Characteristics of suspended particulate matter in the northern South China Sea affected by internal solitary waves
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摘要: 悬浮颗粒物在“源−汇”沉积体系中扮演着关键角色,而南海常见的动力现象—内孤立波,则被证实是影响悬浮颗粒物分布和沉积过程的重要因素。该项研究于2022年9月在吕宋海峡至东沙群岛海域开展,采用LISST-deep与CTD设备进行同步观测,以研究悬浮颗粒物的粒径及体积浓度分布。通过调查期内的卫星遥感数据,划定了内孤立波的影响范围,并结合海床基观测内孤立波影响悬浮颗粒物分布过程,从动力学的角度揭示了内孤立波对悬浮颗粒物在输运过程中特征变化的影响。研究发现:(1)在内孤立波的振幅深度区间(6~79 m)内,以较小粒径的悬浮颗粒物(15~25 μm)分布为主,且越接近内孤立波的波谷深度,出现较小粒径悬浮颗粒物的频率越高。(2)悬浮颗粒物分布由内孤立波波峰线中心区域扩散到两侧,在中心为体积浓度低值区(≤91 μL/L),而波峰线两侧区域与内孤立波传播路径远端区域为体积浓度高值区(≥500 μL/L)。此外,研究进一步揭示了内孤立波通过改造作用使聚集状态的悬浮颗粒物被分解为粒径较小、组成单一的颗粒,通过控制作用改变悬浮颗粒物在波峰线不同位置、传播路径和振幅深度上的体积浓度分布,为理解南海源−汇沉积体系提供了重要的理论依据。Abstract: Suspended particulate matter (SPM) plays a key role in the “source-sink” deposition system, and internal isolated waves, a common dynamical phenomenon in the South China Sea, have been shown to be an important factor influencing the distribution of SPM and the deposition process. The study was carried out in September 2022 in the sea area from Luzon Strait to Dongsha Islands, using LISST-deep and CTD equipment for simultaneous observation to study the distribution of suspended particulate matter in terms of particle size and volume concentration. The satellite remote sensing data during the investigation period were used to delineate the influence range of internal isolated waves and to reveal the influence of internal isolated waves on the characterization changes of suspended particulate matter during transport from a kinetic point of view. It was found that: (1) the distribution of suspended particulate matter of smaller sizes (15−25 μm) was dominated in the amplitude depth interval (6−79 m) of the inner isolated wave, and the closer the depth of the trough of the inner isolated wave was, the higher the frequency of the occurrence of suspended particulate matter of smaller sizes. (2) The distribution of suspended particles spreads from the center of the inner isolated wave crest line to both sides, forming a low volume concentration zone (≤91 μL/L) in the center, and forming a high concentration zone (≥500 μL/L) on both sides of the crest line and the distal end of the propagation path of the inner isolated wave. In addition, the study further reveals that the internal isolated wave breaks down the aggregated suspended particles into smaller size and single composition particles through modification, and changes the volume concentration distribution of the suspended particles at different locations of the crest line, propagation path and amplitude depth through control, which provides an important theoretical basis for the understanding of the South China Sea source-sink deposition system.
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图 1 调查期间南海北部观测站位与内孤立波a、b、c、d分布
A. 海床基观测内孤立波,B. 内孤立波与观测站位,C. GF1卫星观察到的内孤立波b、c、d,D. HJ2A卫星观察到的内孤立波a
Fig. 1 Distribution of observation stations and internal isolated waves a, b, c, d in the northern part of the South China Sea during the survey period
A. Seabed based internal solitary wave observations, B. internal solitary wave vs. observation station, C. internal solitary wave b, c, d observed by GF1 satellite, D. internal solitary wave a observed by HJ2A satellite
图 5 内孤立波传播过程及影响区域
主要影响海域为调查时期多个内孤立波传播的重叠区域,次要影响海域为调查时期仅受单个内孤立波影响的区域
Fig. 5 Internal isolated wave propagation processes and regions of influence
The main affected sea area is the overlapping area where multiple internal isolated waves propagated during the survey period, and the secondary affected sea area is the area affected by only one single internal isolated wave during the survey period
图 12 10 × 10滤膜SPM显微镜图像
a. 内孤立波未影响海域C1站位SPM,b. 内孤立波未影响海域C2站位SPM,c. 内孤立波影响海域B5站位SPM
Fig. 12 10 × 10 filter membrane SPM microscope image
