Classification of seamount morphology and its evaluating significance of ferromanganese crust in the central Pacific Ocean

Using the SeaBeam technology, the morphology of seamount and its relation to the formation of cobalt-rich crust in the central Pacific Ocean were surveyed during the cruise in 2003 for marine mineral resources. The result shows that seamounts can be divided morphologically into the spire seamount and the fiat topped seamount. These two types of seamount bear great differences in their landform, lithology and cobalt-rich crust. On the upper portion of the fiat topped seamount, the fiat top and the sharp escarpments are unfavorable to the growth of crust, and, consequently, the crusts here are mostly laminar or gravelly, their thicknesses generally show great variations, and the consecutive ore body often develops in its deep water region. On the spire topped seamount, however, the fiat area is small, and its gradient is constant without large variation from the top to the bottom. This favors the growth of cobalt-rich crust and often leads to consecutive tabular ore body of medium thickness, occurring on the spire topped seamount from the shallow water region to the deep water region. The cobalt-rich crust on the spire topped seamount is much better than that on the fiat topped seamount for the crust abundance, crust coverage and number of ore-occurrences within unit area. Furthermore, the crust on the spire topped seamount is rich in cobalt, nickel, manganese elements of high economic value. Because the crust with high quality ore often occurs in the shallow water region on the spire topped seamount, it can be mined and use more easily in the future.

Recognition of Ancient Oceanic Island in Paleo-Tethys,Western Yunnan

A volcano-platform carbonate sequence ,from Carboniferous to Permian , is widely trapped in the deep water deposits in Changning- Menglian belt .Three components can be roughly recognized in ascending order as :the lava .the volcaniclastic and carbonate rocks .In most cases, the sequence is incomplete due to faulting resulted from the strong orogenic compression. But (he stratigraphic succession is continuous except for the two interruptions of paleokarsts . which extended from middle Late Carboniferous to Late Permian and from late Early Permian to Late Permian respectively .A preliminary study indicates that the stratigraphy, petrology , sedimentation , vokanism geochemistry and fossils in the sequence are quite similar to mat in modern and ancient oceanic islands and there may be the relics of ancient oceanic islands in the paleo-Tethys .The differences among these sequences probably suggest a complex configuration of the islands or island chain These islands were formed under infra oceanic environments of the paleo-Tethys ,far from continent and accreted to Simao continental margin in Late Permian .The occurrence of large number of ancient oceanic islands in orogenic belts , including the paleo Tethys, Cordillera , etc ..suggests mat some ancient oceans .such as the paleo Tethys and proto-Pacific ,were full of archipelagoes as their modem counterparts . It is possible that more oceanic islands will be recongnized when sufficient research is done in orogenic belts over the world .

The first record of Ophioleila elegans (Echinodermata:Ophiuroidea) from a deep-sea seamount in the Northwest Pacific Ocean

The rare ophiuroid species, Ophioleila elegans, was collected by the submersible Jiaolongfrom 1 660 m depth on the Caiwei Guyot located in the Magellan Seamount Chain in the Northwest Pacific Ocean. This is the first published record of this species since the types were described from similar habitat off Hawaii. We provide more detailed morphologic characteristics of arm skeleton and a phylogenetic analysis based on CO 1 sequences. Both morphology and phylogeny results suggest that the genus Ophioleila is more closely related to Ophiactids than Hemieuryalids.

Physical oceanography of the Caroline M4 seamount in the tropical Western Pacific Ocean in summer 2017

