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.
ENSO-induced interannual variability in the southeastern South China Sea   总被引：5，自引：0，他引：5  
In this study, El Niño Southern Oscillation (ENSO)-induced interannual variability in the South China Sea (SCS) is documented using outputs from an eddy-resolving data-assimilating model. It is suggested that during an El Niño (La Niña) event, off-equatorial upwelling (downwelling) Rossby waves induced by Pacific equatorial wind anomalies impinge on the Philippine Islands and excite upwelling (downwelling) coastal Kelvin waves that propagate northward along the west coast of the Philippines after entering the SCS through the Mindoro Strait. The coastal Kelvin waves may then induce negative (positive) sea level anomalies in the southeastern SCS and larger (smaller) volume transport through the Mindoro and Luzon Straits during an El Niño (La Niña) event.  相似文献   

2.
Time-series data from sediment trap moorings intermittently deployed during 1991–1999 show that the fluxes of biogenic material (carbonate, opal and organic matter, including amino acids) and other related parameters are temporally and spatially distinct across the Western Pacific Warm Pool (WPWP). These variations resulted from the El Niño and La Niña conditions, which alternately prevailed over the equatorial Pacific Ocean during the mooring deployments. The westernmost WPWP (a hemipelagic region) recorded relatively high average total mass and amino acid fluxes during the El Niño event. This was in sharp contrast to the eastern part of the WPWP (oligotrophic and weak upwelling regions) which recorded higher flux values during the La Niña event. Settling particulate organic matter was rich in labile components (amino acids) during La Niña throughout the study area. Relative molar ratios of aspartic acid to β-alanine together with relative molar content of non-protein amino acids β-alanine and γ-aminobutyric acid) suggested that organic matter degradation was more intense during La Niña relative to that during El Niño in the WPWP. This study clearly shows that during an El Niño event the well documented decrease in export flux in the easternmost equatorial Pacific is accompanied by a significant increase in export flux in the westernmost equatorial Pacific Ocean.  相似文献   

3.
Time-varying air–sea coupled processes in the central to eastern equatorial Pacific associated with strong El Niño development during the 1997–1998 period are examined using a newly developed reanalysis dataset obtained from four-dimensional variational ocean–atmosphere coupled data assimilation experiments. The time series of this data field exhibits realistic features of El Niño evolution. Our analysis indicates that resonance between eastward-propagating oceanic downwelling Kelvin waves and the seasonal rise of sea-surface temperature (SST) in the central to eastern equatorial Pacific generates relatively persistent high SST conditions accompanied by a deeper thermocline and more relaxed easterly winds than usual. The surface condition resulting from the wave-seasonal SST resonance represents a preconditioned state that leads to an enhancement in incident downwelling Kelvin waves to levels sufficient to induce large-amplitude unstable coupled waves in the central to eastern equatorial region. Heat balance estimates using our reanalysis dataset suggest that the unstable coupled waves are categorized within the intermediate regime of coupled Kelvin and Rossby waves and have the potential to grow rapidly. We argue that the seasonal resonance and the unstable coupled waves should play crucial roles in the development of the largest historical El Niño event, which was recorded between late 1997 and early 1998.  相似文献   

4.
The coastal waters of Peru and Chile are among the most productive of the world's oceans. A striking source of interannual variability in this upwelling ecosystem, El Niño, results in large population and community variations. During El Niño the seasonal upwelling ceases and warm, clear oceanic waters occur close inshore, setting a unique oceanographic scenario in which the performance of populations and communities can be studied. While most attention has been focused on the pelagic components of such systems, numerous changes occur in inshore, benthic populations. Likewise, little attention has been paid to the critical role of humans as predators or active users of inshore, benthic resources. Humans as components of the ecosystem can impose significant alterations on population and community structure. In this paper the fishery statistics of three economically important inshore, benthic resources (the gastropod Concholepas concholepas, the cephalopod Octopus vulgaris and the kelp Lessonia nigrescens) are analysed in relation to the strong 1982/83 El Niño event. In particular, trends are described for landings in the far northern regions of Chile, where the marked effect of El Niño was concurrent with high levels of exploitation of C. concholepas and L. nigrescens.  相似文献   

