Fiji Basin Research Articles

Distributions of cadmium, nickel, zinc, copper, and iron in the western South Pacific Ocean: Local sources of the nutrient-type trace metals

This study presents comprehensive sectional distributions of five nutrient-type trace metals (Cd, Ni, Zn, Cu, and Fe) within the total dissolvable (td), dissolved (d), and labile particulate (lp) fractions along the GEOTRACES transect GP19 (∼170°W). Among these trace metals, only dCd exhibits a strong correlation with phosphate, albeit with a notable deviation at around ∼100 m depth for stations situated between 50°S and 0°S. This divergence indicates that the distribution of dCd is primarily influenced by ocean circulation and biogeochemical cycling in the western South Pacific Ocean. Conversely, dNi, dZn, and dCu concentrations increase independently of phosphate in waters exceeding 1500 m depth. These variations can partly be attributed to reversible scavenging, benthic release from sediments in the Fiji Basins and the Southwest Pacific Basin, and/or water mass mixing. While a moderate correlation exists between dFe and PO4 throughout the water column, the slope of the regression line is less than half of the Fe/P ratio observed in phytoplankton, suggesting substantial scavenging of dFe. Furthermore, the distribution of dFe is influenced by local sources such as intense weathering on tropical-subtropical lands and hydrothermal activities.

Lanternfishes of the genus Diaphus collected during cruises ESSCHA, NECTAlis, PUFFAlis and WALLAlis of RV Alis in the tropical southwestern Pacific

The present study contributes to update the checklist of Lanternfishes species of the genus Diaphus known to occur in the tropical southwestern Pacific. The findings are based on material collected from six recent oceanographic cruises of RV Alis in the Coral Sea, the Fiji Basin and the Wallis and Futuna Exclusive Economic Zone (EZZ). Diaphus spp. samples were obtained using pelagic trawl nets. We identified 20 species of the genus Diaphus. Specimens morphologically closest to D. termophilus and belonging to a possibly undescribed species were also sampled from the Wallis and Futuna waters, highlighting persisting gaps in our knowledge regarding this ecologically important group of fishes. Our collection of specimens, all preserved for DNA extraction, will be useful to complement the current Diaphus barcode database for the tropical southwestern Pacific. Dataset published through GBIF (Doi: 10.15470/ek0u3y)

Contrasted phylogeographic patterns of hydrothermal vent gastropods along South West Pacific: Woodlark Basin, a possible contact zone and/or stepping-stone.

Understanding drivers of biodiversity patterns is essential to evaluate the potential impact of deep-sea mining on ecosystems resilience. While the South West Pacific forms an independent biogeographic province for hydrothermal vent fauna, different degrees of connectivity among basins were previously reported for a variety of species depending on their ability to disperse. In this study, we compared phylogeographic patterns of several vent gastropods across South West Pacific back-arc basins and the newly-discovered La Scala site on the Woodlark Ridge by analysing their genetic divergence using a barcoding approach. We focused on six genera of vent gastropods widely distributed in the region: Lepetodrilus, Symmetromphalus, Lamellomphalus, Shinkailepas, Desbruyeresia and Provanna. A wide-range sampling was conducted at different vent fields across the Futuna Volcanic Arc, the Manus, Woodlark, North Fiji, and Lau Basins, during the CHUBACARC cruise in 2019. The Cox1-based genetic structure of geographic populations was examined for each taxon to delineate putative cryptic species and assess potential barriers or contact zones between basins. Results showed contrasted phylogeographic patterns among species, even between closely related species. While some species are widely distributed across basins (i.e. Shinkailepas tollmanni, Desbruyeresia melanioides and Lamellomphalus) without evidence of strong barriers to gene flow, others are restricted to one (i.e. Shinkailepas tufari complex of cryptic species, Desbruyeresia cancellata and D. costata). Other species showed intermediate patterns of isolation with different lineages separating the Manus Basin from the Lau/North Fiji Basins (i.e. Lepetodrilus schrolli, Provanna and Symmetromphalus spp.). Individuals from the Woodlark Basin were either endemic to this area (though possibly representing intermediate OTUs between the Manus Basin and the other eastern basins populations) or, coming into contact from these basins, highlighting the stepping-stone role of the Woodlark Basin in the dispersal of the South West Pacific vent fauna. Results are discussed according to the dispersal ability of species and the geological history of the South West Pacific.

