中国科学院海洋研究所机构知识库

本文基于实测的溶解无机碘（IO₃^-和I^-）数据，结合水文数据（温度，盐度和密度），对黑潮次表层水（Kuroshio Subsurface Water，KSSW）在东海陆架海域的入侵模式（位置、路径和范围）和时间变化（季节变化和年际变化）进行研究；在此基础上，将溶解无机碘引入最优多参数分析（Optimum Multiparameter analysis，OMP），定量估算KSSW在东海陆架海水中的相对贡献率，进一步探讨KSSW入侵的年际变化。

于2014年5-6月（春季）、2014年10-11月（秋季），2015年6月（春季）、2015年8-9月（夏季）、2015年12月-2016年1月（冬季）和2016年6月（春季）对中国东海和台湾以东部分海域开展调查采样，采集海水样品分析溶解无机碘，并通过CTD测定现场盐度、温度和水团密度等水文物理参数。结果显示，在所有航次调查期间，东海陆架海域底层均存在独特的高IO₃^-（>0.37 μM）和低I^-（<0.10 μM）的海水，该海水同时表现出显著的低温、高盐、高密度的特征。这些特征与台湾以东黑潮主轴的KSSW特征接近，并明显区别于东海陆架海域其他水团。溶解无机碘和水文参数的分布均表明东海陆架海域的KSSW入侵主要源于台湾东北部（~25.5 °N）KSSW的上涌；此外，利用溶解无机碘的结果发现在靠北的陆架边缘~28 °N存在另一支较弱的KSSW入侵。该入侵无法通过水文数据发现，仅记录在溶解无机碘的结果中。同时，在KSSW入侵过程中，溶解无机碘和水文参数表现出良好的线性关系。因此，对于KSSW在东海陆架海域的入侵，溶解无机碘可以作为一种保守而有效的辅助指示物。

基于溶解无机碘和水文数据，我们对东海陆架海域KSSW的入侵厚度（垂向上KSSW入侵的上界到海底的深度）进行了估算，并以此刻画KSSW的入侵模式和时间变化。2014-2016年春季和2015年夏季航次的结果均显示，从台湾东北部入侵的KSSW沿北偏西方向运动，在27.5-28.5 °N分为近岸分支和离岸分支。其中近岸分支可以深入到浙江近岸（29 °N以北）50 m等深线以内的次表层区域，离岸分支则沿~100 m等深线继续向北入侵至29 °N以北。相比之下，秋季和冬季KSSW的入侵强度明显小于春夏季，近岸分支基本消失，离岸分支则仅能影响到28 °N附近，东海陆架海域的KSSW入侵呈现出显著的季节变化。比较2014、2015和2016年春季的KSSW入侵，2015年在浙江近岸的入侵最为靠北，但在东海陆架南部外海区域的入侵则明显最弱，推测可能与2015年春季台湾东北部KSSW的入侵位置向外海偏移有关，东海陆架海域的KSSW入侵同样表现出一定的年际变化。然而，以上基于溶解无机碘的东海陆架海域KSSW入侵的定性分析，无法确定2014、2015和2016年春季KSSW入侵强度的变化。

鉴于溶解无机碘在东海陆架海域较好的保守性和对于不同水团尤其是KSSW良好的指示作用，本文首次将溶解无机碘引入OMP分析，结合传统的温度和盐度参数，定量估算KSSW和其他水团对东海陆架海水的相对贡献率，并以此探讨2014、2015和2016年春季东海陆架海域KSSW入侵强度的变化。OMP分析结果显示，2014、2015和2016年春季东海陆架研究区域主要受到长江冲淡水、台湾海峡暖水、黑潮表层水和KSSW的影响。其中KSSW影响几乎整个研究区域底层，最大贡献率（>80%）出现在台湾东北部，而在浙江近岸区域的贡献率也超过50%。比较2014、2015和2016年春季的结果，2016年底层KSSW入侵区域的平均贡献率（78.9%）明显大于2014年（67.9%）和2015年（64.5%）；同样各断面（尤其是28 °N以北的断面）上KSSW的平均贡献率和覆盖范围也表现出2016年大于2014年和2015年的现象。因此，基于OMP分析，2016年春季KSSW在东海陆架海域的入侵明显强于其他两年，而2014年和2015年春季的入侵强度则基本相当。这种变化可能与厄尔尼诺－南方涛动（ENSO）有关，而太平洋年代际变化（PDO）的影响不明显。

Based on the field observations of the dissolved inorganic iodine species (iodate and iodide) combined with hydrographic data (temperature, salinity and density), the intrusion pattern (intrusion location, pathway and extent) of the Kuroshio Subsurface Water (KSSW) onto the East China Sea (ECS) continental shelf and its temporal variation (seasonal and interannual variation) were determined. Furthermore, the Optimum Multiparameter (OMP) method was used to quantify the relative contributions of the KSSW and other water masses in the ECS based on their measured temperature, salinity and dissolved inorganic iodine species, and the quantitative interannual variation of the KSSW intrusion is further discussed.

