An analytical diagnostic model of the Antarctic Circumpolar Current

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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.     

南极绕极流线性理论的一个摄动解

为了模拟南极绕极流区的流动，首先将环形条带区从Drake海峡处分开，并展成以经纬度为坐标的矩形区域。将模拟区划分为边界区和内部区。与Munk的大洋环流理论不同．在我们所考虑的线性化的涡度方程中保留了经向摩擦作用。这是基于绕极流流轴处的强剪切产生的经向摩擦项与β效应同等重要的判断。另外．内部区的北边界取为流线，而2个侧边界区的北边界视为南北水体交换的通道。基于巴西暖流穿过北边界流入和秘鲁寒流穿过北边界流出，以及常年有大于100Sv(平均约134Sv)的水体自西向东穿过Drake海峡的观测事实，引入了净通量条件。计算出了不同于Sverdrup流的更集中的内部区带状流的流线分布，这与观测大体一致。在Drake海峡处引入匹配条件，从而得到了完整的边界解。计算结果与理论分析指出，通过Drake海峡的流量远小于南极绕极流所带动水体的纬向通量是因为Drake海峡偏离绕极流流轴(也是南大洋西风带的主轴)。受南美大陆的阻挡，另一部分水体通过秘鲁寒流流出该海区。     

普里兹湾附近绕极深层水和底层水及其运动特征

利用中国第15次南极科学考察科学考察队的CTD全深度观测资料(1998年11月至1999年2月),分析并讨论了普里兹湾以北的南大洋海域内,绕极深层水(CDW)和南极底层水(AABW)的物理特性及其空间分布.同时还与历史上其他学者的发现进行了比较.指出了在研究海域内,CDW在100～2000m之间从北向南扩展,其高温核(t>1.2℃)和高盐核(S>34.7)在75°E断面上最为深厚,向南扩展得最远;而AABW则在2500m以深由陆坡底部向北扩展,σ_θ>27.875的高密度水体在70°E断面上最为深厚,向北扩展得最远.此外还通过实测的CTD资料证实了CDW和AABW的经向环流特征,以及它们与迪肯流环(Deaconcell)、亚极地流环和深层流环的一致性.     

Ocean basins near the Scotia–Antarctic plate boundary: Influence of tectonics and paleoceanography on the Cenozoic deposits

The distribution of seismic units in deposits of the basins near the Antarctic–Scotia plate boundary is described based on the analysis of multichannel seismic reflection profiles. Five main seismic units are identified. The units are bounded by high-amplitude continuous reflectors, named a to d from top to bottom. The two older units are of different age and seismic facies in each basin and were generally deposited during active rifting and seafloor spreading. The three youngest units (3 to 1) exhibit, in contrast, rather similar seismic facies and can be correlated at a regional scale. The deposits are types of contourite drift that resulted from the interplay between the northeastward flow of Weddell Sea Bottom Water (WSBW) and the complex bathymetry in the northern Weddell Sea, and from the influence of the Antarctic Circumpolar Current and the WSBW in the Scotia Sea. A major paleoceanographic event was recorded by Reflector c, during the Middle Miocene, which represents the connection between the Scotia Sea and the Weddell Sea after the opening of Jane Basin. Unit 3 (tentatively dated ∼Middle to Late Miocene) shows the initial incursions of the WSBW into the Scotia Sea, which influenced a northward progradational pattern, in contrast to the underlying deposits. The age attributed to Reflector b is coincident with the end of spreading at the West Scotia Ridge (∼6.4 Ma). Unit 2 (dated ∼Late Miocene to Early Pliocene) includes abundant high-energy, sheeted deposits in the northern Weddell Sea, which may reflect a higher production of WSBW as a result of the advance of the West Antarctic ice-sheet onto the continental shelf. Reflector a represents the last major regional paleoceanographic change. The timing of this event (∼3.5–3.8 Ma) coincides with the end of spreading at the Phoenix–Antarctic Ridge, but may be also correlated with global events such as initiation of the permanent Northern Hemisphere ice-sheet and a major sea level drop. Unit 1 (dated ∼Late Pliocene to Recent) is characterized by abundant chaotic, high-energy sheeted deposits, in addition to a variety of contourites, which suggest intensified deep-water production. Units 1 and 2 show, in addition, a cyclic pattern, more abundant wavy deposits and the development of internal unconformities, all of which attest to alternating periods of increased bottom current energy.     

