Vertical Structure and Seasonal Variability of Chlorophyll Concentrations in the Southern Tropical Indian Ocean Revealed by Biogeochemical Argo Data

IF 3.3 2区 地球科学 Q1 OCEANOGRAPHY
Xueying Ma, Gengxin Chen, Xiaoqing Chu, Peng Xiu
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Abstract

The variability of chlorophyll (Chla) in the Southern Tropical Indian Ocean (STIO) is not fully understood. This study utilized biogeochemical Argo (BGC-Argo) and satellite observations to investigate the seasonal Chla variations in the upper layer (above 200 m) and their relationships to physical dynamics. The results indicate the existence of a well-developed deep Chla maximum (DCM) layer situated between depths of 50 and 150 m. The shallowest DCM was at the Seychelles-Chagos thermocline ridge because of permanent upwelling. Both the northern (4°S–12°S, 52°E−92°E) and southern (12°S–25°S, 52°E−92°E) regions experience surface blooms during July–August. However, they exhibit distinct Chla changes in response to different physical processes and nitrate concentrations below the mixed layer. In the northern region, the thermocline plays a critical role in regulating DCM depth and intensity. From April to June, subsurface upwelling and near-surface stratification processes promote nutrient and Chla accumulation in the subsurface layer, resulting in elevated surface Chla levels in the subsequent months. In contrast, the southern region is characterized by oligotrophic conditions, where light availability primarily governs Chla variability below the mixed layer. Specifically, from November to January, when light intensity intensifies, Chla increases below the mixed layer. Furthermore, BGC-Argo data revealed a long-lived cyclonic eddy that facilitated the westward transport of Chla, significantly contributing to surface Chla blooms through eddy-pumping and eddy-trapping mechanisms. This research elucidates the fundamental characteristics of Chla distribution from a three-dimensional perspective and furthers our understanding of the complex biophysical interactions within the STIO.

生物地球化学 Argo 数据揭示的南热带印度洋叶绿素浓度的垂直结构和季节变异性
南热带印度洋(STIO)叶绿素(Chla)的变化尚未完全明了。本研究利用生物地球化学 Argo(BGC-Argo)和卫星观测数据,研究了上层(200 米以上)Chla 的季节性变化及其与物理动力学的关系。结果表明,在水深 50 米至 150 米之间存在一个发达的深层 Chla 最大值(DCM)层。北部(南纬 4°-12°,东经 52°-92°)和南部(南纬 12°-25°,东经 52°-92°)地区在 7-8 月间都会出现表层水华。然而,它们因不同的物理过程和混合层下的硝酸盐浓度而表现出截然不同的 Chla 变化。在北部地区,温跃层在调节 DCM 深度和强度方面起着关键作用。从 4 月到 6 月,次表层上升流和近表层分层过程促进了次表层营养物质和 Chla 的积累,导致随后几个月表层 Chla 水平升高。相比之下,南部地区的特点是低营养条件,光照主要决定了混合层以下的 Chla 变化。具体来说,从 11 月到次年 1 月,当光照强度增强时,混合层以下的 Chla 会增加。此外,BGC-Argo 数据显示,一个长期存在的气旋涡促进了 Chla 的西向传输,通过涡泵和涡捕机制显著促进了地表 Chla 的大量繁殖。这项研究从三维角度阐明了 Chla 分布的基本特征,加深了我们对 STIO 内复杂的生物物理相互作用的理解。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Journal of Geophysical Research-Oceans
Journal of Geophysical Research-Oceans Earth and Planetary Sciences-Oceanography
CiteScore
7.00
自引率
13.90%
发文量
429
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