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1.
基于水下滑翔机在2019年8至10月观测到的温盐资料,本研究分析了西北太平洋混合层总体的变化情况,并探讨了混合层异常变化的原因。结果表明,混合层温度总体上呈现随季节转换逐渐降低的趋势,混合层深度总体上呈现随季节转换逐渐增大的趋势。进一步的相关性分析得出,该海域混合层温度、混合层深度的变化特征主要是由外部大气强迫场(海面风场和净热通量)所决定的。水下滑翔机还观测到了混合层温度异常降低、混合层深度异常变浅的现象。通过计算混合层热收支发现,垂向夹卷作用是海洋混合层内温度降低和混合层深度变浅的主要原因。通过进一步计算研究海域冷涡的上升速度与海水垂向夹卷速度的变化情况,并结合卫星遥感资料,得出海洋的中尺度涡旋活动主导了混合层异常现象的发生。  相似文献   

2.
Differences in ecosystem dynamics between the northern and southern parts of the Japan Sea have been investigated with two nitrogen based ecosystem models forced by climatological mixed layer depth and euphotic layer depth. Models having 4 and 9 compartments with the same biochemical parameters were applied to the northern and southern parts. The spring bloom in the southern part is earlier and smaller than that in the northern part according to both models, which is supported by satellite ocean color images. The difference of the timing is related to the variation of mixed layer depth, and the magnitude of blooming is also related to the concentrations of surface nutrient and herbivorous zooplankton in early spring. The simulated seasonal variations of ecosystem characteristics (standing stock of each compartment, primary production and the ratio of export flux of organic particles to the primary production) are not significantly different between two models. The ratio of export flux of organic particles to the primary production are about 36% and 23% in the northern and southern parts according to the 4-compartment model, while the values are 31% and 18% by 9-compartment model. These results suggest that the biological pump in the northern part is more active than that in the southern part of the Japan Sea. Sensitivity analyses have been carried out to examine the differences of the response to the models.  相似文献   

3.
The mixed layer of the ocean and the processes therein affect the ocean’s biological production, the exchanges with the atmosphere, and the water modification processes important in a climate change perspective. To provide a better understanding of the variability in this system, this paper presents time series of the mixed layer properties depth, temperature, salinity, and oxygen from Ocean Weather Station M (OWSM; 66° N,2° E) as well as spatial climatologies for the Norwegian Sea. The importance of underlying mechanisms such as atmospheric fluxes, advective signals, and dynamic control of isopycnal surfaces are addressed. In the region around OWSM in the Norwegian Atlantic Current (NwAC) the mixed layer depth varies between ∼20 m in summer and ∼300 m in winter. The depth of the wintertime mixing here is ultimately restrained by the interface between the Atlantic Water (AW) and the underlying water mass, and in general, the whole column of AW is found to be mixed during winter. In the Lofoten Basin the mean wintertime mixed layer reaches a depth of ∼600 m, while the AW fills the basin to a mean depth of ∼800 m. The temperature of the mixed layer at OWSM in general varies between 12 °C in summer and 6 °C in winter. Atmospheric heating controls the summer temperatures while the winter temperatures are governed by the advection of heat in the NwAC. Episodic lateral Ekman transports of coastal water facilitated by the shallow summer mixed layer is found important for the seasonal salinity cycle and freshening of the northward flowing AW. Atmospheric freshwater fluxes have no significant influence on the salinity of the AW in the area. Oxygen shows a clear annual cycle with highest values in May-June and lowest in August-September. Interannual variability of mixed layer oxygen does not appear to be linked to variations in any of the physical properties of the mixed layer.  相似文献   

4.
南海混合层年循环特征   总被引:22,自引:4,他引:22  
通过分析Levitus1994版气候平均温盐资料,得到南海混合层的时空分布特征,剖析了混合层浓度及其内部温度的季节变化规律。资料分析表明:季风通风流场调整对南海混合层的时空分布着明显的影响。这种影响的复杂性在于它不但通过海洋表层Ekman效应来影响混合层深度,而且还通过大尺度环流造成的幅散或辐合来限制或促进混合层深度的发展。研究发现混合层深度与混合层内温度存在着如下关系:夏季最大混合层的形成是28℃等温线与混合层底达到相互贴合的过程;冬季最大混合层的形成是28℃水体完全消失并且等温度线与混合层达到相交最多、相交最为垂直的过程,这时对应着冬季南海北部温跃层的通风;大于或等于28℃的水体总是位于混合层以内。  相似文献   

