通过对东北印度洋90°E海岭及其临近海域表层沉积物的碳酸钙组成及其空间分布特征的研究，厘清了海岭区不同水深沉积物碳酸钙主要来源，揭示东北印度洋表层沉积物碳酸钙影响因子及其变化机制。基于10个表层沉积物样品的全样碳酸钙及其分粒径碳酸钙测试，结合扫描电镜显微特征与定量统计数据，发现海岭区碳酸钙含量变化在36.95% -74.76%之间，平均含量56.05%，可划分为30%-45%、45%-60%和60%-75%三个等级，碳酸钙区域性分布的影响因子具有多样性。水深在3000米以上的站位，碳酸钙主要来自粒径>150μm的有孔虫壳体；水深接近或超过碳酸钙溶跃面的区域，碳酸钙主要来自粒径<25μm的细颗粒组分；25-38μm组分的显微特征及统计结果显示，表样沉积物中除了钙质超微化石和有孔虫壳体碎片，还首次鉴定出不同属种的钙质沟鞭藻，其占钙质生物比例最高可达73.68%。此外，海岭区碳酸钙含量变化还与陆源物质及硅质生物壳体的稀释作用密切相关。分粒级碳酸钙结合扫描电镜显微特征统计分析，不仅为揭示深海沉积物碳酸钙变化机制研究提供新方法，还可深化对海洋埋藏有机碳和溶解有机碳组成的理解，为全球海洋碳循环研究提供科学依据。

This study addresses the scientific question of the spatial differentiation mechanisms of calcium carbonate (CaCO₃) in surface sediments across the 90°E Ridge in the northeastern Indian Ocean,  employing a multi-scale analytical approach to elucidate controlling factors and biogeochemical processes. Through bulk and size-fractionated (>150 μm, 63~150 μm, 38~63 μm, 25~38 μm, <25 μm) CaCO₃ contribution analyses of surface sediments from 10 stations, combined with quantitative statistical analysis of scanning electron microscopy (SEM) microfeatures, the following findings were obtained: (1) The CaCO₃ content exhibits significant spatial variability (36.95%~74.76%, mean 56.05%), forming a tripartite gradient pattern of 30%~45%, 45%~60%, and 60%~75%. (2) In regions water depths above 3000 m, the dominant CaCO₃ components are >150 μm planktonic foraminiferal shells (contribution >65%), while stations near or above the lysocline are dominated by <25 μm fine-grained fractions (contribution >58%). (3) Quantitative microfeature analysis reveals, for the first time, a co-deposition pattern of calcareous dinoflagellate fossils (relative abundance up to 73.68%) with coccoliths and foraminiferal fragments in the 25~38 μm fraction. Further investigations demonstrate that CaCO₃ distribution is governed by a ternary regulatory mechanism involving water depth-dependent dissolution effects, terrigenous clastic input, and siliceous biological dilution. This study innovatively establishes an integrated methodology of "grain-size separation-microscopic statistics-environmental interpretation," which not only refines theoretical models of CaCO₃ distribution in seamount geomorphic units but also expands the understanding of deep-sea inorganic carbon reservoirs by identifying calcareous dinoflagellate fossils as a novel carbon source. The findings provide a critical case study for comparative research on CaCO₃ preservation mechanisms in global ridge systems and offer vital scientific insights for parameterizing marine carbon cycle models through improved algorithms for size-specific CaCO₃ flux calculations.