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1.
基于政府间气候变化专门委员会(Intergovernmental Panel on Climate Change,IPCC)4种最新辐射强迫情景,利用ECHAM5/MPI-OM(European Centre Hamburg Model 5/Max Planck Institute Ocean Model)气候模式输出的1850—2300年逐月混合层深度、海表面温度、海表面盐度数据,分析大西洋热盐环流下沉区混合层深度的变化情况。结果表明:随辐射强迫增加,热盐环流下沉区混合层深度下降,混合层深度振荡周期在格陵兰-冰岛-挪威海(Greenland Sea–Iceland Sea–Norwegian Sea,GIN)海域减小,在拉布拉多海(Labrador Sea,LAB)海域变化不大;与GIN海域相比,LAB海域混合层深度对辐射强迫变化更敏感;两海区温度对混合层深度的影响时间较长,混合层深度对盐度的变化反应迅速;混合层深度变化的主导因素在LAB海域中为盐度,而在GIN海域,低辐射强迫下温度主导混合层深度变化,中高辐射强迫下温度与盐度共同起主导作用。  相似文献   

2.
基于政府间气候变化专门委员会(Intergovernmental Panel on Climate Change,IPCC)4种最新辐射强迫情景,利用ECHAM5/MPI-OM(European Centre Hamburg Model 5/Max Planck Institute Ocean Model)气候模式输出的1850—2300年逐月混合层深度、海表面温度、海表面盐度数据,分析大西洋热盐环流下沉区混合层深度的变化情况。结果表明:随辐射强迫增加,热盐环流下沉区混合层深度下降,混合层深度振荡周期在格陵兰-冰岛-挪威海(Greenland Sea–Iceland Sea–Norwegian Sea,GIN)海域减小,在拉布拉多海(Labrador Sea,LAB)海域变化不大;与GIN海域相比,LAB海域混合层深度对辐射强迫变化更敏感;两海区温度对混合层深度的影响时间较长,混合层深度对盐度的变化反应迅速;混合层深度变化的主导因素在LAB海域中为盐度,而在GIN海域,低辐射强迫下温度主导混合层深度变化,中高辐射强迫下温度与盐度共同起主导作用。  相似文献   

3.
利用再分析资料以及混合层海温诊断方程, 研究1997—1998与2015—2016年超级厄尔尼诺次年北大西洋海表温度异常(sea surface temperature anomalies, SSTA)的差异及成因。结果显示, 北大西洋SSTA在1998年春季呈明显正负正三极型式分布, 而在2016年呈弱的负正负型态。诊断热带北大西洋SSTA的影响因素表明, 1998年春季暖SSTA除了之前研究强调的海洋表面向大气的潜热输送异常减少, 以及吸收太阳辐射的增加外, 海洋动力过程即Ekman纬向漂流也起着重要的作用。热力过程与厄尔尼诺峰值后出现的北大西洋涛动(North Atlantic Oscillation, NAO)负位相有关, 其可引起亚速尔高压减弱, 产生西南风异常, 通过风-蒸发-海表温度(sea surface temperature, SST)反馈机制使热带北大西洋蒸发减弱, 海表增暖, 沃克环流下沉支的东移对这一增暖也有贡献。与1997—1998厄尔尼诺事件不同, 2015—2016厄尔尼诺事件没有强迫出负位相NAO, 而是出现弱NAO正位相, 热带北大西洋为弱的东风异常, 使海表发生一定的冷却, 形成2016春季北大西洋SSTA与1998年的明显差异。  相似文献   

4.
基于全球海洋-海冰耦合数值模式,研究了不同时间和空间分辨率的海表驱动场对大西洋经向翻转环流(Atlantic Meridional Overturning Circulation,AMOC)和海表面温度(Sea Surface Temperature,SST)模拟的影响。敏感性数值实验结果表明,海表驱动场时间和空间分辨率的不同不仅会影响SST的模拟,而且会显著影响AMOC强度的模拟。相比高时间分辨率的海表驱动场,时间和空间分辨率的降低会造成AMOC模拟强度的减弱和SST的升高。月平均驱动场驱动的AMOC比6h分辨率驱动场驱动的控制实验减少6.7Sv,降低了34%;同为6h分辨率,粗空间分辨率大气驱动场模拟的AMOC比高空间分辨率实验减少1.4Sv,降低了7%。对海洋上层流场和海表热通量进一步分析表明,低时间和空间分辨率的海表风场的减弱是导致AMOC减弱和SST升高的主要原因。  相似文献   

