The detection of hydrothermal plumes is crucial for discovering active seafloor hydrothermal fields and exploring seafloor resources. To improve the efficiency of autonomous underwater vehicles (AUVs) in detecting hydrothermal plumes, this study proposes a comprehensive online identification algorithm that employs deep learning models based on the historical dataset collected by the Qianlong-II AUV at the Southwest Indian Ridge (SWIR). The algorithm integrates sliding window technique, the gated recurrent unit network, and the multi-layer perceptron network to achieve real-time detection of hydrothermal anomaly data, including temperature, turbidity, methane concentration, and oxidation-reduction potential (ORP), and further classifies the fluid types of hydrothermal plumes. To train the deep learning models, point anomaly data (temperature and turbidity) are labeled via the K-medoids clustering algorithm, while subsequence anomaly data (methane and ORP) are labeled using the adaptive iterative algorithm. Experimental results demonstrate that the algorithm achieves accuracies exceeding 98.1% for anomaly detection and 98.2% for fluid types identification. Meanwhile, the ablation experiment confirmed that the anomaly detection module significantly improved the overall identification performance. The proposed algorithm provides an effective and reliable solution for autonomous online identification of hydrothermal plumes, with broad application potential in deep-sea exploration.

Lava flows and associated basalt-hosted hydrothermal fields and fossil lava lakes are ubiquitous on the fast-spreading East Pacific Rise (EPR), but their detailed magnetic signature is not well documented. We analyze high-resolution bathymetric and magnetic data collected by an Autonomous Underwater Vehicle (AUV) over the eastern slope of the EPR at 2 degrees 13 ' S. These high resolution deep-sea magnetic data, with an altitude of 5 m and line spacing of 10 m, suggest that three successive lava flows exist in the study area. Magnetic lows reveal void spaces and collapsed lava lakes, respectively, distributed in the younger and older part of each lava flow. A small-scale hydrothermal field lies at the limit of the two lava flows, bearing a low magnetization. Forward modeling shows that the depth of alteration zone and void space is shallower than 10 m, confirming that the cooling lava flow sustains the hydrothermal field. Such high-resolution magnetic data, combined with high-resolution bathymetry and other data, pave the way for deep-sea studies in volcanology comparable to those conducted on land.

Seafloor hydrothermal systems at mid-ocean ridges are focal points for heat and matter exchange between the seawater and lithosphere. While seafloor seismographs (OBS) and pressure recorders (BPR) are standard for regional monitoring, achieving high-precision, vertical sub-surface data in complex hydrothermal terrains remains a significant technical objective. This study presents a novel in situ penetration probe designed for multi-parameter monitoring of marine hydrothermal vent areas. A key innovation of this work is its operational versatility and engineering efficiency: the probe is specifically designed for post-drilling deployment in boreholes, effectively utilizing existing coring sites to achieve direct coupling with the deep-seated crust, or for targeted placement via Remotely Operated Vehicles (ROVs). The device integrates a titanium-alloy conical tip and cylindrical chamber, housing tri-axial accelerometers and dual temperature-pressure sensors. Numerical simulations using the SST k-ω turbulence model and finite element analysis optimized the cone aperture and assessed fluid–structure stability under deep-sea conditions. Laboratory vibration tests and shallow-water sea trials validated the probe’s basic dynamic response, electromechanical integrity, and capability to acquire coupled environmental parameters. This compact, modular design provides a scalable and cost-effective framework for precise three-dimensional observation of sub-surface hydrothermal processes and deep-sea resource exploration.