Physical oceanography plays an important role in the formation of submarine sediments,and the distribution of nutriments and biocenoses in seamounts.The M4 seamount is located in the Caroline Island Ridge of the Western Pacific Ocean.The physical properties around M4 seamount are preliminarily analyzed based on the in-situ data obtained in summer 2017 in Caroline M4 seamount and open-sourced data.We found that the water in the upper 200 m is controlled by the westward North Equatorial Current(NEC),while the water between 300-1000 m is dominated by the eastward North Equatorial Undercurrent(NEUC).The current direction fluctuates significantly below 300 m at upstream stations.At the same depth of the lee sides,the current direction changes with the distance from seamount.These are likely caused by the obstacle of M4 seamount.The calculation results show that there is an anticyclonic cap above M4 seamount caused by tidal rectification.Tidal currents in M4 seamount are squeezed by the topography and amplified,and the amplified tidal currents play a dominant role in M4 seamount.First,the circulation system generated by the interaction of the amplified tidal current and M4 seamount drives the upward/downward movement of the isotherms.Secondly,the thickness of the surface turbulent layer is changed with the tidal phase.Thirdly,high turbulent diffusivities are found in the bottom of M4 seamount,and these are most likely attributed to the turbulent mixing induced by the mutual effect between semidiurnal tidal currents and steep bathymetry.This article of physical oceanography provides scientific basis for further analysis of the distribution of biological community and deposition mechanism in M4 seamount.

Control factors of DIC in the Y3 seamount waters of the Western Pacific Ocean

An investigation was carried out in the Y3 seamount area of the Western Pacific Ocean in December 2014,and the distribution of dissolved inorganic carbon(DIC)and its relationship with environmental factors in this area were explored.The results show that DIC concentration was higher in the adjacent waters of the Y3 seamount area,and the uplift of DIC isolines at the stations was close to the seamount.Meanwhile,interaction between the North Equatorial Current(NEC)and the Y3 seamount affected the DIC distribution,i.e.,the upwelling in the same direction of the NEC was obvious,resulting in a decreasing trend of average concentration of DIC in the 200 m water column from the top to the two sides in this direction but in the cross direction.The DIC concentration increased with the water depth increase,and its distribution was affected by various environmental factors.In the surface water,high temperature was a decisive factor for the decrease of the DIC concentration,but the photosynthesis of phytoplankton showing only a weak influence.In the North Pacific Tropic Water(NPTW),DIC production rate from organic matter decomposition was higher than that of DIC consumption by phytoplankton photosynthesis,leading to a continual increase of DIC.In the North Pacific Intermediate Water(NPIW),organic matter decomposition played a leading role in the increase of DIC.In the deep water,decomposition of organic matter weakened,and the dissolution of CaCO3 controlled the carbonate system,and DIC had the smallest variation range.

Planktonic ciliate trait structure variation over Yap,Mariana,and Caroline seamounts in the tropical Western Pacific Ocean

Trait structure is increasingly used in plankton ecology to understand diversity and biogeography.However,our knowledge of micro zooplankton(e.g.planktonic ciliates)trait structure and its variation with hydrography is limited.In this study,we analyzed planktonic ciliate trait structure in waters with different hydrography and deep Chlorophyll a maximum(DCM)layers over three seamounts:Yap,Mariana,and Caroline seamounts.Mariana seamount had a lower surface temperature than the Yap and Caroline seamounts.DCM layers over Mariana and Caroline seamounts were deeper than Yap seamount.There was a weak upwelling in upper 50 m around top of Mariana seamount.The ciliate distribution showed bimodal pattern(high abundance appeared in the surface and DCM layers)over three seamounts.At surface layer,the large size-fraction(>30μm)abundance proportion to aloricate ciliate over Yap seamount(44.4%)was higher than Mariana(32.8%)and Caroline(36.1%)seamounts.For tintinnid abundance proportion to total ciliate,Mariana(12.0%)and Caroline(11.5%)seamounts at about 100-m depth were higher than that of Yap seamount(6.4%).Vertically,tintinnid could be divided into 4 groups over the three seamounts.At30-m depth,group I(species occurring from surface to 100 m only)was dominant component over Yap and Caroline seamounts,while group IV(species occurring at every depth)changed into dominant component over Mariana seamount,the weak upwelling might be the reason.Salpingella faurei was the top dominant species,which corresponded to deeper DCM layers over Mariana and Caroline seamounts.Our results showed that the upwelling and the deeper DCM could influence the planktonic ciliate trait structure.

