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Journal of Tropical Oceanography ›› 2026, Vol. 45 ›› Issue (1): 73-80.doi: 10.11978/2025001CSTR: 32234.14.2025001

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Calcium carbonate composition of surface sediments and influencing factors in the 90°E Ridge of the northeastern Indian Ocean*

DU Shuhuan1,2,3(), XIANG Rong1,2,3(), SU Xiang1,2,3(), ZHANG Lanlan1,2,3, PAN Zirui1,3, XIE Jinwo4, LUO Chuanxiu1,2,3, WAN Sui1,2,3   

  1. 1State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 511458, China
    2Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 511458, China
    3University of Chinese Academy of Sciences, Beijing 100049, China
    4School of Geography and Remote Sensing, Guangzhou University, Guangzhou 510006, China
  • Received:2025-01-01 Revised:2025-02-06 Online:2026-01-10 Published:2026-01-30
  • Contact: XIANG Rong, email: rxiang@scsio.ac.cn; SU Xiang, email: suxiang@scsio.ac.cn
  • Supported by:
    Hainan Provincial Joint Project of Sanya Yazhou Bay Science and Technology City(2021JJLH0048); Guangdong Basic and Applied Basic Research Foundation(2023A1515010705); Guangdong Basic and Applied Basic Research Foundation(2023A1515011955); Independent Integration Program, South China Sea Institute of Oceanography, Chinese Academy of Sciences(SCSIO2023HC07); National Natural Science Foundation of China(42176082); Shiptime Sharing Project of National Natural Science Foundation of China (NSFC)(42149910); Shiptime Sharing Project of National Natural Science Foundation of China (NSFC)(42249910)

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Abstract:

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 with water depths above 3000 m, the dominant CaCO3 component is planktonic foraminiferal shells (> 150 μm, contributing > 65%), while stations near or above the lysocline are dominated by the < 25 μm fine-grained fraction (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.

Key words: 90°E Ridge, surface sediments, calcium carbonate composition, particle size of calcium carbonates

CLC Number: 

  • Q913