Thermohaline intrusions in the thermocline of the western tropical Pacific Ocean

The existing high-resolution hydrographic data in the western tropical Pacilit; Ocean are used to explore the spatial distribution and primary characteristics of thermohaline intrusions in the thermocline. Statistics show that the vertical scales of intrusions are 20-40 m in the upper thermocline （22.0-26.0δ0） and 40-80 m in the lower thermocline （26.0-27.2δ0）. In the upper thermocline, the most intensive intrusions exist at the equatorial front （EF） where north/sonth Pacilic water masses converge, anti Ihe westward spreading of the north Pacilic tropical waler （NPTW） in the Philippines Sea also produces patches of intrusions surrounding its high-salinity tongue. In the lower thermocline, intrusions are also strong at the tropical front （TF） which is the boundary between the north Pacilic subtropical/tropical waters. At the bottom of the thermocline （at about 27.0δ0）, intrusions mainly exist near the western boundary, which are produced by intermediate water convergence through the advection of subthermocline western boundary Ilows. Most strikingly a ＂C＂-shape distribution of intrusions at around 26.4δ0 is revealed, covering the vicinity of the EF the TE and the Mindanao Current （MC）, i.e., tile western boundary pathway ol the norlh Pacilic subtrnpical cell （STC）. Synoptic section analysis reveals that intrusions are more prominent on the warm/sally flank ot the fronts, implying more cross-front tongues of cold/fresh water. Among the intrusions, those at the EF are of best lateral coherence which implies a unique driving mechanism involving near-inertial velocity perturbations near the equator.     

Design and calibration of an acoustic telemetry system subject to upwelling events

The experiments described were designed to calibrate a hexagonal array of VEMCO VR2 receivers and transmitters (model V9P-6L-S256) in isothermal and stratified water columns off the south coast of South Africa. The array, configured with 500 m between receivers, was designed to study the influence of water temperature and turbidity on the spawning behaviour of chokka squid Loligo reynaudii. Range tests comprised fixing a single VR2 receiver 2 m from the seabed and placing a V9P transmitter at distances of 0 m, 75 m, 150 m, 225 m, 300 m, 375 m, 450 m and 500 m from the receiver for periods of 10 minutes at each position under isothermal conditions and in the presence of a thermocline. The data indicated a range of 300 m for the former and 75 m for the latter conditions. The field performance of the V9P transmitter in a non-stratified water column compared well with the theoretical range of 352 m calculated using software to calculate range. System saturation was investigated by repeating the range test using four, eight and 14 transmitters simultaneously. Field data indicated a significant decrease in signal detections due to signal collisions when more than eight transmitters were active simultaneously. It was demonstrated that the hexagonal configuration of VR2s is optimal during isothermal conditions but inadequate during stratified conditions when acoustic dead zones of 350 m between VR2 receivers can occur.     

The ecosystem of a mesotrophic lake-II. Interactions among nutrient load,river flow,and epilimnion depth

The management variables which primarily affect phytoplankton biomass (as chl-a) in Lake Mjøsa, Norway, are total phosphorus loading (TP) and the timing and volume of water through flow (by active storage reservoirs). The response of the lake to changes in these factors is studied using a simulation model of the lake ecosystem. Chl-a responses from both observed data and the simulated results are extracted by multiple regression. Results show that decreasing TP load decreases chl-a, but less at low TP levels (< 10 mg TP · m^–3). There is also a certain time period for peak river flow which gives the least yield of chl-a per unit TP. This time period occurs in early summer (i.e., around June 10) if the total phosphorus load is low, and later if the load is high. Both observations and simulation results show that a high water flow increases chl-a at low epilimnion depths (< 15 m), but that the same high water flow decreases chl-a when epilmnion is deep.     

Interannual Thermocline Signals and E1 Nino-La Nina Turnabout in the Tropical Pacific Ocean

One of the fundamental questions concerning the nature and prediction of the oceanic states in the equatorial eastern Pacific is how the turnabout from a cold water state (La Ni?na) to a warm water state (El Ni?no) takes place, and vice versa. Recent studies show that this turnabout is directly linked to the interannual thermocline variations in the tropical Pacific Ocean basin. An index, as an indicator and precursor to describe interannual thermocline variations and the turnabout of oceanic states in our previous paper (Qian and Hu, 2005), is also used in this study. The index, which shows the maximum subsurface temperature anomaly (MSTA), is derived from the monthly 21-year (1980–2000) expendable XBT dataset in the present study. Results show that the MSTA can be used as a precursor for the occurrences of El Ni?no (or La Ni?na) events. The subsequent analyses of the MSTA propagations in the tropical Pacific suggest a one-year potential predictability for El Ni?no and La Ni?na events by identifying ocean temperature anomalies in the thermocline of the western Pacific Ocean. It also suggests that a closed route cycle with the strongest signal propagation is identified only in the tropical North Pacific Ocean. A positive (or negative) MSTA signal may travel from the western equatorial Pacific to the eastern equatorial Pacific with the strongest signal along the equator. This signal turns northward along the tropical eastern boundary of the basin and then moves westward along the north side of off-equator around 16N. Finally, the signal returns toward the equator along the western boundary of the basin. The turnabout time from an El Ni?no event to a La Ni?na event in the eastern equatorial Pacific depends critically on the speed of the signal traveling along the closed route, and it usually needs about 4 years. This finding may help to predict the occurrence of the El Ni?no or La Ni?na event at least one year in advance.     