5.
Lagrangian time series of dimethylsulfide (DMS) concentrations from a cyclonic and an anticyclonic eddy in the Sargasso Sea were used in conjunction with measured DMS loss rates and a model of vertical mixing to estimate gross DMS production in the upper 60 m during summer 2004. Loss terms included biological consumption, photolysis, and ventilation to the atmosphere. The time- and depth (0–60 m)-averaged gross DMS production was estimated to be 0.73±0.09 nM d−1 in the cyclonic eddy and 0.90±0.15 nM d−1 in the anticyclonic eddy, with respective DMS replacement times of 5±1 and 6±1 d. The higher estimated rate of gross production and lower measured loss rate constants in the anticyclonic eddy were equally responsible for this eddy's 50% higher DMS inventory (0–60 m). When normalized to chlorophyll and total dimethylsulfoniopropionate (DMSP), estimated gross production in the anticyclonic eddy was about twice that in the cyclonic eddy, consistent with the greater fraction of phytoplankton that were DMSP producers in the anticyclonic eddy. Higher rates of gross production were estimated below the mixed layer, contributing to the subsurface DMS maximum found in both eddies. In both eddies, gas exchange, microbial consumption, and photolysis were roughly equal DMS loss terms in the surface mixed layer (0.2–0.4 nM d−1). Vertical mixing was a substantial source of DMS to the surface mixed layer in both eddies (0.2–0.3 nM d−1) owing to the relatively high DMS concentrations below the mixed layer. Estimated net biological DMS production rates (gross production minus microbial consumption) in the mixed layer were substantially lower (by almost a factor of 3) than those estimated in a previous study of the Sargasso Sea, which may explain the relatively low mixed-layer DMS concentrations found here during July 2004 (3 nM) compared to previous summers (4–6 nM).  相似文献   

6.
南海混合层近惯性能通量的时空变化   总被引:1,自引:1,他引:0  
On the basis of the QSCAT/NCEP blended wind data and simple ocean data assimilation(SODA), the wind-induced near-inertial energy flux(NIEF) in the mixed layer of the South China Sea(SCS) is estimated by a slab model, and the model results are verified by observational data near the Xisha Islands in the SCS. Then, the spatial and temporal variations of the NIEF in the SCS are analyzed. It is found that, the monthly mean NIEF exhibits obvious spatial and temporal variabilities, i.e., it is large west of Luzon Island all the year, east of the Indo-China Peninsula all the year except in spring, and in the northern SCS from May to September. The large monthly mean NIEF in the first two zones may be affected by the large local wind stress curl whilst that in the last zone is probably due to the shallow mixed layer depth. Moreover, the monthly mean NIEF is relatively large in summer and autumn due to the passage of typhoons. The spatial mean NIEF in the mixed layer of the SCS is estimated to be about 1.25 m W/m2 and the total wind energy input from wind is approximately 4.4 GW. Furthermore, the interannual variability of the spatial monthly mean NIEF and the Ni?o3.4 index are negatively correlated.  相似文献   

7.
杨兵  侯一筠 《海洋与湖沼》2020,51(5):978-990
基于高分辨率CFSR(climate forecast system reanalysis)风场资料、气候态海洋混合层厚度资料和卫星高度计海面高度异常资料,本文估计了大气风场向全球海洋混合层的近惯性能通量和近惯性能量输入功率,并探究了混合层厚度、风场时间分辨率、经验衰减系数和中尺度涡旋涡度对近惯性能通量和能量输入功率的影响。浮标实测风场和流速表明,本文所用的风场和阻尼平板模型可用于估计风场向全球海洋的近惯性能通量。本文计算得到的大气向全球海洋输入近惯性能量的功率为0.56TW(1TW=10~(12)W),其中北半球贡献0.22TW,南半球贡献0.34TW。在时间上,风场的近惯性能通量呈现各个半球冬季最强、夏季最弱的特征,这和西风带风场的季节变化有关。在空间上,近惯性能通量的高值海域为南、北半球西风带海洋,尤其是南大洋。混合层厚度和风场空间不均匀性使得西风带近惯性能通量呈现纬向变化,即海盆西部强于海盆东部。风场时间分辨率对近惯性能通量的估计至关重要,低时间分辨率风场对近惯性能通量的低估达到13%—30%。阻尼平板模型中的经验衰减系数对近惯性能通量估计的影响不超过5%。中尺度涡旋涡度仅改变近惯性能通量的空间分布,而对全球近惯性能量输入功率的影响可以忽略。  相似文献   