Fronts and strong currents of the upper southeast Indian Ocean

1 IntroductionBaroclinic component is the dominant part ofAntarcticCircum polarCurrent (ACC) (FandryandPillsbury,1979),and a baroclinictransportation asso-ciatedwithfrontsmakesupthem ajoritypartoftheto-talbaroclinictransportation oftheACC (Nowlin andCliff…     

An inverse model of the large scale circulation in the South Indian Ocean

An overview of the large-scale circulation of the South Indian Ocean (SIO) (10°S-70°S/20°E-120°E) is proposed based on historical hydrographic data (1903-1996) synthesized with a finite-difference inverse model. The in situ density, potential temperature and salinity fields of selected hydrographic stations are projected on the basis of EOFs. Then the EOF coefficients (the projected values) are interpolated on the model grid (1° in latitude, 2° in longitude) using an objective analysis whose spatial correlation functions are fitted to the data set. The resulting fields are the input of the inverse model. This procedure filters out the small-scale features. Twelve modes are needed to keep the vertical structures of the fields but the first three modes are sufficient to reproduce the large-scale horizontal features of the SIO: the Subtropical Gyre, the Weddell Gyre, the different branches of the Antarctic Circumpolar Current.The dynamics is steady state. The estimated circulation is in geostrophic balance and satisfies mass, heat and potential vorticity conservation. The wind and air-sea heat forcing are annual means from ERS1 and ECMWF, respectively.The main features of the various current systems of the SIO are quantified and reveal topographic control of the deep and bottom circulation. The cyclonic Weddell Gyre, mainly barotropic, transports 45 Sv (1 Sv = 10⁶m³/s), and has an eastern extension limited by the southern part of the Antarctic Circumpolar Current.The bottom circulation north of 50°S is complex. The Deep Western Boundary Currents are identified as well as cyclonic recirculations. South east of the Kerguelen Plateau, the bottom circulation is in good agreement with previous water mass analysis. The comparison between some recent regional analysis and the inverse estimation is limited by the model resolution and lack of deep data.The meridional overturning circulation (MOC) is estimated from the finite difference inverse model. Between 26°S and 32°S the reversal of the current deepens and reaches 1400 m at 32°S. The major part of the deep meridional transport at 32°S is located between the African coast and the Madagascar Ridge, carried by the Agulhas Undercurrent. The mean value for this meridional thermohaline recirculation is 8.8 ± 4.4 Sv between 26°S and 32°S. The Agulhas Undercurrent (11 Sv) is associated with a weak Agulhas Current (55 Sv). The MOC is thus trapped in the western margin of the Southwest Indian Ridge. The corresponding vertical velocity along 32°S between 30°E and 42°E is 7.2 × 10⁻⁵ ± 8.9 × 10⁻⁵ cm s⁻¹. The net meridional heat flux represents −0.53 PW at 18°S and −0.33 PW at 32°S (negative values for southward transports). The intensity of the meridional heat flux is linked to the intensity of the Agulhas Current and to the vertical mixing.     

Seasonal variability of the Antarctic Coastal Current and its driving mechanisms in the Weddell Sea

Insight into the dynamics of the Antarctic Coastal Current (ACoC) is achieved by quantifying the contributions of its driving mechanisms to the seasonal variability of its barotropic and baroclinic components. These mechanisms are sought out in the local wind, the sea-ice concentration, wind curl of the Weddell Gyre (Sverdrup transport) and the thermohaline forcing related to warming/cooling and ice melting and freezing. These driving mechanisms induce most of the seasonal variability of both the barotropic and baroclinic components of the ACoC by deepening the pycnocline towards the coast and sharpening the baroclinic profile following thermal wind balance. The resulting coastal current has mainly a barotropic transport (82%) and a major annual cycle, which explains 37% of this component's variability (tides and other high-frequency events generate 40%). The wind contributes with 58% of the seasonal variability of the barotropic component and 23% of the baroclinic; the sea-ice concentration contributes with 8% and 18%, respectively; Sverdrup transport with 4% and 30% and the thermohaline forcing with 30% and 29%. The results of this study are obtained with analysis of fifteen CTD sections (potential density and geostrophic velocities) of RV-Polarstern obtained between 1992 and 2005, as well as composite, spectral and harmonic analyses of 9 years of time series from moored instruments (current speed and temperature), wind speed, atmospheric pressure and sea-ice concentration of satellite imagery.     