5.
邓凤飞  张旭 《海洋学报》2022,44(9):13-22
大西洋经向翻转环流（Atlantic Meridional Overturning Circulation,AMOC）是气候系统重要的组成部分,其强度变化可直接影响南北半球的热量分配,厘清其变化机理对全球变暖背景下的未来预估至关重要。海洋沉积物记录发现,在晚更新世,AMOC的变化与地球岁差周期有紧密联系,但其物理机理尚不清楚。本文利用海洋?大气耦合气候模型—COSMOS（ECHAM5/JSBACH/MPIOM）模型,通过敏感试验,分析在冰盛期冷期和间冰期暖期气候背景下,AMOC对地球岁差变化的响应机理。结果表明:岁差降低引起的北半球夏季太阳辐射增强,会导致间冰期暖期背景下的AMOC显著减弱,但对冰盛期AMOC的影响并不明显。通过进一步分析发现,在间冰期暖期,夏季太阳辐射增强,造成高低纬大西洋海表的升温,同时促进北大西洋高纬度地区的局地降水,两者导致北大西洋表层海水密度降低,共同削弱大西洋深层水生成。而在冰盛期冷期,大西洋高低纬度地区的响应对AMOC的影响反向—副热带升温触发的海盆尺度低压异常,通过其南侧的西风异常削弱大西洋向太平洋的水汽输送,导致净降水增多,海表盐度下降;同时,高纬度升温造成的海冰减少,促进了海洋热丧失,海表失热变重,有利于大西洋深层水的生成,最终两者的共同作用导致AMOC对岁差变化的响应偏弱。本文系统揭示了不同气候背景下,岁差尺度AMOC变化的控制机理,对理解晚更新世AMOC重建记录中持续存在的岁差周期具有重要启示意义。  相似文献   

6.
自然资源部第一海洋研究所地球系统模式FIO-ESM是自主研发的、以耦合海浪模式为特色的地球系统模式,包括物理气候模式和全球碳循环模式。该模式从第一代版本FIO-ESM v1.0发展到第二代版本FIO-ESM v2.0,其物理气候模式和全球碳循环模式都取得了改进与提升。FIO-ESM v2.0全球碳循环模式的海洋碳循环模式由v1.0的营养盐驱动模型升级为NPZD（Nutrient-Phytoplankton-Zooplankton-Detritus）型的海洋生态动力学碳循环模型,陆地碳循环模型由v1.0的简单的光能利用率模型升级为考虑碳氮相互作用的碳氮（CN）耦合模型;大气碳循环模型仍为CO2的传输过程,考虑了化石燃料排放、土地利用排放等人为CO2排放量。在物理过程参数化方案方面,FIO-ESM v2.0全球碳循环过程在考虑浪致混合作用对生物地球化学参数的作用的基础上,增加了海表面温度的日变化过程对海-气CO2通量的影响。已有数值模拟试验结果表明,FIO-ESM v2.0在考虑了更加复杂的碳循环过程后仍具有较好的全球碳循环模拟能力,为进一步开展海洋与全球碳循环研究提供了更有力的支撑工具,从而更好地服务于国家的双碳目标。  相似文献   

7.
基于南沙群岛海域综合科学考察11个航次的实测资料,研究了南沙群岛海域的混合层深度季节变化特征。研究结果表明,南沙群岛海域混合层深度存在明显的季节变化,并且与季风和海表热通量的变化密切相关。春季,风速较小且风向不稳定,海面得到的净热通量全年最大,上层水体层结稳定,混合层深度较小;夏季,南海西南季风盛行,上层为反气旋式环流,海面得到的净热通量减少,混合层呈加深的趋势;秋季,海面净热通量继续减少,混合层深度达到最大值;冬季,东北季风驱动下形成的上层气旋式环流引起深层冷水的上升,限制了混合层的加深。  相似文献   