8.
A limited area, eddy resolving coupled physical and biological model and data assimilation are used to reproduce and analyse the ecosystem variability observed in the North-East Atlantic in April–May 1997 on Discovery cruise 227. The ecosystem was in a post-bloom grazing controlled regime. The combination of the deep mixing in the upper layer during the cruise and a deeper than average winter convection led to high-nutrient–low-chlorophyll type conditions, which are unusual for this location. These conditions and lack of strong mesoscale physical features led to low spatial variability of phyto- and zooplankton yet strong sensitivity to the variations in the vertical mixing (storm event). Modelling results show that plankton patchiness formation under these conditions was dominated by biological mechanisms (mainly predator–prey oscillations). Furthermore, this mechanism, together with mixing and stirring, are responsible in this order for the observed scales and variability of patchiness from homogeneous low winter concentrations of phyto- and zooplankton.  相似文献   

9.
The major feature,interannual variability and variation cause of the Mindanao Eddy and its impact on the thermohaline structure are analyzed based on the Argo profiling float data,the history observed data and the SODA data.The analysis results show that the Mindanao Eddy is a permanent cyclonic meso-scale eddy and spreads vertically from about 500 m depth upward do about 50 m depth.In addition to its strong seasonal variability,the Mindanao Eddy displays a remarkable interannual variability associated with ENSO.It strengthens and expands eastward during El Nin o while it weakens and retreats westward during La Nin a.The interannual variability in the Mindanao Eddy may be caused by the North Equatorial Counter Current,the North Equatorial Current,the Mindanao Current and the Indonesian Through Flow.The eddy variability can have a great influence on the thermohaline structure pattern in the local upper ocean.When the eddy is strong,the cold and low salinity water inside the eddy moves violently upward from deep layer,the thermocline depth greatly shoals,and the subsurface high salinity water largely decreases,with the upper mixed layer becoming thinner,and vice versa.  相似文献   

10.
I reviewed my research on analysis of temporal and spatial variability of phytoplankton by physical-biological models. This paper was prepared for a lecture of the member awarded the Okada Prize for 1991 from the Oceanographical Society of Japan.Temporal change of phytoplankton in a local upwelling was studied by simulated upwelling experiments conducted with natural phytoplankton communities under natural surface light conditions. Results of the culture experiments was explained by a simple model. This model allows to predict the chlorophyll and nutrient concentration changes in a given upwelled water mass.Above model was verified by a local upwelling observed off Izu, Japan, on May, 1982. Phytoplankton growth and nutrient decrease in surface water of the local upwelling were observed within two days followed by decrease of phytoplankton concentration under depleted nutrient environment. The phytoplankton growth and nutrient decrease could explained by the model with phytoplankton removal rate of about half of the growth rate. Centric diatom was the dominant phytoplankton group and pennate diatom showed less abundance in the upwelled water. Pennate diatom showed fast growth rate when nutrient was abundant and fast decreasing rate after nutrient depleted. On the other hand, flagellate and monads showed relatively slow change of biomass under the change of nutrient concentrations. Furthermore, resting spore formation of centric diatom,Leptocylindrus danicus, was observed in a response to nutrient depletion.Temporal and spatial variability of phytoplankton in the southeastern U.S. continental shelf ecosystem was studied by physical-biological models. First, differences of the biological responses to frontal eddy upwelling during spring and to intrusion during summer was considered by Lagrangian particle tracing experiments with optimally-interpolated flow fields. In spring, particles showed residence time of a few days; however, particles in summer intrusion stayed on the shelf nearly 30 days. It was concluded that difference of particle residence time of upwelled water make the difference of plankton communities. Similar flow fields and particle tracing experiments were used to trace the features in chlorophyll distributions during spring of 1980 derived by Coastal Zone Color Scanner (CZCS). Phytoplankton patchness were created and deformed by frontal eddy events. Eularian physical-biological model was constructed to understand the CZCS-chlorophyll distributions. Statistical comparisons with series of numerical experiments indicate that horizontal advection is an important process for the chlorophyll distributions and that upwelling and associated phytoplankton growth are responsible for the across-shelf gradients and maintenance of concentrations. Furthermore, the CZCS data were assimilated to the model to improve the phytoplankton concentrations, and phytoplankton carbon flux across shelf was estimated. Processes causing the time changes of chlorophyll concentrations were estimated with the model and satellite data further indicated that the both physical and biological forcing is important for the time chages. Several other studies conducted presently were mentioned.  相似文献   