南印度洋中尺度涡统计特征及三维合成结构研究

南印度洋是海洋中尺度涡的多发区域。本文利用卫星高度计资料及Argo浮标资料,对南印度洋（10°~35°S, 50°~120°E）区域中尺度涡的分布、表观特征等进行了统计分析,采用合成方法,构建了该区域中尺度涡的三维温盐结构。结果表明,涡旋频率呈明显的纬向带状分布,在18°~30°S存在一个明显的涡旋频率带状高值区;涡旋半径具有由南至北逐渐增大的趋势;长周期涡旋在其生命周期内,半径、涡动能、涡能量密度、涡度等性质均经历了先增大而后减小的过程;涡旋以西向运动为主,在经向上移动距离较小,长周期气旋（反气旋）涡具有明显的偏向极地（赤道）移动的倾向;涡旋平均移动速度为5.9 cm/s,速度大小大致沿纬向呈带状分布。在混合层以下,气旋涡（反气旋涡）内部分别呈现明显的温度负（正）异常,且分别存在两个位温负（正）异常的冷（暖）核结构;气旋涡（反气旋涡）整体上呈现"正-负"（"负-正"）上下层相反的盐度异常结构。中尺度涡对温盐的平均影响深度可达1 000×104 Pa以上。     

Climatic variability of transport in the upper layer of the Antarctic Circumpolar Current from hydrological and satellite data

Based on the satellite altimetry dataset of sea level anomalies, the climatic hydrological database World Ocean Atlas-2009, ocean reanalysis ECMWF ORA-S3, and wind velocity components from NCEP/NCAR reanalysis, the interannual variability of Antarctic Circumpolar Current (ACC) transport in the ocean upper layer is investigated for the period 1959–2008, and estimations of correlative connections between ACC transport and wind velocity components are performed. It has been revealed that the maximum (by absolute value) linear trends of ACC transport over the last 50 years are observed in the date-line region, in the Western and Eastern Atlantic and the western part of the Indian Ocean. The greatest increase in wind velocity for this period for the zonal component is observed in Drake Passage, at Greenwich meridian, in the Indian Ocean near 90° E, and in the date-line region; for the meridional component, it is in the Western and Eastern Pacific, in Drake Passage, and to the south of Africa. It has been shown that the basic energy-carrying frequencies of interannual variability of ACC transport and wind velocity components, as well as their correlative connections, correspond to the periods of basic large-scale modes of atmospheric circulation: multidecadal and interdecadal oscillations, Antarctic Circumpolar Wave, Southern Annual Mode, and Southern Oscillation. A significant influence of the wind field on the interannual variability of ACC transport is observed in the Western Pacific (140° E–160° W) and Eastern Pacific; Drake Passage and Western Atlantic (90°–30° W); in the Eastern Atlantic and Western Indian Ocean (10°–70° E). It has been shown in the Pacific Ocean that the ACC transport responds to changes of the meridional wind more promptly than to changes of the zonal wind.     

The shedding of mesoscale anticyclonic eddies from the Alaskan Stream and westward transport of warm water