The active Deyin hydrothermal field (DHF) is located at 15.2 degrees S on the Mid-Atlantic Ridge and is hosted by typical basaltic substrate. Here, we report distinct Pb-S-Zn isotopic compositions of pyrite, sphalerite, and chalcopyrite from the DHF, which differ from those of other mid-ocean ridge hydrothermal systems. Key features include: (i) Pb isotopes in pyrite and sphalerite plot within the field of Mid-Atlantic Ridge basalts, whereas chalcopyrite is characterized by depleted 206Pb and enriched 207Pb and 208Pb, resembling nearby 26 degrees S seamount basalts with an enriched mantle signature; (ii) delta 34S values increase progressively from pyrite (0.86%o-3.40%o) to sphalerite (2.08%o-2.84%o) and chalcopyrite (3.02%o-3.64%o), a trend not commonly observed in other hydrothermal fields; and (iii) sphalerite exhibits lower delta 66Zn values (-0.17%o to 0.05%o) than both pyrite (0.08%o-0.57%o) and chalcopyrite (0.01%o-0.09%o), contrary to expectations from Rayleigh fractionation alone. Integrating Pb-S-Zn isotopic data, we propose that while leaching of normal mid-ocean ridge basalts supplied metals and sulfur for pyrite and sphalerite formation, a local volatile-rich magmatic source, termed Deyin enriched mid-ocean ridge basalts, directly contributed additional metals and sulfur during chalcopyrite deposition. This magmatic input also explains the unusually high delta 66Zn values of chalcopyrite relative to sphalerite. Our findings demonstrate that direct magmatic contributions can play a significant role in mid-ocean ridge hydrothermal systems, a process likely substantially underestimated, particularly when hydrothermal fields are proximal to an enriched mantle source.

Phillipsite, a well-documented marine authigenic mineral, is widely recognized as a product of volcanic material alteration. Although phillipsite was historically considered a potential rare earth element and yttrium (REY) carrier in abyssal sediments, subsequent studies have shown that its REY content is generally insignificant, casting doubt on this interpretation. Nevertheless, the precise role of phillipsite in REY-enriched sedimentary systems remains incompletely understood. In this study, we combined morphological characterization and geochemical analyses to investigate phillipsite recovered from box cores collected from the eastern Pacific. Our results indicate that phillipsites occur as single grains, crossed-twinned grains and multiple-twinned grains, with iron (Fe)-manganese (Mn) oxides can be clearly observed along crystal margins and at intercrystalline junctions. Phillipsite consists predominantly of Si, Al, which account for 85-90 wt% of the total composition. The average REY content of phillipsite is 54 ppm, ruling out its role as a potential REY host phase in marine sediments. Through comprehensive comparisons of morphology, elemental ratios (Fe/Ti, Zr/Hf, Nb/Ta, Zr/Nb, and Zr/Ta), and REY distribution patterns, we demonstrate that nodule-hosted phillipsites may share a common origin with the sediment-hosted phillipsites. This indicates that nodule-hosted phillipsites was captured during nodule growth, distinctly differing from phillipsites formed endogenously within the nodules. The pronounced positive Ce anomaly, coupled with the positive correlations among REY, Fe, and Ce in phillipsites, indicates that Fe oxides, rather than phosphorus, serve as the predominant REY hosts within these mineral grains. Our study proposes that REY can hardly enter the phillipsite lattices due to the low cation exchange selectivity for REYs in phillipsite. During early diagenetic stage at the sediment-water interface (SWI), the porous structure of phillipsite exhibits strong adsorption capacity, facilitating the surface adherence and internal incorporation of Fe-Mn oxides and phosphorus. Such incorporation of Fe oxides and phosphorus significantly alters the REY distribution patterns of phillipsite, leading to a pronounced REY enrichment that significantly deviates from the mineral's inherent. Our study proposed that the abundance of phillipsites in abyssal sediments does not exhibit an absolute positive correlation with REY enrichment.

