Tidal currents and mixing at the INSTANT mooring locations     

Robin Robertson 《Dynamics of Atmospheres and Oceans》2010

Tides affect transport and mixing in the Indonesian Seas, impacting the throughflow and the return flow of the global thermohaline circulation. In a previous study, barotropic and baroclinic tides were simulated for the Indonesian Seas at 5 km resolution in order to characterize the tides of the region and to identify and quantify locations of tidal mixing. Baroclinic tidal velocities exceeded barotropic velocities except in shallow regions and their variability was on smaller scales. Model results agreed reasonably with observations and are consistent with the resolution. However, only four mooring locations were available for comparison. The new International Nusantara Stratification (INSTANT) data set enables a more comprehensive comparison. With the exception of Lombok Strait, the model replicated the observed INSTANT velocity spectra, falling within the 90% confidence limits of the observed spectra, both in regions of high and low baroclinic tidal activity for the band of frequencies from 0.02 cph to 0.33 cph (periods of 50–3 h, respectively), which includes the major semidiurnal and diurnal tides and several of their first harmonics. The model overestimated the semidiurnal baroclinic tides in the narrow Lombok Strait, which is not well resolved in the model. Comparisons of vertical profiles of the major axes of the tidal ellipses at the mooring sites generally reproduced the vertical pattern, although there were exceptions, such as Lombok and Ombai Straits. Rms differences between the model estimates and hourly observations for the major axes of the tidal ellipses were typically 1–8 cm s⁻¹ in regions of high tidal activity, 1–5 cm s⁻¹ in regions of low tidal activity, and 1–20 cm s⁻¹ for the semidiurnal tides in Lombok and Ombai Straits. Rms errors of 1–6 cm s⁻¹ are typical in regions of moderate baroclinic tidal activity at this model resolution (5 km). Many of the larger rms differences result from vertical discrepancies in the depths of the internal tidal beams. The local nature of the internal tides generation and beam propagation results in large differences from small vertical shifts in the beams or generation due to topographic differences between the model topography and the actual topography. In addition, the moorings experienced severe blowdown. The blowdown adds uncertainty to the depths of the instruments and introduces errors in the observational tidal analysis in magnitude of the tidal constituents, both of which contribute to rms differences. Tidal mixing was found to occur in intense local regions with strong internal tidal shear. The local regions of mixing were typically along the bottom in steep slopes and over sills. In conclusion, the tidal model was found to reproduce the kinetic energy distribution and transfer of energy from tides to other frequencies in the Indonesian Seas and to roughly replicate the observed structure and magnitude of the tidal currents. Improvements in the tidal simulations in reproducing observations are expected with increased resolution.  相似文献   

What is driving the ITF? An illumination of the Indonesian throughflow with a numerical nested model system     

Bernhard Mayer  Peter E. Damm  Thomas Pohlmann  Syamsul Rizal 《Dynamics of Atmospheres and Oceans》2010

A nested numerical model system has been set up to realistically simulate more than 30 years of the Indonesian throughflow (ITF). A global circulation model delivered the boundary values for sea level, temperature and salinity distributions to a local model covering the region of the ITF. Both models were forced with NCEP data. Results of the regional model are in good agreement with measured data regarding velocity distribution and stratification, as well as transported water masses. Model results show a highly variable and very complex current system. The presence of a realistic throughflow has been simulated even with a barotropic pressure gradient directed from the Indian towards the Pacific Ocean. Furthermore, model experiences indicate that the intensity of the ITF is correlated with the seasonal wind system. It is concluded that the ITF is neither driven by a barotropic or baroclinic pressure gradient nor by local winds. The ITF seems to be, rather, the extension of the very strong tropical Pacific Ocean circulation system westward into the Indonesian seas, where the western boundary is not fully closed due to the passages between the Indonesian islands. A hypothesis for the physical reason is given to explain the existence of the Indonesian throughflow.  相似文献   

Simulated and observed circulation in the Indonesian Seas: 1/12° global HYCOM and the INSTANT observations     