Triple oxygen isotope constraints on the origin of ocean island basalts

Understanding the origin of ocean island basalts(OIB) has important bearings on Earth's deep mantle.Although it is widely accepted that subducted oceanic crust, as a consequence of plate tectonics, contributes material to OIB's formation, its exact fraction in OIB's mantle source remains ambiguous largely due to uncertainties associated with existing geochemical proxies. Here we show, through theoretical calculation, that unlike many known proxies, triple oxygen isotope compositions(i.e.D^(17 )O) in olivine samples are not affected by crystallization and partial melting. This unique feature, therefore, allows olivine D^(17 )O values to identify subducted oceanic crusts in OIB's mantle source. Furthermore, the fractions of subducted ocean sediments and hydrothermally altered oceanic crust in OIB's mantle source can be quantified using their characteristic D^(17 )O values. Based on published D^(17 )O data, we estimated the fraction of subducted oceanic crust to be as high as 22.3% in certain OIB, but the affected region in the respective mantle plume is likely to be limited.

Low-temperature alteration of oceanic island basalts and their contribution to transition metal circulation of the ocean

The major elements, rare earth elements （REE） and trace elements of four basalt samples from central and western Pacific ferro- manganese crust provinces have been analyzed using chemical methods and ICP - MS, respectively. The results indicate that the samples have been extensively altered and that the contents of their major elements have changed significantly. However, the similarity of REE partition patterns and trace element contents of basalt samples to those of fresh oceanic island basalts （OIB） indicate that the basalt samples originated as OIB. Because of low-temperature alteration, the contents of A1203 , Fe203 , MnO, K20 and P205 increased, while MgO and FeO decreased. Active components, such as magnesium and iron, were leached from OIB resulting in the relative enrichment of SiO2. The leaching of active components can cause the relative enrichment of REE, while the precipitation of LREE-rich ferromanganese oxides in vesicles and fissures not only causes an increase of REE contents, but also induces ＂fractionation＂ of LREE and HREE. Based on the enrichment mechanism of REE contents, the theoretical quantities of precipitated ferromanganese oxides and the depleted quantities of active components are calculated ： the depleted quantities of active components for the unit mass of fresh basalts vary in the range of 0.15 ～ 0. 657, and the precipitated quantities of ferromanganese oxides for the unit mass of fresh basahs vary in the range of 0. 006 ～ 0. 042. Of the major elements, the two most depleted are iron, and magnesium, with 18.28% ～ 70.95% of iron and 44.50% ～ 93.94% of magnesium in the fresh basalts was leached out. Theoretical calculation and geochemistry results both indicate that low-temperature alteration of basalts can supply abundant amount of metals to seawater, and may play an important role in ocean metal circulation.

Oceanic Island Basalts within the West Junggar Ophiolitic Mélanges: Petrogenetic and Tectonic Implications

Recently, we focused on the Darbut and Karamay ophiolitic m41anges in West Junggar of the Central Asian Orogenic Belt （CAOB, SengOr et al., 1993; Windley et al., 2007; Xiao and Santosh, 2014）, and made much progress. This study was supported by the National Nature Science Foundation of China （No. 41303027） and Special Fund for Basic Scientific Research of Central Colleges Project （No. 2014G1271058）. The achievements are illustrated as follows.

Analysis of differences in nutrients chemistry in seamount seawaters in the Kocebu and M4 seamounts in Western Pacific Ocean

Comprehensive surveys were conducted in the Kocebu deep seamount and the M4 shallow seamount in the Western Pacific Ocean in March 2018 and May 2019,respectively.The distributions of nutrients in euphotic zone of the two seamount-areas were revealed,and the causative controlling factors were analyzed.Results show that the vertical distribution of nutrients in the two seamount-areas accorded with the general law of the oligotrophic ocean.The concentrations of NO_(3)-N,PO_(4)-P,and SiO_(3)-Si generally increased gradually with the increase of water depth,and they were extremely low in water layers within100 m.The area of high NO_(2)-N concentration well agreed with the Deep Chlorophyll Maximum Layer.On the other hand,the distribution of water masses and phytoplankton and hydrological conditions in the two seamount-areas were different,resulting in lower concentrations of NO_(3)-N,PO_(4)-P,and SiO_(3)-Si in the water layers below 100 m in the Kocebu seamount area than those in the M4 seamount area.In addition,NO_(2)-N was affected by the distribution of phytoplankton,and distributed mainly in the water layers of 150 and100 m.There was upwelling in the euphotic zone of M4 seamount area,causing accumulations of nutrients and phytoplankton around the seamount,forming a"seamount effect";however,no such an effect was found in Kocebu seamount area.Affected by the composition of biological community and the"seamount effect",the nitrogen limitation in the M4 seamount area was not significant,and the dissolved inorganic nitrogen(DIN):PO_(4)-P and SiO_(3)-Si:DIN were closer to the Redfield ratios.

