Channel piracy on the lower Bengal Fan

Differences in morphology between the most recently active valley and older valleys suggest that channel piracy occurred on the lower Bengal Fan. Cutoff of two older valleys took place in the late Wisconsinan fan lobe between Sri Lanka and the 85°E Ridge at about 5°N and 83°E.     

An Interpretation of the Seafloor Spreading History of the West Enderby Basin between Initial Breakup of Gondwana and Anomaly C34

The seafloor spreading evolution in the Southern Indian Ocean is key to understanding the initial breakup of Gondwana. We summarize the structural lineaments deduced from the GEOSAT 10 Hz sampled raw altimetry data as well as satellite derived gravity anomaly map and the magnetic anomaly lineation trends from vector magnetic anomalies in the West Enderby Basin, the Southern Indian Ocean. The gravity anomaly maps by both Sandwell and Smith 1997, J. Geophys. Res. 102, 10039–10054 and 10 Hz raw altimeter data show almost the same general trends. However, curved structural trends, which turn from NNW–SSE in the south to NNE–SSW in the north, are detected only from gravity anomaly maps by 10 Hz raw altimeter data just to the east of Gunnerus Ridge. NNE–SSW structural trends and magnetic anomaly lineation trends that are perpendicular to them are observed between the Gunnerus Ridge and the Conrad Rise. To the west of Gunnerus Ridge, structural elements trend NNE–SSW and magnetic polarity changes are normal to them. In contrast, almost NNW–SSE structural trends and ENE–WSW magnetic polarity reversal strikes are dominant to the east of Gunnerus Ridge. Curved structural trends, which turn from WNW–ESE direction in the south to NNE–SSW direction in the west, and magnetic polarity reversal strikes that are almost perpendicular to them are observed just south of Conrad Rise. The magnetic polarity reversals may be parts of the Mesozoic magnetic anomaly sequence that formed along side of the structural lineaments before the long Cretaceous normal polarity superchron. Curved structural trends, detected only from gravity anomaly maps by 10 Hz raw altimeter data, most likely indicate slight changes in spreading direction from an initial NNW–SSE direction to NNE–SSW. Our results also suggest that these curved structural trends are fracture zones that formed during initial breakup of Gondwana.     

Geoid height versus topography of the Northern Ninetyeast Ridge: implications on crustal compensation

In this paper we focused on understanding the isostatic compensation of the Ninetyeast Ridge in the overall context of the Bay of Bengal oceanic lithosphere and the interaction of the ridge system with the north Andaman subduction zone from north of 7–18°N. This region is characterized by the initial interaction of the Kerguelen hotspot with the Bay of Bengal oceanic lithosphere. We used satellite altimeter-derived marine geoid, as it should comprehensively reflect the compensations caused by large spatial wavelength dominated deeper anomaly sources in a hotspot affected lithospheric load like the Ninetyeast Ridge. Our analyses of the geoid-to-topography ratio (GTR), residual geoid, gravity-to-topographic kernel and upward continuation of anomalies show the existence of two different types of source compensation bodies beneath the northern (12–18°N) and southern (7–12°N) Ninetyeast Ridge. In the northern region, the geoid to topography ratio varies from 0.63 ± 0.05 to 0.44 ± 0.03, while in the southern region it ranges from 1.34 ± 0.09 to 1.31 ± 0.07 which resulted in a north to south increase in the apparent compensation depth from ~9 to 28 km. The presence of a shallow Moho, low GTR, broader gravity to topography kernel and the absence of a ridge anomaly from the mantle density dominated upward continued anomaly at z = 300 km indicates that at the northern segment the underplated low density crustal melt is the dominant isostatic compensating body. However, at the southern ridge segment the high GTR, strong gravity-to-topography kernel and the subsistence of the anomaly at long wavelengths, even at z = 300 km represents the existence of large volumes of hotspot related underplated dense material as the source of compensation. The proximity of the dense source compensating body of the southern Ninetyeast Ridge to the Andaman subduction zone affected the regional mantle driven density gradient flow, as observed from the z = 300 km continued gravity anomaly. The existence of a southern Ninetyeast Ridge in such a transpressional regime has caused the formation of a forearc sliver at its eastern flank, which is a major crustal deformational structure developed as a result of ridge-trench collision.     

