Water masses and currents of deep circulation southwest of the Shatsky Rise in the western North Pacific

We conducted full-depth hydrographic observations in the southwestern region of the Northwest Pacific Basin in September 2004 and November 2005. Deep-circulation currents crossed the observation line between the East Mariana Ridge and the Shatsky Rise, carrying Lower Circumpolar Deep Water westward in the lower deep layer (θ<1.2 °C) and Upper Circumpolar Deep Water (UCDW) and North Pacific Deep Water (NPDW) eastward in the upper deep layer (1.3–2.2 °C). In the lower deep layer at depths greater than approximately 3500 m, the eastern branch current of the deep circulation was located south of the Shatsky Rise at 30°24′–30°59′N with volume transport of 3.9 Sv (1 Sv=10⁶ m³ s⁻¹) in 2004 and at 30°06′–31°15′N with 1.6 Sv in 2005. The western branch current of the deep circulation was located north of the Ogasawara Plateau at 26°27′–27°03′N with almost 2.1 Sv in 2004 and at 26°27′–26°45′N with 2.7 Sv in 2005. Integrating past and present results, volume transport southwest of the Shatsky Rise is concluded to be a little less than 4 Sv for the eastern branch current and a little more than 2 Sv for the western branch current. In the upper deep layer at depths of approximately 2000–3500 m, UCDW and NPDW, characterized by high and low dissolved oxygen, respectively, were carried eastward at the observation line by the return flow of the deep circulation composing meridional overturning circulation. UCDW was confined between the East Mariana Ridge and the Ogasawara Plateau (22°03′–25°33′N) in 2004, whereas it extended to 26°45′N north of the Ogasawara Plateau in 2005. NPDW existed over the foot and slope of the Shatsky Rise from 29°48′N in 2004 and 30°06′N in 2005 to at least 32°30′N at the top of the Shatsky Rise. Volume transport of UCDW was estimated to be 4.6 Sv in 2004, whereas that of NPDW was 1.4 Sv in 2004 and 2.6 Sv in 2005, although the values for NPDW may be slightly underestimated, because they do not include the component north of the top of the Shatsky Rise. Volume transport of UCDW and NPDW southwest of the Shatsky Rise is concluded to be approximately 5 and 3 Sv, respectively. The pathways of UCDW and NPDW are new findings and suggest a correction for the past view of the deep circulation in the Pacific Ocean.     

南大洋物理过程在全球气候系统中的作用

南大洋是全球面积最大的一个大洋。传统观点倾向于认为由于南大洋与北半球相距遥远而与北半球气候系统关系不大,其全球性气候效应也较弱,这主要是由于以往对南大洋的了解不足。随着观测分析、数值模拟与理论研究的加强,以及对南大洋的认识不断加深,南大洋的气候效应日益凸显。从南极底层水、南极绕极流、南大洋海冰、南大洋与热带之间的遥相关、以及南大洋对气候变化的响应等多个角度梳理了南大洋物理过程特别是动力过程在全球气候系统中的作用,较为完整地总结了对南大洋气候效应的已有认识,并结合南大洋研究现状对未来有价值的科学问题和潜在的研究热点进行了探讨,以期强调南大洋在全球气候系统中的重要地位,推动南大洋研究不断走向深入。     

近百年来的南极绕极波变化特征

采用2011年发布的20世纪全球大气环流再分析资料,结合长期观测序列,分析了百余年来大气中南极绕极波的强弱变化和传播过程。结果显示,南极绕极波有显著的年代际变化,在1940~1960年和1980~2000年附近出现和活跃,而在其他年代消失。东南太平洋南极绕极波振幅最强,该区域的海气耦合过程可能是绕极波信号增强的关键之一。初步揭示了百年来南极绕极波和南极涛动的对应关系,偏强的南极涛动有利于南极绕极波的出现,但并非决定绕极波产生的唯一因素。     

冰芯和台站记录的近50 a来东南极冰盖边缘地区气候变化格局

对取自东南极冰盖Lambert冰流东、西两侧共支雪芯,恢复了过去50 a来稳定同位素温度序列和积累率序列.对比发现,位于Lambert冰流东侧,即位于Wilks地和Princess Elizabeth 地的5支雪芯(GC₃0, GD03, GD15, DT001和DT085),过去50 a来积累率总体为上升趋势,δ¹⁸O上升速率介于0.34～2.6 kg·m^-2·a^-1; 稳定同位素显示其气温亦呈整体上升趋势, 上升速率介于0‰～0.02‰·a^-1. 但对位于Lamb ert冰流西侧, 即位于Dronning Maud地、Mizuho高原和Kamp地的5支雪芯(Core E,DML 05,W2 00, LGB16和MGA),过去50 a来积累率总体为下降趋势,下降速率介于-0.01～-2.3 6 kg·m^-2·a^-1; 稳定同位素温度变化则十分复杂:Dronning Maud 地西侧为上升, Mizuho高原和Kamp地为下降或变化不明显. 分布于LGB两侧沿岸气象站记录也印证了上述格局. 这种格局可能是南大洋独特的环流形式-环南极波(ACW)-在特殊地形( 如大的冰盆)影响下, 在南极冰盖边缘的表现形式.     

An analytical diagnostic model of the Antarctic Circumpolar Current

ＡｎａｎａｌｙｔｉｃａｌｄｉａｇｎｏｓｔｉｃｍｏｄｅｌｏｆｔｈｅＡｎｔａｒｃｔｉｃＣｉｒｃｕｍｐｏｌａｒＣｕｒｒｅｎｔ￥ＱｉａｏＦａｎｇｌｉ；ＺｈａｎｇＱｉｎｇｈｕａａｎｄＨｅＷｅｎ（ＲｅｃｅｉｖｅｄＮｏｖｅｍｂｅｒ１０，１９９５；ａｃｃｅｐｔｅｄＮ...     

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。     

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.     

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.     

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.     

Temperature variation and its driving forces over the Antarctic coastal regions in the past 250 years

By comparing the oxygen isotopic temperatures recorded by many shallow ice cores from the coastal regions of Antarctica, this paper presents the special characteristics of the temperature variations over the Antarctic coastal regions in the past 50 years, 150 years and 250 years. In the past 50 years, the isotopic temperatures recorded in the ice cores over different sites on the Antarctic coastal regions differ greatly. For instance, although increasing isotopic temperatures have been reported for many sites studied, many sites show decreasing trends, the regional regularity in temperature variations is still insignificant. In the past 150 years, the isotopic temperature trends in the coastal regions of Antarctica show an alternate-distributing pattern. In the past 250 years, all the ice cores from the coastal regions of Antarctica have recorded the so-called Little Ice Age (LIA). The above-mentioned spatial characteristics of the temperature variations over the Antarctic coastal regions are likely to reflect the impacts of the unique Southern Hemisphere atmospheric circulation, the Antarctic Circumpolar Wave (ACW) and the special terrain (such as the large drainage basins) on the coastal regions of Antarctica. Furthermore, the impacting intensity of the unique Southern Hemisphere atmospheric circulation, the Antarctic Circumpolar Wave and the special terrain differs in terms of the temporal scale of the temperature change.