Sample collection was conducted across the ECS and Kuroshio east of Taiwan during cruises in May to June 2014 (spring), October to November 2014 (autumn), June 2015 (spring), August to September 2015 (summer), December 2015 to January 2016 (winter) and June 2015 (spring). Discrete seawater samples were collected for the dissolved inorganic iodine species analyses, and the temperature, salinity and density were measured with a conductivity-temperature-depth (CTD) recorder. Our study shows that a unique iodate-rich (>0.37 μM) and iodide-poor (<0.10 μM) water occurred at the bottom of the ECS shelf during all six oceanographic cruises, and this water always exhibits cold, saline and dense characteristics. The characteristics of this water are similar to those of the KSSW and obviously distinct from other water masses in the ECS. The evidence from both the dissolved inorganic iodine species and hydrographic data suggest that the KSSW mainly intrudes onto the ECS shelf from northeast of Taiwan (25.5 °N) via upwelling. However, in addition to the main intrusion center northeast of Taiwan, the dissolved inorganic iodine species concentrations indicate that another weaker intrusion from the KSSW occurs at ~28 °N along the shelf edge. This phenomenon can not be observed via hydrographic data alone; in addition, the dissolved inorganic iodine species have good linear relationships with the hydrographic data during the KSSW intrusion. Thus, the dissolved inorganic iodine species can be used as complementary and effective tracers of the KSSW intrusion.

Based on the characteristics of the dissolved inorganic iodine species and hydrographic data, we determined the thickness of the KSSW intrusion (depth from the upper boundary of the KSSW intrusion to the seabed) at each station, which was used to draw the intrusion pattern of the KSSW on the ECS shelf. In spring of 2014 to 2016 and summer of 2015, the KSSW intrusion northeast of Taiwan flowed northwestward then bifurcated into a nearshore branch and an offshore branch at 27.5-28.5 °N. The nearshore branch flowed approximately northward and finally appeared in the subsurface layer within the 50-m isobath off the Zhejiang coast (north of 29 °N); the offshore branch flowed along the 100-m isobath and reached north of 29 °N. The KSSW intrusion northeast of Taiwan was obviously weaker in autumn and winter than that in spring and summer. In autumn and winter, the nearshore branch was not observed, and the offshore branch reached only ~28 °N. The KSSW intrusion in the ECS shows significant seasonal variation. When comparing the KSSW intrusion in spring of 2014, 2015 and 2016, the KSSW intrusion northeast of Taiwan in spring of 2015 intruded northernmost off the Zhejiang coast in the nearshore area, but was weakest in the southern region (south of 28 °N), this may because the center of the KSSW intrusion northeast of Taiwan was shifted seaward. The KSSW intrusion in the ECS also has the feature of interannual variation. However, only the above qualitative research of the KSSW intrusion based on the dissolved inorganic iodine species cannot determine the intrusion intensity variation of the KSSW in these three years.

Because dissolved inorganic iodine species can behave as quasi-conservative tracers and indicate the movement of seawater (especially the KSSW) in the ECS, we modified the OMP analysis by adding the DIIS as additional parameters. The dissolved inorganic iodine species were added first into the OMP analysis, which enabled us to quantitatively estimate the water composition in the extremely dynamic and productive ECS and discuss the intrusion intensity variation of the KSSW in spring of 2014, 2015 and 2016. The OMP results indicate that seawater in the study region of the ECS mainly consisted of Changjiang Diluted Water (CDW), Taiwan Strait Warm water (TSWW), Kuroshio Surface Water (KSW) and KSSW. In spring of 2014, 2015 and 2016, the KSSW dominated in the deep water, intruded into the ECS shelf from the northeast of Taiwan (where the KSSW contribution can be >80%) and could reached north of 29 °N off the Zhejiang coast (where the KSSW contribution can be >50%). When comparing the KSSW intrusion in spring of 2014, 2015 and 2016, the average KSSW contribution of the bottom KSSW area in spring of 2016 (78.9%) was greater than in the previous two years (67.9% and 64.5%). In each transect (especially north of 28 °N), the KSSW intrusion in spring of 2016 also contained the greatest average KSSW contribution and the maximum coverage area. Thus, according to the OMP results, the KSSW intrusion was strongest in spring of 2016, and may be comparable in spring of 2014 and 2015. This interannual variability of the KSSW intrusion is likely related to the El Niño-Southern Oscillation (ENSO) rather than the Pacific Decadal Oscillation (PDO).