Magnetic studies in the northern Bay of Bengal

Total magnetic intensity and bathymetric surveys were carried out in the northern Bay of Bengal between 6° to 11° 45 N latitudes and east of 84° to 93° 30 E longitudes. The hitherto known 85° E Ridge is characterised as a subsurface feature by a large amplitude, positive magnetic anomaly surrounded by Mesozoic crust. A newly identified NE to NNESSW trending magnetic anomaly between 7° N, 87° 30 E and 10° 30 N, 89–90° E may be one of the unidentified Mesozoic lineations in the northern Bay of Bengal. The Ninetyeast Ridge is not associated with any recognizable magnetic anomaly. The Sunda Trough to the east of the Ninetyeast Ridge is characterised by a positive magnetic anomaly. A combined interpretation, using Werner deconvolution and analytical signal methods, yields basement depths ~ 10 km below sea level. These depths are in agreement with the seismic results of Curray (1991).Deceased 24 December 1991     

Spreading rates,rift propagation,and fracture zone offset histories during the past 5 my on the Mid-Atlantic Ridge; 25°–27°30′ S and 31°–34°30′ S

The southern Mid-Atlantic Ridge (MAR) is spreading at rates (34–38 mm yr⁻¹) that fall within a transitional range between those which characterize slow and intermediate spreading center morphology. To further our understanding of crustal accretion at these transitional spreading rates, we have carried out analysis of magnetic anomaly data from two detailed SeaBeam surveys of the MAR between 25°–27°30′S and 31°–34°30′S. Within these areas, the MAR is subdivided into 9 ridge segments bounded by large- and short-offset discontinuities of the ridge axis. From two-dimensional Fourier inversions of the magnetic anomaly data we establish the history of spreading within each ridge segment for the past 5 my and the evolution of the bounding ridge-axis discontinuities. We see evidence for the initiation and diminishment of small-offset discontinuities, and for the transition of rigid large-offset transform faults to less stable short-offset features. Individual ridge segments display independent spreading histories in terms of both the sense and amount of asymmetric spreading within each which have given rise to changes through time in the lengths of bounding ridge-axis discontinuities. Over the past 3–5 my, the short-offset discontinuities within the area have lengthened/shortened by approximately the same amount (∼ 10 km). During this same time period, larger-offset transform faults have remained comparatively constant in length. A shift in plate motion at anomaly 3 time may have given rise to change in the length of short-offset second-order discontinuities. However, the pattern of lengthening/shortening short-offset discontinuities we see is not simply related to the geometry of the plate boundary in these regions which precludes a simply relationship between plate motion changes and response at the plate boundary. We document a case of rapid (minimum 60 mm yr⁻¹) small-scale rift propagation, occurring between 2.5 and 1.8 my, associated with transition of the Moore transform fault to an oblique-trending ridge-axis discontinuity. Propagation across the Moore discontinuity and similar propagation within the 31°–34°30’S area may be associated with the reduced age contrast in lithosphere across second-order discontinuities. Total opening rates within our northern survey area decreased from anomaly 4′ to 2 time and rates within both areas have increased since the Jaramillo. Total opening rates measured for anomaly intervals differ along the plate boundary significantly, more than expected with changing distance to the pole of rotation. These differences imply a degree of short-term non-rigid plate behaviour which may be associated with ridge segments acting as independent spreading cells. Magnetic polarity transition widths from our inversion studies may be used to infer a zone of crustal accretion which is 3–6 km wide, within the inner floor of the rift valley. A systematic increase of transition width with age would be expected if deeper crustal sources dominate the magnetic signal in older crust but this is not observed. We present results from three-dimensional analysis of magnetic anomaly data which show magnetization highs located at the intersection of the MAR with both large- and short-offset discontinuities. Within the central anomaly the highs exceed 15 A m⁻¹ compared with a background of approximately 8–10 A m⁻¹ and they persist for at least 2.5 my. The highs may be caused by eruption of fractionated strongly magnetized basalts at ridge-axis discontinuities with both large and small offsets.     

