What induced the trend shift of mixed-layer depths in the Antarctic Circumpolar Current region in the mid-1980s?

An obvious trend shift in the annual mean and winter mixed layer depth(MLD)in the Antarctic Circumpolar Current(ACC)region was detected during the 1960–2021 period.Shallowing trends stopped in mid-1980s,followed by a period of weak trends.The MLD deepening trend difference between the two periods were mainly distributed in the western areas in the Drake Passage,the areas north to Victoria Land and Wilkes Land,and the central parts of the South Indian sector.The newly formed ocean current shear due to the meridional shift of the ACC flow axis between the two periods is the dominant driver for the MLD trends shift distributed in the western areas in the Drake Passage and the central parts of the South Indian sector.The saltier trends in the regions north to Victoria Land and Wilkes Land could be responsible for the strengthening mixing processes in this region.

Improving the estimate of wind energy input into the Ekman layer within the Antarctic Circumpolar Current

Based on the data and method offered by Liu et al. （2009）, the direct wind and Stokes drift-induced energy inputs into the Ekman layer within the Antarctic Circumpolar Current （ACC） area are reestimated since the results of the former have been proved to be underestimated. And the result shows that the total rate of energy input into the Ekman-Stokes layer within the ACC area is 852.41 GW, including 649.75 GW of direct wind energy input （76%） and 202.66 GW of Stoke drift-induced energy input （24%）. Total increased energy input, due to wave-induced Coriolis-Stokes forcing added to the classical Ekman model, is 52.05 GW, accounting for 6.5% of the wind energy input into the classical Ekman layer. The long-term variability of direct wind and Stokes drift-induced energy inputs into the Ekman layer within the ACC is also investigated, and the result shows that the Stokes drift hinders the decadal increasing trend of direct wind energy input. Meanwhile, there is a period of 4-5 a in the energy spectrums, as same as the Antarctic circumpolar wave.

Fronts,baroclinic transport,and mesoscale variability of the Antarctic Circumpolar Current in the southeast Indian Ocean

Fronts, baroclinic transport, and mesoscale variability of the Antarctic Circumpolar Current （ACC） along 115°E are examined on the basis of CTD data from two hydrographic cruises occupied in 1995 as a part of the World Ocean Circulation Experiment （WOCE cruise I9S） and in 2004 as a part of CLIVAR/CO2 repeat hydrography program. The integrated baroclinic transport across I9S section is （97.2×106±2.2×106） m3/s relative to the deepest common level （DCL）. The net transport at the north end of I9S, determined by the south Australian circulation system, is about 16.5× 106 m3/s westward. Relying on a consistent set of water mass criteria and transport maxima, the ACC baroclinic transport, （117×106±6.7×106） m3/s to the east, is carried along three fronts： the Subantarctic Front （SAF） at a mean latitude of 44°-49°S carries （50.6×106=t=13.4×106） m3/s; the Polar Front （PF）, with the northern branch （PF-N） at 50.5°S and the southern branch （PF- S） at 58°S, carries （51.3×106±8.7×106） m3/s; finally, the southern ACC front （SACCF） and the southern boundary of the ACC （SB） consist of three cores between 59°S and 65°S that combined carry （15.2× 106±1.8× 106） m3/s. Mesoscale eddy features are identifiable in the CTD sections and tracked in concurrent maps of altimetric sea level anomalies （SLA） between 44°-48°S and 53°-57°S. Because of the remarkable mesoseale eddy features within the SAF observed in both the tracks of the cruises, the eastward transport of the SAF occurs at two latitude bands separating by 1°. Both the CTD and the altimetric data suggest that the mesoscale variability is concentrated around the Antarctic Polar Frontal Zone （APFZ） and causes the ACC fronts to merge, diverge, and to fluctuate in intensity and position along their paths.

An analytical diagnostic model of the Antarctic Circumpolar Current

Based on a linear quasi-geostrophic vorticity equation, we have set up an analytical diagnostic mode for the Antarctic Circumpolar Current. The results show that the balance among wind stress,ocean horizontal viscous stress and the β-effect is the basic balance of the Antarctic Circumpolar Current, and the center velocity of the jet, coming from the Drake Passage,will decrease due to the ocean dynamic adjustment, and the width in the north-south direction will decreasegradually. The jet coming from the Drake Passage moves about 4°northward because of the inducement of winddrivencurrents. The clockwise vorticity appearing in the south-west corner corresponds to the Weddell Gyre.The characters of the Antarctic Circumpolar Current described by the model are congruous with observations basically.

