Carbon and nitrogen contents and their isotopic components, and AMS (Accelerator Mass Spectrometry) radiocarbon dating ages, were measured for 57 coastal sediments from Weizhou Island to analyze the distribution of total inorganic carbon (TIC) and its carbon and oxygen isotopic components (δ13Ccarb and δ18Ocarb), total organic carbon (TOC) and total nitrogen (TN) contents and their stable isotopic components (δ13CTOC and δ15NTN), and their environmental significance. The results showed that the oldest age of coastal sediments on Weizhou Island was 2750 cal. a BP (before present), and the average TIC contents of cores A1, A2, B1, C1, and D1 in the intertidal zone were all greater than 5%, where δ13Ccarb and δ18Ocarb were enriched, whereas the TIC contents in cores A3, C2, and D2 of the supra-tidal zone were low, where δ13Ccarb and δ18Ocarb were depleted. Moreover, TIC decreased sharply, 4.95% on average, to close to zero from the estuary to the upstream region in the C1-C2 section. The average C/N ratio was 7.02, and δ13CTOC and δ15NTN were between −14.96‰ and −27.26‰ and −14.38‰ and 4.12‰, respectively. These measurements indicate that the TIC in coastal sediments mainly came from seawater. Cores A1, A2, and B1 in the northern intertidal zone exhibited organic terrestrial signals because of C3 and C4 plant inputs, which indicates that the important source on the northern coast of Weizhou Island came from island land but followed the decrease in C3 plants. The lacustrine facies deposits were mainly distributed in the upper reaches of the river, the northern coastline was advancing toward the sea, and part of the southwestern coastal sediments rapidly accumulated on the shore under the influence of a storm surge. The relative sea level of the Weizhou Island area has continuously declined at a rate of approximately 2.07 mm/a, using beach rock as a marker, since the Holocene.

中文翻译：

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北部湾涠洲岛沿岸沉积物中碳氮分布作为环境意义指标

对涠洲岛57处海岸沉积物进行碳氮含量及其同位素组成、AMS（加速器质谱）放射性碳测年，分析总无机碳（TIC）及其碳氧同位素组成（δ13Ccarb和δ18Ocarb)、总有机碳 (TOC) 和总氮 (TN) 含量及其稳定同位素组分 (δ13CTOC 和 δ15NTN) 及其环境意义。结果表明，涠洲岛海岸沉积物的最古老年龄为2750 cal。a BP（之前），潮间带A1、A2、B1、C1、D1核心的TIC平均含量均大于5%，其中δ13Ccarb和δ18Ocarb富集，而核心A3的TIC含量，潮上带的 C2 和 D2 较低，其中 δ13Ccarb 和 δ18Ocarb 被耗尽。此外，C1-C2段从河口到上游区域，TIC平均下降4.95%，接近于零。平均C/N比为7.02，δ13CTOC和δ15NTN分别在-14.96‰和-27.26‰以及-14.38‰和4.12‰之间。这些测量表明沿海沉积物中的 TIC 主要来自海水。由于C3和C4植物输入，潮间带北部A1、A2和B1核心呈现有机陆地信号，表明涠洲岛北部海岸的重要来源来自岛地，但随着C3植物的减少而减少。湖相沉积主要分布在河流上游，北部海岸线向海推进，西南沿海的部分沉积物在风暴潮的影响下迅速堆积在岸边。自全新世以来，涠洲岛地区的相对海平面以海滩岩为标志，以约2.07 mm/a的速度持续下降。