E.J. Metzger  H.E. Hurlburt  X. Xu  Jay F. Shriver  A.L. Gordon  J. Sprintall  R.D. Susanto  H.M. van Aken 《Dynamics of Atmospheres and Oceans》2010

A 1/12° global version of the HYbrid Coordinate Ocean Model (HYCOM) using 3-hourly atmospheric forcing is analyzed and directly compared against observations from the International Nusantara STratification ANd Transport (INSTANT) program that provides the first long-term (2004–2006) comprehensive view of the Indonesian Throughflow (ITF) inflow/outflow and establishes an important benchmark for inter-basin exchange, including the net throughflow transport. The simulated total ITF transport (−13.4 Sv) is similar to the observational estimate (−15.0 Sv) and correctly distributed among the three outflow passages (Lombok Strait, Ombai Strait and Timor Passage). Makassar Strait carries ∼75% of the observed total ITF inflow and while the temporal variability of the simulated transport has high correlation with the observations, the simulated mean volume transport is ∼37% too low. This points to an incorrect partitioning between the western and eastern inflow routes in the model and is the largest shortcoming of this simulation. HYCOM simulates the very deep (>1250 m) overflow at Lifamatola Passage (−2.0 Sv simulated vs. −2.5 Sv observed) and indicates overflow contributions originating from the North (South) Equatorial Current in boreal winter–spring (summer–autumn). A new finding of INSTANT is the mean eastward flow from the Indian Ocean toward the interior Indonesian Seas on the north side of Ombai Strait. This flow is not robustly simulated at 1/12° resolution, but is found in a 1/25° version of global HYCOM using climatological forcing, indicating the importance of horizontal resolution. However, the 1/25° model also indicates that the mean eastward flow retroflects, turning back into the main southwestward Ombai Strait outflow, and in the mean does not enter the interior seas to become part of the water mass transformation process. The 1/12° global HYCOM is also used to fill in the gaps not measured as part of the INSTANT observational network. It indicates the wide and shallow Java and Arafura Seas carry −0.8 Sv of inflow and that the three major outflow passages capture nearly all the total Pacific to Indian Ocean throughflow.  相似文献   

The South China Sea throughflow: linkage with local monsoon system and impact on upper thermal structure of the ocean   总被引：1，自引：0，他引：1  

刘钦燕  王东晓  谢强 《中国海洋湖沼学报》2012,30(6):1001-1009

The tendency of South China Sea throughflow (SCSTF) variation associated with the local monsoon system, and its impact on upper-layer thermal structure, are studied using the Simple Ocean Data Assimilation (SODA) dataset, combined with Ishii reanalysis data. Luzon Strait Transport (LST) is measured and used as an index for studying the SCSTF variation. Results show that LST had an increasing tendency over the last 50 years, mainly in summer and fall. The increasing tendency was 0.017 1 Sv/a in summer and 0.027 4 Sv/a in fall, as estimated by SODA, and 0.018 0Sv/a in summer and 0.018 9 Sv/a in fall, as estimated by "Island Rule" theory. LST increased by 0.53Sv in JJA (June-July-August) and 0.98Sv in SON (September-October-November) after climate shift, as inferred by SODA data. The average LST anomaly in JJA and SON is strongly related to the local monsoon system, especially to variability of the meridional wind stress anomaly after application of a 3-year running mean, with correlation coefficients 0.57 and 0.51, respectively. In addition to the basin-scale wind forcing, the local northeasterly wind stress anomaly in the SCS can push Pacific water entering the SCS more readily in JJA and SON after climate shift, and an SCSTF-associated cooling effect may favor subsurface cooling more frequently after climate shift.  相似文献   

The distribution of chlorophyll a in the tropical eastern Indian Ocean in austral summer   总被引：1，自引：0，他引：1  

HONG Lish  WANG Chunsheng  ZHOU Yadong  CHEN Mianrun  LIU Hongbin  LIN Zhongyang  SONG Xunshu 《海洋学报(英文版)》2012,31(5):146-159