Observation of physical oceanography at the Y3 seamount (Yap Arc) in winter 2014

Seamounts aff ect the surrounding physical oceanography and form unique dynamic processes.The infl uences of these processes on biological and sedimentary distributions are quite diff erent in seamount areas at diff erent depths.The Y3 seamount is located in the Yap Arc of the tropical Western Pacifi c Ocean.The water depth of its summit is~280 m.Based on fi eld data obtained in December 2014 and other open-access data,the physical oceanography around the Y3 seamount was preliminarily analyzed.The results show that the upper layer(0-150 m)was under the infl uence of the westward-fl owing North Equatorial Current(NEC),while the eastward-fl owing North Equatorial Undercurrent(NEUC)controlled the water between 200-800 m.The NEC was strong and steady,but the NEUC was disturbed by the Y3 seamount.The cold dome above the Y3 seamount was not caused by a Taylor cap or tidal rectifi cation but probably by upwelling during the survey time.Tidal currents were squeezed against topography and greatly amplifi ed in the Y3 seamount.The thicknesses of the surface turbulent layers were greatly infl uenced by the spring-neap tidal cycle.The turbulent diff usivities in the sea surface layer above the Y3 seamount were much larger than those in the open ocean.Calculations showed that the surface wind stress greatly aff ected the turbulent mixing in the surface layer of the Y3 seamount.The reciprocal action between the amplifi ed tidal currents and topography was the most likely cause of the turbulent mixing near the bottom of the Y3 seamount.This study can provide a scientifi c basis for further study of biological and depositional characteristics at the Y3 seamount.

Reaction between basaltic melt and orthopyroxene at 3.0–4.5 GPa:Implications for the evolution of ocean island basalts in the mantle

Interactions between basaltic melt and orthopyroxenite(Opx)were investigated to gain a better understanding of the consequences of the residence and transport of ocean island basalts(OIBs)within the mantle.The experiments were conducted using a DS-3600 six-anvil apparatus at 3.0–4.5 GPa and 1300–1450℃.The basaltic melt and Opx coexisted at local equilibrium at these pressures and temperatures;the initial melts dissolved Opx,which modified their chemical composition,and clinopyroxene(Cpx)precipitated with or without garnet(Grt).The trace-element contents of Grt,Cpx,and melt were measured and the mineral–melt distribution coefficients(D)of Cpx–melt and Grt–melt were calculated,which can be used to assess the distribution of trace elements between basalt and minerals in the mantle.Two types of reaction rim were found in the experimental products,Cpx,and Cpx+Grt;this result indicates that residual rocks within the mantle should be pyroxenite or garnet pyroxenite.Both rock types are found in mantle xenoliths from Hawaii,and the rare-earth-element(REE)pattern of Cpx in these mantle pyroxenites matches those of Cpx in the experimental reaction rims.Furthermore,residual melts in the experimental products plot in similar positions to Hawaiian high-SiO_(2)OIBs on major-element Harker diagrams,and their trace-element patterns show the signature of residual Grt,particularly in runs at1350℃ and 4.0–4.5 GPa.Trace-element concentrations of the experimental residual melts plot in similar positions to the Hawaiian OIBs on commonly used discrimination diagrams(Ti vs.Zr,Cr vs.Y,Cr vs.V,Zr/Y vs.Zr,and Ti/Y vs.Nb/Y).These results indicate that reaction between basaltic melt and pyroxenite might contribute to the generation of Hawaiian high-SiO2 OIBs and account for their chemical variability.