5.
We investigate an overlooked mechanism—coastal upwelling—for sea surface temperature (SST) cooling in the western side of the mean location of the Pacific warm pool (WSWP: 5°S–5°N, 140°E–150°E) prior to El Niño onset. We analyze various observed data such as the TRIangle Trans-Ocean buoy Network (TRITON) moored buoy data, Conductivity-Temperature-Depth (CTD) data, satellite data and a hindcast experiment output by a high-resolution ocean general circulation model (OGCM). We focus on the precondition of the 2002/03 El Niño event, for which many datasets are available. Relatively cool water upwelled along the north coast of Papua New Guinea (PNG) during December 2001, prior to the onset of the 2002/03 El Niño event, and then spread out over a wider area to the northeast. Simultaneously, strong west-northerly surface winds occur along the north coast. Heat budget analysis of TRITON buoy data in the WSWP reveals that negative zonal heat advection due to eastward current is the main factor for cooling the mixed layer in the WSWP in contrast to the warming effect of the surface heat flux during the period. This cooling requires a source of colder water to the west. Similar analysis of OGCM outputs also suggests that the upwelled relatively cool water along the PNG north coast, and its northeastward extension to the equatorial region, contributes to cooling of the surface water over the WSWP mainly via negative zonal heat advection. Similar mechanisms are confirmed also for the 1982/83 and 1997/98 El Niño events by analyses of OGCM outputs and historical SST data. The low SST in the WSWP generated a positive zonal SST gradient together with high SST east of the WSWP. It may contribute to enhancement of the westerly surface wind in this region, leading to the onset of the 2002/03 El Niño event.  相似文献   

6.
The impact of quasi-decadal (QD: 8 to 18 years) variability in the tropical Pacific on ENSO events is investigated. It is found that there is a significant difference in the behavior of ENSO events between the phases of positive and negative anomalies of the QD Niño-3.4 index. During the period of negative QD-scale Niño-3.4 index, ENSO events, especially La Niña events, occur more frequently, and larger amplitudes of thermal anomalies related to El Niño events appear over the central to eastern equatorial Pacific. Furthermore, propagations of upper ocean heat content anomaly and a phase relationship between upper ocean heat content and Niño-3 index in the equatorial Pacific, which have been pointed out by previous studies, are clearly detected during the period of negative QD Niño-3.4 index.  相似文献   

7.
气候模式FIO-ESM对2015/16年厄尔尼诺的预测   总被引：1，自引：0，他引：1  
Recently atmospheric and oceanic observations indicate the tropical Pacific is at the El Ni?o condition. However,it's not clear whether this El Ni?o event of this year is comparable to the very strong one of 1997/98 which brought huge influence on the whole world. In this study, based on the Ensemble Adjusted Kalman Filter(EAKF)assimilation scheme and First Institute of Oceanography-Earth System Model(FIO-ESM), the assimilation system is setup, which can provide reasonable initial conditions for prediction. And the hindcast results suggest the skill of El Ni?o-Southern Oscillation(ENSO) prediction is comparable to other dynamical coupled models. Then the prediction for 2015/16 El Ni?o by using FIO-ESM is started from 1 November 2015. The ensemble results indicate that the 2015/16 El Ni?o will continue to be strong. By the end of 2015, the strongest strength is very like more than 2.0°C and the ensemble mean strength is 2.34°C, which indicates 2015/16 El Ni?o event will be very strong but slightly less than that of 1997/98 El Ni?o event(2.40°C) calculated relative a climatology based on the years1992–2014. The prediction results also suggest 2015/16 El Ni?o event will be a transition to ENSO-neutral level in the early spring(FMA) 2016, and then may transfer to La Ni?a in summer 2016.  相似文献   

8.
The El Ni?o Southern Oscillation(ENSO) is a natural phenomenon that relates to the fluctuation of temperatures over the Pacific Ocean. The ENSO significantly affects the ocean dynamics including upwelling event and coastal front. A recent study discovered the seasonal upwelling in the east coast of Peninsular Malaysia(ECPM), which is significant to the fishery industry in this region. Thus, it is vital to have a better understanding of the influence of ENSO towards the coastal upwelling and thermal front in the ECPM. The sea surface temperature(SST) data achieved from moderate resolution imaging spectroradiometer(MODIS) aboard Aqua satellite are used in this study to observe the SST changes from 2005 to 2015. However, due to cloud cover issue, a reconstruction of data set is applied to MODIS data using the data interpolating empirical orthogonal function(DINEOF) to fill in the missing gap in the dataset based on spatial and temporal available data. Besides, a wavelet transformation analysis is done to determine the temperature fluctuation throughout the time series. The DINEOF results show the coastal upwelling in the ECPM develops in July and reaches its peak in August with a clear cold water patch off the coast. There is also a significant change of SST distribution during the El Ni?o years which weaken the coastal upwelling event along the ECPM. The wavelet transformation analysis shows the highest temperature fluctuation is in 2009–2010 which indicates the strongest El Ni?o throughout the time period. It is suggested that the El Ni?o is favourable for the stratification in water column thus it is weakening the upwelling and thermal frontal zone formation in ECPM waters.  相似文献   