8.
末次冰消期时,南大洋深层水流通性增强和大气CO_2分压(大气p_(CO_2))升高存在密切联系。该时期南大洋深部流通性增强的同时会伴随着大气与大洋环流模式的一系列变化,例如南半球西风带(Southern Hemisphere Westerly Winds Belt,SWW)位置和强度以及大西洋经向翻转流(Atlantic Meridional Overturning Circulation,AMOC)强度的变化。一些关于控制南大洋流通性变化机制方面的研究发现,SWW的经向摆动可对南大洋深部流通性产生强烈影响。末次冰消期时SWW南移,会强化南大洋风驱上升流,增强南大洋的通风。另一些研究认为AMOC变化对南大洋深部流通性具有更为强烈的影响,末次冰消期时北大西洋深层水(North Atlantic Deep Water,NADW)生成减弱导致AMOC强度减弱,这一过程使得NADW与绕极深层水(Circumpolar Deep Water,CDW)的混合边界北移,从而减弱南大洋水体成层化,增强了南大洋深层水上涌。上述2种模式均可能引起南大洋深部流通状况的改变,并最终导致冰消期大气p_(CO_2)上升。除SWW与AMOC驱动南大洋深部流通状况的改变之外,最新研究发现南大洋罗斯海似乎可以通过其自身底层水的北向扩张与极向退却进一步影响南大洋深部流通状况。总的来说,控制南大洋深部流通状况的并非单一机制,SWW与AMOC以及罗斯海底层水等诸多因素在控制南大洋流通状况变化的同时也会以不同的方式在一定程度上积极的响应大气p_(CO_2)的变化。  相似文献   

9.
北太平洋副热带模态水形成区混合层热动力过程诊断分析   总被引：2，自引：0，他引：2  
利用NCEP海洋数据和COADS海气通量资料,通过诊断分析,揭示了海表热力强迫、垂直夹卷、埃克曼平流和地转平流效应在北太平洋副热带模态水形成过程中的贡献。研究表明,在北太平洋副热带3个模态水形成海域冬季混合层降温过程中,海表热力强迫和垂直夹卷效应是主导因素,二者的相对贡献分别约为67%和19%(西部模态水)、53%和21%(中部模态水)、65%和30%(东部模态水);并且在东部模态水形成海域,埃克曼平流和地转平流皆是暖平流效应,而在西部和中部模态水形成海域,仅有地转平流是暖平流效应。进一步的分析表明,海洋平流(地转平流、埃克曼平流)对北太平洋副热带模态水形成海域秋、冬季混合层温度的年际、年代际异常有显著影响,在西部模态水形成海域,海表热力强迫(62%)和地转平流(32%)是导致混合层温度年际、年代际变化的主要因子;在中部模态水形成海域,混合层温度的年际、年代际变化是埃克曼平流(32%)、地转平流(30%)和海表热力强迫(25%)共同作用的结果;相对而言,东部模态水形成海域混合层温度的年际、年代际异常主要受海表热力强迫(67%)控制。  相似文献   

10.
为了进一步认识上层海洋中混合层和障碍层的时空变化特征。本文基于Argo (Array for real-time geostrophic oceanography)海洋观测网2007—2018年的温盐数据,使用差值法计算了全球海洋混合层深度(Mixed layer depth, MLD)和障碍层厚度(Barrier layer thickness, BLT),讨论了二者的月均值、季节均值和年均值的空间分布特征和形成机制。研究表明,全球海洋的混合层普遍在夏季浅、在冬季深,随季节变化的特征显著。北半球混合层变化幅度较大,大西洋混合层比同纬度的太平洋深;赤道海区混合层较浅;南半球混合层呈纬向带状分布,60°S附近大洋海域存在显著的深混合层带,南极大陆与该深混合层带之间的海域混合层常年较浅。全球障碍层呈"哑铃状"分布,两半球的高纬度海区是障碍层高发区,障碍层不仅厚且持续时间长,以半年为周期变化,南大洋60°S附近海域显著的厚障碍层带随季节变化;南半球中低纬度海区长期存在障碍层,障碍层冬厚夏薄,且厚度大部分不超过40 m。  相似文献   

