Pacific Abyssal Transport and Mixing: Through the Samoan Passage versus around the Manihiki Plateau
Pacific Abyssal Transport and Mixing: Through the Samoan Passage versus around the Manihiki Plateau
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DOI：
10.1175/jpo-d-18-0124.1
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发表时间：
2019-06
影响因子：
3.5
通讯作者：
L. Pratt;Gunnar Voet;A. Pacini;Shuwen Tan;M. Alford;G. Carter;J. Girton;D. Menemenlis
中科院分区：
文献类型：
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作者：
L. Pratt;Gunnar Voet;A. Pacini;Shuwen Tan;M. Alford;G. Carter;J. Girton;D. Menemenlis
北太平洋深海环流的主要来源是通过萨摩亚海峡向北的5-6 Sverdrups（Sv; 1 Sv <$106 m3 s−1）的深层气流。最近的一次现场活动表明，这种流动是水力控制的，它经历了水力跳跃，伴随着强烈的混合和耗散集中在几个深槛附近。根据我们的估计，与这种混合相关的贯向密度通量远大于在北太平洋深海延伸的典型等密度面的贯向通量。根据历史水文观测，北太平洋深海水的第二个来源是2.3-2.8西弗的密集水流，该水流绕过马尼希基高原向东转移，绕过萨摩亚海峡。该旁通流不限于通道，因此不太可能经历与水力过渡相关的强烈混合。因此，深流两个分支之间的通量分配可能与太平洋深海混合的分布有关。为了深入了解控制这两个分支之间的分区的因素，我们开发了一个深海和赤道附近的“岛屿规则”的扩展。新的特点包括规定存在的水力跃变，以及确定一个适当的集成电路的深海层以东的岛屿。相应的循环积分的评估导致预测0.4-2.4 Sv的旁路流量。环流积分清楚地将萨摩亚海峡内的耗散和摩擦阻力效应确定为划分水流的关键因素。
The main source feeding the abyssal circulation of the North Pacific is the deep, northward flow of 5–6 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) through the Samoan Passage. A recent field campaign has shown that this flow is hydraulically controlled and that it experiences hydraulic jumps accompanied by strong mixing and dissipation concentrated near several deep sills. By our estimates, the diapycnal density flux associated with this mixing is considerably larger than the diapycnal flux across a typical isopycnal surface extending over the abyssal North Pacific. According to historical hydrographic observations, a second source of abyssal water for the North Pacific is 2.3–2.8 Sv of the dense flow that is diverted around the Manihiki Plateau to the east, bypassing the Samoan Passage. This bypass flow is not confined to a channel and is therefore less likely to experience the strong mixing that is associated with hydraulic transitions. The partitioning of flux between the two branches of the deep flow could therefore be relevant to the distribution of Pacific abyssal mixing. To gain insight into the factors that control the partitioning between these two branches, we develop an abyssal and equator-proximal extension of the “island rule.” Novel features include provisions for the presence of hydraulic jumps as well as identification of an appropriate integration circuit for an abyssal layer to the east of the island. Evaluation of the corresponding circulation integral leads to a prediction of 0.4–2.4 Sv of bypass flow. The circulation integral clearly identifies dissipation and frictional drag effects within the Samoan Passage as crucial elements in partitioning the flow.