11.
《Oceanologica Acta》1999,22(5):487-498
We present series of data describing the small-scale structure of the boundary layer stratification in the vicinity and away from a 1.5 m pressure ridge keel. We then analyze the influence of pressure ridges on the spatial and temporal variability of the ocean boundary layer. Our experiment was done during the melt in order to use small-scale salinity gradients to study the variability in intensity of mixing processes. High-resolution salinity records sampled at 0+, 25 and 50 cm from the ice-water interface were analyzed at two stations, one at 5 m and the other at 75 m from a pressure ridge keel. We observed that, in the immediate vicinity of the ridge, melting is associated with the periodic development and dissipation of a melt layer in relation with the orientation of tidal currents relative to the ridge. In contrast, away from the region under the sheltering influence of the ridge keel, the boundary layer did not show any evidence of stratification during the whole experiment. Data recorded in the vicinity of the ridge are then used to compute eddy diffusivity coefficients for sheltered and non-sheltered events. The observation of a stable melt layer in the vicinity of a ridge keel confirms that pressure ridges drastically modify the dynamics of vertical exchanges in their wake. Besides, our data show a significant spatial and temporal eddy diffusivity variability with a factor 10 between sheltered and non-sheltered areas. Thus, considering that ridges and rubble fields form a substantial fraction of ice-covered areas, our results suggest that effects in their wake may be important in the global budget of ocean-ice exchanges.  相似文献   

12.
热带印度洋上层水温的年循环特征   总被引:1,自引:0,他引:1  
通过分析多年气候月平均的Levitus水温资料,结合多年气候月平均海表面风场资料以及观测的热带印度洋上层海流的分布状况,探讨热带印度洋上层水温的时空分布特征,剖析了热带印度洋混合层深度及印度洋暖水的季节变化规律。分析表明:热带印度洋的海表面温度低值区始终位于大洋的南部,而高值区呈现明显的季节变化,冬季位于赤道附近,在夏季则处于大洋的东北部;在热带印度洋的中西部、赤道偏南海域的次表层终年存在一冷心结构;热带印度洋表面风场的季节变化是影响该海域混合层深度季节性变化的主要因素;印度洋暖水在冬、春季范围较大,与西太平洋暖池相连,而在夏、秋季范围较小,并与西太平洋暖池分开。  相似文献   

13.
The spatial and seasonal variability of primary production in the Japan Sea from 1998 to 2002 was estimated using a satellite primary production model. A size-fractionated primary production model was validated by in situ primary production data measured in the Japan Sea. Estimated primary production and in situ primary production showed a good positive correlation. Estimated primary production showed spatial variability. Annual primary production levels were 170, 161, 191 and 222 gC m−2year−1 at the Russian coast, in the middle of the Japan Basin, the southeastern area and the southwestern area, respectively. It was higher to the south around 40°N than to the north, and higher in the western area than in the eastern one. Peaks of primary production appeared twice, in spring and fall, in the southern area, while a single peak appeared in the northern area. Primary production along the Russian coast was higher than in other areas during summer. The spring bloom contributed 42% to the annual primary production in these four areas. Furthermore, estimated primary production showed an interannual variability that was largest in spring. Primary production in fall also showed interannual variability, especially in the middle of the Japan Basin and the southwestern area. This corresponded mainly to the size of the phytoplankton bloom in each year. Winter convection by wind and the depth of nutrient-rich, cold subsurface water underlying the Tsushima Current may contribute to the nutrient supply to upper layer and interannual variations of primary production in spring.  相似文献   