南沙海区晚上新世海水上层结构变化

对南沙海区水深2772m的ODP1143站100～150m井段共101块沉积样品进行了浮游有孔虫分析,结果表明,从3．27Ma到2．55Ma该区表层海水温度逐步降低,温跃层逐步加深,推测是晚上新世北半球冰盖形成过程中,东亚季风相应加强的结果。与此同时,南沙与南海北部的温跃层深度差值不断加大,可能是西太平洋暖池最终形成或加强的表现。3．2Ma前后,表层海水温度和海水温跃层深度都发生了急剧变化,反映出北半球冰盖和西太平洋暖池的发育可能存在一定的相关性。     

热带海洋温跃层深度与南海夏季风强度关系探讨

计算了1975～1999年南海夏季风强度指数,针对季风强、弱年进行太平洋至印度洋20℃等温面的深度(温跃层深度)距平场合成分析,得到强、弱季风年温跃层深度距平的4种分布形式.使用历年季风强度指数与各月温跃层深度距平作相关计算,发现孟加拉湾和赤道中太平洋的深度距平与季风强度具有很好的正相关,台湾以东海域呈较高的负相关,可作为季风预测的重要因子.     

台风过境对黄海冷水团及其环流结构的影响

台风能够对黄海的水文结构及人民群众的生产生活产生重要的影响,严重威胁了人们的生命财产安全。利用ROMS(regional ocean modeling system)模式,分析了台风"灿鸿"在过境黄海期间对黄海温度及环流结构的影响过程。结果表明,台风期间强烈的风致混合能够使温跃层的深度增大,强度减弱,同时,使得近岸的底层温度迅速升高,推动底层的温度锋面向黄海内区移动。台风过境也会对黄海冷水团环流产生重要的影响,台风过境前,混合层中的北向流会迅速加深增强,同时伴随着混合层及温跃层的下移,从而使得黄海冷水团环流的流核下移至跃层以下。当台风过境时,黄海上空的气旋式风场会加剧黄海上层的气旋式环流,导致黄海冷水团环流的流幅及流量迅速增加。当台风登陆后,黄海上层的温度及黄海冷水团环流的结构开始逐渐恢复。     

Responses of Yellow Sea Cold Water Mass to Typhoon Bolaven

A two-month seabed-mounted observation(YSG1 area) was carried out in the western Yellow Sea Cold Water Mass(YSCWM) using an RDI-300 K acoustic Doppler current profiler(ADCP) placed at a water depth of 38 m in late summer, 2012. On August 2012, Typhoon Bolaven passed east of YSG1 with a maximum wind speed of 20 m s-1. The water depth, bottom temperature, and profile current velocities(including u, v and w components) were measured, and the results showed that the typhoon could induce horizontal current with speed greater than 70 cm s-1 in the water column, which is especially rare at below 20 meters above bottom(mab). The deepening velocity shear layer had an intense shear velocity of around 10 cm s-1 m-1, which indicated the deepening of the upper mixed layer. In the upper water column(above 20 mab), westward de-tide current with velocity greater than 30 cm s-1 was generated with the typhoon's onshore surge, and the direction of current movement shifted to become southward. In the lower water column, a possible pattern of eastward compensation current and delayed typhoon-driven current was demonstrated. During the typhoon, bottom temperature variation was changed into diurnal pattern because of the combined influence of typhoon and tidal current. The passage of Bolaven greatly intensified local sediment resuspension in the bottom layer. In addition, low-density particles constituted the suspended particulate matter(SPM) around 10 mab, which may be transported from the central South Yellow Sea by the typhoon. Overall, the intensive external force of the Typhoon Bolaven did not completely destroy the local thermocline, and most re-suspended sediments during the typhoon were restricted within the YSCWM.     

2015/2016年超强厄尔尼诺事件基本特征及生成和消亡机制

全球变暖背景下, 2015/2016年超强厄尔尼诺(El Ni?o)事件倍受关注, 此次事件是中部型和东部型El Ni?o的混合。研究发现, 西风爆发和北太平洋经向模态对触发此次事件均有所贡献。通过对比2015/2016年、1997/1998年与中部型事件可知, 2015/2016年事件在暖背景中产生, 其发展形态与中部型事件较为相似, 后期海表面温度异常迅速衰退主要与赤道东太平洋海域持续的东风异常以及纬向平流较弱有关。较之1997/1998年事件, 2015/2016年事件的海洋动力调整较弱, 表现为较弱的温跃层反馈和海洋波动, 纬向平流反馈的贡献大于温跃层反馈, 大气强迫影响显著, 中部海域相关要素异常值较大。在2015/2016年事件期间, 赤道海域以及近赤道海域海洋上层热含量的变化基本呈负相关, 且变化较为同步; 衰退阶段热含量的流失主要集中在5°S—5°N海域, 向两极的热输送明显。     

浅海双跃层脉冲声传播

利用在东海测量的双跃层声速剖面和修改的单跃层声速剖面,数值模拟了2种跃层条件下不同收发深度声脉冲传播的波形。模拟结果表明,当声源或接收器位于上混合层时,信号波形在2种条件下都出现梳状多途结构。当声源和接收器都位于下混合层时,信号波形在2种条件下均相似。当声源位于中间均匀层时,信号波形在除上混合层以外的4层都有显著差异。用简正波的深度-简正波号域的幅度和相应的群速度解释了双跃层和单跃层声速剖面条件下信号波形特点以及异同的原因。