Active hydrothermal vents in the Woodlark Basin may act as dispersing centres for hydrothermal fauna

Here we report the discovery of a high-temperature hydrothermal vent field on the Woodlark Ridge, using ship-borne multibeam echosounding and Remotely Operated Vehicle (ROV) exploration. La Scala Vent Field comprises two main active areas and several inactive zones dominated by variably altered basaltic rocks, indicating that an active and stable hydrothermal circulation has been maintained over a long period of time. The Pandora Site, at a depth of 3380 m, is mainly composed of diffuse vents. The Corto site, at a depth of 3360 m, is characterized by vigorous black smokers (temperature above 360 °C). The striking features of this new vent field are the profusion of stalked barnacles Vulcanolepas sp. nov., the absence of mussels and the scarcity of the gastropod symbiotic fauna. We suggest that La Scala Vent Field may act as a dispersing centre for hydrothermal fauna towards the nearby North Fiji, Lau and Manus basins.

GMT Based Comparative Geomorphological Analysis of the Vityaz and Vanuatu Trenches, Fiji Basin

The study is geographically focused on the two deep-sea trenches: Vanuatu and Vityaz, Fiji Basin, East Australia, located in the area of the double convergent complex boundary of Pacific and Indo-Australian plates in the North Fiji back-arc basin. Complex geophysical settings results in the formation of the trenches, seismicity, geodynamic complexity and instability of the region. The work aimed at modelling and comparative statistical analysis of the bathymetry and geomorphology of two trenches. Technically, the methodology of this work is based on the Generic Mapping Tools (GMT) using cartographic mapping of the geophysical, tectonic and geological settings, 2D and 3D modelling, visualizing raster grids GEBCO, ETOPO1, ETOPO5. Histogram topographic equalization (equalized, normalized, quadratic) was done using module ’grdhisteq’. Modelling geoid and gravity was based on EGM96 by sequence of GMT modules. The cross-spectrals of 2D binary raster grids were compared and their coherency plotted by ’grdfft’. The automated cross-sectioning was done using ’grdtrack’ module. The results include modelled transects visualizing trenches asymmetry, bathymetric and geomorphic variations. Vityaz Trench is shallower with depths <–6,100 m, has ’bell-shape’ data distribution with two peaks at ranges –3,500 m to –3,700 m, and –4,800 m to –5,000 m. Vanuatu Trench reaches up to –7,000 m with majority of values between –5,000 m to –3,000 m, even data distribution with depth increasing at –2,200 m to –800 m. Geomorphic form of both trenches varies: Vityaz has flat wide bottom similar to a trough, steeper gradient eastern slope. Vanuatu has V-form classic shape with gentle shapes on both slopes. Selected segment of Vityaz has shallower depths with maximal <–5,000 m while Vanuatu is deeper (–6,000 m). Cartographic functionality of the GMT is presented by various cartographic projections: Mercator, Behrman, Cylindrical Stereographic, Hammer retroazimuthal. 3D modelling was done using GMT module ’grdview’. Trenches were visualized and rotated at 160°/45°azimuth. Presented maps, 2D and 3D models and graphics are plotted and visualized by GMT with selected code snippets explained. Current work contributes to the methods of the modelling of deep-sea trenches geomorphology.

SW Pacific arc and backarc lavas and the role of slab-bend serpentinites in the global halogen cycle

In order to better understand the global halogen cycle and the behaviour of halogens during subduction, we investigated the concentrations of F, Cl, Br and I in suites of rare submarine glasses formed during subduction initiation on the Hunter Ridge (N. Fiji Basin) and from the northernmost part of the Tonga Arc. Additional submarine glasses from mature arcs and backarcs including the Tonga arc (Volcano A), North Fiji, Lau, Manus and Woodlark Basins were also investigated. The aim was to constrain the relative abundances of all four halogens (F/Cl, Br/Cl and I/Cl) in subducted components in proto-arc, arc and backarc lavas for the first time. This enables an assessment of slab-fluid evolution from incipient arcs to mature backarcs, and a comparison of halogens in slab-fluids with possible subduction inputs and other mantle outputs. The various arc and backarc lavas investigated are strongly enriched in Cl, Br and I relative to Nb, and weakly enriched in F compared to Pr, demonstrating metasomatism of incipient sub-arc mantle and sub-arc/backarc mantle by slab-components with strikingly similar ranges of F/Cl (0.11 ± 0.09), Br/Cl (0.0028 ± 0.0008) and I/Cl (0.000013-0.001) (2 standard deviations). The F/Cl ratio, which is much higher than seawater and other surface fluids, is attributed to enhanced mobility of F in saline fluids in sub-arc environments, with slab-melts ascribed an additional minor role. The slab-fluid Br/Cl and I/Cl ratios are strikingly similar to altered oceanic crust and seafloor serpentinites, and distinctly different from sediment pore waters, sediments and most forearc serpentinites. The median Br/Cl and I/Cl ratios of slab fluids in sub-arc and sub-backarcs are also indistinguishable from median mid-ocean ridge and ocean island basalt values, which have I/Cl ratios lower than estimated for the primitive mantle. The data are interpreted to indicate that sedimentary volatile components present in sediments and forearc serpentinites are efficiently returned to the surface through forearc regions. In contrast, halogens in altered ocean crust and lithospheric serpentinites are recycled through magmatic arcs and into the deeper mantle with the result that the mantle's I/Cl ratio has decreased over time. Mass balance considerations suggest that serpentinisation of the lithospheric mantle at the slab-bend immediately prior to subduction is more significant than estimated previously and is driven by seawater-derived fluids without sedimentary components. Lithospheric serpentinites are likely to represent a dominant source of halogens and other volatiles, including noble gases, in the Earth's mantle.