14.
Quantifying the gross and net production is an essential component of carbon cycling and marine ecosystem studies.Triple oxygen isotope measurements and the O_2/Ar ratio are powerful indices in quantifying the gross primary production and net community production of the mixed layer zone,respectively.Although there is a substantial advantage in refining the gas exchange term and water column vertical mixing calibration,application of mixed layer depth history to the gas exchange term and its contribution to reducing indices error are unclear.Therefore,two cruises were conducted in the slope regions of the northern South China Sea in October 2014(autumn) and June 2015(spring).Discrete water samples at Station L07 in the upper 150 m depth were collected for the determination of δ~(17)0,δ~(18)O,and the O_2/Ar ratio of dissolved gases.Gross oxygen production(GOP) was estimated using the triple oxygen isotopes of the dissolved O_2,and net oxygen production(NOP) was calculated using O_2/Ar ratio and O_2 concentration.The vertical mixing effect in NOP was calibrated via a N_2O based approach.GOP for autumn and spring was(169±23) mmol/(m~2·d)(by O_2) and(189±26) mmol/(m~2·d)(by O_2),respectively.While NOP was 1.5 mmol/(m~2·d)(by O_2) in autumn and 8.2 mmol/(m~2·d)(by O_2) in spring.Application of mixed layer depth history in the gas flux parametrization reduced up to 9.5% error in the GOP and NOP estimations.A comparison with an independent O_2 budget calculation in the diel observation indicated a26% overestimation in the current GOP,likely due to the vertical mixing effect.Both GOP and NOP in June were higher than those in October.Potential explanations for this include the occurrence of an eddy process in June,which may have exerted a submesoscale upwelling at the sampling station,and also the markedly higher terrestrial impact in June.  相似文献   

15.
An anticyclonic mesoscale eddy is found using the current and temperature data obtained at six moorings near the eastern foot of the Mascarene Ridge (Southern Hemisphere). Its spatial parameters radius, depth of penetration, and direction of the vertical axis tilt are given. The volume of water transported by the eddy across its radial section is calculated. Numerical characteristics of the spatial-temporal variability of the current and temperature field in the eddy are obtained. The relative contributions of the variability of mesoscale, tidal and inertial, and high-frequency oscillations are estimated.Translated by Mikhail M. Trufanov.  相似文献   

16.
River plumes have important effects on marine ecosystems. Variation in the extent and dispersal of river plumes is often associated with river discharge, wind characteristics and ocean circulation. The objectives of this study were to identify the Tokachi River plume by satellite, determine its relationship with river discharge and clarify its temporal and spatial dynamics. SeaWiFS multispectral satellite data (normalized water-leaving radiance: nLw) with 1.1 km spatial resolution were used to determine the spatial and temporal variability of the plume during 1998–2002. Supervised maximum likelihood classification using six channels of nLw at 412, 443, 490, 510, 555 and 670 nm with each band's spectral signature statistic was used to define classes of surface water and to estimate the plume area. Supervised maximum likelihood classification separated three to four classes of coastal water based on optical characteristics as a result of wind stress events. The satellite-observed plume area was correlated with the amount of river discharge from April to October. The plume distribution patterns were influenced by wind direction and magnitude, the occurrences of a near-shore eddy field and surface currents. Empirical orthogonal function (EOF) was used to express the spatial and temporal variability of the plume using anomalies of nLw(555) monthly averaged images. The first mode (44% of variance) showed the turbid plume distribution resulting from re-suspension by strong wind mixing along the coast during winter. This mode also showed the plume was distributed along-shelf direction in spring to early autumn. The second mode (17% of variance) showed spring pattern across-shelf direction. EOF analysis also explained the interannual variability of the plume signature, which might have been affected by the flow of the Oyashio Current and the occurrence of a near-shore eddy field.  相似文献   