To study the effect of hydrographic factors on the spatial distributions of chlorophyll a (Chl a), an investigation was carried out in the tropical eastern Indian Ocean (80 -100 E along 7 S, and 7 -18 S along 80 E) in December 2010. The fluorescent method was used to obtain total Chl a and size-fractioned Chl a at the 26 stations. The results show that surface Chl a concentration averaged at (0.168 ± 0.095) mg/m 3 s.d. (range: 0.034-0.475 mg/m 3 ), concentrations appeared to be higher in the west for longitudinal variations, and higher in the north for latitudinal variations. Furthermore, the surface Chl a concentration was lower (0.034-0.066 mg/m 3 ) in the region to the south of 16 S. There was a strong subsurface Chl a maximum layer at all stations and the depth of the Chl a maximum increased towards to the east and south along with the respective nitracline. The spatial variation of Chl a was significant: correlation and regression analysis suggests that it was primarily affected by PO 3 4 , N(NO 3 -N+NO 2 -N) and temperature. Size-fractionated Chl a concentration clearly showed that the study area was a typical oligotrophic open ocean, in which picophytoplankton dominated, accounting for approximately 67.8% of total Chl a, followed by nanophytoplankton (24.5%) and microphytoplankton (7.6%). The two larger fractions were sensitive to the limitation of P, while picophytoplankton was primarily affected by temperature.  相似文献   

晚中新世西太平洋暖池的浮游有孔虫和氧同位素证据   总被引：1，自引：0，他引：1  

李前裕  李保华  钟广法  周祖翼  成鑫荣  王吉良  汪品先 《地球科学》2006,31(6):754-764

浮游有孔虫深水种Globoquadrina dehiscens于10Ma左右从西太平洋和南海绝灭, 要比其他地区早大约3Ma.伴随这一事件还见以表层暖水种增多而深水种大幅度减少为主要特征的生物群变化.古生物和氧同位素结果指示当时表层水变暖和温跃层变深, 我们认为是与早期西太平洋暖池的发育有关.该种在西北和西南太平洋呈阶段性消失也说明暖水堆集比赤道区更强, 尽管印尼海道在晚中新世已大为变窄, 穿越印尼海道的径流可能尚保持较高的通量水平而使赤道区暖水堆集不特别明显.南海的浮游氧同位素值通常比开放西太平洋的低, 也说明中新世时期的上层海水环境与现代相似, 都是暖池边缘区比中心区变化大.暖池边缘区水体环境多变和温度梯度较高可能是受季风的影响, 结果造成深水种的降低和G.dehiscens提早从南海地区绝灭.   相似文献   

Temporal-spatial variability of Chukchi Sea ice area under the influence of Bering Strait throughflow          下载免费PDF全文

Deng Yongfei  Gao Guoping  Zhang Yu  Chen Changsheng 《极地研究》1988,31(4):383

  相似文献   

南海贯穿流荷载中尺度过程能量学诊断     

姚景龙  李晗  刘钦燕  王强  肖福安  王东晓  俎婷婷 《海洋与湖沼》2017,48(6):1257-1268

本文利用南海海洋再分析产品REDOS(Reanalysis Dataset of the South China Sea)和风场资料CCMP(Cross-Calibrated,Multi-Platform),通过能量诊断探讨了越南沿岸南海西边界流(南海贯穿流主体部分)区域夏季(6—9月)涡流相互作用的年际变化特征以及平均流对中尺度过程的贡献。结果显示,在季风和西边界强流、南海贯穿流的共同影响下,越南沿岸东向急流和双涡结构的能量分布和收支有显著的年际差异。尽管涡动能(EKE,Eddy Kinetic Energy)和涡动有效势能(EPE,Eddy available Potential Energy)的量级基本一致,但二者在水平和垂向空间分布上存在明显差异,这与夏季风影响下的南海西部边界流,越南离岸流的上层海洋密度梯度、流速大小和剪切导致的斜压、正压不稳定性等因素相关。同时随着深度的增加,密度梯度变化相对水平速度剪切对海洋涡流过程的影响逐渐凸显。EKE能量收支分析表明,压强与风应力主要做正功,是维持EKE稳定的主要能量来源,而EKE平流项既可以促进涡旋的增长,也会造成涡旋的消耗,对EKE的年际变率影响比较显著。正压不稳定导致的能量转换主要影响南海西部边界流区域,并存在显著年际变化,并且在风和平均流的影响下,沿贯穿流方向存在显著空间分布差异。越南离岸流正异常年,整体呈现平均流向涡旋传递能量;负异常年,出现EKE反哺平均动能的情况。  相似文献   