赤道东印度洋和孟加拉湾障碍层厚度的年际变化及其影响机制

Interannual variability(IAV) in the barrier layer thickness(BLT) and forcing mechanisms in the eastern equatorial Indian Ocean(EEIO) and Bay of Bengal(BoB) are examined using monthly Argo data sets during 2002–2017. The BLT during November–January(NDJ) in the EEIO shows strong IAV, which is associated with the Indian Ocean dipole mode(IOD), with the IOD leading the BLT by two months. During the negative IOD phase, the westerly wind anomalies driving the downwelling Kelvin waves increase the isothermal layer depth(ILD). Moreover, the variability in the mixed layer depth(MLD) is complex. Affected by the Wyrtki jet, the MLD presents negative anomalies west of 85°E and strong positive anomalies between 85°E and 93°E. Therefore, the BLT shows positive anomalies except between 86°E and 92°E in the EEIO. Additionally, the IAV in the BLT during December–February(DJF) in the BoB is also investigated. In the eastern and northeastern BoB, the IAV in the BLT is remotely forced by equatorial zonal wind stress anomalies associated with the El Ni?o-Southern Oscillation(ENSO). In the western BoB, the regional surface wind forcing-related ENSO modulates the BLT variations.     

Delineating the northern part of the Socotra Basin, offshore Korea, using marine magnetics

A marine magnetic survey was carried out in and around the northern part of Socotra Basin, offshore Korea (31°42′32″–32°46′29″N and 123°56′26″–125°49′16″E), in order to better delineate its northern and eastern boundaries. Analyses of the observed magnetic field and estimation of the basement depth were used to assess these boundaries. The power spectrum and the three-dimensional analytical signal methods were used for depth estimation and to reconstruct basement configuration. Estimated depths resulting from the power spectrum method range from 1.5 to 6.0 km for deep sources (basement troughs), and from 0.3 to 1.7 km for shallower sources (basement peaks). An isopach map shows that the sedimentary sequence varies from 1.4 to 6.0 km in thickness. Estimated depths from the analytic signal method fluctuate in the range 1.2–6 km. The results of the observed field analysis and depth estimation indicate good agreement with the formerly proposed eastern boundary but disagreement with the northern boundary. The findings suggest either an extension of the Socotra Basin or the existence of other sub-basins possibly interconnected with the study area.     

Structural Configuration of Mahanadi Offshore Basin,India: An Aeromagnetic Study

Aeromagnetic data collected over the Offshore Mahanadi Basin along the Eastern margin of India display high amplitude magnetic anomalies. The presence of a Cretaceous volcanic sequence masks the seismic response from the underlying basement and results in poor quality seismic data. In this study spectral analysis of the aeromagnetic data collected over this part of the Offshore Mahanadi Basin was carried out. Results of this analysis indicate the presence of a high density, highvelocity (6.45 km/s) mafic layer within the crystalline basement varying from 4–6 km depth. This intra-basement layer seems to have been affected by a number of lineaments, which have played a role in the evolution of the Mahanadi Offshore Basin. The western part of the offshore basin is affected by the volcanism related to the 85°E Ridge, whereas the intense anomaly band (900 nT) offshore Puri, Konark and Paradip is interpreted as a combined effect of crystalline Precambrian basement overlain (i) by Cretaceous volcanic rocks of variable thickness (25–860 m) and (ii) by a mafic layer within the basement.     

Interannual SST variability in the Japan/East Sea and relationship with environmental variables

Interannual variability of the Japan/East Sea (JES) sea surface temperature (SST) is investigated from the reconstructed NOAA/AVHRR Oceans Pathfinder best SST data (1985–2002) using the complex empirical function (CEOF) analysis. The iterative empirical function analysis is used for the SST data reconstruction. The first two leading CEOFs account for 86.0% of total variance with 66.4% for the first mode and 19.6% for the second mode. The first CEOF mode represents a standing oscillation and a maximum belt in the central JES. There are two near-7-year events and one 2–3-year event during the period of 1985–2002. The first mode oscillates by adjacent atmospheric systems such as the Aleutian Low, the North Pacific High, the Siberian High, and the East Asian jet stream. Positive correlation in a zonal belt between the first mode JES SST anomaly and the background surface air temperature/SST anomaly reveals intensive ocean-atmosphere interaction near the Polar Front in the North Pacific. The second CEOF mode represents two features: standing oscillation and propagating signal. The standing oscillation occurs in the northern (north of 44°N) and southern (south of 39°N and west of 136°E) JES with around 180° phase difference. A weak southwestward propagating signal is detected between the two regions. The eastward propagating signal is detected from the East Korean Bay to near 135°E. The second mode contains 4–5-year periodicity before 1998 and 2–3-year periodicity thereafter. It is associated with the Arctic Oscillation, which leads it by 1–5-year. Furthermore, a strong correlation with the background surface air temperature/SST anomaly is detected in the tropical to subtropical western Pacific.     

