Organic carbon cycling in SE Asia is data-sparse and poorly studied, although high sediment yield and organic carbon intensity occur in the tropical region. In the present study, we evaluated the role of tropical monsoon pertaining to fluvial discharge, sediment load, coastal current and water stratification on seasonal organic carbon dynamics during four sampling campaigns in the Upper Gulf of Thailand (UGoT). This study demonstrates that particulate organic carbon (POC) is closely correlated with the river influx of suspended sediment, which is generally regulated by the local rainfall. Higher POC is found near the large estuarine section (Chao Phraya River, CHAO) during southwest monsoon period and the small estuarine section (Mae Klong River, MK) during November 2013 when tropical cyclones impacted. POC in the estuarine sections is more significantly influenced by the seasonal shift compared with the coastal sections. Land-derived organic matter prevails in the small estuarine and coastal sections, while marine-derived organic matter dominates in the estuarine sections impacted by CHAO and MK. Anthropogenic inputs and dam regulation also influences the river export of organic matter during the high precipitation periods. Total organic carbon (TOC) however displays less significant seasonal monsoon variations than POC. Further, TOC tends to accumulate in the sub-silt fraction of sediments, which mainly occurs in the small estuarine and eastern coastal sections and is more obviously influenced by marine-derived factors. TOC in sediment of the CHAO and MK influenced sections however displays more seasonal variations with prevailing river input evidenced by coarser sediment and higher C/N ratios. Moreover, the almost year round water stratification across the region acts as the barrier in retaining organic carbon in the estuaries and their vicinities from dispersal into the lower portion of Gulf of Thailand. High sedimentation rate (~1.1 cm·yr⁻¹) further facilitates the organic carbon burial in the study area. The delivery, dispersal and burial of organic carbon are closely associated with the climate-controlled precipitation, and thus the tropical monsoon climatology under the global warming in particular is an important factor influencing the organic carbon in the UGoT.

尽管在热带地区发生了高产沙量和高有机碳强度，但东南亚的有机碳循环数据稀少且研究较少。在本研究中，我们在泰国上海湾（UGoT）的四次采样活动中评估了热带季风与河流流量，泥沙负荷，沿海水流和水分层有关的季节性有机碳动态的作用。这项研究表明，颗粒有机碳（POC）与悬浮泥沙的河流入流密切相关，这通常受当地降雨的调节。在西南季风期间，在大河口段（昭拍耶河，CHAO）附近发现了较高的POC；在2013年11月，受热带气旋影响，在小河口段（湄公河，MK）附近发现了较高的POC。与沿海地区相比，河口地区的POC受季节变化的影响更大。在河口和沿海地区，陆地有机物占主导地位，而受CHAO和MK影响的海域有机物占主导地位。在高降水期，人为投入和水坝调节也影响河流有机物的出口。然而，总有机碳（TOC）的季节性季风变化不如POC显着。此外，TOC倾向于在沉积物的亚淤泥部分中积累，这主要发生在小河口和东部沿海地区，并且更明显地受到海洋因素的影响。但是，受CHAO和MK影响断面的沉积物中的TOC表现出更多的季节性变化，主要是河流输入，这表现为沉积物较粗和C / N比较高。此外，该地区近一年四季的水分层是将有机碳保留在河口及其附近地区扩散至泰国湾下部的障碍。高沉降速率（〜1.1 cm·yr^-1）进一步促进了研究区域内有机碳的埋葬。有机碳的输送，扩散和埋藏与气候控制的降水密切相关，因此，特别是全球变暖下的热带季风气候是影响UGoT中有机碳的重要因素。