focus of the Russian R/V Geolog Fersmans expeditionin 1987–1988.The EPR axial zone in the study area is comprised of three segmentsseparated by overlapping spreading centers (OSCs) near 21°44 and22°08 S. The northern segment is the shallowest of three and hasa distinct massive axial ridge, trapeziodal in cross-section, toppedby a very wide flat summit surface and cut by a well-developedcentral graben. These features testify to intense magmatism and to avoluminous crustal magmatic chamber underlying the whole segment.Fine-scale segmentation is most clearly revealed in the structure ofthe central graben within which several 4th-order segments can bedistinguished. This scale of segmentation is also reflected on flanks of theaxis by variations in the character and intensity of faulting.According to structural and petrologic data, the magmatism is mostintense in the central part of the segment which is probably locateddirectly over a magmatic diapir supplying the melt to the whole segment.Magma migration at the subcrustal level from the center towards the ends ofthe segment with discrete injection into the crustal magmatic chamber ispresumed.The central segment is broken into two morphologically distinct partsseparated by a deval. In the subsided northern part, the wide summit of theaxial ridge is cut by a well-developed, intensely fractured axialgraben. In the southern part, the axial ridge is relatively elevated, butnarrow with an ephemeral graben along its crest. The character and intensityof faulting on the axial flanks are also considerably different in thenorthern and southern parts of the segment. Thus, the magmatic supply tothese two parts is thought to originate from two different sources. If so,then at present the magma chamber underlying the southern part of thesegment is probably at the stage of replenishment, while in the north it isat the stage of deep cooling.The southern segment is structurally similar to the central one. Howeverthere is considerably less intensive magmatic activity in this region,especially south of 22°30 S where the axial ridge is narrow, andtriangular in cross-section.Both OSCs studied are marked by abrupt narrowing and sharp subsidence ofthe tips of axial ridges within the northern limbs. The southern OSC limbsare morphologically similar to normal sections of axial ridges. In bothcases the flanks are structurally and morphologically disrupted adjacent tothe OSCs and oblique structures can be traced far southward of the OSCflanks. Due to the spatial position of oblique structures on the the flanksit is presumed that the OSC near 22°07 S is migrating northward.The 21°44 S OSC zone has apparently undergone small spatialoscillations. In spite of the small amplitude of lateral displacement, thiszone is marked by prominent bathymetric anomalies.Numerous massive sulfide deposits were discovered atop the axial ridgealong the entire length of the uplifted and hydrothermally active northernsegment. Ore metal concentrations in near-bottom waters are maximumover the southern part of the northern segment, while maximum concentrationsof the same metals in surficial sediments are confined to the central partof the same segment. We surmise that there has been a recentalong-axis shift of the zone of maximum hydrothermal activity fromthe middle of the segment to its present position in the southern part ofthe segment. Considering sedimentation rates, the age of this shift can beapproximately estimated to be 5 to 10 thousand years before the present.The relatively Mg-enriched basalts of the middle part of thenorthern segment represent a tike of a more primitive pattern, while therelatively Fe-rich rocks of its southern part probably reflect alarge degree of fractionation at shallow crustal levels. Considering thistrend, in addition to morphotectonic data we presume that subaxial magmaflow from the middle to the southern part of the segment is responsible forthe along-axis shift of hydrothermal activity.In the central segment of the study area, massive sulfides have only beendiscovered south of the 21°55 S deval, where the axial ridgeshoals and where the existence of a subjacent magma chamber is presumed.The very weak manifestations of recent volcanism within the southernsegment explain the absence of hydrothermal activity and sulfide depositswithin this segment.  相似文献   

8.
The relations between the processes occurring in the equatorial latitudes of the Pacific and Atlantic oceans were studied on the basis of the Granger causality analysis and a simulation of phase dynamics using the indices of the El Niño-Southern Oscillation (ENSO) and the equatorial Atlantic mode (EAM). Data on the monthly means of the sea-surface temperature over the period 1870–2006 for the Niño 3 (5° S-5° N, 150° W-90° W) and Niño 3.4 (5° S-5° N, 170° W-120° W) regions in the Pacific and the Atlantic 3 region (20° W-0, 3° S-3° N) in the Atlantic Ocean were used as the ENSO and EAM indices. The statistically significant influence of the EAM on the ENSO is noted. The lag time of this influence is estimated at two months. No significant reverse effect is revealed. An increase in the EAM’s influence on the ENSO was observed in the second half of the 20th century.  相似文献   

9.
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10.
Izvestiya, Atmospheric and Oceanic Physics - Regional anomalies in the frequency of atmospheric blockings in the Northern Hemisphere detected on the basis of reanalysis data since 1979 during...  相似文献   