Two equilibria of the Antarctic Circumpolar Current and its associated Meridional Overturning Circulation

The Antarctic Circumpolar Current (ACC) and its associated Meridional Overturning Circulation (MOC) is investigated through a nonlinear inertia theory model, which consists of two layers--an upper Ekman layer driven mainly by sea surface wind stress and a lower thermocline controlled by ideal fluid nonlinear equations which can be solved by identifying the form of the arbitrary functions. The results show that the thermocline has a two-equilibrium solution though given the same Ekman layer condition. Compared to the first equilibrium, the second one has a heavier intensity and deeper circulation, which seems more consistent with the existing data.

Fronts and surface zonal geostrophic current along 115°E in the southern Indian Ocean

Altimeter and in situ data are used to estimate the mean surface zonal geostrophic current in the section along 115°E in the southern Indian Ocean,and the variation of strong currents in relation to the major fronts is studied.The results show that,in average,the flow in the core of Antarctic Circumpolar Current（ACC） along the section is composed of two parts,one corresponds to the jet of Subantarctic Front（SAF） and the other is the flow in the Polar Front Zone（PFZ）,with a westward flow between them.The mean surface zonal geostrophic current corresponding to the SAF is up to 49 cm · s^-1 at 46°S,which is the maximal velocity in the section.The eastward flow in the PFZ has a width of about 4.3 degrees in latitudes.The mean surface zonal geostrophic current corresponding to the Southern Antarctic Circumpolar Current Front（SACCF） is located at 59.7 °S with velocity less than 20 cm · s^-1.The location of zonal geostrophic jet corresponding to the SAF is quite stable during the study period.In contrast,the eastward jets in the PFZ exhibit various patterns,i.e.,the primary Polar Front（PF1） shows its strong meridional shift and the secondary Polar Front（PF2） does not always coincide with jet.The surface zonal geostrophic current corresponding to SAF has the significant periods of annual,semi-annual and four-month.The geostrophic current of the PFZ also shows significant periods of semi-annual and four-month,but is out of phase with the periods of the SAF,which results in no notable semi-annual and fourmonth periods in the surface zonal geostrophic current in the core of the ACC.In terms of annual cycle,the mean surface zonal geostrophic current in the core of the ACC shows its maximal velocity in June.

全球气候变化下海洋环流多尺度演变:联动协同与环境生态效应初探

海洋环流是海洋系统物质能量收支、配置、平衡、维持和变化的关键通道与机制。从全球海洋视角,基于目前海洋环流多变率动力过程与趋势演变的认知,重点综述气候变化下海洋环流的海盆尺度三维联动特征机制、洋际交换与协同、世界大洋经向输运变化以及相关的海洋气候与环境生态效应,依据研究现状和需求,提出研究建议。结果表明:全球一致性变暖路径与进程调控下,受驱动因子的演变与胁迫,海洋环流变化对副热带中高纬地区年际、年代际气候与环境变迁具有突出作用影响,并可产生显著环境生态效应和严重致灾风险。建议加大专精特新观测仪器自主研发,通过国际合作加大中高纬海洋环流多尺度动力过程综合调查的参与度和主导性,增强多学科融合交叉研究力度,有效提升深层次海洋环流变异及动力、环境、生态灾害影响的气候变化综合风险预测预评估和防治能力,为海洋领域能源开发、生态系统保护、气候变化应对与灾害风险治理提供必要的动力学参考。

ENSO循环过程与南极海冰变化

应用1951-2001年ENSO特征指数(NINO1+2、NINO3、NINO4、NINO3 4、SOI)和1973-1998年南极海冰北界范围以及1950-2001年SODA海洋温度资料,分析探讨了ENSO循环过程与南极海冰之间的关系,研究了南大洋和太平洋海表温度与南极海冰之间的内在联系。结果表明,南极海冰变化与ENSO循环过程存在一定联系,特别是东南极海冰的变化与ENSO循环过程较为密切。这种遥相关关系表明,ENSO循环过程不仅与热带海洋自身的海 气相互作用存在密切关系,而且与南极海冰之间也存在一定的联系。当东南极海冰范围出现异常增大和减小时,在时滞一年之后,NINO循环指数将出现减弱和加强,而南方涛动指数将出现加强和减弱。这种相关关系的机制是通过大洋环流这一载体将异常海温向北输送来实现的。南极海冰范围的异常增加或减少,会直接影响南极绕极流的冷暖结构进而影响经向水体输送的异常,从而导致热带和副热带太平洋上层海温场的异常变化,对ElNino和LaNina事件的发生起到推动作用。