The Longqi-1 hydrothermal field (LQ-1 HF), the first active high-temperature vent field discovered along the ultraslow-spreading Southwest Indian Ridge (SWIR), provides a valuable setting for studying seafloor sulfide mineralisation. However, spatially resolved constraints on physicochemical gradients during chimney growth remain limited. This study presents mineralogical, trace element, and sulfur isotopic analyses of Cu-rich, Zn-Ferich, and Zn-rich chimneys from the LQ-1 HF, revealing systematic mineral zonation and metal enrichment across sulfide chimney walls. The Cu-rich chimney displays well-developed zonation, transitioning from anhydrite, pyrite, or marcasite with minor sphalerite at the exterior to massive chalcopyrite at the interior. The presence of bornite, covellite, and digenite suggests episodic seawater infiltration and oxidation during chimney evolution. Pyrite from outer zones is enriched in Mn, Mo, Tl, U, and V due to low-temperature precipitation from seawater mixing, while increasing Co in pyrite and Se in chalcopyrite toward the interior reflect higher temperatures and conditions favouring the stability of Cu-rich sulfides. In contrast, the Zn-Fe-rich and Zn-rich chimneys exhibit colloform to dendritic pyrite, marcasite, and sphalerite with minor chalcopyrite, consistent with lower-temperature, seawater-influenced precipitation conditions. Sulfur isotope gradients (delta 34S: 4.5-9.9 parts per thousand) reflect a mixed sulfur source from seawater sulfate and host rocks, with early-formed zones more seawater influenced. Elevated Sn and low Cd/Zn ratios are consistent with metal inputs from a heterogeneous lithological source, potentially involving ultramafic components and possibly facilitated by deep detachment faults. These results reveal the influence of host-rock composition, temperature, redox state, and seawater mixing on sulfide mineralisation at the detachment fault-controlled LQ-1 HF on the ultraslow-spreading SWIR.

Copper content in sulfides on mid-ocean ridges (MOR) is controlled by the variation and abundance of Cu-rich minerals, that sulfides in ultramafic-hosted hydrothermal fields commonly contain higher Cu, compared with those in mafic-hosted hydrothermal fields. Recently, a new ultramafic-hosted hydrothermal field at 49.28 degrees E was discovered on the ultraslow-spreading Southwest Indian Ridge. Sulfides collected show remarkably high Cu contents (averaged 26.88 wt%), greater than those of typical ultramafic-hosted hydrothermal fields (averaged 17.94 wt%). In this study, we integrate sulfide mineralogy, bulk geochemistry and sulfur-isotope analysis of typical Cu-rich and Fe-rich sulfide samples. Our findings indicate that the collected sulfides consist predominantly of primary chalcopyrite, bornite, pyrite and secondary copper minerals, with bulk compositions enriched in Cu (similar to 26.88 +/- 12.47 wt%, N = 19, 1SD), Au (similar to 5.1 +/- 5.66 ppm), Co (similar to 730.96 +/- 434.27 ppm), and Se (similar to 454.4 +/- 247.21 ppm), while being depleted in Ni (similar to 7.46 +/- 17.54 ppm). Additionally, these sulfides display relatively positive but uniform delta S-34 values, ranging from + 4.49 to + 6.9 parts per thousand (averaged + 5.49 parts per thousand; N = 42), except for one value of + 2.3 parts per thousand. These characteristics combined indicate deep ultramafic sourced metals, with restricted seawater entrainment (19-30%), and sulfide deposition occurring in a high-temperature (>300 degrees C), reducing, and relatively closed system. We propose that these conditions were resulted from the immature Yuhuang detachment fault, which promotes early serpentinization of ultramafic rocks and low permeability, distinguishing from matured detachment fault controlled hydrothermal systems. Our results constrain hydrothermal systems formed at the terminus of immature detachment faults and provide new insights into ore-forming processes in ultramafic-hosted systems along ultraslow-spreading ridges.