Evidence for an Independent 26-s Microseismic Source near the Vanuatu Islands

The 26 s peak in the ambient seismic noise spectrum is persistently excited and observed at stations globally. Using noise cross-correlation functions (NCFs), the location suggests that the source could be situated in the Gulf of Guinea and Fiji Basin. However, the Fiji Basin was proposed to be the mirror site (near antipode) of the Gulf of Guinea source instead of an independent source, assuming that the surface waves more efficiently propagate along the major-arc paths of oceanic movements. To investigate the propagation of the Rayleigh waves along continental and oceanic paths, we analyzed the surface wave data recorded from an earthquake near the Gulf of Guinea and found that Rayleigh waves travel along continental minor-arc paths more efficiently than along oceanic major-arc paths. We then located the source in the western Pacific Ocean from group velocities measured with earthquake data by using the travel time misfit in NCFs after calibration and concluded that the source is in the Vanuatu Islands. Moreover, the temporal variation of the 26 s microseismic peak observed in the western Pacific seismic stations is very different from that in stations near the Gulf of Guinea, which suggests that they are excited by independent sources. Therefore, the Vanuatu source should be an independent microseismic source. As it is close to volcanoes in the Vanuatu islands, the Pacific 26 s microseismic source might be excited by magmatic processes, which are also responsible for very-long-period volcanic tremors.

&lt;i&gt;Spinaxinus&lt;/i&gt; (Bivalvia: Thyasiroidea) from sulfide biogenerators in the Gulf of Mexico and hydrothermal vents in the Fiji Back Arc: chemosymbiosis and taxonomy

Two new species of the thyasirid genus Spinaxinus (S. emicatus Oliver n. sp. and S. phrixicus Oliver n. sp.) are described from the Gulf of Mexico and the southwest Pacific, respectively. Both are compared with the type species of the genus, the eastern Atlantic S. sentosus Oliver and Holmes, 2006. Living specimens from the Gulf of Mexico were retrieved from artificial sulfide bio-generators on the upper Louisiana Slope. Gill morphology and molecular markers from the symbiotic bacteria confirm that Spinaxinus is chemosynthetic and that the chemoautotrophic bacteria are related to sulfide oxidizing Gammaproteobacteria. Living specimens from the southwest Pacific were retrieved from hydrothermal vent sites in the Fiji and Lau Back Arc Basins. In the Atlantic Spinaxinus is now recorded from two anthropogenic situations and appears to be generally absent from natural cold seep sites and not yet recorded at any hydrothermal sites. The primarily anthropogenic distribution of Spinaxinus in the Atlantic is discussed with reference to the natural hydrothermal vent habitat of the Pacific S. phrixicus .

