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<p>Particulate organic carbon (POC) is a key component of marine carbon cycling. However, its spatiotemporal dynamics in the Arabian Sea remain poorly understood. We investigated the distribution, seasonal variability, and environmental drivers of POC using moderate resolution Imaging Spectroradiometer Aqua (MODIS-Aqua) satellite data (2001–2021) and vertical profiles from the Pelagic Interactions Scheme for Carbon and Ecosystem Studies (PISCES) biogeochemical reanalysis model (Copernicus Marine Services). Surface POC concentrations exhibited profound seasonal variability. Values peaked at 500 mg/m<sup>3</sup> in coastal zones during winter (January–March) and monsoon (July–August). The highest monthly averages were recorded in February (254.8±45.5 mg/m<sup>3</sup>), January (208.36±50.2 mg/m<sup>3</sup>), and March (196.45±75.3 mg/m<sup>3</sup>). Regional analysis revealed distinct patterns: Region A (Pakistan/Iran coast) had winter maxima (504.2 mg/m<sup>3</sup> in January); Region B (Oman) peaked during the monsoon upwelling (835.4 mg/m<sup>3</sup> in July); Region C (India) showed moderate values (327.9 mg/m<sup>3</sup>), while Region D (open sea) exhibited stable concentrations (∼114 mg/m<sup>3</sup>). All regions showed declining POC trends, with the most profound decrease in Region A (−0.28 mg/m<sup>3</sup>). Surface POC was strongly correlated with chlorophyll <i>a</i> (Chl <i>a</i>), at 0.64 in coastal and 0.69 in offshore waters. Vertical profiles revealed strong correlations (&gt;0.8) between POC, Chl <i>a</i>, and sea surface temperature (SST). Weaker associations were found with nutrients (NO<sub>3</sub>, PO<sub>4</sub>), salinity, pH, and oxygen. Seasonal SST maxima (29.1±0.7 °C in May) and deep mixed layers (54.3±5.1 m in January) influenced vertical carbon fluxes. Silicate and oxygen showed depth-dependent patterns. Surface waters were depleted (&lt;2 mmol/m<sup>3</sup>), while mesopelagic layers were enriched (20–45 mmol/m<sup>3</sup>). This study provided the first integrated satellite-model analysis of POC dynamics in the Arabian Sea. It fills a critical knowledge gap in regional carbon cycling. The findings improved the ability to predict biogeochemical responses to monsoon variability and climate-driven oceanographic shifts, and they also have important implications for global carbon budget estimates.</p>

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Decadal trends in particulate organic carbon in the Arabian Sea: biogeochemical drivers across coastal and offshore waters

  • 期刊论文

  • 发表日期：

    2026年1月26日

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  • Muhsan Ali Kalhoro,
  • Veeranjaneyulu Chinta,
  • Muhammad Tahir,
  • Chunli Liu,
  • Tony Song,
  • Zhiyuan He,
  • Lixin Zhu,
  • Zhenlin Liang,
  • Jun Song

摘要

Particulate organic carbon (POC) is a key component of marine carbon cycling. However, its spatiotemporal dynamics in the Arabian Sea remain poorly understood. We investigated the distribution, seasonal variability, and environmental drivers of POC using moderate resolution Imaging Spectroradiometer Aqua (MODIS-Aqua) satellite data (2001–2021) and vertical profiles from the Pelagic Interactions Scheme for Carbon and Ecosystem Studies (PISCES) biogeochemical reanalysis model (Copernicus Marine Services). Surface POC concentrations exhibited profound seasonal variability. Values peaked at 500 mg/m3 in coastal zones during winter (January–March) and monsoon (July–August). The highest monthly averages were recorded in February (254.8±45.5 mg/m3), January (208.36±50.2 mg/m3), and March (196.45±75.3 mg/m3). Regional analysis revealed distinct patterns: Region A (Pakistan/Iran coast) had winter maxima (504.2 mg/m3 in January); Region B (Oman) peaked during the monsoon upwelling (835.4 mg/m3 in July); Region C (India) showed moderate values (327.9 mg/m3), while Region D (open sea) exhibited stable concentrations (∼114 mg/m3). All regions showed declining POC trends, with the most profound decrease in Region A (−0.28 mg/m3). Surface POC was strongly correlated with chlorophyll a (Chl a), at 0.64 in coastal and 0.69 in offshore waters. Vertical profiles revealed strong correlations (>0.8) between POC, Chl a, and sea surface temperature (SST). Weaker associations were found with nutrients (NO3, PO4), salinity, pH, and oxygen. Seasonal SST maxima (29.1±0.7 °C in May) and deep mixed layers (54.3±5.1 m in January) influenced vertical carbon fluxes. Silicate and oxygen showed depth-dependent patterns. Surface waters were depleted (<2 mmol/m3), while mesopelagic layers were enriched (20–45 mmol/m3). This study provided the first integrated satellite-model analysis of POC dynamics in the Arabian Sea. It fills a critical knowledge gap in regional carbon cycling. The findings improved the ability to predict biogeochemical responses to monsoon variability and climate-driven oceanographic shifts, and they also have important implications for global carbon budget estimates.