Internal structure of the 85°E ridge,Bay of Bengal: Evidence for multiphase volcanism

The 85°E Ridge, located in the Bay of Bengal of the northeastern Indian Ocean is an enigmatic geological feature as it possesses unusual geophysical signatures. The ridge's internal structure and mode of eruptions are unknown due to lack of deep seismic reflection and borehole data control. Here, we analyze 10 km of long-streamer seismic reflection data to unravel the ridge's internal structure, and thereby to enhance the understanding of how the ridge was originated and grew over a geologic time. Seismic facies analysis reveals the ridge structure consisting of volcanic vent and several stratigraphic units including packs of prograding clinoforms. The clinoform sequences are interpreted as volcanic successions, and led to the formation of lava-delta fronts. Interpreted features of lava-fed deltas and intervening erosional surfaces, and mass flows along ridge flanks suggest that the 85°E Ridge is a volcanic construct, and was built by both subaqueous and multiphase sub-marine volcanism during the Late Cretaceous (approximately from 85 to 80 Ma). At later time, from Oligocene-Miocene (∼23 Ma) onwards the ridge was buried under the thick sediments of the Bengal Fan system.     

Morpho-sedimentary evidence for a canyon�Cchannel�Ctrench interconnection along the Taiwan�CLuzon plate margin, South China Sea

Examining bathymetric and seismic reflection data collected from the deep-sea region between Taiwan and Luzon in 2006 and 2008, we identified a connection between a submarine canyon, a deep-sea channel, and an oceanic trench in the northern South China Sea. The seafloor of the South China Sea north of 21°N is characterized by two broad slopes: the South China Sea Slope to the west, and the Kaoping Slope to the east, intersected by the prominent Penghu Canyon. This negative relief axis parallels the strike of the Taiwan orogen, extends downslope in an approx. N–S direction, and eventually merges with the northern Manila Trench via a hitherto unidentified channel. The discovery of this channel is pivotal, because it allows connecting the Penghu Canyon to the Manila Trench. This channel is 80 km long and 20–30 km wide, with water depths of 3,500–4,000 m. The progressive morphological changes recorded in the aligned canyon, channel, and trench suggest that they represent three distinct segments of the same longitudinal sediment conduit from southern Taiwan to the northern Manila Trench. Major sediment input would be via the Kaoping Canyon and Kaoping Slope, with a smaller contribution from the South China Sea Slope. We determined the northern end of the Manila Trench to be located at about 20°15′N, 120°15′E, where sediment accumulation has produced a bathymetry shallower than 4,000 m, thereby abruptly terminating the trench morphology. Comparison with existing data reveals a similarity with, for example, the Papua New Guinea–Solomon Sea Plate convergent zone, another modern analog of a mountain source to oceanic sink longitudinal sediment transport system comprising canyon–channel–trench interconnections.     

The role of meso-scale eddies in mixed layer deepening and mode water formation in the western North Pacific

Distributions of mixed layer depths around the centers of anti-cyclonic and cyclonic eddies in the North Pacific Ocean were composited by using satellite-derived sea surface height anomaly data and Argo profiling float data. The composite distributions showed that in late winter, deeper mixed layers were more (less) frequently observed inside the cores of the anti-cyclonic (cyclonic) eddies than outside. This relationship was the clearest in the region of 140°E–160°W and 35°N–40°N, where the temperature and salinity of the deep mixed layers were similar to those of the lighter variety of central mode water (L-CMW). A simple one-dimensional bulk mixed layer model showed that both strong sea-surface heat and momentum fluxes and weak preexisting stratification contributed to formation of the deep mixed layer. These conditions were associated with the anti-cyclonic eddies, suggesting that these eddies are important in the formation of mode waters, particularly L-CMW.     

Seismic structure and tectonics of the Shackleton Fracture Zone (Drake Passage,Scotia Sea)