11.
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12.
We discuss nitrous oxide (N2O) and methane (CH4) distributions in 49 vertical profiles covering the upper ∼300 m of the water column along two ∼13,500 km transects between ∼50°N and ∼52°S during the Atlantic Meridional Transect (AMT) programme (AMT cruises 12 and 13). Vertical N2O profiles were amenable to analysis on the basis of common features coincident with Longhurst provinces. In contrast, CH4 showed no such pattern. The most striking feature of the latitudinal depth distributions was a well-defined “plume” of exceptionally high N2O concentrations coincident with very low levels of CH4, located between ∼23.5°N and ∼23.5°S; this feature reflects the upwelling of deep waters containing N2O derived from nitrification, as identified by an analysis of N2O, apparent oxygen utilization (AOU) and NO3−, and presumably depleted in CH4 by bacterial oxidation. Sea-to-air emissions fluxes for a region equivalent to ∼42% of the Atlantic Ocean surface area were in the range 0.40–0.68 Tg N2O yr−1 and 0.81–1.43 Tg CH4 yr−1. Based on contemporary estimates of the global ocean source strengths of atmospheric N2O and CH4, the Atlantic Ocean could account for ∼6–15% and 4–13%, respectively, of these source totals. Given that the Atlantic Ocean accounts for around 20% of the global ocean surface, on unit area basis it appears that the Atlantic may be a slightly weaker source of atmospheric N2O than other ocean regions but it could make a somewhat larger contribution to marine-derived atmospheric CH4 than previously thought.  相似文献   

13.
应用分子系统发育学的方法,以蟹类18S rDNA和线粒体细胞色素C氧化酶亚单位Ⅰ(COⅠ)基因序列片段为分子标记,结合形态学特征对10种蟹类的分类地位进行探讨.实验共获得10条18S rDNA序列,长度为1 780～1 787 bp,其中A、T、G、C平均含量分别为23.72％,24.58％,24.52％和27.17％;通过序列对比,发现18S rDNA序列相对保守,只含有1个从88 bp到130 bp约50 bp的高可变区;物种间碱基距离比较小,从0.001到0.017.18S rDNA系统发育树为方蟹总科、沙蟹总科和梭子蟹总科起源于同一海洋蟹类祖先提供了分子生物学证据,并且支持将厚蟹属从相手蟹科移至弓蟹科.获得的5条CO Ⅰ基因序列,长度均为709 bp,A、T、G、C平均含量分别为26.88％,37.62％,17.50％和18.00％;COⅠ基因片段变异性高,物种间碱基距离从0.016到0.138.CO Ⅰ基因系统发育树真实地反映了归蟳属各物种之间的进化关系,和传统分类非常吻合,为形态特征相似的蟳类鉴定提供了一种快速准确的方法.  相似文献   

14.
The central Pacific(CP) zonal wind divergence and convergence indices are defined, and the forming mechanism of CP El Nio(La Nia) events is discussed preliminarily. The results show that the divergence and convergence of the zonal wind anomaly(ZWA) are the key process in the forming of CP El Nio(La Nia) events. A correlation analysis between the central Pacific zonal wind divergence and convergence indices and central Pacific El Nio indices indicates that there is a remarkable lag correlation between them. The central Pacific zonal wind divergence and convergence indices can be used to predict the CP events. Based on these results, a linear regression equation is obtained to predict the CP El Nio(La Nia) events 5 months ahead.  相似文献   

15.
The article deals with the influence of wind and atmospheric pressure on the barotropic variability of the Antarctic Circumpolar Current (ACC). This effect is studied using a global barotropic model under idealized and realistic atmospheric forcings. The results of barotropic modeling demonstrate that variations in the wind forcing over the ACC, together with the effects of the topography and coastline, lead to the variability in the meridional water flux in the Southern Ocean. The variability of these fluxes is negatively correlated with the wind strength over the ACC. A possible link between the short-period variability of the water flux in the Pacific sector of the Southern Ocean and El Niño is demonstrated using 3D ocean modeling and correlation analysis. It is shown that the variability of the meridional water flux caused by atmospheric perturbations over the ACC can lead to short-period density anomalies in the Southern Ocean north of 47°S, which later can be transferred to low latitudes by means of the wave mechanism described in [15] and strongly influence the tropical region.  相似文献   

16.
Swath MR1 data from the remnant Colville and active Kermadec arc margins, south of 33°30 S (SW Pacific), record the structural morphology and evolution of the rifted, and now separate portions, of the proto-Colville–Kermadec arc flanking the actively widening southern Havre Trough back-arc basin associated with Pacific-Australian plate convergence. Both the remnant Colville and active Kermadec arc margins comprise opposing, asymmetric, partially basement exposed, segmented ridges. Differences in morphology between the two ridges are, however, observed. The single, near linear, border fault system, with relief of 1000 m, along the western edge of the Kermadec margin is interpreted to be the exposed fault escarpment of a major, west-dipping, detachment fault. In contrast, two major zig-zag border fault systems along the eastern edge of the Colville Ridge, bounding a back-tilted ridge flank terrace, are interpreted as major antithetic faults between the remnant arc and back-arc region. This contrast in structural morphology coincides with, respectively, lesser and greater degrees of both active tectonism and channel-canyon erosion, on the remnant Colville and active Kermadec margins. These differences are interpreted to reflect the progressive trenchward collapse and associated greater rift flank uplift and incisive erosion of the Kermadec foot-wall contrasting with the non-collapse and relatively lesser rift flank uplift and ridge erosion of the Colville hanging-wall. The data provide further constraints on the early evolution of the Havre Trough in particular, and back-arc basins in general.  相似文献   

