ABSTRACT

This paper analyzes the characteristics of the thermohaline fine-scale structure of the sub-Arctic front (SAF) in the Kuroshio–Oyashio confluence region using temperature, salinity, and current data obtained from surveys in June 2016. Thermohaline intrusion is found to be prevalent in the sea area of the SAF, occurring predominantly in frontal zones with depths less than 200 m and in North Pacific intermediate water (NPIW) layers with depths greater than 350 m. The intrusion in the SAF zones with depths less than 200 m has a higher intensity but smaller dimensions in the NPIW. According to our analysis, the thermohaline intrusion in the SAF sea zone is mainly attributable to the joint effect of double diffusion and flow instability. At depths of 0–350 m, the thermohaline intrusion is vulnerable to the influences of salt fingering, diffusive convection, and symmetric instability. At depths deeper than 350 m, diffusive convection is significant. In addition, shear instability might be a contributor. Considering that the effect of turbulent mixing is primarily governed by symmetric instability in the SAF sea areas, the flow instability characterized by a dominant contribution from symmetric instabilities might exert a more significant influence on thermohaline intrusion. The more distinct thermohaline staircases at layers deeper than 350 m, which are mainly produced by diffusive convection, have larger vertical scales than the staircases in other layers.

摘要

本文利用 2016 年 6 月调查中获得的温度、盐度和电流数据分析了黑潮-亲潮汇合区亚北极锋 (SAF) 温盐细尺度结构的特征。在 SAF 海域，主要发生在深度小于 200 m 的锋区和深度大于 350 m 的北太平洋中间水 (NPIW) 层。深度小于 200 m 的 SAF 带的侵入强度较高，但在 NPIW 中的尺寸较小。根据我们的分析，SAF海区温盐入侵主要是由于双重扩散和流动不稳定的共同作用。在 0~350 m 深度，温盐侵入易受盐指影响，扩散对流和对称不稳定性。在深度超过 350 m 处，扩散对流很重要。此外，剪切不稳定性可能是一个因素。考虑到湍流混合的影响主要受 SAF 海域的对称不稳定性控制，以对称不稳定性为主要贡献的流动不稳定性可能对温盐入侵产生更显着的影响。深度大于350 m 的温盐阶梯较明显，主要由扩散对流产生，其垂直尺度大于其他层的阶梯。考虑到湍流混合的影响主要受 SAF 海域的对称不稳定性控制，以对称不稳定性为主要贡献的流动不稳定性可能对温盐入侵产生更显着的影响。深度大于350 m 的温盐阶梯较明显，主要由扩散对流产生，其垂直尺度大于其他层的阶梯。考虑到湍流混合的影响主要受 SAF 海域的对称不稳定性控制，以对称不稳定性为主要贡献的流动不稳定性可能对温盐入侵产生更显着的影响。深度大于350 m 的温盐阶梯较明显，主要由扩散对流产生，其垂直尺度大于其他层的阶梯。