越南沿岸上升流海表叶绿素的季节内尺度变异及机制

doi:10.11978/2022166

摘要/Abstract

摘要：

在夏季, 南海西部的越南沿岸上升流系统(Vietnam boundary upwelling system, VBUS)时常出现高浮游植物生物量。其中由马登-朱利安振荡(Madden-Julian oscillation, MJO)主导的季节内尺度(30~60d)变率占到重要作用, 但MJO对海表叶绿素的调控效应及机制尚不清楚。本研究采用重建的遥感叶绿素数据与多源观测资料, 探究MJO事件中VBUS叶绿素季节内变化特征及成因。复合分析结果显示, 在MJO事件末期, 该海域叶绿素浓度达到季节内最高值, 海表温度(sea surface temperature, SST)、地转流纬向分量与Ekman泵吸及风场与该海域叶绿素浓度相位模态高度对应, 且与叶绿素相位序列相关性按该顺序递减。进一步将VBUS分成近岸和离岸两个子区域, 通过广义加性模型分析叶绿素浓度的主导调控因子。结果显示VBUS海域沿岸与离岸区域叶绿素浓度影响因子及其强度并不相同, SST同为两个区域最强影响因子, 沿岸区域次要影响因子为地转流纬向分量及Ekman泵吸, 离岸次要影响因子为地转流纬向分量, 且其影响强度与SST平分秋色。通过进一步分析该调控在不同厄尔尼诺年的不同, 发现当MJO处于第4—8相位时, MJO能有效地补偿强厄尔尼诺事件导致的叶绿素浓度骤降。总体而言, MJO所处相位决定了其对VBUS海域叶绿素影响的程度, 且在不同子区域中因素的影响强度并不相同。本研究揭示了海洋生态系统和动力的短期变率特征, 能够为南海叶绿素浓度变异的理解提供新视角。

关键词: 越南沿岸上升流, 叶绿素, 季节内变化

Abstract:

In summer, high phytoplankton biomass often occurs in the Vietnam Boundary upwelling System (VBUS) of the western South China Sea. Therein, the variation of surface chlorophyll concentration at the intra-seasonal scale (30~60 days) dominated by Madden-Julian Oscillation (MJO) can account for considerable variation, but the regulating effects and mechanism of the modulation to sea surface chlorophyll remain unclear. In this study, reconstructed remote sensing chlorophyll data and multi-source observation data were used to explore the characteristics and causes of the VBUS chlorophyll changes during MJO events. Composite analysis showed that in the late phases of MJO events, chlorophyll reached its intraseasonal maximum, while sea surface temperature (SST), zonal geostrophic current, Ekman pumping and wind speed were highly correlated in a decreasing order. Furthermore, the VBUS was divided into two sub-regions: nearshore and offshore regions. The analysis results of generalized additive model showed that the influencing factors and intensity of chlorophyll concentration in the coastal and offshore areas of VBUS were different. SST was the most important influencing factor in both regions. For the coastal region, zonal geostrophic current and Ekman pumping contributed secondly. For the offshore region, the second influence factor was zonal component of geostrophic current, and its influence was nearly equal to that of SST. We further investigated the MJO’s modulation in different El Niño years. When MJO is in the fourth to eighth phases, the El Niño’s negative effects on the chlorophyll can be compensated. In general, our study showed that the MJO’s phase determined the impact of MJO on chlorophyll in the VBUS. At the same time, the chlorophyll concentration in VBUS sea area under MJO events was controlled by SST, geostrophic zonal component and Ekman pump suction, and the impacts of different factors on VBUS were different. The study reveals the short-term variability of marine ecosystems and dynamics and can provide a new perspective for understanding the variation of chlorophyll in the South China Sea.

Key words: Vietnam boundary upwelling system, chlorophyll, intraseasonal variability

林少文, 任姮烨, 卢文芳. 越南沿岸上升流海表叶绿素的季节内尺度变异及机制[J]. 热带海洋学报, 2023, 42(4): 113-124.

LIN Shaowen, REN Hengye, LU Wenfang. Intra-seasonal regulation and mechanism on sea surface chlorophyll in the upwelling off the coast of Vietnam[J]. Journal of Tropical Oceanography, 2023, 42(4): 113-124.

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因素	与叶绿素浓度的相关系数(r)	p值
SST	-0.94	<0.001
降水	0.12	0.78
风速	0.64	<0.1
海表动能	0.71	<0.05
地转流纬向分量	0.82	<0.05
地转流经向分量	-0.07	0.87
Ekman泵吸速率	0.81	<0.05

区域	因素	估计自由度	参考自由度	F值	p值
沿岸区域	SST	6.316	7.503	98.355	<2×10^-16***
	海表动能	8.093	8.778	3.503	2.53×10^-4***
	地转流纬向分量	8.776	8.983	16.272	<2×10^-16***
	Ekman泵吸	2.362	3.081	11.241	5.19×10^-7***
	海表风速	2.309	2.918	8.063	3.64×10^-5***
离岸区域	SST	7.290	8.296	78.722	<2×10^-16***
	海表动能	8.648	8.961	11.181	<2×10^-16***
	地转流纬向分量	8.517	8.931	64.410	<2×10^-16***
	Ekman泵吸	3.896	4.931	2.501	2.69×10^-2*
	海表风速	1.787	2.252	4.052	1.25×10^-2*

年份	因素	估计自由度	参考自由度	F值	p值
2010	SST	3.376	4.112	2.823	3.743×10^-2*
	海表动能	7.433	8.273	3.561	3.56×10^-3**
	地转流纬向分量	7.448	8.287	10.318	<2×10^-16***
	Ekman泵吸	1.395	1.668	1.808	1.3650×10^-1
	海表风速	1.000	1.000	21.935	3.95×10^-5***
2016	SST	3.477	4.428	12.371	1.10×10^-6***
	海表动能	7.371	8.306	15.703	<2×10^-16***
	地转流纬向分量	9.000	9.000	51.157	<2×10^-16***
	Ekman泵吸	7.853	8.611	5.760	4.24×10^-5***
	海表风速	1.000	1.000	0.271	6.05×10^-1