9.
This study investigated the eastern Pacific Intertropical Convergence Zone (ITCZ) as an atmospheric forcing to the ocean by using various observed and reanalysis data sets over 29 years. Climatologically, a zonal band of positive wind stress curl (WSC) with a 10° meridional width was exhibited along the ITCZ. A southward shift of the positive WSC band during the El Niño phase induced a negative (positive) WSC anomaly along the northern (southern) portion of the ITCZ, and vice versa during the La Niña phase. This meridional dipole accounted for more than 25 % of interannual variances of the WSC anomalies (WSCAs), based on analysis of the period 1993–2008. The negative (positive) WSCA in the northern portion of the ITCZ during the El Niño (La Niña) phase was collocated with a positive (negative) sea surface height anomaly (SSHA) that propagated westward as a Rossby wave all the way to the western North Pacific. This finding indicates that this off-equatorial Rossby wave is induced by the WSCA around the ITCZ. Our analysis of a 1.5-layer reduced gravity model revealed that the Rossby waves are mostly explained by wind stress forcing, rather than by reflection of an equatorial Kelvin wave on the eastern coastal boundary. The off-equatorial Rossby wave had the same SSHA polarity as the equatorial Kelvin wave, and generation of a phase-preserving Rossby wave without the Kelvin wave reflection was explained by meridional movement of the ITCZ. Thus, the ITCZ acts as an atmospheric bridge that connects the equatorial and off-equatorial oceanic waves.  相似文献   

10.
Four year-long time-series sediment trap experiments were conducted along the equatorial Pacific Ocean in order to understand the biogeochemistry of particulate organic matter (POM) on the basis of amino acid (AA) and hexosamine (HA) compositions of the settling particles. Total mass flux in the study area varied over 4 orders of magnitude without a common seasonality among all trap sites. Planktonic blooms were apparent in terms of total mass and AA fluxes at the easternmost end of the Niño-4 region. AA fluxes closely followed the total mass flux profiles, suggesting that increased particle flux delivered a greater amount of labile OM to the deep ocean. A labile OM index (LI)-based classification showed that during the El Niño conditions in 2002, the eastern side of the equatorial Pacific transported relatively more labile OM than the western equatorial Pacific. An overall change in AA and HA composition of settling particles could be revealed with the help of discriminant analysis, suggesting that settling particles during El Niño were compositionally different from those settling during La Niña condition in the equatorial Pacific.  相似文献   

11.
西风爆发、次表层暖水东移与厄尔尼诺现象   总被引：7，自引：2，他引：7       下载免费PDF全文
利用最近20 a的大气海洋资料,分析了厄尔尼诺事件与赤道太平洋西风异常以及赤道太平洋次表层海温之间的关系.结果表明,赤道西太平洋(5°S～5°N,120°～160°E)和赤道中东太平洋(5°S～5°N,160°E～160°W)西风异常都存在着与厄尔尼诺周期一致的年际变化,但前者还包含有显著的2～3个月季节内振荡.赤道西太平洋次表层冷暖水东移也呈现年和年际时间尺度的振荡周期.在厄尔尼诺发生前,赤道西太平洋次表层海水出现持续性增暖,赤道西太平洋西风异常频率加快,强度增强.随后赤道中太平洋(160°E～160°W)出现持续性(3个月以上)强西风异常(即西风爆发),并进一步向东扩展,同时次表层暖水沿着赤道波导东移到赤道东太平洋混合层,导致赤道东太平洋海表大面积异常增暖,形成一次厄尔尼诺现象.最后,模式模拟了1980～1984年赤道太平洋海温的变化,进一步证实了赤道纬向西风异常对暖水东移起着重要的作用.  相似文献   