The south-flowing waters of the Kamchatka and Oyashio Currents and west-flowing waters of the Alaskan Stream are key components of the western sub-Arctic Pacific circulation. We use CTD data, Argo buoys, WOCE surface drifters, and satellite-derived sea-level observations to investigate the structure and interannual changes in this system that arise from interactions among anticyclonic eddies and the mean flow. Variability in the temperature of the upstream Oyashio and Kamchatka Currents is evident by warming in mesothermal layer in 1994–2005 compared to 1990–1991. A major fraction of the water in these currents is derived directly from the Alaskan Stream. The stream also sheds large anticyclonic (Aleutian) eddies, averaging approximately 300 km in diameter with a volume transport significant in comparison with that of the Kamchatka Current itself. These eddies enclose pools of relatively warm and saline water whose temperature is typically 4 °C warmer and salinity is 0.4 greater than that of cold-core Kamchatka eddies in the same density range. Aleutian eddies drift at approximately 1.2 km d⁻¹ and retain their distinctive warm and salty characteristics for at least 2 years. Selected westward pathways during 1990–2004 are identified. If the shorter northern route is followed, Aleutian eddies remain close to the stream and persist sufficiently long to carry warm and saline water directly to the Kamchatka Current. This was observed during 1994–1997 with substantial warming of the waters in the Kamchatka Current and upstream Oyashio. If the eddies take a more southern route they detach from the stream but can still contribute significant quantities of warm and saline water to the upstream Oyashio, as in 2004–2005. However, the eddies following this southern route may dissipate before reaching the western boundary current region.     

Antarctic Intermediate Water variability in the northern New Zealand region

In the region between 30°S and northern New Zealand, vertical salinity profiles through the core of the Antarctic Intermediate Water (AAIW) show a high degree of spatial and temporal variability, and this variability is much larger than that found in nearby ocean areas. Characteristic features are interleaving of salinity layers and large changes in the salinity minimum between adjacent stations. Quantifying the changes through the calculation of an intrusion index highlights the degree of variability and the importance of boundary mixing along the New Zealand slope. However, the main cause of the variability is the meeting and mixing of higher salinity AAIW, arriving from the north‐west (having travelled around the subtropical gyre) with lower salinity AAIW arriving by more direct entry from the north‐east. These waters meet in the region through the action of the meso‐scale eddy field. Present data indicate that where strong salinity interleaving occurs, the length scales are of the order of 10 km and the time scales are of the order of a few days. Resolution of the processes at work will require studies on finer scales than presently available.     

Western Indian Ocean SST signal and anomalous Antarctic sea-ice concentration variation

Teleconnection between El Nino/La Nina-Southern Oscillation (ENSO) phenomenon and anomalous Antarctic sea-ice variation has been studied extensively.In this study,impacts of sea surface temperature in the Indian Ocean on Antarctic sea-ice change were investigated during Janaury 1979 and October 2009.Based on previous research results,sea areas in the western Indian Ocean (WIO;50°–70°E,10 °–20 °S) are selected for the resreach.All variables showed 1-10 year interannual timescales by Fast Founer Tranaform (FFT) transformation.Results show that i) strong WIO signals emerged in the anomalous changes of Antarctic sea-ice concentration;ii) significant positive correlations occurred around the Antarctic Peninsula,Ross Sea and its northwest peripheral sea region iii) negative correlation occurred in the Indian Ocean section of the Southern Ocean,Amundsen Seas,and the sea area over northern Ross Sea;and iv) the atmospheric anomalies associated with the WIO including wind,meridional heat flux,and surface air temperature over southern high latitudes were the possible factors for the teleconnection.     

A model of the upper branch of the meridional overturning of the southern ocean

A zonal-average model of the upper branch of the meridional overturning circulation of the southern ocean is constructed and used to discuss the processes – wind, buoyancy, eddy forcing and boundary conditions – that control its strength and sense of circulation. The geometry of the thermocline ‘wedge’, set by the mapping between the vertical spacing of buoyancy surfaces (the stratification) on the equatorial flank of the Antarctic Circumpolar Current and their outcrop at the sea surface, is seen to play a central role by setting the interior large-scale potential vorticity distribution. It is shown that the action of eddies mixing this potential vorticity field induces a residual flow in the meridional plane much as is observed, with upwelling of fluid around Antarctica, northward surface flow and subduction to form intermediate water. Along with this overturning circulation there is a concomitant air-sea buoyancy flux directed in to the ocean.     