17.
渤海垂直湍流混合强度季节变化的数值模拟   总被引:4,自引:1,他引:4  
渤海为极浅陆架海 ,其中湍流耗散作用显著。将三维斜压陆架海模式 HAMSOM应用于渤海 ,以渤海周边台站每天 4次的常规气象资料作为风和热驱动 ,渤海海峡开边界以 5个主要分潮调和常数计算水位强迫 ,计算了渤海 1982年水文要素和流场变化 ,并用模式以湍的局地平衡理论封闭计算出垂直湍流粘性的时空分布。结果表明 :渤海湍流混合冬强夏弱 ,变化幅度较大 ( 10~ 2 0 0 cm2 / s) ,这是风搅拌和潮混合的湍流输入在密度层化调整下的结果 ;风的作用在冬季强于潮的作用 ,而底层则由潮混合控制呈现半月周期 ;渤海湍粘性系数的空间分布十分复杂 ,这是在渤海地形和岸形轮廓限制下 ,由一定大气条件驱动的流场和密度场导致的湍流混合强度不同所致  相似文献   

18.
李琦  陈朝晖 《海洋与湖沼》2022,53(2):305-319
利用深海潜标所搭载的声学多普勒流速剖面仪(acoustic doppler current profiler,ADCP)得到的后向散射强度Sv,研究了黑潮-亲潮混合区浮游动物的垂向分布、其昼夜垂直迁移(diel vertical migration;DVM)的基本特征、多时间尺度变化及对反气旋式中尺度暖涡的响应.结果表...  相似文献   

19.
《Coastal Engineering》2006,53(2-3):209-222
A non-linear shallow water wave model operating on the time-scale of wave groups is compared with measurements of infragravity motions on a rip-channel beach to verify the model concepts and assess the model performance. The measurements were obtained during the RIP-current EXperiment (RIPEX) in concert with the Steep Beach Experiment (SBE) performed at Sand City, Monterey Bay, CA, during the spring of 2001. The nearshore bathymetry was made up of shore-connected shoals incised by relatively narrow rip-channels spaced approximately 125 m apart. The comparison considers a 20-day period during which significant changes in both the offshore wave climate and nearshore bathymetry occurred. The temporal variation in infragravity conditions during the experiment is strong, with computational results typically explaining 70% to 80% of the observed infragravity motions within the nearshore. In contrast to the temporal variation, the alongshore spatial variation in infragravity intensity during the experiment is generally weak, even though the underlying bathymetry shows strong depth variations. Model computations suggest preferential coupling between the computed edge wave motions and the quasi-periodic bathymetry is present, a prerequisite for strong spatial variability. However, the infragravity field is dominated by cross-shore infragravity motions, which are only weakly coupled to the quasi-periodic bathymetry, resulting in a weak alongshore variability of the total infragravity motions.  相似文献   

20.
Recent realistic high resolution modeling studies show a net increase of submesoscale activity in fall and winter when the mixed layer depth is at its maximum. This submesoscale activity increase is associated with a reduced deepening of the mixed layer. Both phenomena can be related to the development of mixed layer instabilities, which convert available potential energy into submesoscale eddy kinetic energy and contribute to a fast restratification by slumping the horizontal density gradient in the mixed layer. In the present work, the mixed layer formation and restratification were studied by uniformly cooling a fully turbulent zonal jet in a periodic channel at different resolutions, from eddy resolving (10 km) to submesoscale permitting (2 km). The effect of the submesoscale activity, highlighted by these different horizontal resolutions, was quantified in terms of mixed layer depth, restratification rate and buoyancy fluxes. Contrary to many idealized studies focusing on the restratification phase only, this study addresses a continuous event of mixed layer formation followed by its complete restratification. The robustness of the present results was established by ensemble simulations. The results show that, at higher resolution, when submesoscale starts to be resolved, the mixed layer formed during the surface cooling is significantly shallower and the total restratification is almost three times faster. Such differences between coarse and fine resolution models are consistent with the submesoscale upward buoyancy flux, which balances the convection during the formation phase and accelerates the restratification once the surface cooling is stopped. This submesoscale buoyancy flux is active even below the mixed layer. Our simulations show that mesoscale dynamics also cause restratification, but on longer time scales. Finally, the spatial distribution of the mixed layer depth is highly heterogeneous in the presence of submesoscale activity, prompting the question of whether it is possible to parameterize submesoscale effects and their effects on the marine biology as a function of a spatially-averaged mixed layer depth.  相似文献   

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