12.
The water masses of the central and western equatorial Pacific can be divided into two parts: the Western Pacific Warm Pool (WPWP) and the Equatorial Upwelling Region (EUR). The behavior of the WPWP plays a significant role in global climate changes such as the El Niño-Southern Oscillation (ENSO), and it drastically modifies the oceanographic conditions in the area every few years. It is important to evaluate changes in time-series diatom fluxes during both the El Niño and the La Niña events. As a part of the Global Carbon Cycle and Related Mapping based on Satellite Imagery (GCMAPS) Program, time-series sediment trap moorings were deployed and recovered along the Equator at seven stations (Sites MT1–MT7) during five R/V Mirai cruises in the central and western Pacific during January 1999–January 2003. The entire length of this study is divided into two phases depending on the oceanographic conditions: the La Niña event (1999 and 2000); and the El Niño event (2002). Site MT3 was located in the WPWP and Sites MT5–MT7 were in the EUR. Annual means of total diatom fluxes increased towards the east in each year. The fluxes observed at Sites MT4–MT6 decreased from the La Niña event to the El Niño event. However, the fluxes observed at Site MT3 in 2001 and 2002 were higher than those in 2000. Total diatom fluxes showed different seasonal patterns at all sites. The diatom assemblages in the WPWP differed from those of the EUR. Pennate diatoms (e.g., Nitzschia bicapitata, Thalassionema nitzschioides) dominated in the WPWP, while the relative abundances of centric diatoms (e.g., Rhizosolenia bergonii, Azpeitia spp., Thalassiosira spp.) were higher than those of pennate diatoms in the EUR. The diatom fluxes during the La Niña event reflected seasonal oscillation of the WPWP in spatial extent. At Site MT3 during El Niño, terrestrial materials appeared to have been transported by subsurface currents, which might be a secondary influence on total diatom fluxes. The spatial extent of the WPWP reached Site MT7 in 2002, when total diatom fluxes decreased in the sediment traps located in the eastern region including Site MT7. Therefore, we conclude that the relationships between the ENSO and diatoms fluxes in the western and central equatorial Pacific can be explained by the geographic (west–east) expansion or contraction of the WPWP.  相似文献   

13.
Partial pressure of CO2 (pCO2) in surface seawater has been measured in the northeastern Pacific Ocean at Station P and along Line P since 1973. These data have been divided into ‘oceanic’ and ‘coastal/transition’ zones, and the seasonal and interannual variability and the long-term trends for each zone have been examined. The oceanic zone shows little seasonality in surface seawater pCO2, with undersaturation throughout the year. A strong, biologically-driven seasonal cycle is offset by variation in temperature-dependent solubility of CO2. The coastal/transition zone shows a decline in pCO2 from winter–spring through summer and fall that is likely the result of seasonal stratification and convection rather than coastal upwelling. Interannual variability all along Line P is correlated with the multivariate ENSO index (MEI), with lower seawater pCO2 associated with El Niño conditions. Correlations with the Pacific Decadal Oscillation Index are similar but weaker, in part because there are few data prior to the 1976 regime shift. The long-term trend in seawater pCO2 in the oceanic zone is +1.36±0.16 μatm year?1, indistinguishable from the atmospheric growth rate, and varies little among the seasons. In the coastal/transition zone a slow increase in the pCO2 of surface seawater relative to that of the atmosphere has led to increasing undersaturation, particularly in spring. Aliasing of the seasonal and interannual variability due to sampling frequency may explain part of the observed trend in the coastal/transition zone, but real changes in physical or biological processes are also possible and require more detailed study.  相似文献   

14.
The sediments of the Bay of Concepción and the adjacent shelf underlie one of the most productive upwelling areas in the SE Pacific margin. Reports on factors controlling meiofaunal community structure in these kinds of organic‐rich and oxygen‐deficient habitats are scarce in the literature. In this study, five sites along a transect from the mid‐Bay of Concepción (27 m) to the outer shelf (120 m) were studied on fives dates (May, August, November 1997, and March and May 1998) in order to assess the dynamic relationships between sedimentary organic matter and metazoan meiofauna. The sampling period coincided with the 1997–1998 El Niño event. Sediment parameters investigated were the redox potential discontinuity depth, photosynthetic pigment concentrations (chlorophyll a and phaeopigments), organic carbon, nitrogen, total lipids, carbohydrates, and proteins. In general, lowest values of meiofauna abundance and biomass were found within the naturally eutrophic Bay of Concepción and towards the shelf break, while maximum values occurred at intermediate depths. During the whole period, the meiofaunal abundance was negatively correlated with the concentration of most of the biochemical components of organic matter, as well as with the sediment phaeopigment content. However, positive correlations were found with chlorophyll a derived indices and with bottom‐water oxygen content. Most of the sediment parameters displayed a seasonal cycle, but towards the beginning of 1998, an effect of the 1997–1998 El Niño was evident. Typical austral‐summer (i.e. oxygen‐deficient) conditions did not develop, and sedimentary parameters reflected a decreased input of phytodetritus. Along the transect, the magnitude of this effect on meiofauna varied among sites. An overall positive response, in terms of meiofaunal abundance was observed, probably due to the amelioration of low oxygen conditions in the sediment.  相似文献   