The structural framework of the southern part of the Shackleton Fracture Zone has been investigated through the analysis of a 130-km-long multichannel seismic reflection profile acquired orthogonally to the fracture zone near 60° S. The Shackleton Fracture Zone is a 800-km-long, mostly rectilinear and pronounced bathymetric lineation joining the westernmost South Scotia Ridge to southern South America south of Cape Horn, separating the western Scotia Sea plate from the Antarctic plate. Conventional processing applied to the seismic data outlines the main structures of the Shackleton Fracture Zone, but only the use of enhanced techniques, such as accurate velocity analyses and pre-stack depth migration, provides a good definition of the acoustic basement and the architecture of the sedimentary sequences. In particular, a strong and mostly continuous reflector found at about 8.0 s two-way traveltime is very clear across the entire section and is interpreted as the Moho discontinuity. Data show a complex system of troughs developed along the eastern flank of the crustal ridge, containing tilted and rotated blocks, and the presence of a prominent listric normal fault developed within the oceanic crust. Positive flower structures developed within the oceanic basement indicate strike-slip tectonism and partial reactivation of pre-existing faults. Present-day tectonic activity is found mostly in correspondence to the relief, whereas fault-induced deformation is negligible across the entire trough system. This indicates that the E–W-directed stress regime present in the Drake Passage region is mainly dissipated along a narrow zone within the Shackleton Ridge axis. A reappraisal of all available magnetic anomaly identifications in the western Scotia Sea and in the former Phoenix plate, in conjunction with new magnetic profiles acquired to the east of the Shackleton Fracture Zone off the Tierra del Fuego continental margin, has allowed us to propose a simple reconstruction of Shackleton Fracture Zone development in the general context of the Drake Passage opening.     

东海营养盐结构的时空分布及其对浮游植物的限制

本文根据2013年东海海域(120°—128°E、25°—33°N)春、夏、秋、冬的4个航次调查资料,分析了营养盐结构的时空分布并探讨其对浮游植物生长限制的情况。结果表明:(1)东海DIN(无机氮)/P(磷)、Si(硅)/DIN及Si/P比值受各种水团及浮游植物生长周期的影响较为明显,长江冲淡水与沿岸水的交汇作用控制着全航次DIN/P比值,基本呈近岸高、远海低的分布规律,而Si/DIN比值的分布则相反。春、夏季Si/P高值区主要分布在近岸,而秋、冬季则开始由中部海域向远海扩展。(2)研究海域浮游植物的生长主要受到N和P的限制,126°E以西的近岸及中部海域以P限制为主,而126°E以东的黑潮区受N限制;在季节变化上又以夏季受到营养盐的限制最明显。(3)与2001—2010年同期历史资料相比,2013年夏季航次受P限制站位数量比过往10年有所增加,限制范围由28°—32°N、123°E以西的长江口及浙北沿岸海域扩展到了126°E以西的东海中部及近岸水域;受N限制站位基本集中在126°—127°E以东黑潮区海域,但空间范围比十年前增大。     

Geophysical investigations over a segment of the Central Indian Ridge, Indian Ocean

 Swath bathymetric, gravity, and magnetic studies were carried out over a 55 km long segment of the Central Indian Ridge. The ridge is characterized by 12 to 15 km wide rift valley bounded by steep walls and prominent volcanic constructional ridges on either side of the central rift valley. A transform fault at 7°45′S displaces the ridge axis. A mantle Bouguer anomaly low of −14 mGals and shallowing of rift valley over the middle of the ridge segment indicate along axis crustal thickness variations. A poorly developed neovolcanic zone on the inner rift valley floor indicate dominance of tectonic extension. The off-axis volcanic ridgs suggest enhanced magmatic activity during the recent past. Received: 24 May 1996 / Rivision received: 13 January 1997     

Influence of ridges on hydrographic parameters in the Southwest Indian Ocean

The objective of the paper is to use the data collected along two meridional sections (45° E and 57°30′ E) during the austral summer (January–March) 2004 to understand the influence of seabed topography across the Madagascar and Southwest Indian Ridges on hydrographic parameters. The study was supplemented by World Ocean Circulation Experiment (WOCE) Conductivity-Temperature-Depth data collected during February–March 1996 along 30° E, as well as Levitus climatology. A southward shift of 2° latitude (between 45° E and 57°30′ E) was recorded for the two predominant frontal structures, i.e., the Agulhas Return Front and Southern Subtropical Front, which is attributed to the influence of seabed topography on hydrographic parameters. No significant spatial variation of these fronts was noted between the 30° E and 45° E meridional sections. Between latitudes 31° S and 42° S, the temperature and salinity structures show deepening over the ridges. The Antarctic Circumpolar Current core was detected between 40°15′ S and 43° S.     