Seafloor massive sulfide (SMS) deposits formed by hydrothermal circulation generate measurable self-potential (SP) anomalies in seawater, providing an effective geophysical indicator of sulfide mineralization. In this study, a remotely operated vehicle (ROV)-borne SP survey was conducted at the Yuhuang hydrothermal field on the Southwest Indian Ridge to investigate the spatial distribution of SMS mineralization. The survey operated at a near-bottom altitude of approximately 10 m, substantially lower than that typically achieved by autonomous underwater vehicles (AUVs) or towed systems, enabling high-resolution data acquisition with improved signal quality. To efficiently discretize complex seafloor topography under irregular data coverage, an adaptive octree mesh was employed, enabling computationally efficient three-dimensional inversion over a large survey area and recovery of the subsurface source current density distribution. The inversion results resolve a main anomaly zone spatially correlated with known SMS mineralization, as well as an additional anomaly zone that was not resolved by previous surveys and suggests potential mineralization. Anomalies associated with known mineralization show good spatial agreement with independent near-bottom observations and drilling results. The results demonstrate that ROV-borne SP surveying combined with adaptive meshing and three-dimensional inversion provides a reliable approach for imaging SMS mineralization in deep-sea environments.

Abyssal hydrothermal vents are regarded as reactors for simple reduced carbon transforming into more complex forms of prebiotic organic chemistry. While the organic geochemical continuum and evolutionary transitions remain elusive, due to the intense hydrothermal alteration. We apply a metabolomics-inspired molecular fingerprinting strategy integrating mass spectral networking and hierarchical organization, to construct a molecular relatedness phylogenetic tree for vents from ultraslow-spreading Indian Ridge. Here we show that organic molecules from different vent fields and activity states share common molecular connection patterns. The observed progressive molecular evolution from alkanes through aromatics to complex heteroatom-bearing compounds reveals a systematic increase in molecular functionalization and polarity. This finding helps bridge the gap between simple reduced carbon and prebiotic molecular complexity, underscoring the role of hydrothermal systems in shaping life's essential feedstock on the primordial Earth. This framework may contribute to the search for life-markers on other astrobiological contexts, e.g., Mars, Enceladus, Callisto and Europa.

Aerosols are integral in supplying bio-essential trace elements (TEs) to the upper ocean. Given rapid environmental change, a comprehensive understanding of the current status and historical trends of TEs in marine aerosols is essential. This study conducted a 90-day investigation of aerosol TEs extending from the South China Sea (SCS) to the Indian Ocean (IO). The results show a decline in aerosol TE concentrations from the SCS to the Equatorial IO (EIO) and further to the Southern IO (SIO), with significant enrichment of most TEs observed throughout the regions. Historical comparisons indicate that present-day aerosol TE concentrations and enrichment factors generally exceed 1980s levels but remain substantially below their early-21st-century peak. This trend reflects dynamic shifts in aerosol sources over the IO, attributable to regional industrialization followed by the adoption of emission controls. Source apportionment indicated a predominantly mineral origin for Fe, Ti, and Mn, a mixed mineral-anthropogenic source for Ba and Co, and a dominantly anthropogenic origin for V, Cr, Cu, Zn, Ni, As, Se, Cd, Sn, and Pb. Statistical analysis identified potential sources for anthropogenic TEs, such as Zn, As, Se, Sn, and Pb, which were likely influenced by coal combustion. The evaluated bulk deposition fluxes of the TEs generally showed the following spatial distribution: SCS > EIO > SIO. Notably, wet deposition is dominant, except in the SIO. These findings provide valuable insights into the spatial variability, sources, fluxes, and historical trends of aerosol TEs over the IO. Plain Language Summary Aerosols influence the global environment and climate system through continuous supply of both bio-essential and toxic trace elements (TEs). This is particularly relevant for the Indian Ocean (IO), where ecosystems experience such micronutrient deposition while facing increasing exposure to emissions from Africa's rapid industrialization. However, comprehensive, basin-scale knowledge regarding the current characteristics and historical trends of aerosol TEs in this region remains insufficient. This study characterizes spatial variations in concentrations of multiple TEs across the South China Sea (SCS) and IO. Results reveal a distinct spatial gradient generally characterized by the highest TE concentrations and fluxes in the SCS, intermediate levels in the EIO, and the lowest values in the remote SIO. Anthropogenic sources contributed nearly 70% of V, 80% of Cr, and >90% of Cu, Zn, Ni, As, Se, Cd, Sn, and Pb. The main anthropogenic sources were identified as coal combustion, metal smelting, ship emissions, and vehicle exhaust. Historical trend analysis shows that enrichment levels of most anthropogenic TEs are now notably higher than in the 1980s, yet remain well below peaks recorded in the early 2000s, reflecting the dual effects of regional industrialization and environmental policies. This study advances our understanding of aerosol TE dynamics in the IO, informing future climate research and policies.