用TOPEX/POSEIDON高度计数据研究南极绕极流流域海面高度的低频变化

采用TOPEX/POSEIDON(T/P)卫星高度计 1 993年 1月— 2 0 0 0年 1 2月海面高度数据 ,研究包含了整个南极绕极流流系 (40°— 6 0°S)的海面高度低频变化。首先采用EOF分解方法获取南大洋时空分布的主要模态 ,前 3个EOF模态分别占总方差的 2 4 .8%、1 3 .8%和 1 0 .7%。然后采用EMD方法分别分析了各个EOF模态的时间系数曲线的组成成分 ,对南极绕极流海域的各种时间尺度变化给出了清晰的描述 ,对于不同尺度变化所占的比例得到了定量的结果。研究结果表明 ,EOF的各个模态不仅在形态上存在差异 ,而且具有相互独立的物理背景。EOF的第一模态主要体现了以太阳辐射冬夏差异形成的年周期变化 ,另一个显著的特征就是南极绕极流从 1 993— 2 0 0 0年海面的整体上升趋势。EOF的第二模态体现了陆地地形对南极绕极流的约束作用 ,同时也显示了ENSO过程对南极绕极流 ,特别是对南太平洋的海面高度变化的影响。EOF的第三模态则体现了南极绕极流对南大洋表面风场东西方向不均匀变化的响应。同时 。

联合卫星重力和卫星测高确定南极绕极流

联合基于GRACE重力卫星观测资料恢复的重力场模型(EIGEN-GL04S1)和卫星测高推求的平均海面高模型(KMSS04)来构造南极绕极流区域的平均海面动力地形,并利用小波滤波方法去掉短波及噪声信号,进而推算大、中尺度的绕极流。与非卫星重力场模型、同化资料及海洋水文资料确定相应结果的验证分析表明:基于新的卫星重力场模型推算的南极绕极流区域的海面动力地形、PF、SAF和表层流场等都与海洋学结果相吻合,且局部特征更加清晰。表明卫-卫跟踪重力卫星计划确定的地球重力场模型较之以前存在的重力场模型在中长波部分精度有较大提高,从大地测量(从空间)角度来探测南极绕极流已达到较高的精度。

南极绕极流研究进展综述

南极绕极流是自西向东横贯太平洋、大西洋和印度洋的全球性环流,也是世界上唯一一支和地球上所有其他洋流都有关联的洋流。尽管对南极绕极流的观测和研究历史相对较短,但是对其特征、变化和机制的研究已取得了许多重要进展,对其在全球变化中的作用的研究也日益深入。南极绕极流成为海洋和大气科学领域的前沿研究内容。以绕极流锋面分布、流速特征、纬向输运、经向输运及其响应的动力机制为重点,总结了过去数十年里对绕极流观测和理论的研究结果,明确了研究中仍然薄弱的环节,并提出了相应的工作建议,以促进我国关于南极绕极流及相关海洋和大气过程的研究。

南极绕极波研究综述

南极绕极波是近年来发现的海洋现象。关于南极绕极波的研究历史虽然很短,但是对南极绕极波的变化规律和生成机制的研究却已取得了许多重要进展,对南极绕极波在全球变化中的作用研究日益深入,成为海洋和大气科学领域的前沿研究内容。根据南极绕极波的主要研究成果,评述了有关南极绕极波的研究进展和发展方向,以促进我国关于南极绕极波及相关海洋和大气过程的研究。

北极环极边界流研究及其主要科学问题

北极环极边界流是新近揭示的重要海洋现象 ,是对北冰洋海洋环流长期研究结果综合得到的概念。在本文中 ,详细介绍了北极环极边界流的主要结构和水团特征 ,论述了研究北极环极边界流的意义和前景 ,深入探讨了北极环极边界流面对的科学问题 ,指出了解决这些问题的关键科研工作。文章指出 ,从整体上研究北极环极边界流是非常重要的 ,需要全面考察北冰洋的质量和能量平衡、深层水通风过程以及水体的混合过程。在进一步的研究工作中需要更多的有针对性的现场观测、开展多学科协作研究。数值模拟仍然是北极环极边界流的重要研究手段 ,需要改善数值模式 ,提高数值模拟的质量。