Formation Process of North Pacific Intermediate Water Revealed by Profiling Floats Set to Drift on 26.7 σθ Isopycnal Surface

Six newly developed floats, which were set to drift on the 26.7 σ_θ isopycnal surface and to profile temperature, salinity and pressure above 1000 dbar once a week, were deployed in the Oyashio and Kuroshio Extension (KE) in order to examine the circulation, formation site and time scale of newly formed North Pacific Intermediate Water (NPIW). The floats were deployed in February or May 2001, and the data from their deployments to December 2002 are analyzed here. Four of the six floats were deployed near the KE axis at around the first meander crest, and they moved eastward to 157°E–176°W at latitudes of 30°N–45°N. The other two floats deployed in the Oyashio water with low-potential vorticity near the south coast of Hokkaido moved southward to reach the KE front and then moved eastward to the same region as the first four floats. The temperature and salinity at 26.7 σ_θ measured by the profiling floats indicate that the source waters of NPIW, Oyashio and Kuroshio waters are drastically mixed and modified in the mixed water region west of 160°E. The floats were separated into the three paths east of 160°E between the Kuroshio Extension front and the north of Water-Mass front (nearly subarctic front). New NPIW is judged to be formed along these three paths since the vertical profiles of temperature and salinity are quite smooth, having a salinity minimum at about 26.7σ_θ along each path. Kuroshio-Oyashio isopycnal mixing ratios of the new NPIW are 7:3, 6:4 and 5:5 at 26.7σ_θ along the southern, middle and northern paths, respectively. Potential vorticity converges to about 14–15 × 10⁻¹¹ m⁻¹s⁻¹ along these paths. The time scale of new NPIW formation is estimated to be 1–1.5 years from the merger of Oyashio and Kuroshio waters to the formation of the new NPIW. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dissolved and labile particulate Zr,Hf, Nb,Ta, Mo and W in the western North Pacific Ocean

Dissolved and labile particulate Zr, Hf, Nb, Ta, Mo and W were determined at stations K1 (51°N, 165°E), K2 (47°N, 160°E), KNOT (44°N, 155°E) and 35N (35°N, 160°E) in the western North Pacific Ocean. A portion of seawater for dissolved species (D) was passed through a 0.2 μm Nuclepore filter and acidified to pH 2.2 with HCl and HF. A portion of seawater for acid-dissolvable species (AD) was acidified without filtration. Labile particulate (LP) species is defined as AD minus D, which represents a chemically labile fraction of particulate species. D-Zr, Hf and Ta increase with depth, Nb shows a slight depletion in surface water, whereas Mo and W have a conservative vertical profile. The concentration range of D-Zr, Hf, Nb, Ta and W is 31–275, 0.14–0.95, 4.0–7.2, 0.08–0.29 and 40–51 pmol kg⁻¹, respectively, whereas that of Mo is 97–105 nmol kg⁻¹. LP-species of Zr, Hf and Ta account for 10–14% of AD in average and increase up to 25% below 4000 m, whereas those for Mo and W are negligible. In contrast, LP-Nb shows maxima (up to 27%) in surface water. We also found that D-Zr/Hf, Nb/Ta and Mo/W mole ratios generally increase in the order continental crust < river water < coastal sea < open ocean.     

Habitat suitability index of Chub mackerel (<Emphasis Type="Italic">Scomber japonicus</Emphasis>) from July to September in the East China Sea

The habitat quality of Chub mackerel (Scomber japonicus) in the East China Sea has been a subject of concern in the last 10 years due to large fluctuations in annual catches of this stock. For example, the Chinese light-purse seine fishery recorded 84000 tons in 1999 compared to 17000 tons in 2006. The fluctuations have been attributed to variability in habitat quality. The habitat suitability Index (HSI) has been widely used to describe fish habitat quality and in fishing ground forecasting. In this paper we use catch data and satellite derived environmental variables to determine habitat suitability indices for Chub mackerel during July to September in the East China Sea. More than 90% of the total catch was found to come from the areas with sea surface temperature of 28.0°–29.4°C, sea surface salinity of 33.6–34.2 psu, chlorophyll-a concentration of 0.15–0.50 mg/m³ and sea surface height anomaly of −0.1–1.1 m. Of the four conventional models of HSI, the Arithmetic Mean Model (AMM) was found to be most suitable according to Akaike Information Criterion analysis. Based on the estimation of AMM in 2004, the monthly HSIs in the waters of 123°–125°E and 27°30′–28°00′ N were more than 0.6 during July to September, which coincides with the catch distribution in the same time period. This implies that AMM can yield a reliable prediction of the Chub mackerel’s habitat in the East China Sea.