Geochemical characteristics of the oceanic islandtype volcanic rocks in the Chiang Mai zone,northern Thailand

The oceanic island volcanic rocks in the Chiang Mai zone, northern Thailand, are usually covered by Lower Carboniferous and Upper Permian shallow-water carbonate rocks, with the Hawaii rocks and potash trachybasalt being the main rock types. The alkaline series is dominant with sub-alkaline series occurring in few cases. The geochemical characteristics are described as follows: the major chemical compositions are characterized by high TiO2, high P2O5 and medium K2O; the rare-earth elements are characterized by right-inclined strong LREE-enrichment patterns; the trace element patterns are of the upward-bulging K-Ti enrichment type; multi-component plots falling within the fields of oceanic island basalts and alkali basalts, belonging to the oceanic island-type volcanic rocks, which are similar to the equivalents in Deqin and Gengma (the Changning-Menglian zone) of Yunnan Province, China.

Early Palaeozoic Evolution of the Zhen' an- Xichuan Block and the Small Qinling Multi-Island Ocean Basin

Based on studies of palaeogeography, palaeobiogeography, palaeomagnetism, geochemistry and volcanism, this paper proposes that the Zhen'an-Xichuan area was a small Early Palaeozoic block rifted away from South Qinling and suturing onto North Qinling earlier than the other parts of South Qinling. In the Early Palaeozoic Qinling was a small archipelagic ocean basin with 5 rows of islands including the Zhen'an-Xichuan block. The drifting of the Yangtze and North China plates and the islands between them in the same direction at different speeds caused their suturing process to be different from the classic plate collision, which is the major feature of the suturing of the multi-island Tethys ocean basin. This also explains the problem that the Caledonian collision did not result in orogeny in eastern Qinling.

Temporal dynamics of shallow subtidal meiobenthos from a beach in Tenerife (Canary Islands, northeast Atlantic Ocean)

A shallow subtidal （3 m deep） meiofaunal assemblage in Los Abrigos Bay, Tenerife, Canary Islands was sam- pled during May 2000-April 2001. The main aims were to （1） find temporal variations in meiofaunal assem- blage structure and overall abundance, as well as in the most abundant meiofaunal species throughout the study period, and （2） identify environmental variables （sedimentary composition, organic matter content, and total nitrogen） that better explain meiofaunal assemblage structure during the study year. The most abundant species were the nematodes Siphonolaimus sp. 2 and Catanema sp., which represented 46.2% of the overall meiofaunal abundances and varied significantly throughout the study duration. Overall meio- faunal abundance and the most abundant taxonomic groups （nematodes, copepods, and oligochaetes） showed significant temporal variations during the study period. Nematodes overwhelmingly dominated during the study period, ranging from 78% in May to 97.34% in February. Multivariate analyses showed seasonality in meiofaunal community structure during the study year, with the lowest abundances in May. Keywords： Meiofauna, assemblage structure, subtidal, Canary Islands, Atlantic Ocean

Petrogenesis and Tectonic Implications of Middle Ordovician Ocean Island Basalts from the Chagantaolegai Ophiolitic Mélange in Junggar,NW China

Seamount accretion is one of the most significant accretionary orogenic processes in the Central Asian Orogenic Belt,but there are few paleo-seamounts reported from and debate on the tectonic evolution of the Junggar Ocean still exists.In this study,we present geochronological,mineralogical,geochemical and isotopic data for basalts from the Chagantaolegai ophiolitic mélanges in Junggar.Zircon U-Pb dating on one basalt yielded a weighted mean^(206)Pb/^(238)U age of 469±7 Ma,which suggests that it formed in the Middle Ordovician.All rock samples belong to alkaline basalt and show similar geochemical characteristics,displaying high TiO_(2)(~3 wt%),(La/Yb)N(17.6–19.0),ΣREE(232–289 ppm)and enrichment in Nb and Ta,which implies an ocean island basalt(OIB)affinity.Based upon positiveεN d(t)(+4.16 to+4.23),ΔNb(0.20–0.22)and low initial^(87)Sr/^(86)Sr(0.70425 to 0.70452)and Zr/Nb(3.35–3.57),we suggest that the Chagantaolegai OIB samples were likely derived from a fertile mantle source related to plume.The OIB rock assemblage,chert and marble in the southern part of the Chagantaolegai ophiolitic mélange indicates that a Middle Ordovician seamount was accreted to the Boshchekul-Chingiz arc due to the northward subduction of the Junggar-Balkhash Ocean.