The Role of Southern High Latitude Wind Stress in Global Climate

In this paper, the role of westerly winds at southern high latitudes in global climate is investigated in a fully coupled ocean-atmosphere general circulation model. In the model, the wind stress south of 40°S is turned off with ocean and atmosphere fully coupled both locally and elsewhere. The coupled model explicitly demonstrates that a shutdown of southern high latitude wind stress induces a general cooling over the Antarctic Circumpolar Current （ACC） region, with surface Ekman flow and vertical mixing playing competitive roles. This cooling leads to an equatorward expansion of sea ice and triggers an equivalent barotropic response in the atmosphere to accelerate westerly anomalies. The shutdown of southern high latitude wind stress also significantly reduces global meridional overturning circulation （MOC）. The Antarctic MOC （AnMOC） nearly disappears while the Atlantic MOC （AMOC） is weakened by 50%, suggesting a strong control of the southern high latitude winds over the thermohaline circulation （THC）. In spite of a substantial weakening of the AMOC, the interhemispheric SST seesaw appears to be not significant due to an equatorward extension of the southern extratropical cooling through coupled wind-evaporation-SST （WES） feedback. In addition, it is found that the weakening of Atlantic MOC by as much as 50% is capable of cooling the time mean subpolar Atlantic temperature by only about 1°C.

南极绕极流的表层环流结构和能量分布特征

利用历史的表面漂流浮标资料研究了南极绕极流的平均结构、变化规律和能量特征。强劲的南极绕极流沿着纬向从西向东流动,并伴随着复杂多变的海洋锋面,主导着整个南大洋的海洋环流系统。首先,标准方差椭圆表明,阿加勒斯回流和东澳大利亚暖流是南极绕极流重要的流量补充。在南半球的冬季,南极绕极流的流速随着西风的增强而增强。在南极绕极流经向摆动的影响下,流核上的经向流速比纬向流速具有更加不稳定的特征。另外,南极绕极流从非洲南部开始自西向东逐渐减弱。其次,从能量的角度讨论了南极绕极流的细节特征。平均动能、扰动动能及其均方根在流核区域都很强,扰动动能和平均动能比值的趋势恰恰相反,强(弱)能量分布区域的涡旋耗散反而比较弱(强)。除了扰动动能和平均动能的比值之外,所有的能量形式都呈现了从西向东减弱的趋势。涡动耗散对南大洋北部的平均动能影响更大。

南极普里兹湾73°E断面地转流及水文特征分析

在整理历次中国南极考察在普里兹湾及附近海域水文观测数据的基础上,选取第15、16、18、21、25、26和27次科学考察即1998-12-1999-01,2000-01,2002-01-02,2004-12,2009-02,2009-12和2011-01获得的普里兹湾及附近海域73°E断面CTD调查资料,采用动力计算方法计算了73°E断面上各年份的纬向地转流,并进行了通过断面的纬向地转体积通量和热通量的计算;结合多年温、盐分布情况分析了陆架上层水北扩、绕极深层水涌升以及陆缘水边界等断面典型水文现象的时空变化特征。结果表明,73°E断面上的纬向地转流呈相间带状分布,在65°48′S和68°00′S附近存在两个流切变;陆架区(66°30′S以南)最大东向流速多年变化范围为4.0～9.3cm·s-1,最大西向流速多年变化范围为1.0～3.2cm·s-1;海盆区(62°00′～66°30′S)最大东向流速多年变化范围为4.0～6.5cm·s-1,最大西向流速多年变化范围为0.2～3.8cm·s-1;断面上62°00′S以南纬向总体积和热量输运均为东向输运,多年年平均体积通量和热量通量分别为1.52×107 m3·s-1和1.64×1016 W,其中海盆区为1.47×107 m3·s-1和1.60×1016 W,陆架区为0.50×106 m3·s-1和4.00×1014 W。陆架上层水的多年北向扩展范围在62°54′～65°12′S之间变化,其中在初夏考察航次期间,扩展程度最大,最北可扩展到62°54′S;陆缘水边界的多年经向变化范围在63°00′36″～65°07′12″S之间,在初夏航次北移最大,最北移至63°00′S;在7次考察期间有5次绕极深层水扩展至陆架。陆架上层水北扩和绕极深层水涌升的时空变化直接影响到陆缘水边界强度和位置的变化。