A fungal epizootic in mussels at a deep‐sea hydrothermal vent

AbstractMass mortalities due to disease are important determinants of population and community structure in marine ecosystems, but the speed at which an epizootic may sweep through a population, combined with rapid selection for disease‐resistant stocks, can mask the ecological impact of disease in all but the most closely monitored populations. We document an emergent epizootic event in the deep sea that is occurring in mussels (Bathymodiolus brevior) at the Mussel Hill hydrothermal vent in Fiji Basin and we identify the causal agent as a black yeast (order Chaetothyriales) that elicits a pronounced host immune response and is associated with tissue deterioration. The yeast was not observed in other invertebrate taxa (the gastropods Ifremeria nautilei, Alviniconcha aff. hessleri; the limpets Lepetodrilus schrolli, Symmetromphalus aff. hageni; the polychaetes Branchipolynoe pettiboneae, Amphisamytha cf. galapagensis) associated with the mussel bed, nor in mussels (Bathymodiolus brevior) collected from adjacent Lau Basin mussel beds. Massive mussel mortality resulting from the fungal infection is anticipated at the Mussel Hill site in Fiji Basin; we expect that epizootic outbreaks in dense invertebrate communities have the potential to be major determinants of community structure in deep‐sea chemosynthetic ecosystems. The possibility that submersible assets may serve as vectors for transport of the fungus warrants further attention.

Molecular Phylogeny of the East Pacific Squat Lobsters of the Genus Munidopsis (Decapoda: Galatheidae) with the Descriptions of Seven New Species

Numerous specimens of the genus Munidopsis from the East Pacific, and including the East Pacific Rise (EPR), are reviewed using morphological characters and mitochondrial cytochrome oxidase subunit I (COI) sequences. Six new Munidopsis species from the East Pacific are described (M. bracteosa, M. hirsuta, M. kensmithi, M. scotti, M. segonzaci, and M. tiburon), and the status of M. recta is revised. A seventh new species (M. vrijenhoeki) from Fiji Basin (SW Pacific) is also included. A combined morphological and molecular analysis revealed that the most common species on the EPR is Munidopsis recta. Most of the new species can be differentiated from closely related species by subtle morphological characters, which correspondingly match the molecular phylogeny and large molecular divergence, confirming the existence of sibling species in the genus Munidopsis. Most Munidopsis individuals formerly considered M. subsquamosa from the East Pacific Rise appear to be members of M. recta. One potential sister taxa to M. recta is M. bracteosa, which is found at the Juan de Fuca hydrothermal vents, the Mendocino Fracture Zone, and a Monterey Bay whalefall. Our findings suggest that Munidopsis populations are tightly interconnected between distant and discrete locations, and challenge models for the predicted dispersal of these species. Additional sampling of Munidopsis populations on localized habitats (wood, hydrothermal vents, and whale falls), as well as intervening abyssal areas, are required to fully understand the complex evolutionary history and diversity of this group.

Physiological Responses to Stress Conditions and Barophilic Behavior of the Hyperthermophilic Vent Archaeon Pyrococcus abyssi

The physiology of the deep-sea hyperthermophilic, anaerobic vent archaeon Pyrococcus abyssi, originating from the Fiji Basin at a depth of 2,000 m, was studied under diverse conditions. The emphasis of these studies lay in the growth and survival of this archaeon under the different conditions present in the natural habitat. Incubation under in situ pressure (20 MPa) and at 40 MPa increased the maximal and minimal growth temperatures by 4(deg)C. In situ pressure enhanced survival at a lethal high temperature (106 to 112(deg)C) relative to that at low pressure (0.3 MPa). The whole-cell protein profile, analyzed by one-dimensional sodium dodecyl sulfate gel electrophoresis, did not change in cultures grown under low or high pressure at optimal and minimal growth temperatures, but several changes were observed at the maximal growth temperature under in situ pressure. The complex lipid pattern of P. abyssi grown under in situ and 0.1- to 0.5-MPa pressures at different temperatures was analyzed by thin-layer chromatography. The phospholipids became more complex at a low growth temperature at both pressures but their profiles were not superimposable; fewer differences were observed in the core lipids. The polar lipids were composed of only one phospholipid in cells grown under in situ pressure at high temperatures. Survival in the presence of oxygen and under starvation conditions was examined. Oxygen was toxic to P. abyssi at growth range temperature, but the strain survived for several weeks at 4(deg)C. The strain was not affected by starvation in a minimal medium for at least 1 month at 4(deg)C and only minimally affected at 95(deg)C for several days. Cells were more resistant to oxygen in starvation medium. A drastic change in protein profile, depending on incubation time, was observed in cells when starved at growth temperature.