Detachment faults (DF) and non-transform discontinuities (NTD) usually couple together in the same segment, but how they interact is unclear. Here, we report high-precision geomorphologic and magnetic data collected by autonomous underwater vehicles over inter-coupled DFs and NTDs along the southwest Indian ridge, and recognize and analyze their structures to investigate their interaction. The results show that large scale mass wasting, resulting from gravitational collapse on the continuously raised detachment footwall at these inside corners, contributes to the NTD development. Conversely, discontinuity offset decreases when crustal accretion is dominated by magmatism. We reconstruct the evolutionary coupling process of DFs and NTDs and conduct 3D geodynamic simulations, which reveal that inside corner with focused stress plays an important role in both NTD development and hydrothermal activity. Additionally, this evolutionary coupling is also applicable to slow ridges, which would promote the study of mid-ocean ridge tectonic evolution and hydrothermal circulation.

Hydrothermal plumes play a critical role in chemical fluxes and element transport in the oceans. However, the impact on the sediments along mid-ocean ridge flanks is not well constrained. In this study, samples from three sediment cores (MC03/04/05) were analyzed for their geochemical records located at the Southwest Indian Ridge (SWIR) flanks over the past 40 ka. In addition to the dominant CaO content, these flank sediments show elevated concentrations of Fe, Mn, Cu, Zn, and REEs with positive Y anomalies. We also constructed two geochemical diagrams (Cu/Zn-Mn/Fe-REE/Fe and REE/Fe vs. Mn/Fe) to identify hydrothermal plume inputs. Based on these results, we revealed four distal plume events at 32-30 ka (MC04), 16-14 ka (MC05), 10-8 ka (MC05), and 7.5-6.5 ka (MC03). Furthermore, cluster analysis indicates that these plume events originated from the Yuhuang Hydrothermal Field (YHF), and they correspond temporally to periods of sulfide formation within the field. Finally, we propose that the YHF plume dispersion was coupled with the Agulhas Return Current (ARC) migration, resulting in the following processes: (1) 32-30 ka southward ARC transported plume material to MC04; (2) 16-14 ka and 10-8 ka northward shifts deposited plume fallout at MC05; (3) 7.5-6.5 ka southward ARC movement led to MC03 deposition. Our findings reveal metal (Fe, Mn, REE) transport mechanisms from the SWIR axial zones to distal flanks, highlighting plume-ARC interactions over millennial timescales.

Mid-ocean ridges, seamounts, and back-arc basins are focal points for deep-sea research due to their abundant mineral and biological resources. Unlike the sediment-covered deep-sea plains, the above areas have complex topography due to frequent geological activity, which has greatly constrained the accuracy of seafloor classification using shipborne underwater acoustic remote sensing. With the development of autonomous underwater vehicles (AUVs), near range measurements become feasible. Here, we present a method for fusing acoustic and magnetic AUV data on a meter scale, thereby providing evidence for improved seafloor classification. First, a space scale normalized model was built for obtaining high spatial resolution seafloor magnetic anomalies. In the second step, nine features were extracted from the acoustic backscatter mosaic, the bathymetry, and the seafloor magnetic anomaly. Finally, deep neural network (DNN) models were built for training, testing, and classification. To evaluate the classification performance of the model, the method was applied to the survey of the Chinese contract area for polymetallic sulfide exploration on the Southwest Indian Ridge (SWIR) and validated by field data (seafloor video). The integration of acoustic and magnetic data, as opposed to using single acoustic data, improved the overall classification accuracy and Kappa coefficient of DNN for basalts, breccias, and sediment by 6.4% and 0.096, respectively. The experimental results show that the method can fully mine the acoustic and magnetic properties of the seafloor, effectively respond to the challenges of seafloor classification presented by the deep-sea complex environment, and provide a fresh idea for the research of near-bottom high-precision seafloor classification methods.