15.
A time-series sediment trap was deployed from October 2007 to May 2011 in the western subtropical Pacific with the aim of understanding the seasonal and inter-annual variability on particle flux in response to El Niño-Southern Oscillation (ENSO) events. Total mass fluxes varied from 3.04 mg m−2 day−1 to 31.1 mg m−2 day−1, with high fluxes during February–April and low fluxes during other months. This seasonal variation was also characterized by a distinct change in the CaCO3 flux between the two periods. The marked increase in particle flux during February–April may be attributed to enhanced biological productivity in surface waters caused by strong wind-driven mixing in response to the western North Pacific monsoon system. The 2009/10 strong El Niño was accompanied by a significant reduction in particle flux, whereas the La Niña had no recognizable effect on particle flux in the subtropical Pacific. In particular, in the mature phase of the 2009/10 strong El Niño, the fluxes of organic carbon and biogenic silica decreased by 70–80% compared with those during the normal period, implying that the El Niño acted to suppress biological productivity in surface waters. The suppression of biological productivity during the 2009/10 strong El Niño is attributed to the decrease in precipitation due to the shift in the western Pacific warm pool. This finding is opposite that of other studies of the western equatorial Pacific, where El Niño events were observed to result in an increase in biological productivity and particle flux. The difference in particle flux between the western equatorial and subtropical Pacific is attributed to the regional differences in oceanic and atmospheric circulation systems generated by the strong El Niño.  相似文献   

16.
热带太平洋第二类El Nio事件及其对中国气候的影响   总被引：1，自引：0，他引：1  
基于热带太平洋次表层海温资料,分析了热带太平洋第二类El Nio事件海温异常的分布特征及其形成机制,讨论了与经典El Nio事件、El Nio Modoki、WP(西太平洋暖池)及CT(冷舌)El Nio事件之间的关系,揭示了第二类El Nio事件对中国降水的影响,得到以下结论。(1)第二类El Nio事件表征为热带太平洋次表层海温异常第三模态,占总方差贡献的4.7%。在海洋表面层,第二类El Nio事件暖期赤道东太平洋为沿赤道西伸的冷舌,热带中西太平洋为环绕冷舌的马蹄型大范围暖区。该型具11a和30~40a年代际振荡及3~4a年际变率,峰值多出现在春季。第二类El Nio事件是热带太平洋异常海面风应力场和赤道两侧的风应力旋度共同作用的结果,在赤道东印度洋-中西太平洋与赤道东太平洋-南美洲上空出现以反号垂直运动为特征的异常Walker环流。(2)El Nio Modoki与第二类El Nio事件有密切关系,它实质上是第二类El Nio事件次表层海温与近海面大气相互作用的结果,捕捉了第二类El Nio事件的主要信息。(3)第二类El Nio事件对中国春季及夏初降水有一定影响。在事件暖期,东海地区存在一个显著的异常反气旋性环流,其南侧的中国南方地区盛行异常东北气流,水汽来源减少,导致该地区少雨,其西侧的异常偏南气流北上直达华北地区,异常多水汽向北输送,并与北方的偏北流场相遇,导致该地区降水偏多。在第二类El Nio事件冷期相反。本文结果还指出,WP与CT El Nio事件是由经典El Nio事件第一模态与El Nio Modoki事件组合而成,它们不是独立的El Nio类型。此外,还讨论了夏半年El Nio事件对大气环流影响的物理过程。  相似文献   

