Water masses and baroclinic transports in the South Atlantic and Southern oceans
Water masses and baroclinic transports in the South Atlantic and Southern oceans
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南大西洋和南大洋的水团和斜压输送
DOI：
10.1357/002224002762688687
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发表时间：
2002
影响因子：
0.5
通讯作者：
B. King
中科院分区：
文献类型：
--
作者：
K. Heywood;B. King
我们描述了从南极洲到巴西的世界海洋环流实验 (WOCE) A23 水文剖面，名义上沿 35W。该剖面穿过威德尔环流中心、南极绕极流（ACC）和阿根廷盆地的副热带环流。我们精确定义锋面的位置、锋面水团特性的变化及其输送。南极坡锋穿过南极洲大陆坡上方，产生 4 西弗的斜压输送，是 19 西弗的气旋性威德尔环流环流的一部分。我们重复了 1973 年威德尔海的一个剖面，发现流入的温暖深水层明显变暖了约 0.2°C，但流出的环流北翼没有明显的变化。观察到与威德尔海深水（WSDW）具有相同特征的最近通风水流从东部流入威德尔海。威德尔锋线在南纬 61°7' 处穿过，ACC 南部边界 (SB)（通常称为斯科舍锋线）在南纬 58°38' 处穿过。它们之间是威德尔-斯科舍交汇处，贡献了 16 希沃的向东运输。南 ACC 阵线 (SACCF) 的第一个渡口位于南乔治亚岛以南，海拔约 55°30'S。然后它以反气旋方式环绕南乔治亚岛，并在南纬 53°40' 处遭遇，然后在南纬 53°30' 处逆反射并向东返回。每次穿越时的斜压传输约为 15 Sv。在该地区，SACCF 最明显的特征是温度最低层盐度的降低。极锋（PF）的核心位于~49S，等温线急剧向北下降，并输送了 67 Sv。 PF 和亚南极锋 (SAF) 几乎无法区分，只有一个站明显位于极锋区。输送 57 Sv 的 SAF 在南纬 48°45' 附近遭遇，此处南极中层水 (AAIW) 的次表层盐度最小值开始下降。副热带锋（STF）标志着副热带环流水域与南部较冷、较新鲜的亚南极水域之间的边界；它最南端的过境点位于南纬 44-45 度，输送约 25 希弗。这里比该经度上的 STF 历史地点向南偏远数百公里。巴西洋流锋 (BCF) 在 ~38S 处遭遇，输送 43 Sv。之前的观测发现，STF 是巴西洋流与海岸分离后向东流动的主要方式，而在 A23 期间，我们发现 BCF 承担了大部分这种运输。另一个深锋可能标志着副热带环流的中心，在南纬 34°22' 穿过，伴随着 2.5 Sv 的输送。在韦马海峡西部，我们遇到了巴西洋流的再循环，该洋流向东北流动，输送量为 23 希弗。该路段在没有穿越巴西洋流的情况下提前结束。要关闭副热带环流输送，需要巴西洋流大大超过基于浅层参考水平的历史估计。 SACCF 和 STF 都表现出可能由测深造成的曲流。 STF 曲流可能是由扎皮奥拉海隆周围环流的东端引起的。 SB 和 PF 都有相关的涡流。 SB 向北部释放了一个气旋涡流，随后被当地的水覆盖。它沿方位角传输 8 Sv。 PF 向南部释放了一个反气旋涡流，该涡流也被封顶并循环至少 3 希弗。在维马通道中观察到 AAIW 的小型反气旋地下透镜体，其传输量级为 I Sv。在维马海峡，北大西洋深水和下环极深水 (LCDW) 之间的静止水平使从阿根廷到巴西盆地的北向净流量为 1.2 Sv WSDW 和 4 Sv LCDW。
We describe the World Ocean Circulation Experiment (WOCE) A23 hydrographic section from Antarctica to Brazil, nominally along 35W. The section crossed the center of the Weddell Gyre, the Antarctic Circumpolar Current (ACC) and the Subtropical Gyre in the Argentine Basin. We precisely define the locations of fronts, the changes in water mass properties across them, and their transports. The Antarctic Slope Front was crossed above the continental slope of Antarctica, with a baroclinic transport of 4 Sv, part of the cyclonic Weddell Gyre circulation of 19 Sv. We repeated a section in the Weddell Sea occupied in 1973, and saw a marked warming of the inflowing Warm Deep Water layer by some 0.2°C, but no discernible change in the outflowing northern limb of the gyre. An inflow of recently ventilated water with the same characteristics as Weddell Sea Deep Water (WSDW) was observed flowing into the Weddell Sea from the east. The Weddell Front was crossed at 61°7'S and the Southern Boundary (SB) of the ACC (often referred to as the Scotia Front) at 58°38'S. Between these lay the Weddell-Scotia Confluence, contributing 16 Sv of eastward transport. The first crossing of the Southern ACC Front (SACCF) lay south of South Georgia at ~55°30'S. It then wrapped anticyclonically around South Georgia and was encountered at 53°40'S before retroflecting and returning eastward at ~53°30'S. The baroclinic transport was ~15 Sv at each crossing. In this region the SACCF is most clearly identified by a decrease in the salinity of the temperature minimum layer. The core of the Polar Front (PF) lay at ~49S where the isotherms plunged down sharply to the north, and transported 67 Sv. The PF and Subantarctic Front (SAF) were barely distinguishable with only one station clearly in the Polar Frontal Zone. The SAF, transporting 57 Sv, was encountered at ~48°45'S where the subsurface salinity minimum of Antarctic Intermediate Water (AAIW) began to descend. The Subtropical Front (STF) marks the boundary between the waters of the subtropical gyre and the colder, fresher subantarctic waters to the south; its southernmost crossing was at 44-45S transporting ~25 Sv. This is several hundred kilometers farther south than historical locations of the STF at this longitude. The Brazil Current Front (BCF) was encountered at ~38S transporting 43 Sv. Whereas previous observations found the STF to be the primary means for eastward flow of the waters of the Brazil Current after it has separated from the coast, during A23 we find that the BCF carries the majority of this transport. A further Deep Front, possibly marking the center of the subtropical gyre, was crossed at 34°22'S associated with a transport of 2.5 Sv. In the western Vema Channel we encountered a recirculation of the Brazil Current, flowing to the northeast with a transport of 23 Sv. The section ended prematurely without crossing the Brazil Current. To close the subtropical gyre transport would require a Brazil Current significantly in excess of the historical estimates based on shallow reference levels. Both the SACCF and STF exhibited meanders probably caused by bathymetry. The STF meander may be caused by the eastern end of the circulation around the Zapiola Rise. Both the SB and PF had associated eddies. The SB had shed a cyclonic eddy to the north, which had subsequently been capped by local water. It transported 8 Sv azimuthally. The PF had shed an anticyclonic eddy to the south, which was also capped and circulated at least 3 Sv. A small anticyclonic subsurface lens of AAIW was observed in the Vema Channel with a transport of the order of I Sv. In the Vema Channel, a level of no motion between the North Atlantic Deep Water and the Lower Circumpolar Deep Water (LCDW) gives a net northward flow of 1.2 Sv WSDW and 4 Sv LCDW from the Argentine to the Brazil Basin.