The mineralization process below the surface of the seafloor in a hydrothermal field has an important influence on the distribution and enrichment of elements. The Duanqiao hydrothermal field (DHF) is located on the new axial volcanic ridge of the ultraslow-spreading Southwest Indian Ridge. Owing to the limited surface sulfide samples, the metallogenic processes occurring below the seafloor surface such as the element enrichment mechanism and the temporal evolution of the sulfide deposits remain unclear. In this study, we conducted mineral texture, geochemical, 230Th/U dating, and laser ablation inductively coupled plasma mass spectrometer analyses of a drill core containing shallow sulfide deposits to study their evolution process. The results revealed that pyrite is enriched in Mn, Co, As, Mo, Ag, Cd, Sb, Tl, and Pb, chalcopyrite is characterized by high concentrations of Se, Sn, In, As, Ag and Pb, and sphalerite is enriched in Co, Ga, Ge, As, Ag, Cd, Sb, and Pb. The 230Th/U dating data suggested five different mineralization periods during 4,552–2,297 years. Apart from the top and bottom, the core exhibited obvious characteristics of gradual accumulation of mineralization. Results revealed that the variations in the elemental contents of different layers and different types of pyrite were controlled by the interaction of seawater and hydrothermal fluids within the sulfide mound over five different mineralization periods. Compared with other hydrothermal fields on other mid-ocean ridges, DHF pyrite is generally enriched in Zn, Pb, As, Ag, Cd, Mo, and Sb, which might reflect shallow subsurface mixing during different periods of hydrothermal activity.

Rock types of basement determine the magnetic signature of hydrothermal fields. Low magnetization zone (LMZ) is commonly observed at the basalt-hosted hydrothermal fields due to the fluid-rock interaction destroying the magnetic minerals inside basalt. We here report a near-seafloor magnetic survey conducted by the Autonomous Underwater Vehicle (AUV) over a basalt-hosted hydrothermal field on the East Pacific Rise (EPR). Inversed magnetization and Reduced-To-the-Pole (RTP) magnetic anomaly both show negative reduced magnetic signature centered on the hydrothermal field, reflecting enhanced demagnetization alteration process. Meanwhile, we delineate the range of the LMZ and compare it with the previous high-resolution near-seafloor magnetic studies on the fast-spread EPR, slow-spread Mid-Atlantic Ridge, and ultra-slow-spread Southwest Indian Ridge and Mohns Ridge. The statistical result shows that the diameter of LMZ increases with the decreasing spreading rate, suggesting the stable tectonic environment and focused melt supply at slower spreading ridge favor the birth of larger hydrothermal field.

Off-axis inactive hydrothermal fields may harbor significant sulfide deposits. However, their distribution and abundance remain poorly constrained due to the challenges in their detection, as they lack associated hydrothermal plumes. Here, we present the first assessment on the abundance of off-axis inactive fields along four segments of the ultraslow-spreading Southwest Indian Ridge, based on a systematic sediment geochemistry survey. We found distinct dispersion patterns of hydrothermal Cu and Zn between magmatic- and detachment fault- controlled hydrothermal fields. These patterns are likely attributed to multiple factors, including variable physicochemical conditions of the hydrothermal plume,seafloor topography and bottom current. Up to 15 potential fields and their approximate locations were identified by the dispersion distance of hydrothermal Zn, Cu, and Fe. Among these fields, 8-14 are located off-axis, and 3-7 are likely newly identified inactive fields. The latter may have been active within the last 10 ka, with more than 60% spatially associated with detachment faults. The number of inactive fields is at least 2 times greater than previously reported for active fields within 40 km of the axial zone of the studied segments. As the studied sediments represent only the last 10 ka, significantly more buried inactive hydrothermal fields would be expected to be identified over longer time intervals. These findings significantly revise previous estimates of sulfide resources on ultraslow-spreading ridges.

