Northern Tasman Sea Research Articles

The South Pacific Current

The Southern Hemisphere Subtropical Front (STF) is a narrow zone of transition between upper-level subtropical waters to the north and subantarctic waters to the south. It is found near 40 degrees S across the South Atlantic and South Indian Oceans and is associated with an eastward geostrophic current band, The current band in each basin is found at or just north of the surface front except near the eastern boundaries where most of the subtropical waters turn north into the eastern limbs of the subtropical gyres. The bands associated with the STF are thus distinct features separated from the strong zonal flows of the Antarctic Circumpolar Current farther south. The authors have referred to the current bands in the two respective oceans as the South Atlantic Current and the South Indian Ocean Current. In this paper the authors use the historical database from the South Pacific Ocean to investigate the geostrophic flow associated with the STF there. The STF extends across the southern Tasman Sea from south of Tasmania to southern New Zealand, and a weak eastward flow appears to be associated with it. The transport amounts to only about 3 Sv (1Sv = 10(6) m(3) s(-1)), little of which passes south of New Zealand. Mixing within the eddy-rich Tasman Sea may account for this weakness, while also setting up another more significant front in the northern Tasman Sea, the Tasman Front. It branches off from the East Australian Current toward the north of New Zealand, along which moves a flow of about 14 Sv. After passing north of New Zealand, a portion of this current flows east to contribute to a current band near 30 degrees S, while another portion turns south as the East Auckland Current and meets with subantarctic waters near Chatham Rise (44 degrees S), thus reestablishing the STF. An enhanced eastward current band is associated with the front there, one that extends across the remainder of the South Pacific and is referred to as the South Pacific Current. In comparison with its counterparts in the other basins, which typically begin by carrying 30 Sv (Atlantic) to 60 Sv (Indian) in the upper 1000 m in their western portions before weakening to 10-15 Sv in the east, the South Pacific Current is weak. Near Chatham Rise, it starts with a transport of approximately 5 Sv, and it remains near this strength as it shifts gradually north across the basin toward South America. The current appears to split into two smaller bands in the region of 115 degrees-85 degrees W, while near 28 degrees 5, 83 degrees W it begins to turn more strongly north and becomes shallower and weaker. Potential vorticity distributions indicate that this current acts as an impediment toward the northward spreading of Antarctic Intermediate Water, But why the South Pacific Current east of New Zealand should be so much weaker than its counterparts in the other basins is not particularly clear. It may be due to the presence of New Zealand and other topographic barriers to deep now east of Australia, to the axis of the subtropical gyre in the South Pacific shifting more rapidly southward with depth than those elsewhere, thus causing greater reductions in the underlying zonal velocities, and to strong poleward eddy heat and salt fluxes in the other two basins leading to smaller cross-STF gradients in the Pacific.

Selenoscopus turbisquamatus, a new genus and species of Uranoscopid fish from Japan and the Norfolk Ridge

A new stargazer,Selenoscopus turbisquamatus, is described from 30 specimens from the Kyushu-Palau Ridge, the coasts of Kii Peninsula, Japan, and the Norfolk Ridge, northern Tasman Sea. The species appears to be most closely related to the genusUranoscopus in having two dorsal fins, a spinous dorsal fin consisting of feeble spines, a stout cleithral spine, an externally visible pelvic spur, two supracleithral spines, and no postcleithrum, but differs from it in having a smooth posterior margin of the gill flap, uniserial dentary teeth, random arrangement of body scales, no subopercular spine, an intervention of the pterosphenoid (=alisphenoid) between the frontal and the parasphenoid, and the first and second haemal spines depressed on the centra. A new genus,Selenoscopus, is therefore proposed, based on these characters.

Marine magnetic anomalies over the Lord Howe Rise and the Tasman Sea: Implications for the magnetization of the lower continental crust

Marine geophysical and geological data provide evidence for a continental origin of the Lord Howe Rise, a submarine plateau east of Australia. Our marine geomagnetic data reveal a long-wavelength anomaly associated with the western margin of the rise. Forward and inverse modeling shows that the anomalies can be best explained by strong magnetization of the lower crust of the Lord Howe Rise. A geomagnetic map of the northern Tasman Sea that includes Dampier Ridge, another elongated piece of presumably continental crust, shows positive anomalies over areas of continental origin and negative ones over the deep sea basin. This indicates higher values of the product of magnetization times thickness for the continental crust than for the oceanic crust. Three-dimensional model calculations show that the high magnetization in the lower crust of eastern Australia is limited to a maximum depth of 15–20 km. This is in accordance with geothermal results that indicate the Curie isotherm is at a shallow depth there. The anomalies of the Tasman Sea are negative due to the negative part of the edge anomaly on the seaward side of the continental margin. It is not necessary to hypothesize strong reversed magnetization in the lower oceanic crust and upper mantle.

Some analyses of lipid classes in marine organisms, sediments and seawater using thin-layer chromatography—flame ionisation detection

Applications of the silica gel Chromarod-Iatroscan TH-10 thin-layer chromatography—flame ionisation detection (FID) system for identifying and quantifying the non-polar lipids in a variety of marine samples are presented. Excellent results can be obtained with a speed and sensitivity which is lacking in other analytical procedures. However, the non-linearity of the FID response at the low loadings (< 2 μg) required for most samples of interest makes the use of FID calibration curves mandatory. Seawater and sediment samples contain large amounts of polar lipids, degraded organic matter and pigments which can also interfere with the lipid analyses. Lipid compositional data are presented for the unicellular algae Thalassiosira eccentrica and Emiliania huxleyi, the marine copepods Paralabidocera antarctica and Calanus finmarchicus, seawater particulate matter from northern Tasman Sea waters off the East Australian coast and sediments from Ace Lake, Antarctica and the Great Barrier Reef of Australia.