a. SPM at station C1 in the sea area not affected by internal isolated waves, b. SPM at station C2 in the sea area not affected by internal isolated waves, c. SPM at station B5 in the sea area affected by internal isolated waves
图 13 内孤立波在波峰线、传播路径对SPM控制的机理示意图
内孤立波沿密度跃层非线性传播阶段,振幅深度80~90 m、波长10 km、波峰线长度50 km
Fig. 13 Schematic diagram of the mechanism of SPM controlled by internal isolated waves at crest line and propagation paths
Phase of nonlinear propagation of internal isolated waves along the density jump layer, amplitude depth 80−90 m, wavelength 10 km, crest line length 50 km
表 1 吕宋海峡至东沙群岛海域水体参数
Tab. 1 Parameters of the water column in the sea area from Luzon Strait to Dongsha Islands
ρ1 /(kg·m−3) ρ2 /(kg·m−3) h1/m h2/m α β 1021.554 1023.420 45 1683 −0.029 11202.898 1022.864 1025.069 72.5 638.5 −0.014 5819.519 1019.945 1020.962 20.5 255.5 −0.029 376.564 表 2 调查站位CTD观测记录表
Tab. 2 Survey station CTD observation record sheet
站位 海况等级 风速/(m·s−1) 气压/hPa 平均浪高/m A1 3 8.4 1006.8 2.0 A2 2 8.8 1007.0 2.0 A3 3 5.1 1006.4 0.6 A4 3 10.4 1007.3 2.0 B4 2 7.1 1006.3 1.0 B5 1 0.6 1007.4 0.0 B6 1 7.7 1009.4 1.0 C1 2 4 1005.6 0.6 C2 3 9.7 1006.3 2.0 C3 1 5.4 1006.8 0.6 D1 2 5.8 1003.6 1.0 D2 2 6.0 1002.4 1.0 E2 2 7.0 1008.5 1.0 表 3 吕宋海峡至东沙群岛海域的内孤立波参数反演
Tab. 3 Parameter inversion of internal waves in the Luzon Strait to Dongsha Islands
名称 纬度 经度 亮暗间距/m 反演振幅/m 相速度/(m·s−1) 波峰线长度/km 内孤立波a 20°24′41″N 117°48′46″E 1099.60 6.68 0.95 41.53 内孤立波b 21°52′16″N 116°40′00″E 479.77 37.76 1.35 96.84 内孤立波c 21°14′25″N 116°28′55″E 719.96 34.72 0.76 66.23 内孤立波d 21°37′51″N 117°00′08″E 1615.96 66.89 1.07 138.40 表 4 吕宋海峡至东沙群岛海域的内孤立波传播过程参数反演
Tab. 4 Parameter inversion of propagation process of internal solitary waves from Luzon Strait to Dongsha Islands
名称 反演振幅/m 振幅变化值/m 相速度/(m·s−1) 相速度变化值/(m·s−1) C1 = C0 + (A1 − A0) × 0.0016 内孤立波a 6.68 变化率: 0.67 2.07 0.54 2.83 0.95 0.97 0.97 0.96 0.98 9.97 13.83 7.47 21.13 内孤立波b 37.76 变化率: 0.76 1.84 0.72 1.71 1.35 1.36 1.40 1.37 1.42 49.68 69.48 50.02 85.54 内孤立波c 34.72 变化率: 0.85 1.71 0.82 1.22 0.76 0.77 0.80 0.78 0.80 40.85 59.37 48.68 59.39 内孤立波d 66.89 变化率: 1.24 1.48 0.76 1.54 1.07 1.00 1.02 1.04 1.09 27.63 34.26 50.71 78.09 表 5 观测站位内孤立波与悬浮颗粒物特征对应关系
Tab. 5 Correspondence between isolated waves and suspended particulate matter characteristics within the observing stations
站位 观测时间 纬度 经度 水深
/m内孤立波经过时刻 所处内孤
立波位置影响范围
/km2相对粒径
/μm绝对粒径
/μm平均浓度
/(μL·L−1)内孤立波a 内孤立波b 内孤立波c 内孤立波d A1 2022.09.21
02:58−03:0620°59.908′N 115°59.900′E 300 − − 09.21
05:21− 波峰线
北翼0.310 30.079 17.320 43.320 A2 2022.09.21
06:54−07:0820°33.583′N 116°13.702′E 583 − − 09.21
03:56− 波峰线
中心0.193 31.259 19.560 46.886 A3 2022.09.21
17:23−17:3620°13.728′N 116°33.546′E 480 − − 09.21
01:23− 波峰线
南翼0.213 29.761 16.810 51.677 A4 2022.09.21
22:25−22:5719°59.586′N 117°0.325′E 1500 − − − − 波峰线
远端0.058 33.699 14.840 58.942 B4 2022.09.06
09:14−09:2921°0.040′N 117°30.089′E 638 09.05
05:20− − − 传播路径前 3.483 29.366 20.620 77.743 B5 2022.09.06
20:15−20:4521°0.318′N 117°59.764′E 1520 09.05
06:14− − − 传播路径中 0.019 28.637 21.320 67.295 B6 2022.09.07
02:58−03:4420°59.872′N 118°30.102′E 2450 09.05
01:32− − − 传播路径后 N/A 28.225 19.250 71.198 C1 2022.09.14
19:53−20:1119°59.956′N 114°59.956′E 720 − − − − − N/A 29.457 14.170 33.343 C2 2022.09.14
13:32−14:0119°29.845′N 115°0.220′E 1510 − − − − − N/A 36.648 14.210 67.328 C3 2022.09.14
08:19−09:0219°0.126′N 115°0.289′E 2222 − − − − − N/A 32.577 15.680 64.302 D1 2022.09.05
22:28−22:4621°45.337′N 118°0.049′E 831 − − − − − N/A 29.611 16.320 56.011 D2 2022.09.05
09:13−09:5521°45.144′N 119°0.101′E 2260 − − − − − N/A 30.432 15.580 53.238 E2 2022.09.21
11:04−11:3020°0.113′N 115°59.887′E 1212 − − − − − N/A 31.624 12.360 85.014 注:内孤立波经过时刻根据内孤立波与站位实际距离和传播速度进行计算,相对粒径、绝对粒径和平均浓度均以100 m深的数据平均计算。“−”表示在调查期间未观察到显著的内孤立波事件,“N/A”表示未在内孤立波显著影响区域。 -
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