德雷克海峡绕极流流量变化的影响因素分析

为研究南极绕极流(ACC)流量变化无明显年代际变化的原因,利用长时间序列(1993—2017年)再分析月平均三维流速场、海面高度异常和海面风场等变量数据,计算ACC穿过德雷克海峡的流量、涡动能(EKE)和平均风速,并对3个变量之间的相关关系进行了分析。结果显示:涡动能和平均风速随着时间的推移而不断增大,但ACC流量则保持平稳。风速与滞后其7个月、8个月、16个月和19个月的涡动能呈弱正相关关系,相关系数分别为0.177 8、0.160 0、0.123 0和0.238 7。ACC流量和涡动能为立即响应的弱负相关关系,相关系数为-0.149 2。风速与滞后其1个月的ACC流量呈弱正相关关系,相关系数为0.131 5,风速与滞后其6个月的ACC流量呈弱负相关关系,相关系数为-0.133 3。3个变量相互之间的相关关系表明,随着平均风速的增大,ACC流量随着风应力的增长而升高,风应力的增长会促进涡动能增长,而涡动能又会反过来耗散部分风场输入的动能,导致ACC流量降低,从而维持ACC流量年代际变化的稳定。

德里克海峡附近绕极流和锋面研究的进展

本文概括了近几十年来,关于德里克海峡附近绕极流研究的进展.这些研究主要以实际观测资料为基础,说明了德里克海峡附近海洋锋面分布和绕极流的体积输运。其中,主要的海洋锋面有:亚南极锋(SAF),极锋(PF)和陆缘水边界(CWB);而德里克海峡绕极流的体积输运则代表了太平洋和大西洋两大洋之间通过德里克海峡的水量交换。读者可通过本文加深关于德里克海峡锋面成因和绕极流机制的理解。

南极绕极流区中尺度涡动动能年际变化和转换机制

提要采用多种资料研究南大洋南极绕极流(Antarctic Circumpolar Current,ACC)区中尺度涡的年际变化规律及机制。通过分析网格化融合卫星海洋资料AVISO(Archiving,Validation and Interpretation of Satellites Oceanographic DATA-AVISO)卫星高度计资料发现,ACC区涡动能(Eddy Kinetic Energy,EKE)的季节变化不明显,但年际变化非常显著。对纬向风应力与年际南半球环状模(Southern Annular Mode,SAM)异常事件的分析表明,纬向风应力极大/极小值超前EKE极大/极小值3年左右出现,EKE对风应力延时响应的时间及强度依赖于风应力异常的强度。此外,还采用海洋环流与气候评估协会(Estimating the Circulation and Climate of the Ocean,ECCO)温盐数据,计算了南极绕极流区斜压能量转化率的分布,并基于此来分析年际尺度上风场、背景海洋间的能量传递关系。研究认为:ACC区中尺度涡的年际变化是由于年际南半球环状模相关的风应力变化引起ACC流量变化以及ACC相关洋域的等密面倾斜程度发生改变,导致背景海洋向中尺度涡的斜压能量转换改变,造成中尺度涡的活动产生年际调整。

2013年夏季南极南设得兰群岛周边海域透光层水团结构

南设得兰群岛位于德雷克海峡南侧,南经布兰斯菲尔德海峡与南极半岛相望。该区域一直是南大洋海洋学研究的热点区域,近些年已成为南极磷虾渔业的重要作业区。透光层作为海洋生物活动最为集中的区域,也是海洋中生产力最为丰富的区域。了解透光层水团的特性及变化,一方面可为南极半岛海洋学研究提供基础信息,同时也可为南极磷虾等中上层海洋生物的分布及其致因提供科学支撑。通过分析2013年1月至3月南设得兰群岛周边海域5个断面的透光层温、盐数据,本研究梳理了该区域的水团属性和分布。结果显示,南设得兰群岛北侧较深水区水团垂向结构明显,由上至下依次为南极夏季表层水、冬季水和绕极深层水。位于南设得兰群岛南侧的布兰斯菲尔德海峡内,威德尔海过渡水特征几乎占据了整个布兰斯菲尔德海峡。但布兰斯菲尔德海峡西南侧水团结构较为复杂,包括了威德尔海过渡水、别林斯高晋海过渡水和德雷克海峡水等。阐明南设得兰群岛周边复杂的水团结构对于进一步开展南大洋生物-物理相互作用研究具有重要的科学意义。