The Agulhas Return Current (ARC) transports warm tropical and subtropical waters eastward into the southern Indian Ocean. It plays a crucial role in the oceanographic connections between the Indian, Atlantic, and Southern oceans. Modern oceanographic observations show that the latitudinal position of the ARC varies interannually. However, its historical positional variations remain poorly understood. Calcareous nannofossils can be a good indicator of ancient current migration, although their record in the Southwest Indian Ocean is poorly studied. This research aims to understand the characteristics and downcore variation of the calcareous nannofossil assemblages and trace the record of the ancient ARC. To achieve these goals, this study analyzed pelagic sediments of multicore 34IV-SWIR-S021MC03, 34IV-SWIR-S032MC04, and 34IV-SWIR-S040MC05 from the Southwest Indian Ocean. A total of 13 nannofossil species have been identified. The assemblages belong to the subtropical convergence zone regime. They are characterized by warm and cold water species, dominated by Emiliania huxleyi, Calcidiscus leptoporus, Gephyrocapsa muellerae, and Florisphaera profunda. According to the AMS14C age model and phytoplankton ecological signatures, this study establishes a calcareous nannofossil indicator to trace the migration of the ancient ARC during the last 40 kyr. The result shows three periods of migration: 40–22 kyr, the ancient ARC was in the far north and was moving southward; 22–14 kyr, a transitional period, the ancient ARC was moving northward; 14–3 kyr, the ARC was moving southward. This further suggests that the migration of the ancient ARC is more complex than the two recognized phases, and there were essential turning points around the last glacial maximum period. It also acknowledges that the ancient ARC is sensitive to interglacial periods and can be influenced simultaneously by the Southern Hemisphere monsoon and westerly winds.

The Indian Ocean ridges are shaped like the Greek letter lambda (i.e., lambda), and are up to approximately 18,000 km in length with various full spreading rates (<12-80 mm/yr) including the Carlsberg, Central, Southeast, and Southwest Indian Ridges. To date, in total of 15 active hydrothermal fields have been reported at these ridges with varying intensities of activity, but the distribution and morphology of their sulfide structures, which are formed by the venting of hot fluid in cold seawater, have not been well studied. In this paper, we review the published literature and compile descriptions of sulfide structure morphology in the active hydrothermal fields of Indian Ocean ridges by combining relevant video and images. These hydrothermal fields are hosted by ultramafic rocks, basalts, or both, but the host rock is not the sole factor controlling the morphology of sulfide structures. Some hydrothermal fields contain sulfide structures sharing similar features despite different host rocks. In addition, some hydrothermal fields have large sulfide structures indicating a relatively stable tectonic environment while others only have small and short structures indicating a weak supply of materials. Nevertheless, these characteristics alone are not sufficient to demonstrate significant differences in morphology between the sulfide structures in the Indian Ocean and at the slow-spreading Mid-Atlantic Ridge. The Longqi-1 field on the Southwest Indian Ridge is unique for hosting large flanges on sulfide edifices, which contrasts with most hydrothermal fields particularly in sediment-starved areas. Regardless of the level of activity, a long-term locally stable tectonic setting and a continuous heat supply are necessary for the formation of large sulfide structures. The various morphologies in these hydrothermal fields do not correspond strictly to the tectonic settings they're located, and some local conditions such as the various permeability of the subseafloor crust could be more directly influencing the morphology of the hydrothermal structures. This review can aid in evaluating Indian Ocean ridges for mineral resources and enhance understanding of the formation of hydrothermal fields on the seafloor.