11.
Cores raised during IODP Expedition 303 off southern Greenland (Eirik Ridge site 1305) and off the Labrador Coast (Orphan Knoll site 1302/1303) were analyzed to establish an isotope stratigraphy, respectively for the “inner” and “outer” basins of the Labrador Sea (LS). These isotopic data also provide information on the Atlantic Meridional Overturning Circulation (AMOC), notably with regard to the intensity of the Western Boundary Under Current (WBUC), which is tightly controlled by the production of Denmark Strait Overflow Water (DSOW), and the production of Labrador Sea Water (LSW) in the inner basin through winter cooling and convection. The upper 184 m of sediment at Eirik Ridge spans marine isotope stages (MIS) 32 to 1. At this site, two distinct regimes are observed: prior to MIS 20, the isotopic record resembles that of the open North Atlantic records of the interval, whereas a more site-specific pattern is observed afterwards. This later pattern was characterized by i) high DSOW production rates and strong WBUC during interglacial stages, as indicated by sedimentation rates, ii) large amplitude δ18O-shifts from glacial stages to interglacial stages (> 2.5‰) and iii) an overall range of δ18O-values significantly more positive than before. At Orphan Knoll, the 105 m record spans approximately 800 ka and provides direct information on linkages between the northeastern sector of the Laurentide Ice Sheet and the North Atlantic. At this site, a shift towards larger amplitude glacial/interglacial ranges of δ18O-values occurred after MIS 13, although isotopic records bear a typical North Atlantic signature, particularly during MIS 5, in contradiction to those of Eirik Ridge, where substages 5a to 5c are barely recognized. Closer examination of δ18O-records in planktic and benthic foraminifera demonstrates the presence of distinct deep-water masses in the inner vs. outer LS basins during MIS 11 and more particularly MIS 5e. Data confirm that the modern AMOC, with LSW formation, seems mostly exclusive to the present interglacial, and also suggest some specificity of each interglacial with respect to the production rate of DSOW and the AMOC, in general.  相似文献   

12.
Labrador Sea convection was most intense and reached the greatest depths in the early 1990s, followed by weaker, shallower, and more variable convection after 1995. The Simple Ocean Data Assimilation (SODA) version 2.0.2/2.0.4 assimilation model is used to explore convective activity in the North Atlantic Ocean for the period from 1992 to 2007. Hydrographic conditions, which are relatively well observed during this period, are used to compare modeled and observed winter mixed-layer depths and water mass anomalies in relation to Deep Western Boundary Current transports and meridional overturning circulation (MOC) changes at the exit of the subpolar basin. The assimilation differs markedly from local observations in the March mixed-layer depth, which represents deep convection and water mass transformation. However, mean MOC rates at the exit of the subpolar gyre, forced by stratification in the mid-latitudes, are similar to estimates based on observations and show no significant decrease during the 1992–2007 period. SODA reproduces the deep Labrador Sea Water formation in the western North Atlantic without any clear indication of significant formation in the Irminger Sea while the lighter upper Labrador Sea Water density range is reached in the Irminger Sea in the 1990s, in agreement with existing assumptions of deep convection in the Irminger Sea and also supported by computed lag correlations with the Labrador Sea. Deep Water transformation mainly takes place in the eastern North Atlantic. The introduction of CFC-11 into the SODA model as a tracer reproduces the mean and multiyear variations of observed distributions.  相似文献   

13.
The influence of changes in the rate of deep water formation in the North Atlantic subpolar gyre on the variability of the transport in the Deep Western Boundary Current is investigated in a realistic hind cast simulation of the North Atlantic during the 1953–2003 period. In the simulation, deep water formation takes place in the Irminger Sea, in the interior of the Labrador Sea and in the Labrador Current. In the Irminger Sea, deep water is formed close to the boundary currents. It is rapidly exported out of the Irminger Sea via an intensified East Greenland Current, and out of the Labrador Sea via increased southeastward transports. The newly formed deep water, which is advected to Flemish Cap in approximately one year, is preceded by fast propagating topographic waves. Deep water formed in the Labrador Sea interior tends to accumulate and recirculate within the basin, with a residence time of a few years in the Labrador Sea. Hence, it is only slowly exported northeastward to the Irminger Sea and southeastward to the subtropical North Atlantic, reaching Flemish Cap in 1–5 years. As a result, the transport in the Deep Western Boundary Current is mostly correlated with convection in the Irminger Sea. Finally, the deep water produced in the Labrador Current is lighter and is rapidly exported out of the Labrador Basin, reaching Flemish Cap in a few months. As the production of deep-water along the western periphery of the Labrador Sea is maximum when convection in the interior is minimum, there is some compensation between the deep water formed along the boundary and in the interior of the basin, which reduces the variability of its net transport. These mechanisms which have been suggested from hydrographic and tracer observations, help one to understand the variability of the transport in the Deep Western Boundary Current at the exit of the subpolar gyre.  相似文献   