Source and magmatic evolution of ocean island basalts from the Pohnpei Island,Northwest Pacific Ocean:Insights from olivine geochemistry

The compositional variability of ocean island basalts(OIBs)is thought to reflect partial melting of a lithologicallyheterogeneous mantle source dominated by either pyroxenite or peridotite.The Pohnpei Island in Micronesia,which is associated with the Caroline hotspot,is suggested to have been generated from partial melting of a pyroxenite-rich mantle.To examine this hypothesis,we present new major-and trace-element compositions of olivine phenocrysts in basalts from the island.The olivines exhibit large systematic inter-and intra-crystalline compositional variability.In Sample DS1,olivines record compositional zonation,in which cores have relatively high Fo(77–85),Ni(550×10^(-6 )–2392×10^(-6 )),and Fe/Mn ratios(66–82),whereas rims have lower Fo(71–78),Ni(526×10^(-6 )–1537×10^(-6 )),and Fe/Mn ratios(51–62).By contrast,olivines within other samples preserve no clear compositional zonation,exhibiting similar or slightly lower Fo values(66–78),Ni contents(401×10^(-6 )–1268×10^(-6 )),and Fe/Mn ratios(53–69)as the rims of zoned crystals.The distinct chemical contrast between the two different types of olivine suggests they formed in magma chambers at different depths.Analysis using forward petrological modeling and multi-element indicators(Fe/Mn,Zn/Fe,FC3MS(FeO^(T)/CaO-(3×MgO/SiO^(2))),Mn/Zn,and Ni/(Mg/Fe))of whole-rock samples and high-Fo olivines is inconsistent with a pyroxenite-rich mantle source.We suggest these inconsistencies reflect an influence on the partition coefficients of Ni and Mn between olivine and liquid during melting at variable pressures and temperatures.In addition,magma recharge and mixing within the magmatic plumbing system can change the composition of olivine.We suggest that identification of the mantle source of OIBs in volcanic islands such as the Pohnpei Island using olivine geochemistry should be treated with caution.

Distribution of Rare Earth Elements in Early Permian Reef-Island Ocean Sediments in Eastern Kunlun

Abstract: Based on the study of stratigraphy and fossils, the Early Permian ocean in eastern Kunlun is recognized as a kind of reef-island ocean, in which there exist many different kinds of sediment, including patch carbonate platform, reef facies, transitional facies and deep basin sediments. It has been found that the total contents of REEs increase gradually from carbonate platform facies to deep basin facies. Meanwhile, sediments of different facies have different REE distribution patterns and different Ce anomalies. Most of the sediments of patch carbonate platform facies or reef facies are characterized by extremely negative Ce anomalies or moderately negative Ce anomalies (Ce/Ce*=0.33 to 0.55), and medium or thin-bedded limestones of transitional facies by moderately negative Ce anomalies (Ce/Ce*=0.49 to 0.60). However, sediments of deep basin facies show weak or no negative Ce anomalies (Ce/Ce*=0.69 to 1.47), among which the value of Ce/Ce* in the radiolarian chert is 1.47.

First Recorded Account of a White Shark Agonistic Pectoral Fin Depression Behavior at Guadalupe Island, Mexico

An agonistic display by a white shark was observed and photographed during a cage dive at Guadalupe Island in November 2015. Exhibiting exaggerated pectoral fin depression, agonistic behaviors have been previously observed and described in several shark species. This account may be the first record of a white shark in close proximity to a caged diver, exhibiting strong pectoral fin depression significantly dipped, in the mid-agonistic display. Such displays should be considered as aggressive and potentially life-threatening by those using the ocean for recreational or professional purposes.