Deep currents of the northern Tasman Sea Basin

Off the southeast Australian cost in the Tasman Basin, north of 40°S, the deeper structure obtained from hydrological data is highly correlated with the surface flow, especially in the region east of Sydney where the East Australian Current forms southwards meanders that often break off to form large, warm-core rings. This indicates that the East Australian Current and its warm-core rings have a dominant influence on the baroclinic flow down to abyssal depths. Typical current shears below 2000 m are estimated to be of order 4 cm s−1 km−1. Further north, between 30 and 32.5°S, the correlation between deep and shallow structure is of similar magnitude and there is a definite correlation between parameters of the deep flow and distance offshore. It is concluded that the correlation is due to an east-west tilt of the surface of no motion. Still further north, no significant correlations exist between the deep structure and either distance offshore or shallow structure parameters. No evidence has been found for a swift, narrow, western boundary undercurrent in the Tasman Sea north of 40°S.

An oceanographic survey of the Tasman Front

Abstract Results of a detailed expendable bathythermograph survey in the northern Tasman Sea are presented. The Tasman Front, with its origin in the edge of an East Australian Current eddy, extended throughout the survey region. The front marked a coherent, meandering, zonal jet which crosses the Tasman Sea and hence links at least part of the East Australian Current to the other western boundary currents in the subtropical gyre. The frontal meandering derives from both the variability of the East Australian Current system and the topographic effects of the major ridge systems in the north Tasman Sea. The front is less distinct over the crests of these ridges. The flow field in the survey area contained a number of anticyclonic eddies, and current records show that the oceanic eddies are long‐lived features similar to the eddies in the East Australian Current.

Sea Floor Spreading in the Tasman Sea: a Lord Howe Rise — Eastern Australian Reconstruction

New finite poles have been calculated for the Tasman Sea based on both pre-existing magnetic data and recently released Australian Bureau of Mineral Resources magnetic data. The pole positions are more southerly than previously calculated; the stage pole positions imply that strike slip motion in the northern Tasman Sea was concurrent with accretion in the southern Tasman Sea during the early stages of opening from anomalies 33 to 32. Progressive northward movement of the stage poles from anomaly 32 time reflects the increasing development of spreading ridges and corresponding reduction in strike slip motion in the northern Tasman Sea until accretion was active throughout the entire basin from anomaly 30 time until its cessation at anomaly 24 time. Many of the characteristic features of the southeastern Australian margin, including its steep slope, its narrow width and scarcity of sediments, all difficult to reconcile with previously postulated rifted models, are more consistent with the present model of margin development.

Sediments and stratigraphy of deep-sea cores from the Tasman Basin

Abstract Twelve deep-sea cores from the northern Tasman Sea are described and grouped according to sediment characteristics and foraminiferal faunas. Six of the cores from the area between Australia and the Dampier Ridge consist dominantiy of clastics which have been derived from the Australian continental shelf and slope mainly by turbidity currents. Intervening periods when pelagic sedimentation was dominant have occurred. These cores were all taken from depths near the carbonate solution boundary and consequently calcareous foraminiferal tests in the pelagic intervals have been affected by solution. East of Dampier Ridge six cores were taken from the Lord Howe Rise, New Caledonia Basin, and Norfolk Ridge. These consist almost entirely of the calcareous remains of planktonic organisms, mainly foraminifera. Most of the cores are uppermost Pleistocene and Holocene in age, but in one core from the western slope of the Lord Howe Rise Middle to Upper Miocene sediment is unconformably overlain by uppermost Pl...

Seabirds seen in the northern Tasman Sea in winter

Summary The distribution of birds in the northern Tasman Sea was observed during August and September 1967 from r.v. Argo. Subantarctic species (Diomedea exulans, D. melanophris and Daption capensis) ranged further north in the western than in the eastern Tasman Sea, probably because western waters have a higher phosphate content and hence contain more food. New northernmost sightings were recorded for Pachyptila sp., Pterodroma macroptera, Pelecanoides sp. and Procellaria cinereus.

Some Aspects of the Deep Circulation of the Tasman and Coral Seas

Data from selected stations deeper than 2000 m in the Tasman and Coral Seas are used to prepare meridional sections of salinity, oxygen, and phosphate along the meridian 155� E. between latitudes 14� S. and 42� S., and zonal sections of the same properties between meridians 149� E. and 155� E. in the latitude range 14-15� S. Meridional changes in the salinity minimum, phosphate maximum, and deep salinity maximum indicate circulation below 1500 m. Utilizing all available data, the general circulation of these waters in the Tasman and Coral Seas as a whole is described. Phosphate-rich waters from the Equatorial Western Pacific and probably from the Indian Ocean are found distributed along the western margin to the north and south of the region, at about the 2000 m level. Below this level, well-oxygenated waters of high salinity, presumably from the South-West Pacific, enter the northern Tasman Sea, through the New Caledonian trench. By comparison of temperature, salinity, and oxygen values the depth of the sill connecting the Tasman and Coral Seas is estimated at 3000 m. Along the 155� E. meridian temperatures recorded during the late nineteenth century were warmer by 0. 15-0.3�C than those obtained recently.