14.
K. V. Lebedev 《Oceanology》2016,56(2):172-181
We analyze the newly developed Argo-Based Model for Investigation of the Global Ocean (AMIGO), which consists of a block for variational interpolation of the profiles of drifting Argo floats to a regular grid and a block for model hydrodynamic adjustment of variationally interpolated fields. Such a method makes it possible to obtain a full set of oceanographic characteristics—temperature, salinity, density, and current velocity—using irregularly located Argo measurements. The resulting simulations are represented as monthly mean, seasonal, and annual means and climatological fields. The AMIGO oceanographic database developed at the Shirshov Institute of Oceanology from model simulations covers the 10-year period from 2005 to 2014. Analysis of transport variations in the propagation of North Atlantic Current jets to the Arctic based on the AMIGO data showed that during this period, anomalous winter transports were observed, which correlate with anomalous winter temperatures in regions of northwestern Europe, northern European Russia, and Iceland, which are subjected to the influence of these currents. Comparative analysis of variations in mass and heat transport by the currents and the North Atlantic Oscillation (NAO) index in the period of 2005–2014 shows a well pronounced correlation between them. The low winter values of the NAO index correspond to the low values of winter transports by the Faroe–Shetland branch of the North Atlantic current, and usually, to the high values of winter transports by the North Icelandic branch of the Irminger Current. High winter value of the NAO index results in a substantial increase in the winter transport by the Faroe–Shetland branch of the North Atlantic Current without notable influence on the transport of the North Icelandic branch of the Irminger Current.  相似文献   

15.
Both the Atlantic Meridional Overturning Circulation (AMOC) and the North Atlantic Ocean (NA) biosphere have recognized associations with the North Atlantic Oscillation (NAO). These multidecadal physical–biological affinities inspired a closer look at AMOC influences on bottom-up control of NA and South Atlantic Ocean (SA) pelagic ecosystem variability. Various ocean models associate changes in the AMOC with sea surface temperature (SST) differences in the western subpolar NA and SA represented as the Atlantic Dipole SST Anomaly (ADSA) index. The Extended Reconstructed SST version 2 (ERSSTv2) dataset for 2° quadrangles from 1890 to 2007 was used here to represent Atlantic Ocean SST patterns and to gauge 20th century AMOC variability using an Atlantic Dipole SST (ADS) index, an un-normalized version of ADSA index. Temperature–phosphate (T–PO4) linear regressions were used to convert temperature to phosphate concentration ([PO4]). The interannual stability of T–PO4 linear regressions first was examined using 26 Bermuda area T–PO4 datasets between 1958 and 2001. Within the constraints provided by the Bermuda analysis, climatological T–PO4 linear regressions based on GEOSECS-derived slopes and NODC-derived X-intercepts supported the conversion of monthly Atlantic Ocean ERSSTv2 temperatures for each 2° quadrangle to monthly surface [PO4]. A representative annual surface phosphate utilization (SPU) was calculated for each 2° quadrangle by subtracting monthly minimum surface [PO4] from monthly maximum surface [PO4] to determine the annual surface [PO4] ranges from 1890 to 2007. Annual average SST tended to increase and overall annual average SPU tended to decrease through the 20th century in both the NA and SA, but the NA exhibited more temporal variability. An Atlantic Dipole Phosphate Utilization (ADPU) index related to the ADS index was calculated for each year from 1890 to 2007. The ADS and ADPU indices were inversely correlated with about 57% of the variability in the ADPU index explained by the ADS index. The ADPU index exhibited three distinct cycles through the 20th century. Cross-correlation analysis showed that the NAO led the ADS and ADPU indices by about 14 years. Differences in annual average SPU for each Atlantic Ocean 2° quadrangle between the three high and four low years of the ADPU cycles yielded six maps that, when averaged, clearly exhibited reversed east–west patterns distributed in alternating latitudinal bands in both the NA and SA. The east–west patterns spatially corresponded to the NA and SA surface circulation and temporally resembled NA patterns previously associated with the NAO. AMOC variability, mediated by Kelvin and Rossby waves associated with changes in both deep and surface arm circulation, likely contributed to meridional continuity of phosphate-classified, NA, and SA pelagic ecosystem variability, including fisheries, through the 20th century. Based on the results, future global warming influences on the AMOC, well short of shutdown, likely will have complex pelagic ecosystem impacts throughout the Atlantic Ocean.  相似文献   