Shear-wave splitting in the mantle of the pacific

SUMMARY The bulk of previously known data on seismic anisotropy in the suboceanic mantle was obtained from observations of azimuthal variations of the surface-wave and P, velocities. Our study of azimuthal anisotropy in the mantle of the Pacific is based on observations of shear-wave splitting. The idea of our method of measurement (Vinnik & Farra 1992) is to analyse evolution of the waveform of the long-period multiple reflected ScS and SSCS phases as a function of the order of reflection. The estimates of anisotropy correspond to circular regions with a radius of several hundred kilometres around the surface bounce points. The technique was applied to the digital recordings of deep and intermediate events from the circum-Pacific seismic belt at seismograph stations in and around the Pacific. The estimates of polarization direction of the fast split wave and time lag of the slow wave are obtained for a few regions of the Pacific basin, marginal basins and the Andes. In the back-arc extensional basins whose spreading has continued to the present time or ended later than about 15Ma, the inferred direction of extension in the mantle is close to that imprinted in the crust (Lau basin, Japan Sea). In the back-arc basins whose active development ended 15-20 Ma or earlier (South Fiji and Parece Vela basins), the inferred directions of extension in the mantle are in strong disagreement with the crustal data. In the Central Andes, the region of plate collision and low-angle subduction, the inferred direction of flow in the mantle is perpendicular to the plate boundary, contrary to the regularity previously found in several other collisional belts. The fast direction of anisotropy in the mantle beneath the southwestern part of the 100Ma old Pacific plate is very close to the absolute plate motion direction; the magnitude of anisotropy corresponds to the lowest values found in the continental mantle and is much lower than in most of the marginal basins and the Andes. The weakness of this, presumably asthenospheric, anisotropy in comparison with asthenospheric anisotropy under some old continental plates is probably related to a difference in upper mantle viscosities.

New reef targets for oil and gas exploration in Fiji, Southwest Pacific

Fiji forms part of the Southwest Pacific island arc system which marks the boundary between the Indo-Australia and Pacific plates_ The territorial waters cover almost 1.3 million km2 and contain two shallow water Tertiary sedimentary basins_ Bligh Water Basin, covering some 9500 km2, has sediment thicknesses in excess of 5 km and has excellent potential for hydrocarbons_ Bau Waters Basin is also prospective, having a shallow water area of about 1600 km2, with sediment thicknesses up to 4 km_ Fiji lies on the same regional play trend of Miocene reefs which produce oil in Irian Jaya, Indonesia and gas/condensate in offshore Papua New Guinea. Indeed Fiji's basins have many similarities with the oil and gas producing, arc-related basins of Southeast Asia. Source rocks of Oligocene, Miocene and Pliocene age are exposed onshore in Fiji and have been encountered by drilling in the offshore basins. An oil seep in Bligh Water Basin and oil and gas shows in wells provide evidence that hydrocarbons have been generated in the basins. Modelling studies indicate peak oil generation to be at about 2.6 km below sea floor. Miocene and Pliocene reefal limestones form spectacular outcrops in Fiji and represent the best potential reservoirs. Reefs of the same age have been identified on seismic data from the offshore basins and represent attractive targets for exploration. Common forms are reefal mounds and prograded platforms. Over twenty structural reefal traps have been identified on seismic lines in the Late Miocene and Pliocene sequences, mostly in Bligh Water Basin. Estimates of potential unrisked recoverable reserves are 270 million barrels of oil per structure. If structural-stratigraphic trapping occurs, recoverable reserves could increase to over 1 billion barrels of oil per structure. There is considerable scope for more reefal structures in the deeper Oligocene-Middle Miocene interval which cannot be resolved on the existing seismic data, and in areas where seismic coverage is sparse. Limestone turbidite lobes have also been identified on seismic data. These constitute a secondary play and may contain estimated recoverable reserves of 100-200 million barrels of oil per structure. There are no exploration or production licences at present. Fiji has comprehensive petroleum legislation and the Government seeks to encourage exploration investment by oil companies. All reports and data are available in the Fiji Petroleum Data Package which may be ordered from the SOPAC Petroleum Data Bank, Canberra.

Isolation and characterization of Thiobacillus hydrothermalis sp. nov., a mesophilic obligately chemolithotrophic bacterium isolated from a deep-sea hydrothermal vent in Fiji Basin

A novel obligately chemolithotrophic Thiobacillus species isolated from a deep-sea hydrothermal vent is described. This organism grows lithoautotrophically on thiosulphate, tetrathionate, sulphide and sulphur which are oxidized to sulphate. The isolate is slightly halophilic and markedly halotolerant, showing optimum growth at pH 7.5 and at 35°C. The G+C content of the DNA is 67.1 mol%. The 16S rRNA sequence is distinct from any other Thiobacilli sequences. Phylogenetic analysis shows the organism to be a representative of the γ-group of proteobacteria and a specific relative of Thiobacillus neapolitanus. The ubiquinone is ubiquinone-8. These characters distinguish the isolate from any other Thiobacillus or Thiomicrospira species previously reported and is a new species described as Thiobacillus hydrothermalis. The type strain is isolate R3, DSM7121.

