Observations of long‐duration episodic bottom currents in the Middle America Trench: Evidence for tidally initiated turbidity flows
Observations of long‐duration episodic bottom currents in the Middle America Trench: Evidence for tidally initiated turbidity flows
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DOI：
10.1029/2010jc006166
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发表时间：
2010-10
影响因子：
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通讯作者：
R. Thomson;E. Davis;Martin Heesemann;H. Villinger
中科院分区：
文献类型：
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作者：
R. Thomson;E. Davis;Martin Heesemann;H. Villinger
[1]从2005年11月到2007年4月，使用停泊在距海底21 m、深度为4386 m的单点声学海流计的时间序列，对哥斯达黎加太平洋沿岸中美洲海沟的底流进行了研究。除了显著的（10.1 m s−1）潮流外，该仪器还记录了一系列12个大致每月持续的沿海沟向西北方向的间歇性潮流事件。事件速度通常超过0.25 m s-1，并与增强的声学后向散射强度同步。事件以快速（<1天）逆转为东南流和减少后向散射结束。附近两个大洋钻探计划（ODP）钻孔观测站的海底温度记录显示，流动事件伴随着底层水温的稳步上升。在每次事件结束时，温度突然下降到背景值。事件时序一般跟踪潮流调制的包络。根据2002年11月至2009年2月的钻孔观测温度记录，这些事件的平均持续时间为40（±20）天，事件间间隔为30（±25）天。研究结果表明，情节流可能旋转修改，自悬浮浊流的潮汐流再悬浮的沉积物以上浅滩沟底的停泊点的东南部发起。浊流中的悬浮颗粒估计为0.0003%至0.006%的电流体积。结果表明，潮汐引起的浊流可能是常见的陡峭，良好的混合区域的深海毗邻沉积物丰富的大陆边缘。
[1] Benthic flow in the Middle America Trench off the Pacific coast of Costa Rica is examined using time series from a single-point acoustic current meter moored 21 m above bottom at 4386 m depth at the southern end of the trench from November 2005 to April 2007. In addition to significant (∼0.1 m s−1) tidal currents, the instrument recorded a series of 12 episodic northwestward along-trench flow events of roughly monthly duration. Event velocities often exceeded 0.25 m s−1 and were contemporary with enhanced acoustic backscatter intensity. Events ended with a rapid (<1 day) reversal to southeastward flow and reduced backscatter. Seafloor temperature records from two nearby Ocean Drilling Program (ODP) borehole observatory sites reveal that the flow events were accompanied by a steady rise in bottom water temperature. Temperatures dropped abruptly to background values at the end of each event. The event timing generally tracked the envelope of the tidal current modulation. On the basis of the November 2002 to February 2009 borehole observatory temperature records, the events had a mean duration of 40(±20) days and were separated by a between-event interlude of 30(±25) days. Findings indicate that the episodic flows were likely rotationally modified, autosuspending turbidity currents initiated by tidal current resuspension of sediments above the shoaling trench floor to the southeast of the mooring site. Suspended particles in the turbidity currents are estimated to range from 0.0003% to 0.006% of the current by volume. Results suggest that tidally induced turbidity currents may be common to steep, well-mixed regions of the deep ocean adjacent to sediment rich continental margins.