16.
In the period 1991–1996 the WOCE hydrographic section A1E/AR7E between Greenland and Ireland was repeated five times. The observed thermohaline changes altered the baroclinic structure along the eastern margin of the subpolar gyre significantly. Between June 1995 and August 1996 an overall increase of the temperature and thickness and a decrease of the density of the Subpolar Mode Water (SPMW) layer were observed, accompanied by an increase of its salinity east of the Reykjanes Ridge and a decrease of its salinity in the Irminger Sea. The changes were most pronounced in the Iceland Basin, where the Subarctic Front retreated westwards, coinciding with a strong weakening of the Westerlies as determined by the North Atlantic Oscillation. They are related to a local reduction of the Ekman upwelling and the ocean-to-atmosphere heat flux on the one hand and to the advection of anomalies from the subtropics on the other hand.The eastward spreading of the different Labrador Sea Water (LSW) vintages led to a corresponding cooling of the LSW in the Irminger Sea and in the Iceland Basin in the period 1991–1996. The renewal of the LSW in the Rockall Trough occurred more sporadically, indicating that the North Atlantic Current (NAC) impedes the southward spreading of LSW in the eastern Atlantic. The changes in 1996 seem to have also counteracted this spreading.  相似文献   

17.
《Ocean Modelling》2011,36(4):304-313
We implemented an explicit forcing of the complete lunisolar tides into an ocean model which is part of a coupled atmosphere–hydrology–ocean–sea ice model. An ensemble of experiments with this climate model shows that the model is significantly affected by the induced tidal mixing and nonlinear interactions of tides with low frequency motion. The largest changes occur in the North Atlantic where the ocean current system gets changed on large scales. In particular, the pathway of the North Atlantic Current is modified resulting in improved sea surface temperature fields compared to the non-tidal run. These modifications are accompanied by a more realistic simulation of the convection in the Labrador Sea. The modification of sea surface temperature in the North Atlantic region leads to heat flux changes of up to 50 W/m2. The climate simulations indicate that an improvement of the North Atlantic Current has implications for the simulation of the Western European Climate, with amplified temperature trends between 1950 and 2000, which are closer to the observed trends.  相似文献   

18.
Winter convection in the Irminger Sea leading to the formation of Labrador Sea Water (LSW) is analyzed using CTD data collected along the 59.5° N transatlantic section in 2004–2014, winter Argo data from 2012–2014, and daily North American regional reanalysis (NARR). The interannual variability of LSW in the Irminger Sea is investigated. The dissolved oxygen saturation rate of 93% is used to indicate maximal local convection depth. It is shown that the deepest convection (up to 1000 m) resulting in the largest LSW volume that formed in the Irminger Sea in 2008 and 2012. These years were characterized by numerous storms with anomalously strong turbulent heat loss from the ocean to the atmosphere and negative air temperature to the east of the southern tip of Greenland in January–March. LSW became warmer by 0.42°C, saltier by more than 0.03 PSU, and more oxygenated by 8 µmol/kg between 2004 and 2014. A strong LSW decay in the Iceland Basin is also noted.  相似文献   

19.
《Marine Geology》1999,153(1-4):29-39
During Ocean Drilling Program (ODP) Legs 160 and 161, sapropels were recovered both in the western and eastern Mediterranean. This obliges to a reassessment of the previous studies focused on sapropels from only the eastern Mediterranean, and to consider the changes which occurred in the Mediterranean climate but also in the water characteristics both in the Atlantic and in the western Mediterranean. In the North Atlantic, the position of the polar front which migrated southwards during glacial times and the melting of northern ice caps during interglacial periods, together with the convection in the Labrador and Norwegian Seas, appear essential to control the salinities of the waters facing the Strait of Gibraltar. The salinities of the surface and intermediate layers constitute the first driving force of the Mediterranean dynamics, the second driving force being the Mediterranean climate. The stagnation of deep waters leading to sapropel deposition in the western Mediterranean may be explained by a drastic weakening of the density difference between Mediterranean outflow and Atlantic intermediate waters facing the Strait of Gibraltar. This weakening was induced primarily by the salinity decrease of Atlantic surface water and secondly by a rather high salinity in the Atlantic intermediate layer, rather than by a drastic deterioration of the Mediterranean climate. This scenario probably concerns most of the sapropel events and it may be used for the knowledge of Atlantic and Mediterranean functioning over climatic changes.  相似文献   

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