Tectonic Fabric of Northern North Fiji and Lau Basins from GLORIA Sidescan: ABSTRACT

Tectonic Fabric of Northern North Fiji and Lau Basins from GLORIA Sidescan: ABSTRACT

Reversed-phase chromatographic separation and analysis of marine metal—organic complexes

Metal—organic complexes were isolated from seawater by adsorption on reversed-phase chromatographic supports such as C 18 Sep-Pak cartridges and XAD-2 resin and subsequent elution with methanol, acetonitrile or tetrahydrofuran. Preliminary results indicate that Sep-Pak cartridges packed with Styragel are also suitable, although back pressures are higher and low blank values are difficult to achieve. Analysis of the extracts by high-performance liquid chromatography with atomic fluorescence detection of trace metals showed that methanol extracts remain unchanged for up to three months in polypropylene at temperatures between −20°C and 20°C and in glass at −20°C. No changes were observed in acetonitrile extracts stored for one week at −20°C, even though the wet extract separated into two phases. Rapid freezing of C 18 Sep-Pak cartridges to /t-195°C also seemed to be a suitable method for preserving samples for future analysis. High-intensity lamps improved the sensitivity of the atomic fluorescence detector by 1/2-2 orders of magnitude and zinc, magnesium, copper, nickel and iron could be determined simultaneously with detection limits ranging from 0.05 μg l −1 (zinc) to 7 μg l −1 (iron). The chromatograms were calibrated by standard additions of trace metals. All the chromatographic columns investigated (C 18 Resolve, C 18 Nova-Pak, PRP-1 and Protein-Pak 125) contained impurity sites that could interfere with the analysis of metal—organic compounds at the ultra-trace level. As interference was most pronounced for magnesium—organic complexes, magnesium was used as an indicator of the presence of coordinating sites on the chromatographic support. Interference effects could be reduced by the addition of modifying agents containing alkali metal salts at a concentration of 50 m M. The most suitable salt was potassium trifluoromethanesulfonate. Metal—organic compounds were isolated on XAD-2 resin (waters from Storm Bay, Tasmania), and on C 18 Sep-Pak cartridges (waters from south-east Australian waters and the Fiji Basin). The concentrations of copper (410 p M), zinc (650 p M) and iron (800 p M) organic complexes from south-east Australian waters were higher than the values obtained for copper (60/2-120 p M), zinc (50/2-150 p M and iron (150/2-180 p M) organic complexes isolated from the Fiji Basin.

On tsunami propagation

The propagation of the Alaskan tsunamis of 1946 and 1964 has been studied using an iterative algorithm designed to handle continuous optimal problems. The results of calculations for the 1946 tsunami to Sitka demonstrate its capabilities and show that the great circle does not always furnish reliable approximations to the travel time and path. Calculations for the 1964 tsunami permit the description of its propagation and the plotting of the ray paths to locations along the American coast. In the southwest Pacific, most of the wave train was dispersed by the complex bathymetry northeast of Australia but some wave energy passed through the Fiji basin into the Tasman Sea. The reflection of the wave by the Undulla Deep explains the late arrivals in New Zealand and the remarkable tide record from Macquarie Island.

The Flow of Water into the Deep Sea Basins of the Western South Pacific Ocean

The hydrographic conditions in the deep sea basins of the western South Pacific Ocean are analysed using relations between potential temperature and salinity, based on observations made from H.M.A.S. Gascoyne in 1960. It is shown that the bottom waters in the Coral Sea Basin and in the Solomon Basin are both characterized by a comparatively high salinity and that they come from the East Australian Basin. The bottom waters in the New Hebrides Basin, the New Caledonia Trough, and the Fiji Basin come from the central Pacific Basin. The water in the New Hebrides Basin and that in the New Caledonia Trough both have a slight admixture of water of higher salinity which has escaped over the ridges on the east sides of the Coral Sea Basin and the Solomon Basin. The Coral Sea Basin and the Solomon Basin considered as a unit is an example, probably the unique case, of . the inflow into a basin occurring at a higher level than the outflow. The sill depths of the different basins are determined by using potential temperature characteristics. The water exchange of the Coral Sea Basin is discussed theoretically. The upward velocity at depths between 3000 and 4000 m is of the order of 1.5 × 10-5 cm/sec and the rate of inflow 0.04 million m3/sec.