17.
Diatom assemblages of the surface and in core sediment samples from Lake Saroma (Japan) were examined for the purpose of evaluating anthropogenic effect on the coastal environmental changes. Before the first inlet excavation, the lake's water quality and ecology were controlled by water exchange with the Okhotsk Sea as well as lake-level variation. However, large-scale ecological modification occurred, mainly due to artificial excavation and shellfish industrial farms. A distinct record of the succession of the dominant diatom taxa was preserved in core sediments. Low-oxygen water was prevalent in the lake in 1929, before the first inlet excavation. Immediately after the first inlet excavation, the low-oxygen water in the western basin of the lake began to disappear, in a trend that became increasing transparent, which has been attributed to an increasing rate of water exchange. However, the lacustrine environment of bottom sediments resumes deterioration 20 years after since the first artificial excavation: the resultant deposition of river-mouth materials into the deep basin caused eutrophication and environmental disturbance of the lake bottom. At the same time, the eutrophication of surface water became intensified with the onset of intense scallop culturing beginning in 1966. Increasing organic loads deposited onto the bottom layer in the form of excreta from the scallop nursery led to more oxygen deficiency and the elution of nitrogen and phosphorus from the sediment, which again brought about eutrophication of the surface layer. Such environmental change was reflected in a decrease of benthic diatom taxa and an increase of planktonic taxa, trends which have continued until today. Particularly, the numbers of diatom assemblage have been decreasing all over the lake during the last 10 years, which suggests that Lake Saroma's present-day deterioration and eutrophication will continue or become even worse.  相似文献   

18.
Long time-series of sea surface temperature (SST) and pseudo wind stress (τ) in six areas in the South-East Atlantic are analysed as possible inputs into fisheries models. The areas encompass oceanic and coastal regimes. A clear seasonal signal is evident in all areas, with an amplitude in SST of 3–4°C in the upwelling areas and 5°C farther offshore and on the Agulhas Bank. Warming lags in the north and offshore by 1–2 months. Monthly variability is highest in the upwelling areas. An increasing trend in SST is suggested in all areas, the post-World War II era being about 1,0°C warmer than earlier periods. Some coherence occurs between areas at times, although at other times the anomalies are distinctly out of phase. There is a suggestion of an upward trend in the equatorward wind stress in some offshore areas after 1964, with a sharp change in 1975. Benguela Niños are evident in the environmental record and have a periodicity of around 10 years.  相似文献   

19.
Primary productivity (PP) and phytoplankton structure play an important role in regulating oceanic carbon cycle. The unique seasonal circulation and upwelling pattern of the South China Sea (SCS) provide an ideal natural laboratory to study the response of nutrients and phytoplankton dynamics to climate variation. In this study, we used a three-dimensional (3D) physical–biogeochemical coupled model to simulate nutrients, phytoplankton biomass, PP, and functional groups in the SCS from 1958 to 2009. The modeled results showed that the annual mean carbon composition of small phytoplankton, diatoms, and coccolithophores was 33.7, 52.7, and 13.6 %, respectively. Diatoms showed a higher seasonal variability than small phytoplankton and coccolithophores. Diatoms were abundant during winter in most areas of the SCS except for the offshore of southeastern Vietnam, where diatom blooms occurred in both summer and winter. Higher values of small phytoplankton and coccolithophores occurred mostly in summer. Our modeled results indicated that the seasonal variability of PP was driven by the East Asian Monsoon. The northeast winter monsoon results in more nutrients in the offshore area of the northwestern Luzon Island and the Sunda Shelf, while the southwest summer monsoon drives coastal upwelling to bring sufficient nutrients to the offshore area of southeastern Vietnam. The modeled PP was correlated with El Niño/Southern Oscillation (ENSO) at the interannual scale. The positive phase of ENSO (El Niño conditions) corresponded to lower PP and the negative phase of ENSO (La Niña conditions) corresponded to higher PP.  相似文献   

20.
According to the summarized data on the distribution of the Cenozoic siliceous sediments inl the Japanese and Okhotsk seas, the silica accumulation in them initiated in the early Miocene and Oligocene, respectively. This process was preceded by relatively sharp cooling in the Eocene, which stimulated the development of the diatom flora. The global circulation system in the World Ocean favored the upwelling of deep waters in the North Pacific. These nutrient-enriched oceanic waters invaded the marginal seas to determine their high bioproducticvity and intense silica accumulation. In the terminal Pliocene, the share of biogenic silica in the sediments became sharply reduced. This phenomenon corresponds to the onset of the continental glaciations in the Northern Hemisphere 2.6 Ma ago. The water column became stratified to form a distinct halocline, which reduced the bioproductivity. In the present-day Sea of Japan, the water exchange with the Pacific is limited by the shallow and narrow straits between these basins. The Sea of Okhotsk is connected with the ocean by deep straits so that deep nutrient-rich oceanic waters intrude into this basin providing its high bioproductivity. Dissimilar to the Neogene sediments, the Quaternary sequences demonstrate periodicity in the silica accumulation: it was strongly suppressed due to the ice cover during the glaciations and recommenced during the warm interglacial periods.  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