17.
Sea‐level data from two sites in northern New Zealand, along with the Southern Oscillation Index (SOI), are analysed for interannual and decadal variability using wavelets. The analysis shows, using statistically significant wavelet power, there is a significant relationship between mean sea level (MSL) and SOI. However, the relationship is highly variable, both in magnitude and in the range of time‐scales over which it occurs. This non‐stationarity necessitates the use of techniques such as wavelets for analysis. An interdecadal response in MSL around northern New Zealand has been isolated, with shifts occurring in 1950 and the late 1970s. This behaviour in MSL appears to coincide with shifts in the Pacific Decadal Oscillation, thought previously to be largely centred in the North Pacific. A strong correlation between SOI and sea surface temperature (SST) is also demonstrated. This relationship appears to be stable in magnitude (a large change in SOI produces a large change in SST) and to occur over the same range of time‐scales. More SST and MSL data are required for other parts of New Zealand to determine whether these findings apply elsewhere.  相似文献   

18.
文中综述了El Ni(?)o现象的调整、监测及研究的进展,同时指出了尚待进一步研究的问题。此外,还简介了根据“中美热带西太平洋海气相互作用联合研究”四个航次的考察资料并结合美国NOAA提供的SST和夏威夷大学Wyrtkl博士赠送的水位资料对1986—1987El Ni(?)o期间的海洋事件的研究结果。  相似文献   

19.
The Bonnet Carré Spillway, located 28 miles northwest of New Orleans, was constructed in the early 1930s as part of an integrated flood-control system for the lower Mississippi River system. From 11 April to 8 May 2008, Mississippi River water was diverted through the spillway into the 629-square-mile Lake Pontchartrain, which is hydraulically connected to the Gulf of Mexico. On 8 April, prior to the opening of the spillway, water-quality instruments were deployed and recorded hourly measurements of water temperature, dissolved oxygen, specific conductance, pH, and nitrate. Discrete water-quality and phytoplankton (algae) samples were collected in Lake Pontchartrain from 8 April to 3 October 2008 to assess the water-quality nutrient enrichment effects of the diversion on the lake. The maximum influence of river water in the southern portion of the lake was captured with continuous (hourly) monitoring of nitrate concentrations, and field measurements such as of specific conductance during the critical period in late April to early May. By late May, the deployed instruments had recorded the arrival, peak, and decline of selected constituents associated with the freshwater influx from the Mississippi River/Bonnet Carré Spillway diversion. The continuous monitoring data showed the short-term interactions of high-nitrate, low-specific conductance river water and low-nitrate, high-specific conductance lake water. The phytoplankton community composition, as an indicator of water quality, illustrated an extended response from the river water evident even after the continuous and discrete samples indicated that the lake had returned to pre-diversion conditions. The initial phytoplankton community response to nutrient increases was related to accumulations of diatoms. During periods of low nutrient concentrations, accumulations of blue-greens occurred by July and August. As blue-green algae cell densities and biovolumes increased in the summer, so did the species richness of blue-green algae, particularly the harmful algae bloom taxa. Cell densities and biovolume of the phytoplankton lake indicator taxa Skeletonema costatum, Anabaena sp., and Cylindrospermopsis raciborskii were highest and dominated the diatom and blue-green algae communities during the period of most river water influence on the lake and immediately following the freshwater inflows. The dominance and recession of these indictor taxa reflect the dramatic changes that occurred in the phytoplankton community in response to an increase in nutrient-rich freshwater from the diversion into the lake, and not normal seasonal phytoplankton compositional differences. Water-quality data indicated a gradual reversion to pre-diversion lake conditions by June to July, but shifts in the phytoplankton composition were still evident through August 2008. Observations from this study were similar to results from previous studies of Mississippi River/Bonnet Carré Spillway diversion opening in 1997.  相似文献   

20.
前 言 E1 Ni(?)o现象越来越引起人们的注意。因为E1 Ni(?)o现象经常伴随着出现全球大气的异常。E1 Ni(?)o年会使原来干旱的赤道东太平洋地带有强烈的降水。南美和北美沿岸也常造成洪水灾害。1982年强E1 Ni(?)o年中加利福尼亚的洪水造成了几亿美元的损失。而印度尼西亚和澳大利亚以及南非却会遭受持久的干旱。E1 Ni(?)o现象对我国的气候也有明显的影响,有人认为我国东北地区夏季的低温冷害和南方梅雨的多寡与E1 Ni(?)o现象有关。 近年来,对E1 Ni(?)o现象的研究已作了很多工作。本文试图对E1 i(?)o现象的研究概况作一简要的介绍。  相似文献   

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