CSIR - National Institute of Oceanography, Regional Centre, Kochi, 682 018, India.
CSIR - National Institute of Oceanography, Dona Paula, Goa, 400 003, India.
Environ Monit Assess. 2021 Mar 13;193(4):188. doi: 10.1007/s10661-021-08968-5.
The present study examined the seasonal cycling of phosphorous (P) along the southwest coast of India (SWCI) based on two cruises during the southwest monsoon (SWM) and northeast monsoon (NEM) of 2018. During SWM, the entire SWCI experienced intense upwelling manifested by the incursion of cold, nutrient-rich, and hypoxic waters. During NEM, the region was transformed into a warm, well-oxygenated and nutrient-deplete environment. Dissolved inorganic phosphorus (DIP) was significantly high in the subsurface during SWM due to its release from sediments. The sediment P was high and showed an increasing trend towards the south, principally dependent on the sediment texture, organic carbon, and Fe concentrations. Bioavailable P, the sum of exchangeable (P) and reducible (P) fractions, was almost consistent (5-20%) over seasons, though P showed a marked reduction during SWM. Authigenic fraction (P) was the most dominant (46%), followed by detrital (P 41%) and residual (P 8%) fractions. Principal component analysis (PCA) of geochemical parameters for SWM was indicative of the high dissolution of Fe (oxy)hydroxides under hypoxia releasing P and its complexation with organic matter and Fe. PCA results for the NEM were different, as it indicated increased preservation of P-associated organic matter and Fe, alternately favouring the formation of P in sediments. The study's significance is the observation that the bottom water oxygen concentration can significantly influence sedimentary P cycling in tropical coastal upwelling zones.
本研究基于 2018 年西南季风（SWM）和东北季风（NEM）期间的两次考察，考察了印度西南海岸（SWCI）磷（P）的季节性循环。在 SWM 期间，整个 SWCI 经历了强烈的上升流，表现为寒冷、富营养和缺氧水的入侵。在 NEM 期间，该地区转变为温暖、富含氧气和营养物质匮乏的环境。由于从沉积物中释放，SWM 期间次表层的溶解无机磷（DIP）含量很高。由于沉积物质地、有机碳和 Fe 浓度的影响，沉积物 P 含量较高，并呈现向南增加的趋势。生物可利用磷（P）是可交换（P）和可还原（P）分数的总和，尽管在 SWM 期间 P 含量明显减少，但在各季节基本保持一致（5-20%）。自生相（P）是最主要的（46%），其次是碎屑相（P 41%）和残余相（P 8%）。SWM 条件下地球化学参数的主成分分析（PCA）表明，缺氧条件下 Fe（氢）氧化物的高溶解会释放 P，并与有机质和 Fe 络合。NEM 的 PCA 结果则不同，因为它表明与 P 相关的有机质和 Fe 的保存增加，从而有利于沉积物中 P 的形成。本研究的意义在于观察到底层水氧浓度会显著影响热带沿海上升流区的沉积物 P 循环。