Geochemical characteristics from tests of four modern planktonic foraminiferal species in the Indonesian Throughflow region and their implications     

Peng Zhang  Rina Zuraida  Yair Rosenthal  Ann Holbourn  Wolfgang Kuhnt  Jian Xu 《地学前缘(英文版)》2019,10(2):505-516

Test geochemistry of planktonic foraminifera is an indispensable tool in reconstructing past ocean hydrological changes. It is essential to investigate region-specific implications of test geochemistry,although those established from other regions can be broadly applied. In this study, characteristics of6180 and Mg/Ca from tests of four planktonic foraminiferal species, Globigerinoides ruber sensu stricto(s.s.), Globigerinoides sacculifer, Pulleniatina obliquiloculata and Neogloboquadrina dutertrei, from 60 coretop sediment samples retrieved from the Indonesian Throughflow(ITF) region were studied. These geochemical data were compared with modern hydrographic profiles in order to assess their relations and to investigate potential implications of test geochemical parameters in reconstructing past oceanographic change in the ITF region. Calcification depths of these four species were first estimated based on comparison between measured test δ180 and predicted calcite δ¹⁸O that was calculated from modern temperature and salinity. The results indicate that G. ruber s.s. and G. sacculifer calcify within the mixedlayer at 0-50 m and 20-75 m, respectively, whereas P. obliquiloculata and N. dutertrei calcify within the thermocline at around 75 to 125 m. A combined study of excess Mg/Ca(difference between measured and predicted Mg/Ca) and salinity suggests that salinity exerts a negligible impact on test Mg/Ca of these foraminiferal species in the ITF region. Comparison of test Mg/Ca-derived temperatures with temperature profiles of the upper 200 m of the water column from the seas of the ITF region also indicate calcification depths of these species, which match well with the above estimations using test δ¹⁸O. It further indicates that G. sacculifer may be more sensitive in reflecting changes in the depth of the mixedlayer, highlighting a potential use of Mg/Ca temperature difference between G. ruber s.s. and G. sacculifer in reconstructing the depth of the mixed-layer in the ITF region.  相似文献   

巽他海峡BAR9442岩心30 kaBP以来的沉积记录与古季风活动     

赵悦  丁旋 《地球科学》2011,36(4):610-620

为重建巽他海峡区古季风活动历史,通过对BAR9442岩心氧同位素、AMS14C测年、陆源碎屑标准偏差区间粒径分布,以及上升流种Globigerina bulloides等变化特点分析,并结合前人对该岩心粘土矿物的研究,获得如下认识:末次冰期30~17 kaBP,海平面下降,陆源粉砂物质输入增加; 南半球夏季日照率高,然而受冰期热带辐聚带位置影响,西北季风受阻,东南信风持续吹过研究海域形成类似东南季风的效应,气候冷干; 受印度东北季风影响,伊利石含量最高,上升流活动不发育, 古生产力降低.17~8 kaBP,海平面迅速上升,出现较强的表层穿越流活动,粘土物质成为沉积物的主要组分; 此时东南与西北季风都有增强,说明当时研究区气候有着更强的季节性.全新世8 kaBP以来,全球海平面上升使穿越流活动加强,沉积物粘土组分含量最大,西北季风带来温暖湿润的气候条件.   相似文献