Deep ventilation in the Okinawa Trough induced by Kerama Gap overflow
Deep ventilation in the Okinawa Trough induced by Kerama Gap overflow
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DOI：
10.1002/2016jc011822
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发表时间：
2016-08
影响因子：
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通讯作者：
A. Nishina;Hirohiko Nakamura;Jaehun Park;D. Hasegawa;Yuki Tanaka;Seongbong Seo;T. Hibiya
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文献类型：
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作者：
A. Nishina;Hirohiko Nakamura;Jaehun Park;D. Hasegawa;Yuki Tanaka;Seongbong Seo;T. Hibiya
在冲绳海槽中，近底层水流过Kerama Gap的岩床，然后在5 - 10年的停留时间内向上涌至1100 m以下的深水。本研究利用2013年6月和2014年6月在该区域进行的密集船上观测所获得的温度、盐度、溶解氧、海流和湍流的综合剖面数据，跟踪这一现象。在主岩床顶部西侧约100米厚的地层中观察到了速度超过0.5 m s−1的强近底亚潮流。沿Kerama缺口沿着的温度和盐度剖面显示，强溢流下游的深水存在一些凹陷和翻转，表明存在破碎的重力内波和水力跃变。使用索普尺度和浮力频率估算的相关垂直扩散系数比在开阔洋温跃层中观察到的典型值（10 - 5 m2 s-1）大3至4个数量级。溶解氧剖面也显示出强烈的垂直混合和相关的上升流，近底溢流水被夹带到冲绳海槽黑潮下的下温跃层中。本研究不仅支持了先前的概念模型，而且提供了新的证据表明，冲绳海槽是一个上升流的位置，营养丰富的菲律宾海中层水被吸入黑潮以下的下温跃层。本文受版权保护。All rights reserved.
Near-bottom water flowing over the Kerama Gap's sills is thought to ventilate the deep water below ∼1100 m depth in the Okinawa Trough and then upwell with 5‒10 years residence time. The present study follows up on this phenomenon, using comprehensive profile data of temperature, salinity, dissolved oxygen, currents and turbulence obtained by intensive shipboard observations performed in June 2013 and June 2014 in the region. Strong near-bottom sub-tidal flow with speeds exceeding 0.5 m s−1 was observed within a layer of about 100 m thickness over the western side of the peak of the main sill. Temperature and salinity sections along the Kerama Gap indicated some depressions and overturns of the deep water downstream of the strong overflow, suggesting the existence of breaking internal gravity waves and hydraulic jumps. Associated vertical diffusivities, estimated using the Thorpe scale and the buoyancy frequency, were three to four orders of magnitude larger than typical values observed in the thermocline of the open ocean (∼10−5 m2 s−1). The dissolved oxygen section also indicated strong vertical mixing and associated upwelling with the entrainment of the near-bottom overflow water into the lower thermocline beneath the Kuroshio in the Okinawa Trough. The present study not only supports the previous conceptual model but also provides new evidence that the Okinawa Trough is an upwelling location where nutrient rich Philippine Sea intermediate water is sucked up into the lower thermocline below the Kuroshio. This article is protected by copyright. All rights reserved.