Chaotic and regular trajectories in the Antarctic Circumpolar Current

Methods from chaos theory are applied to the analysis of the circulation in the Southern Ocean, using velocity fields produced by a realistic global ocean model. We plot the intersections of individual trajectories encircling Antarctica with a vertical plane in the Drake passage. This so-called Poincaré section shows a drastic difference between regular trajectories in a core region of the Antarctic Circumpolar Current (ACC), and chaotic, mixing trajectories in the surrounding region. It also shows that there is a region with overturning circulation of approximately 3.5 Sv in the ACC, with downwelling on the northern side and upwelling on the southern side, which may be related to the Deacon cell.     

季风转换期印度洋经向热输运的年际变异及其机理

本文采用SODA3.4.2再分析数据和POP2海洋模式研究了季风转换期间（春季和秋季）热带印度洋经向热输运异常（Meridional Heat Transport Anomaly, MHTA）的年际变异特征。春季MHTA存在两个主要模态,即一致模态和辐合辐散模态：一致模态表现为热带印度洋上层一致的向北输运,受热带印度洋海温一致模相关的赤道反对称风场（赤道以北/南为东北风/西北风异常）调控;辐合辐散模态则呈现关于赤道对称的表层辐散次表层辐合特征,受控于赤道以南的热带西南印度洋和副热带东南印度洋海温偶极子。然而,秋季MHTA仅表现为辐合辐散模态,受到印度洋偶极子期间赤道东风和赤道外反气旋式风应力异常影响。此外,POP2敏感性试验也验证了印度洋海温模态影响下异常风场对MHTA的调控作用,即反对称的风引起一致向北的MHTA,赤道东风异常引起MHTA表层辐散、次表层辐合现象。因此,热带印度洋海气耦合模态年际变化对印度洋上层热量再分配有着重要的意义。     

CO2 in the Weddell Gyre and Antarctic Circumpolar Current: austral autumn and early winter

Quasi-continuous fugacity of CO₂ (fCO₂) data were collected in the eastern Weddell Gyre and southern Antarctic Circumpolar Current (ACC) of the Southern Ocean during austral autumn 1996. Full depth Total CO₂ (TCO₂) sections are presented for austral autumn and winter (1992) cruises. Pronounced fCO₂ gradients were observed at the Southern Ocean fronts. In the Weddell Gyre, fCO₂ regimes appeared to coincide with surface and subsurface hydrographic regimes. The southern ACC was supersaturated with respect to CO₂, as was part of the northern Weddell Gyre. The southern Weddell Gyre was markedly undersaturated. The great potential of autumn cooling for generating undersaturation and CO₂ uptake from the atmosphere was demonstrated. In the northeastern Weddell Gyre, upwelling of CO₂- and salt-rich deep water was shown to play a role as the horizontal fCO₂ distribution closely resembled that of the surface salinity. The total uptake of atmospheric CO₂ by the Weddell Gyre in autumn (45 days) was calculated to be 7·10¹² g C. The deep TCO₂ distribution noticeably reflected the different water masses in the region. A new deep TCO₂ maximum was detected in the ACC, which apparently characterizes the boundary between the equatorward flowing Antarctic Bottom Water (AABW) and the Circumpolar Deep Water (CDW). East of the Weddell Gyre, the AABW stratum is much thicker (>2000 m) than more to the west, on the prime meridian (<300 m).     

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

硅藻具有形态各异、结构复杂、精美绝伦的硅质细胞壁,是海洋中进行生物硅化最主要的生物体。硅质细胞壁的形成同样是一个错综复杂的过程,它涉及硅藻细胞将硅酸从胞外转运到胞内;硅酸在细胞内的转移;在硅沉积囊泡(SDV)中的浓缩沉积;最后合成具种类特异性的细胞壁。重点介绍硅酸转运基因(SITs)的分子特征与作用机制;与生物硅化相关的三种蛋白即硅体蛋白(frustulins)、亲硅蛋白(silaffins)和侧壁蛋白(pleuralins)的结构与功能;硅质结构如何在硅沉积囊泡内最终形成的模式。     

Energy of the Jets of the Antarctic Circumpolar Current and of Their Eddies in the Surface Layer of the Southern Ocean

Oceanology - The kinetic energy of six jets of the Antarctic Circumpolar Current (ACC) and of the cyclonic and anticyclonic mesoscale eddies generated by these jets is studied in application to the...